Executive Summary

The Hong Kong-Zhuhai-Macao Bridge (HZMB) Hong Kong Link Road (HKLR) serves to connect the HZMB Main Bridge at the Hong Kong Special Administrative Region (HKSAR) Boundary and the HZMB Hong Kong Boundary Crossing Facilities (HKBCF) located at the north eastern waters of the Hong Kong International Airport (HKIA).

The HKLR project has been separated into two contracts. They are Contract No. HY/2011/03 Hong Kong-Zhuhai-Macao Bridge Hong Kong Link Road-Section between Scenic Hill and Hong Kong Boundary Crossing Facilities (hereafter referred to as the Contract) and Contract No. HY/2011/09 Hong Kong-Zhuhai-Macao Bridge Hong Kong Link Road-Section between HKSAR Boundary and Scenic Hill.

China State Construction Engineering (Hong Kong) Ltd. was awarded by Highways Department as the Contractor to undertake the construction works of Contract No. HY/2011/03. The main works of the Contract include land tunnel at Scenic Hill, tunnel underneath Airport Road and Airport Express Line, reclamation and tunnel to the east coast of the Airport Island, at-grade road connecting to the HKBCF and highway works of the HKBCF within the Airport Island and in the vicinity of the HKLR reclamation. The Contract is part of the HKLR Project and HKBCF Project, these projects are considered to be “Designated Projects”, under Schedule 2 of the Environmental Impact Assessment (EIA) Ordinance (Cap 499) and EIA Reports (Register No. AEIAR-144/2009 and AEIAR-145/2009) were prepared for the Project. The current Environmental Permit (EP) EP-352/2009/D for HKLR and EP-353/2009/K for HKBCF were issued on 22 December 2014 and 11 April 2016, respectively. These documents are available through the EIA Ordinance Register. The construction phase of Contract was commenced on 17 October 2012.

BMT Hong Kong Limited was appointed by the Contractor to implement the Environmental Monitoring & Audit (EM&A) programme for the Contract in accordance with the Updated EM&A Manual for HKLR (Version 1.0) and provided environmental team services to the Contract until 31 July 2020.

Meinhardt Infrastructure and Environment Limited has been appointed by the Contractor to implement the Environmental Monitoring & Audit (EM&A) programme for the Contract in accordance with the Updated EM&A Manual for HKLR (Version 1.0) and provide environmental team services to the Contract with effective from 1 August 2020.

Ramboll Hong Kong Limited was employed by HyD as the Independent Environmental Checker (IEC) and Environmental Project Office (ENPO) for the Project until 30 September 2022.

ANewR Consulting Limited has been employed by HyD as the Independent Environmental Checker (IEC) and Environmental Project Office (ENPO) for the Project with effective from 1 October 2022.

This is the forty-sixth Quarterly EM&A report for the Contract which summarizes the monitoring results and audit findings of the EM&A programme during the reporting period from 1 December 2023 to 29 February 2024.

Environmental Monitoring and Audit Progress

The EM&A programme were undertaken in accordance with the Updated EM&A Manual for HKLR (Version 1.0). A summary of the monitoring activities during this reporting period is presented as below:

Monitoring Activity		Monitoring Date
Monitoring Activity		Dec 2023	Jan 2024	Feb 2024
Air Quality	1-hr TSP at AMS5	5, 11, 15, 21 and 27	2, 8, 12, 18, 24 and 30	5, 9, 15, 21 and 27
	1-hr TSP at AMS6	Not applicable.^{(see remark 1)}	Not applicable.^{(see remark 1)}	Not applicable.^{(see remark 1)}
	24-hr TSP at AMS5	4, 8, 14, 20 and 26	1, 5, 11, 17, 23 and 29	2, 8, 14, 20 and 26
	24-hr TSP at AMS6	Not applicable.^{(see remark 1)}	Not applicable.^{(see remark 1)}	Not applicable.^{(see remark 1)}
Noise		5, 11, 21 and 27	2, 8, 18, 24 and 30	5, 15, 21 and 27
Water Quality		1, 4, 6, 8, 11, 13, 15, 18, 20, 22, 25, 27 and 29	1, 3, 5, 9, 10, 12, 15, 17, 19, 22, 24, 26, 29 and 31	2, 5, 7, 9, 14, 16, 19, 21, 23, 26 and 28
Chinese White Dolphin		4, 6, 8 and 11	9, 12, 18, 19 and 25	1, 16, 20, and 21
Mudflat Monitoring (Ecology)		2, 3, 4 and 5	-	-
Mudflat Monitoring (Sedimentation rate)		4	-	-
Site Inspection		5, 15, 21 and 29	2, 9, 16, 24 and 31	1, 7, 16, 21 and 29

Remarks:

1) The existing air quality monitoring location AMS6 – Dragonair / CNAC (Group)Building (HKIA) was handed over to Airport Authority Hong Kong on 31 March 2021. 1-hr and 24-hr TSP monitoring at AMS6 was temporarily suspended starting from 1 April 2021. A new alternative air quality monitoring location is still under processing during the reporting period.

The access to the WQM station SR4(N2) (Coordinate: E814688, N817996) is being blocked by the silt curtains of the Tung Chung New Town Extension (TCNTE) project. Water quality monitoring has been temporarily conducted at alternative stations, namely SR4(N3) (Coordinate: E814779, N818032) until 1 March 2023. Proposal for permanently relocating the SR4(N2) was approved by EPD on 3 March 2023. The water quality monitoring has been conducted at stations SR4(N3) since 3 March 2023.

Breaches of Action and Limit Levels

A summary of environmental exceedances for this reporting period is as follows:

Environmental Monitoring	Parameters	Action Level (AL)	Limit Level (LL)
Air Quality	1-hr TSP	0	0
Air Quality	24-hr TSP	0	0
Noise	L_eq_{(30 min)}	0	0
Water Quality	Suspended solids level (SS)	0	0
	Turbidity level	0	0
	Dissolved oxygen level (DO)	0	0
Dolphin Monitoring	Quarterly Analysis (December 2023 to Feb 2024)	0	1

The Environmental Team investigated all exceedance and found that they were not project related.

All investigation report for exceedance of the Contract has been submitted to ENPO/IEC for comments and/or follow up to identify whether the exceedances occurred related to other HZMB contracts.

Implementation of Mitigation Measures

Site inspections were carried out to monitor the implementation of proper environmental pollution control and mitigation measures for the Project. Potential environmental impacts due to the construction activities were monitored and reviewed.

Complaint Log

There was no complaints received in relation to the environmental impacts during this reporting period.

Notifications of Summons and Prosecutions

There were no notifications of summons or prosecutions received during this reporting period.

Reporting Changes

This report has been developed in compliance with the reporting requirements for the subsequent EM&A reports as required by the Updated EM&A Manual for HKLR (Version 1.0).

The proposal for the change of Action Level and Limit Level for suspended solid and turbidity was approved by EPD on 25 March 2013.

The revised Event and Action Plan for dolphin monitoring was approved by EPD on 6 May 2013.

The original monitoring station at IS(Mf)9 (Coordinate: 813273E, 818850N) was observed inside the perimeter silt curtain of Contract HY/2010/02 on 1 July 2013, as such the original impact water quality monitoring location at IS(Mf)9 was temporarily shifted outside the silt curtain. As advised by the Contractor of HY/2010/02 in August 2013, the perimeter silt curtain was shifted to facilitate safe anchorage zone of construction barges/vessels until end of 2013 subject to construction progress. Therefore, water quality monitoring station IS(Mf)9 was shifted to 813226E and 818708N since 1 July 2013. According to the water quality monitoring team’s observation on 24 March 2014, the original monitoring location of IS(Mf)9 was no longer enclosed by the perimeter silt curtain of Contract HY/2010/02. Thus, the impact water quality monitoring works at the original monitoring location of IS(Mf)9 has been resumed since 24 March 2014.

Transect lines 1, 2, 7, 8, 9 and 11 for dolphin monitoring have been revised due to the obstruction of the permanent structures associated with the construction works of HKLR and the southern viaduct of TM-CLKL, as well as provision of adequate buffer distance from the Airport Restricted Areas. The EPD issued a memo and confirmed that they had no objection on the revised transect lines on 19 August 2015.

The water quality monitoring stations at IS10 (Coordinate: 812577E, 820670N) and SR5 (811489E, 820455N) are located inside Hong Kong International Airport (HKIA) Approach Restricted Areas. The previously granted Vessel's Entry Permit for accessing stations IS10 and SR5 were expired on 31 December 2016. During the permit renewing process, the water quality monitoring location was shifted to IS10(N) (Coordinate: 813060E, 820540N) and SR5(N) (Coordinate: 811430E, 820978N) on 2, 4 and 6 January 2017 temporarily. The permit has been granted by Marine Department on 6 January 2017. Thus, the impact water quality monitoring works at original monitoring location of IS10 and SR5 has been resumed since 9 January 2017.

Transect lines 2, 3, 4, 5, 6 and 7 for dolphin monitoring have been revised and transect line 24 has been added due to the presence of a work zone to the north of the airport platform with intense construction activities in association with the construction of the third runway expansion for the Hong Kong International Airport. The EPD issued a memo and confirmed that they had no objection on the revised transect lines on 28 July 2017. The alternative dolphin transect lines are adopted starting from August’s dolphin monitoring.

A new water quality monitoring team has been employed for carrying out water quality monitoring work for the Contract starting from 23 August 2017. Due to marine work of the Expansion of Hong Kong International Airport into a Three-Runway System (3RS Project), original locations of water quality monitoring stations CS2, SR5 and IS10 are enclosed by works boundary of 3RS Project. Alternative impact water quality monitoring stations, naming as CS2(A), SR5(N) and IS10(N) was approved on 28 July 2017 and were adopted starting from 23 August 2017 to replace the original locations of water quality monitoring for the Contract.

The role and responsibilities as the ET Leader of the Contract was temporarily taken up by Mr Willie Wong instead of Ms Claudine Lee from 25 September 2017 to 31 December 2017.

The topographical condition of the water monitoring stations SR3 (Coordinate: 810525E, 816456N), SR4 (Coordinate: 814760E, 817867N), SR10A (Coordinate: 823741E, 823495N) and SR10B (Coordinate: 823686E, 823213N) cannot be accessed safely for undertaking water quality monitoring. The water quality monitoring has been temporarily conducted at alternative stations, namely SR3(N) (Coordinate 810689E, 816591N), SR4(N) (Coordinate: 814705E, 817859N) and SR10A(N) (Coordinate: 823644E, 823484N) since 1 September 2017. The water quality monitoring at station SR10B was temporarily conducted at Coordinate: 823683E, 823187N on 1, 4, 6, 8 September 2017 and has been temporarily fine-tuned to alternative station SR10B(N2) (Coordinate: 823689E, 823159N) since 11 September 2017. Proposal for permanently relocating the aforementioned stations was approved by EPD on 8 January 2018.

The works area WA5 was handed over to other party on 22 June 2013.

According to latest information received in July 2018, the works area WA7 was handed over to other party on 28 February 2018 instead of 31 January 2018.

Original WQM stations IS8 and SR4(N) are located within the active work area of TCNTE project and the access to the WQM stations IS8 (Coordinate: E814251, N818412) and SR4(N) (Coordinate: E814705, N817859) are blocked by the silt curtains of the Tung Chung New Town Extension (TCNTE) project. Alternative monitoring stations IS8(N) (Coordinate: E814413, N818570) and SR4(N2) (Coordinate: E814688, N817996) are proposed to replace the original monitoring stations IS8 and SR4(N). Proposal for permanently relocating the aforementioned stations was approved by EPD on 20 August 2019. The water quality monitoring has been conducted at stations IS8(N) and SR4(N2) on 21 August 2019.

There were no marine works conducted by Contract No. HY/2011/03 since July 2019. A proposal for temporary suspension of marine related environmental monitoring (water quality monitoring and dolphin monitoring for the Contract No. HY/2011/03) was justified by the ET leader and verified by IEC in mid of September 2019 and it was approved by EPD on 24 September 2019. Water quality monitoring and dolphin monitoring for the Contract will not be conducted starting from 1 October 2019 until marine works (i.e. toe loading removal works) be resumed. As discussed with Contract No. HY/2012/08, they will take up the responsibility from Contract No. HY/2011/03 for the dolphin monitoring works starting from 1 October 2019.

According to information received in January 2020, the works area WA3 and WA4 were handed over to Highways Department on 23 December 2019 and 14 March 2019 respectively.

The role and responsibilities as the IEC of the Contract has been taken up by Mr. Manson Yeung instead of Mr. Ray Yan since 18 May 2020.

Mr. Leslie Leung was Environmental Team Leader of the Contract for July 2020. The role and responsibilities as the Environmental Team Leader of the Contract has been taken up by Ms. Claudine Lee with effective from 1 August 2020.

The existing air quality monitoring location AMS6 – Dragonair / CNAC (Group) Building (HKIA) was handed over to Airport Authority Hong Kong on 31 March 2021. 1-hr and 24-hr TSP monitoring at AMS6 was temporarily suspended starting from 1 April 2021. A new alternative air quality monitoring location is still under processing.

The role and responsibilities as the IEC of the Contract has been taken up by Mr Brian Tam instead of Mr Manson Yeung since 12 April 2021.

The role and responsibilities as the IEC of the Contract has been taken up by Mr Adi Lee instead of Mr Brian Tam since 3 May 2022.

The role and responsibilities as the IEC of the Contract has been taken up by Mr Brian Tam instead of Mr Adi Lee since 25 July 2022.

The role and responsibilities as the ENPO Leader of the Contract has been taken up by Mr Louis Kwan from ANewR Consulting Limited instead of Mr H.Y. Hui from Ramboll Hong Kong Limited Since 1 October 2022.

The role and responsibilities as the IEC of the Contract has been taken up by Mr James Choi from ANewR Consulting Limited instead of Mr Brian Tam from Ramboll Hong Kong Limited since 1 October 2022.

Environmental Monitoring	Description	Monitoring Station	Frequencies	Remarks
Air Quality	1-hr TSP	AMS 5 & AMS 6	At least 3 times every 6 days	While the highest dust impact was expected.
24-hr TSP	At least once every 6 days	--
Noise	L_eq_(30mins)_, L₁₀_(30mins)and L₉₀_(30mins)	NMS 5	At least once per week	Daytime on normal weekdays (0700-1900 hrs).
Water Quality	· Depth · Temperature · Salinity · Dissolved Oxygen (DO) · Suspended Solids (SS) · DO Saturation · Turbidity · pH	· Impact Stations: IS5, IS(Mf)6, IS7, IS8/IS8(N), IS(Mf)9 & IS10(N), · Control/Far Field Stations: CS2(A) & CS(Mf)5, · Sensitive Receiver Stations: SR3(N), SR4(N)/ SR4(N2), SR5(N), SR10A(N) & SR10B(N2)	Three times per week during mid-ebb and mid-flood tides (within ± 1.75 hour of the predicted time)	3 (1 m below water surface, mid-depth and 1 m above sea bed, except where the water depth is less than 6 m, in which case the mid-depth station may be omitted. Should the water depth be less than 3 m, only the mid-depth station will be monitored).
Dolphin	Line-transect Methods	Northeast Lantau survey area and Northwest Lantau survey area	Twice per month	--
Mudflat	Horseshoe crabs, seagrass beds, intertidal soft shore communities, sedimentation rates and water quality	San Tau and Tung Chung Bay	Once every 3 months	--

Parameter (unit)	Water Depth	Action Level	Limit Level
Dissolved Oxygen (mg/L)	Surface and Middle	5.0	4.2 except 5 for Fish Culture Zone
Bottom	4.7	3.6
Turbidity (NTU)	Depth average	27.5 or 120% of upstream control station’s turbidity at the same tide of the same day; The action level has been amended to “27.5 *and* 120% of upstream control station’s turbidity at the same tide of the same day” since 25 March 2013.	47.0 or 130% of turbidity at the upstream control station at the same tide of same day; The limit level has been amended to “47.0 *and* 130% of turbidity at the upstream control station at the same tide of same day” since 25 March 2013.
Suspended Solid (SS) (mg/L)	Depth average	23.5 or 120% of upstream control station’s SS at the same tide of the same day; The action level has been amended to “23.5 *and* 120% of upstream control station’s SS at the same tide of the same day” since 25 March 2013.	34.4 or 130% of SS at the upstream control station at the same tide of same day and 10mg/L for Water Services Department Seawater Intakes; The limit level has been amended to “34.4 *and* 130% of SS at the upstream control station at the same tide of same day and 10mg/L for Water Services Department Seawater Intakes” since 25 March 2013

3 Environmental Monitoring and Audit

3.1 Implementation of Environmental Measures

3.1.1 Details of site audit findings and the corrective actions during the reporting period are presented in Appendix F.

3.1.2 A summary of the Implementation Schedule of Environmental Mitigation Measures (EMIS) is presented in Appendix E. Most of the necessary mitigation measures were implemented properly.

3.1.3 Regular marine travel route for marine vessels were implemented properly in accordance to the submitted plan and relevant records were kept properly.

3.1.4 Dolphin Watching Plan was implemented during the reporting period. No dolphins inside the silt curtain were observed. The relevant records were kept properly.

3.2 Air Quality Monitoring Results

3.2.1 The monitoring results for 1-hour TSP and 24-hour TSP are summarized in Tables 3.1 and 3.2 respectively. Detailed impact air quality monitoring results and relevant graphical plots are presented in Appendix G. The existing air quality monitoring location AMS6 – Dragonair / CNAC (Group) Building (HKIA) was handed over to Airport Authority Hong Kong on 31 March 2021. 1-hr and 24-hr TSP monitoring at AMS6 was temporarily suspended starting from 1 April 2021.

Table 3.1 Summary of 1-hour TSP Monitoring Results Obtained During the Reporting Period

Reporting Period	Monitoring Station	Average (mg/m³)	Range (mg/m³)	Action Level (mg/m³)	Limit Level (mg/m³)
Dec 2023	AMS5	60	31-84	352	500
Dec 2023	AMS6			360
Jan 2024	AMS5	58	26-173	352
Jan 2024	AMS6			360
Feb 2024	AMS5	49	27-88	352
Feb 2024	AMS6			360

Table 3.2 Summary of 24-hour TSP Monitoring Results Obtained During the Reporting Period

Reporting Period	Monitoring Station	Average (mg/m³)	Range (mg/m³)	Action Level (mg/m³)	Limit Level (mg/m³)
Dec 2023	AMS5	90	54-121	164	260
Dec 2023	AMS6			173
Jan 2024	AMS5	59	47-75	164
Jan 2024	AMS6			173
Feb 2024	AMS5	42	16-62	164
Feb 2024	AMS6			173

3.2.2 No Action and Limit Level exceedances of 1-hr TSP and 24-hr TSP were recorded at AMS5 during the reporting period.

3.3 Noise Monitoring Results

3.3.1 The monitoring results for construction noise are summarized in Table 3.3 and the monitoring results and relevant graphical plots for this reporting period are provided in Appendix H.

Table 3.3 Summary of Construction Noise Monitoring Results Obtained During the Reporting Period

Reporting period	Monitoring Station	Average L_eq_{(30 mins)}, dB(A)*	Range of L_eq_{(30 mins)}, dB(A)*	Action Level	Limit Level L_eq_{(30 mins)}, dB(A)
Dec 2023	NMS5	61	59-64	When one documented complaint is received	75
Jan 2024		61	58-66
Feb 2024		60	57-63

*A correction factor of +3dB(A) from free field to facade measurement was included.

3.3.2 No Action/Limit Level exceedances for noise were recorded during daytime on normal weekdays of the reporting period.

3.3.3 Other noise sources during the noise monitoring included aircraft/helicopter noise, construction activities by other parties and human activities nearby.

3.4 Water Quality Monitoring Results

3.4.1 Impact water quality monitoring was conducted at all designated monitoring stations during the reporting period. Impact water quality monitoring results and relevant graphical plots are provided in Appendix I.

3.4.2 For marine water quality monitoring, no Action Level and Limit Level exceedances of dissolved oxygen level, turbidity level and suspended solid level were recorded during the reporting period.

3.4.3 Water quality impact sources during water quality monitoring were nearby construction activities by other parties and nearby operating vessels by other parties.

3.5 Dolphin Monitoring Results

Data Analysis

3.5.1 Distribution Analysis – The line-transect survey data was integrated with the Geographic Information System (GIS) in order to visualize and interpret different spatial and temporal patterns of dolphin distribution using sighting positions. Location data of dolphin groups were plotted on map layers of Hong Kong using a desktop GIS (ArcView© 3.1) to examine their distribution patterns in details. The dataset was also stratified into different subsets to examine distribution patterns of dolphin groups with different categories of group sizes, young calves and activities.

3.5.2 Encounter rate analysis – Encounter rates of Chinese White Dolphins (number of on-effort sightings per 100 km of survey effort, and total number of dolphins sighted on-effort per 100 km of survey effort) were calculated in NEL and NWL survey areas in relation to the amount of survey effort conducted during each month of monitoring survey. Dolphin encounter rates were calculated in two ways for comparisons with the HZMB baseline monitoring results as well as to AFCD long-term marine mammal monitoring results.

3.5.3 Firstly, for the comparison with the HZMB baseline monitoring results, the encounter rates were calculated using primary survey effort alone, and only data collected under Beaufort 3 or below condition would be used for encounter rate analysis. The average encounter rate of sightings (STG) and average encounter rate of dolphins (ANI) were deduced based on the encounter rates from six events during the present quarter (i.e. six sets of line-transect surveys in North Lantau), which was also compared with the one deduced from the six events during the baseline period (i.e. six sets of line-transect surveys in North Lantau).

3.5.4 Secondly, the encounter rates were calculated using both primary and secondary survey effort collected under Beaufort 3 or below condition as in AFCD long-term monitoring study. The encounter rate of sightings and dolphins were deduced by dividing the total number of on-effort sightings (STG) and total number of dolphins (ANI) by the amount of survey effort for the present quarterly period.

3.5.5 Quantitative grid analysis on habitat use – To conduct quantitative grid analysis of habitat use, positions of on-effort sightings of Chinese White Dolphins collected during the quarterly impact phase monitoring period were plotted onto 1-km² grids among Northwest Lantau (NWL) and Northeast (NEL) survey areas on GIS. Sighting densities (number of on-effort sightings per km²) and dolphin densities (total number of dolphins from on-effort sightings per km²) were then calculated for each 1 km by 1 km grid with the aid of GIS.

3.5.6 Sighting density grids and dolphin density grids were then further normalized with the amount of survey effort conducted within each grid. The total amount of survey effort spent on each grid was calculated by examining the survey coverage on each line-transect survey to determine how many times the grid was surveyed during the study period. For example, when the survey boat traversed through a specific grid 50 times, 50 units of survey effort were counted for that grid. With the amount of survey effort calculated for each grid, the sighting density and dolphin density of each grid were then normalized (i.e. divided by the unit of survey effort).

3.5.7 The newly-derived unit for sighting density was termed SPSE, representing the number of on-effort sightings per 100 units of survey effort. In addition, the derived unit for actual dolphin density was termed DPSE, representing the number of dolphins per 100 units of survey effort. Among the 1-km² grids that were partially covered by land, the percentage of sea area was calculated using GIS tools, and their SPSE and DPSE values were adjusted accordingly. The following formulae were used to estimate SPSE and DPSE in each 1-km² grid within the study area:

SPSE = ((S / E) x 100) / SA%

DPSE = ((D / E) x 100) / SA%

where S = total number of on-effort sightings

D = total number of dolphins from on-effort sightings

E = total number of units of survey effort

SA% = percentage of sea area

3.5.8 Behavioural analysis – When dolphins were sighted during vessel surveys, their behaviour was observed. Different activities were categorized (i.e. feeding, milling/resting, traveling, socializing) and recorded on sighting datasheets. This data was then input into a separate database with sighting information, which can be used to determine the distribution of behavioural data with a desktop GIS. Distribution of sightings of dolphins engaged in different activities and behaviours would then be plotted on GIS and carefully examined to identify important areas for different activities of the dolphins.

3.5.9 Ranging pattern analysis – Location data of individual dolphins that occurred during the 3-month baseline monitoring period were obtained from the dolphin sighting database and photo-identification catalogue. To deduce home ranges for individual dolphins using the fixed kernel methods, the program Animal Movement Analyst Extension, was loaded as an extension with ArcView© 3.1 along with another extension Spatial Analyst 2.0. Using the fixed kernel method, the program calculated kernel density estimates based on all sighting positions, and provided an active interface to display kernel density plots. The kernel estimator then calculated and displayed the overall ranging area at 95% UD level.

3.5.10 During the period of December 2023 to February 2024, six sets of systematic line-transect vessel surveys were conducted to cover all transect lines in NWL and NEL survey areas twice per month.

3.5.11 From these surveys, a total of 807.81 km of survey effort was collected, with 99.3% of the total survey effort being conducted under favourable weather conditions (i.e. Beaufort Sea State 3 or below with good visibility). Among the two areas, 292.80 km and 515.01 km of survey effort were conducted in NEL and NWL survey areas respectively.

3.5.12The total survey effort conducted on primary lines was 576.36 km, while the effort on secondary lines was 231.45 km. Survey effort conducted on both primary and secondary lines were considered to be on-effort survey data. A summary table of the survey effort is shown in Annex I of Appendix J.

3.5.13 During the six sets of monitoring surveys conducted between December 2023 and February 2024, a total of three groups of eight Chinese White Dolphins was sighted, with the summary table of dolphin sighting shown in Annex II of Appendix J. All three dolphin groups were sighted on primary line during on-effort search.

3.5.14 Notably, the three dolphin groups were all sighted in NWL, and no dolphin was sighted at all in NEL. In fact, since August 2014, only two sightings of two lone dolphins were made in NEL during HKLR03/TMCLKL monitoring surveys.

Distribution

3.5.15 Distribution of dolphin sighting made during HKLR03 monitoring surveys conducted from December 2023 to February 2024 is shown in Figure 1 of Appendix J. Two of the three dolphin groups were sighted at the northwestern end of NWL survey area, while the other group was sighted at the southwestern corner of NWL survey area to the south of HKLR alignment. As consistently recorded in previous monitoring quarters, the dolphins were completely absent from the central and eastern portions of North Lantau waters (Figure 1 of Appendix J). Moreover, the dolphin sightings were located very far away from the HKLR03 and HKBCF reclamation sites as well as along the TMCLKL bridge alignments. (Figure 1 of Appendix J).

3.5.16 Sighting distribution of dolphins during the present impact phase monitoring period (December 2023 - February 2024) was drastically different from the one during the baseline monitoring period (Figure 1 of Appendix J). In the present quarter, dolphins have disappeared from the NEL region, which was in stark contrast to their frequent occurrences around the Brothers Islands, near Shum Shui Kok and in the vicinity of HKBCF reclamation site during the baseline period (Figure 1 of Appendix J). The complete abandonment of NEL region by the dolphins has been consistently recorded in the past eight years of HKLR03/TMCLKL monitoring.

3.5.17 In NWL survey area, dolphin occurrence was also drastically different between the baseline and impact phase periods. During the present impact monitoring period, dolphins were rarely sighted there, and their distribution was restricted to the western portion of the survey area, which was in stark contrast to their frequent occurrences throughout the area during the baseline period (Figure 1 of Appendix J).

3.5.18 Another comparison in dolphin distribution was made between the six quarterly periods of winter months in 2018-24. Across the six winter periods, the majority of dolphin sightings were made consistently at the western end of the North Lantau region, but during the past two winter periods in 2022-23 and 2023-24, there was a dramatic decline in their occurrence as well as a complete

3.5.19 absence from the Sha Chau and Lung Kwu Chau Marine Park (Figure 2 of Appendix J).

Encounter Rate

3.5.20 During the present three-month study period, the encounter rates of Chinese White Dolphins deduced from the survey effort and on-effort sighting data from the primary transect lines under favourable conditions (Beaufort 3 or below) for each set of the surveys in NEL and NWL are shown in Table 3.4. The average encounter rates deduced from the six sets of surveys were also compared with the ones deduced from the baseline monitoring period (September – November 2011) (Table 3.5).

Table 3.4 Dolphin Encounter Rates (Sightings Per 100 km of Survey Effort) During Reporting Period (Dec 2024 to Feb 2024)

SURVEY AREA	DOLPHIN MONITORING DATES	Encounter rate (STG) (no. of on-effort dolphin sightings per 100 km of survey effort)	Encounter rate (ANI) (no. of dolphins from all on-effort sightings per 100 km of survey effort)
SURVEY AREA	DOLPHIN MONITORING DATES	Primary Lines Only	Primary Lines Only
Northeast Lantau	Set 1 (4 & 6 Dec 2023)	0.00	0.00
	Set 2 (8 & 11 Dec 2023)	0.00	0.00
	Set 3 (9 ,12& 18 Jan 2024)	0.00	0.00
	Set 4 (19 & 25 Jan 2024)	0.00	0.00
	Set 5 (1 & 16 Jan 2024)	0.00	0.00
	Set 6 (20 & 21 Feb 2024)	0.00	0.00
Northwest Lantau	Set 1 (4 & 6 Dec 2023)	1.61	3.23
	Set 2 (8 & 11 Dec 2023)	0.00	0.00
	Set 3 (9,12 & 18 Jan 2024)	1.71	5.12
	Set 4 (19 & 25 Jan 2024)	1.62	4.87
	Set 5 (1 & 16 Feb 2024)	0.00	0.00
	Set 6 (20 & 21 Feb 2024)	0.00	0.00

Table 3.5 Comparison of average dolphin encounter rates from impact monitoring period (December 2023 to February 2024) and baseline monitoring period (September – November 2011)

	Encounter rate (STG) (no. of on-effort dolphin sightings per 100 km of survey effort)		Encounter rate (ANI) (no. of dolphins from all on-effort sightings per 100 km of survey effort)
	December 2023 – February 2024	September – November 2011	December 2023 – February 2024	September – November 2011
Northeast Lantau	0.0	6.00 ± 5.05	0.0	22.19 ± 26.81
Northwest Lantau	0.82 ± 0.90	9.85 ± 5.85	2.20 ± 2.50	44.66 ± 29.85

Notes:
1) The encounter rates deduced from the baseline monitoring period have been recalculated based only on survey effort and on-effort sighting data made along the primary transect lines under favourable conditions.

2) ± denotes the standard deviation of the average encounter rates.

3.5.21 To facilitate the comparison with the AFCD long-term monitoring results, the encounter rates were also calculated for the present quarter using both primary and secondary survey effort. The encounter rates of sightings (STG) and dolphins (ANI) in NWL were 0.59 sightings and 1.57 dolphins per 100 km of survey effort respectively, while the encounter rates of sightings (STG) and dolphins (ANI) in NEL were both nil for this quarter.

3.5.22 In NEL, the average dolphin encounter rates (both STG and ANI) in the present three-month impact monitoring period were both zero with no on-effort sighting being made, and such extremely low occurrence of dolphins in NEL have been consistently recorded in past summer quarters of HKLR03/ TMCLKL monitoring since HKLR03 construction began in late 2012 (Table 3.6). This is a serious concern as the dolphin occurrence in NEL in the past few years (0.0-1.0 for ER(STG) and 0.0-3.9 for ER(ANI)) have remained exceptionally low when compared to the baseline period (Table 3.6). Dolphins have been virtually absent from NEL waters since August 2014, with only two lone dolphins sighted there on two separate occasions despite consistent and intensive survey effort being conducted in this survey area.

Table 3.6 Comparison of Average Dolphin Encounter Rates in Northeast Lantau Survey Area from All Winter Quarters of Impact Monitoring Period and Baseline Monitoring Period (Sep – Nov 2011)

	Encounter rate (STG) (no. of on-effort dolphin sightings per 100 km of survey effort)	Encounter rate (ANI) (no. of dolphins from all on-effort sightings per 100 km of survey effort)
September-November 2011 (Baseline)	6.00 ± 5.05	22.19 ± 26.81
December 2012-February 2013 (HKLR03 Impact)	3.14 ± 3.21	6.33 ± 8.64
December 2013-February 2014 (HKLR03 Impact)	0.45 ± 1.10	1.34 ± 3.29
December 2014-February 2015 (HKLR03 Impact)	0.00	0.00
December 2015-February 2016 (HKLR03 Impact)	0.00	0.00
December 2016-February 2017 (HKLR03 Impact)	0.00	0.00
December 2017-February 2018 (HKLR03 Impact)	0.00	0.00
December 2018-February 2019 (HKLR03 Impact)	0.00	0.00
December 2019-February 2020 (HKLR03 Impact)	0.00	0.00
December 2020-February 2021 (TMCLKL Post-Construction)	0.00	0.00
December 2021-February 2022 (TMCLKL Post-Construction)	0.00	0.00
December 2022-February 2023 (HKLR03 Impact)	0.00	0.00

2) ± denotes the standard deviation of the average encounter rates.

3.5.23 On the other hand, the average dolphin encounter rates (STG and ANI) in NWL during the present impact phase monitoring period were only tiny fractions of the ones recorded during the three-month baseline period, indicating a dramatic decline in dolphin usage of this survey area as well during the present impact phase period (Table 3.7).

3.5.24 Notably, when comparing among the 12 quarterly periods in winter months since 2013, the quarterly encounter rates in NWL in the past three winter periods plummeted to an exceptionally low level (Table 5). In fact, the present quarterly period has also recorded the lowest ER(STG) and ER(ANI) ever during the entire HKLR03 construction period (even lower than the previous lowest in 2022-23 monitoring period). The dramatic drop in dolphin occurrence in NWL in recent years should raise serious concerns, and such temporal trend should be closely monitored in the upcoming monitoring quarters as the construction activities of HZMB works will soon be completed in coming months.

Table 3.7 Comparison of Average Dolphin Encounter Rates in Northwest Lantau Survey Area from All Winter Quarters of Impact Monitoring Period and Baseline Monitoring Period (Sep – Nov 2011)

	Encounter rate (STG) (no. of on-effort dolphin sightings per 100 km of survey effort)	Encounter rate (ANI) (no. of dolphins from all on-effort sightings per 100 km of survey effort)
September-November 2011 (Baseline)	9.85 ± 5.85	44.66 ± 29.85
December 2012-February 2013 (HKLR03 Impact)	8.36 ± 5.03	35.90 ± 23.10
December 2013-February 2014 (HKLR03 Impact)	8.21 ± 2.21	32.58 ± 11.21
December 2014-February 2015 (HKLR03 Impact)	2.91 ± 2.69	11.27 ± 15.19
December 2015-February 2016 (HKLR03 Impact)	2.64 ± 1.52	10.98 ± 3.81
December 2016-February 2017 (HKLR03 Impact)	3.80 ± 3.79	14.52 ± 17.21
December 2017-February 2018 (HKLR03 Impact)	4.75 ± 2.26	15.73 ± 15.94
December 2018-February 2019 (HKLR03 Impact)	2.40 ± 1.88	7.95 ± 6.60
December 2019-February 2020 (HKLR03 Impact)	1.96 ± 2.23	8.15 ± 10.85
December 2020-February 2021 (TMCLKL Post-Construction)	3.01 ± 2.83	8.47 ± 9.07
December 2021-February 2022 (TMCLKL Post-Construction)	1.63 ± 1.47	3.52 ± 3.87
December 2022-February 2023 (HKLR03 Impact)	0.87 ± 0.96	3.35 ± 4.84

3.5.25 A two-way ANOVA with repeated measures and unequal sample size was conducted to examine whether there were any significant differences in the average encounter rates between the baseline and impact monitoring periods. The two variables that were examined included the two periods (baseline and impact phases) and two locations (NEL and NWL).

3.5.26 For the comparison between the baseline period and the present quarter (35th quarter of the impact phase being assessed), the p-values for the differences in average dolphin encounter rates of STG and ANI were 0.0014 and 0.0067 respectively. If the alpha value is set at 0.01, significant differences were still detected between the baseline and present quarters in both the average dolphin encounter rates of STG and ANI.

3.5.27 For the comparison between the baseline period and the cumulative quarters in impact phase (i.e. the first 46 quarters of the HKLR03/TMCLKL monitoring programme being assessed), the p-values for the differences in average dolphin encounter rates of STG and ANI were 0.000000 and 0.000000 respectively. Even if the alpha value is set at 0.00001, significant differences were still detected in both the average dolphin encounter rates of STG and ANI (i.e. between the two periods and the locations).

3.5.28 As indicated in both dolphin distribution patterns and encounter rates, dolphin usage has been dramatically and significantly reduced in both NEL and NWL survey areas during the present quarterly period when compared to the baseline period, and such low occurrence of dolphins has also been consistently documented in previous quarters of the past eight years throughout the HZMB construction.

3.5.29 The significant decline in dolphin usage of North Lantau region raises serious concern, as the timing of the decline in dolphin usage in North Lantau waters coincided well with the construction schedule of the HZMB-related projects. Not only there has been no sign of recovery of dolphin usage, such usage has continued to fall to near-absence level for the entire region, even though almost all marine works associated with the HZMB construction have been completed, and the Brothers Marine Park has been established in late 2016 as a compensation measure for the permanent habitat loss in association with the HKBCF reclamation works.

Group size

3.5.30 Three groups of Chinese White Dolphins were sighted during December 2023 to February 2024, resulting in an average group size of 2.67. This was compared with the ones deduced from the baseline period in September to November 2011, as shown in Table 3.8.

Table 3.8 Comparison of average dolphin group sizes from impact monitoring period (September – November 2023) and baseline monitoring period (September – November 2011) (Note: ± denotes the standard deviation of the average group size)

	Average Dolphin Group Size
	December 2023 – February 2024	September – November 2011
Overall	2.67 ± 0.58 (n = 3)	3.72 ± 3.13 (n = 66)
Northeast Lantau	---	3.18 ± 2.16 (n = 17)
Northwest Lantau	2.67 ± 0.58 (n = 3)	3.92 ± 3.40 (n = 49)

3.5.31 The average dolphin group size in NWL waters during the present quarterly period was lower than the one recorded during the three-month baseline period, but it should be cautioned that the very small sample size of only three dolphin groups in the present quarter was only a tiny fraction of the sample size of 66 dolphin groups sighted during the baseline period (Table 3.8).

Habitat Use

3.5.32 From December 2023 to February 2024, a total of three grids in North Lantau waters recorded dolphin occurrence (each with a single sighting) during on-effort search. They were located to at the northwest and southwest corners of the NWL survey area respectively, with moderately low to moderately high densities (Figures 3a and 3b of Appendix J).

3.5.33 Notably, all grids near HKLR03/HKBCF reclamation sites as well as TMCLKL bridge alignments did not record any presence of dolphins at all during on-effort search in the present quarterly period (Figures 3a and 3b of Appendix J).

3.5.34 It should be emphasized that the amount of survey effort collected in each grid during the three-month period was fairly low (6-12 units of survey effort for most grids), and therefore the habitat use pattern derived from the three-month dataset should be treated with caution. A more complete picture of dolphin habitat use pattern should be examined when more survey effort for each grid is collected throughout the impact phase monitoring programme.

3.5.35 When compared with the habitat use patterns during the baseline period, dolphin usage in NEL and NWL has drastically diminished in both areas during the present impact monitoring period (Figure 4 of Appendix J). During the baseline period, many grids between Siu Mo To and Shum Shui Kok in NEL recorded moderately high to high dolphin densities, which was in stark contrast to the complete absence of dolphins there during the present impact phase period.

3.5.36 The density patterns were also drastically different in NWL between the baseline and impact phase monitoring periods, with high dolphin usage recorded throughout the area during the baseline period, especially around Sha Chau, near Black Point, to the west of the airport, as well as between Pillar Point and airport platform. In contrast, only a few grids with recorded dolphin density was located at the western territorial border during the present impact phase period (Figure 4 of Appendix J).

Mother-calf pairs

3.5.37 During the present quarterly period, only one unspotted juvenile was sighted with its mother in the North Lantau region. Notably, the last young calf being sighted during the HKLR03/TMCLKL EM&A monitoring was nearly three years ago in May 2021. The mother-calf pair was located at the southwestern corner of NWL survey area, very close to the WL survey area near Shum Wat (Figure 5 of Appendix J). The very rare occurrence of young calves in the present quarter as well as in recent year was drastically from their regular occurrence in North Lantau waters during the baseline period (Figure 5 of Appendix J). This should be a serious concern, and the occurrence of young calves in North Lantau waters should be closely monitored in the upcoming quarters.

Activities and associations with fishing boats

3.5.38 During the present quarterly period, the three dolphin groups sighted were not engaged in any activities. Furthermore, they were not found to be associated with any operating fishing vessel during the present impact phase period.

Summary of photo-identification works

3.5.39 From December 2023 to February 2024, around 800 digital photographs were taken during the impact phase monitoring surveys for the photo-identification work.

3.5.40 From two of the three dolphin sightings, a total of three individual dolphins were identified (see summary table in Annex III of Appendix J and photograph of the identified individuals in Annex IV of Appendix J). All individuals were re-sighted only once, and their re-sightings were only made in NWL during the quarterly period.

Individual range use

3.5.41 Ranging patterns of the three individual dolphins identified during the three-month study period was determined by fixed kernel method, and is shown in Appendix V. They were all utilizing NWL waters only, but have completely avoided NEL waters where many of them have utilized as their core areas in the past, which is in contrary to the extensive movements between NEL and NWL survey areas observed in the baseline period and the first two years of impact monitoring period.

3.5.42 Notably, all three individuals have primarily centered their range use in West Lantau waters in the past, and two of them (WL145 and WL315) have only extended just a kilometer into NWL waters during this quarterly period. On the contrary, WL79 was rarely sighted in NWL waters before, but have ventured further north (to the north of Lung Kwu Chau) away from its primary

3.5.43 range during this quarterly period (Appendix V).

Conclusion

3.5.44 During the present quarter of dolphin monitoring, no adverse impact from the activities of this construction project on Chinese White Dolphins was noticeable from general observations.

3.5.45 Although dolphins rarely occurred in the area of HKLR03 construction in the past and during the baseline monitoring period, it is apparent that dolphin usage has been dramatically reduced in NEL since 2012, and many individuals have shifted away completely from the important habitat around the Brothers Islands.

3.5.46 It is critical to continuously monitor the dolphin usage in North Lantau region to determine whether the dolphins are continuously affected by the construction activities in relation to the HZMB-related works, and whether suitable mitigation measure can be applied to revert the situation.

3.6 Mudflat Monitoring Results

Sedimentation Rate Monitoring

3.6.1 The baseline sedimentation rate monitoring was in September 2012 and impact sedimentation rate monitoring was undertaken on 4 December 2024. The mudflat surface levels at the four established monitoring stations and the corresponding XYZ HK1980 GRID coordinates are presented in Table 3.8 and Table 3.9.

Table 3.8 Measured Mudflat Surface Level Results

	Baseline Monitoring (September 2012)			Impact Monitoring (Dec 2023)
Monitoring Station	Easting (m)	Northing (m)	Surface Level (mPD)	Easting (m)	Northing (m)	Surface Level (mPD)
S1	810291.160	816678.727	0.950	810291.164	816678.711	1.138
S2	810958.272	815831.531	0.864	810958.261	815831.541	0.994
S3	810716.585	815953.308	1.341	810716.585	815953.322	1.471
S4	811221.433	816151.381	0.931	811221.448	816151.385	1.106

Table 3.9 Comparison of Measurement

	Comparison of Measurement			Remarks and Recommendation
Monitoring Station	Easting (m)	Northing (m)	Surface Level (mPD)	Remarks and Recommendation
S1	0.004	-0.016	0.188	Level continuously increased
S2	-0.011	-0.001	0.126	Level continuously increased
S3	0.022	-0.037	0.122	Level continuously increased
S4	0.015	0.004	0.175	Level continuously increased

3.6.2 This measurement result was generally and relatively higher than the baseline measurement at S1, S2, S3 and S4. The mudflat level is continuously increased.

Water Quality Monitoring

3.6.3 The mudflat monitoring covered water quality monitoring data. Reference was made to the water quality monitoring data of the representative water quality monitoring station (i.e. SR3(N)) as in the EM&A Manual. The water quality monitoring location (SR3(N)) is shown in Figure 2.1 of Appendix I.

3.6.4 Water quality monitoring in San Tau (monitoring station SR3(N)) was conducted in December 2023 as part of mudflat monitoring. The monitoring parameters included dissolved oxygen (DO), turbidity and suspended solids (SS).

3.6.5 The water monitoring result for SR3(N) were extracted and summarised in Table 3.10:

Table 3.10 Impact Water Quality Monitoring Results (Depth Average) at Station SR3(N)

	Mid Ebb Tide			Mid Flood Tide
	DO (mg/L)	Turbidity (NTU)	SS (mg/L)	DO (mg/L)	Turbidity (NTU)	SS (mg/L)
1-Dec-2023	6.13	3.48	2.58	5.58	2.95	2.10
4-Dec-2023	6.08	3.18	2.50	6.47	3.63	1.00
6-Dec-2023	6.88	3.78	2.10	7.20	4.00	2.50
8-Dec-2023	6.76	3.45	2.68	7.05	3.60	2.68
11-Dec-2023	6.77	3.33	2.13	6.41	3.45	2.08
13-Dec-2023	6.18	3.80	6.23	5.90	3.83	6.65
15-Dec-2023	6.23	3.45	2.80	5.95	3.53	2.55
18-Dec-2023	6.24	2.70	3.95	6.45	2.68	4.33
20-Dec-2023	6.42	2.78	3.73	6.64	2.85	2.68
22-Dec-2023	6.69	3.18	3.80	6.67	3.50	2.00
25-Dec-2023	6.76	2.83	3.13	6.40	3.63	3.58
27-Dec-2023	7.09	3.10	3.45	7.21	2.90	4.48
29-Dec-2023	7.26	3.20	5.95	7.14	2.85	6.03
Average	6.58	3.25	3.46	6.54	3.34	3.28

Mudflat Ecology Monitoring

Sampling Zone

3.6.6 To collect baseline information of mudflats in the study site, the study site was divided into three sampling zones (labeled as TC1, TC2, TC3) in Tung Chung Bay and one zone in San Tau (labeled as ST) (Figure 2.1 of Appendix O). The horizontal shoreline of sampling zones TC1, TC2, TC3 and ST were about 250 m, 300 m, 300 m and 250 m, respectively (Figure 2.2 of Appendix O). Survey of horseshoe crabs, seagrass beds and intertidal communities were conducted in every sampling zone. The present survey was conducted in December 2023 (totally 4 sampling days 2^nd (for ST), 3^rd (for TC3), 4^th (for TC2) and 5^th (for TC1).

3.6.7 Since the field survey of June 2016, increasing number of trashes and even big trashes (Figure 2.3 of Appendix O) were found in every sampling zone. It raised a concern about the solid waste dumping and current-driven waste issues in Tung Chung Wan. Respective measures (e.g., manual clean-up) should be implemented by responsible governmental agency units.

Horseshoe Crabs

3.6.8 Active search method was adopted for horseshoe crab monitoring by two experienced surveyors in every sampling zone. During the search period, any accessible and potential area would be investigated for any horseshoe crab individuals within 2-3 hour of low tide period (tidal level below 1.2 m above Chart Datum (C.D.)). Once a horseshoe crab individual was found, the species was identified referencing to Li (2008). The prosomal width, inhabiting substratum and respective GPS coordinate were recorded. A photographic record was taken for future investigation. Any grouping behavior of individuals, if found, was recorded. The horseshoe crab surveys were conducted on 2nd (for ST), 3rd (for TC3), 4th (for TC2) and 5th December 2023, which were cloudy days.

3.6.9 In June 2017, a big horseshoe crab was tangled by a trash gill net in ST mudflat (Figure 2.3 of Appendix O). It was released to sea once after photo recording. The horseshoe crab of such size should be inhabiting sub-tidal environment while it forages on intertidal shore occasionally during high tide period. If it is tangled by the trash net for few days, it may die due to starvation or overheat during low tide period. These trash gill nets are definitely ‘fatal trap’ for the horseshoe crabs and other marine life. Manual clean-up should be implemented as soon as possible by responsible governmental agency units.

Seagrass Beds

3.6.10 Active search method was adopted for seagrass bed monitoring by two experienced surveyors in every sampling zone. During the search period, any accessible and potential area would be investigated for any seagrass beds within 2-3 hours of low tide period. Once seagrass bed was found, the species, estimated area, estimated coverage percentage and respective GPS coordinates were recorded. The seagrass beds surveys were conducted on 2^nd th (for ST), 3^rd (for TC3), 4^th (for TC2) and 5^th (for TC1) December 2023, which were cloudy days.

Intertidal Soft Shore Communities

Field Sampling

3.6.11 The intertidal soft shore community surveys were conducted in low tide period on 2^nd th (for ST), 3^rd (for TC3), 4^th (for TC2) and 5^th (for TC1) December 2023, which were cloudy days. In every sampling zone, three 100m horizontal transect lines were laid at high tidal level (H: 2.0m above C.D.), mid tidal level (M: 1.5m above C.D.) and low tidal level (L: 1.0m above C.D.). Along every horizontal transect line; ten random quadrats (0.5 m x 0.5m) were placed.

3.6.12 Inside a quadrat, any visible epifauna was collected and was in-situ identified to the lowest practical taxonomical resolution. Whenever possible a hand core sample (10 cm internal diameter ´ 20 cm depth) of sediments was collected in the quadrat. The core sample was gently washed through a sieve of mesh size 2.0 mm in-situ. Any visible infauna was collected and identified. Finally, the top 5 cm surface sediment was dug for visible infauna in the quadrat regardless of hand core sample was taken.

3.6.13 All collected fauna were released after recording except some tiny individuals that were too small to be identified on site. These tiny individuals were taken to laboratory for identification under dissecting microscope.

3.6.14 The taxonomic classification was conducted in accordance to the following references: Polychaetes: Fauchald (1977), Yang and Sun (1988); Arthropods: Dai and Yang (1991), Dong (1991); Mollusks: Chan and Caley (2003), Qi (2004), AFCD (2018).

Data Analysis

3.6.15 Data collected from direct search and core sampling was pooled in every quadrat for data analysis. Shannon-Weaver Diversity Index (H’) and Pielou’s Species Evenness (J) were calculated for every quadrat using the formulae below,

H’= -Σ ( Ni / N ) ln ( Ni / N ) (Shannon and Weaver, 1963)

J = H’ / ln S, (Pielou, 1966)

where S is the total number of species in the sample, N is the total number of individuals, and Ni is the number of individuals of the i^th species.

Mudflat Ecology Monitoring Results and Conclusion

Horseshoe Crabs

3.6.16 No Tachypleus tridentatus was found in present survey. Only dead bodies of horseshoe crabs

3.6.17 were found. Photo records of previously observed horseshoe crab is shown in Figure 3.1 of

3.6.18 Appendix I and the present survey result regarding horseshoe crab are presented in Table 3.1.

3.6.19 The complete survey records are presented in Annex II of Appendix I.

3.6.20 No Carcinoscorpius rotundicauda was recorded in present survey.

3.6.21 For Tachypleus tridentatus, 18 individuals with average body size 59.09 mm (prosomal width ranged 46.21 – 77.25 mm) were found in ST and 9 individuals with average body size 66.6 (prosomal width ranged 46.5-84.13 mm) were found in TC3 in present survey. The search records in ST (3.0 ind. hr-1. Person-1) and in TC3 (1.5 ind. Hr-1. Person-1).

3.6.22 In the survey of March 2015, there was one important finding that a mating pair of Carcinoscorpius rotundicauda was found in ST (prosomal width: male 155.1mm, female 138.2mm). It indicated the importance of ST as a breeding ground of horseshoe crab. In June 2017, mating pairs of Carcinoscorpius rotundicauda were found in TC2 (male 175.27 mm, female 143.51 mm) and TC3 (male 182.08 mm, female 145.63 mm) (Figure 3.2 of of Appendix O). In December 2017 and June 2018, one mating pair was of Carcinoscorpius rotundicauda was found in TC3 (December 2017: male 127.80 mm, female 144.61 mm; June 2018: male 139 mm, female 149 mm). In June 2019, two mating pairs of Tachypleus tridentatus with large body sizes (male 150mm and Female 200mm; Male 180mm and Female 220mm) were found in TC3. Another mating pair of Tachypleus tridentatus was found in ST (male 140mm and Female 180mm). In March 2020, a pair of Tachypleus tridentatus with large body sizes (male 123mm and Female 137mm was recorded in TC1. Figure 3.2 of Appendix O shows the photographic records of the mating pair found. The recorded mating pairs were found nearly burrowing in soft mud at low tidal level (0.5-1.0 m above C.D.). The smaller male was holding the opisthosoma (abdomen carapace) of larger female from behind. A mating pair was found in TC1 in March 2020, it indicated that breeding of horseshoe crab could be possible along the coast of Tung Chung Wan rather than ST only, as long as suitable substratum was available. Based on the frequency of encounter, the shoreline between TC3 and ST should be more suitable mating ground. Moreover, suitable breeding period was believed in wet season (March – September) because tiny individuals (i.e. newly hatched) were usually recorded in June and September every year (Figure 3.3 of Appendix O). One mating pair was found in June 2022. 3 adult individuals (prosomal width >100mm) of Carcinoscorpius rotundicauda were recorded in September 2022 survey, with one alive, one dead in TC3 and one dead in TC2. June 2022, 7 large individuals (prosomal width >100mm) of Carcinoscorpius rotundicauda was recorded (prosomal width ranged 131.4mm - 140.3mm) in TC3. In December 2018, one large individual of Carcinoscorpius rotundicauda was found in TC3 (prosomal width 148.9 mm). In March 2019, 3 large individuals (prosomal width ranged 220 – 310mm) of Carcinoscorpius rotundicauda were observed in TC2. In June 2019, there were 3 and 7 large individuals of Tachypleus tridentatus recorded in ST (prosomal width ranged 140 – 180mm) and TC3 (prosomal width ranged 150 – 220mm), respectively. In March 2020, a mating pair of Tachypleus tridentatus was recorded in TC1 with prosomal width 123 mm and 137mm. Base on their sizes, it indicated that individuals of prosomal width larger than 100 mm would progress its nursery stage from intertidal habitat to sub-tidal habitat of Tung Chung Wan. The photo records of the large horseshoe crab are shown in Figure 3.4 of Appendix O. These large individuals might move onto intertidal shore occasionally during high tide for foraging and breeding. Because they should be inhabiting sub-tidal habitat most of the time. Their records were excluded from the data analysis to avoid mixing up with juvenile population living on intertidal habitat.

3.6.23 Some marked individuals were found in the previous surveys of September 2013, March 2014, and September 2014. All of them were released through a conservation programme in charged by Prof. Paul Shin (Department of Biology and Chemistry, The City University of Hong Kong (CityU)). It was a re-introduction trial of artificial bred horseshoe crab juvenile at selected sites. So that the horseshoe crab’s population might be restored in the natural habitat. Through a personal conversation with Prof. Shin, about 100 individuals were released in the sampling zone ST on 20 June 2013. All of them were marked with color tape and internal chip detected by specific chip sensor. There should be second round of release between June and September 2014 since new marked individuals were found in the survey of September 2014.

3.6.24 The artificial bred individuals, if found, would be excluded from the results of present monitoring programme in order to reflect the changes of natural population. However, the mark on their prosoma might have been detached during moulting after a certain period of release. The artificially released individuals were no longer distinguishable from the natural population without the specific chip sensor. The survey data collected would possibly cover both natural population and artificially bred individuals.

Population difference among the sampling zones

3.6.25 Figure 3.5 and 3.6 of Appendix O show the changes of number of individuals, mean prosomal width and search record of horseshoe crabs Carcinoscorpius rotundicauda and Tachypleus tridentatus in respectively in each sampling zone throughout the monitoring period.

3.6.26 To consider the entire monitoring period for TC3 and ST, medium to high search records (i.e. number of individuals) of both species (Carcinoscorpius rotundicauda and Tachypleus tridentatus) were usually found in wet season (June and September). The search record of ST was higher from September 2012 to June 2014 while it was replaced by TC3 from September 2014 to June 2015. The search records were similar between two sampling zones from September 2015 to June 2016. In September 2016, the search record of Carcinoscorpius rotundicauda in ST was much higher than TC3. From March to June 2017, the search records of both species were similar again between two sampling zones. It showed a natural variation of horseshoe crab population in these two zones due to weather condition and tidal effect. No obvious difference of horseshoe crab population was noted between TC3 and ST. In September 2017, the search records of both horseshoe crab species decreased except the Carcinoscorpius rotundicauda in TC3. The survey results were different from previous findings that there were usually higher search records in September. One possible reason was that the serial cyclone hit decreased horseshoe crab activity (totally 4 cyclone records between June and September 2017, to be discussed in 'Seagrass survey' section). From December 2017 to September 2018, the search records of both species increased again to low-moderate level in ST and TC3. From December 2018 to September 2019, the search records of Carcinoscorpius rotundicauda change from very low to low while the change of Tachypleus tridentatus was similar during this period. Relatively higher population fluctuation of Carcinoscorpius rotundicauda was observed in TC3. From March 2020 to September 2020, the search records of both species, Carcinoscorpius rotundicauda and Tachypleus tridentatus, were increased to moderate level in ST. However, the search records of both species, Carcinoscorpius rotundicauda and Tachypleus tridentatus, were decreased from very low to none in TC3 in this period. From March 2021 to September 2021, the search records of both species, Carcinoscorpius rotundicauda and Tachypleus tridentatus, were kept at low-moderate level in both ST and TC3. It is similar to the previous findings of June. It shows another growing phenomenon of horseshoe crabs and it may due to the weather variation of starting of wet season. The survey results were different from previous findings that there were usually higher search records in September. One possible reason was that September of 2021 was one of the hottest month in Hong Kong in record. As such, hot and shiny weather decreased horseshoe crab activity. In December 2021, no juvenile was recorded similar to the some previous in December due to the season. In March 2022, only juvenils recorded in both ST and TC3, no adult specimen was observed. In June 2022, total of 13 individuals of Carcinoscorpius rotundicauda and Tachypleus tridentatus were found, with 6 juveniles, 6 adults and 1 died recorded. In September 2022, total of 7 individuals of were found, with 4 juveniles, 3 adults (1 alive and 2 died) recorded. In March 2023, total of 12 individuals of juveniles Carcinoscorpius rotundicauda and Tachypleus tridentatus were found and recorded. In June 2023, total of 27 individuals of juveniles Tachypleus tridentatus were found and recorded. In September 2023, total of 2 individuals of juveniles Tachypleus

3.6.27 tridentatus were found and recorded.

3.6.28 For TC1, the search record was at low to moderate level throughout the monitoring period. The change of Carcinoscorpius rotundicauda was relatively more variable than that of Tachypleus tridentatus. Relatively, the search record was very low in TC2. There were occasional records of 1 to 4 individuals between March and September throughout the monitoring period. The maximum record was 6 individuals only in June 2016.

3.6.29 About the body size, larger individuals of Carcinoscorpius rotundicauda were usually found in ST and TC1 relative to that in TC3 from September 2012 to June 2017. But the body size was higher in TC3 and ST followed by TC1 from September 2017 to March 2020. From June 2020 to December 2020, there was no individuals of Carcinoscorpius rotundicauda recorded in TC3 but in ST. The body size of Carcinoscorpius rotundicauda in ST was recorded gradually increased (from mean prosomal width 23.6mm to 49.6mm) since March 2020 to September 2020. From December 2020 to March 2021, the body size of Carcinoscorpius rotundicauda in ST was recorded decreased (from mean prosomal width 49.6mm to 43.3mm). In March 2021, the body size of Carcinoscorpius rotundicauda in TC3 (mean prosomal width 46.2mm) was recorded larger than that in ST (mean prosomal width 43.3mm). From September 2021 to June 2022, the body size of Carcinoscorpius rotundicauda in ST was recorded increased (from mean prosomal width 39.8mm to 54.42mm). For Tachypleus tridentatus, larger individuals were usually found in ST and TC3 followed by TC1 throughout the monitoring period. In June 2019, all found horseshoe crabs were large individuals and mating pairs. It is believed that the sizes of the horseshoe crabs would be decrease and gradually rise afterward due to the stable growth of juveniles after the spawning season. From March 2019 to September 2021, Tachypleus tridentatus were only recorded in TC3 and ST. The body size in TC3 was increased from September 2019 to December 2019 then decreased in March 2020 and no recorded species in TC3 for three consecutive quarters from June 2020 to December 2020. From March 2020 to Sep 2021, the body size of Tachypleus tridentatus in TC3 increased (from mean prosomal width 34.00mm to 38.8mm). It showed a natural variation of horseshoe crab population in TC3. Apart from natural mortality, migration from nursery soft shore to subtidal habitat was another possible cause. The body size in ST was gradually growth since December 2019 to September 2020 then slightly dropped in December 2020. In June 2022, Tachypleus tridentatus were only recorded in ST, the body size in ST decreased from mean prosomal width 77.59mm to 54.02mm in March 2022. In September 2022 Tachypleus tridentatus were only recorded in TC3. The mean prosomal was 61.09mm. In March 2023, 7 Tachypleus tridentatus were recorded in ST and TC3. The mean prosomal was 62.68mm.

3.6.30 In general, it was obvious that the shoreline along TC3 and ST (western shore of Tung Chung Wan) was an important nursery ground for horseshoe crab especially newly hatched individuals due to larger area of suitable substratum (fine sand or soft mud) and less human disturbance (far from urban district). Relatively, other sampling zones were not a suitable nursery ground especially TC2. Possible factors were less area of suitable substratum (especially TC1) and higher human disturbance (TC1 and TC2: close to urban district and easily accessible). In TC2, large daily salinity fluctuation was a possible factor since it was flushed by two rivers under tidal inundation. The individuals inhabiting TC1 and TC2 were confined in small foraging area due to limited area of suitable substratum. Although there were mating pairs seldomly found in TC1 and TC2, the hatching rate and survival rate of newly hatched individuals were believed very low.

Seasonal variation of horseshoe crab population

3.6.31 6.5.12 Throughout the monitoring period, the search records of horseshoe crabs were fluctuated and at moderate – very low level in June (Figure 3.5 and 3.6 of Appendix O). Low – Very low search record was found in June 2013, totally 82 individuals of Tachypleus tridentatus and 0 ind. of Carcinoscorpius rotundicauda were found in TC1, TC3 and ST. Compare with the search record of June 2013, the numbers of Tachypleus tridentatus were gradually decreased in June 2014 and 2015 (55 ind. in 2014 and 18 ind. in 2015); the number of Carcinoscorpius rotundicauda raise to 88 and 66 ind. in June 2014 and 2015 respectively. In June 2016, the search record increased about 3 times compare with June 2015. In total, 182 individuals of Carcinoscorpius rotundicauda and 47 individuals of Tachypleus tridentatus were noted, respectively. Then, the search record was similar to June 2016. The number of recorded Carcinoscorpius rotundicauda (133 ind.) slightly dropped in June 2017. However, that of Tachypleus tridentatus rapidly increased (125 ind.). In June 2018, the search record was low to moderate while the numbers of Tachypleus tridentatus dropped sharply (39 ind.). In June 2019, 10 individuals of Tachypleus tridentatus were observed in TC3 and ST. All of them, however, were large individuals (prosomal width >100mm), their records are excluded from the data analysis to avoid mixing up with the juvenile population living on intertidal habitat. Until September 2020, the number of Carcinoscorpius rotundicauda and Tachypleus tridentatus gradually increased to 39 ind. and 28 ind., respectively. In December 2020, the number of Carcinoscorpius rotundicauda and Tachypleus tridentatus greatly decreased to 3 ind. and 7 ind., respectively. In March 2022, the number of Carcinoscorpius rotundicauda and Tachypleus tridentatus gradually decreased to 7 ind. and 2 ind., respectively in comparing with the March of previous record. The drop of abundance may be related to the unusual cold weather in the beginning of March 2022. Throughout the monitoring period, similar distribution of horseshoe crab population was found.

3.6.32 The search record of horseshoe crab declined obviously in all sampling zones during dry season especially December (Figure 3.5 and 3.6 of Appendix O) throughout the monitoring period. Very low – low search record was found in December from 2012 to 2015 (0-4 ind. of Carcinoscorpius rotundicauda and 0 – 12 ind. of Tachypleus tridentatus). The horseshoe crabs were inactive and burrowed in the sediments during cold weather (<15 ºC). Similar results of low search record in dry season were reported in a previous territory-wide survey of horseshoe crab. For example, the search records in Tung Chung Wan were 0.17 ind. hr^-1person^-1 and 0.00 ind. hr^-1 person^-1 in wet season and dry season respectively (details see Li, 2008). Compare with the search record of December from 2012 to 2015, which of December 2016 were much higher relatively. There were totally 70 individuals of Carcinoscorpius rotundicauda and 24 individuals of Tachypleus tridentatus in TC3 and ST. Since the survey was carried in earlier December with warm and sunny weather (~22 ºC during dawn according to Hong Kong Observatory database, Chek Lap Kok station on 5 December 2016), the horseshoe crab was more active (i.e. move onto intertidal shore during high tide for foraging and breeding) and easier to be found. In contrast, there was no search record in TC1 and TC2 because the survey was conducted in mid December with colder and cloudy weather (~20°C during dawn on 19 December). The horseshoe crab activity would decrease gradually with the colder climate. In December of 2017, 2018 and 2019, very low search records were found again as mentioned above. No record of houseshoe crab was recorded in December 2022 and 2023.

3.6.33 From September 2012 to December 2013, Carcinoscorpius rotundicauda was less common species relative to Tachypleus tridentatus. Only 4 individuals were ever recorded in ST in December 2012. This species had ever been believed of very low density in ST hence the encounter rate was very low. In March 2014, it was found in all sampling zones with higher abundance in ST. Based on its average size (mean prosomal width 39.28 – 49.81 mm), it indicated that breeding and spawning of this species had occurred about 3 years ago along the coastline of Tung Chun Wan. However, these individuals were still small while their walking trails were inconspicuous. Hence there was no search record in previous sampling months. Since March 2014, more individuals were recorded due to larger size and higher activity (i.e. more conspicuous walking trail).

3.6.34 For Tachypleus tridentatus, sharp increase of number of individuals was recorded in ST during the wet season of 2013 (from March to September). According to a personal conversation with Prof. Shin (CityU), his monitoring team had recorded similar increase of horseshoe crab population during wet season. It was believed that the suitable ambient temperature increased its conspicuousness. However similar pattern was not recorded in the following wet seasons. The number of individuals increased in March and June 2014 and followed by a rapid decline in September 2014. Then the number of individuals fluctuated slightly in TC3 and ST until March 2017. Apart from natural mortality, migration from nursery soft shore to subtidal habitat was another possible cause. Since the mean prosomal width of Tachypleus tridentatus continued to grow and reached about 50 mm since March 2014. Then it varied slightly between 35-65 mm from September 2014 to March 2017.Most of the individuals might have reached a suitable size (e.g. prosomal width 50 – 60 mm) strong enough to forage in sub-tidal habitat. In June 2017, the number of individuals increased sharply again in TC3 and ST. Although mating pair of Tachypleus tridentatus was not found in previous surveys, there should be new round of spawning in the wet season of 2016. The individuals might have grown to a more conspicuous size in 2017 accounting for higher search record. In September 2017, moderate numbers of individual were found in TC3 and ST indicating a stable population size. From September 2018 to March 2020, the population size was low while natural mortality was the possible cause. From June 2020 to September 2020, the population size of Tachypleus tridentatus increased to moderate level in ST while the mean proposal width of them conitued to grow and reach about 55mm. The population size of Tachypleus tridentatus slightly decreased in ST from March 2021 to March 2022 and the mean proposal width of them increased to about 77.59mm.

3.6.35 In recent year, the Carcinoscorpius rotundicauda was a more common horseshoe crab species in Tung Chung Wan. It was recorded in the four sampling zones while the majority of population located in TC3 and ST. Due to potential breeding last year, the number of Tachypleus tridentatus increased in ST. Since TC3 and ST were regarded as important nursery ground for both horseshoe crab species, box plots of prosomal width of two horseshoe crab species were constructed to investigate the changes of population in details.

Box plot of horseshoe crab populations in TC3

3.6.36 Figure 3.7 of Appendix O shows the changes of prosomal width of Carcinoscorpius rotundicauda and Tachypleus tridentatus in TC3. As mentioned above, Carcinoscorpius rotundicauda was rarely found between September 2012 and December 2013 hence the data were lacking. In March 2014, the major size (50% of individual records between upper (top box) and lower quartile (bottom box)) ranged 40 – 60 mm while only few individuals were found. From March 2014 to September 2018, the median prosomal width (middle line of whole box) and major size (whole box) decreased after March of every year. It was due to more small individuals found in June indicating new rounds of spawning. Also there were slight increasing trends of body size from June to March of next year since 2015. It indicated a stable growth of individuals. Focused on larger juveniles (upper whisker), the size range was quite variable (prosomal width 60 – 90 mm) along the sampling months. Juveniles reaching this size might gradually migrate to sub-tidal habitats. In March 2022, 2 Carcinoscorpius rotundicauda with body size (prosomal width 52.21-54.63mm) were found in TC3. The findings were relatively lower than the previous record in March. This can due to the natural variation caused by multi-environmental factors.

3.6.37 For Tachypleus tridentatus, the major size ranged 20-50 mm while the number of individuals fluctuated from September 2012 to June 2014. Then a slight but consistent growing trend was observed from September 2014 to June 2015. The prosomal width increased from 25 – 35 mm to 35 – 65 mm. As mentioned, the large individuals might have reached a suitable size for migrating from the nursery soft shore to subtidal habitat. It accounted for the declined population in TC3. From March to September 2016, slight increasing trend of major size was noticed again. From December 2016 to June 2017, similar increasing trend of major size was noted with much higher number of individuals. It reflected new round of spawning. In September 2017, the major size decreased while the trend was different from previous two years. Such decline might be the cause of serial cyclone hit between June and September 2017 (to be discussed in the 'Seagrass survey' section). From December 2017 to September 2018, increasing trend was noted again. It indicated a stable growth of individuals. From September 2018 to that of next year, the average prosomal widths were decreased from 60mm to 36mm. It indicated new rounds of spawning occurred during September to November 2018. In December 2019, an individual with larger body size (prosomal width 65mm) was found in TC3 which reflected the stable growth of individuals. In March 2020, the average prosomal width (middle line of the whole box) of Tachypleus tridentatus in TC3 was 33.97mm which is smaller than that in December 2019. It was in normal fluctuation. From June 2020 to December 2020, no horseshoe crab was recorded in TC3. In Sep 2021, only one Tachypleus tridentatus with body size (prosomal width 38.78mm) was found in TC3. The decrease in the species population was considered to be related to hot weather in September, which may affect their activity. Across the whole monitoring period, the larger juveniles (upper whisker) usually reached 60 – 80 mm in prosomal width, even 90 mm occasionally. The juveniles reaching this size might gradually migrate to sub-tidal habitats.

Box plot of horseshoe crab populations in ST

3.6.38 Figure 3.8 of Appendix O shows the changes of prosomal width of Carcinoscorpius rotundicauda and Tachypleus tridentatus in ST. As mentioned above, Carcinoscorpius rotundicauda was rarely found between September 2012 and December 2013 hence the data were lacking. From March 2014 to September 2018, the size of major population decreased and more small individuals (i.e. lower whisker) were recorded after June of every year. It indicated new round of spawning. Also there were similar increasing trends of body size from September to June of next year between 2014 and 2017. It indicated a stable growth of individuals. The larger juveniles (i.e. upper whisker usually ranged 60 – 80 mm in prosomal width except one individual (prosomal width 107.04 mm) found in March 2017. It reflected juveniles reaching this size would gradually migrate to sub-tidal habitats.

3.6.39 For Tachypleus tridentatus, a consistent growing trend was observed for the major population from December 2012 to December 2014 regardless of change of search record. The prosomal width increased from 15 – 30 mm to 60 – 70 mm. As mentioned, the large juveniles might have reached a suitable size for migrating from the nursery soft shore to subtidal habitat. From March to September 2015, the size of major population decreased slightly to a prosomal width 40 – 60 mm. At the same time, the number of individuals decreased gradually. It further indicated some of large juveniles might have migrated to sub-tidal habitat, leaving the smaller individuals on shore. There was an overall growth trend. In December 2015, two big individuals (prosomal width 89.27 mm and 98.89 mm) were recorded only while it could not represent the major population. In March 2016, the number of individual was very few in ST that no box plot could be produced. In June 2016, the prosomal width of major population ranged 50 – 70 mm. But it dropped clearly to 30 – 40 mm in September 2016 followed by an increase to 40 – 50 mm in December 2016, 40 – 70 mm in March 2017 and 50 – 60mm in June 2017. Based on overall higher number of small individuals from June 2016 to September 2017, it indicated another round of spawning. From September 2017 to June 2018, the major size range increased slightly from 40 – 50 mm to 45 – 60 mm indicating a continuous growth. In September 2018, decrease of major size was noted again that might reflect new round of spawning. Throughout the monitoring period, the larger juveniles ranged 60-80 mm in prosomal width. Juveniles reaching this size would gradually migrate to sub-tidal habitats.

3.6.40 As a summary for horseshoe crab populations in TC3 and ST, there were spawning ground of Carcinoscorpius rotundicauda from 2014 to 2018 while the spawning time should be in spring. The population size was consistent in these two sampling zones. For Tachypleus tridentatus, small individuals were rarely found in both zones from 2014 to 2015. It was believed no occurrence of successful spawning. The existing individuals (that recorded since 2012) grew to a mature size and migrated to sub-tidal habitat. Hence the number of individuals decreased gradually. From 2016 to 2018, new rounds of spawning were recorded in ST while the population size increased to a moderate level.

3.6.41 In March 2019 to June 2019 and Dec 2021, no horseshoe crab juveniles (prosomal width <100mm) were recorded in TC3 and ST. All recorded horseshoe crabs were large individuals (prosomal width >100mm) or mating pairs which were all excluded from the data analysis. From September 2019 to September 2020, the population size of both horseshoe crab species in ST gradually increased to moderate level while their body sizes were mostly in small to medium range (~23 – 55mm). It indicated the natural stable growth of the horseshoe crab juveniles. In December 2020, the population size of both horseshoe crab species in ST dropped to low level while their body sizes were mostly in small to medium range (~28 – 56mm). It showed the natural mortality and seasonal variation of horseshoe crab. In June 2022, the population size of both horseshoe crab species in ST was kept as low-moderate level while their body sizes were mostly in small to medium range (~51–78mm). In September 2022, the population size of both horseshoe crab species in TC3 and ST was kept as low-moderate level while their body sizes were mostly in small to medium range (~56–62mm). In September 2022, the population size of both horseshoe crab species in TC3 and ST was kept as low-moderate level while their body sizes were mostly in small to medium range (~44-79mm).

Impact of the HKLR project

3.6.42 It was the 46^thsurvey of the EM&A programme during construction period. Based on the monitoring results, no detectable impact on horseshoe crab was revealed due to HKLR project. The population change was mainly determined by seasonal variation, no abnormal phenomenon of horseshoe crab individual, such as large number of dead individuals on the shore had been reported.

Seagrass Beds

3.6.43 Two seagrass species Halophila ovalis and Zostera japonica were found in present survey.

3.6.44 Halophila ovalis was found in TC3 and ST and Zostera japonica was found only in ST. In ST,

3.6.45 there were six large sized of Halophila ovalis found at tidal zone 1.5m above C.D nearby

3.6.46 mangroves plantation. The larger strand had area ~5500m2 in moderate vegetation coverage

3.6.47 (30 - 40%), ~4000m2 in moderate vegetation coverage (10 - 20%), ~800m2 in moderate

3.6.48 vegetation coverage (10 - 20%) and three ~120 - 300m2 in low to moderate vegetation coverage

3.6.49 (10 - 20%). In TC3, 3 large patches of Halophila ovalis were found at tidal zone 1.5m above

3.6.50 C.D. The larger strand had area ~1200m2 in moderate vegetation coverage (20 - 40%),

3.6.51 ~1000m2 in moderate vegetation coverage (10 - 20%) and ~600m2 in moderate vegetation

3.6.52 coverage (10 - 20%). At close vicinity to mangrove, one small sized (20m2) of Zostera japonica

3.6.53 beds were observed at tidal zone 2.0m above C.D in ST. Table 3.2 summarizes the results of

3.6.54 present seagrass beds survey and the photograph records of the seagrass are shown on Figure 3.9 of Appendix O. The complete record throughout the monitoring period is presented in Annex III of Appendix O.

3.6.55 Since the commencement of the EM&A monitoring programme, two species of seagrass Halophila ovalis and Zostera japonica were recorded in TC3 and ST (Figure 3.10 of Appendix O). In general, Halophila ovalis was occasionally found in TC3 in few, small to medium patches. But it was commonly found in ST in medium to large seagrass bed. Moreover, it had sometimes grown extensively and had covered significant mudflat area at 0.5 – 2.0 m above C.D. between TC3 and ST. Another seagrass species Zostera japonica was found in ST only. It was relatively lower in vegetation area and co-existed with Halophila ovalis nearby the mangrove strand at 2.0 m above C.D.

3.6.56 According to the previous results, majority of seagrass bed was confined in ST, the temporal change of both seagrass species was investigated in details:

Temporal variation of seagrass beds in ST

3.6.57 Figure 3.11 of Appendix O shows the changes of estimated total area of seagrass beds in ST along the sampling months. For Zostera japonica, it was not recorded in the 1^st and 2^nd surveys of monitoring programme. Seasonal recruitment of few, small patches (total seagrass area: 10 m²) was found in March 2013 that grew within the large patch of seagrass Halophila ovalis. Then, the patch size increased and merged gradually with the warmer climate from March to June 2013 (15 m²). However the patch size decreased and remained similar from September 2013 (4 m²) to March 2014 (3 m²). In June 2014, the patch size increased obviously again (41 m²) with warmer climate followed by a decrease between September 2014 (2 m²) and December 2014 (5 m²). From March to June 2015, the patch size increased sharply again (90 m²). It might be due to the disappearance of the originally dominant seagrass Halophila ovalis resulting in less competition for substratum and nutrients. From September 2015 to June 2016, it was found coexisting with seagrass Halophila ovalis with steady increasing patch size (from 44 m² to 115 m²) and variable coverage. In September 2016, the patch size decreased again to (38 m²) followed by an increase to a horizontal strand (105.4 m²) in June 2017. And it did no longer co-exist with Halophila ovalis. Between September 2014 and June 2017, an increasing trend was noticed from September to June of next year followed by a rapid decline in September of next year. It was possibly the causes of heat stress, typhoon and stronger grazing pressure during wet season. However, such increasing trend was not found from September 2017 to March 2021, while no patch of Zostera japonica was found. From June 2021, the species was recorded again in area of 45m². The recorded area of the seagrass bed in September 2021 survey was slightly decreased to 15m².

3.6.58 For Halophila ovalis, it was recorded as 3 – 4 medium to large patches (area 18.9- 251.7 m²; vegetation coverage 50 – 80%) beside the mangrove vegetation at tidal level 2 m above C.D. in September 2012. The total seagrass bed area grew steadily from 332.3 m² in September 2012 to 727.4 m² in December 2013. Flowers were observed in the largest patch during its flowering period. In March 2014, 31 small to medium patches were newly recorded (variable area 1 – 72 m² per patch, vegetation coverage 40-80% per patch) in lower tidal zone between 1.0 and 1.5 m above C.D. The total seagrass area increased further to 1350 m². In June 2014, these small and medium patches grew and extended to each other. These patches were no longer distinguishable and were covering a significant mudflat area of ST. It was generally grouped into 4 large patches (1116 – 2443 m²) of seagrass beds characterized of patchy distribution, variable vegetable coverage (40-80%) and smaller leaves. The total seagrass bed area increased sharply to 7629 m². In September 2014, the total seagrass area declined sharply to 1111m². There were only 3-4 small to large patches (6 – 253 m²) at high tidal level and 1 large patch at low tidal level (786 m²). Typhoon or strong water current was a possible cause (Fong, 1998). In September 2014, there were two tropical cyclone records in Hong Kong (7^th – 8^thSeptember: no cyclone name, maximum signal number 1; 14^th – 17^thSeptember: Kalmaegi, maximum signal number 8SE) before the seagrass survey dated 21^stSeptember 2014. The strong water current caused by the cyclone, Kalmaegi especially, might have given damage to the seagrass beds. In addition, natural heat stress and grazing force were other possible causes reducing seagrass beds area. Besides, very small patches of Halophila ovalis could be found in other mud flat area in addition to the recorded patches. But it was hardly distinguished due to very low coverage (10 – 20%) and small leaves.

3.6.59 In December 2014, all the seagrass patches of Halophila ovalis disappeared in ST. Figure 3.12 of Appendix O shows the difference of the original seagrass beds area nearby the mangrove vegetation at high tidal level between June 2014 and December 2014. Such rapid loss would not be seasonal phenomenon because the seagrass beds at higher tidal level (2.0 m above C.D.) were present and normal in December 2012 and 2013. Similar incident had occurred in ST in the past. The original seagrass area had declined significantly during the commencement of the construction and reclamation works for the international airport at Chek Lap Kok in 1992. The seagrass almost disappeared in 1995 and recovered gradually after the completion of reclamation works. Moreover, incident of rapid loss of seagrass area was also recorded in another intertidal mudflat in Lai Chi Wo in 1998 with unknown reason. Hence, Halophila ovalis was regarded as a short- lived and r- strategy seagrass that could colonize areas in short period but disappears quickly under unfavourable conditions

Unfavourable conditions to seagrass Halophila ovalis

3.6.60 Typhoon or strong water current was suggested as one unfavorable condition to Halophila ovalis (Fong, 1998). As mentioned above, there were two tropical cyclone records in Hong Kong in September 2014. The strong water current caused by the cyclones might have given damage to the seagrass beds.

3.6.61 Prolonged light deprivation due to turbid water would be another unfavorable condition. Previous studies reported that Halophila ovalis had little tolerance to light deprivation. During experimental darkness, seagrass biomass declined rapidly after 3-6 days and seagrass died completely after 30 days. The rapid death might be due to shortage of available carbohydrate under limited photosynthesis or accumulation of phytotoxic end products of anaerobic respiration. Hence the seagrass bed of this species was susceptible to temporary light deprivation events such as flooding river runoff.

3.6.62 In order to investigate any deterioration of water quality (e.g. more turbid) in ST, the water quality measurement results at two closest monitoring stations SR3 and IS5 of the EM&A programme were obtained from the water quality monitoring team. Based on the results from June to December 2014, the overall water quality was in normal fluctuation except there was one exceedance of suspended solids (SS) at both stations in September. On 10^th September 2014, the SS concentrations measured during mid-ebb tide at stations SR3 (27.5 mg/L) and IS5 (34.5 mg/L) exceeded the Action Level (≤ 23.5 mg/L and 120% of upstream control station’s reading) and Limit Level (≤ 34.4 mg/L and 130% of upstream control station’s reading) respectively. The turbidity readings at SR3 and IS5 reached 24.8 – 25.3 NTU and 22.3 – 22.5 NTU, respectively. The temporary turbid water should not be caused by the runoff from upstream rivers. Because there was no rain or slight rain from 1^st to 10^th September 2014 (daily total rainfall at the Hong Kong International Airport: 0 – 2.1 mm; extracted from the climatological data of Hong Kong Observatory). The effect of upstream runoff on water quality should be neglectable in that period. Moreover the exceedance of water quality was considered unlikely to be related to the contract works of HKLR according to the ‘Notifications of Environmental Quality Limits Exceedances’ provided by the respective environmental team. The respective construction of seawall and stone column works, which possibly caused turbid water, was carried out within silt curtain as recommended in the EIA report. Moreover there was no leakage of turbid water, abnormity or malpractice recorded during water sampling. In general, the exceedance of suspended solids concentration was considered to be attributed to other external factors, rather than the contract works.

3.6.63 Based on the weather condition and water quality results in ST, the co-occurrence of cyclone hit and turbid waters in September 2014 might have combined the adverse effects on Halophila ovalis that leaded to disappearance of this short-lived and r-strategy seagrass species. Fortunately Halophila ovalis was a fast-growing species (Vermaat et al., 1995). Previous studies showed that the seagrass bed could be recovered to the original sizes in 2 months through vegetative propagation after experimental clearance (Supanwanid, 1996). Moreover it was reported to recover rapidly in less than 20 days after dugong herbivory (Nakaoka and Aioi, 1999). As mentioned, the disappeared seagrass in ST in 1995 could recover gradually after the completion of reclamation works for international airport (Fong, 1998). The seagrass beds of Halophila ovalis might recolonize in the mudflat of ST through seed reproduction as long as there was no unfavourable condition in the coming months.

Recolonization of seagrass beds

3.6.64 Figure 3.12 of Appendix O shows the recolonization of seagrass bed in ST from December 2014 to June 2017. From March to June 2015, 2 – 3 small patches of Halophila ovalis were newly found co-inhabiting with another seagrass species Zostera japonica. But the total patch area of Halophila ovalis was still very low compare with previous records. The recolonization rate was low while cold weather and insufficient sunlight were possible factors between December 2014 and March 2015. Moreover, it would need to compete with seagrass Zostera japonica for substratum and nutrient, because Zostera japonica had extended and covered the original seagrass bed of Halophila ovalis at certain degree. From June 2015 to March 2016, the total seagrass area of Halophila ovalis had increased rapidly from 6.8 m² to 230.63 m². It had recolonized its original patch locations and covered its competitor Zostera japonica. In June 2016, the total seagrass area increased sharply to 4707.3m². Similar to the previous records of March to June 2014, the original patch area of Halophila ovalis increased further to a horizontally long strand. Another large seagrass beds colonized the lower tidal zone (1.0 – 1.5 m above C.D.). In September 2016, this patch extended much and covered significant soft mud area of ST, resulting in sharp increase of total area (24245 m²). It indicated the second extensive colonization of this r-selected seagrass. In December 2016, this extensive seagrass patch decreased in size and had separated into few, undistinguishable patches. Moreover, the horizontal strand nearby the mangrove vegetation decreased in size. The total seagrass bed decreased to 12550 m². From March to June 2017, the seagrass bed area remained generally stable (12438- 17046.5 m²) but the vegetation coverage fluctuated (20 – 50% in March 2017 to 80 – 100% in June 2017). The whole recolonization process took about 2.5 years.

Second disappearance of seagrass bed

3.6.65 In September 2017, the whole seagrass bed of Halophila ovalis disappeared again along the shore of TC3 and ST (Figure 3.12 of Appendix O). Similar to the first disappearance of seagrass bed occured between September and December 2014, strong water current (e.g. cyclone) or deteriorated water qualities (e.g. high turbidity) was the possible cause.

3.6.66 Between the survey periods of June and September 2017, there were four tropical cyclone records in Hong Kong (Merbok in 12- 13^th, June; Roke in 23^rd, Jul.; Hato in22 – 23^rd, Aug.; Pakhar in 26 – 27^th, Aug.) (Online database of Hong Kong Observatory) All of them reached signal 8 or above, especially Hato with highest signal 10.

3.6.67 According to the water quality monitoring results (July to August 2017) of the two closest monitoring stations SR3 and IS5 of the respective EM&A programme, the overall water quality was in normal fluctuation. There was an exceedance of suspended solids (SS) at SR3 on 12 July 2017. The SS concentration reached 24.7 mg/L during mid-ebb tide, which exceeded the Action Level (≤ 23.5 mg/L). But it was far below the Limit Level (≤ 34.4 mg/L). Since such exceedance was slight and temporary, its effect to seagrass bed should be minimal.

3.6.68 Overall, the disappearance of seagrass beds in ST has believed the cause of serial cyclone hit in July and August 2017. Based on previous findings, the seagrass beds of both species were expected to recolonize in the mudflat as long as the vicinal water quality was normal. The whole recolonization process (from few, small patches to extensive strand) would be gradually lasting at least 2 years. From December 2017 to March 2018, there was still no recolonization of few, small patches of seagrass at the usual location (Figure 3.12 of Appendix O). It was different from the previous round (March 2015 – June 2017). Until June 2018, the new seagrass patches with small-medium size were found at the usual location (seaward side of mangrove plantation at 2.0 m C.D.) again, indicating the recolonization. However, the seagrass bed area decreased sharply to 22.5 m² in September 2018. Again it was believed that the decrease was due to the hit of the super cyclone in September 2018 (Mangkhuton 16^th September, highest signal 10). From December 2018 to June 2019, the seagrass bed area increased from 404 m² to 1229 m² while the vegetation coverage is also increased (December 2018: 5– 85%; March 2019: 50 – 100% and June 2019: 60 – 100%). Relatively, the whole recolonization process would occur slower than the previous round (more than 2 years). From September 2019 to March 2021, the seagrass bed area in ST slightly decreased from 1200 m²to 942.05 m²,which were in normal fluctuation. From March 2021 to December 2021, the seagrass bed area in ST decreased from 942.05 m²to 680m²,which were in normal fluctuation. In March 2022, the seagrass bed area in ST increased significantly to approximately 2040 m^2,which believed to be related to more rain in current dry season. It was observed that the brown filemental algae bloom occurred at ST site in March 2022. Distribution of the algae was overlap with seagrass beds, mainly the species Halophila ovalis and the algae was grown over the top of the seagrass. In some areas, the brown filemental algae full covered the seagrass bed, refer to Figure 3.9 of Appendix O. The seagrass was still alive when checked during the field survey. Whether the algae bloom will kill seagrass in longer period time is unknown. The seagrass distritrution and health condition should be checked in coming June monitoring. The algae bloom of the brown filemental algae at the seagrass bed is disappeared as observed in June 2022, refer to Figure 3.9 of Appendix O. Seagrass in December 2022 and September 2022 have decreased compare to June 2022 due to normal seasonal change. Seagrass in March 2023 have increased compare to previous quarter due to normal seasonal change. Seagrass in June 2023 have further increased around 20% compared to previous period. Seagrass in September and December 2023 have decreased compared to previous quarter due to normal seasonal change.

Impact of the HKLR project

3.6.69 It was the 46^thsurvey of the EM&A programme during construction period. It was the 46th survey of the EM&A programme during construction period. Throughout the monitoring period, the disappearance of seagrass beds was believed the cause of cyclone hits rather than impact of HKLR project. The seagrass bed was recolonizing since there had been a gradual increase in the size and number from December 2018 to June 2019 after the hit of the super cyclone in September 2018. The seagrass bed area decreased from March 2021 to December 2021, which were in normal fluctuation. It is observed that the seagrass Halophila ovalis covered larger area than before. Total seagrass bed area significantly increased from March 2022 to June 2022 and slightly reduced in September 2022. Seagrass in June 2023 have increased compared to previous quarter due to normal seasonal change. Seagrass in September and December 2023 have decreased compared to previous quarter due to normal seasonal change.

Intertidal Soft Shore Communities

Substratum

3.6.70 Table 3.3 of Appendix O and Figure 3.13 of Appendix O show the substratum types along the horizontal transect at every tidal level in all sampling zones. The relative distribution of substratum types was estimated by categorizing the substratum types (Gravels & Boulders / Sands / Soft mud) of the ten random quadrats along the horizontal transect. The distribution of substratum types varied among tidal levels and sampling zones:

· In TC1, high percentages of ‘Gravels and Boulders’ (95%) were recorded at high tidal level. At mid tidal level, ‘Gravels and Boulders’ was the main substratum type (60%), following by ‘Soft mud’ (20%) and “Sands’ (20%). At low tidal level, ‘Soft mud’ was the main substratum type (80%), followed by ‘Sands’ (10%) and ‘Gravels and Boulders’ (10%).

· In TC2, high percentages of ‘Gravels and Boulders’ (90%) was recorded at high tidal level, following by ‘Sands’ (5%) and ‘Soft mud’ (5%). At mid tidal level, ‘Gravels and Boulders’ was the main substratum type (70%), following by ‘Sands’ (20%) and ‘Soft mud’ (10%). At low tidal level, ‘Soft mud’ covered 80% , ‘Soft mud’ and ‘Sands ’ covered 20% of the transect.

· In TC3, higher percentage of ‘Gravels and Boulders’ was recorded at high tidal level (65%). At mid tidal levels, ‘‘Gravels and Boulders’ was the main substratum type (50%), following by ‘Soft mud ’ (30%) and ‘Sands’ (20%). At low tidal level, ‘Soft mud’ covered 70% of the transect.

· In ST, ‘Gravels and Boulders’ was the main substratum type (65%) at high tidal level. At mid tidal levels, ‘Gravels and Boulders’ and ‘Soft mud’ was the main substratum type (50% and 30%), following by ‘Sand’ (20%). At low tidal level, ‘Soft mud’ was the main substratum type (90%) and ‘Sands’ covered 10% of the transect.

3.6.71 There was neither consistent vertical nor horizontal zonation pattern of substratum type in all sampling zones. Such heterogeneous variation should be caused by different hydrology (e.g. wave in different direction and intensity) received by the four sampling zones.

Soft shore communities

3.6.72 Table 3.4 of Appendix O lists the total abundance, density and number of taxon of every phylum in this survey. A total of 8731 individuals were recorded. Mollusca was the most abundant phylum (total abundance 7802 ind., density 260 ind. m^-2, relative abundance 89.4%). The second and third were Arthropoda (627ind., 21 ind. m^-2, 7.2%) which followed by Annelida (126 ind., 4 ind. m^-2, 1.4%) and Sipuncula (85 ind., 3 ind. m^-2, 1.0%), respectively. The fifth was Nemertea with total abundance 57 ind., density 2 ind.m^-2and relative abundance 0.7%. The sixth was Cnidania with total abundance 31 ind., density 1 ind.m^-2and relative abundance 0.4%.Platyhelminthes was very low in abundances (density <0 ind. m^-2, relative abundance £0.0%). Moreover, the most diverse phylum was Mollusca (32 taxa) followed by Arthropoda (6 taxa). Annelida (3 taxa) and Sipuncula (2 taxa). There was 1 taxon for Nemertea, Cnidaria and Platyhelminthes.

3.6.73 The taxonomic resolution and complete list of recorded fauna are shown in Annex IV of Appendix O and Annex V of Appendix O respectively. As reported in June 2018, taxonomic revision of three potamidid snail species was conducted according to the latest identification key published by Agriculture, Fisheries and Conservation Department (details see AFCD, 2018), the species names of following gastropod species were revised:

· Cerithidea cingulata was revised as Pirenella asiatica

· Cerithidea djadjariensis was revised as Pirenella incisa

· Cerithidea rhizophorarum was revised as Cerithidea moerchii

Moreover, taxonomic revision was conducted on another snail species while the specie name was revised:

· Batillaria bornii was revised as Clypeomorus bifasciata

3.6.74 In March 2021, an increased number of sea slugs and their eggs were observed in all sampling zones. It may due to the breeding season of sea slug and the increased of algae on the intertidal.

3.6.75 Table 3.5 of Appendix O shows the number of individuals, relative abundance and density of each phylum in every sampling zone. The total abundance (1,671 - 2,522 ind.) varied among the four sampling zones while the phyla distributions were similar. In general, Mollusca was the most dominant phylum (no. of individuals: 1,526 - 2,307 ind.; relative abundance 83.9 – 91.5%; density 203 - 308 ind. m^-2). Other phyla were much lower in number of individuals. Arthropoda (88- 310 ind.; 4.4 – 13.9%; 12 - 41 ind. m^-2) was common phyla relatively. Other phyla were very low in abundance in all sampling zones.

Dominant species in every sampling zone

3.6.76 Table 3.6 of Appendix O lists the abundant species in every sampling zone. In the present survey, most of the listed abundant species were of high or very high density (>100 ind. m^-2), which were regarded as dominant species. Few of the listed species were of low to moderate densities (42 – 95 ind. m^-2). Other listed species of lower density (<42 ind. m^-2) were regarded as common species.

3.6.77 In TC1, the substratum was mainly ‘Gravels and Boulders’ at high and mid tidal levels. At high tidal level, the rock oyster Saccostrea cucullata (mean density 109 ind. m^-2; relative abundance 42%) was the dominant species found at moderate density and the gastropod Monodonta labio (62 ind. m^-2; relative abundance 24%) was of low to moderate density. At mid tidal level, the rock oyster Saccostrea cucullata (69ind. m^-2, 37%) was at dominant species with low to moderate density. The gastropod Monodonta labio (36 ind. m^-2, 19%) was at lower density. At low tidal level (main substratum type ‘Soft mud’), the Batillaria multiformis (46 ind. m^-2, 20%) was dominant at low to moderate densities, the Barbatia virescens (33 ind. m^-2, 15%) and Nodilittorina radiata (33 ind. m^-2, 15%) were of lower density, regarded as common species.

3.6.78 In TC2, the substratum types were mainly ' Gravels and Boulders' at high tidal level. The rock oyster Saccostrea cucullata (136 ind. m^-2, 39%) was dominant at high density. The gastropod Monodonta labio (59 ind. m^-2, 17%) was dominant at low to moderate density. ), the Batillaria multiformis (38 ind. m^-2, 11%) was dominant at low densities. At mid tidal level (main substratum types ‘Soft mud’ and ‘Gravels and Boulders’), rock oyster Saccostrea cucullata (92 ind. m^-2, 29%), gastropods Monodonta labio (62 ind. m^-2, 17%) and Batillaria zonalis (48 ind. m^-2, 15%) were dominant at low to moderate densities. Substratum types ‘Soft Mud’ were mainly distributed at low tidal level, the Barbatia virescens (43 ind. m^-2, 19%) was dominant at low to moderate densities, the Batillaria multiformis (33 ind. m-2, 15%) were of lower densities, regarded as common species.

3.6.79 In TC3, the substratum type was mainly ‘Gravels and Boulders’ at high tidal level. The rock oyster Saccostrea cucullata (144 ind. m^-2, 40%) was of dominant species at high density and the gastropod Monodonta labio (92 ind. m^-2, 21%) was of low to moderate density. At mid tidal level (main substratum types ‘Soft mud’), the rock oyster Saccostrea cucullata (83 ind. m^-2, 24%) was of dominant species at low to moderate density. The gastropod Monodonta labio (45 ind. m^-2, 13%) was at low density level. At low tidal level, the major substratum type was ‘Soft mud’. The Lunella granulate 53 ind. m^-2, 18%), the Batillaria multiformis (47 ind. m^-2, 16%), Batillaria zonalis (42 ind. m^-2, 14%) and the Barbatia virescens (53 ind. m^-2, 18%) at lower density.

3.6.80 In ST, the major substratum type was ‘Gravels and Boulders’ at high tidal level. At high tidal level, the rock oyster Saccostrea cucullata (130 ind. m^-2, 40%) was abundant at high density. The gastropods Monodonta labio(54 ind. m^-2, 17%) was at low to moderate densities and Batillaria multiformis (39 ind. m^-2, 12%) was at lower density. At mid tidal level (main substratum types ‘Gravels and Boulders’ and ‘Soft mud’), the rock oyster Saccostrea cucullata (113 ind. m^-2, 35%) was the dominant species at high density, and followed by the gastropod Monodonta labio (59 ind. m^-2, 18%) at low to moderate density. At low tidal level (major substratum: ‘Soft mud’), the Batillaria zonalis (52 ind. m^-2, 19%) was at low to moderate demsities and Lunella granulata (46 ind. m^-2, 17%) was at lower density.

3.6.81 In general, there was no consistent zonation pattern of species distribution across all sampling zones and tidal levels. The species distribution was determined by the type of substratum primarily. In general, rock oyster Saccostrea cucullata (876 ind.), gastropods Monodonta labio (468 ind.) and Batillaria multiformis (165 ind.) were the most common species on gravel and boulders substratum. Batillaria zonalis (142 ind.) was the most common species on sands and soft mud substrata.

Biodiversity and abundance of soft shore communities

3.6.82 Table 3.7 of Appendix O shows the mean values of species number, density, and biodiversity index H’and species evenness J of soft shore communities at every tidal level and in every sampling zone. As mentioned above, the differences among sampling zones and tidal levels were determined by the major type of substratum primarily.

3.6.83 Among the sampling zones, the mean species number was varied from 14 - 21 spp. 0.25 m^-2 among the four sampling zones. The mean densities of TC3 (336 ind. m^-2) was higher than ST (307 ind. m^-2) followed by TC2 (298 ind. m^-2) and TC1 (223 ind. m^-2). The higher densities of TC3 and ST are due to the relatively high number of individuals in each quadrat. The mean H’ for TC2 was 2.23, TC3 was 2.27, TC1 was 2.07 and ST were 2.13, followed by while the mean J of TC2 and ST were 0.8, which were slightly higher than TC3 (0.77) and TC1. This can be due to the relatively non-even taxa distribution.

3.6.84 In the present survey, no clear trend of mean species number, mean density, H’ and J observed among the tidal level.

3.6.85 Figures 3.14-3.17 of Appendix O show the temporal changes of mean species number, mean density, H’ and J at every tidal level and in every sampling zone along the sampling months. In general, all the biological parameters fluctuated seasonally throughout the monitoring period. Lower mean species number and density were recorded in dry season (December) but the mean H' and J fluctuated within a limited range.

3.6.86 From June to December 2017, there were steady decreasing trends of mean species number and density in TC2, TC3 and ST regardless of tidal levels. It might be an unfavorable change reflecting environmental stresses. The heat stress and serial cyclone hit were believed the causes during the wet season of 2017. From March 2018 to September 2023 (present survey), generally increases of mean species number and density were observed in all sampling zones. It indicated the recovery of intertidal community.

Impact of the HKLR project

3.6.87 It was the 46^thsurvey of the EM&A programme during the construction period. Based on the results, impacts of the HKLR project were not detected on intertidal soft shore community. Abnormal phenomena (e.g. rapid, consistent or non-seasonal decline of fauna densities and species number) were not recorded.

3.7 Solid and Liquid Waste Management Status

3.7.1 The Contractor registered with EPD as a Chemical Waste Producer on 12 July 2012 for the Contract. Sufficient numbers of receptacles were available for general refuse collection and sorting.

3.7.2 The summary of waste flow table is detailed in Appendix K.

3.7.3 The Contractor was reminded that chemical waste containers should be properly treated and stored temporarily in designated chemical waste storage area on site in accordance with the Code of Practice on the Packaging, Labelling and Storage of Chemical Wastes.

Description of Activities	Site Area
Landscape maintenance works	SHT East Portal
Removal of Temporary Toe Loading Platform	Portion X

	North Lantau Social Cluster
	NEL	NWL
Action Level	STG < 70% of baseline & ANI < 70% of baseline	STG < 70% of baseline & ANI < 70% of baseline
Limit Level	STG < 40% of baseline & ANI < 40% of baseline

	North Lantau Social Cluster
	NEL	NWL
Action Level	STG < 4.2 & ANI < 15.5	STG < 6.9 & ANI < 31.3
Limit Level	(STG < 2.4 & ANI < 8.9) and (STG < 3.9 & ANI < 17.9)

Ramboll Hong Kong Limited was employed by HyD as the Independent Environmental Checker (IEC) and Environmental Project Office (ENPO) for the Project until 30 September 2022.

ANewR Consulting Limited has been employed by HyD as the Independent Environmental Checker (IEC) and Environmental Project Office (ENPO) for the Project with effective from 1 October 2022.

1 Introduction

1.1 Basic Project Information

1.1.4 BMT Hong Kong Limited was appointed by the Contractor to implement the EM&A programme for the Contract in accordance with the Updated EM&A Manual for HKLR (Version 1.0) and provided environmental team services to the Contract until 31 July 2020.

1.1.6 This is the forty-sixth Quarterly Environmental Monitoring and Audit (EM&A) report for the Contract which summarizes the monitoring results and audit findings of the EM&A programme during the reporting period from 1 Dec 2023 to 29 February 2024.

1.2 Project Organisation

1.2.1 The project organization structure and lines of communication with respect to the on-site environmental management structure with the key personnel contact names and numbers are shown in Appendix A.

1.3 Construction Programme

1.3.1 A copy of the Contractor’s construction programme is provided in Appendix B.

1.4 Construction Works Undertaken During the Reporting Period

1.4.1 A summary of the construction activities undertaken during this reporting period is shown in

Table 1.1. The works areas of the Contract are showed in Appendix C.

2 EM&A Requirement

2.1 Summary of EM&A Requirements

2.1.1 The EM&A programme requires environmental monitoring of air quality, noise, water quality, dolphin monitoring and mudflat monitoring as specified in the approved EM&A Manual.

2.1.2 A summary of Impact EM&A requirements is presented in Table 2.1. The locations of air quality, noise and water quality monitoring stations are shown as in Figure 2.1. The transect line layout in Northwest and Northeast Lantau Survey Areas is presented in Figure 2.2.

2.2 Action and Limit Levels

2.2.1 Table 2.2 presents the Action and Limit Levels for the 1-hour TSP, 24-hour TSP and noise level.

2.2.2 The Action and Limit Levels for water quality monitoring are given as in Table 2.3.

2.2.3 The Action and Limit Levels for dolphin monitoring are shown in Tables 2.4 and 2.5.

2.3 Event Action Plans

2.3.1 The Event Actions Plans for air quality, noise, water quality, dolphin monitoring and mudflat monitoring and Action Plan for Landscape Works are annexed in Appendix D.

2.4 Mitigation Measures

2.4.1 Environmental mitigation measures for the contract were recommended in the approved EIA Report. Appendix E lists the recommended mitigation measures and the implementation status.

3 Environmental Monitoring and Audit

3.1 Implementation of Environmental Measures

3.1.1 Details of site audit findings and the corrective actions during the reporting period are presented in Appendix F.

3.1.2 A summary of the Implementation Schedule of Environmental Mitigation Measures (EMIS) is presented in Appendix E. Most of the necessary mitigation measures were implemented properly.

3.1.3 Regular marine travel route for marine vessels were implemented properly in accordance to the submitted plan and relevant records were kept properly.

3.1.4 Dolphin Watching Plan was implemented during the reporting period. No dolphins inside the silt curtain were observed. The relevant records were kept properly.

3.2 Air Quality Monitoring Results

3.2.2 No Action and Limit Level exceedances of 1-hr TSP and 24-hr TSP were recorded at AMS5 during the reporting period.

3.3 Noise Monitoring Results

3.3.1 The monitoring results for construction noise are summarized in Table 3.3 and the monitoring results and relevant graphical plots for this reporting period are provided in Appendix H.

*A correction factor of +3dB(A) from free field to facade measurement was included.

3.3.2 No Action/Limit Level exceedances for noise were recorded during daytime on normal weekdays of the reporting period.

3.3.3 Other noise sources during the noise monitoring included aircraft/helicopter noise, construction activities by other parties and human activities nearby.

3.4 Water Quality Monitoring Results

3.4.1 Impact water quality monitoring was conducted at all designated monitoring stations during the reporting period. Impact water quality monitoring results and relevant graphical plots are provided in Appendix I.

3.4.2 For marine water quality monitoring, no Action Level and Limit Level exceedances of dissolved oxygen level, turbidity level and suspended solid level were recorded during the reporting period.

3.4.3 Water quality impact sources during water quality monitoring were nearby construction activities by other parties and nearby operating vessels by other parties.

3.5 Dolphin Monitoring Results

Data Analysis

3.5.10 During the period of December 2023 to February 2024, six sets of systematic line-transect vessel surveys were conducted to cover all transect lines in NWL and NEL survey areas twice per month.

3.5.12The total survey effort conducted on primary lines was 576.36 km, while the effort on secondary lines was 231.45 km. Survey effort conducted on both primary and secondary lines were considered to be on-effort survey data. A summary table of the survey effort is shown in Annex I of Appendix J.

3.5.14 Notably, the three dolphin groups were all sighted in NWL, and no dolphin was sighted at all in NEL. In fact, since August 2014, only two sightings of two lone dolphins were made in NEL during HKLR03/TMCLKL monitoring surveys.

Distribution

3.5.19 absence from the Sha Chau and Lung Kwu Chau Marine Park (Figure 2 of Appendix J).

Encounter Rate

Table 3.7 Comparison of Average Dolphin Encounter Rates in Northwest Lantau Survey Area from All Winter Quarters of Impact Monitoring Period and Baseline Monitoring Period (Sep – Nov 2011)

Group size

3.5.30 Three groups of Chinese White Dolphins were sighted during December 2023 to February 2024, resulting in an average group size of 2.67. This was compared with the ones deduced from the baseline period in September to November 2011, as shown in Table 3.8.

Habitat Use

3.5.33 Notably, all grids near HKLR03/HKBCF reclamation sites as well as TMCLKL bridge alignments did not record any presence of dolphins at all during on-effort search in the present quarterly period (Figures 3a and 3b of Appendix J).

Mother-calf pairs

Activities and associations with fishing boats

3.5.38 During the present quarterly period, the three dolphin groups sighted were not engaged in any activities. Furthermore, they were not found to be associated with any operating fishing vessel during the present impact phase period.

Summary of photo-identification works

3.5.39 From December 2023 to February 2024, around 800 digital photographs were taken during the impact phase monitoring surveys for the photo-identification work.

Individual range use

3.5.43 range during this quarterly period (Appendix V).

Conclusion

3.5.44 During the present quarter of dolphin monitoring, no adverse impact from the activities of this construction project on Chinese White Dolphins was noticeable from general observations.

3.5.46 It is critical to continuously monitor the dolphin usage in North Lantau region to determine whether the dolphins are continuously affected by the construction activities in relation to the HZMB-related works, and whether suitable mitigation measure can be applied to revert the situation.

3.6 Mudflat Monitoring Results

Sedimentation Rate Monitoring

3.6.2 This measurement result was generally and relatively higher than the baseline measurement at S1, S2, S3 and S4. The mudflat level is continuously increased.

Water Quality Monitoring

3.6.4 Water quality monitoring in San Tau (monitoring station SR3(N)) was conducted in December 2023 as part of mudflat monitoring. The monitoring parameters included dissolved oxygen (DO), turbidity and suspended solids (SS).

3.6.5 The water monitoring result for SR3(N) were extracted and summarised in Table 3.10:

Sampling Zone

Horseshoe Crabs

Seagrass Beds

Intertidal Soft Shore Communities

Field Sampling

3.6.13 All collected fauna were released after recording except some tiny individuals that were too small to be identified on site. These tiny individuals were taken to laboratory for identification under dissecting microscope.

3.6.14 The taxonomic classification was conducted in accordance to the following references: Polychaetes: Fauchald (1977), Yang and Sun (1988); Arthropods: Dai and Yang (1991), Dong (1991); Mollusks: Chan and Caley (2003), Qi (2004), AFCD (2018).

Data Analysis

3.6.15 Data collected from direct search and core sampling was pooled in every quadrat for data analysis. Shannon-Weaver Diversity Index (H’) and Pielou’s Species Evenness (J) were calculated for every quadrat using the formulae below,