8               Dolphin acoustic behaviour

 

8.1               Thirty days of acoustic monitoring surveys were conducted between 15 January and 22 February 2013 for the baseline period. During this period, 1,885 km of survey effort were conducted to search for dolphins in the western and northwestern waters of Lantau. A total of 196 groups, numbering 694 dolphins, were sighted during these surveys, and 238 sound samples were taken from some of these dolphin groups.

 

8.2               The data obtained during the initial phase provide a pre-construction baseline for measuring the potential consequences of construction activities on dolphin behaviour. The dolphin acoustic activities measured using both acoustic survey and passive acoustic monitoring methods provide quantitative metrics against which to measure any changes in the behaviour or occurrence of dolphins near the bridge construction area once construction has begun.

 

8.3               Major findings from the analysis of the above data are summarized as follows:

·       The calibrated hydrophone data showed a general increase in whistles and clicks by group size, and most of these sounds occurred during socializing.

·       The EAR(ecological acoustic recorders) data showed a lull in recorded dolphin sounds in mid-month and a tendency for some changes in diel sound (or dolphin occurrence) structure.

·       Acoustic activity levels increased with group size and were highest during socializing periods. Larger groups have more animals that can contribute signals to recordings and it is common for dolphins to be more vocally active during periods of socializing.

·       The EAR data indicate that dolphin acoustic activity is greater at site Fan Lau than at bridge alignment area. In addition, the average number of daily encounters and the duration of encounters were greater at site Fan Lau than at bridge alignment area. More dolphin activity was recorded at Fan Lau despite the higher ambient noise levels occurring there compared to bridge alignment area.

·       Bridge alignment exhibited a diel pattern of activity while the control site (Fan Lau) did not, suggesting a differential pattern of habitat use.

·       The numerical summary of the monitoring results is presented in Tables 8.1.

 

 

Table 8.1  Values of the two response variables of dolphin acoustic behaviour collected by calibrated hydrophone (average clicks and whistles per minutes) by size of group, behavioural state and time of day

 

Average clicks

Average whistles

　

per minute ( ± s.d.)

 

per minute ( ± s.d.)

 

 

 

 

Group Size

 

 

1 dolphins

62.19 ± 77.73 (n=20)

0.21 ± 1.49 (n=20)

2-6 dolphins

54.03 ± 179.32 (n=125)

0.56 ± 1.70 (n=12)

6-9 dolphins

118.00 ± 310.31 (n=37)

1.58 ± 4.63 (n=37)

10+ dolphins

289.33 ± 140.58 (n=35)

2.74 ± 1.99 (n=35)

 

 

 

Behavioural State

 

 

Feeding

30.95 ± 69.90 (n=28)

0.62 ± 1.33 (n=28)

Milling

71.29 ± 205.44 (n=138)

0.66 ± 1.85 (n=138)

Socializing

287.48 ± 326.22 (n=25)

3.78 ± 4.14 (n=25)

Traveling

13.16 ± 208.94 (n=11)

0.25 ± 1.48 (n=11)

Resting

0.10 ± 70.35 (n=5)

0.13 ± 1.43 (n=5)

 

 

 

Time of day

 

 

09:00-10:59

38.14 ± 69.90 (n=28)

0.70 ± 1.33 (n=28)

11:00-12:59

79.97 ± 144.51 (n=93)

0.68 ± 1.86 (n=93)

13:00-14:59

159.41 ± 303.43 (n=61)

1.74 ± 3.80 (n=61)

15:00-16:59

65.40 ± 140.58 (n=35)

1.16 ± 1.99 (n=35)

 

Event and Action Plan

·       It is proposed that to take the response variables (clicking and whistling rates; and the hours in peak occurrence at the two EAR sites) into account for formulating the Action and Limit Levels of the Event and Action Plan:

·       Departures of any of these variables between baseline and construction phases with a 20% difference will be of concern and should trigger the Action Level.

·       Departures of any of these variables between baseline and construction phases with a 40% difference should trigger the Limit Level and immediate action will be required.

·       A shift of 3 hours or more in peak occurrence at the bridge alignment area should trigger the Action Level.

·       A shift of 6 hours or more in peak occurrence at the bridge alignment area should trigger the Limit Level.

·       However, if there is a shift in peak occurrence in both sites (Fan Lau and bridge alignment area), the action or limit level should not be triggered, as the change in peak occurrence does not only occur at the site of impact but also at the control site (Fan Lau), and the changes in peak occurrences of dolphins at both sites may not be directly to the HKLR09 construction works.

·       The detailed Event and Action Plan is presented in Table 8.2.

Table 8.2        Event and Action Plan on Dolphin Movement and Behaviour

EVENT

ACTION

ET Leader

IEC

SO

Contractor

Action Level

With the numerical values presented in Table 1, when any of the response variable for dolphin acoustic behaviour recorded in the construction phase monitoring is 20% lower or higher than that recorded in the baseline monitoring, or when there is a shift of 3 hours or more in peak occurrence at B2 Site (i.e. 00:00 – 01:00), the action level should be triggered

 

1. Repeat statistical data analysis to confirm findings;

2. Review all available and relevant data to ascertain if differences are as a result of natural variation or seasonal differences;

3. Identify source(s) of impact;

4. Inform the IEC, SO and Contractor;

5. Check monitoring data;

6. Carry out audit to ensure all dolphin protective measures are implemented fully and additional measures be proposed if necessary

 

1. Check monitoring data submitted by ET and Contractor;

2. Discuss monitoring with the ET and the Contractor;

 

 

1. Discuss with the IEC the repeat monitoring and any other measures proposed by the ET;

2. Make agreement on measures to be implemented.

 

1. Inform the SO and confirm notification of the non- compliance in writing;

2. Discuss with the ET and the IEC and propose measures to the IEC and the SO;

3. Implement the agreed measures.

Limit Level

With the numerical values presented in Table 1, when any of the response variable for dolphin acoustic behaviour recorded in the construction phase monitoring is 40% lower or higher than that recorded in the baseline monitoring, or when there is a shift of 6 hours or more in peak occurrence at B2 Site (i.e. 00:00 – 01:00), the limit level should be triggered

 

1. Repeat statistical data analysis to confirm findings;

2. Review all available and relevant data to ascertain if differences are as a result of natural variation or seasonal differences;

3. Identify source(s) of impact;

4. Inform the IEC, SO and Contractor;

5. Check monitoring data;

6. Carry out audit to ensure all dolphin protective measures are implemented fully and additional measures be proposed if necessary

7. Discuss additional dolphin monitoring and any other potential mitigation measures (e.g. consider to temporarily stop relevant portion of construction activity) with the IEC and Contractor.

 

1. Check monitoring data submitted by ET and Contractor;

2. Discuss monitoring with the ET and the Contractor;

3. Review proposals for additional monitoring and any other measures submitted by the Contractor and advise ER accordingly.

 

1. Discuss with the IEC the repeat monitoring and any other measures proposed by the ET;

2. Make agreement on measures to be implemented.

 

1. Inform the SO and confirm notification of the non- compliance in writing;

2. Discuss with the ET and the IEC and propose measures to the IEC and the SO;

3. Implement the agreed measures.

Abbreviations: ET – Environmental Team, IEC – Independent Environmental Checker, SO – Supervising Officer

 

8.4              Detailed methodology, results and discussion can be found in the Dolphin Acoustic Behaviour Baseline Monitoring Report in Appendix H.