Contract No. HY/2011/03

Hong Kong-Zhuhai-Macao Bridge Hong Kong Link Road

Section between Scenic Hill and Hong Kong Boundary Crossing Facilities

 

 

 

 

 

 

Quarterly EM&A Report No. 17 (September to November 2016)

 

25 April 2017

 

Revision 1

 

 

 

 

 

 

 

 

 

 

 

 

 

Main Contractor                                                                                                                     Designer

 

 


 


Contents

Executive Summary

1...... Introduction.. 1

1.1                          Basic Project Information. 1

1.2                          Project Organisation. 1

1.3                          Construction Programme. 1

1.4                          Construction Works Undertaken During the Reporting Period. 1

2....... EM&A Requirement 1

2.1                          Summary of EM&A Requirements. 1

2.2                          Action and Limit Levels. 1

2.3                          Event Action Plans. 1

2.4                          Mitigation Measures. 1

3....... Environmental Monitoring and Audit 1

3.1                          Implementation of Environmental Measures. 1

3.2                          Air Quality Monitoring Results. 1

3.3                          Noise Monitoring Results. 1

3.4                          Water Quality Monitoring Results. 1

3.5                          Dolphin Monitoring Results. 1

3.6                          Mudflat Monitoring Results. 1

3.7                          Solid and Liquid Waste Management Status. 1

3.8                          Environmental Licenses and Permits. 1

4....... Environmental Complaint and Non-compliance. 1

4.1                          Environmental Exceedances. 1

4.2                          Summary of Environmental Complaint, Notification of Summons and Successful Prosecution. 1

5....... Comments, Recommendations and Conclusion.. 1

5.1                          Comments. 1

5.2                          Recommendations. 1

5.3                          Conclusions. 1

 

 

 

 

 

 

 

 

 

Figures

 

Figure 1.1         Location of the Site

Figure 2.1         Environmental Monitoring Stations     

Figure 2.2         Transect Line Layout in Northwest and Northeast Lantau Survey Areas

 

                           

Appendices

 

Appendix A       Environmental Management Structure

Appendix B       Construction Programme

Appendix C       Location of Works Areas

Appendix D       Event and Action Plan  

Appendix E       Implementation Schedule of Environmental Mitigation Measures

Appendix F       Site Audit Findings and Corrective Actions

Appendix G      Air Quality Monitoring Data and Graphical Plots

Appendix H       Noise Monitoring Data and Graphical Plots

Appendix I         Water Quality Monitoring Data and Graphical Plots

Appendix J        Dolphin Monitoring Results

Appendix K       Waste Flow Table

Appendix L       Summary of Environmental Licenses and Permits

Appendix M      Record of “Notification of Environmental Quality Limit Exceedances” and Record of “Notification of Summons and Prosecutions”

Appendix N       Cumulative Statistics on Complaints

Appendix O      Mudflat Monitoring Results


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 Asia Pacific 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 will be providing environmental team services to the Contract.

This is the seventeenth 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 September 2016 to 30 November 2016.

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

September 2016

October 2016

November 2016

Air Quality

1-hr TSP

1, 7, 13, 19, 23 and 29

5, 11, 17 and 27

2, 8, 14, 18, 24 and 30

24-hr TSP

6, 12, 17, 22 and 28

4, 8, 14, 20 and 26

1, 7, 11, 17, 23 and 29

Noise

1, 7, 13, 19 and 29

5, 11, 17 and 27

2, 8, 14, 24 and 30

Water Quality

2, 5, 7, 9, 12, 14, 16, 19, 21, 23, 26, 28 and 30

3, 5, 7, 10, 12, 14, 17, 19, 24, 26, 28 and 31

2, 4, 7, 9, 11, 14, 16, 18, 21, 23, 25, 28 and 30

Chinese White Dolphin

13, 14, 21 and 23

4, 7, 11 and 13

2, 7, 18 and 22

Mudflat Monitoring (Ecology)

1, 3, 4, 17 and 18

--

--

Mudflat Monitoring (Sedimentation rate)

1

--

--

Site Inspection

7, 14, 21 and 30

5, 12, 19 and 28

2, 9, 16, 23 and 29

 

 

As thunderstorm warning was hoisted by Hong Kong Observatory on 9 Sep 2016 (from 09:15 to 14:00), water quality monitoring at all stations for mid-flood tide on 9 Sep 2016 was cancelled for safety reason.

Due to boat availability, the dolphin monitoring schedule was rescheduled from 26 Sep 2016 to 23 Sep 2016. As a typhoon was approaching Hong Kong, the dolphin monitoring schedule was rescheduled from 15 Sep to 14 Sep 2016.

Due to boat availability and weather condition, the dolphin monitoring schedule was rescheduled from 19 October 2016 to 13 October 2016.

As Strong Wind Signal No. 3 was hoisted by Hong Kong Observatory on 17 October 2016, water quality monitoring (WQM) was not carried out at stations SR10A and SR10B for mid-ebb tide.

As Tropical Cyclone Warning Signal No. 8 was hoisted by Hong Kong Observatory on 21 October 2016, water quality monitoring (WQM) was not carried out at all stations for mid-ebb tide and mid-flood tide. Due to boat availability, the WQM could not be re-scheduled on 22 October 2016.

As Tropical Cyclone Warning Signal No.8 was hoisted by the Hong Kong Observatory on 21 October 2016, air quality monitoring at AMS5 (Ma Wan Chung Village) and AMS6 (Dragonair Building) were cancelled for safety reason. The monitoring was not able to be re-scheduled on 22 October 2016 because there was some problem with the equipment. Subsequent to internal checking, the equipment is normal for operation as scheduled.

Due to boat availability, the dolphin monitoring schedule was rescheduled from 8 November 2016 to 7 November 2016 and from 15 November 2016 to 18 November 2016.

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

24-hr TSP

0

0

Noise

Leq (30 min)

0

0

Water Quality

Suspended solids level (SS)

1

2

Turbidity level

0

0

Dissolved oxygen level (DO)

0

0

Dolphin Monitoring

Quarterly Analysis (Sep 2016 to Nov 2016)

0

1

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

All investigation reports for exceedances of the Contract have 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 on a weekly basis 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 one complaint received in relation to the environmental impacts during the reporting period.

A summary of environmental complaints for this reporting month is as follows:

 

Environmental Complaint No.

Date of Complaint Received

Description of Environmental Complaints

COM-2016-098

11 November 2016

Water Quality

 

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 quarterly summary 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- East:813273, North 818850) 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.


1        Introduction

1.1                 Basic Project Information

1.1.1       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).

1.1.2       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.

1.1.3       China State Construction Engineering (Hong Kong) Ltd. was awarded by Highways Department (HyD) as the Contractor to undertake the construction works of Contract No. HY/2011/03.  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.  Figure 1.1 shows the project site boundary.

1.1.4       BMT Asia Pacific Limited has been 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) for HKLR and will be providing environmental team services to the Contract.  Ramboll  Environ Hong Kong Ltd. was employed by HyD as the Independent Environmental Checker (IEC) and Environmental Project Office (ENPO) for the Project. The project organization with regard to the environmental works is provided in Appendix A.

1.1.5       This is the seventeenth 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 September 2016 to 30 November 2016.

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.

Table 1.1          Construction Activities during Reporting Period

Description of Activities

Site Area

Dismantling/trimming of temporary 40mm stone platform for construction of seawall

Portion X

Construction of Seawall

Portion X

Loading and Unloading Filling Materials

Portion X

Pipe Piling

Portion X

Excavation and Lateral Support Works at Scenic Hill Tunnel (Cut & Cover Tunnel)

Portion X

Backfilling at Scenic Hill Tunnel (Cut & Cover Tunnel)

Portion X

Construction of Tunnel Box Structure at Scenic Hill Tunnel (Cut & Cover Tunnel)

Portion X

Excavation for HKBCF to Airport Tunnel

Portion X

Excavation for Diversion of culvert PR9 and PR14

Portion X

Works for Diversion

Airport Road

Utilities Detection

Airport Road / Airport Express Line/ East Coast Road

Establishment of Site Access

Airport Road / Airport Express Line/East Coast Road

Mined Tunnel Excavation / Box Jacking

Airport Road and Airport Express Line

Excavation and Lateral Support Works at shaft 3 extension north shaft (Package T1.12.1)

Kwo Lo Wan Road

Excavation and Lateral Support Works &Construction of Tunnel Box Structure for HKBCF to Airport Tunnel East (Cut & Cover Tunnel)

Portion X

Excavation and Lateral Support Works & Construction of Tunnel Box Structure for HKBCF to Airport Tunnel West (Cut & Cover Tunnel)

Airport Road

Utility Culvert Excavation

Portion Y

Sub-structure & superstructure works for Highway Operation and Maintenance Area Building

Portion Y

Excavation for Scenic Hill Tunnel

West Portal

Superstructure works for Scenic Hill Tunnel West Portal Ventilation building

West Portal

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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.

Table 2.1          Summary of Impact EM&A Requirements

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

Leq (30mins),
L10
(30mins) and
L90
(30mins)

NMS5

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, IS(Mf)9 & IS10,

·    Control/Far Field Stations:
CS2 & CS(Mf)5,

·    Sensitive Receiver Stations:
SR3, SR4, SR5, SR10A & SR10B

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

--

 

 

 

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.

Table 2.2         Action and Limit Levels for 1-hour TSP, 24-hour TSP and Noise

Environmental Monitoring

Parameters

Monitoring Station

Action Level

Limit Level

Air Quality

1-hr TSP

AMS 5

352 µg/m3

500 µg/m3

AMS 6

360 µg/m3

24-hr TSP

AMS 5

164 µg/m3

260 µg/m3

AMS 6

173 µg/m3

Noise

Leq (30 min)

NMS 5

When one documented complaint is received

75 dB(A)

 

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

Table 2.3         Action and Limit Levels for Water Quality

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

Notes:

                (1)    Depth-averaged is calculated by taking the arithmetic means of reading of all three depths.

                (2)    For DO, non-compliance of the water quality limit occurs when monitoring result is lower that the limit.

                (3)    For SS & turbidity non-compliance of the water quality limits occur when monitoring result is higher than the limits.

                (4)     The change to the Action and limit Levels for Water Quality Monitoring for the EM&A works was approved by EPD on 25 March 2013. Therefore, the amended Action and Limit Levels are applied for the water monitoring results obtained on and after 25 March 2013.

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

Table 2.4          Action and Limit Level for Dolphin Impact Monitoring

 

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

Remarks:

                 (1)        STG means quarterly average encounter rate of number of dolphin sightings.

                 (2)        ANI means quarterly average encounter rate of total number of dolphins.

                 (3)        For North Lantau Social Cluster, AL will be triggered if either NEL or NWL fall below the criteria; LL will be triggered if both NEL and NWL fall below the criteria.

 

Table 2.5          Derived Value of Action Level (AL) and Limit Level (LL)

 

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)

Remarks:

                 (1)        STG means quarterly average encounter rate of number of dolphin sightings.

                 (2)        ANI means quarterly average encounter rate of total number of dolphins.

                 (3)        For North Lantau Social Cluster, AL will be triggered if either NEL or NWL fall below the criteria; LL will be triggered if both NEL and NWL fall below the criteria.

2.3                Event Action Plans

2.3.1      The Event Actions Plans for air quality, noise, water quality and dolphin monitoring 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       In response to the site audit findings, the Contractor have rectified all observations identified in environmental site inspections undertaken during the reporting period. 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. 

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.

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)

September 2016

AMS5

89

57 - 113

352

500

AMS6

103

59 - 181

360

October 2016

AMS5

130

87 - 179

352

AMS6

115

94 - 146

360

November 2016

AMS5

135

67 - 228

352

AMS6

140

83 - 289

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)

September 2016

AMS5

61

28 - 107

164

260

AMS6

56

26 - 92

173

October 2016

AMS5

33

10 - 45

164

AMS6

45

34 - 63

173

November 2016

AMS5

64

20 - 107

164

AMS6

73

28 - 98

173

 

 

 

 

 

 

 

 

 

 

 

 

 

 

3.2.2       No Action and Limit Level exceedances of 1-hr TSP and 24-hr TSP were recorded at AMS5 and AMS6 during the reporting month.

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 Leq (30 mins), dB(A)*

Range of Leq (30 mins), dB(A)*

Action Level

Limit Level Leq (30 mins), dB(A)

September 2016

NMS5

58

54 - 63

When one documented complaint is received

75

October 2016

59

54 - 60

November 2016

59

59 - 61

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

3.3.2       There were no Action and Limit Level exceedances for noise during daytime on normal weekdays of the reporting period.

3.3.3       Major noise sources during the noise monitoring included construction activities of the Contract and nearby traffic noise and insect noise.

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      During the reporting period, an Action Level exceedance of suspended solids was recorded at station IS10 during mid-flood tide on 19 September 2016. Limit Level exceedances of suspended solids were recorded at station IS10 and SR5 during mid-flood tide on 16 November 2016 respectively. Record of “Notification of Environmental Quality Limit Exceedances” is provided in Appendix M. No exceedances of Action and Limit Level for dissolved oxygen level and turbidity level were recorded.

3.4.3       Water quality impact sources during the water quality monitoring were the construction activities of the Contract, 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 NWL and 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.  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). 

3.5.6       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

3.5.7       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. 

3.5.8       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.

Summary of Survey Effort and Dolphin Sightings

3.5.9       During the period of September to November 2016, six sets of systematic line-transect vessel surveys were conducted to cover all transect lines in NWL and NEL survey areas twice per month.

3.5.10    From these surveys, a total of 892.57 km of survey effort was collected, with 96.5% 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, 341.30 km and 551.27 km of survey effort were conducted in NEL and NWL survey areas respectively. 

3.5.11    The total survey effort conducted on primary lines was 640.35 km, while the effort on secondary lines was 252.22 km.  Survey effort conducted on both primary and secondary lines were considered as on-effort survey data.  A summary table of the survey effort is shown in Annex I of Appendix J.

3.5.12    During the six sets of monitoring surveys in September to November 2016, a total of 13 groups of 48 Chinese White Dolphins were sighted.  A summary table of the dolphin sightings is shown in Annex II of Appendix J.

3.5.13    For the present quarterly period, all dolphin sightings were made during on-effort search, while all except one on-effort dolphin sightings were made on primary lines.  In addition, all dolphin groups were 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 respectively in NEL during HKLR03 monitoring surveys.

Distribution

3.5.14    Distribution of dolphin sightings made during monitoring surveys in September to November 2016 is shown in Figure 1 of Appendix J.

3.5.15    Dolphin sightings made in the present quarter were mainly located around Sha Chau and Lung Kwu Chau near western territorial boundary (Figure 1 of Appendix J).  A few sightings were also made near Black Point, Pillar Point and Sham Wat respectively (Figure 1 of Appendix J).  On the other hand, the dolphins were completely absent from the central and western portions of North Lantau waters (Figure 1 of Appendix J).

3.5.16    All dolphin sightings were located far away from the HKBCF and HKLR03 reclamation sites as well as along the alignment of Tuen Mun-Chek Lap Kok Link (TMCLKL).  However, one group of two dolphins was sighted adjacent to the HKLR alignment near Sham Wat (Figure 1 of Appendix J).

3.5.17    Sighting distribution of dolphins during the present impact phase monitoring period (September to November 2016) was drastically different from the one during the baseline monitoring period (September to November 2011)  In the present quarter, dolphins have disappeared from the NEL region, which was in stark contrast to their frequent occurrence 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 nearly complete abandonment of NEL region by the dolphins has been consistently recorded in the past 15 quarters of HKLR03 monitoring, which has resulted in zero to extremely low dolphin encounter rates in this area.

3.5.18    In NWL survey area, dolphin occurrence was also very different between the baseline and impact phase periods.  During the present impact monitoring period, much fewer dolphins occurred in this survey area (mostly to the east of Lung Kwu Chau and west of Sha Chau) than during the baseline period, when many dolphin groups were frequently sighted between Lung Kwu Chau and Black Point, around Sha Chau, near Pillar Point and to the west of the Chek Lap Kok Airport (Figure 1 of Appendix J). 

3.5.19    Another comparison in dolphin distribution was made between the four quarterly periods of summer months in 2013-16 (Figure 2 of Appendix J).  Among the four summer periods, dolphins were regularly sighted throughout the North Lantau region in 2013, but their usage there has gradually diminished in 2014 and subsequently to a very low level in 2015 and 2016 with only occurrences concentrated around 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) (See Table 3.5).

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 2.50 sightings and 9.21 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.

Table 3.4         Dolphin Encounter Rates (Sightings Per 100 km of Survey Effort) During Reporting Period (September to November 2016) 

Survey Area

Dolphin Monitoring

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 surve
y effort)

Primary Lines Only

Primary Lines Only

Northeast  Lantau

Set 1 (13 & 14 Sep 2016)

0.00

0.00

Set 2 (21 & 23 Sep 2016)

0.00

0.00

Set 3 (4 & 7 Oct 2016)

0.00

0.00

Set 4 (11 & 13 Oct 2016)

0.00

0.00

Set 5 (2 & 7 Nov 2016)

0.00

0.00

Set 6 (18 & 22 Nov 2016)

0.00

0.00

Northwest Lantau

Set 1 (13 & 14 Sep 2016)

0.00

0.00

Set 2 (21 & 23 Sep 2016)

5.75

30.17

Set 3 (4 & 7 Oct 2016)

4.13

9.64

Set 4 (11 & 13 Oct 2016)

2.85

8.54

Set 5 (2 & 7 Nov 2016)

1.66

1.66

Set 6 (18 & 22 Nov 2016)

2.79

15.34

Table 3.5         Comparison of average dolphin encounter rates from impact monitoring period (September to November 2016) and baseline monitoring period (September – November 2011)

Survey Area

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)

Reporting Period

Baseline Monitoring Period

Reporting Period

Baseline Monitoring Period

Northeast Lantau

0.0

6.00 ± 5.05

0.0

22.19 ± 26.81

Northwest Lantau

2.86 ± 1.98

9.85 ± 5.85

10.89 ± 10.98

44.66 ± 29.85

Notes:
1) The encounter rates deduced from the baseline monitoring period have been recalculated based only on the 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.

 

3.5.22    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 the past 15 quarters of HKLR03 monitoring (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 January 2014, with only three groups of six dolphins sighted there since then 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 Quarters of Impact Monitoring Period and Baseline Monitoring Period (Sep – Nov 2011)

Monitoring Period

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 (Impact)

3.14 ± 3.21

6.33 ± 8.64

March-May 2013 (Impact)

0.42 ± 1.03

0.42 ± 1.03

June-August 2013 (Impact)

0.88 ± 1.36

3.91 ± 8.36

September-November 2013 (Impact)

1.01 ± 1.59*

3.77 ± 6.49*

December 2013-February 2014 (Impact)

0.45 ± 1.10

1.34 ± 3.29

March-May 2014 (Impact)

0.00

0.00

June-August 2014 (Impact)

0.42 ± 1.04

1.69 ± 4.15

September-November 2014 (Impact)

0.00*

0.00*

December 2014-February 2015 (Impact)

0.00

0.00

March-May 2015 (Impact)

0.00

0.00

June-August 2015 (Impact)

0.44 ± 1.08

0.44 ± 1.08

September-November 2015 (Impact)

0.00*

0.00*

December 2015-February 2016 (Impact)

0.00

0.00

March-May 2016 (Impact)

0.00

0.00

June-August 2016 (Impact)

0.00

0.00

September-November 2016 (Impact)

0.00*

0.00*

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) The encounter rates in summer months were in blue and marked with asterisk.

 

3.5.23    On the other hand, the average dolphin encounter rates (STG and ANI) in NWL during the present impact phase monitoring period (reductions of 71.0% and 75.6% respectively) were only small 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    During the same summer quarters, dolphin encounter rates in NWL during 2016 reached to the lowest point among the four summer periods, and were much lower than the ones recorded in 2013 and 2014 (Table 3.7).  Such temporal trend should be closely monitored in the upcoming monitoring quarters.

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

Monitoring Period

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 (Impact)

8.36 ± 5.03

35.90 ± 23.10

March-May 2013 (Impact)

7.75 ± 3.96

24.23 ± 18.05

June-August 2013 (Impact)

6.56 ± 3.68

27.00 ± 18.71

September-November 2013 (Impact)

8.04 ± 1.10*

32.48 ± 26.51*

December 2013-February 2014 (Impact)

8.21 ± 2.21

32.58 ± 11.21

March-May 2014 (Impact)

6.51 ± 3.34

19.14 ± 7.19

June-August 2014 (Impact)

4.74 ± 3.84

17.52 ± 15.12

September-November 2014 (Impact)

5.10 ± 4.40*

20.52 ± 15.10*

December 2014-February 2015 (Impact)

2.91 ± 2.69

11.27 ± 15.19

March-May 2015 (Impact)

0.47 ± 0.73

2.36 ± 4.07

June-August 2015 (Impact)

2.53 ± 3.20

9.21 ± 11.57

September-November 2015 (Impact)

3.94 ± 1.57*

21.05 ± 17.19*

December 2015-February 2016 (Impact)

2.64 ± 1.52

10.98 ± 3.81

March-May 2016 (Impact)

0.98 ± 1.10

4.78 ± 6.85

June-August 2016 (Impact)

1.72 ± 2.17

7.48 ± 10.98

September-November 2016 (Impact)

2.86 ± 1.98*

10.89 ± 10.98*

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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) The encounter rates in summer months were in blue and marked with asterisk.

3.5.25    As discussed recently in Hung (2016), the dramatic decline in dolphin usage of NEL waters in the past few years (including the declines in abundance, encounter rate and habitat use in NEL, as well as shifts of individual core areas and ranges away from NEL waters) was possibly related to the HZMB construction works that were commenced since 2012.  It appeared that such noticeable decline has already extended to NWL waters progressively in the past few years.

3.5.26    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). 

3.5.27    For the comparison between the baseline period and the present quarter (16th quarter of the impact phase being assessed), the p-values for the differences in average dolphin encounter rates of STG and ANI were 0.0051 and 0.0296 respectively.  If the alpha value is set at 0.05, significant differences were detected between the baseline and present quarters in both the average dolphin encounter rates of STG and ANI.

3.5.28    For the comparison between the baseline period and the cumulative quarters in impact phase (i.e. first sixteen quarters of the impact phase being assessed), the p-values for the differences in average dolphin encounter rates of STG and ANI were 0.000004 and 0.000001 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).

3.5.29    As indicated in both dolphin distribution patterns and encounter rates, dolphin usage has been significantly reduced in both NEL and NWL survey areas during the present quarterly period, and such low occurrence of dolphins has also been consistently documented in previous quarters.  This 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 (Hung 2016).

3.5.30    To ensure the continuous usage of North Lantau waters by the dolphins, every possible measure should be implemented by the contractors and relevant authorities of HZMB-related works to minimize all disturbances to the dolphins.

Group Size

3.5.31    Group size of Chinese White Dolphins ranged from one to eleven individuals per group in North Lantau region during September to November 2016. The average dolphin group sizes from these three months were 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 between Reporting Period (Jun 2016 – Aug 2016) and Baseline Monitoring Period (Sep – Nov 2011)

Survey Area

Average Dolphin Group Size

Reporting Period

Baseline Monitoring Period

Overall

3.69 ± 2.87 (n = 13)

3.72 ± 3.13 (n = 66)

Northeast Lantau

---

3.18 ± 2.16 (n = 17)

Northwest Lantau

3.69 ± 2.87 (n = 13)

3.92 ± 3.40 (n = 49)

 

 

 

 

 

 

 

 

 

 

 

Note:

1)     ± denotes the standard deviation of the average group size.

3.5.32    The average dolphin group size in NWL waters during September to November 2016 was slightly lower than the one recorded during the three-month baseline period (Table 3.8). Most of these dolphin groups were composed of 1-4 individuals only, while there were three medium-sized groups of 5-7 individuals respectively, and one large group of eleven individuals.

3.5.33    Distribution of the larger dolphin groups (i.e. five individuals or more per group) during the present quarter is shown in Figure 3 of Appendix J, with comparison to the one in baseline period.  During the autumn months of 2016, the three medium-sized groups were sighted adjacent to Lung Kwu Chau and to the north of the island, while the one large group of eleven individuals was sighted to at the northeast corner of Lung Kwu Chau as well (Figure 3 of Appendix J). Such distribution pattern was very different from the baseline period, when the larger dolphin groups were more frequently sighted and more evenly distributed in NWL waters, with a few more sighted in NEL waters (Figure 3 of Appendix J).

Habitat Use

3.5.34    From September to November 2016, the more important habitats utilized by Chinese White Dolphins were mostly located around Lung Kwu Chau (Figures 4a and 4b of Appendix J).  One grid located to the west of Shum Wat just to the south of the HKLR09 alignment also recorded moderate density of dolphins.  On the contrary, all grids near HKLR03/HKBCF reclamation sites as well as TMCLKL alignment did not record any presence of dolphins at all during on-effort search in the present quarterly period (Figures 4b of Appendix J).

3.5.35    However, 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 will be collected throughout the impact phase monitoring programme.

3.5.36    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 5 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 (Figure 5 of Appendix J). 

3.5.37    The density patterns were also very different in NWL between the baseline and impact phase monitoring periods, with higher dolphin usage throughout the area, especially around Sha Chau, near Black Point, to the west of the airport, as well as between Pillar Point and airport platform during the baseline period.  In contrast, the only areas with moderate to high dolphin densities were restricted to the waters near Sha Chau and Lung Kwu Chau during the present impact phase period. (Figure 5 of Appendix J). 

Mother-calf Pairs

3.5.38    During the present quarterly period, neither unspotted calf nor unspotted juvenile was sighted with any female in the North Lantau region.

3.5.39    The absence of young calves in the past four consecutive quarters was in stark contrast to their regular occurrence in North Lantau waters during the baseline period.  This should be of 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

3.5.40    Four of the thirteen dolphin groups were engaged in feeding activity, while none of them was engaged in socializing, traveling or milling/resting activity during the three-month study period.

3.5.41    The percentage of sightings associated with feeding activities (30.8%) was much higher than the one recorded during the baseline period (11.6%).  However, it should be noted the sample size on total numbers of dolphin sightings during the present quarter (13 dolphin groups) was much lower than the baseline period (66 dolphin groups).

3.5.42    Distribution of dolphins engaged in various activities during the present impact phase period and the baseline period is shown in Figure 6 of Appendix J.  The four dolphin groups engaged in feeding activities were sighted around Lung Kwu Chau as well as to the west of Shum Wat near the HKLR09 alignment during the present quarterly period, which was very different from the baseline period when various dolphin activities occurred throughout the North Lantau region (Figure 6 of Appendix J).

3.5.43    Notably, one group of seven dolphins was found to be associated with an operating gill-netter adjacent to Lung Kwu Chau within the marine park during the present impact phase period.

Summary Photo-identification works

3.5.44    From September to November 2016, over 2,100 digital photographs of Chinese White Dolphins were taken during the impact phase monitoring surveys for the photo-identification work.

3.5.45    In total, 21 individuals sighted 34 times altogether were identified (see summary table in Annex III of Appendix J and photographs of identified individuals in Annex IV of Appendix J).  All of these re-sightings were made in NWL. Six individuals (CH34, NL136, NL202, NL269, NL286 and NL320) were re-sighted multiple times during the three-month period

3.5.46    Notably, none of these 21 individuals was also sighted in West Lantau waters during the HKLR09 monitoring surveys from September to November 2016.  However, one individual (NL269) was sighted in both NWL and SWL survey areas during the same quarter, showing its extensive individual movement between different survey areas.

Individual range use

3.5.47    Ranging patterns of the 21 individuals identified during the three-month study period were determined by fixed kernel method, and are shown in Annex V of Appendix J.

3.5.48    All identified dolphins sighted in the present quarter were utilizing NWL waters only, but have completely avoided NEL waters where many of them have utilized as their core areas in the past (Annex V of Appendix J).  This is in contrary to the extensive movements between NEL and NWL survey areas observed in the earlier impact monitoring quarters as well as the baseline period.

3.5.49    On the other hand, only one of these individuals consistently utilized both North Lantau waters in the past have extended their range use to SWL waters during the present quarter.  In the upcoming quarters, individual range use and movements should be continuously monitored to examine whether there has been any consistent shifts of individual home ranges from North Lantau to West or Southwest Lantau, as such shift could possibly be related to the HZMB-related construction works (see Hung 2015, 2016).

Action Level / Limit Level Exceedance

3.5.50    There was one Limit Level exceedance of dolphin monitoring for the quarterly monitoring data (between September 2016 – November 2016). According to the contractor’s information, the marine activities undertaken for HKLR03 during the quarter of September 2016 – November 2016 included piling works, removal of surcharge materials, temporary drainage diversion, ground investigation, box culvert diversion, construction of permanent seawall and maintenance of silt curtain.

3.5.51    There is no evidence showing the current LL non-compliance directly related to the construction works of HKLR03 (where the amounts of working vessels for HKLR03 have been decreasing), although the generally increased amount of vessel traffic in NEL during the impact phase has been partly contributed by HKLR03 works since October 2012. It should also be noted that reclamation work under HKLR03 (adjoining the Airport Island) situates in waters which has rarely been used by dolphins in the past, and the working vessels under HKLR03 have been travelling from source to destination in accordance with the Marine Travel Route to minimize impacts on Chinese White Dolphin (CWD).  In addition, the contractor will implement proactive mitigation measures such as avoiding anchoring at Marine Department’s designated anchorage site – Sham Shui Kok Anchorage (near Brothers Island) as far as practicable. 

3.5.52    According to Monitoring of Chinese White Dolphins in Southwest Lantau Waters – Fourth Quarterly Report (December 2015 to February 2016) which is available on ENPO’s website, with their primary ranges centered in North and West Lantau waters, some individuals showed apparent range shifts or extensions to Southwest Lantau waters in 2015-16.  For example, three individual dolphins (NL120, WL46 and WL221) indicated obvious shifts in their range use from NWL to West Lantau (WL) and Southwest Lantau (SWL) waters. Moreover, many individuals (e.g. NL212, NL260, WL200, SL55, WL232, WL237 and WL265) have extended their ranges from WL waters to SWL waters.  It remains to be seen whether some of these individuals have permanently shifted their ranges away from their primary ranges in North Lantau, or begin to spend more times in SWL waters as part of their ranges. 

3.5.53    ENPO updated that the Hong Kong-Zhuhai-Macao Bridge Authority (HZMBA) for the Mainland section of Hong Kong-Zhuhai-Macao Bridge (HZMB) has commenced an interim survey on fisheries resources and CWD in the Mainland waters. ENPO presented the preliminary findings of the HZMBA interim survey on CWD sighting and photo-identification works which provide solid evidence that some CWD that were previously more often sighted in HK waters have expanded their ranges into the Mainland waters, and some with reduced usage in HK waters. These preliminary data were mentioned in Monitoring of Chinese White Dolphins in Southwest Lantau Waters – Fourth Quarterly Report (December 2015 to February 2016) which is available on ENPO’s website.

3.5.54    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). 

3.5.55    For the comparison between the baseline period and the present quarter (16th quarter of the impact phase being assessed), the p-values for the differences in average dolphin encounter rates of STG and ANI were 0.0051 and 0.0296 respectively.  If the alpha value is set at 0.05, significant differences were detected between the baseline and present quarters in both the average dolphin encounter rates of STG and ANI.

3.5.56    For the comparison between the baseline period and the cumulative quarters in impact phase (i.e. first sixteen quarters of the impact phase being assessed), the p-values for the differences in average dolphin encounter rates of STG and ANI were 0.000004 and 0.000001 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).

3.5.57    The AFCD monitoring data during September to November 2016 has been reviewed by the dolphin specialist.  During the same quarter, no dolphin was sighted from 176.90 km of survey effort on primary lines in NEL, while three groups of six dolphins were sighted from 255.36 km of survey effort on primary lines in NWL. This review has confirmed that the extremely low occurrence of dolphins reported by the HKLR03 monitoring surveys in autumn 2016 in NEL and NWL survey area is accurate.

3.5.58    All dolphin protective measures are fully and properly implemented in accordance with the EM&A Manual. According to the Regular Marine Travel Route Plan, the travelling speed of vessels must not exceed 5 knots when crossing the edge of the marine park. The Contractor will continue to provide training for skippers to ensure that their working vessels travel from source to destination to minimize impacts on Chinese White Dolphin and avoid anchoring at Marine Department’s designated anchorage site - Sham Shui Kok Anchorage (near Brothers Island) as far as practicable. Also, it is recommended to complete the marine works of the Contract as soon as possible so as to reduce the overall duration of impacts and allow the dolphins population to recover as early as possible.

3.5.59    A meeting was held on 10 February 2017 with attendance of representative of ENPO, Resident Site Staff (RSS), Environmental Team (ET) and dolphin specialist for Contract Nos. HY/2010/02, HY/2011/03, HY/2012/07, HY/2012/08. The discussion/recommendation as recorded in the minutes of the meeting, which might be relevant to HKLR03 Contract are summarized below.

3.5.60    It was concluded that the HZMB works is one of the contributing factors affecting the dolphins. It was also concluded the contribution of impacts due to the HZMB works as a whole (or individual marine contracts) cannot be quantified nor separate from the other stress factors.

3.5.61    The dolphin specialists of the projects confirmed that the CWD sighting around the North of Sha Chau and Lung Kwu Chau Marine Park (SCLKCMP) has significantly decreased, and it was apparently related to the re-routing of high speed ferry (HSF) from Skypier.

3.5.62    It was reminded that the ETs shall keep reviewing the implementation status of the dolphin related mitigation measures and remind the contractor to ensure the relevant measures were fully implemented.

3.5.63    It was recommended that the marine works of HZMB projects should be completed as soon as possible so as to reduce the overall duration of impacts and allow the dolphins population to recover as early as possible.

3.5.64    It was also recommended that the marine works footprint (e.g., reduce the size of peripheral silt curtain) and vessels for the marine works should be reduced as much as possible, and vessels idling / mooring in other part of the North Lantau shall be avoided whenever possible.

3.5.65    It was suggested that the protection measures (e.g., speed limit control) for the Brothers Marine Park (BMP) shall be brought forward so as to provide a better habitat for dolphin recovery. It was noted that under the Regular Marine Travel Route (RMTR) Plan, the contractors have committed to reduce the vessel speed in BMP. HyD updated that the draft map of the proposed BMP was gazetted in February 2016. ENPO updated that the BMP was approved by the Chief Executive in the Executive Council in August 2016. The ETs were reminded to update the BMP boundary in the RMTR Plan. The BMP was designated on 30 December 2016.  It was reminded that trespassing the BMP is not allowed under the RMTR Plan.

3.5.66    There was a discussion on exploring possible further mitigation measures, for example, controlling the underwater noise. It was noted that the EIA reports for the projects suggested several mitigation measures, all of which have been implemented.

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 1 September 2016. The mudflat surface levels at the four established monitoring stations and the corresponding XYZ HK1980 GRID coordinates are presented in Table 3.9 and Table 3.10.

Table 3.9          Measured Mudflat Surface Level Results

Baseline Monitoring
(September 2012)

Impact Monitoring
(
March 2016)

Monitoring Station

Easting
(m)

Northing (m)

Surface Level
(mPD)

Easting
(m)

Northing (m)

Surface Level

(mPD)

S1

810291.160

816678.727

0.950

810291.189

816678.707

1.044

S2

810958.272

815831.531

0.864

810958.257

815831.465

0.929

S3

810716.585

815953.308

1.341

810716.522

815953.252

1.372

S4

811221.433

816151.381

0.931

811221.407

816151.382

0.959

Table 3.10       Comparison of Measurement  

Comparison of measurement

Remarks and Recommendation

Monitoring Station

Easting
(m)

Northing (m)

Surface Level
(mPD)

S1

0.029

-0.020

0.094

Level continuously increased

S2

-0.015

-0.066

0.065

Level continuously increased

S3

-0.063

-0.056

0.031

Level continuously increased

S4

-0.026

0.001

0.028

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) as in the EM&A Manual.  The water quality monitoring location (SR3) is shown in Figure 2.1. 

3.6.4       Impact water quality monitoring in San Tau (monitoring station SR3) was conducted in September 2016. The monitoring parameters included dissolved oxygen (DO), turbidity and suspended solids (SS).

3.6.5       The Impact monitoring result for SR3 were extracted and summarised below:

 

Table 3.11      Impact Water Quality Monitoring Results (Depth Average)

Date

Mid Ebb Tide

Mid Flood Tide

DO (mg/L)

Turbidity (NTU)

SS (mg/L)

DO (mg/L)

Turbidity (NTU)

SS (mg/L)

2-Sep-16

5.89

14.65

17.55

5.48

7.20

7.25

5-Sep-16

6.23

9.30

9.30

5.90

5.90

6.85

7-Sep-16

5.98

7.35

6.05

5.91

4.20

6.10

9-Sep-16

6.29

3.20

4.20

See Remark 1

See Remark 1

See Remark 1

12-Sep-16

5.90

4.75

4.15

6.59

2.85

3.35

14-Sep-16

6.86

5.75

6.80

6.91

7.05

8.65

16-Sep-16

6.89

4.85

5.20

7.13

5.00

6.45

19-Sep-16

5.66

9.30

10.60

5.31

7.65

9.90

21-Sep-16

5.43

6.35

10.70

5.53

6.60

11.95

23-Sep-16

6.15

5.10

4.25

5.73

5.75

6.55

26-Sep-16

5.86

3.20

5.30

6.23

4.30

6.00

28-Sep-16

5.78

10.45

14.10

6.10

7.75

9.95

30-Sep-16

5.99

11.20

13.65

5.75

10.50

13.15

Average

6.07

7.34

8.60

6.05

6.23

8.01

Remark:

1.     As thunderstorm warning was hoisted by Hong Kong Observatory on 9 Sep 2016 (from 09:15 to 14:00), water quality monitoring at all stations for mid-flood tide on 9 Sep 2016 was cancelled for safety reason.

Mudflat Ecology Monitoring

Sampling Zone

3.6.6       In order 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 length of sampling zones TC1, TC2, TC3 and ST were about 250 m, 300 m, 300 m and 250 m, respectively. Survey of horseshoe crabs, seagrass beds and intertidal communities were conducted in every sampling zone. The present survey was conducted in September 2016 (totally 6 sampling days between 1st and 18th September 2016).

Horseshoe Crabs

3.6.7       Active search method was conducted for horseshoe crab monitoring by two experienced surveyors at every sampling zone. During the search period, any accessible and potential area would be investigated for any horseshoe crab individuals within 2-3 hours 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 1st (for TC3 and ST), 3rd (for TC1) and 18th (for TC2) September 2016. The weather was generally cloudy with intermittent rains on 1st and 3rd September. It was sunny and hot on 18th September 2016.

Seagrass Beds

3.6.8       Active search method was conducted for seagrass bed monitoring by two experienced surveyors at 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 1st (for TC3 and ST), 3rd (for TC1) and 18th (for TC2) September 2016. The weather was generally cloudy with intermittent rains on 1st and 3rd September. It was sunny and hot on 18th September 2016.

Intertidal Soft Shore Communities

3.6.9       The intertidal soft shore community surveys were conducted on 3rd (for TC1), 4th (for ST), 17th (for TC3) and 18th (for TC2) September 2016. In every sampling zone, three 100 m horizontal transect lines were laid at high tidal level (H: 2.0 m above C.D.), mid tidal level (M: 1.5 m above C.D.) and low tidal level (L: 1.0 m above C.D.). Along every horizontal transect line, ten random quadrats (0.5 m x 0.5m) were placed.

3.6.10    Inside a quadrat, any visible epifauna were collected and were 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 were collected and identified. Finally the top 5 cm surface sediments were dug for visible infauna in the quadrat regardless of hand core sample was taken.

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

3.6.12    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).

Data Analysis

3.6.13    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 ith species.

Mudflat Ecology Monitoring Results and Conclusion

Horseshoe Crabs

3.6.14    In the present survey, two species of horseshoe crab Carcinoscorpius rotundicauda (total 227 ind.) and Tachypleus tridentatus (total 37 ind.) were recorded. For one sight record, grouping of 2-28 individuals was observed at same locations with similar substratum (fine sand or soft mud). Photo records were shown in Figure 3.1 of Appendix O while the complete records of horseshoe crab were shown in Annex II of Appendix O.

3.6.15    Table 3.1 of Appendix O summarizes the survey results of horseshoe crab in present survey. For Carcinoscorpius rotundicauda, there were 36, 1, 64 and 126 individuals in TC1, TC2, TC3 and ST respectively. For ST, the search record was the highest (21.0 ind. hr-1 person-1) while the average body size was 33.96 mm (prosomal width ranged 14.58-72.34 mm). TC3 had the second high search record (10.7 ind. hr-1 person-1) with average body size 30.32 mm (prosomal width ranged 14.96-64.01 mm). For TC1, there was less number of individual but the search record (9.0 ind. hr-1 person-1) was comparable to TC3 with less average body size 26.84 mm (prosomal width ranged 10.93-64.75mm). For TC2, there was only one individual (prosomal width: 41.39 mm) hence the search record was very low (0.3 ind. hr-1 person-1).

3.6.16    For Tachypleus tridentatus, there were 17 and 20 individuals in TC3 and ST respectively. For ST, the search record was 3.3 ind. hr-1 person-1 while the average body size was 35.69 mm (prosomal width ranged 27.19-72.55 mm). For TC3, the search record was 2.8 ind. hr-1 person-1 while the average body size was 51.88 mm (prosomal width ranged 34.75-79.18 mm).

3.6.17    In the previous survey of March 2015, there was one important finding that a mating pair of Carcinoscorpius rotundicauda was found in ST (prosomal width: male 155.1 mm, female 138.2 mm) (Figure 3.2 of Appendix O). It indicated the importance of ST as a breeding ground of horseshoe crab. Moreover, two moults of Carcinoscorpius rotundicauda were found in TC1 with similar prosomal width 130-140 mm (Figure 3.2 of Appendix O). It reflected that a certain numbers of moderately sized individuals inhabited the sub-tidal habitat of Tung Chung Wan after its nursery period on soft shore. These individuals might move onto soft shore during high tide for foraging, moulting and breeding. Then it would return to sub-tidal habitat during ebb tide. Because the mating pair should be inhabiting sub-tidal habitat in most of the time. The record was excluded from the data analysis to avoid mixing up with juvenile population living on soft shore. In another previous survey of Jun. 2016, the records of the two big individuals of Carcinoscorpius rotundicauda (prosomal width 117.37 mm and 178.17 mm) in TC1 were excluded from data analysis according to the same principle.  

3.6.18    No marked individual of horseshoe crab was recorded in present survey. Some marked individuals were found in previous surveys conducted in September 2013, March 2014 and September 2014. All of them were released through a conservation programme conducted 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 crabs 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.

3.6.19    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

3.6.20    Figures 3.3 and 3.4 of Appendix O show the changes of number of individuals, mean prosomal width and search record of horseshoe crabs Carcinoscorpius rotundicauda and Tachypleus tridentatus respectively in every sampling zone throughout the monitoring period. In general, high to medium search records (i.e. number of individuals) of both species were always found in ST and TC3. The search record of ST was higher from Sep. 2012 to Jun. 2014 while it was replaced by TC3 from Sep. 2014 to Jun. 2015. The search records were similar between two sampling zones from Sep. 2015 to Jun. 2016. In present survey, the search record of Carcinoscorpius rotundicauda in ST was much higher than TC3. For TC1, the search record was at low to medium 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 (2 ind. in Sep. 2013; 1 ind. in Mar., Jun., Sep. 2014, Mar. and Jun. 2015; 4 ind. in Sep. 2015; 6 ind. in Jun. 2016; 1 ind. in Sep. 2016). For the body size, larger individuals of Carcinoscorpius rotundicauda were usually found in ST and TC1 relative to those in TC3. For Tachypleus tridentatus, larger individuals were usually found in ST followed by TC3 and TC1.

3.6.21    Throughout the monitoring conducted, it was obvious that 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 either 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 substrata.

Seasonal variation of horseshoe crab population

3.6.22    Throughout the monitoring period conducted, the search record of horseshoe crab declined obviously during dry season especially December (Figures 3.3 and 3.4 of Appendix O). In December 2013, no individual of horseshoe crab was found. In December 2014, 2 individuals of Carcinoscorpius rotundicauda and 8 individuals of Tachypleus tridentatus were found only.  In December 2015, 2 individuals of Carcinoscorpius rotundicauda, 6 individuals of Tachypleus tridentatus and one newly hatched, unidentified individual were found only. 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-1 person-1 and 0.00 ind. hr-1 person-1 in wet season and dry season respectively (details see Li, 2008). After the dry season, the search record increased with the warmer climate.

3.6.23    From September 2012 to December 2013, Carcinoscorpius rotundicauda was a 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. Since 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. From March 2014 to September 2015, more individuals were recorded due to larger size and higher activity (i.e. more conspicuous walking trail).

3.6.24    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 Mar. and Jun. 2014 followed by a rapid decline in Sep. 2014. Then the number of individuals fluctuated slightly in TC3 and ST until Sep. 2016 (present survey). 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 Mar. 2014. Then it varied slightly between 35-65 mm from Sep. 2014 to Jun. 2016 (present survey). Most of the individuals might have reached a suitable size strong enough to forage in sub-tidal habitat.

3.6.25    Since TC3 and ST were regarded as important nursery ground for horseshoe crab, 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

3.6.26    Figure 3.5 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 Sep. 2012 and Dec. 2013 hence the data were lacking. In Mar 2014, the major size (50% of individual records between upper and lower quartile) ranged 40-60 mm while only few individuals were found. From Mar. 2014 to Sep. 2016 (present survey), the size of major population decreased and more small individuals were recorded after Mar. of every year. It indicated new rounds of successful breeding and spawning of Carcinoscorpius rotundicauda in TC3. It matched with the previous mating record in ST in Mar. 2015. Focused on much larger sized individuals (circle dots above the box in the box plots), the size range was quite variable (prosmal width 60-90 mm) along the sampling month. It was yet to determine their size of migrating to sub-tidal habitat in TC3.

3.6.27    For Tachypleus tridentatus, the major size ranged 20-50 mm while the number of individuals fluctuated from Sep. 2012 to Jun. 2014. Then a slight but consistent growing trend was observed from Sep. 2014 to Jun. 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 Mar. to Sep. 2016 (present survey), slight increasing trend of major size was noticed again. Across the monitoring period, the maximum prosomal width of major population ranged 60-70 mm. It reflected individuals reaching this size would gradually migrate to sub-tidal habitats.

Box plot of horseshoe crab populations in ST

3.6.28    Figure 3.6 of Appendix O shows the changes of prosomal width of Carcinoscorpius rotundicauda and Tachypleus tridentatus