EIS 1078 Vol 2
ABO1 9707
Sand extraction in Griffins Bay : environmental impact
statement ' flfl!•IIIflIJfl•&flfl SW DEPT PR1AR INDUSTRIES
AB01 9707
SOUTH COAST EQUIPMENT PTY LTD
SAND EXTRACTION I IN GRIFFINS BAY
VOLUME 2 I ENVIRONMENTAL IMPACT STATEMENT WORKING PAPERS SOUTH COASTEQUIPMENT PTY LTD
SAND EXTRACTION IN GRIFFINS BAY
VOLUME 2 ENVIRONMENTAL IMPACT STATEMENT WORKING PAPERS
April 1995 GUTTERIDGE HASKINS & DAVEY PlY LTD 39 Regent Street, RAILWAY SQUARE NSW 2000 Telephone: (02) 690 7070 Facsimile: (02) 698 1780
© Gutteridge Haskins & Davey Pty Ltd 1995 This document is and shall remain the property of Gutteridge Haskins & Davey Pty Ltd. The document may only be used for the purpose for which it was commissioned and in accordance with the Terms of Engagement for the commission. Unauthorised use of this document in any form whatsoever is prohibited.
217/027419/00 R4438 lJ:LT CONTENTS
Acoustical Impact Assessment Proposed Dredging of Griffins Bay, Lake illawarra, NSW
James Madden Cooper Atkins Pty Ltd, 1994
Soclo-Economic Impacts of the Proposal to Extract Sand from Griffins Bay, Lake Illawarra
Economic Planning Impact Consultants Pty Ltd, 1995
An Assessment of Impacts on Marine Flora, Fauna and Fisheries of a Proposal to Extract Sand from Griffins Bay, Lake Illawarra
The Ecology Lab Pty Limited, 1995.
Griffins Bay Sand Extraction EIS
Gutteridge Haskins & Davey Pty Ltd M114182 ACOUSTICAL IMPACT ASSESSMENT
PROPOSED DREDGING OF GRIFFINS BAY,
LAKE ILLAWARRA NSW
JAMES MADDEN COOPER ATKINS PTY LTD, 1994
Griffins Bay Sand Extraction EIS
Gutteridge Haskins & Davey Pty Ud M114182 JAMES MADDEN COOPER ATKINS PlY LIMITED. CONSULTING ACOUSTICAL & VIBRATION ENGINEERS
ACOUSTICAL IMPACT ASSESSMENT PROPOSED DREDGIIG OF GR1FFIT' BAY LAKE ILLAWARRA NSW 24.2467.R2:GA37
Prepared for: Gutteridge Haskins & Davey Pty Limited 39 Regent Street RAILWAY SQUARE. NSW 2000
May 1994 8-10 Wharf Road, Gladesville, N.S.W. 2111 AUSTRALIA Telephone: 879.6844 Fax: 879.6622 Principals Member Firm of the Association Steven E. Cooper Graham F. Atkins A.C.N. of Australian Acoustical Oonsultants. BSc (Eng), MSc (Arch M I.E. (AUST BE (Mech.), M.A AS.. M.I.E. (AUST.) 002 353 497 A.A.A.C. CONTENTS
1.0 INTRODUCTION
2.0 GENERAL DESCRIPTION OF SITE AND PROPOSAL 2 2.1 Plant and Equipment 2 2.1.1 Main Dredge Plant 2 2.1.2 Screen and Booster Pump 3 2.1.3 Processing Plant 3 2.1.4 Road Transport 3
3.0 PROCEDURES 4 3.1 Instrumentation 4 3.2 Methodology 4 3.2.1 Noise Level Descriptors 4
4.0 CRITERIA FOR NOISE ASSESSMENT 5
5.0 AMBIENT BACKGROUND NOISE SURVEYS 6 5.1 Methodology 6 5.2 Measurement Locations 6 5.3 Survey Dates 6 5.4 Weather Conditions 7 5.5 Results 7
6.0 PREDICTION OF NOISE EMISSIONS FROM PROPOSED EQUIPMENT AND SITE OPERATIONS 8 6.1 Main Dredge 8 6.2 Booster Pump 8
7.0 NOISE ASSESSMENT 9 7.1 Continuous Noise 9
8.0 NOISE CONTROLS AND PLANNING 10
9.0 CONCLUSION 11
APPENDICES
APPENDIX A: SITE LOCATION AND ASSESSMENT LOCATIONS APPENDIX B: SITE LAYOUT APPENDIX C: CALCULATION OF PLANT SOUND PRESSURE LEVELS Gutteridge Haskins & Davey Pty Limited. Page 1 Rev 02 Dxdging of Griffin Bay. Lake Illawarra.
i 1NTROD]JCTION
This Report presents the results and findings of an assessment of the likely noise impact associated with the proposed sand dredging operations on (iriffins Bay, Lake Illawarra (Appendix A).
The assessment is based on:
an inspection and evaluation of the proposed dredging site and nearby residential areas,
the measurement of ambient background noise levels in nearby residential areas, the measurement of noise emissions from similar plant and equipment, and
the assessment of the likely noise emissions from the proposed dredging operations and their impact on the existing acoustic amenity of the area.
The Report has been prepared for the particular investigation described herein, and no part of it should be used in any other context or for any other purposes. Gutteridge Haskins & Davey Pty Limited. Page 2 RevO2 Dredging of Griffin Bay. Lake Illawarra. I
2.0 GENERAL DESCRIPTION OF SITE AND PROPOSAL
The overall strategy of the proposed dredging programme is detailed in the Environmental Impact Study prepared by Gutterridge Haskings & Davey Pty Limited.
The plan is to electrify the dredge and install a floating screen. The dredge will pump the sands and residues from the lake bed and pump it to the screen. The screen will have the ability to be floated or be based on skids, which will allow it to be moved easily and rapidly to other locations.
The screen will scalp the material and only allow material below 5mm pass onto the rest of the process. The oversize material which will consist of rocks, shells and other materials of an oversize nature, will be deposited on the island site (if recommended) initially. Once the island is formed the screen will be floated to area A and start filling the area.
A booster pump installed with the screen, will pump the sand from the lake direct to the Korrungulla processing area. This will eliminate the requirement for a booster station in Nicolle Avenue.
2.1 Plant and Equipment
2.1.1 Main Dredge
The major noise source associated with the proposal is associated with the electrified dredge. The dredge will be a cutter suction type with a motor capacity of approximately 300Kw.
It is proposed that dredging will commence on the north section of the dredge area and proceed in a southerly direction. The dredging programme will be undertaken in four (4) stages (Appendix B). The envisaged time frame for completion of each stage is dependent upon demand requirements. Under the present requirements (20,000 tonne per month) it is envisaged that stage 1 will be completed in three (3) years, stage 2 four (4) years, stage 3 four (4) years and stage 4 three (3) years.
2.1.2 Screen and Booster Pump
Due to the distances involved in pumping the sand slurry from the dredging areas it will be necessary to install and use a booster pump. The pump will be powered by an electric motor with a capacity of 200Kw.
The booster pump which will be housed in an acoustic enclosure will be located on the floating screen, (Appendix B). Gutteridge Haskins & Davey Pty Limited. Page 3 Rev 02 Dredging of Griffin Bay. Lake Illawarra.
2.1.3 Processing Plant
It is proposed to process the sand through the existing land facility (Appendix B) at Korrongulla, hence noise emission from this established site has not been considered as an acoustic issue in this assessment.
2.1.4 Road Transport
As there will be no increase in truck movements at the existing K000ngulla land base site. It is not envisaged that there will be a change to the existing traffic noise in the area as a result of this development. Guttcndgc Haskins & Davey Pty Limited. Page 4 Rev 02 Ddging of Gnffin Bay. Lake Illawarra.
3.0 PROCEDIJRES
This assessment has been undertaken generally in accordance within the recommendations of the N.S.W, Environmental Protection Authority (EPA), "Environmental Noise Control Manual (1985)" and the Australian Standard AS 1055 - 1984 "Acoustics - Description and Measurement of Environmental Noise".
3.1 Instrumentation.
For the purpose of our measurements the instrumentation selected consisted of, a;
Bruel & Kjaer Statistical Noise Level Analyser Type 4426, fitted with a 12mm Microphone Type 4165, and a
Bruel & Kjaer Precision Sound Level Meter Type 2203, fitted with a 12mm Microphone Type 4165.
The reference levels of the instruments were checked prior to and after measurements with a Bruel & Kjaer Sound Level Calibrator Type 4230.
3.2 Methodology
The methodology adopted for the assessment was based on the percentile exceedance sound pressure levels (LAN) measured at selected reference locations. In accordance with the EPA recommendations the measurements were recorded over fifteen minute sample periods..
3.2.1 Noise Level Descriptions
Fluctuating environmental noise is normally described by reference to the percentile noise levels or noise exceedance levels.
The most common percentile levels commonly referenced, and normally determined by statistical sound level measurement equipment, are the statistical values designated as "LAN" The parameters regarded as being the most significant amongst these are:
"LAI", the A-weighted sound level exceeded for 1% of the sample period.
"LAb ", the A-weighted sound level exceeded for 10% of the sample period, which is commonly termed the "average maximum noise level";
"LA901', the A-weighted sound level exceeded for 90% of the sample period and which is commonly termed the "average minimum noise level' or the background level";
"LAeq", is the energy equivalent sound level or what is described as the average energy level for the sample period. Guttcridgc Haskins & Davcy Pty Limited. Page 5 Rev 02 Dredging of Griffin Bay. Lake Illawarra.
4.0 CRITERIA FOR NOISE ASSESSMENT
The noise criterion normally recommended for the assessment of noise emissions from new development, are those recommended in the Environmental Protection Authority (EPA), Environmental Noise Control Manual. The EPA Manual states that noise emissions from a development should not increase the background (LA90) noise level at any affected residential premises by more than SdB(A). For assessment purposes, the noise is assessed as a contribution and in terms of a LA10 noise level. This criteria and procedure has been adopted for this assessment. Gutteridge Haskins & Davey Pty Limited. Page 6 RevO2 Dredging of Griffin Bay. Lake Illawarra. I
5.0 AMBIIENT BACKGROUND NOISE SURVEYS
5.1 Methodology
For our assessment of the ambient background noise levels, statistical noise level measurements were conducted during the month of August '91. From more recent inspections of the area, in our opinion the ambient noise levels measured in '91 would not have changed significantly, and are representative of the existing noise levels in the area.
5.2 Measurement Locations
Measurements were conducted at five (5) reference locations.
Location 1 - This location represents the rear boundary of residential properties in Northcliffe Drive west of the Illawarra Yatch Club. It was approximately 200 metres north of the northern extremity of the main dredge area and will have a direct line of sight to the dredge. The noise levels in this area are controlled by local traffic and the local natural habitat of boats, birds, wind, etc.
Location 2 - Location 2, was located on the eastern side of the Illawarra Yatch Club on the corner of Jackson Avenue and Northcliffe Drive. The measurement location was approximately 500 metres north of the main dredge area. The residents in this area will be partly shielded from the dredge when it is working on the northern foreshore of the bay. The prevailing noise climate of this area is controlled by road traffic and the local activities of the residents.
Location 3 - This location was located on Lakesview Drive on the south side of the bay. The measurement location was selected to represent residential properties approximately 500 metres south of the southern extremity of the main dredge area and 30 metres from the likely trimming activities along the edge of the dredging area. The residents in this area will have a direct line of sight to both dredging areas. The prevailing noise climate of this area was controlled by distant road traffic, industrial noise from Port Kembla, local road traffic and the natural habitat of people, birds, breezes, etc.
Location 4 - This location was similar to location 3 on the south side of the bay. The location was approximately 250 metres south of the main dredging area.
Location 5 - This location is also on the south side of the bay, and is similar to locations 3 and 4. The location was also approximately 250 metres south of the main dredging area.
5.3 Survey Dates
The ambient noise level surveys were undertaken on the mornings of Tuesday 27th August, Wednesday 28th August 1991. Gutteridge Haskins & Davey Pty Limited. Page 7 Rev 02 Dredging of Griffin Bay. Lake Illawarra.
5.4 Weather Conditions
The weather conditions throughout the surveys were fine with negligible wind. On Tuesday 27th August, the sky was clear there was no wind and the temperature ranged between 12'C - 16'C. While during Wednesday 28th August, the sky was overcast there was a slight breeze and the temperature ranged between 14'C - 16'C.
5.5 Results
The results of our field measurements are presented as percentile exceedance noise levels in Table 1.
Table I: Statistical Ambient Noise Levels Sound Pressure Level dB(A) re: 20 x 106 Pa Location Date Time LAeg LAI L LAl Location 1. Northcliffe Drive
27 Aug 0615 60.5 58.5 56.5 63.0 27 Aug 1305 59.1 59.0 56.8 62.0 28 Aug 0645 51.1 56.0 47.3 53.5 28 Aug 1011 55.8 60.0 54.0 57.5 Location 2. Northeliffe Drive
27 Aug 0638 70.6 78,5 59.0 74.0 27 Aug 1245 67.3 76.0 51.0 71.5 28 Aug 0625 67.2 75.8 53.0 72.0 28 Aug 1030 59.1 77.8 53.5 73.0 Location 3. Lakeview Drive
27 Aug 0703 54.1 66.3 49.0 55.5 27 Aug 1218 45.8 52.0 44.0 48.8 28 Aug 0712 49.7 53.8 46.5 51.5 28 Aug 1115 56.2 63.3 45.0 51.0 Location 4. Lakeview Drive
27 Aug 0720 51.5 53.5 51.0 52.5 27 Aug 1154 48.9 51.0 48.5 50.0 28 Aug 0755 48.5 54.3 45.5 51.5 28 Aug 1134 49.1 57.3 45.0 48.5 Location 5. Lakeview Drive
27Aug 1412 45.1 53.0 41.5 48.3 28Aug 0815 53.5 62.3 44.5 57.5 28 Aug 1155 49.1 57.3 45.0 48.5 Gutteridge Haskins & Davey Pty Limited. Page 8 RevO2 Dredging of Griffin Bay. Lake Illawarra.
6.0 PREDICTION OF NOISE EMISSIONS FROM PROPOSED EqUIPMENT AND SITE OPERATIONS
For the purpose of assessing the noise emissions from the proposed dredging operation, the noise level predictions have been based on the attenuation of sound as a result of hemispherical dispersion. For the purpose of establishing sound power levels for the plant, noise levels from previous measurements on similar equipment have been used.
The main plant evaluated in terms of predicting the operational noise, include the main dredge and the booster pump.
6.1 Main Dredg
The electric drive motor and hydraulic pumps are the main noise sources associated with the dredge. To reduce noise emissions from these sources, they will be housed in a plant room enclosure on the dredge.
The calculated sound power level of the dredge motor and pumps is 98dB(A) re: 1 (112 Watts. The likely noise spectrum for this source is:
dB(A) 63 125 250 500 1K 2K 4K 8K 98 97 104 96 97 93 90 82 78
6.2 Booster Pump
The booster pump will be powered by an electric motor, it also will be housed in an enclosure mounted on the floating screens. The sound power determined for the booster pump installation is 85dB(A) re: 102 Watts. The sound spectrum from this source will be generally broadband. Gutteridge Haskins & Davey Pty Limited. Page 9 Rev 02 I Dredging of Griffin Bay. Lake illawarra.
7.0 NOISE ASSESSMENT
7.1 Continuous Noise
Appendix C, presents the calculations for the noise emissions from the plant referenced to the referenced assessment locations, the results of these calculations are summarised in Table II.
Table H. Calculated Noise Level Contributions.
Sound Pressure Levels dB(A) re: 20 x 10 Pa
Location Stage 1 Stage 2 Stage 2A Stage 3 Stage 4 Measured I Background LA10 LA10 LA10 LAID LAD0 L Northcliffe Drive 24/26 19/24 28/37 26/32 23/28 56 I Northeliffe Drive 23/26 20/25 23/28 19/27 17/23 51 Lakeview Drive 24/27 25/5 1 19/23 19/24 17/25 44 Lakeview Drive 28/32 23/5 1 23/24 I 22/28 2 1/23 41 Lake view Drive 25/28 7/19 2 1/23 22/25 2 1/28 43
I In summary the range of noise levels have been calculated to give the resultant noise levels for each stage of the dredging programme. For the most exposed residences on Lakeview I Drive (Location 3 and 4), the resultant noise level is LA10 5ldB(A). This level represents the worst situation when the dredge is working in close proximity to the foreshore, and at its closest distance to the residences, as the dredge moves away from this exposed location the I noise levels will decrease (Appendix C).
Our assessment has shown that the predicted noise levels generally satisfy the recommended EPA goals and are generally less than the measured background LA90 noise levels. The only exceptions being for Locations 3 and 4 (Lakeview Drive) where the LA10 noise level exceeds the measured background noise by up to lOdB(A). At this time, it is envisaged that the dredge could be working in close proximity to the foreshore for periods of less than a week. It is therefore considered that the exceedances would not normally be considered to be significant in terms of being offensive. If required a time restriction could be placed on the dredging activities, whilst the dredge is in close proximity to the foreshore, i.e., within a distance of approximately sixty (60) metres from any residential boundary.' Gutteridge Haskins & Davey Pty Limited. Page 10 Rev 02 Dredging of Griffin Bay. Lake Illawarra.
&O NOISE CONTROLS AND PLANNThG
Listed below are the noise controls and planning recommendations that have been incorporated into our assessment.
8.1 Main Dredge
The overall sound power specified for the acoustically modified dredge plant is 85dB(A) re: 10 12 Watts.
8.2 Booster Pump
The pump will be enclosed in a pump house with acoustic air intake. The maximum sound power rating for the booster pump installation is 90dB(A) re: 1 012 Watts. 8.3 Operating Hours
Operations of the dredge and the pump shall be restricted to 7am to 5pm from Monday to Friday, with no operations on Saturdays, Sundays or Public Holidays. Gutteridge Haskins & Davey Pty Limited. Page 11 Rev 02 I Dredging of Griffin Bay. Lake Illawarra. I I 9.0 CONCLUSION This report presents the results, findings and recommendations from our assessment of the likely noise impact associated with the proposed dredging operations at Griffins Bay, Lake I Illawarra. This assessment has been based on ambient noise levels measured in August '91. From I recent inspections of the area, it is our opinion the ambient noise levels measured in '91 have not changed significantly, and are representative of the existing noise levels in the area.
I Our assessment has confirmed that with the selection of plant detailed in this report, the predicted noise levels contributions at the reference residential locations will generally satisfy the reconmended EPA goals, and will be generally less than the measured background LA90 I noise levels. The only exception being for Locations 3 and 4 (Lakeview Drive) where the LA10 noise level exceeds the measured background noise by up to lOdB(A), when the dredge is working in close proximity to the foreshore. These likely exceedances would not normally I be considered to be significant due to the activities being restricted to less than a period of two (2) to three (3) weeks. If required, during these operations a time restriction could be placed on the dredging activities, whilst the dredge is in close proximity to the foreshore, i.e., I within a distance of approximately sixty (60) metres from any residential boundary.
As it is proposed to process the dredged sand through the existing land facility, the proposal I will not add to the existing traffic volumes in the area. Hence, noise emission from the existing sand processing area and its associated traffic, are not considered to be an acoustic I issue in this assessment. Our assessment of the activities associated with the proposed dredging operations at Griffins Bay, Lake Illawarra, has shown that the likely resultant noise levels can be controlled, and I would not normally be considered to result in a significant loss of acoustic amenity in the I area. I I I I APPENDIX A: SITE LOCATION AND ASSESSMENT LOCATIONS.
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Reference Loctj0 1: li APPENDIX B: SITE LAYOUT
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CHANNEL STAGE PRIMBEE BAY
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SITE LAYOUT AND STAGING
ommo H4.lJr.. Dsqy Py Ud U 2I• *1 )H 5•4 to tJII It P%f . AWNDLX : CALCULATION OF PLANT SOUND PRESSURE LEVEL Reference Location 1: Northcliffe Drive
Noise Sources A-weighted Distance Distance Excess Noise Resultant Sound Attenuation Attenuation Control Level Power Level dB(A) In dB dB dB dB STAQJ Dredge 98 500/650 62/64 - 10 26/24 Booster Pump 90 500/650 62/64 - 10 18/16 STAQ Dredge 98 650/1100 64/69 - 10 24/19 Booster Pump 90 650/1100 64/69 - 10 16/11 STAGE 28 Dredge 98 150/420 51/60 - 10 37/28 Booster Pump 90 150/420 51/60 - 10 29/20 STAGE 3 Dredge 98 250/500 56/62 - 10 32/26 Booster Pump 90 250/500 56/62 - 10 24/18 STAA
Dredge 98 420/800 60/66 - 10 28/22 Booster Pump 90 420/800 60/66 - 10 20/14 I I I APPENDIX C: CALCULATION OF PLANT SOUND PRESSURE LEVEL I Reference Location 2: Northcliffe Drive
Noise Sources A-weighted I Distance Distance Excess Noise Resultant Sound Attenuation Attenuation Control Level Power Level dB(A) In dB dB dB dB I STAGE 1 Dredge 98 500/700 62/65 - 10 26/23 Booster Pump 90 I 500/700 62/65 - 10 18/15 STAGE 2 Dredge 98 550/1000 63/68 - 10 25/20 Booster Pump 90 550/1000 63/68 - 10 17/12 STAGE 2B Dredge 98 1 400/750 60/65 - 10 28/23 Booster Pump 90 400/750 60/65 - 10 20/15 I STAGE 3 Dredge 98 450/1100 61/69 - 10 27/19 Booster Pump 90 450/1100 61/69 - 10 19/11 1 STAGE 4 Dredge 98 700/1500 65/71 - 10 23/17 Booster Pump 90 I 700/1500 65/71 - 10 15/9 I I I I I U I I I APPENDIX C: CALCULATION OF PLANT SOUND PRESSURE LEVEL Reference Location 3: Lakeview Drive
Noise Sources A-weighted Distance Distance Excess Noise Resultant Sound Attenuation Attenuation Control Level Power Level dB(A) In dB dB dB dB STAGE 1 Dredge 98 475/625 61/64 - 10 27/24 Booster Pump 90 475/626 61/64 - 10 19/16 STAGE 2 Dredge 98 30/550 37/63 - 10 5 1/25 Booster Pump 90 30/550 37/63 - 10 42/15 STAGE 2 B Dredge 98 750/1100 65/69 - 10 23/19 Booster Pump 90 750/1100 65/69 - 10 15/11 STAGE 3 Dredge 98 650/1150 64/69 - 10 24/19 Booster Pump 90 650/1150 64/69 - 10 16/11 STAGE 4 Dredge 98 600/1400 63/71 - 10 25/17 Booster Pump 90 600/1400 63/71 - 10 17/9 1 I 1 APPENDIX C: CALCULATION OF PLANT SOUND PRESS1JRE LEVEL I Reference Location 4: Lakeview Drive
Noise Sources A-weighted Distance Distance Excess Noise Resultant I Sound Attenuation Attenuation Control Level Power Level I dB(A) In dB dB dB dB STAGE 1 Dredge 98 250/400 56/60 - 10 32/28 I Booster Pump 90 250/400 56/60 - 10 24/20 STAGE 2 I Dredge 98 30/700 37/65 - 10 5 1/23 Booster Pump 90 30/700 37/65 - 10 43/15 STAGE 2 B I Dredge 98 650/750 64/65 - 10 24/23 Booster Pump 90 650/750 64/65 - 10 16/15 I STAGE 3 Dredge 98 400/850 60/66 - 10 28/22 Booster Pump 90 400/850 60/66 - 10 20/14 1 STAGE 4 Dredge 98 250/900 56/67 - 10 32/21 I Booster Pump 90 250/900 56/67 - 10 24/13 I I 1 I 1 I I I I APPENDIX C: CALCULATION OF PLANT SOUND PRESSU E LEVEL Reference Location 5: Lakeview Drive
Noise Sources A-weighted Distance Distance Excess Noise Resultant Sound Attenuation Attenuation Control Level Power Level dB(A) In dB dB dB dB STAGE 1 Dredge 98 400/600 60/63 - 10 28/25 Booster Pump 90 400/600 60/63 10 10 10/7 STAGE 2 Dredge 98 200/800 54/66 15 10 19/7 Booster Pump 90 200/800 54/66 15 10 11/- STAGE 2 B Dredge 98 700/900 65/67 - 10 23/21 Booster Pump 90 700/900 65/67 - 10 15/13 STAGE 3 Dredge 98 600/850 63/66 - 10 25/22 Booster Pump 90 600/850 63/66 - 10 17/14 STAGE 4 Dredge 98 400/900 60/67 - 10 28/2 1 Booster Pump 90 400/900 60/67 - 10 20/13 SOCIO-ECONOMIC IMPACT OF THE
PROPOSAL TO EXTRACT SAND FROM
GRIFFINS BAY, LAKE ILLAWARRA
ECONOMIC PLANNING IMPACT CONSULTANTS PTY LTD, 1995
Griffins Bay Sand Extraction EIS
Gutteridge Haskins & Davey Pty Ltd Ml14182 SOCIO-ECONOMIC IMPACTS OF THE PROPOSAL TO EXTRACT SAND FROM GRIFFINS BAY, LAKE ILLAWARRA
EPIC Pty Ltd
March 1995 SAND EXTRACTION IN GRIFFINS BAY - SOCIO-ECONOMICS -Page 1
SOCIO-ECONOMICS
THE EXISTING ENVIRONMENT The estimated resident population of the Illawarra Statistical Division for June 30th 1993 was 359,600. It is forecast that the region will grow to between 401,300 and 452,100 persons by the year 2006 (DOP, 1990). The region's economic base has traditionally been in the heavy manufacturing sector. However, in recent years there has been significant reductions in the manufacturing workforce, and Councils and other regional development authorities have attempted to diversify the local economies, highlighting in particular its potential as a recreation and tourism destination.
DESCRIPTION OF RELEVANT INDUSTRIES The construction industry The construction industry is an important industry in the Illawarra region. In the year ending October, 1994 the value of building approvals in the region was over $539,545,000. About 25 percent of the total value of approvals is for non-residential construction. The construction industry is a large consumer of sand, mainly as a raw material for concrete, although general construction, fill and mortar uses are also important.
The fishing industry. Commercial fishing The Illawarra region is an important centre for the NSW commercial fishing industry. Fishing occurs in both the lakes and estuaries of the region and also in the ocean. Fishing is largely regulated in New South Wales by the NSW Fisheries and Oyster Farms Act and its associated regulations. Commercial fishermen are required to hold a licence and to provide details of their catch. Fishing activities are often subject to closures in various areas and at different times of the year. It may also be subject to restrictions on the types of gear that can be used.
At present, of the 100 licensed fishers in the Lake Illawarra area, approximately 50 use Lake Illawarra at some time during the year. The following description of the commercial fishing activities in Lake Illawarra was summarised from discussions with several local fishers, representatives of the CFAC and the local NSW Fisheries inspector and reported in TEL (1995).
This section is based on the report of The Ecology Lab (TEL, 1995) SAND EXTRACTION IN GRIFFINS BAY - SOCIO-ECONOMICS -Page 2
Prawning:The prawn season is generally from September through to May or June. Approximately 18 crews of 2 people each deploy nets for prawns in Lake Illawarra. There are several methods used to catch prawns. These include pocket set nets, snigging nets and running nets. No prawning takes place within the area which is planned to be dredged, although it is undertaken near the dredged areas. Meshing for fish and crabs: Meshing for fish and crabs occurs lake-wide, including the area proposed for dredging. Hauling for fish: Hauling for fish also occurs lake wide but requires shallow areas to haul the net onto and a lack of any obstructions on the hauling ground. The area proposed for dredging is one of a large number of recognised hauling grounds. Cockles: Cockles are collected by hand within seagrass beds on the eastern shore of the lake up to the entrance into Griff ins Bay, on the western side near Purrah Bay and to the west of Bevans island. There are up to 4 harvesters and the amount harvested is variable depending on price.
Figure 1 shows the weight of a variety of commercial species caught by fishers between the years 1985 to 1992. Whilst for most species there is a significant variation in the amount caught from year to year, there is no indication that there have been substantial changes overall in the amount of fish caught between 1985 and 1992. The exceptions to this are cockles, blue swimmer crabs and mudcrabs which were harvested in increasing quantities in the 1990s.
In comparison with other similar fishing areas, Lake Illawarra is ranked 11th out of 41 major estuaries in NSW in terms of production (kg) of 37 major species of commercial fish during 1990/91 (NSW Fisheries statistics). Lake Illawarra is a regionally significant commercial fishery, particularly for prawns and cockles. No data are available on the relative significance of the commercial catch from Griff ins Bays since only lake-wide data are available.
Recreational fishing Information on recreational fishing was obtained by the Ecology Lab from the NSW Fisheries Inspector, members of the Windang Hotel Fishing club and observations made by the Ecology Lab staff, during field sampling. On the basis of these discussions and observations it is considered that most recreational fishing in Lake Illawarra is in the entrance channel, and that Griffin Bay is only of limited significance to recreational fishing. This may change as a result of foreshore improvements, which may increase access to the water. I SAND EXTRACTION IN GRIFFINS BAY - SOCIO-ECONOMICS -Page 3
Figure 1 The total weight per year (in 1000 kilograms) of 6 selected species caught by commercial fishers in Lake Illawarra from 1985 to 1992.
h)
3i
2
1985 1986 1987 1988 1989 1990 1991 1992
i) eastern king prawn j)
15 ,
10
5
1985 1986 1987 1988 1989 1990 1991 1992
k) blue swimmer crab 1) cockies
60
50 ii 2 40 1 30 Hi I :120
1985 1986 1987 1988 1989 1990 1991 1992 1985 1986 1987 1988 1989 1990 1991 1992
Source: TEL (1995)- Table 14
SAND EXTRACTION IN GRIFFINS BAY - SOCIO-ECONOMICS -Page 4
Figure 1. The total weight per year (in 1000 kilograms) of all commercial species, all finfish and 4 selected species caught by commercial fishers in Lake Illawarra from 1985 to 1992.
a) All species b) All finfish
300 200
250 150 200
150 100
100 50 50
1985 1986 1987 1988 1989 1990 1991 1992 1985 1986 1987 1988 1989 1990 1991 1992
0 0 0 c) river garfish d) yellowfln bream -4
12 40
10 30 8
20
10
1985 1986 1987 1988 1989 1990 1991 1992 1985 1986 1987 1988 1989 1990 1991 1992
0
e) luderick f) flathead
35 25
30 20 25 15 20
15 10 10 5 5
1985 1986 1987 1988 1989 1990 1991 1992 1985 1986 1987 1988 1989 1990 1991 1992
Source: TEL (1995)- Table 14 SAND EXTRACTION IN GRIFFINS BAY - 50Gb-ECONOMICS -Page 5
OTHER IMPORTANT GROUPS AND ORGANISATIONS
The Lake Illawarra Authority The Lake Illawarra Authority commenced operation in 1987 after gazettal of the Lake Illawarra Authority Act. A central aim of the Act was "to constitute the Lake Illawarra Authority (LIA) for the purpose of improving the environment of Lake Illawarra, its foreshores and environment; and for related purposes". The LIA is the determining authority for all development within the lake below the mean high water mark. The LIA in their Draft Strategy Plan for Improvements to Lake Illawarra have identified the dredging of Griff ins and other bays as a priority.
Recreational Boating A previous demand assessment for boating facilities in Griff ins Bay, undertaken by Hassell Planning Consultants (1992) for the Public Works Department, indicated that demand over existing levels of use in Lake Illawarra are expected to increase by 70% over the next 5 years, 92% over the next 10 years and 115% over the next 15 years if appropriate improvements are undertaken. By 2001 they estimate that demand relating to boating activities could reach about 28,000 in the Illawarra. The study made the point that Griff ins Bay is excellently located being easy to access, close to amenities and conspicuous, and that over 2 million people live within a reasonable driving distance of the lake. The study also made the point that the use of the Lake for recreational boating is inhibited by the common perception that the water is unclean and by the smell from decomposing weed. The Illawarra Yacht Club is located adjacent to Griff ins Bay. The Yacht club is a major Illawarra Region recreation facility, with a large licensed club. It offers sailing in a number of classes for both dinghies and yacht sailing. Its current membership is 5100 of which 400 are sailing members, and 130 junior sailors. The club hosted two international events in 1994, namely the Windsurfer World Championships and the World University Windsurfing Championships. The club hopes to attract some major events as "warm-up" events for the Sydney 2000 Olympics. Officials of the club consider that the present state of Griff ins Bay is not conducive to boating activities. In particular they are concerned with the shallowness of the water and the water quality. Their use of Griff ins Bay is restricted to the deeper water at the entrance to the bay.
Local Residents Residents, especially those who have visual views of Griff ins Bay have expressed concerns at the current state of the bay, and are keen to see improvements undertaken. In particular, they have expressed concerns about the water quality in the Lake and the offensive odours which occur when algal blooms decompose. They have expressed support at public meetings for improvement works undertaken in recent years. SAND EXTRACTION IN GRIFFINS BAY - SOCIO-ECONOMICS -Page 6
IMPACTS OF THE PROPOSED DEVELOPMENT
The operation of the dredging and cleaning operations will involve the employment of 5 people directly. The construction will provide 9 jobs for two years. It is estimated that through the multiplier effect, about another 5 jobs will be generated. I When the project is fully operational, royalty payments of about $500,000 per annum will be made to the Lake lllawarra Authority. In addition, the proposal will have an impact on a number of other industries, I especially the construction industry and the fishing industry.
The construction industry The proposed development will be to generate an important source of local sand for the construction industry. Section 4.1 has highlighted the relative shortage of sand. At the end of 1994, construction sand reserves within the Wollongong Statistical District are dwindling. Sand is available from Dunmore Sand and Soil at Dunmore, but this must be mixed with coarser sand for concrete manufacture. Some sand is also available from the Shoalhaven LGA (from Cleary Brothers at Seven Mile Beach), but it is estimated that this will be exhausted by 1998. Sand is available from several sites in the Southern Highlands, but the use of this sand has a number of disadvantages: The sand has to be carted a considerable distance: this additional cartage adds to the production costs of the Illawarra Construction Sector. The cost disadvantage, compared to local sand, is about $7.50 per tonne; The cartage of the sand from the Southern Highlands adds considerably to truck traffic (about 30 movements per day). Much of this cartage takes place on roads which are not suited to heavy vehicle movements, such as the Macquarie Pass.;
The use of sand from Gruff ins Bay would overcome these problems.
The fishing industry Table 1, which is reproduced from Table 15 of the TEL summarises the likely impact of the project on the commercial fishing industry. During dredging commercial fishing would be impacted through the loss of recognised fishing grounds where dredging is occurring. TEL estimate the impact of the proposal on prawning in the following terms: ° Changes in the circulation of water along the northern foreshore are predicted to be minimal (GHD, 1994). On this basis it would be expected that prawning in this area would be viable and similar to pre-dredging operations. The extension TABLE 1: LIKELY IMPACT OF THE PROPOSAL ON THE FISHING INDUSTRY
N- Undertaken Undertaken Likely tobe - Why? - Fishing Method within near impacted by dredged areas dredged area project (,) 0 z0 COMMERCIAL 0 0 Prawning: w a Pocket set nets No No No Only undertaken in entrance channel 0 Yes Possible Undertaken lakewide, but disturbance to area may alter 0 Snigging nets No Cl) prawn behaviour and movement >- Running nets No Yes Possible Undertaken lakewide, but disturbance to area may alter ca prawn behaviour and movement zC,) LL Meshing for Fish and Crabs LI- Splash method Yes Yes Yes Loss of fishing ground, during and after dredging (!3 z Set net Yes Yes Yes Loss of fishing ground, during and after dredging z0 Hauling for Fish Yes Yes Yes Loss of fishing ground, during and after dredging I- 0 Hand-collecting of Cockles No Yes Unlikely Only if smothering by settling of fines over seagrass on cr eastern foreshore I- x w z0 C')
Source: Table 15, TEL (1995)
— — — — — — — — — — — — — — — — — — — — — I SAND EXTRACTION IN GAl FFINS BAY - SOCIO-ECONOMICS -Page 8 of the channel in the southern part of Griffins Bay may provide another area available for prawning. If, however, the movement and behaviour of prawns has I been altered by the dredging works, this may not be the case" (TEL, 1995;p42)
In regard to other forms of fishing, in the short term, TEL indicate "that there will be a decrease in the productivity of the area where dredging takes place near Gruff ins Bay" (TEL, 1995;p39). 1 However, it should be stressed that fishers use a variety of sites in the Lake not just Gruff ins Bay. If they can increase their catches in other parts of the Lake in order to I compensate for any losses in the areas subject to dredging then the net impact on the fishing industry will be negligible. However, it is possible that there might be a loss in the productivity of the whole lake as a result of the loss of the seagrass I habitat. However, since its estimated that only 2.4 to 5 percent of the lakes total seagrass bed will be affected in the short term, it is considered that any loss on overall productivity is likely to be small. There is evidence that seagrass has I recolonised other dredged areas of the lake, so it is considered that in the long term the loss of seagrass will be much smaller than in the short term. It is not considered likely that cockles will be impacted by the proposal. Any loss of production will affect the income of fishers who use the Lake, but in many cases they will be able to reduce the impact of any loss by increasing their I activity in other fishing grounds.
It is considered that there will no adverse impacts on the recreational fishing industry. There will be a minor impact on bait collection since this is currently undertaken near the dredged areas. However, other areas where bait could be collected away from dredging operations are available.
The Lake Illawarra Authority The proposal will have a number of positive impacts for the Lake Illawarra Authority. Firstly, it will allow for the completion of part of the Authority's Lake Improvement program by dredging a shallow section of the Lake. Second, envisaged project sand sales will have the added benefit of providing royalty payments of about $500,000 per annum. These payments will allow for the completion of other improvement works by the authority.
Recreational Boating Improving water quality, deepening shallow water areas at the mouth of the bay and removing silt along the Primbee foreshore will have a positive impact on the recreational potential of the Bay. Organised events conducted by the Illawarra Yacht Club and the Illawarra Sailing and Rowing Club will benefit directly from the proposed development. In particular, the proposal will assist the Lake Illawarra Yacht Club in a number of ways:- SAND EXTRACTION IN GRIFFINS BAY - SOCIO-ECONOMICS -Page 9
Increase in depth of the Griff ins Bay will provide the potential for the club to hold races in water closer to the club and in a sheltered location. This will be of particular assistance for the safety of junior sailors; The increase in the depth will help alleviate congestion - boats currently have to leave and return to the club in a narrow channel; The increase in amenity will assist the club with their efforts to establish themselves as a venue for pre-Olympic regattas.
Local Residents For similar reasons, nearby residential properties will be enjoy improvements in amenity after the completion of the project. However, they will experience other short term negative impacts from the operation of the project, including access to areas being dredged and reclaimed as well as minor visual impacts. It is considered that the residents will regard them only as minor annoyances, given the improvements in amenity that they will enjoy at the completion of the project. I- SAND EXTRACTION IN GRIFFINS BAY - SOCIO-ECONOMICS -Page 10 I REFERENCES I Australian Bureau of Statistics, Building Approvals, NSW - various 1993 and 1994 I issues, Cat No 8731.1. Australian Bureau of Statistics (1994), Regional Population Growth, Australia, Cat No 3218.0. Hassell Planning Consultants (1992) "Boating Facilities - Griff ins Bay Warrawong -, Demand Assessment", Report prepared for the NSW Department of Public Works I The Ecology Lab (1995) "An Assessment of Impacts on Marine Flora, Fauna and Fisheries of a Proposal to Extract Sand from Gruff ins Bay, Lake lilawarra". AN ASSESSMENT OF IMPACTS ON
MARINE FLORA, FAUNA AND FISHERIES
OF A PROPOSAL TO EXTRACT SAND
FROM GRIFFINS BAY, LAKE ILLAWARRA
THE ECOLOGY LAB PTY LIMITED, 1995
Griffins Bay Sand Extraction EIS
Gutteridge Haskins & Davey Pty Ud M114182 I I I I An Assessment of Impacts on Marine Flora, Fauna and Fisheries of a Proposal to Extract Sand from I Griffins Bay, Lake Illawarra I I April, 1995 I I FINAL REPORT I I I
I Report prepared for: Gutteridge Haskins and Davey I 39 Regent Street I Railway Square, Sydney, 2000 Report Prepared by: I The Ecology Lab Pty Limited I 14/28-34 Roseberry Street Balgowlah, NSW, 2093 I I I I TABLE OF CONTENTS Summary...... 1.0 Introduction ...... 1 1.1 Background and Aims ...... I 1.2 Existing Information ...... 2 1.2.1 Physical and Chemical Conditions ...... 2 1.2.1.1 Lake Illawarra ...... 2 1.2.1.2 Griffins Bay ...... 4 1.2.2 Seagrass Beds ...... 6 1.2.3 Saitmarshes and Mangroves ...... 8 1.2.4 Benthic Macrofauna ...... 8 1.2.5 Fish and Mobile Invertebrates ...... 8 1.2.6 Commercial and Recreational Fishing Activities ...... 9 1.3 Matters Arising from Previous EIS ...... 9
2.0 Study Methods ...... 11 2.1 Benthic Macrofauna ...... 11 2.1.1 Survey Procedures ...... 11 2.1.2 Statistical Analyses ...... 12 2.1.2.1 Multivariate Analyses ...... 12 2.1.2.2 Univariate Analyses ...... 13 2.2 Fish and Mobile Invertebrates ...... 13 2.2.1 Survey Procedures ...... 13 2.2.1.1 Beam Trawling ...... 14 2.2.1.2 Beach Seining ...... 14 2.2.2 Statistical Analyses ...... 14 2.2.3 Sizes of Fish ...... 15 2.3 Commercial Fishing ...... 15 2.3.1 Description of Commercial Fishing Activities ...... 15 2.3.2 Commercial Fisheries Statistics for Lake Illawarra ...... 15 2.4 Recreational Fishing ...... 16 2.4.1 Description of Recreational Fishing Activities ...... 16
3.0 Study Results ...... 16 3.1 Benthic Macrofauna ...... 17 3.1.1 Analysis of Assemblages ...... 17 3.1.2 Analyses of Populations ...... 18 3.2 Fish and Mobile Invertebrates ...... 19
I 3.2.1 Beam Trawis . 19 I 3.2.1.1 Analysis of Assemblages ...... 20 3.2.1.2 Analyses of Populations ...... 21 3.2.1.2.1 Spatial Comparisons ...... 21 1 3.2.1.2.2 Sizes of Fish ...... 22 3.2.2 Beach Seines ...... 22 I 3.2.2.1 Analysis of Assemblages ...... 23 3.2.2.2 Analyses of Populations ...... 23 I 3.2.2.2.1 Spatial Comparisons ...... 23 3.2.2.2.2 Sizes of Fish ...... 24 I 3.3 Commercial Fishing ...... 25 3.3.1 Description of Commercial Fishing Activities ...... 25 3.3.2 Commercial Fisheries Statistics for Lake Illawarra ...... 27 1 3.3.2.1 Temporal Comparisons ...... 27 3.3.2.2 Comparisons with other NSW lakes ...... 28 I 3.4 Recreational Fishing ...... 28 3.4.1 Description of Recreational Fishing Activities ...... 28 I 3.5 Conclusions from Field Studies ...... 29 3.5.1 Benthic Macrofauna ...... 29 I 3.5.2 Fish and Mobile Invertebrates ...... 30 3.5.3 Commercial and Recreational Fisheries ...... 31
4.0 Assessment of Impacts ...... 31 4.1 Brief Description of the Pmposal ...... 31 I 4.2 Dredging Areas A to D and the Channel Extension ...... 33 4.2.1 Impacts during Dredging ...... 33 I 4.2.1.1 Seagrass Beds ...... 35 4.2.1.2 Benthic Macrofauna ...... 36 I 4.2.1.3 Fish and Mobile Invertebrates ...... 39 4.2.1.4 Commercial Fisheries ...... 41 4.2.1.5 Recreational Fisheries ...... 42 I 4.2.2 Impacts after Dredging ...... 42 4.2.2.1 Seagrass Beds ...... 43 I 4.2.2.2 Benthic Macrofauna ...... 44 4.2.2.3 Fish and Mobile Invertebrates ...... 45 I 4.2.2.4 Commercial Fisheries ...... 45 4.2.2.5 Recreational Fisheries ...... 45 I 4.3 Creation of Deep Hole ...... 45 4.4 Creation of Channel ...... 47 4.5 Creation of Island . 48 4.6 Interactions with Other Proposals for Lake Illawarra ...... 48 4.7 Recommendations ...... 50 4.7.1 Mitigation of Impacts ...... 50 4.7.2 Rehabilitation of Seagrass ...... 51 4.7.3 Environmental Monitoring Programme ...... 53 4.7.3.1 General Considerations ...... 53 4.7.3.2 Seagrasses ...... 55 4.7.3.2.1 Natural Colonisation of Dredged Areas ...... 56 4.7.3.2.2 Indirect Loss or Damage ...... 58 4.7.3.3 Benthic Macrofauna ...... 58 4.7.3.4 Fish and Mobile Invertebrates ...... 59 4.7.3.5 Commercial Fisheries ...... 59 Acknowledgments ...... 60 References ...... 61 Tables Figures Appendices
LIST OF TABLES Table 1: Concentration of heavy metals and their detection limits in sediment samples from different locations in and around Griffins Bay. Table 2: Results of SIMPER analyses listing the 10 species of benthic macrofauna contributing most to the dissimilarity between groups identified in the MDS and tested using ANOSIM. Table 3: Summary of ANOVAs comparing mean values of benthic macrofauna at three spatial scales; between Griffins Bay and a reference area, locations and sites. Table 4: Results of pairwise comparisons of locations sampled for fish and mobile invertebrates collected by beam trawling using ANOSIM. Table 5: Results of SIMPER analyses listing the species of fish and mobile invertebrates collected in beam trawls contributing most to the dissimilarity between groups identified in the MDS and tested using ANOSIM. Table 6: Summary of ANOVAs comparing mean values of fish and mobile invertebrates collected in beam trawls at 5 locations and 2 sites per location in Lake Illawarra. Table 7: Summary of sizes of fish of commercial importance caught by beam trawling. Table 8: Results of pairwise comparisons of locations sampled for fish and mobile invertebrates collected by beach seining using ANOSIM. Table 9: Results of SIMPER analyses listing the species of fish and mobile invertebrates collected in beach seines contributing most to the dissimilarity between groups identified in the MDS and I tested using ANOSIM. I Table Summary of ANOVAs comparing mean values of fish and mobile invertebrates collected in beach seine nets at 5 locations and 2 sites per location in Lake Illawarra. Table Summary of sizes of fish of commercial importance caught by beach seining. I Table 12: Summary of ANOVAs comparing the annual catch by commercial fishers between 1985 and 1992. I Table 13: Comparison of the production (catch by fishers) in Lake illawarra with other lakes in NSW in 1991. I Table 14: Summary of details of the dredging proposal most relevant to aquatic ecological impacts. Table 15: Summary of impacts on different methods of fishing.
I LIST OF FIGURES Figure Si: Map of Griffins Bay indicating stages and areas to be dredged for proposal to extract sand. Figure 1: Comparison of distribution of seagrasses in Lake Illawarra as mapped by West et al. (1985) and King et al. (1991). I Figure 2: Comparison of distribution of seagrasses in Griffins Bay as mapped by West et al., 1985 and WBM Oceanics (1993). I Figure 3: Location of sampling sites for benthic macrofauna collected by cores. Figure 4: Location of sampling sites for fish and mobile invertebrates collected by beam trawl. Figure 5: Location of sampling sites for fish and mobile invertebrates collected by beach seines. I Figure 6: Two dimensional MIDS plot of benthic macrofauna assemblages at Griffins Bay, the reference area along the eastern shore and muddy areas. I Figure 7: Mean (+1 SE) abundance of selected species, total number of taxa and number of individuals of benthic macrofauna at all sampling sites. I Figure 8: Two dimensional MDS plot of fish and mobile invertebrate assemblages collected by beam trawls at two locations in Griffins Bay and three other locations in Lake Illawarra. I Figure 9: Mean (+1 SE) abundance of selected species, total number of taxa, total number of individuals and total number of commercial species of fish and mobile invertebrates collected by beam trawls at all sampling sites. Figure 10: Two dimensional MDS plot of fish and mobile invertebrate assemblages collected by beach seines at two locations in Griffins Bay and three other locations in Lake Illawarra. I Figure 11: Mean (+1 SE) abundance of selected species, total number of taxa, total number of individuals and total number of commercial species of fish and mobile invertebrates collected by I beach seines at all sampling sites. Figure 12: Length frequency distributions of sand mullet collected by beach seining at 5 locations. I Figure 13: Map of locations used by commercial fishers for setting prawn running nets. Figure 14: Total weight of commercial species harvested by fishers in Lake Illawarra from 1985 to 1992. Figure 15: Map of Griffins Bay indicating stages and areas to be dredged for proposal to extract sand. I
LIST OF APPENDICES I Appendix A: Mean and standard error of each species of benthic macrofauna per site collected by cores. Appendix B: Mean and standard error of each species of fish and mobile invertebrate per site collected by beam trawis. Appendix C: Mean and standard error of each species of fish and mobile invertebrate per site collected by beach seines. Appendix D: Data summarised from NSW Fisheries database on the species caught by commercial I fishers in Lake Illawarra from 1985 to 1992.
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I The Ecology Lb Pty. Ltd Griffins Bay sand extraction - Marine Ecology - Final Report, April 1995
SUMMARY
I Introduction The Ecology Lab Pty Ltd was commissioned by Gutteridge Haskins and Davey (GHD) to describe I the existing estuarine environment of Lake Illawarra and to assess potential impacts of a proposal by South Coast Equipment Pty Ltd (SCE) to extract sand near the entrance to Griffins Bay. The L proposal to dredge the entrance to Griffins Bay has been the subject of a previous environmental impact statement (EIS). Reviews of that EIS indicated that some issues associated with the proposed development required further work and those issues related to aquatic ecology have been incorporated into the present study, which in turn have been incorporated in the new EIS. I prepared by GHD.
II Description of the Existing Environment
Lake Illawarra is a barrier estuary and is separated from the ocean by a long, shallow channel. The lake covers an area of about 35 km2 and has a catchment of about 270 km2. Tidal range within the lake is 3-5 cm and is 10-25 cm within the entrance channel. Residence time of water in the lake has been estimated as 26 to 39 weeks. Several studies have been done on the levels of contaminants in the sediments of Lake Illawarra. Sources of heavy metals in sediments are believed to be the Port I Kembla industrial complex, the Dapto smelting works (closed in 1906) and Tallawarra Power Station (decommissioned in 1989). Urban run-off also contributes to the load of contaminants. The I lake is surrounded almost entirely by urban and industrial development.
I Griffins Bay is in the north-east of Lake Illawarra. GHD studied water circulation, water chemistry and sediment chemistry in Griffins Bay as part of the EIS. A hydrological model used by GHD indicated that currents (which were in a southerly direction) in Griffins Bay were wind-induced and that there was little or no tidal influence. Water temperature in Griffins Bay was found to vary little with depth or location within Griffins Bay, but concentrations of dissolved oxygen were low near the bay floor. Sediment samples collected by GHD in Griffins Bay were analysed for six heavy metals. Of these, mercury was not detected, cadmium, lead and copper were detected in some samples and chromium and zinc were detected in all samples. The concentration of chromium was greater in sediments collected from Primbee Bay than elsewhere in Griffins Bay The Ecology Lab Pty. LtiL Griffins Bay sand extraction - Marine Ecology - Final Report, April1995 and the concentration of zinc was greater in Primbee Bay and north of Puny Burry Point than all other locations sampled. The concentrations of chromium and zinc in the sediments were probably large enough to have the potential to affect organisms living in the substratum.
Preliminary tests done by GI-ID (1995) on the sediments in Griffins Bay indicated that there was the potential for acid sulphate soils to occur in Griffins Bay. GI-ID (1995) recommended that a more comprehensive survey be undertaken prior to dredging. An assessment of the effects of acid sulphate soils on aquatic biota cannot be made using the data collected to date. Therefore, the potential for acid sulphate soils needs to be quantified and investigated further. Acid sulphate soils (ASS) are found in many places along the Australian coast. They contain iron pyrite, a naturally occurring mineral in estuarine sediments. Iron pyrite is stable under waterlogged (reducing) conditions where it is no threat to the environment. When exposed to air, however, it reacts rapidly with oxygen to produce sulphuric acid and iron. Exposure to air can happen naturally (e.g. during drought) or through a human activity such as dredging and some agricultural practices. The oxidation of pyrite to sulphuric acid and iron decreases the pH of the sediment making it acidic. The lowered pH levels may affect groundwater as well as surface water bodies. Elements such as aluminium and iron can dissolve and reach concentrations high enough to be detrimental to aquatic biota. The influx of acidic water high in aluminium and iron clogs the gills of fish, crustaceans and oysters causing 'fish kills'.
Apart from phytoplankton and algae, three types of aquatic vegetation are significant in NSW, saltmarshes, mangroves and seagrasses. This vegetation may be ecologically important as it contributes to the productivity of the estuary, and provides food and shelter for many aquatic animals, some of which are economically valuable. Significant saltmarshes are limited to one small area in Koona Bay and there are no mangrove forests reported in Lake Illawarra. Seagrasses, however, are very common in the lake, where at least four species occur, Zostera capricorni, Ruppia megacarpa, Halophila oval is and Halophila decipiens. Large beds of seagrass occur in the shallows off the shoreline and are mainly formed by Zostera. In Lake Illawarra, seagrasses appear to be limited in depth between the intertidal zone and -2 m Australian Height Datum (AHD). Since 1976, estimates of the total area of seagrasses in Lake Illawarra have ranged from 5. 12-10.9 km2. In a recent study of seagrasses in the lake, it was found that, following dredging, Zostera successfully recolonised in one area - Koonawarra Bay - but that in another area - Griffins Bay - recolonisation was minor. It was concluded that the extent and rate of recolonisation were probably related to the final depth of the substratum and possibly the type of dredging.
Prior to the present study, there was little information on the animals inhabiting the sediments of
11 The Ecology Lab Pty. Ltd. Griffins Bay sand extraction - Marine Ecology - Final Report, April 1995
Griffins Bay. One group of these animals is known as benthic macrofauna and consists mostly of invertebrates which are retained on a 1 mm sieve. Examples include marine worms (po!ychaetes), snails (gastropods) and crustaceans (e.g. amphipods). They are important because they are eaten by a variety of predators (e.g. birds and fish), they play an important role in pathways of detrital and nutrient recycling and they are good indicators of environmental disturbance (e.g. pollution). Like the benthic macrofauna, there is little information on the fish and mobile invertebrates (e.g. prawns) occurring in Lake Illawarra. Some studies have been commissioned along the western shores of the take, but there is vety little information on the fishes of Griffins Bay.
During field studies for the EIS, The Ecology Lab made several qualitative observations of the biota of Lake Illawarra. First, some isolated saltmarsh (Sarcocornia quinqueflora) was observed at Purry Burry Point and rushes grew along parts of the shoreline of the Point. Second, just offshore from Purry Burry Point along the entire eastern shore of lake there were masses of filamentous algae. The occurrence of this algae is probably seasonal. Numerous observations were made of water birds during the field studies, including pelicans, silver gulls, black cormorants, pied cormorants and black swans. The black swans formed large flocks off the eastern shore of the lake, well to the south of Griffins Bay. The other birds showed no obvious patterns in their distribution.
Quantitative field studies done by The Ecology Lab for the supplementary EIS focused on benthic macrofauna, fish and mobile invertebrates and commercial and recreational fisheries. Benthic macrofauna were collected at two sites within each of eight locations in Lake Illawarra in November 1993. Three locations were on the sand body proposed for dredging at the entrance to Griffins Bay, one location was on muddy substratum within Griffins Bay, three locations were on sand along the eastern shore of Lake Illawarra and were sampled as reference locations to compare with the locations on sand at Griffins Bay. A final location was on muddy substratum at the southern end of Lake Illawarra. At each site, five samples of sediment were collected by a diver using a corer and sieved through a 1 mm mesh. Fish and mobile invertebrates were sampled in seagrass beds using a beam trawl and a beach seine in November 1993. Collections were made at two sites within five locations, two at Griffins Bay and three at reference locations around Lake Illawarra. At each site, four replicate samples were obtained.
The use of reference locations was crucial to the study because they provided a geographical context against which the findings for Griffins Bay could be compared.
The study of benthic macrofauna yielded a total of 8 235 individuals, representing 47 taxa. Most of the species are common in estuaries in New South Wales. Statistical analysis of the assemblage of
111 The Ecology Lab Pty. Ltd. Griffins Bay sand extraction - Marine Ecology - Final Report, April 1995
macrofauna indicated two major trends: 1) there were differences in the assemblages of benthic macrofauna between sandy and muddy substrata, while the assemblages of the muddy substratum were very similar, despite being collected from opposite ends of Lake Illawarra. 2) The samples taken from the proposed dredge area were relatively distinct from those taken from the reference locations along the eastern shore of the lake. Statistical analysis of biodiversity, total abundance and populations of macrofauna yielded a variety of trends. The mean number of taxa did not vary significantly at any of the spatial scales examined, indicating that the biodiversity of benthic macrofauna in Griffins Bay was, at the time of sampling, similar to other parts of Lake Illawarra. Some of the samples taken from Griffins Bay were taken near to, or within, areas that had been previously dredged. Variability in total abundance was large among locations in the proposed dredge area in Griffins Bay compared to the eastern shore, despite the fact that locations were much further apart on the eastern shore. In terms of individual species that were numerically abundant, there was no statistical distinction between Griffins Bay and the Eastern shore and variability often occurred at small spatial scales.
The beam trawl samples yielded at total of 42 967 fish and mobile invertebrates, representing 30, 7 and 1 species of fish, crustaceans and cephalopods, respectively. The most abundant species of fish were two gobies and a pipefish, representing 65% of the total catch. Species of economic value represented only 0.5% of the catch, the most abundant of which were the six-spined leatherjacket, blue groper and luderick (79% of the catch of economically valuable fishes). King prawns and blue swimmer crabs were also collected. Statistical analysis of the assemblage sampled with the beam trawl indicated that samples from the two locations within Griffins Bay (one of which appears to have been in a previously dredged area) were similar to most of the other locations sampled within Lake Illawarra. The exception was the southern side of Windang Channel, which was distinctive compared to all other locations, due primarily to very large numbers of the non- commercial shrimp, Macrobrachium intermedium. The diversity of biota sampled by beam trawl in locations in Griffins Bay was within the range found at the other locations within Lake Illawarra. None of the species collected was considered to be rare or endangered. On average, there were 5 - 10 individuals of commercially important fish caught per trawl at all locations except the eastern shore, where the average was slightly less. No significant difference between sampling locations or sites was found for the abundance of king prawns or blue groper, leatherjackets did vary among locations, but mean abundance in Griffins Bay was within the range observed elsewhere. The total abundance of individuals sampled by beam trawl was significantly larger at one location in the Windang Channel, due to the very large abundance of Macrobrachium. Other species examined varied in abundance at the scales of locations or sites and in general Griffins Bay was within the range observed at other locations. Measurements of the sizes of fish collected by beam trawl
lv The Ecology Lab Pty. Ltd. Griffins Bay sand extraction - Marine Ecology - Final Report, April 1995
revealed that all species of economic value were juveniles, many of which had probably settled from the plankton shortly before capture.
Sampling with the beach seine yielded a total of 38 275 fish and mobile invertebrates, representing 43, 6 and I species of fish, crustaceans and cephalopods, respectively. The most abundant species of fish were the Port Jackson perchlet, transparent goby and smalimouth hardyhead, representing 62% of the total catch. Species of economic value represented 10.3% of the catch, the most abundant of which were sand mullet, luderick and tarwhine (55% of the catch of economically valuable fishes). King prawns represented 99.5% of the catch of commercially important crustaceans, with a few blue swimmer crabs making-up the remainder. Statistical analysis of assemblages suggested that each location had a distinct assemblage of fish and mobile invertebrates. The location in Windang Channel was distinguished by the presence of large numbers of Macrobruchium, as was found with the beam trawis. The location at Furry Burry Point (Griffins Bay) was distinctive, due to the presence of smallmouth hardyheads and the absence of tarwhine, sand mullet and luderick. These species are relatively mobile and were probably under- sampled by the beam trawl, hence the different findings for the seine netting (it may also be due to the positions of sampling, as the beam trawls were done further offshore). The biodiversity of fish and mobile invertebrates at one location in Griffins Bay (on the northern shore of the bay, east of the yacht club) was within the range recorded at the reference locations, but biodiversity off Purry Burry Point tended to be less than elsewhere. The total abundance of species of economic value was significantly greater on the northern shore of Griffins Bay compared to all other locations. The total abundance of all species caught in the beach seines was highly variable among locations and within sites, but variability in Griffins Bay was similar to the reference locations. All the fish caught by beach seine were juveniles (many recently settled) except for a few adults of three species of mullet.
The following conclusions can be drawn from the field studies described above. First, assemblages of benthic macrofauna in the proposed dredge area were distinctive compared with similar sandy habitats along the eastern shore of Lake Illawarra. The assemblages of muddy habitats within Griffins Bay were very distinctive compared to sandy habitats, but were very similar to muddy habitats sampled at the southern end of lake Illawarra. The biodiversity of benthic macrofauna and abundance of the species examined varied at several spatial scales. None of the data suggest that the proposed dredge area is particularly rich in benthic macrofauna, nor that the sediments within Griffins Bay are poor in macrofauna. Note, however, that this conclusion is based on one survey and no measure of temporal variability was made. GElD found that oxygen levels in bottom waters of Griffins Bay can be low, hence there may be times when the benthic macrofauna is
V The Ecology l.ah Pt y. Ltd. Griffins Bay sand extraction - Marine Ecology - Final Report, April 2995
affected by poor water quality within the bay.
Second, assemblages of fish and mobile invertebrates showed similarities and differences when sampled by beam trawl and beach seine. The most notable similarity was the distinctive nature of one location in Windang Channel, which was numerically dominated by Macrobrachium. The most notable difference was the distinctive nature of the assemblage at Puny Buny Point sampled by beach seine - here attributed to the collection of very mobile fish in the seine net that could probably avoid the beam trawl. Another notable finding from the beach seining was the presence of relatively large numbers of fish of commercial value in the seagrass bed on the northern shore of Griffins Bay. These fish were all juveniles, suggesting that particular bed may be a relatively important nursery area. Studies by other workers in NSW have found that some beds consistently rate highly in terms of their value as nursery habitat and this may be due to a number of factors, such as aspects of the beds or the nature of currents transporting larval fish to the bed. This site in Griffins Bay was in the vicinity of previous dredging works which were completed in September 1991. This provides anecdotal evidence that seagrass beds which have been exposed to dredging close by function as nursery habitat several years after dredging was completed. The findings for Griffins Bay must be considered cautiously as only one survey was done, but they do have important consequences for the present proposal. The seagrass beds on the northern shore of the bay are not within the proposed dredge area, but the dredging operation can and would need to be managed so that a) current patterns are not significantly altered by the dredging and b) indirect effects, such as plumes, are mininiised. The hydrological model (GI-ID, 1995) predicts negligible changes in current speed (maximum change of 0.05 rn/sec in the northern channel) and no change in the direction of currents from present conditions.
Commercial and Recreational Fishing
Approximately 50 licensed fishers use Lake Illawarra at some time of the year. Four major types of fishery were identified in the lake. First, prawns (mostly king prawns) are caught using pocket set nets in Windang Channel and snigging nets and running nets in other parts of the lake. Snigging may be done virtually anywhere in the lake outside the channel (where it is prohibited), running nets are laid shore-normal and rely on currents running longshore to transport prawns to the nets. Running nets are prohibited in Windang Channel, but are set in several parts of the lake, including the shore to the north of Griffins Bay and, at times, in Griffins Bay itself. Second, fish and crabs are taken by mesh-netting throughout the lake, including the area proposed for dredging. Third, beach hauling occurs lake-wide for fish and crabs. This method requires the presence of a gently-
VI The Ecology Lab Pty. Ltd. Griffins Bay sand extraction - Marine Ecology - Final Report, April 1995
I sloping shore without obstructions. One area hauled is off the western part of the proposed dredge area. Fourth, cockles are collected by hand within seagrass beds along the eastern shore up to the I entrance of Griffins Bay.
Data compiled by NSW Fisheries were examined to determine variation in the commercial catch over about the last 8 years. For most of the species examined, and for the total commercial catch, there was significant variation from year to year, but, with two exceptions, there were no long I term trends apparent. The exceptions were cockles and crabs (blue swimmer and mud crabs), I which have been caught in increasing numbers during the early 1990's. Ina regional context, Lake Illawarra ranked 11th of 41 major estuaries in NSW in terms of production (kg) of 37 major species of commercial fish during 1990/91. Comparing the lake to six other, similar lakes in NSW, Lake Illawarra produced the largest catch of cockles and king prawns and substantial catches of garfish, bream, luderick, sea mullet and school prawns. On this basis, it is concluded that Lake Illawarra has a regionally significant commercial fishery. Note that the data do not allow a comparison of different areas within Lake Illawarra.
' It is estimated that some 90% of recreational fishing for finfish occurs within Windang Channel and therefore well to the south of Griffins Bay. It appears that very little recreational fishing is done in Griffins Bay. Recreational prawning is done in Windang Channel and along the eastern I shore of Lake Illawarra, with little done in Griffins Bay. Bait is also collected in the lake. Blackfish- weed is collected along the shallows as far north as the entrance to Griffins Bay and worms and I flippers are collected in Windang Channel and along the eastern shore.
Assessment of Impacts
The main parts of the proposal that need to be considered in assessing the impacts on the aquatic environment are: 1) direct removal of habitat such as seagrass and unvegetated substratum by dredging, 2) indirect effects of dredging on surrounding habitats; 3) direct creation of new habitats, including an island off Purry Burry Point, extension of a channel out of Griffins Bay and if the embankments were removed, creation of a hole to 14 m depth; and 4) indirect effects of the newly created habitats.
vii The Ecology Lab Pty. Ltd. Griffins Bay sand extraction - Marine Ecology - Final Report, April 7995
Impacts Associated with Dredging
Seagrasses. The proposed dredging, including the channel extension, would cause the direct removal of seagrasses from the entrance to Griffins Bay. The estimated loss is between 25 and 26.4 ha, or in the range of 2.4 - 5% of the total area of seagrass in Lake Illawarra depending on which estimate of total area of seagrass is used. The loss of seagrass would be progressive through the life of the project and the rate of removal of seagrass would depend on the progress of the dredging operations. Thus, the 2.4 - 5% loss represents the maximum removed over a period of 10- 13 years. Once one area of the seabed had been dredged, it may be possible for seagrasses to recolonise that area, which would reduce the overall loss. The success of recolonisation would depend, however, on the conditions in the dredged areas, particularly depth, which would need to be less than 2 m (ideally less than 1.5 m) to allow seagrasses to grow. Two of the designated dredge areas (part of Area A and all of Area B - see Figure Si) would be at a suitable depth, although other areas would either be too deep (unless backfilled) or form part of an island proposed as part of the project. If recolonisation by seagrasses of Areas A (excluding the island) and B occurred, the overall loss of seagrasses at the end of the project would be 80.2% of the estimated total removed by the proposal. If Areas C and D were also backfilled to a suitable depth for seagrass to grow, then the overall loss of seagrasses, following recolonisation, would be negligible. The water quality of Griffins Bay would probably need to improve from its present condition, however, to allow seagrasses to grow at a depth of 1.5 m or more.
Potentially, seagrasses could also be lost due to indirect effects, such as smothering of beds by sediment plumes, changes in water quality and physical damage due to anchoring and other dredging activities. The extent of these effects can and would be ininimised by anticipating them and adopting mitigative measures and by compliance monitoring. Mitigative measures include the use of silt curtains and design of work practices to minimise or avoid damage to seagrasses.
Benthic macrofauna. Dredging would cause the removal of benthic macrofauna associated with seagrass beds and unvegetated sandy substrata. Following the completion of dredging, macrofauna would recolonise the disturbed areas, particularly in Areas A and B. It is impossible to predict accurately the rate of recolonisation or the structure of the assemblage occurring after dredging. It is expected, however, that initial colonisation would be relatively rapid (i.e. over periods of months), but that the structure of the assemblage would be highly variable through time and space, depending on the staging of other parts of the dredging, the possibility of using some areas
for fill from other dredging works (which is not part of the present proposal), the availability of colonising organisms in the area, water quality and the nature of the changes to the substratum The Ecology Lab Pty. Ltd. Griffins Bay sand extraction - Marine Ecology - Final Report, April 1995
through time (e.g. due to possible colonisation by seagrasses). It seems likely that Area B, which would be similar in depth and sediment type to the pre-dredging condition, potentially could be recolonised by an assemblage of benthic macrofauna similar to that found prior to dredging. For the other dredged areas it is difficult to predict what animals could recolonise because the substratum would be at different depths and have different sediment characteristics to the pre- dredged condition.
As with the seagrasses, benthic macrofauna may be affected by indirect effects of the proposal, particularly the settlement of sediment plumes. Associated with this is the potential effect of smothering and the release of toxic contaminants (e.g. chromium and zinc). A preliminary test indicated that heavy metals would remain bound to the fine sediments rather than be released into the water column after being washed and returned to the lake as backfill for the island and Area A (Cl-ID, 1995). The use of a silt curtain around all dredging operations should minimise the potential for indirect effects on benthic macrofauna.
Fish and mobile invertebrates. During the dredging, many fish and mobile invertebrates would be able to avoid being sucked into the head of the dredger, but there are two exceptions to this. First, small fish and mobile invertebrates associated with seagrasses that would be removed when the dredging first began would also be lost. This loss would include fish and prawns of economic value utilising the seagrasses as nursery habitat. It may be possible to minimise the loss of economically valuable species utilising the seagrass beds by removing seagrass at times of the year when significant settlement is not expected. Second, some relatively sedentary fish (e.g. flathead, leatherjackets) may be trapped occasionally by the dredger, but such losses would be expected to be relatively small.
Once the seagrasses had been removed from the proposed dredge areas, the potential of these areas to act as nursery habitat in subsequent years would be reduced, pending the recolonisation of seagrasses. There are three possible consequences for fish and mobile invertebrates that could have utilised these beds: 1) that they will simply redistribute to other beds in the lake and their development will be unaffected; 2) that they will redistribute to other beds in the lake and their development will be affected due to increased competition from animals using these beds; 3) that they will not be transported to any other beds, or transport will take much longer, thus extending the planktonic period and an increase in the risk of lack of food or predation in the planktonic phase. The scientific understanding of such mechanisms is not well understood, but there are studies which suggest that particular seagrass beds in NSW can support relatively large numbers of fish and mobile invertebrates. It is therefore predicted that there is likely to be a loss in the The Ecology Lab Ply. Ltd. Griffins Bay sand extraction - Marine Ecology - Final Report, April 1995
productivity of fish and mobile invertebrates associated with the loss of seagrasses from the dredging operation, but that this loss would be less than that directly proportional to the area of seagrass lost.
As with the benthic macrofauna, indirect effects of the proposal have the potential to affect fish and mobile invertebrates beyond the actual dredging areas. In particular, any effects on the seagrass bed on the northern shore of Griffins Bay could be significant due to the large numbers of species of commercial value found there during the field studies. According to GI-ID, the proposal would increase water movement into Griffins Bay, so presumably larval transport to the bed would be maintained. Other possible effects, such as movement of turbid water, could be controlled using silt curtains during dredging.
Fishing. Commercial fishing could be affected by: 1) loss of fishing grounds; 2) interference with currents affecting the movement of harvested species, particularly prawns; and 3) reduction in productivity. There would be a loss of hauling grounds and splash meshing grounds at the entrance to Griffins Bay. According to GHD, currents would not be affected by more than 0.05 m/s (increase or decrease in flow velocity depends on the prevailing winds) in areas where prawn running nets are deployed, near the northern shore of Griffins Bay close to dredging areas. The extension of the channel in Griffins Bay on the southern shore may provide a new area where running nets could be deployed. As discussed above, there is likely to be some loss in the productivity of the lake due to the loss of habitat. In the long term, recolonisation of the dredged areas by species of commercial value may restore productivity. Improvements to the water quality of Griffins Bay, as predicted by Gl-[D, may also lead to an increase in fisheries productivity within Griffins Bay, after completion of dredging. Recreational fishing is unlikely to be affected negatively by the dredging proposal, although construction of the channel may improve access to Griffins Bay for anglers, which would be a positive benefit.
Creation of New Habitats
Deep Hole. GI-ID have predicted that water quality and circulation in the dredged hole (Areas C and D, Fig. Si) would be different to other parts of Lake Illawarra. Water temperature could be less and oxygen levels depleted. Under these conditions, the hole would provide poor habitat and, if poor quality water were transported out of the hole, may have detrimental effects on biota elsewhere in Lake Illawarra. However, under the proposal, this problem would be mitigated by the isolation of the hole from the lake by an embankment and the use of an aeration system to mix
x The Ecology Lab Pty. Ltd. Griffins Bay sand extraction - Marine Ecology - Final Report, April 1995
the waters of the hole to avoid stratification. Compliance monitoring would be essential to ensure
that adequate conditions of water quality were maintained in the hole at all times in case of escape
of this water to the rest of the lake. The ELS includes plans to monitor the dissolved oxygen and
temperature at several depths within the deep hole so that adjustments can be made, if necessary,
to the aeration system. The bunding of the hole would also prevent this area from being a sink for
debris such as seagrass, algae and gross pollutants. The hole would be bunded for the duration of
the dredging project. According to the EIS, after the dredging contract is completed, the Lake
Illawarra Authority would be responsible for the maintenance of the embankments around the
deep hole. I
If the embankments around the deep hole were removed before backfllling, the hole would
provide a new habitat in Lake Illawarra and it is impossible to predict accurately the biota that
would occupy them. It is clear, however, that no seagrasses would colonise the hole beyond about
2 m depth. Some species of benthic macrofauna recorded in Lake Illawarra have been recorded to
depths of 20 m in other estuaries. It is therefore expected that, provided dissolved oxygen levels
are maintained, there would be colonisation of the substratum of the hole. Studies of the use by
fish and prawns of deep holes in Botany Bay indicated the presence of a wide variety of species,
and it was concluded that the deeper habitats there provided feeding areas for some commercially
valuable fish in winter. Extrapolation of these results to Lake Illawarra is questionable, however,
for two reasons. First, the holes were relatively close to the entrance to Botany Bay and colonisers
included species of fish from adjacent coastal waters. The hole in Lake Illawarra would be
relatively remote from the sea. Second, the hole would be isolated from Lake Illawarra by bunds
and it is not clear if any fish would be able to gain access to the hole (e.g. as larvae or small
juveniles transported in slurry water). Therefore, it is predicted that, provided adequate water
quality were maintained, the deep hole may be utilised by some fish, but it is not possible to
predict the structure of assemblages or occurrence and abundance of particular species.
Creation of Channel. Increased water circulation as a result of the channel would improve water
quality within Griffins Bay and should therefore reduce the risk of deoxygenated bottom waters in
Griffins Bay. There are two potentially adverse effects, however, that need to be considered. First,
there may be transport of silt out of Griffins Bay into the lake in the first six months or so
following dredging. Thus, there may be short-term smothering of benthic macrofauna in areas
where the silt settles. There may also be transport of contaminated sediments (e.g. with chromium
and zinc) out of the bay which may have direct toxic effects or bioaccumulate. Removing the silt
prior to dredging the channel would substantially reduce the risk of adverse effects on the benthic
macrofauna at the western end of the channel extension. Compliance monitoring is recommended
xi The Ecology Lab Ply. Ltd. Griffins Bay sand extraction - Marine Ecology Final Report, April 1995
to evaluate the success of this. Second, maintenance dredging may be required to maintain the channel at a navigable depth. Where such dredging is required, use of a silt curtain should be considered and dredging should be programmed to avoid damage to seagrass beds within the bay
Creation of island. The location of the island in the more south westerly position would allow increased water flow into Griffins Bay. The island would provide a habitat for bird life. To prevent erosion of the island from wind-waves, reinforcement may be required around the island's perimeter. This reinforcement would provide a habitat for aquatic biota.
Cumulative Effects
The proposal to dredge Griffins Bay was considered in relation to a proposal for dredging the channel at the entrance to Lake Illawarra. On the basis of a review of this EIS, it is concluded that the cumulative effects (apart from effects already discussed with regard to the Griffins Bay proposal) would be negligible.
It is possible that the deep hole in Areas C and D may be used for placement of spoil obtained from other works in Lake Illawarra. Subject to assessing the effects of the dredging and disposal operations for these other works, the filling of the dredge hole could, ultimately, return the area to a state similar to its pre-dredged condition, which may allow for the recolonisation of seagrasses, restoration of estuarine productivity and return of fishing grounds. It would also obviate the need to find disposal sites for spoil from the other works. In this case, cumulative effects would be beneficial, provided that the subsequent dredging and disposal operations were environmentally sound.
Mitigation of Impacts
Mitigation of impacts has been discussed in relation to specific aspects of the proposal. The following measures are recommended: 1) minimising overall loss of seagrass; 2) preventing the escape and spread of fine sediments; 3) minimising the frequency and extent that bottom sediments are disturbed; 4) bunding of the deep hole; 5) aerating the deep hole to prevent stratification; and 6) allowing fishers access to areas not being dredged at any one time.
xii The Ecology Lab Pty. Ltd. Griffins Bay sand extraction - Marine Ecology - Final Report, April 1995
It is also recommended that a programme be initiated to restore seagrasses as quickly as possible by: 1) contouring as much of the dredged areas as possible to the appropriate depth (say 0.5-1.5 m below AHD) to promote the growth of seagrasses; and 2) if necessary, considering transplanting of seagrasses - particularly Zostera - to enhance restoration.
I Monitoring
The Director of the Department of Planning requires that a monitoring plan be formulated for the proposal. The aims of the plan should be to: 1) distinguish impacts associated with the dredging proposal from natural variation or other human induced impacts; 2) test predictions made in the EIS; and 3) assist in formulating strategies to mitigate any unforeseen impacts after dredging has commenced. It is recommended that seagrasses, benthic macrofauna, fish and mobile invertebrates be monitored for the current proposal, in addition to any monitoring of water quality, water circulation and sediments that may be recommended by GELD. Also, consideration should be given to monitoring the potential effects of the proposal on fishing in Lake Illawarra.
The essential elements of monitoring are the use of adequate temporal and spatial controls, which 1 means sampling on several occasions before, during and after the project and at appropriate reference areas. In addition, prior to initiating monitoring, it is recommended that the dredging I operator, the Lake Illawarra Authority, other regulatory authorities and interest groups determine the limits of change in biota, water quality, etc, that can occur before alternative management I strategies are initiated. Once these limits are set, the most sensitive and cost effective monitoring programme can be designed.
I Given the ecological significance of seagrasses and the large size of the area of seagrasses that ' would be directly lost or disturbed by the proposal, it is recommended that a plan of management be formulated to be initiated if recolonisation of seagrass beds does not occur or is unacceptably slow. The recommended plan of management is outlined as follows:
Step 1. Areas where seagrass had been removed and where dredging and backfilling is completed should be inspected for; i) the presence of seagrass and ii) the growth of seagrass from adjacent undredged areas, at regular intervals (e.g. 3 monthly) over two years to observe if and how seagrass is colonising the dredged area.
Step 2. If seagrasses are detected during the inspection period, patches of seagrass should
xiii
I The Ecology Lab Ply, Ltd. Griffins Bay sand extraction - Marine Ecology - Final Report, April 1995 be mapped accurately and their area determined. In addition, measurements of the density and length of leaves of seagrass should be obtained in the colonised patches and compared to measurements obtained in reference (i.e. undisturbed) beds. Inspections of the dredged area should continue regularly to identify any new patches.
Step 2a. The growth of colonising patches should be monitored through time, so that the rate of patch growth (i.e. increase in area) and the proportion of the dredged area covered by seagrasses may be determined. There is no information available to suggest how quickly patches of seagrass should grow, or what the rate of development of new patches should be, so it is difficult to assign a period of time for complete recolonisation (defined here as the areal coverage of seagrass equivalent to the amount removed). At this stage, it is suggested that an arbitrary criterion of 10% of the dredged area be recolonised per year, after a 1 year period of stabilisation following dredging and backfilling. At this rate, complete recolonisation would be expected to take 11 years after dredging of a particular area was completed. For example, dredged Area B would be the first area available for colonisation of seagrass approximately 3 years after the dredging proposal commenced. Area B is 2.4 ha., thus, the criteria for growth of seagrass would be 0.24 ha. per year. If seagrasses are present but the 10% rate of growth is not being achieved after five years, transplantation of seagrasses should be considered to assist with seagrass growth and to help meet the objective of complete recolonisation.
Step 3. If seagrasses are not detected during the inspection period of two years, two options should be considered. First, if the area is at the lower depth limit for growth of seagrass in Lake Illawarra (i.e. 1.5 - 2.0 m below Al-ID), consideration should be given to further backfilling with sand to make the substratum shallower either over the whole of that particular dredged area, or within a portion of it, as an experiment. If backfilling is done, a further period of inspection should be initiated and Step 2a followed. Second, if the area is already suitably shallow (i.e. <-1.5 m AHD), transplantation of seagrass should be initiated.
Step 4. If seagrass recolonisation does not occur following Step 3 - which is considered most unlikely, given that seagrasses have already recolonised other dredged areas in Lake Illawarra - further research and remediation works should be considered to facilitate the growth of seagrasses (e.g. further backfilling).
One further advantage of the above plan of management is that monitoring of colonisation of Area B would take place after 3 years from the start of the dredging programme and run for 7 to 10 years before any of the other dredged areas were ready for seagrass to colonise. In other words,
WA The Ecology Lab Ply. Ltd. Gr[fins Bay sand extraction - Marine Ecology - Final Report, April 1995 the plan of management for Areas A and possibly Areas C and D can be modified, if necessary, to incorporate the information collected from Area B. Thus, the monitoring of Area B would provide a good test case of the management plan.
Clearly, there are a number of possible approaches that could be adopted for a plan of management for seagrasses in the proposed dredge areas. The final approach should be determined in consultation between SCE, the Lake Illawarra Authority and other relevant organisations, such as the NSW Environment Protection Authority (EPA), NSW Fisheries and the Commercial Fisherman's Advisory Council (CFAC).
N
-. =---
(XIS-T WO 0 ,• — - ____ - A4O CAHNEL - - AzaB ••Th . GRIFflNS Phase I
Stage 4 AreaA / / •1 \. -... - 2 / /7/ Stage 1 , 2200 - -.1 AreaD 'S ( i - z- ui ,e 2
ii r — --- —fl--- — Stage2-channel extension . PRM Poon-
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/ .
EXSTING CONTOURS 1 / 1 I CONTOUR ARE ON STRLIN / hOGHT OTUM (r ftD.) fi /
Figure SI: Map of Griffins Bay indicating the stages and areas to be dredged for sand extraction in Griffins Bay. The Ecology Lab Pty Lid Griffins Bay sand extraction - Marine Ecology - Final Report, April 1995
1.0 INTRODUCTION I 1.1 Background and Aims
I The Ecology Lab Pty Ltd was commissioned by Gutteridge Haskins & Davey (GHD) to describe the existing estuarine environment of Lake Illawarra and to assess potential impacts of a proposal to dredge and extract sand near the entrance to Griffins Bay by South Coast Equipment Pty Ltd (SCE). Specifically, The Ecology Lab was contracted to do field studies on the estuarine fauna of I Lake Illawarra, with emphasis on Griffins Bay, and to use existing information to describe the environment of Lake Illawarra. A thorough description of the commercial and recreational fishing I activities of Lake Illawarra was also required. Using these descriptions as background information, in addition to information provided by GHD on the nature of the proposal and on predicted physical and chemical effects, impacts were assessed, suggestions to mitigate impacts I made and a preliminary monitoring programme formulated.
The proposal to dredge the entrance to Griffins Bay by South Coast Equipment Pty Ltd has been the subject of a previous environmental impact statement, or EIS (KayBond, 1993). Reviews of the I previous EIS by some government departments and interest groups identified some issues which required further work. Issues relating to marine ecology were incorporated into the present study. The specific aspects of the existing environment that required field sampling were the benthic macrofauna within seagrass beds and the fish and mobile invertebrates within seagrass beds. These aspects plus descriptions of fishing activities, were identified by NSW Fisheries, the I Australian Museum, Commercial Fisheries Advisory Council (CFAC), Ocean Watch Environmental Protection Authority and others as requiring further information to supplement the I previous EIS.
To assess the significance of the assemblages of benthic macrofauna, fish and mobile invertebrates in Griffins Bay, it was important to compare the bay with other areas in Lake Illawarra. Thus, the field sampling design included; i) several areas within and near the proposed area of dredging in Griffins Bay and ii) several areas within reference locations in similar habitats situated away from the proposed dredge area. Comparisons of abundance and species composition can then be made within and among locations (Andrew and Mapstone, 1987). The value of this sampling design is twofold. First, the relative importance of the proposed dredge area can be assessed and second, I the range of natural variation in the abundance and distribution of assemblages prior to dredging can be used to measure the impacts of that activity.
I The Ecology Lab Pty Ud Griffins Bay sand extraction - Marine Ecology - Final Report, April 1995
The aims of the study were:
to describe the estuarine environment of Lake Illawarra with specific reference to Griffins Bay using field sampling of benthic macrofauna, fish and mobile invertebrates and existing information,
to describe the commercial and recreational fishing activities on Lake Illawarra by interviewing local fishers and NSW Fisheries Inspectors and using existing information,
to assess the impacts of the dredging proposal on the estuarine environment and fishing activities of Lake Illawarra,
to suggest any measures that would assist in minimising the predicted effects of the proposal so that they could be incorporated into the final design of the project and
to outline a monitoring strategy should the proposal to dredge proceed.
1.2 Existing Information
1.2.1 Physical and Chemical Conditions
1.2.1.1 Lake Illawarra
Lake Illawarra is a barrier estuary (Adam et al., 1985) and is separated from the ocean by a long, shallow channel (2.4 km long, 600 m wide and maximum depth of 2 m). The position of the mouth of the channel varies depending on rainfall, wave action and sediment redistribution and on several occasions in the last 50 years, heavy shoaling at the mouth has resulted in the complete closure of the lake from the ocean (Ellis et al., 1977). This occurred most recently occurred in 1971. The lake's water level is about 25-30 cm above mean sea level (Clarke and Eliot, 1984 in Yassini and Jones 1987). The maximum depth of the lake is 3 m
Lake Illawarra covers an area of 35 km2 and its catchment area is about 270 km2. The tidal range is 3-5 cm in the body of the lake and 10-25 cm in the entrance channel (Clarke and Eliot, 1984 in Yassini and Jones, 1987). Tidal currents are mainly limited to the entrance channel (36 cm s') whereas currents within the lake are generated by wind action (Clarke and Eliot, 1984 in Yassini and Jones, 1987). Residence time of the water in the lake varies between approximately 26 and 39
weeks (Ellis et al., 1977). The Ecology Lab Ply Ud Griffins Bay sand extraction - Marine Ecology - Final Report, April 1995
The long-term average salinity for the lake is 28.50 / but extremes of 8.7°/ during flood and I 42.5 0/ during drought have been recorded (Elcom, 1987). The difference in salinity between the bottom and surface waters ranges from 0.4 to 2.9 O/ and no difference between the eastern and I western sides of the lake has been reported.
Variations in the temperature of water in Lake Illawarra were measured by Elcom from 1981 - I 1983, Ellis and Kanamori (1977a) from 1973 -1974 and CSIRO from 1976 - 1978 (in Yassini and Jones, 1987). Ellis and Kanamori (1977a) reported a range of water temperatures of 11.6 - 25.6°C I for Lake Illawarra. Comparison of the surface water of the lake to the nearby ocean showed that the lake experiences greater temperature extremes and the timing of maximum and minimum I temperatures is one month earlier than in the adjacent ocean.
The concentration of dissolved oxygen in the surface waters of Lake Illawarra during the day varies between 4 - 11 mg 1.1 (Ellis and Kanamori, 1977b). Yassini and Jones (1987), in October 1984, measured dissolved oxygen concentrations in areas of Lake Illawarra affected by macroalgal I blooms, such as the eastern side of the lake and Griffins Bay. They found that the dissolved oxygen levels were very small at night (0.5 mg 1.1) and this could enhance denitrification and the I release of phosphorous into the water column.
The quality of sediment and water of Lake Illawarra has been assessed previously in several ways. Ellis and Kanamori (1977b) measured the concentration of heavy metals in several areas within Lake Illawarra and found greater concentrations of metals (copper, lead, zinc and cadmium) in the I top 10 cm of sediment in Griffins Bay and Koona Bay. They concluded that the main source of these metals was the Port Kembla industrial complex, the Dapto smelting works (closed in 1906) I and Tallawarra Power Station (decommissioned in 1989). Urban run-off is also a source as Lake Illawarra is almost entirely surrounded by residential development. Yassini (1992) attributed the I presence of heavy metal contaminants to both industrial activities and urban run-off. He found concentrations of metals such as zinc and cadmium in molluscs and plant tissue exceeded the sediment background levels. Algal species had greater concentrations of sulphur and seagrasses had greater concentrations of phosphorous. Yassini and Clarke (1986) reported a fourfold increase in the mean levels of phosphate and nitrate in the lake over the period from 1974 to 1986. Sources of nutrients included rural and urban runoff, sediments, sewage overflows, coastal waters and precipitation. The Electricity Commission (now Pacific Power) have monitored the nutrient status of the lake since 1981 and reported an increase in the level of phosphorous and nitrogen (Dames and Moore, 1993). These levels exceed the guidelines recommended by ANZECC (1992) and indicate that phosphorous and nitrogen in these concentrations are likely (according to Dames and
3 The Ecology Lab Pty Ltd Griffins Bay sand extraction - Marine Ecology - Final Report, April 1995
Moore, 1993) to be causing some eutrophication.
1.2.1.2 Griffins Bay
Griffins Bay is located in the north-east of Lake Illawarra. As part of the preparation of the EIS for sand extraction in Griffins Bay, GI-ID (1995) collected data on water quality, water circulation and heavy metal content of the sediment within the vicinity of Griffins Bay. This was required as background information so that predictions about changes in these physical conditions due to the proposal could be made. These results are discussed in the ETS but have been summarised here because reference will be made to these results in later sections of this report.
Patterns of water circulation in and around Griffins Bay were determined by drogue and dye tracking on one day in April 1994 when the wind was calm in the morning but increased to 6 m/s from the north east in the afternoon. These measurements were taken to calibrate the hydrological model (GHD, 1995). Results indicated that the southerly movement of drogues and dye plumes was wind induced, with velocity increasing in the surface current with increasing wind speed. The lake level did not change throughout the day, indicating either closure at the entrance to Lake Illawarra or negligible tidal influence in Griffins Bay. There was little evidence for transport of material in an east-west or west-east direction suggesting little current flow in the bay. The maximum current in Griffins Bay was predicted to be 0.1 m/s occurring in the northern channel for a 10 knot westerly wind. The maximum current along the southern shore was 0.05 m/s (GI-ID, 1995).
Salinity, water temperature and dissolved oxygen concentration were examined through the water column at eight locations in and around Griffins Bay on one day in January 1994. Water temperature varied little with depth or location around Griffins Bay. Salinity did not vary with depth but the two locations along the southern shoreline of Griffins Bay (in Primbee Bay and Joes Bay) had lower salinities than the other locations. Dissolved oxygen concentration at approximately 30 cm below the surface did vary among locations around Griffins Bay (range: 7.5 - 10.3 mg/L) and with depth such that surface waters ranged from 8.5 to 10.5 mg/L whilst at the bed of the lake concentrations ranged from 3.4 to 4.7 mg/L. These values are within the range recorded previously from Lake Illawarra (Section 1.2.1.1). Levels below 6 mg/L are deemed unsatisfactory by the water quality standards of ANZECC (1992).
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Heavy Metals A previous study of sediments in Lake Illawarra recorded concentrations of heavy metals (copper, zinc, lead and cadmium) in Griffins Bay up to 10 times that of locally-defined background levels (Chenhall et al., 1994). The other sites studied exhibited only slightly greater concentrations than background in nearsurface sediments.
For this proposal, sediment samples were collected from 8 locations in and around Griffins Bay and analysed for 6 heavy metals (GI-ID, 1995). Of these metals, cadmium and mercury were not I detected in any of the samples, lead and copper were detected in some of the samples (20% and 47% respectively) and chromium and zinc were detected in all samples. Only chromium and zinc I occurred in enough samples to address statistically if any differences occurred among the locations within Griffins Bay. The concentration of chromium was greater in the location in Primbee Bay compared to all other locations and the concentration of zinc was greater in the locations in I Primbee Bay and North of Purry Burry Point compared to all other locations. The range of concentrations in samples for all metals is given in Table 1A. Because the detection limits were U high for these samples, additional samples were taken from 2 locations in Griffins Bay where the proposed dredging would occur and were analysed at lower detection limits (Table 1B). With the I lower detection limit, Cadmium was also detected in the samples.
Table I also contains guidelines for assessing whether the concentrations of metals are likely to affect organisms in contact with the sediment. The criteria for the quality of sediment are those compiled by MacDonald (1992) and are based on data from the US EPA's National Status and I Trends estuarine sediment quality monitoring program. The use of these criteria is necessitated by the lack of suitable data from Australia. These criteria are expressed in dry weight, which I necessitated the conversion of the Griffins Bay data from wet weight to dry weight using the percentage of moisture given per sample. The criteria reflect the minimum concentration at which I effects on organisms can be detected. Concentrations less than the screening level (SL) are unlikely to affect even the most sensitive organisms in contact with the sediment. Concentrations between the SL and probable effects level (PEL) may have effects on sensitive organisms whilst I concentrations larger than PEL are likely to adversely affect sensitive organisms. Applying these criteria to the samples collected around Griffins Bay, the concentration of chromium, copper and I zinc may be having adverse effects on some organisms because some samples exceeded the SL and several samples had chromium levels exceeding the PEL. The samples that exceeded these limits I for chromium, copper and zinc were taken from Primbee Bay and north-east of Purry Burry Point. For chromium, samples taken from a location outside but near Griffins Bay also exceeded the SL. I The Ecology Lab Pty Ltd Griffins Bay sand extraction - Marine Ecology - Final Report, April 1995
Samples taken from the proposed dredge areas and analysed at lower detection limits had no metals exceeding the SL and PEL.
Acid Sulphate Soils Samples of sediment were taken from the proposed dredged areas in Griffins Bay and analysed for their potential as acid sulphate soils (GHD, 1995). The tests indicated that the sediments in Griffins Bay have the potential to become acid sulphate. The intensity of the chemical reaction that was used as a test varied considerably among sites and between depths of sediment (GI-ID, 1995). The preliminary tests, however, did not quantify this potential. GI-ID (1995) recommend a more comprehensive survey be undertaken prior to dredging.
1.2.2 Seagrass Beds
Four species of seagrass occur in Lake Illawarra; Zostera capricorni, Ruppia megacarpa, Halophila ovciiis and Halophila decipiens. Large beds of seagrass grow in the shallows off the shoreline and are mainly formed by Zostera but there are stands consisting of predominantly Ruppia and mixed stands of Zostera and Ruppia. The densest seagrass beds in the lake are located along the Windang Peninsula, on medium-grained sand and extend out to a maximum depth of 2 metres. In other parts of the lake, seagrass beds are also limited to a depth of 2 metres and occur on sandy and muddy substrate (Yassini, 1993). In Lake Illawarra, Ruppia grows in a maximum depth of 40 cm whereas Zostera grows in a maximum depth of 2 m (Yassini, 1993). Factors that may influence the growth and extension of seagrass beds include; water depth, turbidity, temperature, salinity, nutrient supply and the nature of the substratum (Larkum et cii., 1989).
Since 1976, estimates of the total area of seagrass in Lake Illawarra have ranged from 5.12 km2 to 10.9 km2 (see Harris, 1977; Evans and Gibbs, 1981 in WBM Oceanics, 1993; West et cii., 1985; King, 1988; King et cii., 1991). Some of the differences are inevitably related to the technique used to estimate cover but most of the variation probably represents real changes in the area of Lake Illawarra covered by seagrass beds. Changes in the cover of seagrass have not been strongly linked to seasonal or environmental changes (King, 1988). The area of seagrass mapped by West et cii. (1985) (a total of 5.12 km2) and the area of seagrass mapped by King (1991) (a total of 10.9 km2) is presented in Figure 1.
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The most recent survey of the seagrasses of Lake Illawarra did not estimate the entire area of seagrass within the lake but examined in detail five smaller areas within the lake using aerial photography (1:6 800) and field surveys (WBM Oceanics, 1993). The present cover and characteristics of seagrass in two areas that had a history of dredging (Koonawarra Bay and Griffins Bay) and in three areas that had no history of dredging (Purry Burry Point, Duck Creek and Mullet Creek) were compared to the cover estimated in 1988 using aerial photography (1:16 300) and maps in King (1988) from a survey in March 1987. Seagrass beds at Mullet Creek, Koonawarra Bay and Duck Creek have expanded in area indicating that Zostera can extensively I and rapidly recolonise some dredged areas such as Koonawarra Bay. In Griffins Bay, however, there has only been minor recolonisation of Zostera in the dredged area since 1991. Figure 2 I illustrates the decrease in the area of seagrass in Griffins Bay from 1988 to August 1993 using maps drawn by WBM Oceanics (1993). Dredging in Griffins Bay was done to construct a navigation channel at approximately - 1.5 m AHD along the northern and eastern perimeter of the I bay. This depth is greater than the range of depths examined by WBM Oceanics (1993) but is within the depth range of Zostera reported in other studies (Yassini, 1993). WBM Oceanics I concluded that the extent and rate of recovery are related to the final depth and turbidity after dredging. Thus, it may be possible that if dredging works improve circulation and turbidity is I reduced, the depth distribution of seagrass may be extended (WBM Oceanics, 1993). I WBM Oceanics (1993) found that the structural characteristics of Zostera, such as the density of shoots, number of leaves per shoot and length of leaves varied among depths and among the 5 locations sampled in the lake. There tended to be a greater density of shoots with decreasing I water depth. The density of shoots within Griffins Bay was also greater compared to the other locations for 3 depth ranges. The overall mean density of shoots among locations ranged from I 1025 to 3336 shoots per m2. There was no relationship between the number of leaves per shoot or the length of leaves with water depth. The overall mean length of leaves ranged from 24.7 to 31.7 I cm and there were, on average, 4 leaves per shoot. Variability in structural characteristics of Zostera is not unusual, for example, Larkum et al. (1984) reported that Zostera in Botany Bay had I smaller densities of shoots and longer leaves with increasing depth and reduced exposure to waves. Furthermore, the structural characteristics of Zostera in Lake Illawarra are within the range I found for other places on the NSW coast (WBM Oceanics, 1993; The Ecology Lab Pty Ltd, 1994).
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1.2.3 Saitmarshes and Mangroves
According to West et al. (1985) there is only one small area (0.203 km2) in Koona Bay, in the south of Lake Illawarra, that has saltmarsh habitat (see Figure 1). There are no stands of mangroves on any of the shores of the lake.
1.2.4 Benthic Macrofauna
Benthic macrofauna typically comprise invertebrate animals such as marine worms (polychaetes), shells (bivalves and gastropods) and crustaceans which live on or in the seafloor (often termed the 'substratum'). Benthic invertebrates exhibit a wide range of sizes and 'macrofauna' are defined conveniently as those invertebrates which are retained by a 1 mm sieve.
Very little information exists on the assemblages of benthic macrofauna in Lake Illawarra. Garcia (1986) compared the abundance of macrofauna at seven sites around the lake, sampling once each in summer and winter. Differences were found among locations and related to differences in the grain size of sediment and the presence and type of vegetation. Yassini and Jones (1987) sampled the sediments for ostracods and found more species at the entrance channel than inside the lake. Within the lake, the diversity of ostracods was related to the presence of benthic flora with the most diverse assemblages occurring in areas covered by seagrasses. The deeper areas of the lake where the sediment is predominantly muddy had a different assemblage of ostracods compared to shallow, vegetated, sandy areas.
1.2.5 Fish and Mobile Invertebrates
Few studies have examined the distribution and abundance of fishes in Lake Illawarra. Of these, Jordan (1986) concluded that Lake Illawarra supported a rich and diverse fish fauna comparable to other similar lakes in N.S.W. In his study, the greatest diversity of fish occurred at a site near the entrance to Mullet Creek in a bed of Zostera capricorni. The diversity of fishes within the lake did not change seasonally except at a site on the eastern shore in the Ruppia megacarpa bed and a site at the entrance to Griffins Bay in the Zostera capricorni bed. At these sites, diversity was greatest in February and April mainly due to the abundance of silver biddy (Gerres subfasciatus), tarwhine (Rhcthdosargus sarba) and flat-tail mullet (Liza cirgentea). The abundance and biomass of commercial and recreational species of fish, however, were significantly greater in summer and autumn, largely due to the significant increase in abundance of luderick (Girelici tricuspidata), tarwhine
8 The Ecology Lab Ply Ltd Griffins Bay sand extraction - Marine Ecology - Final Repert, April 1995
(PJzabdosargus sarba) and bream (Acanthopagrus australis) in October at most sites sampled in Lake Illawarra. Also, in spring many species of fish settle from the plankton into seagrass beds. For I example, McNeill et al. (1992) reported consistently large abundances of Acanthopagrus austraiis, Rhabdosargus sarba, Girella tricuspidata, Achoerodus viridis and Meuschenia trachylepis between June I and March compared to other times of the year in a seagrass bed in Botany Bay. Non-commercial species that were caught in large numbers included perchlet (Ambassis jacksoniensis), hardy-head I (Atherinosoma microstoma) and gobies (Pseudogobius olorum and Favonigobius tainarensis). 1 The abundance of commercially and recreationally important species of fish and mobile invertebrates have been compared among different locations along the western shores of the lake with locations near Tallawarra Power Station (Scanes et al., 1991). No differences among locations I was detected statistically but differences occurred at different times of the year. More species of fish were found in autumn than in summer and less were found in spring and winter. The total k number of fish was greater in summer, autumn and spring compared to winter.
I 1.2.6 Commercial and Recreational Fishing Activities I Studies on the fisheries of Lake Illawarra are few. The Fisheries Research Institute studied the impact of the Tallawarra Power Station on the fish and fisheries of Lake Illawarra in 1990 and found that the assemblages of fish at Tallawarra power station were not significantly different from the other areas sampled (Scanes et al., 1991). Sampling effort for this study was concentrated in the area of the power station and along the western shore of the lake and as such does not I contain information directly relevant to the present study. Scanes et al. (1991) also suggested that the size of the commercial catch, although variable, is decreasing from a peak in the late 1960's and early 1970's but commercial catch per person is similar to that for Lake Macquarie. The commercial catch from Lake Illawarra is supposedly more seasonal than other lakes with a definite I low point in winter (Scanes et al., 1991).
1.3 Matters Arising from Previous EIS
The review of existing information in Section 1.2 has highlighted the need for further work because of insufficient data to adequately assess the likely impacts of sand extraction in Griffins Bay on the marine ecology of Lake Illawarra. Data on the relative abundance and distribution of benthic macrofauna, fish and mobile invertebrates in Griffins Bay compared to other areas within the lake are needed. Likewise, a thorough description of the commercial and recreational fishing
9 The Ecology Lab Pty Ltd Griffins Bay sand extraction - Marine Ecology - Final Report, April 1995
activities carried out in Lake Illawarra is also required. Information on production of fish and prawns for Lake Illawarra needs also to be placed in a regional context.
There is insufficient information on the spatial patterns of distribution and abundance of benthic macrofauna in the lake. These animals are important in estuarine ecosystems for several reasons; they are a source of food for fish, mobile invertebrates and birds, they play an important role in pathways of detrital and nutrient recycling and they are good indicators of environmental distuthance (e.g. Warwick1 1993). The proposal to dredge in Griffins Bay may affect this group of animals, which may in turn affect the abundance and diversity of fish and other biota. Therefore, it is necessary to obtain data on the relative importance of Griffins Bay compared to other areas in the lake.
There are no data on the relative significance of different areas of seagrass as habitat for fish and mobile invertebrates in Lake Illawarra. Bell and Pollard (1989) provide a very comprehensive analysis of the value of seagrass habitats to fish and fisheries in Australia. There are two aspects of seagrasses that make them important as habitat for fish and mobile invertebrates. First, they typically support a greater diversity and abundance of fishes and invertebrates than nearby unvegetated substrata. Second, many fish and invertebrates spawn their eggs into the water column, or on to the seabed, from which the hatchlings ('larvae') disperse via the water column. When they return to the seabed, many of these larvae use seagrass beds as 'nursery' areas, because of the food and shelter supplied there. Therefore, seagrass beds play a very important role as nursery habitat in NSW estuaries. Research has shown that the locations of seagrass beds within an estuary can be important in determining the relative abundance of fish and mobile invertebrates (McNeill et al., 1992). Characteristics of seagrasses such as the density of shoots and length of leaves may also influence the abundance and species composition of fish and mobile invertebrates (Bell and Westoby, 1986a; Bell and Westoby, 1986b). In addition, successful recruitment from planktonic to juvenile and sub-adult stages is dependent on the availability of suitable benthic habitat at the time when larvae are competent to settle from the plankton (Bell and Westoby 1986c; Bell et al., 1987). There is a need, therefore, to assess the relative value of the seagrass beds of Griffins Bay in relation to other beds in the estuary
No field studies were required by The Ecology Lab to describe the seagrass beds themselves because a recently published description of the seagrass beds in Griffins Bay and other areas within Lake Illawarra (VVBM Oceanics, 1993) was considered by GHID to be adequate for this study. Information on seagrass beds is necessary because recent research has emphasised the
10 The Ecology Lab Pty Ud Griffins Bay sand extraction - Marine Ecology - Final Report, April 1995
importance of seagrasses in the ecology of shallow estuarine environments (reviewed by Larkum et al., 1989). Seagrasses stabilise sediments (Fonseca et al., 1982), provide an important habitat for juvenile fishes and mobile invertebrates, many of which are of commercial or recreational importance (Bell and Pollard, 1989) and are significant components in the cycling of nutrients in I estuaries (Kenworthy et al., 1982). 1 I 2.0 STUDY METHODS 2.1 Benthic Macrofauna I 2.1.1 Survey Procedures I Benthic macrofauna were collected from 8 locations (100's metres to kilometres apart) in Lake Illawarra on the 8-9 November 1993 (Figure 3). At each location, 2 sites (10's metres apart) were sampled. The design of the sampling programme enabled a comparison to be made of the assemblages of macrofauna at 3 locations (Sites 1-6) at or near the proposed dredging area (entrance to Griffins Bay) with 3 reference locations (Sites 13-16) away from the proposed dredging area (along the eastern shore of Lake Illawarra). At all these locations the sediment was sandy (The Ecology Lab (TEL), observation). Additional samples were taken from 2 other locations, one in Kully Bay within Griffins Bay (Sites 7 and 8) and the other in Burroo Bay (Sites 9 and 10) (Figure 3). At these locations the sediment was muddy (TEL observation).
Five samples were taken at each site by a scuba diver using a hand-held corer (19 cm diameter, surface area of 0.028 m2) that penetrated approximately 10 cm into the sediment. A total of 80 samples was collected. All samples were taken from bare substratum located within the seagrass I bed rather than directly through the seagrass itself, as sorting of these samples would have taken I too long due to the presence of the seagrass root mat. Samples of benthic macrofauna were sieved through a 1 mm mesh screen and the animals and other material retained on the sieve were preserved in 10% formalin. The samples were stained with Rose Bengal in the laboratory and all animals sorted with the aid of magnifying lamps (approximately 2X). Crustaceans and molluscs were sorted into species groups and a representative selection was identified to species by the staff at the Australian Museum. Most polychaetes were identified to species except for a few family groups that were not very abundant.
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Some rare groups (oligochaetes, nemerteans, hydroids and holothurians) were counted but not identified further due to a lack of taxonomic information.
2.1.2 Statistical Analyses
2.1.2.1 Multivariate Analyses
Variation in the assemblages of benthic macrofauna among all 16 sites (8 locations) was examined using the multivariate procedures proposed by Clarke (1993). These analyses use a measure of similarity between samples to map the relationships among samples in an ordination using non- metric Multi-Dimensional Scaling (MDS). They produce a graphical representation of the similarity (and dissimilarity) of the samples from all sites sampled.
The data matrix (species by samples) was double square-root transformed to reduce the weighting given to abundant taxa and increase the weighting given to rarer species. Similarities among samples were calculated using the Bray-Curtis Similarity measure and used to construct the two- dimensional MDS plots. The adequacy of the two dimensional representations of the similarities among samples is assessed by examining the stress value. Stress values of < 0.1 indicate a good representation which may be easily interpreted and plots with stress < 0.2 provide a reasonable representation of the data. Plots where the stress value exceeds 0.2 indicate a poor representation of the relationship among samples in 2 dimensions and are of little value. For this reason, the plots are not presented when stress exceeds 0.2.
The significance of any apparent differences among areas was determined using the ANOSIM randomisation test (Clarke, 1993). The null hypothesis being tested is one of no difference among areas in the structure of benthic assemblages. The significance levels in pairwise tests were adjusted to allow for multiple comparisons using the Bonferroni Correction formula (Winer, 1971).
Similarity analyses (SIMPER) were used to determine the relative contribution that particular species or taxa make to the dissimilarity of groupings and are based on the Bray-Curtis similarity measures among all samples (Clarke, 1993). SIMPER identifies which species or taxa are good discriminators between areas. All species can potentially contribute to the dissimilarity among areas but for reasons of brevity, only the first few species that contribute the most to the dissimilarity among areas are presented and discussed.
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2.1.2.2 Univariate Analyses
Analysis of variance (ANOVA) was used to compare the abundance of common taxa, the total I number of individuals and the number of taxa per sample at three spatial scales; between Areas (Griffins Bay versus Eastern Shore), among Locations (within Areas) and among Sites (within Locations and Areas). The analytical design was a three factor ANOVA, in which Griffins Bay I versus Eastern Shore was a fixed factor, Locations was a random factor and nested within Areas and Sites was a random factor and nested within Locations and Areas. Post-hoc pooling I procedures were used if higher-order interaction were non-significant at P >0.25 to provide a more powerful test (Winer, 1971; Underwood, 1981).
Cochran's C statistic was used to test the assumption of homogeneous error variances (Winer, 1 1971; Underwood, 1981). Data were transformed using ln(x+1) only when Cochran's C was significant at P < 0.05. If, after transformation, Cochran's C was still significant, the ANOVA on the untransformed data was used and statistical significance determined with a = 0.01 instead of a = 0.05 (a reduced probability of making a Type I error (Underwood, 1981)). Post-hoc comparisons among means were done using Student-Newman-Keuls (SNK) procedures when the I ANOVA produced a significant effect.
I 2.2 FIsh and Mobile Invertebrates 1 2.2.1 Survey Procedures
Fish and mobile invertebrates were sampled using two methods; beam trawling and beach seining. Each method has various advantages and disadvantages. The beach seining technique is better at catching very mobile fish such as mullet, bream and tailor but it cannot be readily used to sample in areas away from the shoreline. Beam trawling was necessary to sample in areas offshore, such as, the area proposed for dredging at the entrance to Griffins Bay.
For each method, 5 locations were sampled in the lake, two of these in or near Griffins Bay. At each location, 2 sites were sampled and four replicate beam trawis or beach seines were taken in each site. Each sample was preserved in 10% formalin and sorted back in the lab. All fish and mobile invertebrates (crustaceans and molluscs) were identified to species and counted. Species of 1 commercial importance were measured to fork length (LCF). The number of Mucrobrachium a small and sometimes very abundant carid shrimp, was estimated by weight. The I intcrmecJium, 13 1 The Ecology Lab Pty Ltd Griffins Bay sand extraction - Marine Ecology - Final Report, April 1995
average weight of 5 replicate batches of 50 shrimp was used to calculate the number of shrimp from the total weight of the sample.
2.2.1.1 Beam Trawling
Beam trawl samples were collected in 5 locations; 2 near Griffins Bay, 2 in Windang Channel and 1 on the eastern shore of Lake Illawarra (Figure 4). The beam trawl was 1 m wide and 0.5 m high. The net was 2.5 m long with 5 mm mesh around the frame and 2.5 mm mesh in the bag. The beam trawl was towed behind a small, outboard-powered punt. Each replicate tow, of 4 minutes duration, was in a straight line through seagrass.
Some samples were very large and full of algae and seagrass making it necessary to subsample because of the large amount of time involved in sorting them. A small pilot study indicated that sorting 3/ 5 of the sample was adequate, in terms of precision, to estimate the abundance in the whole sample. Samples were divided into fifths by weight and 3 randomly chosen to sort.
2.2.1.2 Beach Seining
Beach seine samples were collected at 5 locations; 2 near Griffins Bay, I in Windang Channel, 1 in Boat Harbour and 1 in Hennegar Bay (Figure 5).
The seine net was 25 m long and approximately 3 m deep with 8 mm mesh size. The net was hauled through seagrass and over sand onto the shore.
2.2.2 Statistical Analyses
Multivariate analyses were done on each data set as described in Section 2.1.2.1 except that locations rather than areas are the spatial scale of interest. For the ANOSIM randomisation test, the null hypothesis of no difference among locations in the structure of fish and mobile invertebrate assemblages was examined. Similarly, SIIvIPER was used to determine the relative contribution that particular species or taxa made to the dissimilarity of groupings, which for sampling fish and mobile invertebrates are the locations.
Data from the beam trawls and beach seines were also analysed using analysis of variance (ANOVA) to compare the abundance of the more common taxa, the total number of individuals,
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the number of individuals of commercially important species and the total number of taxa per sample among the locations and sites sampled. The analytical design was the same for the beam I trawls and beach seines and consisted of two factors, locations (random factor) and sites, nested within location (random factor). Cochran's C statistic and SNK procedures were used as described I in Section 2.1.2.2.
2.2.3 Sizes of Fish
The length of all species of fish of commercial importance caught either by beam trawling or beach seining were measured to the caudal fork (LCF). The range, mean and standard error for each species was calculated and life history stage was determined from published data on length at maturity for fish in Botany Bay by SPCC (1981). If species were very abundant, length-frequency distributions for each location (sites pooled) were plotted and interpreted graphically. The length frequency distributions for some less abundant species were examined by pooling data from all I locations. 2.3 Commercial Fishing
2.3.1 Description of Commercial Fishing Activities
Discussions were held with several local commercial fishers to ascertain what areas of Lake Illawarra they fished in, what methods they used and what species were targeted. The local NSW Fisheries Inspector was also interviewed. This information was used to describe the commercial fishing operations in Lake Illawarra.
2.3.2 Commercial Fisheries Statistics for Lake Illawarra
The NSW Fisheries database was used to examine the commercial fishing activities of Lake Illawarra. The data available covers the financial years from July 1984 to June 1992. For example, 1985 covers the period from July 1984 to June 1985. The database contains information on the catch (weight of each species), effort and methods used per month during this time around Lake Illawarra.
One factor ANOVAs were used to compare years in the catch of individual species of fish, crustaceans and molluscs and the total of all species caught using the NSW Fisheries database.
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The catches per month were used as replicates for each year. Many species were caught in abundance all year so the catch for all 12 months was used. For species that were seasonally caught, however, only the months that had an average catch (over 8 years) of greater than 100 kg were used to reduce within-year variability (which would have made the test much less sensitive to among-year variability). Therefore, the number of replicate months used in the analyses varied according to the species analysed.
Commercial fisheries statistics for NSW for 1991 (July 1990 to June 1991) were available for all estuaries in NSW and these data were used to compare Lake Illawarra with other estuarine lakes in NSW.
2.4 Recreational Fishing
2.4.1 Description of Recreational Fishing Activities
Discussions were held with several local recreational fishers from the Windang Hotel Fishing Club to ascertain what areas of Lake Illawarra they fished in, what methods they used and what species were targeted. The local NSW Fisheries Inspector was also consulted regarding recreational fishing activities. This information and observations made by TEL of recreational fishing activities during the field studies, were used to describe recreational fishing on Lake Illawarra.
3.0 STUDY RESULTS
Although West et al. (1985) identified only one saltmarsh - in the southern portion of Lake Illawarra - a few saltmarsh plants were observed at Purry Burxy Point. These included a few isolated Sarcocornia quinqueflora and a band of unidentified rushes growing along the water's edge close to the shore. There were also masses of filamentous algae. Studies done in the Shoalhaven Estuary suggest that the occurrence of this algae may be seasonal (The Ecology Lab Pty Ltd, unpublished data).
During the field studies in November 1993, numerous waterbirds were observed, including pelicans, silver gulls, black cormorants, pied cormorants and black swans. The black swans formed large flocks off the eastern shore of the lake, well to the south of Griffins Bay. The other birds showed no obvious pattens in their distribution during the field studies.
16 The Ecology Lab Pty Ltd Griffins Bay sand extraction - Marine Ecology - Final Reix,rt, April 1995
The remainder of this section discusses the findings of quantitative surveys of benthic macrofauna, fish and mobile invertebrates, and describes fishing activities.
3.1 Benthic Macrofauna
A total of 8 235 individuals of benthic macrofauna were collected, representing 47 taxa. Most of I these were identified to species. Polychaetes and molluscs were the numerically dominant groups. Appendix A lists the species collected and the mean abundance and standard error per species per I site. I 3.1.1 Analysis of assemblages
The two-dimensional plot derived from the ML'S ordination indicated two major trends (Figure 6). First, there were differences in the assemblages of benthic macrofauna between samples from sandy and muddy substratum. Second, the samples taken from the proposed dredge area did not I overlap (except for two samples) with those taken from the reference locations on the eastern shore of Lake Illawarra. Thus, although these locations were all from the sandy substratum within a I seagrass bed, the assemblages were distinct at the time of sampling. The MDS plot suggested that the sites and locations sampled fell into three groupings; i) the proposed dredge area locations on I sandy sediment, ii) the reference locations on sandy sediment and iii) the locations on muddy sediment (Figure 6). The stress value of 0.191 indicated that the 2-D plot gives an acceptable presentation of the (dis)similarities in faunal composition among locations and sites. The ANOSIM I randomisation test showed that this grouping was a significant factor at p < 0.01 (ANOSIM, R=0.648) and that all pairwise comparisons between each group were significantly different at p < I 0.02 (probability level corrected for multiple comparisons).
SIMPER analyses were used to identify which species made the greatest contribution to the dissimilarity between groups. Table 2 lists the 10 principal taxa ranked in descending order of their individual magnitude of contribution to the overall average dissimilarity. Generally, the principal contributors are species that are abundant in one group and not very abundant in the other. The bivalve, So1eellinu alba, was very abundant in the sandy sediment of Griffins Bay (Sites 1-6, Figure 3) but absent from the muddy sediment grouping (Sites 7 & 8, Figure 3) (Table 2a). an amphipod, contributed most to the dissimilarity between Griffins Bay andLirohaustorius the Eastern metungi, Shore (Sites 11-16, Figure 3) and to the dissimilarity between the muddy sediments
17 The Ecology Lab Ply Ud Griffins Bay sand extraction - Marine Ecology - Final Report, April 1995
and the Eastern Shore as it was largely absent from Griffins Bay and muddy sediments and vety abundant on the Eastern Shore (Table 2b,c).
SIMPER analyses were also used to identify which species were good discriminators between groups. These species have a large ratio of average dissimilarity to standard deviation, i.e. their abundance is spatially consistent and not very variable. Species that were good discriminators
between the groups differ according to the comparison being made. The bivalve, Theorafragilis, discriminated well between Griffins Bay sandy sediments and muddy sediments and also between the sandy sediments on the Reference area and muddy sediments because it consistently occurred in large numbers in the muddy sediments and was largely absent from sandy sediments (Table 2a,c). Another bivalve, Tellina deltoidalis, was a good discriminator between the sandy sediment areas, being consistently more abundant in Griffins Bay than the Eastern Shore (Table 2b).
3.1.2 Analyses of Populations
The mean number of taxa did not vary among any of the spatial scales examined (Table 3, Figure 7a). Thus, the biodiversity of benthic macrofauna in Griffins Bay was, at the time of sampling, similar to other parts of Lake Illawarra. The overall abundance of individuals of benthic macrofauna, however, differed among locations nested within areas (Table 3, Figure 7b). The locations in Griffins Bay were significantly different from each other whereas the locations on the Eastern Shore were not different from each other (Table 3, Figure Th). Location A in Griffins Bay had the largest mean number of benthic macrofauna (Figure 7b). Thus, variability in the abundance of macrofauna was large among locations in the proposed dredge area in Griffins Bay compared to the abundance along the eastern shore. This is despite the fact that locations were much further apart on the eastern shore (Figure 3).
There were no individual species that differed in abundance at the largest spatial scale examined, that is, between Griffins Bay and the Eastern Shore (Table 3). Variation in abundance occurred only at the smaller spatial scales of locations and sites. Therefore, in terms of the abundance of individual species that were numerically dominant, there was no statistical distinction between Griffins Bay and the Eastern Shore.
The abundance of several species varied significantly among Locations i.e. at a spatial scale of 100's of metres (Table 3). These species can be divided into those that were variable among locations in: Griffins Bay only (Tellina deltoidalis, Rarantolla lepte and Gweniafusiformis) (Figure 7c,d,e);
18 The Ecology Lab Pty Ltd Griffins Bay sand extraction - Marine Ecology - Final Report, April 1995
the Eastern Shore only (Mysella sp., Urohaustorius metungi and Corophium volutator) (Figure 7f,g,h); and both areas (Spisula trigonella) (Figure 7i).
Location A (Sites I & 2) in Griffins Bay had more individuals of benthic macrofauna and more I individuals of the species T. deltoidalis, B. lepte, 0. fusiformis and S. alba than the other locations in Griffins Bay (Figure 7b,c,d,e,j). For the Reference locations, there appeared to be no consistent I differences among locations in their abundance of different species. I Although they were highly variable in abundance, there tended to be more T. deltoidalis in locations at Griffins Bay compared to locations on the Eastern Shore (Figure 7c). The abundance of T. deltoidalis was greatest, however, at the location in Griffins Bay on muddy sediment (Figure 7c, Appendix A). The amphipod, U. metungi, was very abundant at two of the Eastern Shore locations (eastern shore mid and eastern shore south) but occurred only in very small numbers at all the I locations in Griffins Bay (Figure 7g).
Several taxa differed significantly between sites situated only 10's metres apart (Table 3). These species were C. vol utator, Soletellina alba, Australonereis ehiersi and Cirrformia filigera (Figure 7h,j,k,l).
The spatial pattern in the abundance of A. ehlersi (commonly known as squirt worm) illustrates the magnitude of differences in abundance of some species of benthic macrofauna that can occur within the same habitat (in this case, sandy sediment within a seagrass bed) at only small distances apart (see also Morrisey et al., 1993). Processes that affect the abundance and distribution of benthic macrofauna at these small spatial scales may be abiotic, biotic or a combination of both (Thrush et al., 1991).
3.2 Fish and Mobile Invertebrates
3.2.1 Beam Trawis
An estimated abundance of 42 967 individual fish and mobile invertebrates were sampled using the beam trawL All these animals were identified to species. There were 30 species of fish, 7 species of crustaceans and I species of cephalopod mollusc. The most abundant species of fish
were two gobics (Pscudogobius olorum and Gobiopterus semivestitus) and a pipefish (Stigmatopora
nigra) representing 301/o, 25% and 101/c, respectively, of the total catch. Species of economic value comprised 0.5% of the total catch. The most abundant species of fish of economic value were six-
19 The Ecology Lab Pty Ltd Griffins Bay sand extraclion - Marine Ecology - Final Repoit, April 7995 spined leatherjacket (Meuschenia freycineti), blue groper (Achoerodus viridis) and luderick (Gircila tricuspidata) representing 39%, 26% and 14%, respectively, of the economically valuable fish catch. Eastern king prawns (Penaeus plebejus) and blue swimmer crabs (Portunus pelagicus) were the only economically important crustaceans caught in the beam trawls (95% and 5% of the catch respectively). Appendix B lists all the species collected and their mean abundance and standard error per site.
3.2.1.1 Analysis of Assemblages
The two-dimensional plot derived from the MDS ordination does indicate some differences in the assemblages of fish and mobile invertebrates sampled by beam trawling at five locations in Lake Illawarra (Figure 8). Samples from the two locations at Griffins Bay overlap and indicate that the assemblages at these locations are not distinct from each other. Samples from the Eastern Shore do not form a cohesive group and overlap with samples from Windang Channel North and Griffins Bay A. The samples from Windang Channel South, however, form a tight group with no overlap with samples from other locations indicating that the assemblage at this location is quite distinct from those at the other 4 locations. The ANOSIM randomisation test indicated that locations were significantly different at p < 0.01 (ANOSIM, R=0.528). Pairwise comparisons of locations, however, indicated that only half of the comparisons were significantly different (Table 4).
Table 5 summarises the results of SIMPER analyses for those comparisons between locations that were significant in the ANOSIM test. In 3 of the 5 comparisons, the shrimp Macrobrachium intermedium contributed the most to the overall dissimilarity between locations (range from 15.41% to 22.949,,) (Table 5). In all comparisons with Windang Channel South, Macrobrachium contributed most to the dissimilarity because there was an order of magnitude greater abundance there than other locations. Pseudogobius olorum contributed most to the dissimilarity between Griffins Bay B and Windang Channel North and Griffins Bay B and Eastern Shore because of the large abundance of this species at Griffins Bay B. Good discriminating species between location groups that were identified as different in the SIMPER analyses were Macrobrachium and the gobies Favonogobius tamarensis, Pseudogobius olorum, Redigobius macros toma and Arenigobius bifrenatus which all had ratios (average contribution to dissimilarity/standard deviation) of greater than 2.
20 The Ecology Lab Pty Ltd Griffins Bay sand extraction - Marine Ecology - Final Report, April 1995
3.2.1.2 Analyses of Populations
3.2.1.2.1 Spatial Comparisons
The number of taxa of fish and mobile invertebrates sampled by beam trawling varied among locations in Lake Illawarra but was statistically consistent at the smaller spatial scale of sites (Table 6). Both locations in Windang Channel appeared to support slightly more taxa than both locations in Griffins Bay, although these differences could not be resolved by the SNK tests (Table 6, Figure 9a). In summary, the biodiversity of biota sampled by beam trawling in locations in Griffins Bay was within the range found at the other locations in Lake Illawarra.
The abundance of individuals of commercial species caught using beam trawls did vary significantly among locations and sites sampled but SNK tests could not resolve these differences (Table 6). Although variable, on average there were between 5 and 10 individuals of commercially important fish caught per trawl per site except at the locations on the eastern shore where the average was slightly less (Figure 9c). There were 10 species of fish and 2 species of crustaceans that were of commercial importance that were caught in the beam trawls (see Appendix B). Of these species, the only ones abundant enough to analyse formally were the blue groper (Achoerodus
viridis), leatherjackets (Meuschenia spp.) and eastern king prawn (Penueus plebejus). There were no differences among locations and sites in the abundance of either blue groper or the eastern king prawns (Table 6, Figure 9d,j) although variability among trawls within sites was very large (as shown by the large standard errors in Figure 9d,j) which may have masked potential differences among locations. The abundance of leatheijackets varied significantly among locations but these differences were not resolved in the SNK tests (Table 6; Figure 9e). The abundance of leatheriackets in the locations in Griffins Bay did, however, fall within the range of abundance of the other locations in Lake Illawarra.
The total abundance of individuals caught in beam trawls was significantly greater at Windang Channel South (Table 6, Figure 9b). This difference was due to the large numbers of a non- commercial shrimp, Macrobrachium inlermedium, at Windang Channel South (Figure 9k). There were also significant differences in total abundance between sites within each location except on the Eastern Shore. All abundant non-commercial species analysed showed differences predominantly at the spatial scale of locations but also among sites. The exception was the eastern I fortesque (Centropogon australis), which did not vary in abundance among locations or sites (Table 6, Figure 9g). Two species of gobies, I' seudogobi us olorum and Cobiopterus semivest it us, were
21
i The Ecology Lab Pty Ltd Griffins Bay sand extraction - Marine Ecology - Final Report, April 1995 significantly more abundant at location B in Griffins Bay (Table 6, Figure 9f,i). The bridled goby, Arenigobius bfrenatus, and the snub-nosed pipefish, Lirocam pus carinirostris, were also most abundant at location B in Griffins Bay, although SNK tests could not detect differences among the locations (Table 6, Figure 9h). The abundance of the remaining species of non-commercial fish analysed (the porcupine fish, Dicotolichthys punctulatus, the large-mouth goby, Redigobius macrostoma, and the wide-bodied pipefish, Stiginatopora nigra) varied significantly among locations, such that, the locations at Griffins Bay fell within the range of the other locations. The squid, idiosepius notoides, varied significantly between sites at location A in Griffins Bay, Windang Channel North and the Eastern Shore (Table 6, Figure 91).
3.2.1.2.2 Sizes of Fish
The size ranges and numbers of individuals of fish of commercial importance collected by beam trawling are summarised in Table 7. All individuals were within the size range for juveniles of each species. For most species the size range was relatively small and Meuschenia trachylepis had the broadest size range.
3.2.2 Beach Seines
A total of 38 275 individual fish and mobile invertebrates were sampled using beach seining. All of these were identified to species. There were 43 species of fish, 6 species of crustaceans and 1 species of cephalopod mollusc. Species of economic value comprised 10.390' of the total catch. In the seine nets, twenty-one species of fish and 2 species of crustaceans of commercial importance were collected (see Appendix C). The most abundant species of fish were perchlet (Ambassis jacksoniensis), transparent goby (Gobiopterus setnivestitus) and hardyhead (Atherinosoma microstorna) representing 249o, 2017o and 189o' respectively of the total catch. The most abundant commercial species of fish were sand mullet (Myxus elorzgatus), luderick (Girella tricuspidata) and tarwhine (Rhabdosargus sarba) representing 25%, 17% and 13% of the commercial fish catch. Eastern king prawns (Penaeus plebejus) represented 99.5% of the commercially important crustacean catch with blue swimmer crabs (Portunus pelagicus) making up the remaining 0.59o. Appendix C lists the species collected and the mean abundance and standard error per site.
22 The Ecology Lab Pty Ltd Griffins Bay sand extradion - Marine Ecology - Final Report, April 1995
3.2.2.1 Analysis of Assemblages
There was little overlap in the position of samples from different locations on the MDS ordination plot which suggested that each location had a distinct assemblage of fish and mobile invertebrates (Figure 10). Furthermore, samples from Griffins Bay A were positioned closely together but at a distance away from the other four locations (Figure 10). This result should be interpreted with caution; however, as the two-dimensional plot derived from the NMS ordination had a stress value of 0.197, which is borderline for a reasonable interpretation of the plot. The MDS plot was still presented but caution should be used when interpreting the plot because the relationship among the samples in two dimensions may not reflect adequately their true relationship. The ANOSIM randomisation test indicated that locations were significantly different at p < 0.01 (ANOSIM, R=0.799). Pairwise comparisons of locations indicated that all locations were significantly different at p < 0.005 except for the comparison between Griffins Bay B and Boat Harbour (Table 8).
Table 9 summarises the results of SIMPER analyses for those comparisons between locations that I were significant in the ANOSIM test. As with the beam trawling, Macrobrachium intermedium contributed most to the dissimilarity between Windang Channel and all other locations. At I Windang Channel an order of magnitude more Macrobrachium were caught than at any other location. Griffins Bay A was distinguishable from the other locations largely due to a greater I abundance of /ktherinosoma microstoma and an absence of fish such as Rhabdosargus sarba, Liza argen tea, Ambassis jacksoniensis and Girella tricuspidata.
3.2.2.2 Analyses of Populations
3.2.2.2.1 Spatial Comparisons
The number of taxa of fish and mobile invertebrates collected using seine nets varied significantly at the spatial scales of location and sites but significant differences among locations were not I resolved by the SNK tests (Table 10). The locations at Griffins Bay B was within the range of the other locations but biodiversity at Griffins Bay A was relatively small compared to the other I locations (Figure ha). The numbers of taxa at sites within locations were similar at all locations except Windang Channel (Table 10, Figure ha).
The total abundance of the commercial species was significantly greater at location B in Griffins Bay compared to all other locations (Table 10, Figure lIc). The individual species of commercial
23 i I The Ecology Lab Pty Ltd Griffins Bay sand extraction - Marine Ecology - Final Report, April 1995 importance that were relatively more abundant at location B in Griffins Bay were; sand whiting (Sillago ciliata), river garfish (Hyprohainphus regularis) and tarwhine (Rhabdosargus sarba) (Table 10, Figure lld,j). A further 7 species of commercial importance were analysed and 3 of these, yellowfin bream (Acanthopagrus australis), sand mullet (Myxus elongatus) and sea mullet (Mugil cephalus), did not differ in abundance among locations or sites (Table 10, Figure lle,f). The abundance of flat-tail mullet (Liza argentea) was largest at Hennegar Bay compared to all the other locations (Table 10). Significant differences in abundance between sites within locations were evident for the blue groper (Achoerodus viridis), luderick (Girella tricuspidata) and eastern king prawn (Penaeus plebejus) with sites at the locations in Griffins Bay just as variable as sites within other locations (Table 10, Figure llg,h,i).
The total abundance of all species caught in beach seines was highly variable among locations and between sites within locations (Table 10). The locations at Griffins Bay fell within the range of abundance of the other locations although differences among the locations could not be detected by the SNK tests (Table 10, Figure lib). The abundance of the carid shrimp, Macrobrachium intermediurn, was significantly larger at Windang Channel than other locations (Table 10, Figure Ilk). This is similar to the result from beam trawling. The abundance of the non-commercial fish species, perchiet (Ambassis jacksoniensis), was significantly greater at location B in Griffins Bay than elsewhere (Table 10, Figure 111). The abundance of the goby, Pseudogobius olorum, also differed significantly among locations with greater abundances occurring at both locations in Griffins Bay and Boat Harbour than elsewhere (Table 10). The abundance of transparent gobies, Gobiopterus seniivestitus, and hardyheads, Atherinosoina microstoina, varied between sites at most locations (Table 10).
3.2.2.2.2 Sizes of Fish
All the fish caught by beach seining were juveniles except for some species of mullet (Liza argentea, Mugil cephalus and Myxus elongatus), where a few individuals caught were of adult size (Table 11). Sand mullet, Myxus elongatus, were abundant enough to compare their size distributions among locations (Figure 12). The locations at Griffins Bay show similar distributions in their lengths to the other locations. A few larger individuals were caught at location B in Griffins Bay, Windang Channel and Hennegar Bay.
24 The Ecology Lab Pty Ltd Griffins Bay sand extraction - Marine Ecology - Final Report, April 1995
3.3 Commercial Fishing
Fishing is largely regulated in New South Wales by the Fisheries and Oyster Farms Act and its associated regulations. Fishing activities are often subject to closures in various areas and at different times of the year. It may also be subject to restrictions on the types of gear that can be used. In Lake Illawarra, there are restrictions on the places and times that commercial fishing may take place. In particular, the entrance channel to the lake is closed to most forms of commercial fishing. Also, there are restrictions on the timing of some activities, such as mesh netting.
Under the Fisheries and Oyster Farms Act, it is an offence to obstruct recognised fishing grounds. For example, emplacement of objects in areas where beach hauling takes place would be in breach of the Act if fishing is significantly affected. Clearly, the present proposal has the potential to affect some fishing activities in Lake Illawarra. The following sections describe fishing practices in the lake, including the types of fishing and all the areas in which each activity is done, with emphasis on the waters around Griffins Bay. Trends in fishing in recent years are also described.
3.3.1 Description of Commercial Fishing Activities
At present, of the 100 licensed fishers in the Lake Illawarra area, approximately 50 use Lake Illawarra at some time during the year (W. Winter, NSW Fisheries Inspector, pers. comm.). The following description of the commercial fishing activities in Lake Illawarra was summarised from discussions with several local fishers, representatives of CFAC and the local NSW Fisheries Inspector.
I Prawning There are no seasonal closures on prawning in Lake Illawarra but the prawn season is generally from September through to May or June. Approximately 18 crews of 2 people each, deploy nets for prawns in Lake Illawarra (W. Winter, NSW Fisheries Inspector). There are several methods used to catch prawns. These include pocket set nets, snigging nets and running nets. The pocket set net method is used only in the entrance channel where fishing is restricted and places where nets may be deployed are allocated by ballot (18 crews). Pocket set nets are 5 m long with a mesh of 30-36 mm.
The snigging net method is used lake-wide outside of the entrance channel to the lake. Nets are generally 140 metres long with 220 metre hauling lines on each side and with a mesh size of 30 -
25 The Ecology Lab Pty Ltd Griffins Bay sand ext raclion - Marine Ecology Final Reprrt, April 1995
36 mm. By-catch from this method includes small fish and blue-swimmer crabs. This method is prohibited on weekends and public holidays and requires I licensed fisher.
Prawn running nets are used lake-wide but predominantly on the eastern and northern shores of the lake (see Figure 13). With respect to Griffins Bay, they are used on the northern shore near and within Griffins Bay and along the south-eastern shore between Joes Bay and Primbee Bay. Prawn running nets rely on the presence of currents and the movement of prawns for a successful catch. The net is set in shallow water and is shot out into deeper water, sometimes into deeper channels. This method requires 2 licensed crew and the net can only be shot for 1 hour at a time. The net dimensions are 140 m long and approximately 3 m deep with a mesh size between 25 - 36 mm. The season is from September through to May/June and there is no temporal closure imposed.
Meshing for fish and crabs Meshing for fish and crabs occurs lake-wide, including the area proposed for dredging. The splash method is done all year-round whereas the set net method is allowed only in winter. Nets may not be left unattended. The size of the mesh depends on the species targeted e.g. bream - 100 mm, mullet - 80 mm, flathead - 70 mm.
Hauling for fish Hauling for fish also occurs lake-wide but requires shallow areas to haul the net onto and a lack of any obstructions on the hauling ground. Hauling in Lake Illawarra is done from autumn through to spring as there is a closure on hauling from the end of November until March throughout the lake. The hauling nets are generally 725 m long with 750 m hauling lines and the mesh is from 80 mm to 30 mm in the smallest part of the bunt. Hauling is done in many locations along the eastern and western shores. The area proposed for dredging appears to be one of a relatively large number of recognised hauling grounds.
Cockles Cockles are collected by hand within seagrass beds on the eastern shore of the lake up to the entrance into Griffins Bay, on the western side near Purrah Bay and to the west of Bevans Island. There are up to 4 harvesters and the amount harvested is variable depending on price.
26 The Ecology Lab Pty LId Griffins Bay sand extraction - Marine Ecology - Final Report, April 1995
3.3.2 Commercial Fisheries Statistics for Lake Jilawarra
3.3.2.1 Temporal Comparisons
Table 9 summarises the results of analyses comparing the weight of commercial species caught by fishers among years from 1985 to 1992. Graphical presentations of the total amount caught annually for some of these species appear in Figure 9. For most species, significant variation occurs in the amount caught from year to year (Table 12). The total catch of commercial species also varies from year to year, with 1985 being the least productive year and 1987 the most productive and other years were not significantly different from each other. Although years were significantly different in the total amount of finfish caught (excludes crustaceans and molluscs), these differences were not resolved by the SNK test (Table 12).
For most species of finfish, there were significant differences in the amount caught from year to year. The exceptions were; river garfish (Table 12, Figure 14c) and silver biddys (Table 12) which showed no changes in the amount caught among years. Peaks in the amount caught per year differ for some species. For instance, yellowfin bream and luderick were caught in their greatest numbers in 1987; flathead, mullet and whiting peaked in 1989 and leatheijackets peaked in 1988 (Table 12, Figure 14d,e,f,g,h).
Eastern king prawns were variable in the amount caught per year, the catch being greatest in 1985 and least in 1992 (Table 12, Figure 14i). The catch of school prawns, however, was not significantly different among years, largely because of the huge variability within individual years (Table 12). The amount of school prawns caught peaked in 1990 and 1991 (Figure 14j). Mudcrabs and blue-swimmer crabs were caught in variable amounts from year to year although both species were collected in significantly greater amounts in 1992 (for blue-swimmers) and in 1991 and 1992 (for niudcrabs) (Table 12, Figure 14k).
Cockles were harvested in significantly different amounts during the years 1985 to 1992 (Table 12). Negligible amounts were collected in 1985, 1986, 1987, 1989 and 1990. In 1992, twice as many cockles were harvested compared to any previous year (Figure 141).
In summary, there were differences in the catch among years for some species, but there is no indication that there have been substantial changes overall in the amount of fish caught between
27 The Ecology Lab Pty Ud Griffins Bay sand extraction - Marine Ecology - Final Report, April 1995
1985 and 1992. The exceptions to this are cockles, blue-swimmer crabs and mudcrabs which were
harvested in increasing amounts in the 1990's. I
3.3.2.2 Comparisons with other NSW lakes
Lake Illawarra is ranked 11th out of 41 major estuaries in NSW in terms of its production (kg) of 37 major species of commercial fish during 1990/91 (NSW Fisheries Statistics). Table 13 summarises some of these data by examining 15 species caught in Lake Illawarra compared to that of 6 other similar lakes in NSW. In this comparison, Lake Illawarra produced the biggest catch of cockles and eastern king prawns and a substantial catch of garfish, bream, flathead, luderick, sea mullet and school prawns. On this basis, it is concluded that Lake Illawarra has a regionally significant commercial fishety, particularly for prawns and cockles.
3.4 Recreational Fishing
3.4.1 Description of Recreational Fishing Activities
The local NSW Fisheries Inspector estimates that some 90% of recreational fishing for finfish occurs in the channel entering Lake Illawarra. The popularity of the channel was confirmed in discussions with some members of the Windang Hotel Fishing Club and observations made by TEL during field sampling. Members of the Windang Hotel Fishing Club maintained that very little recreational fishing is done in or near Griffins Bay and that most occurs off Bevans Island where bream and luderick are caught. There are, however, a few reefs near the entrance to Griffins Bay that are used by recreational fishers for catching bream. New jetties built around Griffins Bay may allow more people to fish from them.
Recreational prawning may occur in many areas of shallow, suitable water in the lake. The majority of recreational fishers, however, use the entrance channel to the lake and to a lesser extent, the eastern shore, for prawning. Recreational fishers are allowed to use scoop nets in these closure areas. There are no seasonal closures but recreational prawning mainly occurs in summer. In the past, prawns were collected in the back of Griffins Bay using 20 foot dragnets (W. Winter, pers. com.).
The 'squirt' worm (Australonereis ehiersi) and 'flippers' (Cullianassu spp.) are used for bait and are collected using a suction core in shallow areas in many places within the lake such as the entrance
28 I
The Ecology Lab Pty Ud Griffins Bay sand extraction - Marine Ecology - Final Report, April 1995
channel and the eastern shore entering Griffins Bay. 'Blackfish weed' (probably Enteromorpha sp.) is also used as bait and is often collected in the shallows on the eastern shore of the lake as far north as the entrance into Griffins Bay, near the Oasis Motel and at the mouths of several small creeks that run into the lake.
On the basis of our discussions, we conclude that most recreational fishing in Lake Illawarra is in I the entrance channel, and that Griffins Bay is of limited significance to recreational fishing. This may change as a result of foreshore improvements, which may increase access to the water.
3.5 Conclusions from Field Studies I 3.5.1 Benthic Macrofauna I The assemblages of benthic macrofauna in Griffins Bay were distinctive when compared to those from similar sandy sediments nearby along the eastern foreshore and from muddy sediments at I two locations within Lake Illawarra. The benthic macrofauna appear to vary with the type of sediment (i.e. sandy versus muddy) and the location within the sandy sediment habitat. This is an I important result because the dredging associated with this proposal would directly remove an area of sandy-sediment habitat and, indirectly, it may change the type of sediment found around the I dredged area through the dispersal of fine sediments.
The abundance of individual species of benthic macrofauna did not differ between Griffins Bay and the reference area - differences were generally greater among the smaller spatial scales of locations and sites within each area. Although locations in Griffins Bay were only 100's metres I apart, the abundance of macrofauna was highly variable in Griffins Bay and, to a lesser extent, the reference area. Thus, Griffins Bay is not unique in the abundance of numerically dominant taxa or I the total number of taxa. Provision for the large variability in the abundance of benthic macrofauna would by necessary if monitoring is required in the future, by sampling at several spatial scales and at several reference locations for an informative comparison. Sampling once has provided a 'snapshot' view of the distribution and abundance of benthic macrofauna in the lake but it has not provided a measure of temporal variability, which would also be necessary should I monitoring be required. I I 29 The Ecology Lab Pty Ltd Griffins Bay sand extraction - Marine Ecology - Final Report, April 1995
3.5.2 Fish and Mobile Invertebrates
The methods of beam trawling and beach seining used to sample fish and mobile invertebrates, were deployed in different sampling locations and collected a different range of species. Most fish caught by these methods were smaller-sized fish and juveniles, with the exception of a few adult mullet caught in the beach seines. Slightly more fish and mobile invertebrates were caught by beam trawling than beach seining whereas more species were caught using beach seines (50 species compared to 38 species). Both methods were used so that a broader range of species were sampled overall.
The number of species and the number of individuals sampled using both methods varied among locations and sites. Generally, the locations at Griffins Bay were within the range of variation for all the sites sampled. There was a noteworthy exception, however. The abundance of juveniles of commercially important species caught by beach seining was greater at the location along the northern shore of Griffins Bay compared to the other locations. Species contributing most to this result were river garfish, sand whiting and tarwhine. On this basis we conclude that this area of Griffins Bay appears to be a relatively important habitat for juvenile fish. It should be noted that this site was located within approximately 100 m of previously dredged areas completed in 1991.
Each location sampled was fairly distinctive in the structure of the assemblages of fish and mobile invertebrates. Locations differed in the presence and relative abundance of species. In some cases, the locations at Griffins Bay differed just as much from each other as they did from the other locations in the lake. Notably, the assemblage sampled by beam trawls at the back of Griffins Bay had large numbers of a goby, Pseudogobius olorum, compared to other places. The assemblages sampled by beach seining were even more distinctive between locations. Most notably, the entrance to Griffins Bay was characterised by the greater abundance of hardy-heads, Atherinsoma microstoma and the absence of juveniles of yellowfin bream, blue groper, tarwhine, flat-tail mullet, perchlets and luderick
These results indicate that areas within Griffins Bay support a diverse fauna of fish and mobile invertebrates that falls generally within the range of abundance and diversity of other locations examined in the lake and should not, on this basis, be regarded as depauperate or degraded. Again, sampling more than once is necessary to determine if these patterns are consistent through time.
30 The Ecology Lab Pty Ud Griffins Bay sand extradion - Marine Ecology - Final Report, April 1995
3.5.3 Commercial and Recreational Fisheries I Information on the commercial catch from different areas within Lake Illawarra is not available so that an assessment of the relative catch from areas in and around Griffins Bay compared to other places in Lake Illawarra is not possible. Griffins Bay and its surrounds are, however, recognised as areas for haul and mesh fishing and places where prawn running nets and snigging nets are set. I These types of fishing activities also happen at other places within Lake Illawarra. The commercial catch of species from Lake Illawarra, although variable from year to year and species to species,
I does not indicate substantial changes overall in the amount of fish caught in the short-term, between 1985 and 1992. There are several aspects of the current proposal which would effect I commercial fishing operations around Griffins Bay and this may in turn effect the production of Lake Illawarra. These issues will be discussed further in Section 4.2.
Most recreational fishing and prawning occurs at the entrance channel into Lake Illawarra. The current proposal is unlikely to impact on the activities of recreational anglers.
1 4.0 ASSESSMENT OF IMPACTS
1 4.1 Brief Description of the Proposal
The proposed extraction of sand would be done by dredging in stages over a period of 10 to 13 years and involve three major components; i) dredging of 4 major areas (denoted Areas A to D), ii) dredging an extension of the channel already in Griffins Bay and iii) creation of an island off Purry Burry Point (Figure 15). The duration of the project would depend on i) the demand for sand and ii) which channel option is adopted (GI-ID, 1995). A summary of the details of these works considered relevant to assessing the impacts on the aquatic environment of dredging the different areas is in Table 14. More information is provided by the EIS (GHD, 1995).
Material dredged from the lake would be screened for rocks, shells and other debris greater than 5 mm before being transported to sandwashing and stockpiling facilities at Korrungulla Swamp. The material would be washed, the sand stockpiled for sale and the residue (sediment finer than 150 xm) returned via pipeline to the lake (SCE pers. comm.). The residue would be added to the coarse material already screened from the sediment to form an island and be used as back fill for dredged Area A.
31 The Ecology Lab Pty Ltd Griffins Bay sand extraction - Marine Ecology - Final Report, April 1995
The first stage of the dredging operation is the creation of embankments around the perimeter of the area designated to form the island and Area A before any dredging starts. The embankments would be made from the surrounding sediment, have a crest height of 1.5 m Al-ID (i.e. 1.2 m above the water level), outward facing slopes of 1:15 and function to prevent erosion of the island during the dredging process. The embankments would stay in place throughout the project and would be used as fill for Area A before capping the area with 50 cm of sand.
The island would be built in two phases. First, the residues from the dredging of Area A would be used to form the first part of the island. Any runoff water from the island would be channelled to Area A which would act as a sedimentation pond, allowing fine sediments to settle out before the water flowed into the lake. This first phase would take 4 months to complete. This part of the island would then be capped by 50 cm of sand which would be suitable for vegetation by native grasses and shrubs (GI-ID, 1995). The second phase would involve placing a floating geofabric curtain on the western side of the island and filling behind it with residues from dredging Area B, Area C and the channel extension. This phase would be complete after 6 years.
Areas A, C and D would be dredged to a depth of -14 m Al-ID and only Area A would be backfilled to a depth sloping between -0.9 m to -1.6 m Al-ID as part of the current proposal. The backfilling of Areas C and D depend on receiving fill from other dredging programs under the control of the Lake Illawarra Authority and are subject to separate approval. Areas C and D would be isolated from the rest of the lake by embankments while they were being dredged. The embankments would be made from material excavated in the surrounding area. The description of the proposal in the previous EIS (KayBond Pty Ltd, 1993) did not involve the isolation of these areas from the rest of the lake. In response to comments on the previous EIS, the dredging proposal now includes the embankment surrounding the deep hole as a way to reduce the risk of movement of stagnant water from the deep hole to the rest of the lake and reduce the potential for the deep hole to be a 'sink' for debris such as dead seagrass and algae. After completion of the dredging contract, the maintenance of the island and embankments around dredge Areas C and D would become the responsibility of the Lake Illawarra Authority (GI-[D, 1995).
Previous dredging in Griffins Bay has created a 50 m foreshore buffer zone which runs adjacent to the shore and is -0.8 m deep Al-ID. Seaward of the buffer zone is a horses hoe-shape d channel, 50 m wide with a slope of 1:6, which was dredged to -1.5 m deep AHD around Griffins Bay. As part of this proposal the existing channel on the southern side of Griffins Bay would be extended out into the main bodv of the lake. The proposed extension of the channel would be 50 m wide, with
32 The Ecology Lab Pt y Ltd Griffins Bay sand extraction - Marine Ecology - Final Report, April 1995
side slopes of 1:6 except where the channel cuts the underwater sand bank, reducing the side slopes to 1:12. Two options are being evaluated for the positioning of the channel extension I (G1-[D, 1995). Option I would pass north of Purry Burry Point and due west. Option 2 would cut through the northern tip of Purry Burzy Point and head in a more north-westerly direction. More I sand would be removed from Areas C and D under Option 2 (Table 14).
In summary, the main parts of this proposal that need to be considered in assessing the impacts on the aquatic environment are:
I i) the direct removal of habitat such as seagrass and unvegetated benthic substratum by dredging,
I ii) the indirect effects of dredging on surrounding habitats;
the direct creation of new habitats such as the island, the channel and the enclosed deep hole; and
the indirect effects of the newly created habitats.
4.2 Dredging Areas A to D and the Channel Extension
The impacts of the dredging part of the proposal are discussed below in two sections: impacts during dredging (Section 4.2.1) and long term impacts after dredging is completed (Section 4.2.2).
I 4.2.1 Impacts During Dredging
Changes to the marine environment associated with the dredging activity which may lead to I impacts on biota include:
i) the release and circulation of suspended fines, nutrients, heavy metals and other contaminants I from the removal and backfilling of sediments in the dredged areas;
ii) changes in water quality (turbidity, salinity, temperature, dissolved oxygen, and nutrients);
iii) physical damage and alteration of the bottom topography of the lake through the activities of boats, equipment and people associated with dredging operations;
iv) creation of barriers to movement of fish and mobile invertebrates e.g. embankments and island;
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