The Recovery of the Holothuria scabra (sandfish) population on Warrior Reef, Torres Strait. Final Report

Transcription

1 The Recovery of the Holothuria scabra (sandfish) population on Warrior Reef, Torres Strait. Final Report CSIRO Marine and Atmospheric Research A report for the Australian Fisheries Management Authority Nicole Murphy, Tim Skewes, Francis Filewood* (CSIRO) Charles David (*Iama Island traditional owner) Paul Seden, Annabel Jones (AFMA) June Project 2009/846

2 ACKNOWLEDGEMENTS This project was funded by AFMA and CSIRO Wealth from Ocean Flagship. It benefitted greatly from the guidance and input of AFMA and TSRA staff, members of the TS Hand Collectables Working group, and the CFG, PBC and Councillors of the Central Torres Strait communities. Traditional Owners from Iama, Francis Filewood and Charles David, and AFMA staff from the Thursday Island Office, Paul Seden and Annabel Jones, also participated in the survey. We would also like to thank the Captain and crew of the vessel MV San Miguel for their able assistance during the survey. This publication should be cited as: Murphy, N.E., Skewes, T.D., Filewood, F., David, C., Seden, P., Jones, A The Recovery of the Holothuria scabra (sandfish) population on Warrior Reef, Torres Strait. CSIRO Wealth from Oceans Flagship. Draft Final Report, CMAR Cleveland. 44 pp. ii

3 Enquiries should be addressed to: Nicole Murphy CMAR (07) Distribution list Annabel Jones, Paul Seden Charles David Steve Hall AFMA Iama Island CFG TSRA Copyright and Disclaimer 2011 CSIRO To the extent permitted by law, all rights are reserved and no part of this publication covered by copyright may be reproduced or copied in any form or by any means except with the written permission of CSIRO. Important Disclaimer CSIRO advises that the information contained in this publication comprises general statements based on scientific research. The reader is advised and needs to be aware that such information may be incomplete or unable to be used in any specific situation. No reliance or actions must therefore be made on that information without seeking prior expert professional, scientific and technical advice. To the extent permitted by law, CSIRO (including its employees and consultants) excludes all liability to any person for any consequences, including but not limited to all losses, damages, costs, expenses and any other compensation, arising directly or indirectly from using this publication (in part or in whole) and any information or material contained in it. iii

4 Contents ACKNOWLEDGEMENTS... ii Summary... 1 Management recommendations Introduction Burying behaviour for Holothuria scabra BIslander consultation Methods Study area - Warrior Reef Previous Warrior Reef surveys Field sampling Data analysis Iama Island survey Results Survey Warrior Reef relative density Holothuria scabra juveniles Size frequency Iama Reef survey Discussion Future surveys Management recommendations References Appendix A - Survey Information flyer posted on Island notice boards Appendix B - Torres News article Appendix C Terms used in stratified analysis iv

5 List of Figures Figure 2-1. Warrior Reef, Dungeness Reef and Zagai Island, Torres Strait and their habitat composition (derived from survey data and satellite image analysis). 8 Figure 3-1. Locations of sample sites on Iama Island, Dungeness Reef, Warrior Reef and Zagai Island, with observed sandfish (Holothuria scabra) densities. 11 Figure 3-8. Sandfish (Holothuria scabra) density (per ha) from six abundance surveys in November/January1995/96, January 1998, January 2000, October 2002, January 2004 and February 2010 on Warrior Reef, Torres Strait (northern and southern section split at 9 42'). 12 Figure 3-9. Sandfish (Holothuria scabra) density (per ha) observed during the 2010 Warrior Reef survey for juvenile (<14 cm TL), and adult (>14 cm TL) sandfish. 13 Figure 3-2. Warrior Reef strata, delineated from habitats and survey data (Skewes et al., 2001) and density of sandfish in Strata used for calculation of stratified density estimates.15 Figure 3-3. Average number of sandfish (Holothuria scabra) per Ha for repeated sites on Warrior Reef for the six sample years. (Error bars are 1 s.e.) 18 Figure 3-4. Average density of juvenile (<14 cm TL), and adult (>14 cm TL) sandfish (Holothuria scabra) per ha for repeated measures sites on Warrior Reef for the six sample years. (Bottom graph shows adult only) (Error bars are 1 s.e.) 18 Figure 3-5. Average number of sandfish (Holothuria scabra) per ha for repeated measures sites split into northern (diamonds) and southern (squares) sections of Warrior Reef for the six sample years. Section split at 9 42'. (Y axis has been resized in bottom graph to better define data pattern) (Error bars are 1 s.e.) 19 Figure 3-6. Average number of adult sandfish (Holothuria scabra) per ha for repeated measures sites split into northern (diamonds) and southern (squares) sections of Warrior Reef for the six sample years. Section split at 9 42'. (Error bars are 1 s.e.) 20 Figure 3-7. Average number of juvenile sandfish (Holothuria scabra) per ha for repeated measures sites split into northern (diamonds) and southern (squares) sections of Warrior Reef for the six sample years. Section split at 9 42'. (Y axis has been resized in bottom graph to better define data pattern) (Error bars are 1 s.e.) 20 Figure Change in Holothuria scabra morphology from juvenile, through to the adult stage. 21 Figure Change (ventral side) in Holothuria scabra morphology from juvenile, through to the adult stage. 22 Figure Juvenile Holothuria scabra expelling its cuvierian tubules. 22 Figure Length frequency distribution of sandfish (Holothuria scabra) for the total number of sites surveyed on Warrior Reef, from the 2010 survey. Size of modes (cohorts) from modal analysis shown in red. 23 Figure Length frequency (mm Total Length (TL)) distribution of sandfish (Holothuria scabra) for repeated measures sites from Warrior Reef, for the six sample years scaled to density (No. per Ha). Dashed line represents14 cm TL, the age of sexual maturation for sandfish H. scabra. Solid line represents 18 cm TL, the fishery minimum legal size. 24 Figure Location of sampling sites on Iama (Yam) Island, Torres Strait, showing cover of seagrass by species (max cover 95%). Green shaded area indicates seagrass habitat considered suitable habitat for sandfish, Holothuria scabra. 25 Figure Seagrass species and total cover at survey transects on Iama Island, Torres Strait. 26 v

6 INTRODUCTION List of Tables Table 2-1. Timing, survey type and number of sample sites for sandfish surveys on Warrior Reef, Torres Strait Table 3-1. Torres Strait Holothuria scabra survey, 2010; transect and sampling method Table 3-2. Comparison of sampling efficiency for detection of sandfish (Holothuria scabra) for transect survey type Table 3-3 Strata mean abundance (y h ) and variance (s 2 h) estimates for the calculation of standing stock estimates for sandfish (Holothuria scabra) for Warrior Reef in February Descriptions of column headings are listed in Appendix C Table 3-4 Stratified mean (y st ), variance (v(y st )) and standing stock estimates and 90% confidence intervals for sandfish (Holothuria scabra) on Warrior Reef in February Table 3-5 Strata mean abundance (y h ) and variance (s 2 h) estimates for the calculation of standing stock estimates for adult (>14 cm TL) sandfish (Holothuria scabra) for Warrior Reef in February Descriptions of column headings are listed in Appendix C Table 3-6 Stratified mean (y st ), variance (v(y st )) and standing stock estimates and 90% confidence intervals for adult (>14 cm TL) sandfish (Holothuria scabra) on Warrior Reef in February Table 3-7 Strata mean abundance (y h ) and variance (s 2 h) estimates for the calculation of standing stock estimates for fishery (>18 cm TL) sandfish (Holothuria scabra) for Warrior Reef in February Descriptions of column headings are listed in Appendix C Table 3-8 Stratified mean (y st ), variance (v(y st )) and standing stock estimates and 90% confidence intervals for fishery (>18 cm TL) sandfish (Holothuria scabra) on Warrior Reef in February Table 3-9. Number of sites where sandfish (Holothuria scabra) were observed out of 41 sites on Warrior Reef (during repeated measures surveys) Table Average density (per ha) of sandfish (Holothuria scabra) sampled at 41 repeated sites in the seagrass habitat during six abundance surveys in November-January 1995/96, January 1998, January 2000, October 2002, January 2004 and February 2010 for the whole study area, for adult (>14 cm TL) and juvenile (<14 cm TL) sandfish, and for the northern and southern sections (split at 9 42'). Standard error (s.e.) of estimate is also shown in brackets Table Average density (per ha) of sandfish (Holothuria scabra) sampled at 41 repeated sites in the seagrass habitat during six abundance surveys for several size ranges Table Output from MIX Modal analysis of population size frequency collected at 70 sites in February 2010 (Fitting Lognormal components; Sigmas constrained to be equal) (Standard errors in brackets). Chi-squared (df 16) = (P = ) vi Warrior Reef survey, December 2010

7 ACRONYMS CSIRO CMAR TSHCWG CFG PBC TS BDM GPS Commonwealth Scientific Industrial Research Organisation CSIRO Marine and Atmospheric Research Torres Strait Hand Collectable Working Group Community Fisher Group Prescribed Body Corporate Torres Strait Bêche-de-Mer (working group) Global Positioning System vii

8

9 SUMMARY SUMMARY A relative abundance survey of sandfish, Holothuria scabra on Warrior Reef was carried out in February We surveyed 127 sites during the survey, including 70 on Warrior Reef, 30 on Dungeness Reef, 7 on Zagai Island and 20 on Iama Island. The densities of sandfish from the survey were compared to previous surveys undertaken in 1995/96, 1998, 2000, 2002 and Survey densities were found to be at similar levels to 2004, and again were ~80% less than observed in 1995/96; at which time the population was considered to be overexploited. Adult (>14 cm TL) sandfish were found to have decreased in density since the 2004 survey; however, the density of fishery sized individuals (>18 cm TL) was the highest since Juveniles showed a large increase compared to Even taking into account the low precision of the biomass estimate, and the potential for survey bias due to burying, the stock is unlikely to be more than one third of virgin biomass levels. No sandfish were observed on Dungeness Reef, and only low densities were observed on the back reef flat at Zagai Island. In the 2010 survey, significant decreases were found in the southern area of Warrior Reef and significant increases found in the northern area, possibly reflecting the higher density of juvenile sandfish that appear to settle preferentially in this part of Warrior Reef. Unlike previous surveys, the sandfish population in 2010 was made up of possible 7 year classes, with relatively high densities of older (4 y.o. and older) individuals. These larger individuals represent a significant breeding potential and may result in a substantive recruitment in early There was an indication during the survey of the potential recruitment of a large number of very young juveniles to the fishery, which supports this observation. While no sandfish were seen on transects at Iama Island, a small number of sandfish were counted in the seagrass habitat of the back reef lagoon. The area of suitable habitat for sandfish on Iama Island was estimated to be 39.9 Ha. This area has a potential carrying capacity of over half a million adult sandfish, or approximately 21 t (gutted weight), based on maximum density observations for sandfish. It is difficult to determine which factors (including differential burrowing rates, illegal fishing or low recruitment) are the cause of the continued low sandfish density in A small experimental fishing exercise would be useful to further assess attribution factors by a comparison with historical catch rates. The fishing effort would be controlled to a level where there would be little risk to the overall population stock status (4 fishing units and <2 tonnes), even at the more pessimistic estimates of current stock size. This will enable further investigation of the accuracy of sandfish relative density estimates and provide additional information on population dynamics and the stock recruitment relationship. It would also offer a significant training and community co-management opportunity. Further assessment of the fishery will allow for a continued monitoring of the population status and possible recovery, focused towards an eventual staged reopening of the population, and the future sustainable fishing of sandfish on Warrior Reef. CSIRO Wealth from Oceans Flagship 1

10 INTRODUCTION Management recommendations 1. We recommend that the fishery remain closed until such a time as it can be demonstrated that the fishery population has recovered to at least 50% virgin biomass. It could be that some limited fishing be allowed before this, however, it must be tightly controlled and there should be minimal risk to the recovering population and a clear benefit within a future co-management framework. 2. Continue to monitor the fishery on a yearly or biyearly basis to provide information on the recovery of the sandfish population, and potentially on burying dynamics and the stock recruitment relationship. 3. Urgently establish strong links with PNG NFA to establish a joint approach to research and management of the Torres Strait sandfish population. 2 Warrior Reef survey, December 2010

11 INTRODUCTION 1. INTRODUCTION The sandfish (Holothuria scabra) fishery of Torres Strait provides an opportunity for Islanders to gain significant income at the community level. Sandfish are a high value species, with high quality dried product currently fetching US$ per kg of dried product (Global Aquaculture Advocate, Jan 2011), which at that value equates to over $5 per kg wet gutted weight. The sandfish fishery on the Australian side of Torres Strait began around 1992 and was heavily exploited over a three-year period from 1994 to 1996, with 1200 to 1400 tonnes (wet gutted weight) estimated being caught in equivalent to at least $6M at today s market price. The first fishery independent survey of the sandfish population was carried out, by CMAR, in late 1995 and found that the density of the breeding year-class (2+ yr old) was relatively low (Long et al., 1996). A second survey in January 1998 found that the population density was lower than in 1995 and that both recruiting (1 year old) and breeding year-classes (2 yr old) were depleted (Skewes et al., 1998). Because of this finding, the fishery was closed in January The sandfish population was surveyed again in January 2000 (Skewes et al., 2000) and 2002 (Skewes et al., 2003), which showed a small recovery. It was hoped that this might provide the basis for a strong recruitment to the fishery by early 2004, however, another survey in 2004 (Skewes et al., 2006) showed that sandfish density actually decreased to similar levels as in 1998, when the fishery was closed. There was some evidence that poaching was occurring on the Australian side of the border by PNG Nationals, and the conclusion was that this was the primary reason for the lack of a recovery in the sandfish population; so AFMA instigated a major operation to maintain surveillance on the PNG-Australian border and apprehend and deter poachers. This operation has now been active for three years and during that time there have been significant apprehensions. By all accounts, the operation has been considered to be successful. Given the apparent success of the surveillance operation that may have reduced illegal poaching of the population, and the subsequent closure of the PNG fishery in late 2009, there was a possibility of some recovery in the Warrior Reef sandfish population. After consultation with management and fisher representatives, it was decided to carry out a relative density survey of the sandfish population of Warrior Reef in early The continued monitoring of the density and dynamics of the depleted sandfish population was deemed essential to developing an understanding of the recovery dynamics of this, and other sea cucumber populations. The survey will also help determine recovery targets for renewed fishing of this species. The outputs from the survey includes an analysis of the relative density of sandfish compared to previous surveys and recommendations for future management strategies. We also gathered information on gross environmental parameters, not only for assessing the effects of fishing, but for mapping and monitoring the environment in general. The information from the survey will be input into developing co-management frameworks being developed for the Torres Strait Hand Collectables fishery, and the Decision Support Tool being developed by CMAR for management strategy development for Torres Strait fisheries. CSIRO Wealth from Oceans Flagship 3

12 INTRODUCTION 1.1 Burying behaviour for Holothuria scabra Holothuria scabra show various cyclical patterns of burying depending on age (Yamanouchi 1939, 1956; Battaglene 1999; Mercier et al., 1999, 2000; Uthicke 2001). Knowing when H. scabra are buried is crucial for conducting visual population surveys for conservation and sustainable management. Juvenile H. scabra are synchronised by day-night regimes, burying at sunrise and reemerging at sunset (Mercier et al., 1999). When juveniles reach about 40 mm in length, they respond more to diel changes in temperature, burying in the middle of the night and emerging late in the morning (Mercier et al., 1999; Wolkenhauer & Skewes, 2008). In clear weather, H. scabra between 40 and 140 mm were found to bury at sunrise, surfacing around midday to early afternoon, with a phase shift towards longer burying noted during rain (Hamel et al., 2001) as supported by Wolkenhauer & Skewes (2008). Studies on the burying activity of adult (>14 cm TL) H. scabra are surprisingly scant, though previous studies have shown differences in burying (Yamanouchi, 1939, 1956; Purcell & Kirby, 2005) and feeding behaviour (Yamanouchi 1939, 1956; Wiedemeyer, 1992; Mercier et al., 1999; Hamel et al., 2001; Purcell et al., 2004) with location, temperature and habitat. The most recent study on adult H. scabra behaviour from Moreton Bay (south east Queensland) showed that burying and feeding behaviour were strongly correlated to changes in water temperature (Wolkenhauer & Skewes, 2008). Buried periods were found to increase with decreasing temperature (Wolkenhauer & Skewes, 2008), however, at temperatures above 18 C, the majority of adult H. scabra were found exposed and feeding between 13:00 and 20:00 hrs and most buried and inactive between 01:00 and 09:00 hrs. A long term mesocosm study corroborated this finding, showing that sandfish were less likely to bury during summer (December-February; 24 C), with at least one month where they did not bury at all (Wolkenhauer et al., in prep). Limited field observations of burying activity have been collected on Warrior Reef (Skewes et al., 2000). Enclosure experiments and repeated transects showed that nondetection due to total or partial burying, particularly in dense seagrass beds and during high tide, was sometimes as much as 60%. This bias was found to be less in areas with moderate to low seagrass cover. As high seagrass cover represented 11% of the habitat surveyed, compared to 63% for sites with moderate to low seagrass cover, the overall underestimation or bias rate would be considerably less than 60% (Skewes et al., 2000). Visual surveys of H. scabra distribution and abundance need to be conducted at consistent diel and seasonal timing, if results are to be compared with previous data. Knowledge of burying behaviour to date, supports the most suitable time to conduct populations surveys of H. scabra in the southern hemisphere, is during summer (December to February), from midday to late afternoon (Wolkenhauer & Skewes, 2008), in clear weather (Hamel et al., 2001). The 2010 survey of H. scabra on Warrior reef was based upon the six previous CMAR surveys undertaken from 1995 to The timing of the survey coincided with the seasonal and lunar phase cycles of the previous surveys, designed to reduce 4 Warrior Reef survey, December 2010

13 INTRODUCTION differences in observer rates resulting from changes in burying behaviour caused by temperature and tidal factors. The survey was carried out at approximately the same time of day (1000 hrs to 1400 hrs) and the same tide (high tide) as previous years. Conditions during most of the survey were optimal with low winds (0-10 kts) and with good water visibility (3-6 m visibility). CSIRO Wealth from Oceans Flagship 5

14 INTRODUCTION 1.2 1BIslander consultation This project included a high level of interaction with Torres Strait Islanders, both in the design and carrying out of the survey, and interpretation of results. Torres Strait Islander representatives from the sea country of Warrior Reef (Iama Island) were collaborated with during the lead up to the survey and a community researcher (Francis Filewood) was engaged as a CSIRO employee for the field survey. This project has been the focus of discussions at the Torres Strait Hand Collectable Working Group (TSHCWG) meetings since 2006, and also directly with Community Fisher Group (CFG) representatives from the central Islands over the past two years. There has been a strong desire for this survey from Torres Strait Islander representatives for some time. The projects overall design was ratified by the TSHCWG in 2009 and the detailed survey design was discussed and ratified during consultations with islander representatives, including CFG, PBC and Island Councillors before the survey in January Letters and communication to were sent to Islander representatives on several Island communities surrounding Warrior Reef in late 2009, and flyers advertising the upcoming survey was posted on Island notice boards (Appendix A). A public meeting was held on Iama Island in January 2010, where the history, status and previous research carried out on the Warrior Reef sandfish fishery was presented. Based on the response to this meeting, we believe that there is a high level of awareness of the fishery status among traditional owners. Visit to Iama Island before survey by Tim Skewes. This included a presentation of scientific knowledge of Torres Strait sea cucumber fisheries to a community meeting, in conjunction with AFMA staff, and an extensive Q and A session. Involvement in the project by Iama traditional owner, Francis Filewood. Iama traditional owner Charles David assisted with the Iama Reef survey. 6 Warrior Reef survey, December 2010

15 METHODS 2. METHODS 2.1 Study area - Warrior Reef The sandfish, Holothuria scabra, population in Torres Strait is almost solely found on the Warrior Reefs, and historically at least, on Dungeness Reef. The three main reefs of the Warrior reef complex, Auwamaza, Wapa and Warrior cover a total area of 48,990 ha. The two main reefs in the Papua New Guinea (PNG) section of the Warrior reef complex, Auwamaza and Wapa reef combined (32,488 ha) are twice as large as Warrior Reef (16,502) in the Australian section of the Warrior reef complex. The Warrior Reef complex is a dominant feature of Torres Strait and extends over a third of the way across Torres Strait as an almost continuous boundary (Figure 2-1). Warrior Reef is one of the largest reefs in Torres Strait. It is approximately 34 km long north-south and averages about 5 km wide and has an area of 165 km 2 (Long et al., 1997). The northern end of the reef abuts the Australian, PNG border. Most of the reef top of the Warrior reef complex is exposed at low tide and are covered by soft sediments. The eastern margins of Warrior and Wapa reefs are ~ 1 m higher than the reef flat, central and back regions of these reefs. The reef crest of the elevated eastern margin is a continuous pavement of coralline algae and pavement is not common in the central regions of the reef (Long et al., 1997) (Figure 2-1). Behind the crest is a transition zone consisting of coralline algal pavement and coral interspersed with shallow pockets of water in which the sea urchin Diadema spp. aggregate in large numbers. Rubble and consolidated rubble are higher here than further inshore. Boulders are not a dominant feature of the top of the reefs. Behind the reef crest zone on Warrior Reef is a band of dense seagrass approximately 1.5 km wide and the seagrass thins out further west to form a mixed seagrass / sand zone along the western margins of the reefs (Long et al., 1997) (Figure 2-1). As the western edge of the reef is approached the water depth gradually increases to a zone of mixed and diverse assemblage of soft corals, algae, hydroids, sponges, coral and seagrass before dropping off to a mud bottom approximately 5 m deep behind these reefs (Long et al., 1997) (Figure 2-1). In contrast, Auwamaza reef is almost completely covered by seagrass except for a thin margin around the edge of the reef and sand patches scattered throughout the western regions of the reef. Along the northern and southern edge are a diverse array of reef building corals and algae, alcyonarians and other reef associated benthos (Long et al., 1997). CSIRO Wealth from Oceans Flagship 7

16 METHODS Figure 2-1. Warrior Reef, Dungeness Reef and Zagai Island, Torres Strait and their habitat composition (derived from survey data and satellite image analysis). 2.2 Previous Warrior Reef surveys In 1995, the primary sampling unit was a 700 x 700 m square, with the area subsampled using a 20 2 m transect. A grid of potential sample sites, located in the centre of each square, was superimposed on the Warrior Reef. Ninety three sites were selected at random from these. Sites were also sampled at regular intervals along the edge of the reef to check for sandfish in this habitat. 8 Warrior Reef survey, December 2010

17 METHODS In 2000, we used the results of the previous survey in November 1995 to optimally allocate the sample sites. The previous survey showed that most sandfish were found in the seagrass habitat, covering approximately one third of Warrior Reef, and that sandfish density was strongly correlated with seagrass cover (Skewes et al., 2001). Interviews with local fishermen carried out before the survey, also indicated that the fishery had previously been centred mainly on the seagrass beds on the eastern half of the reef. Subsequently, 50 sites were surveyed in the seagrass habitat that were sampled in 1995/96, an additional 74 sites from the original 700 m grid throughout the seagrass habitat, and 41 sites throughout the backreef habitat. Smaller relative density surveys were carried out in 1998, 2002, 2004 at 56 sites randomly selected from the original seagrass habitat sites sampled during the 1995/96 survey (Table 2-1) and 73 for the 2010 survey (Table 2-1). Table 2-1. Timing, survey type and number of sample sites for sandfish surveys on Warrior Reef, Torres Strait. Year Date Survey type Sites 1995; /11/1995; 9/1/1996 Full scale /1/1998 Relative /1/2000 Full scale /10/2002 Relative /1/2004 Relative /2/2010 Relative Field sampling The survey was carried out over a 6 day period from the 22 to 28 February Rapid marine assessment techniques developed, improved and applied by CSIRO for reef resource and habitat surveys in several areas of Australia, Papua New Guinea and the Seychelles were used (Skewes et al., 1998, Skewes et al., 2000, Skewes et al., 2006). The 2010 survey was based upon the six previous surveys undertaken from 1995 to The timing of the survey coincided with the seasonal and lunar phase cycles of the previous surveys, designed to reduce differences in observer rates resulting from changes in burrowing behaviour caused by seasonal and tidal factors. The survey was carried out at approximately the same time of day (1000 hrs to 1400 hrs) and the same tide (high tide) as previous surveys. Conditions during most of the survey were optimal with low winds (0-10 kts) and with good water visibility (3-6 m visibility). The sampling was done using a repeated measures design that is more powerful for detecting change in bêche-de-mer population abundance. This method has been previously used to assess the relative status of the sandfish fishery in Torres Strait (Skewes et al., 2003) and Moreton Bay (CSIRO, unpublished data, Skewes et al., 1998, Skewes et al., 1999; Skewes et al., 2000, Skewes et al., 2006). Field work was undertaken by a small team of divers operating from a dinghy and locating sample sites using hand-held GPS. On the reef-top, divers swam or walked along a 40m transect, and recorded resource and habitat information 1-2m either side of the transect line. Occasionally longer transects were swum, particularly on CSIRO Wealth from Oceans Flagship 9

18 METHODS Dungeness Reef where no sandfish were observed, where transects up to 576 m (measured with GPS) were carried out. We also carried out reef walks at low tide some up to 1 km long and repeated surveys of sites by snorkel and reef walks. Bêche-de-mer, trochus and other benthic fauna of commercial or ecological interest were counted and where possible, returned to the dinghy and measured as total length and then returned to the water. At each site, substrate was described in terms of the percentage of sand, rubble, consolidated rubble, pavement and live coral. The growth forms and dominant taxa of the live coral component and the percentage cover of all other conspicuous biota, such as seagrass and algae were also recorded. Estimates of gross environmental parameters collected during the survey, will be used to assess the effects of fishing and to map and monitor the environment in general. 2.4 Data analysis Density counts of sandfish at repeated survey sites were used to calculate population trends for the sandfish population on Warrior Reef. The analysis includes an assessment of recruitment from site counts and size frequency data, a technique that has been shown to be viable from previous surveys. The counts of H. scabra per transect were used to calculate an average and variance of the population abundance in the seagrass habitat on Warrior Reef. These abundance figures were then compared to the abundance figures for the same habitat surveyed since 1995/96. The survey results were also input into a stratified analysis to estimate the current stock size. To increase the accuracy of the stock size estimate, Warrior Reef was stratified into a backreef strata, which was all the reef west of the sandbanks, and four seagrass strata, which consisted of the eastern half of the reef split into four sections in a north-south direction. 2.5 Iama Island survey Iama Island representatives expressed a desire to investigate the potential for Iama Island lagoon for sea ranching of sandfish. To this end, we surveyed the northern and eastern reef flat and lagoon (where it is the widest), to quantify any sandfish population there. We also assessed the suitability of the lagoon for sea ranching in terms of habitat and area. 10 Warrior Reef survey, December 2010

19 RESULTS 3. RESULTS Survey Figure 3-1. Locations of sample sites on Iama Island, Dungeness Reef, Warrior Reef and Zagai Island, with observed sandfish (Holothuria scabra) densities. CSIRO Wealth from Oceans Flagship 11

20 RESULTS Figure 3-2. Sandfish (Holothuria scabra) density (per ha) from six abundance surveys in November/January1995/96, January 1998, January 2000, October 2002, January 2004 and February 2010 on Warrior Reef, Torres Strait (northern and southern section split at 9 42'). 12 Warrior Reef survey, December 2010

21 RESULTS Figure 3-3. Sandfish (Holothuria scabra) density (per ha) observed during the 2010 Warrior Reef survey for juvenile (<14 cm TL), and adult (>14 cm TL) sandfish. We surveyed 127 sites during the survey, including 70 on Warrior Reef (plus 3 resampled at low tide) (Table 3-1, Figure 3-1). Although most repeat (sampled in previous years) sites were 40 m transects, 20 sites were longer, with up to 1,049 m long transects surveyed in an exploratory sense to increase sampling area. In all, over 12 km of transects were surveyed, usually at 4 m width, covering a total area of 5.6 Ha. Despite extensive searching during the afternoon at low tide and during high tide the next morning, we did not see any H. scabra on Dungeness Reef. None were seen on transects at Iama Island (though we saw 4 off transect - see later section), and only 4 were observed at Zagai Island back reef, including the lagoon area behind the first line of mangroves (Table 3-1, Figure 3-1). On Warrior Reef, we observed 454 H. scabra at 28 of the 73 sites surveyed (Figure 3-1; Figure 3-2). The highest density site was again site 1752 in the northern half of Warrior Reef (Figure 3-1, Figure 3-3). This site has consistently had the highest density (except for 2002) (Figure 3-2), and as usual, it was dominated by juvenile (<14 cm TL) sandfish CSIRO Wealth from Oceans Flagship 13

22 RESULTS (>80%) (Figure 3-3). Adult (>14 cm TL; 0 375/Ha) and fishery (>18 cm TL; 0 281/Ha) H. scabra were mainly found in the southern half of Warrior Reef (Figure 3-3), and at no location were they highly aggregated to the same extent as the juvenile high density site. Table 3-1. Torres Strait Holothuria scabra survey, 2010; transect and sampling method. Location Snorkel Walks Resampled Total H.scabra (n) H.scabra (n/ha) Warrior Reef Dungeness Reef Zagai Island Iama Island Comparison of sampling methods for transects undertaken during the survey showed similar efficiencies between swim transects, repeat transects (low and high tide) and the combination of all sampling methods (swim, repeat and walk) (Table 3-2). Walking transects resulted in a higher proficiency (being the equivalent to dedicated searching) (Table 3-2). Table 3-2. Comparison of sampling efficiency for detection of sandfish (Holothuria scabra) for transect survey type. Sampling H.scabra Adults Juveniles Sites Statistic Ha -1 Ha -1 Ha -1 Average swim transects Average repeats Average all (combined) Average walks Survey abundance from 73 sites surveyed in February 2010 were used to estimate the standing stock of the entire H. scabra population (Table 3-3, Table 3-4); adult (>14 cm TL Skewes et al., 2000) population (Table 3-5, Table 3-6); and fishery (>18 cm TL) population (Table 3-7, Table 3-8) on Warrior Reef. Even taking into consideration the low precision of the estimate and the likely underestimation of the abundance due to burrowing (see section 1.1), it is still unlikely that there is more than 480 t (gutted wt) of H. scabra, or 241 t (gutted weight) of adult H. scabra on Warrior Reef in 2010 assuming that 60% were buried and using the upper 90% CI of the mean biomass estimate. This estimate of population biomass is still low when compared with estimates of the 1995 catch of between t, and estimates of virgin biomass over 1600 t (Long et al., 1996, Skewes et al., 2006). The fishery (>18 cm TL) biomass estimate of t (± 17.3 t, 90% CI) (gutted weight) still represents a considerable biomass when compared to 2000 when no fishery sized sandfish were observed; especially considering it is likely to be an underestimate due 14 Warrior Reef survey, December 2010

23 RESULTS to burying. Also, the back reef area is known to have some biomass of larger individuals (CSIRO, unpublished data 1 ) that are not included in this survey. Figure 3-4. Warrior Reef strata, delineated from habitats and survey data (Skewes et al., 2001) and density of sandfish in Strata used for calculation of stratified density estimates. Table 3-3 Strata mean abundance (y h ) and variance (s 2 h) estimates for the calculation of standing stock estimates for sandfish (Holothuria scabra) for Warrior Reef in February Descriptions of column headings are listed in Appendix C. Strata n h Area (ha) W h y h s 2 h Seagrass Seagrass Seagrass Seagrass Backreef Table 3-4 Stratified mean (y st ), variance (v(y st )) and standing stock estimates and 90% confidence intervals for sandfish (Holothuria scabra) on Warrior Reef in February n y st (n/ha) v(y st ) Standing stock (n) Biomass (t, whole weight) Biomass (t, gutted weight) 90% CI (% of mean) , CSIRO staff observed densities of approx 5/Ha of large (>20 cm TL) H. scabra during collection of broodstock for QDPI in CSIRO Wealth from Oceans Flagship 15

24 RESULTS Table 3-5 Strata mean abundance (y h ) and variance (s 2 h) estimates for the calculation of standing stock estimates for adult (>14 cm TL) sandfish (Holothuria scabra) for Warrior Reef in February Descriptions of column headings are listed in Appendix C. Strata n h Area (ha) W h y h s 2 h Seagrass Seagrass Seagrass Seagrass Backreef Table 3-6 Stratified mean (y st ), variance (v(y st )) and standing stock estimates and 90% confidence intervals for adult (>14 cm TL) sandfish (Holothuria scabra) on Warrior Reef in February n y st (n/ha) v(y st ) Standing stock (n) Biomass (t, whole weight) Biomass (t, gutted weight) 90% CI (% of mean) , Table 3-7 Strata mean abundance (y h ) and variance (s 2 h) estimates for the calculation of standing stock estimates for fishery (>18 cm TL) sandfish (Holothuria scabra) for Warrior Reef in February Descriptions of column headings are listed in Appendix C. Strata n h Area (ha) W h y h s 2 h Seagrass Seagrass Seagrass Seagrass Backreef Table 3-8 Stratified mean (y st ), variance (v(y st )) and standing stock estimates and 90% confidence intervals for fishery (>18 cm TL) sandfish (Holothuria scabra) on Warrior Reef in February n y st (n/ha) v(y st ) Standing stock (n) Biomass (t, whole weight) Biomass (t, gutted weight) 90% CI (% of mean) Warrior Reef relative density Holothuria scabra were found at the same number of repeated sampling sites in 2010, as in surveys undertaken in 2004 and 2002 (Table 3-9), and again were most often seen in southern and central Warrior Reef (Figure 3-2). The overall density of H. scabra at the repeated sites in 2010 was similar to those values obtained in 2004; being 40% lower than in 2002 (Table 3-10; Figure 3-5). Adult H. scabra (>14 cm TL) were found to have declined 40% since the 2004 survey, but were still in higher densities than the low densities observed in 1998 (Table 3-10, Figure 3-6). Juveniles (<14 cm TL) however, were found to have increased in density since 2004 by over 500% (Table 3-10, Figure 3-6). Large individuals (>20 cm TL) were 16 Warrior Reef survey, December 2010

25 RESULTS found at relatively high densities in 2010 (Table 3-11) and were the highest since 1995/96. Table 3-9. Number of sites where sandfish (Holothuria scabra) were observed out of 41 sites on Warrior Reef (during repeated measures surveys). Year N sites Table Average density (per ha) of sandfish (Holothuria scabra) sampled at 41 repeated sites in the seagrass habitat during six abundance surveys in November-January 1995/96, January 1998, January 2000, October 2002, January 2004 and February 2010 for the whole study area, for adult (>14 cm TL) and juvenile (<14 cm TL) sandfish, and for the northern and southern sections (split at 9 42'). Standard error (s.e.) of estimate is also shown in brackets. Year Total area (N=41) Adults (>14 cm) (N=41) Sandfish (H.scabra) Ha -1 Juveniles (<14 cm) (N=41) Northern section (N=16) Southern section (N=24) 1995/ (349.32) (21.21) (350.03) (487.26) (24.11) (18.34) (13.24) (3.83) (93.84) (11.60) (98.41) (8.51) (98.05) (137.06) (20.88) (55.06) (41.76) (18.64) (19.83) (58.45) (25.34) (23.65) (4.68) (27.43) (19.07) (49.51) (15.32) (39.60) (68.41) (14.21) Table Average density (per ha) of sandfish (Holothuria scabra) sampled at 41 repeated sites in the seagrass habitat during six abundance surveys for several size ranges. Size range (mm) 1995/ All > > > Holothuria scabra density was found to have declined by 30% in the southern section of Warrior Reef since the previous 2004 survey, an area that had shown an increase in the 2002 survey (Table 3-10; Figure 3-7, Figure 3-2). In comparison, the density of H. scabra in the northern section was 40% higher than the 2004 survey and over 50% higher than results from 2002 (Table 3-10; Figure 3-7, Figure 3-2). CSIRO Wealth from Oceans Flagship 17

26 RESULTS Sandfish per Ha Sample year Figure 3-5. Average number of sandfish (Holothuria scabra) per Ha for repeated sites on Warrior Reef for the six sample years. (Error bars are 1 s.e.) 900 Sandfish per Ha Adult Juvenile 250 Adult sandfish per Ha Sample year Figure 3-6. Average density of juvenile (<14 cm TL), and adult (>14 cm TL) sandfish (Holothuria scabra) per ha for repeated measures sites on Warrior Reef for the six sample years. (Bottom graph shows adult only) (Error bars are 1 s.e.) 18 Warrior Reef survey, December 2010

27 RESULTS South North Sandfish per ha South North 300 Sandfish per ha Sample year Figure 3-7. Average number of sandfish (Holothuria scabra) per ha for repeated measures sites split into northern (diamonds) and southern (squares) sections of Warrior Reef for the six sample years. Section split at 9 42'. (Y axis has been resized in bottom graph to better define data pattern) (Error bars are 1 s.e.) Adult H. scabra were found to have decreased in 2010 from the 2004 survey, for both the northern and southern sections of Warrior Reef (Table 3-10; Figure 3-8). In comparison, juveniles were found to have increased in the northern section in 2010, from 2004, while remaining at a very low density in the southern section (Table 3-10; Figure 3-9). This probably reflects the higher density of juveniles at a known recruitment hotspot in central region of Warrior Reef (Figure 3-3) CSIRO Wealth from Oceans Flagship 19

28 RESULTS South North Adult sandfish per ha Sample year Figure 3-8. Average number of adult sandfish (Holothuria scabra) per ha for repeated measures sites split into northern (diamonds) and southern (squares) sections of Warrior Reef for the six sample years. Section split at 9 42'. (Error bars are 1 s.e.) Juvenils sandfish per ha South North Juvenils sandfish per ha South North Sample year Figure 3-9. Average number of juvenile sandfish (Holothuria scabra) per ha for repeated measures sites split into northern (diamonds) and southern (squares) sections of Warrior Reef for the six sample years. Section split at 9 42'. (Y axis has been resized in bottom graph to better define data pattern) (Error bars are 1 s.e.) 20 Warrior Reef survey, December 2010

29 RESULTS Holothuria scabra juveniles For the first time during six abundance surveys since 1995/96, significant numbers of very young H. scabra were found on transect. Juveniles were found buried beneath seagrass mats and were located through dedicated quadrat searching. The juveniles displayed a distinct change in morphology as they grew in size, of particular note being the gnarled, spiked appearance of the younger stages (Figure 3-10, Figure 3-11) The varying morphology is believed to correspond with a behavioural change associated with habitat occupation, with adults found to occur on top of or partially covered by seagrass, or out in the open/partially buried on sand banks. 2 cm Figure Change in Holothuria scabra morphology from juvenile, through to the adult stage. CSIRO Wealth from Oceans Flagship 21

30 RESULTS 2 cm Figure Change (ventral side) in Holothuria scabra morphology from juvenile, through to the adult stage. Juvenile H. scabra were also observed to regularly expel their cuvierian tubules, which is not commonly seen in adult sandfish (Figure 3-12). Figure Juvenile Holothuria scabra expelling its cuvierian tubules. 22 Warrior Reef survey, December 2010

31 RESULTS Size frequency The length frequency of H. scabra collected during the February 2010 survey was composed of 7 population modes, ranging from 93 to 312 mm TL (Table 3-12, Figure 3-13). It is likely that the smallest cohort is highly truncated for smaller animals due to the highly cryptic nature of small sandfish, causing the next cohort (at 128 mm) to be underrepresented and biased upwards due to under-sampling of smaller juveniles. Holothuria scabra are believed to spawn in Torres Strait from spring (October/November) to mid-summer (January) (Skewes et al., 2001; Morgan, 2000; Hamel et al., 2000). Given established growth rates for this species (Hamel et al., 2001), the smallest mode (93 mm TL) most probably represents larger individuals from the newly settled cohort (0+), making the next cohort (128 mm TL) a little over one year old (1+). The 2+ cohort (164 mm TL) are larger than size at maturity (14 cm TL; Skewes et al., 2001; Hamel et al., 2000) and are close to the minimum legal size of 18 cm TL. The 3+and older cohort make up the bulk of the fishable population, with older individuals making up only 6.8% of the surveyed population (Table 3-12, Figure 3-13). Table Output from MIX Modal analysis of population size frequency collected at 70 sites in February 2010 (Fitting Lognormal components; Sigmas constrained to be equal) (Standard errors in brackets). Chi-squared (df 16) = (P = ) Mode/cohort Proportions (0.015) (0.027) (0.026) (0.031) (0.030) (0.019) (0.006) Mean size (mm TL) (3.08) (1.89) (3.04) (4.13) (6.58) (6.26) (4.68) Sigma (SD) (1.06) Sandfish count Figure Length frequency distribution of sandfish (Holothuria scabra) for the total number of sites surveyed on Warrior Reef, from the 2010 survey. Size of modes (cohorts) from modal analysis shown in red. Comparing size frequency of H. scabra found at the repeated sites only, the 2010 population had a wider spread than previous surveys (apart from the odd larger individual in 2000) (Figure 3-14). In contrast to the two previous surveys undertaken in 2004 and 2002, the 2010 length frequency data indicates a significant population of larger sandfish above the minimum legal size of 180 mm TL (Figure 3-14). CSIRO Wealth from Oceans Flagship 23

32 RESULTS Figure Length frequency (mm Total Length (TL)) distribution of sandfish (Holothuria scabra) for repeated measures sites from Warrior Reef, for the six sample years scaled to density (No. per Ha). Dashed line represents14 cm TL, the age of sexual maturation for sandfish H. scabra. Solid line represents 18 cm TL, the fishery minimum legal size / No. of Sandfish per Ha Total length (mm) 24 Warrior Reef survey, December 2010

33 RESULTS 3.2 Iama Reef survey Twenty walking and snorkel transects were undertaken at Iama Island (Figure 3-15). While no H. scabra were seen on transects, four sandfish were seen off transect in the seagrass dominated reef flat on the northern side of the island (Figure 3-15, Figure 3-16). This suggests (and is corroborated by local islander knowledge), that the reef area is suitable habitat for H. scabra and could be a possible reseeding site. Figure Location of sampling sites on Iama (Yam) Island, Torres Strait, showing cover of seagrass by species (max cover 95%). Green shaded area indicates seagrass habitat considered suitable habitat for sandfish, Holothuria scabra. CSIRO Wealth from Oceans Flagship 25

34 RESULTS Seagrass cover (%) Enhalus acoroides Cymodocea serrulata Syringodium isoetfolium Cymodocea rotundata Halodule uninervis Thalassia hemprichii Survey transect Figure Seagrass species and total cover at survey transects on Iama Island, Torres Strait. After plotting the habitat data, and using a LandSat TM image as a guide, we estimate the area of suitable seagrass habitat on Iama Island to be 39.9 Ha (Figure 3-15). This equates to a potential carrying capacity of over half a million H. scabra, or approximately 21 t (gutted weight) of adult sandfish for Iama Island (based on highest density of H. scabra on Warrior Reef being 14,000 per Ha; often observed as a maximum carrying capacity for H. scabra in the region (Mercier et al., 2001)). This estimate of course is a best case scenario, with high mortality sometimes observed in restocked populations (Purcell, 2004a). 26 Warrior Reef survey, December 2010

35 DISCUSSION 4. DISCUSSION Survey densities of sandfish, Holothuria scabra on Warrior Reef were found to be at similar levels to 2004, and again were ~80% less than observed in 1995/96; at which time the population was considered to be overexploited. Adult (>14 cm TL) sandfish were found to have decreased in density since the 2004 survey; however, the density of fishery sized individuals (>18 cm TL) was the highest since Juveniles showed a large increase compared to Even taking into consideration the low precision of the estimate and the possibility of underestimating the abundance due to burying, it is still unlikely that there is more than 480 t (gutted wt) of H. scabra, or 241 t (gutted weight) of adult H. scabra on Warrior Reef in The fishery (>18 cm TL) biomass estimate of 48.7 t (± 17.3 t, 90% CI) (gutted weight) is still very low when compared with estimates of the 1995 catch of between t, and with estimates of virgin biomass over 1600 t (Long et al., 1996, Skewes et al., 2006). However, this still represents a considerable biomass when compared to 2000 when no fishery sized sandfish were observed; especially considering it is likely to be an underestimate due to burying. Also, this estimate does not include the likely sandfish biomass on the back reef habitat. In the 2010 survey, significant decreases were found in the southern area of Warrior Reef and significant increases found in the northern area, possibly reflecting the higher density of juvenile sandfish that appear to settle preferentially in this part of Warrior Reef. Unlike previous surveys, the sandfish population in 2010 was made up of possible 7 year classes, with relatively high densities of older (4 y.o. and older) individuals. This contrasts with previous adult cohorts that only consisted of 2+ year old animals (Skewes et al., 2004). These larger individuals represent a significant breeding potential, especially given the correlation between animal size and gonad weight for sandfish in Torres Strait (Skewes et al., 2000). This population of larger individuals may result in a substantive recruitment in early During the survey, extensive searching at one location in particular indicated the potential recruitment of a large number of very young juveniles to the fishery, which supports this conclusion. No H. scabra were observed on Dungeness Reef (despite undertaking lengthy transects in suitable habitat), and only low densities were observed on the back reef flat at Zagai Island. Sandfish have been observed at both of these areas previously (Dungeness Reef average density in 1995/96: 43.75/Ha, s.e , n=40), or had sandfish during the fishery in the early 1990s (Iama traditional owners; pers comm.). The absence of sandfish during the survey could reflect a lack of recruitment to these previously populated reefs, or could be due to burying. We were only able to visit Dungeness Reef on a single occasion, so we were not able to sample at different tidal conditions or time of day. Further sampling of Dungeness Reef is required to conclusively indicate a nil population density on that reef. While no H.scabra were seen on transects at Iama Island, a small number of sandfish were observed in the seagrass habitat of the back reef lagoon. The area of suitable habitat for sandfish on Iama Island was estimated to be 39.9 Ha. This area has a CSIRO Wealth from Oceans Flagship 27

36 DISCUSSION potential carrying capacity of over half a million adult H. scabra, or approximately 21 t (gutted weight), based on maximum density observations for sandfish. The lack of a large observable recovery in the H. scabra population in Torres Strait after 12 years of fishery closure could be attributed to one or more of the following factors: 1) Variable burying rates of H. scabra between surveys. Sandfish are known to have variable burying rates in response to diurnal (time of day), seasonal and tidal cycles, and also in relation to seagrass cover. We deliberately carry out population surveys at the same time of year, the same moon phase and similar time of day to endeavour to nullify these factors. The repeated measures sample design should also nullify any variable environmental factors. Previous research has shown that larger H. scabra should have low burying rates in this environment during summer (see section 1.1). We therefore, have some confidence that density comparisons between years are mainly due to real changes, not burying rates. 2) Illegal fishing by PNG fishers. Some poaching probably continued up until the closure of the PNG fishery in late 2009, however, a major surveillance operation by Australian fisheries on the PNG-Australian border to apprehend and deter poachers was instigated in During this time there were significant apprehensions and by all accounts, the operation was considered to be successful. 3) Low recruitment. As H. scabra numbers are still at low densities compared with virgin biomass levels, and the PNG component of the sandfish population is probably very depleted (PNG NFA; unpublished data), there is still the possibility that low recruitments will occur. This is mainly attributed to the dilution (or allee) effect, where breeding adults are dispersed to an extent that fertilization success in the water column is variable and potentially depressed. We are not currently in a position to determine which of these factors is, or are, the cause of the continued low estimated density in 2010, making it very difficult to recommend a reopening of the fishery at this stage. However, a small experimental fishing exercise would be useful to further assess attribution factors by a comparison with historical catch rates. The fishing effort would be controlled to a level where there would be little risk to the overall population stock status (4 fishing units and <2 tonnes), even at the more pessimistic estimates of current stock size. During the 2002 survey, a marked change in the distribution of H. scabra on Warrior Reef was noted from previous surveys in 1995/96, 1998 and Large and significant increases in the southern area of Warrior Reef were found, with significant decreases found for the northern area. In the 2010 survey, contrary decreases were found in the southern area of Warrior Reef and significant increases found in the northern area. The increase in H. scabra numbers in the northern half of Warrior may reflect the higher density of juvenile sandfish that appear to settle preferentially in this part of Warrior Reef, indicating possible recruitment to the fishery. This change in distribution pattern may be caused by differential settlement, and/or the movement of sandfish from high density juvenile habitat in the north to adult habitat in the south. Consequently, the decrease in sandfish numbers in the southern section 28 Warrior Reef survey, December 2010

37 DISCUSSION may suggest previous illegal fishing that occurred to some extent since 2004 (as supported by Islander observations). There is also a possibility that the differences in abundance were caused by changes in burying rates during the survey; however, the survey of the northern and southern sections was carried out on consecutive days over a six day period. As conditions were very similar during that time, it is doubtful if burying rates varied considerably between sample days. The strong stock-recruitment relationship indicated by the survey data supports the assumption that the Warrior Reef H. scabra population is self-seeding. There are no substantial populations of sandfish in proximity to Warrior Reef that could supply recruits to the fishery, and research has shown limited gene flow between sandfish populations on the Australian east coast (Uthicke & Benzie, 2001). 4.1 Future surveys Future surveys are required to determine which factors (differential bury rates or low recruitment) are the cause of the continued low sandfish density, and to assess the possible recovery of the population. The opportunity exists for a small experimental fishing trial to further assess attribution factors and provide more information on population dynamics and the stock recruitment relationship. It would also offer a significant training and community co-management opportunity. The fishing effort would be controlled to a level where we feel there would be little risk to the overall population stock status (4 fishing units and <2 tonnes), even at the more pessimistic estimates of current stock size. This catch limit is relatively small compared to the fishery biomass estimate, and almost insignificant compared to the catch of the PNG fishery of 200 to 400 t up to at least 2006 (Skewes et al., 2009). Future surveys will allow for a continued monitoring of the population status and possible recovery, focused towards an eventual staged reopening of the population in a co-management framework, and the future sustainable fishing of sandfish on Warrior Reef. 4.2 Management recommendations 1. We recommend that the fishery remain closed until such a time as it can be demonstrated that the fishery population has recovered to at least 50% virgin biomass. It could be that some limited fishing be allowed before this, however, it must be tightly controlled and there should be minimal risk to the recovering population and a clear benefit within a future co-management framework. 2. Continue to monitor the fishery on a yearly or biyearly basis to provide information on the recovery of the sandfish population, and potentially on burying dynamics and the stock recruitment relationship. 3. Urgently establish strong links with PNG NFA to establish a joint approach to research and management of the Torres Strait sandfish population. CSIRO Wealth from Oceans Flagship 29

38 REFERENCES 5. REFERENCES Battaglene, S.C Culture of tropical sea cucumbers for stock restoration and enhancement. NAGA, The ICLARM Quarterly 22: Chauvet, C., Audabran, D., Hoffschir, C., Meite, H Report on the introduction of trochus (Trochus niloticus) juveniles to Lifou (Loyalty Islands). In Trochus information bulletin, Number 5 October (Eds). Passfield, K Conand, C Fishery resources of the Pacific islands. Part 2. The Holothurians. FAO Fisheries Technical Paper, 272.2, FAO, Rome, 108 pp. Hamel, J.F., Conand, C., Pawson, D.L., Mercier, A The sea cucumber Holothuria scabra (Holothuroidea: Echinodermata): Its biology and exploitation as bêche-de-mer. Advances in Marine Biology 41: Long, B.G., Skewes, T.D., Taranto, T Distribution and abundance of bêche-demer on the Warrior reefs, Torres Strait. Report to the Queensland Fisheries Management Authority, Brisbane Queensland, January 1996, 70 pp. Mercier, A., Battaglene, S.C., Hamel, J.-F Daily burrowing cycle and feeding activity of juvenile sea cucumbers Holothuria scabra in response to environmental factors. Journal of Experimental Marine Biology and Ecology 239: Mercier, A., Battaglene, S.C., Hamel, J.-F Periodic movement, recruitment and size-related distribution of the sea cucumber Holothuria scabra in Solomon Islands. Hydrobiologia 440: Morgan, A.D Aspects of the reproductive cycle of the sea cucumber Holothuria scabra (Echinodermata: Holothuroidea). Bulletin of Marine Science 66: Preston, G Bêche-de-Mer. In: Wright A., Hill, L. (Eds). Inshore marine resources of the South Pacific: information for fishery development and management, Chapter 11. FFA/USP Press, Fiji. pp Purcell, S Rapid growth and bioturbation activity of the sea cucumber Holothuria scabra in earthen ponds. Proceedings of Australasian Aquaculture, Sydney. 244 pp. Purcell, S.W. 2004a. Criteria for release strategies and evaluating the restocking of sea cucumbers. In: Advances in sea cucumber aquaculture and management. A. Lovatelli, C. Conand, S. Purcell, S. Uthicke, J.-F. Hamel and A. Mercier, (Eds.). FAO, Rome. Purcell, S.W., Kirby, D.S Restocking the sea cucumber Holothuria scabra: Sizing no-take zones through individual-based movement modelling. Fisheries Research 80: Skewes, T.D., Burridge, C.M., Hill, B.J Survey of Holothuria scabra on Warrior Reef, Torres Strait. Report to Queensland Fisheries Management Authority. CSIRO Division of Marine Research Report, 12 pp. Skewes T.D., Dennis, D.M., Jacobs, D.R., Gordon, S.R., Taranto, T.J., Haywood, M., Pitcher, C.R., Smith, G.P., Milton, D., Poiner, I.R Survey and stock size estimates of the shallow reef (0-15 m deep) and shoal area (15-50 m deep) marine resources and habitat mapping within the MOU74 box. Volume 1: Stock estimates and Stock status. CSIRO Final Report to the FRRF. 88 pp. 30 Warrior Reef survey, December 2010

39 REFERENCES Skewes, T.D., Dennis, D.M., Burridge, C.M Survey of Holothuria scabra (Sandfish) on Warrior Reef, Torres Strait. January 2000 Report to Queensland Fisheries Management Authority. CSIRO Division of Marine Research Final Report, 26 pp. Skewes, T.D., Dennis, D.M., Koutsoukos, A., Haywood, M. Wassenberg, T., Austin, M Stock survey and sustainable harvest strategies for Torres Strait bêche-de-mer. CSIRO Division of Marine Research Final Report, Cleveland Australia. AFMA Project Number: R01/1343. ISBN , 50pp. Skewes, T.D., Taylor, S., Dennis, D.M., Haywood, M.E.D., Donovan, A Sustainability Assessment of the Torres Strait Sea Cucumber Fishery, CRC-TS Project Task Number: T1.4, 50pp. Uthicke, S., Benzie, J.A.H., Ballment, E Population genetics of the fissiparous Holothurian Stichopus chloronotus (Aspidochirotida) on the Great Barrier Reef, Australia. Coral Reefs 18: Uthicke, S Interactions between sediment feeders and microalgae on coral reefs; grazing losses versus production enhancement. Marine Ecology Progress Series 210: Wiedemeyer, W.L Feeding behaviour of tow tropical holothurians, Holothuria (Metriatyla) scabra (Jaeger 1833) and H. (Halodeima) atra (Jaeger 1833), from Okinawa, Japan. Pp In: Richmond, R.H. (Ed) Proceedings of the 7 th International Coral Reef Symposium. University of Guam Press, Mangilao, Guam. Wolkenhauer, S.-M. and T.D. Skewes (2008) Temperature control of burying and feeding activity of Holothuria scabra (Echinodermata: Holothuroidea). In, Davie, P.J.F. & Phillips, J.A. (Eds), Proceedings of the Thirteenth International Marine Biological Workshop, The Marine Fauna and Flora of Moreton Bay, Queensland. Memoirs of the Queensland Museum Nature 54(1): Brisbane. ISSN Wolkenhauer, S.-M. T.D. Skewes, M. Browne and D. Chetwynd (in prep) Daily and seasonal patterns in behaviour of the commercially important sea cucumber, Holothuria scabra Yamanouchi T (1939) Ecological and physiological studies on the holothurians in the coral reef of Palao Islands. Palao Tropical Biological Station Studies 1, Yamanouchi T (1956) The daily activity rhythms of the holothurians in the coral reef of Palao Island. Publications of the Seto Marine Biological Laboratory 5, CSIRO Wealth from Oceans Flagship 31

40 APPENDIX A - SURVEY INFORMATION FLYER POSTED ON ISLAND NOTICE BOARDS 32 Warrior Reef survey, December 2010

41 APPENDIX B APPENDIX B - TORRES NEWS ARTICLE Sandfish surveyed after 12 years, 25 May - 1 st June,

42 APPENDIX C TERMS USED IN STRATIFIED ANALYSIS APPENDIX C TERMS USED IN STRATIFIED ANALYSIS Stratified sampling techniques. In stratified sampling the population of N units is divided into subpopulations of N1, N2, N3,... NL units respectively. If each stratum is homogenous in that the measurements vary little from one unit to another, a precise estimate of any stratum mean can be obtained in that stratum. These estimates can then be combined to give a precise estimate for the whole population. The notation of terms used for stratified sampling follows below: N total number of possible sampling units in the study area; N h total number of possible sampling units in stratum h; n h actual number of samples taken in stratum h; y hi value obtained from ith unit in stratum h; W h = N h N stratum h weight; f h = n h N h sampling fraction in stratum h; _ yh = n h yhi i=1 n h _ L yst = W _ h y h h=1 s h 2 stratum h mean; stratified mean over all strata; sample estimate of stratum h variance; v( _ L L y st) = W h s h n h W h s h N h=1 h=1 estimated strata variance. 34 Warrior Reef survey, December 2010

43

44