Current status of western blue groper at selected locations in South Australia: results of the 2014 survey and comparison with historical surveys Report to the Conservation Council of South Australia James Brook 2014 Brook (2014) Status of western blue groper in South Australia This publication should be cited as: Brook, J. (2014). Current status of western blue groper at selected locations in South Australia: results of the 2014 survey and comparison with historical surveys. Report to the Conservation Council of South Australia. J Diversity Pty Ltd, Adelaide. Cover photo: Male western blue groper (Achoerodus gouldii) at the Investigator Group, 2006. Photo credit: James Brook. Disclaimer The findings and opinions expressed in this publication are those of the author and do not necessarily reflect those of the Conservation Council of South Australia. While reasonable efforts have been made to ensure the contents of this report are factually correct, the Conservation Council of South Australia and the author do not accept responsibility for the accuracy and completeness of the contents. The author does not accept liability for any loss or damage that may be occasioned directly or indirectly through the use of, or reliance on, the contents of this report. 2 Brook (2014) Status of western blue groper in South Australia Acknowledgements The current report was funded by an Australian Government Community Environment Grant through the Conservation Council of South Australia (CCSA). Thanks are due to: • Alex Gaut (CCSA), Steve Leske (CCSA/Reef Watch), and all of the volunteers who collected the data • Dr Simon Bryars, who was a sounding board for discussion and reviewed a draft of the report • Dr Scoresby Shepherd AO (SARDI) for providing historical data and reviewing a draft of the report. 3 Brook (2014) Status of western blue groper in South Australia Contents Acknowledgements.................................................................................................................................3 Contents..................................................................................................................................................4 Non‐technical summary..........................................................................................................................5 Introduction ............................................................................................................................................6 Methods..................................................................................................................................................7 2014 survey.........................................................................................................................................7 Historical surveys ................................................................................................................................7 Results.....................................................................................................................................................9 2014 survey.........................................................................................................................................9 2014 survey compared with previous surveys .................................................................................12 Discussion .............................................................................................................................................14 Recommendations ................................................................................................................................16 References ............................................................................................................................................17 Appendix 1 ............................................................................................................................................19 4 Brook (2014) Status of western blue groper in South Australia Non‐technical summary The western blue groper (Achoerodus gouldii) is the largest resident reef fish in southern Australian coastal waters. The species is long‐lived (up to 70 years), slow‐growing, sex‐changing and site‐ attached with a small home range. These life history traits of western blue groper (WBG) render the species highly vulnerable to the effects of localised over‐fishing and the species has been fully protected in the central part of South Australia (SA) since the 1980s. The WBG is currently included on the Reef Watch ‘Feral or In Peril’ species list as a species of conservation interest. Historical diver surveys for WBG showed that the species is more abundant in the western parts of SA, which may have been due to a combination of natural distribution patterns and fishing effects. During 2013 a new set of surveys was undertaken by community divers at 25 sites across SA specifically targeting WBG. The surveys were funded by a State Community NRM Grant administered through the Conservation Council of South Australia. A further grant allowed the surveys to be repeated at 12 of these sites, and three additional sites, in 2014. The current report presents the results of the 2014 surveys and comparisons with the previous surveys. The overall patterns of abundance recorded in 2014 were very similar to those of 2013, except at Groper Bay, where the lower abundance in 2014 was likely due to poor visibility, and at Cape Jervis and Fishery Bay, where no groper had been recorded in 2013. With regard to size classes, the most noticeable difference between 2013 and 2014 was the lack of adult WBG recorded at the three Yorke Peninsula sites (Groper Bay, Chinaman’s Hat and Edithburgh) where they had been recorded in 2013. A degree of caution is required when interpreting the status of WBG in SA or comparing the recent surveys with historical surveys, due to inherent limitations in the survey method. Nonetheless, the results showed that the abundances from recent surveys on Eyre and Yorke Peninsula were generally lower than the historical surveys, with the exception of Golden Island Point. Regional abundances of both juveniles and sub‐adults declined, with the former most likely linked to variable recruitment associated with the strength of the Leeuwin Current, but the latter unlikely to be solely due to variable recruitment. The results show that the protection zone is not having a positive influence on populations of sub‐adult or adult groper. Future surveys should focus on long‐term monitoring of the effect of the increased protection afforded by marine park Sanctuary Zones. This would require an increase in survey effort at Chinaman’s Hat and nearby sites, including Groper Bay, as controls. Another zone suitable for monitoring groper populations may be SZ‐3 in the Sir Joseph Banks Group Marine Park, where sub‐ adults have previously been recorded at sites within the zone and nearby. In addition, further monitoring with increased effort (number of replicate transects) is desirable at sites where there were relatively few transects in 2013 or 2014 and discrepancies between those results. These sites include Point Westall, Groper Bay, Chinaman’s Hat, Edithburgh, Cape Jervis and Fishery Bay. Some adjustments to the information recorded during the surveys are also suggested. 5 Brook (2014) Status of western blue groper in South Australia Introduction The western blue groper (Achoerodus gouldii) is the largest resident reef fish in southern Australian coastal waters (Bryars et al. 2012). The life history traits of western blue groper (WBG) renders the species highly vulnerable to the effects of localised over‐fishing as they are long‐lived, slow‐growing, sex‐changing (Coulson et al. 2009), and site‐attached with a small home range (Bryars et al. 2012). The aspect of WBG ecology most relevant to visual surveys of abundance is the shift in habitat of the species with size and age. After a late winter‐to‐spring spawning, groper larvae drift in the sea for 1‐ 2 months in the easterly flowing Leeuwin Current. On settlement in lagoons or back reefs, which is more prevalent when the Leeuwin Current is weak, they have a cryptic brownish‐green colour and feed on tiny mussels and crustaceans. Over the next 15 or so years they become greener in appearance, gradually move into slightly deeper water and, at sexual maturity (~60 cm), males change colour from greenish to the more familiar blue. Most then move offshore to reefs 30–50 m deep, where they feed on crustaceans, molluscs, sea‐urchins, and worms. At a size of 10 cm they are aged ~1 year, at 20 cm ~2 years, and at 60 cm ~15 years (Shepherd and Edgar 2013; Coulson et al. 2009). Numbers of large WBG declined in parts of South Australia (SA) due to intense fishing during the 1950–70s and this led to their total protection within central SA in the 1980s. Outside of central SA there are recreational and commercial catch limits. Nonetheless, the species is still of conservation concern due to ongoing fishing interactions (Baker 2012) and because it has poor post‐release survival rates (McLeay et al. 2002; Bryars et al. 2012). The WBG is currently included on the Reef Watch ‘Feral or In Peril’ species list as a species of conservation interest. Shepherd and Brook (2007) reported on a spatially‐comprehensive set of underwater visual census (UVC) surveys for WBG across SA. Since that time, additional UVC surveys for reef fish (including WBG) have been conducted at some of the same sites, but a more spatially‐comprehensive