Estimates of post-release survival (PRS) of SBT from the recreational sector are unknown. As a gamefish species a catch and release ethic is associated with the fishery where a proportion of fishers target SBT purely for sport with most fish released. In addition, management strategies for recreational fishing of SBT are aimed at limiting individual harvest (bag, possession or boat limits) creating a legislative requirement to release fish. If regulations become more restrictive or as the stock rebuilds, a greater proportion of the catch will be released. It is therefore increasingly important to quantify PRS of SBT and also ensure that survival is maximised by identifying factors that disproportionately contribute to mortality and then communicating an effective code of practice for the release of tuna to the recreational game fishing sector. This project, as part of a portfolio of projects carried out within Victoria and Tasmania (as well as FRDC project 2012/022: Development of methods for obtaining national estimates of the recreational catch of SBT), will contribute to quantifying fishing induced mortality of SBT from the recreational sector and provide a mechanism to assess the appropriateness of current management regulations.
Southern Bluefin Tuna (SBT) are an important component of the recreational game fishery in Australia. Recreational fishers in waters around South Australia, Victoria, Tasmania and New South Wales catch this species seasonally. Each state respectively is responsible for the management of this recreational fishing, with individual fisher catch limits, and in some states boat limits also apply. Excess catch beyond these limits must be released. An assumption underpinning the effectiveness of catch limits is that a major proportion of fish released will survive. This assumption is also key to the practice of sport fishing, where anglers target fish which they don’t intend to keep.
Recent studies reporting on the catch and effort of the recreational SBT fisheries in Victoria and Tasmania estimate that approximately 25% of SBT are released. A low post-release survival rate could contribute a significant source of unaccounted mortality within the recreational fishery. Prior to this study there was no information to quantify the post release survival rates of SBT.
The primary objective of this study was to assess the post-release survival rate of SBT caught by the recreational fishery in Australia. An analysis was also conducted to determine whether the fate of fish after release could be related to factors occurring during capture. Finally, a Code of Practice (COP) for the recreational SBT fishery was compiled. The COP is based on the results of this study integrated with fact-based information from existing literature relevant to the recreational capture of large pelagic species. Both a booklet and a brochure of the COP have also been created to allow easy provision of information to recreational fishers.
The results showed that recreationally caught SBT have a low incidence of mortality (3%) occurring during the capture event related directly to the hooking and retrieval of the fish. The fate of fish that were landed in a non-responsive state was attributed to deep-hooking damage, with the exception of one large fish that became tail wrapped and was retrieved to the boat backwards, effecting its ability to ram ventilate. An exception to the low pre-landing mortality was attributed to seal predation of SBT caught in Tasmanian waters. Seal predation accounted for mortality of 31% of fish hooked adjacent to Tasmania. This was the greatest source of unintended mortality related to recreational capture assessed in this project. The uniqueness of seal mortality occurring in Tasmanian waters is likely due to the fact that the majority of recreational fishing targeting SBT occurs in close proximity to areas frequented by seals, primarily coastline and islands used by seals as haul outs.
Satellite tagged fish caught on lures configured with J-hooks (n = 46) and those caught on circle hooks (n = 8) had similar post-release survival (PRS) rates and were combined to increase sample size, revealing a PRS estimate of 83.0% (95% CI: 75.9 – 90.7%, n = 54). The PRS estimate of fish caught on lures with treble hooks was much lower, 60% (95% CI: 20 – 100%, n = 5). Given the low sample size of fish caught using treble hooks this PRS estimate should be considered indicative, additional samples would improve the statistical robustness of this estimate.
The results indicate that post-release mortality does occur for recreationally caught Southern Bluefin Tuna, but is not significant factor in relation to the total recreational harvest of SBT. Therefore, current management strategies using catch limits, including personal bag or possession limits are reasonably effective. The reported post-release survival rate has been assessed across the size range of fish that is commonly caught by the recreational fishery throughout southeast Australia. These findings will complement future research to investigate the recreational harvest of Southern Bluefin Tuna in Australia (Moore et al. 2015). The combined results of these projects will provide greater transparency around the recreational fishery for Southern Bluefin Tuna, an objective which is an obligation of Australia to the Commission for the Conservation of Southern Bluefin Tuna.
The development of a COP for the recreational capture and handling of Southern Bluefin Tuna based on the results of the study, and others, provides fishers with fact based information to improve fish handling practices, primarily around reducing unintended mortality and reducing impacts on animal welfare. The COP has been endorsed by key recreational fishing representative bodies to champion and assist in dissemination and adoption of the COP document.
Keywords: Southern Bluefin Tuna, Thunnus maccoyi, recreational fishing, physiological stress, post-release survival, responsible fishing, animal welfare, code of practice
Recreational fishers can each play a part in improving the Southern Bluefin Tuna fishery by applying best practices for responsible fishing. Applying best practice considers the welfare of individual fish and minimises impacts on fish stocks. This Code of Practice has been developed based on scientific research specific to the recreational Southern Bluefin Tuna fishery, existing science based literature on the impacts of recreational fishing and consultation with peak recreational fishing groups.
There is no legislative requirement to follow codes of practice; rather they are designed to provide fishers with fact-based information required to fish in a responsible way. Taking the time to read, learn and apply the information in this document will improve the recreational fishing experience for everyone.