Tactical Research Fund: managing inshore stocks of southern rock lobster for a sustainable fishery
University of Tasmania (UTAS)
There is clearly a concern in the Tasmanian lobster industry about the status of inshore component of the stock. Catch has declined in a number of areas, despite improvements in catch rates. In the Northeast, catch is at record lows, but CPUE has remained stable, which is a possible indicator of hyper-stability or false stability. The apparent stability in catch rates occurs because aggregations containing a major proportion of the population are fished down, as the fleet moves from one area of good catch rates to the next, resulting in a serial depletion of the aggregations, which is masked by the apparent stability in the fishing block. This can result in a very sudden decline in biomass once the entire block is depleted, posing a serious and immediate risk to the inshore component of the stock. There are two potential sources of this problem. Firstly, the scale of the current assessment model, of eight inshore areas (<64m) and three offshore areas (>64m) is not be fine enough to detect localised changes in the CPUE or biomass. Secondly there are changes in fishing practices that have increased effort on inshore stocks, and it is unclear whether the extra effort in these practices is adequately recorded in estimates of CPUE. There has been a recent increase in potting effort, commonly referred to as double night fishing, whereby fishers set and haul their pots twice a night, compared to the standard practice of emptying pots once at dusk and/or once during the day. Currently we have no data on the composition of the catch in double night shots, and what proportion of captured lobsters are handled and released, and in fact what consequence this handling has on the overall health of the fishery.
1. Determine the extent of declines in the inshore stock by changing the current stock assessment model to assess stocks at a finer scale (<30m and >30m).
2. Assess whether increased effort in double night shots is adequately recorded in estimates of CPUE; include the differences in catch composition, size structure and the effects of handling on growth in assessments.
3. Assess the cost-effectiveness of double night fishing and compare short and long-term benefits.
4. Develop a management strategy evaluation, presenting options based on the results of the study.
Principal Investigator: Bridget S. Green
Key Words: Southern rock lobster, effort, growth, bycatch, CPUE, double-night fishing, inshore depletion
Summary: The Tasmanian commercial southern rock lobster fishery (TSRLF) is a quota controlled pot fishery operating all around Tasmania. The annual commercial catch is around 1.5 million animals taken by approximately 230 vessels (Hartmann et al. 2010). In addition, there are approximately 21,000 licensed recreational fishers (Lyle and Tracey 2010). Inshore stocks have been declining for a number of years, and total legal biomass of the whole fishery has been in decline since 2007 (Hartmann et al. 2010). Fishing effort and life history demographics of the stock vary dramatically from region to region, and from inshore to offshore. This presents a number of challenges for fisheries assessment and management.
Serious concerns that fishing two shots per night (double night fishing) was depleting inshore stocks was raised by members of the southern rock lobster fishing fleet starting in 2007, through a range of forums. This concern heightened as state-wide fishing effort continued to rise while catch rates fell. Requests from the peak body TRFLA to ban it were complicated by the lack of scientific information on the effect and difficulty in defining a suitable approach to regulation and enforcement. As a result, the TRFLA requested that the Institute for Marine and Antarctic Studies (IMAS) conduct research into the practice of double night fishing.
Our best evidence suggests that of the effect of double night fishing effort on inshore biomass is minor relative to the larger issue of total catch (and thus effort) as regulated through the TACC. Damage due to handling and discarding appeared reduced through double night shot fishing because average weight of lobsters was slightly higher (thus fewer lobsters per unit quota) and catch rates were equivalent to standard night shots. In 2010/11 double night shot fishing did not appear to be as widespread as discussed prior to the project. Interestingly, many fishers who self-identified as double night shot fishers actually rarely conducted this type of fishing. Rather, they sometimes set and haul their gear late in the middle of the night, rather than completing two full shots during the night.
It is difficult to determine whether we have captured the true extent of this activity without broader participation of the fishing fleet and clearer recording of shot times in the logbook. As a result of the is project the logbook is to be adjusted so that fishers no longer record 'shot type' and 'date of month' and instead record the time and date of first pot set and first pot hauled for each shot. The logbook also is also to be amended to prevent shots being combined across a calendar day by reporting double the number of pots. This would allow assessment of fine-scale effort, and correction for potential bias from double night shot fishing in the stock assessment process for the fishery.