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.
Project number: 2009-058
Budget expenditure: $75,000.00
Principal Investigator: Bridget Green
Organisation: University of Tasmania (UTAS)
Project start/end date: 29 Nov 2009 - 14 May 2011
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 >
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.