Ziegler, PE and Haddon, M and Gardner, C, Tasmanian Giant Crab Fishery 2007/08, Fishery Assessment Report, Tasmanian Aquaculture and Fisheries Institute, Hobart, Tasmania, 2009 (2009) [Government or Industry Research]
This assessment of the Tasmanian giant crab fishery covers the period from 1st March 2007 to 29th February 2008, and provides forecasts of the likely response of the fishery to the total allowable commercial catch (TACC) set at a range of values.
Total catch reported in logbooks for the 2007/08 season was 53.2 tonnes, representing only 84% of the 62.1 tonne TACC1. This was 4.1 tonnes lower than the catch taken in the 2006/07 quota year. Industry members indicated that a factor contributing to this decline was the rapidly falling beach price after Christmas.
The limit reference point relating to a State-wide decline of catch rates in two successive years was exceeded. At only about 36% of the standardised catch rates in 1995/96, State-wide catch rates have remained low over the last few years and have shown no signs of recovery. Regionally, the catch rate limit reference point (a reduction of 20% or more in any 2-year period) was exceeded on the West coast (-30.0%) and on the East coast (-36.4%).
Bycatch of crabs by lobster fishers in the 2007/08 season was not of concern for the giant crab fishery, since the reported catch of only 61kg was well below the limit reference point of five tonnes.
Reference points relating to the weight structure of the catch landed at processors (the variation in the proportions of the catch above 5kg or below 3kg) were not assessed. Due to the availability of a stock assessment model, the length frequency data collected by fishers now provides much greater resolution than processor size-splits and is used for the biomass estimation in the stock assessment model.
In addition to the State-wide assessments, the model assessments were used separately for the East and West coast fisheries. Both the State-wide and regional size-based stock assessment models were able to generate acceptable fits to both catch rate and length frequency data, although the East coast model indicated relatively high uncertainty in estimates of biomass and harvest rates due to less length data. Compared to estimates from last year’s assessment, changes in standardised catch rates and improved estimation of biological parameters resulted in higher model predictions of stock productivity in the early years of the giant crab fishery. Therefore, relative levels of estimated current biomass and egg production tended to be lower.
The State-wide model estimated that the State-wide exploitable biomass declined from a maximum of about 1601 tonnes in the early 1990s to about 291 tonnes in 2007/08. This equates to about 18% of the original unfished exploitable biomass. Total biomass and egg production have decreased to 28% and 32% respectively of their initial levels. This level of egg production is considered average for a crustacean fishery. Estimated harvest rates have fallen slightly in 2007/08 to 0.21