Giant Crab Pseudocarcinus gigas

Southern Australian biological stock

The cross-jurisdictional southern Australian biological stock has components in Tasmania, Western Australia, South Australia and Victoria. Each jurisdiction assesses that part of the biological stock that occurs in its waters. Historically, the Tasmanian and Victorian fisheries have constituted the bulk of the Giant Crab fishery; however, both these states have had substantial reductions in total allowable commercial catch (TACC) over the past decade. The status presented here for the entire biological stock has been established using evidence from all four jurisdictions.

For the Tasmanian part of the biological stock (where the majority of the catch has historically been taken), a length-based model has been developed to estimate annual levels of biomass and egg production. The model is based on data that include catch-and-effort data from commercial fisheries⁴. It estimated that egg production is stable at 19 per cent of unfished levels⁵. Although this is adequate relative to benchmarks used in some crustacean fisheries⁶, the slow growth and longevity of Giant Crab increase its susceptibility to becoming recruitment overfished and lead to substantial uncertainty in the modelling. Despite TACC reductions to levels that are expected to result in stock rebuilding (see below), catch per unit effort (CPUE) has decreased gradually since the inception of the Tasmanian fishery, indicating an ongoing biomass decline. However, although in decline, this part of the stock is not yet considered to be recruitment overfished.

The TACC for the Tasmanian part of the biological stock has been reduced in several steps from 104 tonnes (t) in 2003–04 to 38.3 t in 2014–15, with the objective of increasing abundance and catch rates; the latest decrease was from 46.6 t to 38.3 t for the 2014–15 licensing year. The TACC is routinely undercaught by approximately 10 per cent because of limited quota trading and leasing. In the 2013–14 quota year (March–February), only 57 per cent of the TACC was taken. This is partly related to changes in industry regulation and partly to low CPUE. The ongoing decline in catch rates, despite substantial TACC reductions, indicates that the current level of fishing pressure is likely to cause the Tasmanian part of the stock to become recruitment overfished.

Management of fishing mortality in Victoria is through a TACC, and legal minimum lengths to protect mature undersized crabs. The legal minimum lengths aim to ensure that egg production remains at no less than 40 per cent of unfished levels⁷. However, there is considerable uncertainty around the population dynamics of larger females and hence the degree of protection provided by these limits. The TACC was set at 25 t from 2002 to 2009, but has been decreased over several years in response to declining catch rates, to 12 t in 2012–13. Despite these TACC reductions, there has been no observed increase in CPUE⁸. This part of the stock is not yet considered to be recruitment overfished; however, the ongoing decline in catch rates and the lack of response to TACC reductions indicates that, without more stringent constraints on catch, the current level of fishing pressure is likely to cause the Victorian part of the stock to become recruitment overfished within the next few years.

Fishing mortality in South Australia and Western Australia is also managed through TACCs and the same legal minimum length as in Victoria. Catches and catch rates in South Australia⁹ have been stable; however, there are some concerns about the reliability of these data. Combined with a lack of targeted fishery data in Western Australia, this means that insufficient information is available to confidently classify the status of these two parts of the biological stock.

The major component of the biological stock, in terms of historical biomass and catch, occurs in Tasmania and Victoria. As a result, the overall stock status classification is based only on the Tasmanian and Victorian parts of the stock.