The effects of commercial fishing on Octopus pallidus populations in northern Tasmanian waters

The Octopus pallidus Fishery (OPF) is one of the few expanding fisheries in Tasmania, with annual catches approaching 100 t and a strong established market for fresh and value added products. Regardless of this, detailed information on the basic biology of O. pallidus has been unavailable until very recently, thus limiting investigations into the potential effects commercial fishing on stocks. The aim of this research is to determine the sustainability of preset fishing practices in the OPF. To achieve this catch per unit of effort (cpue) and biological information from a fixed position experimental research line were investigated for consistency in stock status patterns and compared with commercial fishery cpue trends. The research line results revealed that cpue could remain stable regardless of size-selective fishing mortality potentially impacting recruitment. Cpue in the commercial fishery was highly seasonal and dominated by females in autumn, when both cpue and spawning periods peaked, thus increasing the potential for negative fishery impacts on egg production. The inability of cpue to account for the effects of continual fishing pressure on recruitment or seasonal changes in sex-specific catchability indicates that cpue alone cannot provide sufficient information on the status of the OPF. In order to minimise the potential impacts of size selective fishing mortality, it is recommended that annual catch limits be based on half degree fishing blocks and that present biological catch sampling requirements are continued. Thus helping to ensure that the OPF remains environmentally and economically sustainable.