Biological and fisheries data for managing deep sea crabs in Western Australia
Since the snow crab is presumably slow growing and long-lived and therefore vulnerable to overfishing, there is a pressing need for collecting baseline biological and fishery data that can be used to produce a preliminary stock assessment for assisting in the management and conservation of this species in Western Australia. Mechanisms for obtaining data on size compositions and catch statistics for the fishery in the early stages of its development need to be established so that the extent to which large animals are depleted as a result of fishing pressure can be determined.
In the early stages of the proposed work, it will be necessary to determine the catch and distribution of the commercial fishery and the size (carapace length), sex ratio and relative abundance by depth of the crabs that form the basis for the fishery. This will enable any future changes that occur in these characteristics as a result of fishing pressure to be detected.
Since snow crabs are expected to have long intermoult periods, it will be necessary to tag crabs as soon as possible to provide, in the relatively near future, information on growth rates, movements, and estimates of yield and eggs (or spawning biomass) per recruit.
Accurate information is needed on the size at which snow crabs first reach maturity and how frequently spawning occurs within a year.
Information is required on the size of gaps in traps that would allow sublegal sized crabs to escape and thereby prevent unnecessary mortality and displacement.
A basic stock assessment is required to meet Environment Australia’s Schedule 4 exemption in the short term and Fisheries WA/Environment Australia requirements whch are to be initiated in December 2002.
Final report
The crystal crab fishery on the west coast of Western Australia has only been commercially fished since the late 1990s. When this project was initiated in 2001, only compulsory monthly catch and effort data were being collected. This project has successfully set up the methods and means to collect and analyse more appropriate commercial catch and effort data for the fishery. Fishers now record detailed daily catch and effort data for legal as well as undersize and berried crabs and the Department of Fisheries, WA, has a regular monitoring programme to record population size structure information.
This project has also allowed for the collection, analysis and interpretation of biological data for the species. An extensive tagging programme has been undertaken over the five-year duration of this project.