The effects of temperature and alongshore wind stress on the catchability of spanner crab (Ranina ranina)

Catchability is a key parameter used for stock management of fisheries. Factors which influence catchability are largely associated with fishing methods and species abundance; however, oceanographic processes play an important role during different stages of many fisheries species’ lifecycles and, therefore, can also influence catch rates. For example, ambient temperature may affect the behaviour of crabs by influencing their energy and activity levels, which in turn affects their emergence patterns and availability to the fishery. Previous work suggest favourable catches of spanner crab can be attributed to stronger currents and warmer ambient temperatures, prompting the need to quantify processes responsible for current and temperature changes in the Bottom Boundary Layer (BBL) of the fishery. In the southern part of the Queensland spanner crab fishery, located on the east coast of Australia, sea surface temperature (SST) and alongshore wind stress was trialled as possible indicators of BBLT temperature (BBLT) and, consequently, catches of spanner crab. Using Generalised Linear Models (GLM), our findings display evidence that cooler BBLT and upwelling-favourable wind stress significantly improves daily spanner crab catch rates. This significant, inversely proportional trend between BBLT and catch rates opposes previous work and, thus, emphasises the importance of multiple hypotheses when relating oceanographic processes to the abundance, distribution, and availability of fisheries species. Future studies on BBLT affecting the catchability of spanner crabs would benefit from taking into consideration the variability of oceanographic processes across greater spatial scales (i.e. the whole fishery).