Environmental drivers of commercial blue swimmer crab (Portunus armatus) catch rates in Western Australian fisheries

Sustainable fisheries management requires accurate stock assessment and an understanding of how targeted populations vary over space time respond to external stressors. Commercial fishery catch rate data (i.e. per unit effort; CPUE) are widely used assess performance can provide a measure abundance. However, changes in environmental conditions influence the two determinants CPUE, i.e. catchability (q) abundance (N). We explore variables (water temperature, wind speed, rainfall, freshwater flow, wave height, lunar illumination, tide height depth) on commercial blue swimmer crab Portunus armatus CPUE five Western Australian fisheries. Generalised additive mixed models (GAMMs) were identify which had greatest enabled predictions these with change. Water temperature significant positive effect all fisheries, although some exhibited decline above optimal range. Wind speed generally (but lower magnitude) effects three investigated, while illumination flow caused or less When annual standardised for effects, they displayed clear variation from nominal (raw) CPUE. These results highlight importance measuring accounting (e.g. through standardisation) when using assessments.