Standardizing CPUE of yellowfin tuna (Thunnus albacares) longline fishery in the tropical waters of the northwestern Indian Ocean using a deterministic habitat-based model

Data collected from a longline fishery in the Indian Ocean were used to evaluate the performance of a deterministic habitat-based standardization (detHBS) method for catch per unit effort (CPUE) standardization. The habitat preference indices of the yellowfin tuna (Thunnus albacares) were estimated for different depth, temperature, and dissolved oxygen (DO) classes. The detHBS was applied for standardizing the yellowfin tuna CPUE based on the habitat preference indices of the yellowfin tuna. Nominal CPUE and normalized nominal CPUE were compared with the standardized CPUE and normalized standardized CPUE, respectively, using Wilcoxon tests. The results showed that (1) there was significant difference between nominal CPUE and standardized CPUEs (p < 0.01); (2) there was no significant difference between normalized nominal CPUE and normalized standardized CPUEs estimated using the data set of depth, temperature, and DO (p > 0.01). This study suggests that detHBS effectively improved the precision of CPUE standardization, and the depth data set was the optimum data set in standardizing CPUE.