Preliminary stock assessments of blue marlin (Makaira mazara) and striped marlin (Kajikia audax) in the Indian Ocean by A Stock-Production Model Incorporating Covariates (ASPIC)

A Stock-Production Model Incorporating Covariates (ASPIC) was used to perform the stock assessment of blue and striped marlins in the Indian Ocean based on total catch data and standardized CPUE series of Taiwanese and Japanese longline fleets. Both of Schaefer and Fox models were adopted for assessment of blue marlin due to problematic estimation of shape parameter of production function. Negligible outcomes can be observed from Schaefer and Fox models, while the assessment result of Schaefer model would be relatively conservative. The result of Schaefer model indicated that the current (2011) biomass is close to that at the MSY level, while current fishing mortality is below the MSY level. However, it should be noted that the model fits to the CPUE series are debatable since standardized both of CPUE series revealed substantial decline around late 1980s. The stock assessment of striped marlin was carried out based on a generalized model (Pella-Tomlinson model). The result indicated that the MSY reference points have been exceed, current (2011) biomass is below the MSY level and current fishing mortality is slightly higher than the MSY level.