Updated CPUE of shortfin mako, Isurus oxyrinchus, caught by Japanese shallow-set longliner in the northwestern Pacific from 1994 to 2019
This working paper provides with an updated standardized CPUE of shortfin mako caught by Japanese offshore and distant-water shallow-set longline fishery from 1994 to 2019 in the northwestern Pacific. The author basically used the same estimation methods used in the previous analysis. Two filtering methods were used to remove the mis-reporting and inappropriate data. Since the zero-inflated negative binomial model had an issue of model convergence, negative binomial model with the same explanatory variables as used in the previous analysis was used as the best model to standardize the CPUE for the filtered data. The annual standardized CPUE indicated that the historical population trend of shortfin mako had gradually increased until 2011, and then a stable trend was observed except in 2016. The author considered that (1) the increase trends until 2004 was caused by the gradual increase of catch number with a slight increase of fishing effort, (2) the steep increase from 2004 to 2011 was mainly caused by the continuous decrease of the fishing effort with stable annual catches, and (3) the stable trends in recent years were caused by the constant catch and fishing efforts.