Updated CPUE of shortfin mako, Isurus oxyrinchus, caught by Japanese research and training vessels in the western and central North Pacific
This working paper presents updated annual standardized catch per unit of effort (CPUE: catch number per 1,000 number of hooks) for shortfin mako caught by longline fishery of Japanese training and research vessels during 1992 and 2019 in the North Pacific. The author used the same estimation methods used in the previous analysis. Since the reporting rates of sharks during 2001 and 2013 are clearly lower than those before 2000, the author removed the data with lower reporting rates using the filtering method based on the prediction of the binomial generalized linear model. Then we standardize the nominal CPUE using two-step model (binomial model for presence/absence and Poisson model for positive catch) in consideration of the characteristics in the data with high zero catch ratio and small over-dispersions. The annual trends in the standardized CPUE slightly increased with large fluctuations until 2007, and then its gradually decreased until 2013. Thereafter, the annual trends in the CPUE sharply increased associated with the lower fishing effort. The CVs of the standardized CPUE were smaller than 0.16 over the years. These results suggested that the recent abundance of shortfin mako in the western and central North Pacific is likely to be on the rise due to the reduction of fishing effort.