Revised standardized CPUE of shortfin mako (Isurus oxyrinchus) caught by the Japanese tuna longline fishery in the north Atlantic ocean between 1994 and 2015

Previous estimates of standardized CPUE for shortfin mako (Isurus oxyrinchus) caught by the Japanese tuna longline fishery in the Atlantic Ocean were revised with consideration for the temporal changes in the operational pattern for the Japanese fleet in the North Atlantic between 1994 and 2015. Investigation of spatiotemporal distribution of fishing effort suggested that displacement of fishing effort for Atlantic bluefin tuna (Thunnus thynnus) especially in the area north of 20˚ N caused an unrealistic decline of CPUE for the North Atlantic shortfin mako in the past five years in the previous analysis. Based on the investigation of number of set and nominal CPUE of shortfin mako, area stratification was revised and explanatory variables included in GLM analysis were modified. Following the data filtering described in Semba et al. (2012), CPUE of North Atlantic shortfin mako was standardized using zero inflated negative binomial model. The revised abundance index showed a declining trend in the earliest few years and a stable trend around 0.1 (fish/1000 hooks) between 1995 and 2005, followed by a continuous increasing and declining trend between 2005 and 2013. Although uncertainty has been left in the estimates of several years, the current analysis improved the uncertainty indicated since the late 2000s in the past analysis and suggested that annual trend of the abundance index would not show a continuous increasing/decreasing trend between 1994 and 2015.