Standardized catch rates of the shortfin mako (Isurus oxyrinchus) caught by the Taiwanese longline fishery in the Atlantic Ocean

In this document, the shortfin mako shark catch and effort data from observers’ records of Taiwanese large longline fishing vessels operating in the Atlantic Ocean from 2007-2015 were analyzed. Based on the shark by-catch rate, four areas, namely, I (north of 20ºN), II (5ºN-20ºN), III (5ºN-15ºS), and IV (south of 15ºS), were categorized. To cope with the large percentage of zero shark catch, the catch per unit effort (CPUE) of shortfin mako shark, as the number of fish caught per 1,000 hooks, was standardized using a two-step delta-lognormal approach that treats the proportion of positive sets and the CPUE of positive catches separately. Standardized indices with 95% bootstrapping confidence intervals are reported. The standardized CPUE of shortfin mako sharks in the South Atlantic was relatively stable from 2007-2014 but decreased in 2015. It peaked in 2009, decreased in 2010 and fluctuated thereafter for the North Atlantic shortfin mako sharks. The shortfin mako shark by-catch in weight of the Taiwanese large-scale longline fishery ranged from 2 tons (1989) to 89 tons (2009) in the North Atlantic Ocean and ranged from 29 tons (1989) to 280 tons (2011) in the South Atlantic Ocean.