Catch rate and stock status of blue shark in the Pacific Ocean inferred from fishery-independent data

Abstract

Among pelagic sharks, the Blue shark, <em>Prionace glauca</em> (<em>Carcharhiniformes, Carcharhinidae</em>) is known to be the most abundant. Although, blue shark is relatively productive, concerns have been raised related to the decline in population of these apex fish predators; and this decline can affect the marine ecology. This paper presents catch per unit effort (CPUE) data of blue sharks obtained from observers’ on-board Chinese pelagic longline fishing vessels from 2009–2014 in the Pacific Ocean. All the blue shark species were incidentally captured (without shark hook). Nominal CPUE ranged from 0 individual per 1000 hooks to 5.21 individuals per 1000 hooks; the highest annual average nominal CPUE recorded in this study was 0.89 individual per 1000 hooks in 2011 while, 0.58 was the lowest recorded in 2010. Our results equally indicates that, blue shark population was so close to MSY level showing that fishing mortality rate might surpass MSY level in the future, since decrease in catches were observed. Therefore, additional management measures should be implemented in the Pacific Ocean in order to achieve a healthy stock status of this species.