Evaluating the impacts of uncertainty on the estimation of biological reference points for the shortfin mako shark, Isurus oxyrinchus, in the north-western Pacific Ocean

Abstract

Biological reference points (BRPs) are commonly used to assess the harvest level and stock status of marine fish populations. However, BRP estimates may be influenced by uncertainties about life-history parameters and fishing practices. The shortfin mako shark, Isurus oxyrinchus, is one of the most important by-catch species for tuna longline fisheries; however, its stock status remains poorly understood. To understand its population dynamics, the present study examined fishery statistics data and biological measurements of the shortfin mako in the north-western Pacific, and evaluated the impact of uncertainties associated with various sources of uncertainty, by using a simulation approach. The simulations indicated that BRPs are especially sensitive to changes in weight–length relationship and the growth parameters. Failure to take this into account may lead to inaccurate estimates and have serious consequences for management decision-making. To improve the accuracy of BRP estimates, biological measurements and life-history parameters should be updated regularly to account for changes in size composition and population structure. Further research could focus on increasing the sex-ratio sample size, updating the weight–length relationship and growth equations, incorporating ageing error into BRP calculations and determining BRPs by using appropriate levels of spawning-potential ratio.