Demographic analysis of the shortfin mako shark in the Northwest Pacific
Published online on 16. April 2014
Demographic analysis of the shortfin mako shark, Isurus oxyrinchus, in the Northwest Pacific using a two-sex stage-based matrix model
Wen-Pei Tsai, Chi-Lu Sun, André E. Punt, Kwang-Ming Liu
ABSTRACT:
Most demographic models are single sex, and assume both sexes have the same vital rates. However, many species, including the shortfin mako shark, are sexually dimorphic in vital rates, which suggests the need for two-sex models. In this study, a two-sex stage-structured matrix model was constructed to estimate shortfin mako shark demography and population dynamics. Monte Carlo simulations were used to evaluate the impact of uncertainties on the estimate of population growth rate. The number of shortfin mako sharks is found to be dropping under current conditions, but will stabilize if size-limit management is implemented. The simulations indicated that population growth rate estimates are mainly influenced by the uncertainty related to survival rate and fecundity. The effects of uncertainty regarding the age at maturity and longevity were found to be relatively minor. Future research should focus on obtaining estimates of natural mortality and reproductive traits for this species to improve the accuracy of demographic estimates.
ICES J. Mar. Sci. (2014) doi: 10.1093/icesjms/fsu056