Numerical approach for evaluating impacts of biological uncertainties on estimates of stock-recruitment relationships in elasmobranchs: Example of the North Pacific shortfin mako

Abstract

Impacts of biological uncertainties on estimates of stock-recruitment relationships (SRRs) in elasmobranchs such as lamniform sharks were evaluated using a numerical approach based on an age-structured model considering reproductive ecology in elasmobranchs. The values of steepness were estimated using several combinations of life history parameters for North Pacific shortfin mako to elucidate whether the numerical approach could identify reasonable values for fundamental life history parameters as well as steepness. The results of the numerical approach indicated that the mean values of steepness and their 95% confidence intervals were highly sensitive to combinations of values for growth rate, maturity ogive, longevity, reproductive cycle, and natural mortality rate. Meanwhile, the most plausible combinations of the biological parameters and values of steepness were identified based on the numerical approach with biological knowledge. The mean values and their standard deviation (SD) for steepness with the Beverton-Holt-SRR model were 0.353 (SD=0.057) and 0.273 (SD=0.046) for 2- and 3-year reproductive cycles, respectively. The numerical approach therefore has high potential to become an important tool for estimating SRR in elasmobranchs such as lamniform sharks, and the application of this approach to other elasmobranchs could greatly contribute to improvements in stock assessment and management.