Estimation of the population status of smooth hammerhead shark (Sphyrna zygaena) and scalloped hammerhead shark (Sphyrna lewini) in the Northwest Pacific Ocean: A data-limited approach

Abstract

While data on fisheries, in general, may be limited, demographic models provide a valuable tool for gaining insights into population dynamics when a more comprehensive understanding is not feasible. Demographic models may be used in the study of population dynamics because they only require life history parameters. We performed a quantitative population projection on the basis of expert knowledge, estimated mortality, and published information on the life history of two hammerhead shark species, smooth hammerhead (Sphyrna zygaena) and scalloped hammerhead (Sphyrna lewini), and we conducted an elasticity analysis determine the sensitivity of each life stage to the population growth rate. This study highlights the overexploitation challenges faced by these two ecologically important and vulnerable species and emphasizes the need to reduce fishing mortality is crucial to achieving population growth. To increase the accuracy of demographic estimates for these species, it is necessary to conduct further investigations into their natural mortality and reproductive traits. The approach used in this study can be applied to other shark species across a diverse range of taxa with limited data on catch and effort. Moreover, this method is easy to use and interpret and can be used to predict future population size for data-limited species.