The relationship between abundance and genetic effective population size in elasmobranchs: an example from the globally threatened zebra shark Stegostoma fasciatum within its protected range

Abstract

Genetic effective population size (Ne) estimators are useful as applied conservation tools. Many elasmobranch (shark and ray) species are threatened at local and global scales, and tools to monitor these populations are greatly needed. This study investigates contemporary Ne and its relationship with census size (Nc) in a population of zebra sharks (Stegostoma fasciatum). Our Ne using the linkage disequilibrium method, 377 (95 % CI 274–584) was found to closely approximate the mark-recapture Nc for this population of mature sharks (458, 95 % CI 298–618), with an Ne/Nc ratio of 0.82 (SE = 0.33). Furthermore, we conducted a series of sensitivity analyses to examine how the numbers of samples and loci affect the precision and accuracy of the estimators. We demonstrate that for this species robust and precise estimates are obtainable with a minimum of 91 samples (approximately 20 % of the census population) and 10 microsatellite loci. These findings contribute important information to the greater body of Ne and Ne/Nc relationships in elasmobranchs and wildlife populations as well as provide important guidelines for implementing genetic monitoring in elasmobranch conservation efforts.