Updated connectivity assessment for the scalloped hammerhead (Sphyrna lewini) in Pacific and Indian Oceans using a multi-marker genetic approach

Abstract

Patterns of genetic connectivity can be used to define the geographic boundaries of fishes and underpin management decisions. This study used a genetic multi-marker approach to investigate the population structure of scalloped hammerheads (Sphyrna lewini) in the Indo–Pacific. Samples from 541 S. lewini were collected from 12 locations across the Indo–Pacific. Samples were analysed using two regions of the mitochondrial genome, nine microsatellite loci and two sets of Single Nucleotide Polymorphisms (SNP). Our study has four key findings; (1) genetic structure of S. lewini across the Indo–Pacific is affected by oceanic basins and can be separated into four distinct regions. (2) Within the central Indo–Pacific, connectivity is facilitated along continental shelves and strong signals of Isolation-By-Distance (IBD) were observed. (3) Mitochondrial haplotypes previously thought only to exist in the Atlantic Ocean are observed in Indo–Pacific populations, suggesting the haplotype should be reconsidered as more widespread than initially thought. (4) Results from microsatellites and SNPs largely agree, however a few differences are apparent with SNPs identifying more discrete population subdivision. Our findings suggest management at the spatial scales and boundaries identified in this study will necessitate international and national cooperation to conserve S. lewini populations.