Weak population structure of the Spot-tail shark Carcharhinus sorrah and the Blacktip shark C.limbatus along the coasts of the Arabian Peninsula, Pakistan, and South Africa.

Dareen Almojil,Julia L Y Spaet,Geremy Cliff

doi:10.1002/ece3.4468

Abstract

The increase in demand for shark meat and fins has placed shark populations worldwide under high fishing pressure. In the Arabian region, the spot‐tail shark Carcharhinus sorrah and the Blacktip shark Carcharhinus limbatus are among the most exploited species. In this study, we investigated the population genetic structure of C. sorrah (n = 327) along the coasts of the Arabian Peninsula and of C. limbatus (n = 525) along the Arabian coasts, Pakistan, and KwaZulu‐Natal, South Africa, using microsatellite markers (15 and 11 loci, respectively). Our findings support weak population structure in both species. Carcharhinus sorrah exhibited a fine structure, subdividing the area into three groups. The first group comprises all samples from Bahrain, the second from the UAE and Yemen, and the third from Oman. Similarly, C. limbatus exhibited population subdivision into three groups. The first group, comprising samples from Bahrain and Kuwait, was highly differentiated from the second and third groups, comprising samples from Oman, Pakistan, the UAE, and Yemen; and South Africa and the Saudi Arabian Red Sea, respectively. Population divisions were supported by pairwise FST values and discriminant analysis of principal components (DAPC), but not by STRUCTURE. We suggest that the mostly low but significant pairwise FST values in our study are suggestive of fine population structure, which is possibly attributable to behavioral traits such as residency in C. sorrah and site fidelity and philopatry in C. limbatus. However, for all samples obtained from the northern parts of the Gulf (Bahrain and/or Kuwait) in both species, the higher but significant pairwise FST values could possibly be a result of founder effects during the Tethys Sea closure. Based on DAPC and FST results, we suggest each population to be treated as independent management unit, as conservation concerns emerge.

Highlights

With an increasing number of conservation challenges and species under threat, population genetics offer a noninvasive tool to uncover otherwise unattainable information (Allendorf & Waples, 1996; Van Wijk et al, 2013)
The identification of genetic structure is fundamental in determining the extent of reproductive isolation between populations (Hartl, 1988) and can have direct implications in designing effective protection plans
This study presents a regional analysis of the genetic population structure of two potentially overexploited shark species (Jabado et al, 2015; Spaet & Berumen, 2015; Spaet et al, 2016) along the coasts of the Arabian Peninsula, Pakistan, and South Africa

Summary

Introduction

With an increasing number of conservation challenges and species under threat, population genetics offer a noninvasive tool to uncover otherwise unattainable information (Allendorf & Waples, 1996; Van Wijk et al, 2013). The identification of genetic structure is fundamental in determining the extent of reproductive isolation between populations (Hartl, 1988) and can have direct implications in designing effective protection plans. The genetic structure observed in different shark species is believed to depend on hard and soft barriers to gene flow. Hard barriers result from ancient events creating a physical landmass barrier to oceanic gene flow (e.g., the terminal Tethyan Event and the Isthmus of Panama, which separated the Indian and Atlantic Oceans and the Pacific and Atlantic Oceans, respectively). Soft barriers to gene flow are those related to a species’ biology and behavior or invisible physical factors such as water currents or temperature (Cowman & Bellwood, 2013)

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