Reproductive philopatry in a coastal shark drives age-related population structure
The cosmopolitan lamniform shark Carcharias taurus (commonly known as the ragged-tooth, grey nurse or sand tiger shark) is threatened by overexploitation in parts of its range. Return migrations of females to specific nursery areas suggest that females exhibit reproductive philopatry, a behaviour that over time might lead to genetically isolated subpopulations over various spatial scales. To investigate genetic evidence for reproductive philopatry, genetic data from mitochondrial and microsatellite markers were generated for 104 young-of-the-year and juvenile sharks. Comparing the smallest versus the largest young sharks revealed a pattern of size-related differentiation between nurseries that was only found in the smaller size class. This not only confirms reproductive philopatry of their mothers, but is also in line with previous observations of larger juvenile sharks increasing their migration range and moving between sites. Our results highlight the need to target young-of-the-year sharks when investigating reproductive philopatry to exclude roaming individuals that obscure size-related signals of genetic differentiation. Given the species’ high susceptibility to overexploitation, the evidence for reproductive philopatry is of direct importance to the management and conservation of C. taurus worldwide. As many nursery areas as possible should be protected to ensure that the number of locally resident juveniles and the pool of the returning females remain stable in the long term. This may warrant protected areas, or time-area closures, prohibiting exploitation in the nursery areas during pupping season.
Special thanks are given to all volunteer anglers that collected samples as part of the Port Elizabeth Museum (PEM) co-operative shark tagging programme. We also thank the PEM Director and staff for their support and infrastructure. We would also like to thank two anonymous reviewers whose constructive comments improved the final version of this manuscript.
This work is based on research supported in part by the National Research Foundation of South Africa through a Thuthuka grant to KLM (Unique Grant no. 99440) and the University of Johannesburg (FRC/URC Grant to PRT). JDK is grateful to the University of Johannesburg for awarding her a Global Excellence and Stature (GES) PhD bursary.
Compliance with ethical standards
Conflict of interest
The authors have no conflict of interest to declare.
All capture and sampling protocols were conducted following guidelines endorsed by the PEMs animal ethics committee.
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