Population genetics of the hound needlefish Tylosurus crocodilus (Belonidae) indicate high connectivity in Tanzanian coastal waters

Abstract

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The hound needlefishTylosurus crocodilus(Belonidae) is a highly demandedfish in the localmarkets of Tanzania, but the growing coastal population threatens its sustainability. As belonidsare highly migratoryfishes utilising various parts of the seascape, increasedfishing pressuremay disrupt connectivity patterns on different spatiotemporal scales and disaggregatepopulations. Using the COI gene, this study assessed the genetic population structure,connectivity patterns, and historical demography ofT. crocodiluscollected in seven sites spreadalong Tanzanian coastal waters. Results showed fourteen haplotypes with low overallnucleotide and haplotype diversity. Pairwise FSTcomparisons revealed no significant differencesamongthesampledsites,exceptforthenorthernmostsite(Tanga)andanislandinthesouth(Songosongo). Analysis of molecular variance (AMOVA) revealed a non-significant geneticstructure among populations (FST= 0.01782), suggesting thefishery across Tanzanian watersexploits the same population. Moreover, there was no correlative relationship between geneticand pairwise geographic distances, rejecting the isolation by distance hypothesis. However,neutrality tests and mismatch distribution analysis revealed that recent demographic expansionmight exist. Empirical evidence of panmixia suggests high genetic connectivity. In combinationwith low genetic diversity, management shouldbe directed to actions that prevent geneticdiversity loss and the effect of genetic drift on populations.