Sex-specific dispersal patterns of the threatened Northern River Shark

Quantifying genetic connectivity between populations of a species is important to understand its conservation and management needs. Genetic connectivity implies gene flow among discrete populations occurring via the dispersal of individuals outside their population of origin, followed by reproduction. This process can be biased between sexes, with increasing evidence of sex-biased dispersal in elasmobranchs (sharks and rays). In this study we assessed the historical and contemporary connectivity of the threatened Northern River Shark ( Glyphis garricki ) using mitochondrial genomes, complemented with a genealogical framework based on close-kin relationships. Almost all of the 11 sampling locations in five regions across their known range formed a distinct breeding unit, with those locations in close geographical proximity sharing more kin. Close-kin results, based on cross-river half siblings and mitochondrial haplotypes, suggested that males had higher dispersal rates (63 % [23–68 %]), compared to females (10 % [5–20 %]). High fixation indices (global ΦST = 0.71) and a large proportion of same-river maternal half siblings (89 % [79–95 %]) indicated that females returned to their river of origin for pupping (i.e. natal philopatry on historical and contemporary timescales). By including full mitochondrial genome data, close-kin methods can detect sex-biased contemporary connectivity over the last couple generations. This is crucially important for the framing of conservation and management actions, and could require a sex-specific assessment of threats.