Dispersal capacities of anadromous Allis shad population inferred from a coupled genetic and otolith approach

Understanding dispersal capacities for migratory species is crucial for their management. By coupling otolith microchemistry and microsatellite genetic analyses, we provided information on snapshot and long-term dispersal capacity of Allis shad (Alosa alosa), an anadromous clupeid in decline throughout its distribution range. The allocation of natal origin was obtained from water chemistry and signatures in otoliths of juveniles and spawners within a Bayesian model. The majority of adults were assigned to a source river with high degrees of confidence; only 4% were undetermined. Otolith natal origins were used to define a population baseline by grouping individuals from the same natal river and not from the same sampling location as usually done. While A. alosa exhibited a high level of natal site fidelity, this species showed weak genetic structure, which supported the evidence of a substantial flow of strayers between river basins in the vicinity or at longer distances. However, long distance straying was probable but not frequent. In a context of global change, straying would be a key mechanism to drive dispersal and allow resilience of Allis shad populations.