Genetic population structure of eastern North Pacific gray whales (Eschrichtius robustus) on winter breeding grounds in Baja California

Sequence data from the mitochondral DNA control region were used to investigate whether gray whale winter habitat-use patterns are influenced by female-directed philopatry. We tested for genetic differentiation among samples of eastern North Pacific gray whales (Eschrichtius robustus ) from two geographically discrete winter breeding lagoons and between each lagoon population and a random sample of the total eastern North Pacific population. An AMOVA detected significant genetic differentiation between females of different reproductive status (cows with calves vs. cows without calves) within Laguna San Ignacio (phiST = 0.088, p = 0.038) and between these cows with calves and a random sample of females from outside of the winter range (phiST = 0.041, p = 0.045). These results indicate a non-random distribution of females in Laguna San Ignacio in calving years, which suggest that female gray whales exhibit female-directed migration-site fidelity to Laguna San Ignacio during the years that they produce a calf.