Spatiotemporal segregation among summer stocks of beluga (Delphinapterus leucas) despite nuclear gene flow: implication for the endangered belugas in eastern Hudson Bay (Canada)

Abstract

Migratory connectivity between areas frequented by wide-ranging animals provides crucial information for conservation and management. In and around Hudson Bay (Canada), three stocks of beluga whales (Delphinapterus leucas) are associated with distinct summering areas. We analyzed genetic variation at mtDNA and 13 microsatellite loci among individuals (N [ 1400) harvested by 23 Inuit communities to identify mating units and assess temporal and spatial differences in the way stocks use common migratory pathways. Strong structure at mtDNA and a lack of convincing evidence for nuclear genetic differentiation indicate that both males and females adopt distinct migratory routes towards summering grounds while probably interbreeding on wintering grounds. Spatiotemporal variation in stock composition indicates that subsistence hunting targets all three stocks. While representing ca. 5% of belugas in Hudson Bay, the endangered Eastern Hudson Bay stock accounts for 17% of the overall subsistence harvest by Inuit communities of northern Nunavik (Quebec), and ca. 30% of the spring harvest along northeastern Hudson Bay. Despite interbreeding, cultural conservatism of maternally transmitted migration routes seems to prevent the re-establishment of stocks in previously frequented estuaries. This phenomenon supports the current use of demographic population models based on stock composition for developing behavior-based management strategies.

Groups of related belugas (Delphinapterus leucas) travel together during their seasonal migrations in and around Hudson Bay

“…There is no evidence for male biases in dispersal away from the distinct summering areas, because males and females exhibit the same pattern of mtDNA differentiation among summering areas [27]. In contrast, we find that male-only and female-only samples are disproportionately common among captures, indicating that the sex composition tends to be more homogeneous than expected if sexes were distributed at random among those groups.…”

“…Satellite transmitters deployed on EHB belugas at two estuaries (Nastapoka and Little Whale rivers) show that belugas in this area make frequent inshore -offshore movements with some movement between summer estuaries [54]. Thus, belugas probably show fidelity to general summering areas [27,34], as is the case for many other migratory cetaceans [39,[55][56][57][58].…”

“…Previous work has shown that for both males and females, there is clear mtDNA differentiation, but no nuclear genetic differentiation among these three beluga stocks [27,34]. Such patterns are likely due to matrilineages showing fidelity to summering areas, with gene flow occurring on common wintering areas [27,35].…”

“…Such patterns are likely due to matrilineages showing fidelity to summering areas, with gene flow occurring on common wintering areas [27,35]. Processes by which site fidelity and distinct migration routes are maintained are undocumented.…”

Regional diving behavior of Pacific Arctic beluga whales Delphinapterus leucas and possible associations with prey

“…Several aspects of beluga behavior, diet, and regional hydrography support this assumption. Belugas are long-lived, social ceta ceans with matrilineally derived migration routes and philo patry (O'Corry-Crowe 2008, Turgeon et al 2012, suggesting that the same regions are used each summer by related social groups. ECS belugas exhibit strong interannual philopatry for areas in the Barrow Canyon and Alaska Beaufort Sea, areas which overlap with the fish survey area (Hauser et al 2014).…”