Population structure of North Pacific gray whales in light of trans‐Pacific movements

Abstract

Recent findings that some gray whales that feed off Sakhalin Island (SI), Russia, in the western North Pacific (WNP) overwinter in the eastern North Pacific (ENP) indicate that population structure in this species is more complex than originally thought. We generated mitochondrial DNA (mtDNA) control region sequences and microsatellite genotypes (n = 12 loci) from 156 whales sampled off SI and compared them to available data from 106 ENP whales. Significant mitochondrial and nuclear genetic differentiation between the SI and ENP whales was found. Genetic cluster analysis identified two groups among the SI whales, one of which was genetically similar to ENP whales. Photographs collected from the biopsied SI whales showed that both groups comprised whales known to migrate to the ENP, suggesting that the clustering pattern was not reflective of some SI whales interbreeding while overwintering in the WNP. Instead, the genetic differentiation observed between the SI and ENP whales may be due to assortative mating of SI whales while west of eastern migratory routes. The rare but continued reports of gray whales off the coasts of Japan and China, however, confirm that some gray whales overwinter in the WNP and highlight the need to collect additional data from these whales.

The migratory whale herd concept: A novel unit to conserve under the ecological paradigm

“…After the initial years of study, the majority of "new" (i.e., previously unidentified) whales photographed on the SI feeding ground have been calves brought to the area by known SI mothers. The mtDNA data provides further evidence that this pattern has persisted over multiple generations (Lang et al, 2021;LeDuc et al, 2002). Although a relatively large number of mtDNA control region haplotypes (n = 22) are found among whales sampled off SI, a high proportion (69%) of the SI whales, including most known reproductive females, carry one of two haplotypes.…”

“…The data available on gray whale reproduction, which are largely based on whales taken under scientific permit whaling off the coast of central California in the late 1950s and 1960s, suggest that most mating takes place during migration, with conception thought to primarily occur during a 3-week period from late November to early December (Rice & Wolman, 1971). For the whales migrating between SI and Mexico, this mating period may occur before the SI whales join the southbound migration of NFG whales, potentially providing a mechanism for SI whales to largely (but likely not exclusively; see Brüniche-Olsen et al, 2018;Lang et al, 2021) interbreed with each other and, in turn, create the signal of nuclear genetic differentiation that has been observed.…”

Downsized: gray whales using an alternative foraging ground have smaller morphology

“…Pressing questions arise, including: when did the PCFG form? While results from microsatellite allele frequencies show no genetic difference between ENP and PCFG, evidence supports differences in mitochondrial DNA haplotype frequencies, suggesting that matrilineal fidelity to this foraging ground contributes to recruitment into the PCFG [58–60]. Indeed, most calves first sighted in the PCFG range are re-sighted as juveniles or adults, further supporting matrilineal fidelity as a significant role in creating population structure [42,61].…”

“…It is possible that colonization/recolonization has occurred several times in the PCFG range due to commercial whaling or other climatic events (i.e. Little Ice Age) [58][59][60].…”

Assessment of a non-invasive approach to pregnancy diagnosis in gray whales through drone-based photogrammetry and faecal hormone analysis

“…Photo-identification of the PCFG has been conducted for over 30 years by multiple research groups that contribute data to a photo-ID catalogue curated by the Cascadia Research Collective (Olympia, WA, USA), enabling age estimation of individuals. Further, sex identification of PCFG whales is often available through genetic sampling [22,55] and observation records of females with calves.…”