The western gray whale: a review of past exploitation, current status and potential threats (original) (raw)
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Journal of Cetacean Research and Management
Gray whales (Eschrichtius robustus) occur along the eastern and western coastlines of the North Pacific as two geographically isolated populations and have traditionally been divided into the eastern (California-Chukchi) and western (Korean-Okhotsk) populations. Recent molecular comparisons confirm, based on differences in haplotypic frequencies, that these populations are genetically separated at the population-level. Both populations were commercially hunted, but only the eastern gray whale has returned to near pre-exploitation numbers. In contrast, the western population remains highly depleted, shows no apparent signs of recovery and its future survival remains uncertain. Research off Sakhalin Island, Russia between 1995 and 1999 has produced important new information on the present day conservation status of western gray whales and provided the basis for the World Conservation Union (IUCN) to list the population as 'Critically Endangered' in 2000. The information presented here, in combination with potential impacts from anthropogenic threats throughout the range of this population, raises strong concerns about the recovery and continued survival of the western gray whale.
A collaborative Russia-U.S. research program on western gray whales (Eschrichtius robustus) summering off northeastern Sakhalin Island, Russia, has been ongoing since 1995 and has produced important new information on the present day conservation status of this critically endangered population. This interim report reviews preliminary findings from 2007 research activities and combines such with data from previous years, in some cases ranging back to 1994. Photo-identification research conducted off Sakhalin Island in 2007 resulted in the identification of 83 whales, including nine calves and two previously unidentified non-calves. When combined with data from 1994-2006, a catalog of 169 photo-identified individuals has been compiled. Not all of these 169 whales can be assumed to be alive, however. The most current mark-recapture analyses conducted estimated the abundance for the population to be 98 (95% CI=89-110) in 2002 and 99 (95% CI = 90-109) in 2003. A recent population assessment using a Bayesian individually based stage-structured model fitted to the same photo-identification data as used in the markrecapture studies, but also including data from 2004 through 2006, estimated the median non-calf population size to be 110 in 2004 and, should current population and demographic trends continue, projected a median non-calf estimate of 121 (90% Bayesian CI = 112-130) in 2007. Of the 169 whales photo-identified, 142 (84%) have been biopsy sampled. From genetic analysis of samples (n = 129) collected through 2006, an overall sex ratio of 58% male and 42% female was determined. Clear genetic differentiation from the eastern gray whale population and negligible gene flow of either sex between populations, based on mitochondrial DNA haplotype frequencies and nuclear DNA, have been documented. A minimum of 24 reproductive females has been observed since 1995. Of the 83 whales observed in 2007, 7.2% (n = 6) were recorded as "skinny". In addition to the biological difficulties that western gray whales are facing, the large-scale offshore oil and gas development programs near their summer feeding ground, as well as fatal net entrapments off Japan during migration, pose significant threats to the future survival of the population.
Critically endangered western gray whales migrate to the eastern North Pacific
Biology letters, 2015
Western North Pacific gray whales (WGWs), once considered extinct, are critically endangered with unknown migratory routes and reproductive areas. We attached satellite-monitored tags to seven WGWs on their primary feeding ground off Sakhalin Island, Russia, three of which subsequently migrated to regions occupied by non-endangered eastern gray whales (EGWs). A female with the longest-lasting tag visited all three major EGW reproductive areas off Baja California, Mexico, before returning to Sakhalin Island the following spring. Her 22 511 km round-trip is the longest documented mammal migration and strongly suggests that some presumed WGWs are actually EGWs foraging in areas historically attributed to WGWs. The observed migration routes provide evidence of navigational skills across open water that break the near-shore north-south migratory paradigm of EGWs. Despite evidence of genetic differentiation, these tagging data indicate that the population identity of whales off Sakhalin I...
Gray whale Eschrichtius robustus population and stock identity
Mammal Review, 2006
1. In response to conservation and management concerns about gray whale Eschrichtius robustus population and stock structure, we provide an overview of the life history and ecology of gray whales as a context for discussion of population and stock structure within the species. Historically eastern and western North Pacific gray whales were managed separately because: (i) their ranges do not overlap; (ii) genetic analyses indicate that the two populations are significantly different; and (iii) eastern gray whales have increased in abundance over the past century while western gray whales have not.