Research Document 2021/020
Recovery Potential Assessment for the Grey Whale (Eschrichtius robustus): Pacific Coast Feeding Group and Western Pacific Population in Canadian Waters
By Gavrilchuk, K. and Doniol-Valcroze, T.
Abstract
Once the Committee on the Status of Endangered Wildlife in Canada (COSEWIC) assesses an aquatic species as Threatened, Endangered or Extirpated, Fisheries and Oceans Canada undertakes actions to support implementation of the Species at Risk Act. In November 2017, COSEWIC split the Eastern North Pacific Grey Whale population into two designatable units (DU): the Northern Pacific Migratory (NPM) population (Not At Risk, ~27,000 individuals) and the Pacific Coast Feeding Group (PCFG, Endangered, 243 individuals). Some individuals from another DU, the Western Pacific (WP) Grey Whale population (Endangered, 282 individuals), migrate across the North Pacific, through Canada and the U.S., to breeding grounds in Mexico. The objective of this RPA is to provide scientific information on the current status of the two Endangered Grey Whale DUs in Canada, threats to survival and recovery, and the feasibility of recovery. All three DUs share breeding grounds in Mexico during the winter and a portion of the migration route along the west coast of North America during spring and fall. The NPM population feeds in the Beaufort, Bering and Chukchi Seas, while the PCFG shows high fidelity to lower-latitude feeding sites, primarily from northern California to northern British Columbia during the summer. The WP population feeds off Sakhalin Island and Kamchatka Peninsula in Russia. PCFG abundance increased from 1998 to 2004, remained relatively stable from 2005 to 2010, and increased from 2011 to 2015. The WP population abundance (including both Sakhalin Island and Kamchatka feeding aggregations), has been steadily increasing at 2 to 5% since the mid-1990s. Primary threats to survival and recovery of the PCFG and WP population are entanglement in fishing gear and vessel collisions. Threats to habitat include coastal industrialization, development projects, or any activity which disrupts or destroys nearshore habitat. Limiting factors for survival and recovery include the impacts of environmental variability and ocean acidification on prey quality, abundance, or availability, exposure to naturally-occurring harmful toxins, and Killer Whale predation. Three recovery abundance objectives are proposed for both the PCFG and the WP population in Canada: 1) Maintain a stable population size, 2) Maintain a growing population size to exceed 250 mature individuals, and 3) Maintain a growing population size to exceed 1,000 mature individuals. Forward projections indicate that reaching objective 1 by 2038 is 86% and 100% probable for the PCFG and WP population respectively, and reaching objective 2 is 11% (PCFG) and 94% (WP) probable, although these probabilities are highly dependent on the current carrying capacity of these populations, which is uncertain for both DUs. Reaching a population abundance of 1000 mature individuals (i.e., no longer an Endangered or Threatened status) has 0% probability for both the PCFG and WP population within a 23-year time frame. A reasonable distribution recovery target for both DUs would be to maintain their current known spatial extent. Using the Potential Biological Removal method, allowable harm was calculated at 1.8 PCFG whales per year and 2.1 WP whales per year (these values are for the entire populations and are assumed to represent anthropogenic mortality over their entire distribution ranges rather than just in Canadian waters.
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