Estimations de l'abondance des cétacés provenant du relevé international de la mégafaune marine dans la région du Pacifique de 2018

Abstract

Several marine mammal species on the west coast of Canada are reported as bycatch in fisheries. A provision of the United States (US) Marine Mammal Protection Act (MMPA) requires Canada, as an exporter of fish products, to provide population estimates and rates of incidental mortality from fisheries operations. However, abundance estimates in Canadian Pacific waters are lacking for most cetacean species, especially for the offshore areas, or are too old to meet MMPA requirements. The objectives of the Pacific Region International Survey of Marine Megafauna (PRISMM) were to provide recent abundance estimates and distribution data for large marine species in inshore and offshore waters of the Canadian Pacific. The survey was conducted between July 4–September 5, 2018, using two Canadian Coast Guard vessels, and produced a total of 8,400 km of visual effort and resulted in 2,000 sightings of 20 marine mammal species. Using design-based distance sampling methods, new abundance estimates were provided for nine cetacean species in Pacific Canadian waters: 30,117 Dall’s Porpoises (95%CI 22,142–40,965), 12,244 Humpback Whales (8,214–18,252), 7,352 Harbour Porpoises (3,547–15,237), 5,882 Pacific White-sided Dolphins (2,941–11,766), 3,829 Fin Whales (2,145–6,834), 2,207 Northern Right Whale Dolphins (726–6,709), 920 Risso’s Dolphins (178–4,758), 199 Blue Whales (59–670), and 70 Sei Whales (24–209). These estimates are corrected for availability bias based on time-in-view and diving behaviour, but uncorrected for perception bias. Except for Pacific White-sided Dolphins, the 2018 abundance estimates for cetaceans in inshore waters suggests that several populations are stable (Dall’s Porpoises, Harbour Porpoises, Fin Whales) or are continuing to recover from past depletion and are expanding to new areas (Humpback Whales). The return of these predators to habitats from which they were previously extirpated will have important ecosystem-level implications. These coast-wide, updated abundance estimates can also inform Potential Biological Removal limits for anthropogenic mortality.