Southern resident killer whales encounter higher prey densities than northern resident killer whales during summer

• Published in: Canadian Journal of Fisheries and Aquatic Sciences
• Main Authors: Sato, Mei, Trites, Andrew W., Gauthier, Stéphane
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Canadian Science Publishing 2021
• Subjects: Canada; Gauthier; Killer Whale; Orca; Orcinus orca; Killer whale
• Online Access: https://hdl.handle.net/1912/27900

© The Author(s), 2021. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Sato, M., Trites, A. W., & Gauthier, S. Southern resident killer whales encounter higher prey densities than northern resident killer whales during summer. Canadian Journal of Fisheries and Aquatic Sciences, 78(11), (2021): 1732–1743, https://doi.org/10.1139/cjfas-2020-0445. The decline of southern resident killer whales (Orcinus orca) may be due to a shortage of prey, but there is little data to test this hypothesis. We compared the availability of prey (Chinook salmon, Oncorhynchus tshawytscha) sought by southern residents in Juan de Fuca Strait during summer with the abundance and distribution of Chinook available to the much larger and growing population of northern resident killer whales feeding in Johnstone Strait. We used ship-based multifrequency echosounders to identify differences in prey fields that may explain the dynamics of these two killer whale populations. Contrary to expectations, we found that both killer whale habitats had patchy distributions of prey that did not differ in their frequencies of occurrence, nor in the size compositions of individual fish. However, the density of fish within each patch was 4–6 times higher in the southern resident killer whale habitat. These findings do not support the hypothesis that southern resident killer whales are experiencing a prey shortage in the Salish Sea during summer and suggest a combination of other factors is affecting overall foraging success. This study was funded by Fisheries and Oceans Canada.