Geographic Distribution of North Atlantic Humpback Whales (Megaptera novaeangliae) with Fluke Scars Caused by Killer Whales (Orcinus orca)

Abstract

Although killer whale (Orcinus orca) predation on humpback whales (Megaptera novaeangliae) is rarely witnessed, resultant scars on humpback flukes provide evidence of non-lethal interactions. Humpback whale photo-identification catalogs from the North Atlantic were used to evaluate humpback flukes (n = 10,957) for the presence and severity of killer whale scarification (e.g., rake marks, teeth indentations, missing tissue). Flukes were coded as none, light, moderate, or severe based on the extent of scarring. Even with increased sample sizes, especially for Norway and Iceland, the distribution of high-latitude humpbacks with killer whale scarring was consistent with prior studies: Atlantic Canada (21.7%), West Greenland (15.5%), Gulf of Maine (13.5%), Iceland (combined with East Greenland, 9.3%), and Norway (7.9%). For the first time, scarring rates are presented based on data from Ireland, Scotland, and England (11.0%) as well. Scarring frequencies generally differed between the eastern and western North Atlantic despite the co-occurrence of all migrating humpbacks in low-latitude breeding grounds, suggesting the occurrence of killer whale interactions in the distinct feeding grounds or along northward migration routes. While it was not possible to determine exactly where these interactions took place, the likelihood of a killer whale encounter and subsequent scar acquisition was greatest for humpbacks that feed in Atlantic Canada.