Differential rates of killer whale attacks on humpback whales in the North Atlantic as determined by scarification

Abstract

As in other populations of killer whales, Orcinus orca, prey selectivity in the North Atlantic population may indicate behaviourally or ecologically distinct types of killer whales. Some killer whale ecotypes are known to prey on large whales, but the ecological impact of such predation events is unknown. Since killer whale attacks on humpback whales, Megaptera novaeangliae, are rarely witnessed, resultant scars may be used to determine the frequency of non-fatal predatory interactions. Using images from the North Atlantic Humpback Whale Catalogue (NAHWC), we examined humpback whale flukes for the presence of rake marks from killer whales (N = 5040). Scarring frequencies range from 2.7 to 17.4% and differ significantly among five regions of the North Atlantic (Gulf of Maine, Canada, West Greenland, Iceland and Norway). The scarring rate in the Canada region is significantly higher than all other regions, and Norway has a significantly lower scarring rate than all other regions, despite more frequently reported killer whale sightings in that region. Within the western North Atlantic, Canada has a scarring rate nearly twice that of either the Gulf of Maine or West Greenland. These data may reflect differential prey choice among killer whale ecotypes and/or the distribution of specific ecotypes across the North Atlantic basin.

Humpback whales interfering when mammal‐eating killer whales attack other species: Mobbing behavior and interspecific altruism?

“…McCordic et al . () reported significant differences in tooth‐rake marks among populations of humpbacks sampled from five different feeding grounds in the North Atlantic, and because nearly all North Atlantic humpbacks breed in the West Indies, they concluded that attacks probably occurred either during migration or on the feeding grounds. When Steiger et al .…”

“…From this it was concluded that calves were probably attacked mainly while en route to high-latitude feeding grounds during their first migration (Clapham 2000(Clapham , 2001Mehta et al 2007). McCordic et al (2014) reported significant differences in tooth-rake marks among populations of humpbacks sampled from five different feeding grounds in the North Atlantic, and because nearly all North Atlantic humpbacks breed in the West Indies, they concluded that attacks probably occurred either during migration or on the feeding grounds. When Steiger et al (2008) analyzed tooth rake marks on humpbacks in the eastern North Pacific, they concluded that calves were attacked mainly on the breeding grounds.…”

Geographic and temporal patterns of non-lethal attacks on humpback whales by killer whales in the eastern South Pacific and the Antarctic Peninsula

“…Although other less exposed parts of the body might also be scarred, they are less visible and thus more difficult to evaluate. Rake marks on humpback whale flukes and on other baleen whales caused by killer whale attacks have been confirmed in different parts of the world (Mehta et al 2007, Steiger et al 2008, Reinhart et al 2013 and are considered to be evidence of unsuccessful or non-lethal attacks (Dolphin 1987, Clapham 2001, Naessig & Lanyon 2004, Mehta et al 2007, Steiger et al 2008, McCordic et al 2014. It is not possible to establish the impact of killer whale predation on humpback whale populations based on such scars because scarred whales are survivors of unsuccessful attacks.…”

Incidence of Odontocetes with Dorsal Fin Collapse in Maui Nui, Hawaii

“…The overall proportion of animals with bent dorsals was calculated by dividing the number of animals with bent dorsals by the total number of cataloged animals. The 95% confidence intervals (CIs) were calculated using the adjusted Wald method for a binomial estimate of the proportion (Lewis & Sauro, 2006;McCordic et al, 2014). The use of the adjusted Wald method for calculating the CIs of proportions from a small sample allows for the derivation of CIs for a binomial estimate of the proportion rather than presenting just a single point estimate (Agresti & Coull, 1998;Lewis & Sauro, 2006).…”