Fussy feeders or fallacy? Investigating the prevalence of prey preference in killer whales, globally and in the Southern Ocean.

Abstract

Killer whales (Orcinus orca, Linnaeus 1758) are a cosmopolitan species, being found in all the world’s oceans and most of its seas. There are currently ten ecotypes recognised globally and these distinct groups can be differentiated by variations in their morphology, societal structure, vocalisations, hunting techniques, genetic information, and prey preference. This study looked at the prevalence of prey preferences in killer whale populations, to understand whether their diets are genuinely as restrictive as they are perceived to be. Through analysing a high volume of literature, killer whales were found to predate on 159 different species. This data was compared to the perceived preferences of each ecotype to see how often the populations strayed from their preference. The Northern Hemisphere ecotypes were found to adhere more strictly to their preferred prey types; the Resident and North Atlantic Type I killer whales were found to not eat anything other than their preferred prey type. The Southern Hemisphere ecotypes displayed slightly more plasticity. The Gerlache (Type B, small) and Subantarctic ecotypes were also found to eat only their preferred prey, although the lack of data available for these isolated groups makes this observation less certain. Five of the remaining ecotypes, Transient, Offshore, Antarctic (Type A), Pack Ice (Type B, large), and Ross Sea (Type C), were found to display more generalist tendencies, feeding on a variety of prey, though still predominantly feeding on their preferred prey type. The conclusions drawn from this study was that, while there are some distinct differences between the ecotypes globally, prey preferences were often less restrictive than previously indicated. As they occupy the role as the top top predator in many of the world’s oceans, understanding the prey each population eat, and how these may be impacted by climate change and future anthropogenic threats, is a crucial step in protecting this keystone species.