DOI: 10.21963/13299
title: Fatty acid proportions in North Atlantic killer whales from the Canadian Arctic to Arctic Norway (2008-2021)

description: Scientists have been studying the feeding habits of killer whales for decades, but there is still much to learn. Recent studies suggest that killer whales from Norway and Iceland mainly feed on fish, while those from Greenland and Canada eat marine mammals. Most of the previous studies that looked at North Atlantic killer whale diets relied on observation at sea. And while observing a predation event is always useful and indicates that a specific species have been consumed at some point, we cannot really conclude on the long-term dietary habits of various populations. This is especially true for remote populations (think the Canadian Arctic and Greenland), because these observation events cannot happen year-long. To better understand what these predators eat, scientists can use time-integrated dietary tracers like stable isotopes or fatty acid signature analysis. These methods provide information about a predator's long-term diet, especially when killer whales are in isolated areas and impossible to observe year-long. That's where quantitative fatty acid signature analysis (QFASA) comes in. This statistical model allows scientists to estimate the relative contributions of each prey species to a predator's diet. This method involves measuring the lipid composition in the killer whales and their potential prey, enabling the team to estimate the exact proportion of different prey in the whales' diets. We measured this fatty acid proportions in killer whales using our newly validated quantitative fatty acid signature analysis (QFASA) approach on nearly 200 killer whales to model their diets across the 5,000 km span of the North Atlantic.
description: Quantifying the diet composition of apex marine predators such as killer whales (Orcinus orca) is critical to assessing their food web impacts. Yet, with few exceptions, the feeding ecology of these apex predators remains poorly understood. Here, we use our newly validated quantitative fatty acid signature analysis (QFASA) approach on nearly 200 killer whales and 900 potential prey to model their diets across the 5,000 km span of the North Atlantic. Diet estimates show that killer whales mainly consume other whales in the western North Atlantic (Canadian Arctic, Eastern Canada), seals in the mid-North Atlantic (Greenland), and fish in the eastern North Atlantic (Iceland, Faroe Islands, Norway). Nonetheless, diet estimates also varied widely among individuals within most regions. This level of inter-individual feeding variation should be considered for future ecological studies focusing on North Atlantic killer whales. These estimates reveal remarkable population- and individual-level variation in the trophic ecology of these killer whales, which can help to assess how their predation impacts community and ecosystem dynamics in changing North Atlantic marine ecosystems. This new approach provides researchers with an invaluable tool to study the feeding ecology of oceanic top predators. We collected 191 blubber samples from biopsied, stranded, or subsistence-harvested individuals, including 58 individuals from the Eastern Canadian Arctic (Pond Inlet and Pangnirtung, Nunavut from 2009 to 2020), five individuals from Eastern Canada (Saint-Pierre & Miquelon, from 2019 to 2021), one individual from West Greenland (Nuuk, 2021), 18 individuals from East Greenland (Tasiilaq and Scoresby Sund, from 2012 to 2021), 48 individuals from Iceland (Grundarfjörður and Vestmannaeyjar, from 2014 to 2016), two individuals from the Faroe Islands (2008), and 59 individuals from Norway (Skjervøy area, from 2017 to 2019). Full sample collection protocol is available is the README file. The samples were then extracted using the Folch method, and the extracts were then trans-esterified in Fatty Acid Methyl-Esters (FAME). The proportion of each FAME (in percentage) was then measured by Gas Chromatography with Flame Ionization Detection. The results represent the proportion of each fatty acid in each sample collected in this study.