Feeding ecology of eastern North Pacific killer whales Orcinus orca from fatty acid, stable isotope, and organochlorine analyses of blubber biopsies

Abstract

Blubber biopsy samples from eastern North Pacific killer whales Orcinus orca were analyzed for fatty acids, carbon and nitrogen stable isotopes and organochlorine contaminants. Fatty acid profiles were sufficiently distinct among the 3 reported ecotypes ('resident,' 'transient' or 'offshore') to enable individual animals to be correctly classified by ecotype and also by mitochondrial DNA (mtDNA) haplotype. Profiles of PCBs also enabled unambiguous classification of all 3 killer whale ecotypes, but stable isotope values lacked sufficient resolution. Fatty acid, stable isotope and PCB profiles of the resident and transient ecotypes were consistent with those expected for these whales based on their reported dietary preferences (fish for resident whales, marine mammals for transients). In addition, these ecotype profiles exhibited broad similarity across geographical regions, suggesting that the dietary specialization reported for resident and transient whales in the well-studied eastern North Pacific populations also extends to the less-studied killer whales in the western Gulf of Alaska and Aleutian Islands. Killer whales of the same ecotype were also grouped by region of sample collection. The mean stable isotope ratios of various regional groups differed considerably, suggesting that the prey preferences of these North Pacific killer whales may be both region and ecotype specific. Furthermore, 3 specific ecotypes of killer whales were found to have measured stable isotope values that were consistent with dietary preferences reported in the literature. Finally, although the offshore population had blubber fatty acid profiles implicating fish as its primary prey, contaminant and stable isotope results were equally congruent with predation on marine mammals.

Use of chemical tracers in assessing the diet and foraging regions of eastern North Pacific killer whales

“…The current study was undertaken to advance the findings of the previous study (Herman et al, 2005) by providing further insight into diet and movements of the North Pacific killer whales from Alaska. Additional biopsy samples (n = 84) were collected from resident, transient and offshore killer whales and were characterized by comparing POP concentrations, patterns and ratios, stable isotope ratios of carbon and nitrogen and fatty acid profiles by killer whale ecotype and region.…”

“…All biopsy samples were stored at À80°C until analyzed. Sample sizes were standardized as reported previously (Herman et al, 2005). The blubber acquired from these whales was analyzed for fatty acids and POPs and the epidermis, when available, for stable isotope ratios (Table 1).…”

“…Stable isotope analyses of epidermis from killer (Alaska), gray (Russia and Alaska) and minke (Aleutian Islands) whales, as well as muscle from northern fur seals (Pribilof Islands) and Steller sea lions (Alaska), were conducted on lipid-extracted tissues as described previously (Herman et al, 2005). The internal laboratory standards were calibrated relative to the following international standards: USGS-24 graphite, NBS-22 oil, IAEA-CH-6 sucrose, IAEA-N-1 ammonium sulfate and IAEA-N-2 ammonium sulfate.…”

“…In addition, patterns of persistent organic pollutants (POPs) have been shown to differentiate cetacean stocks (Krahn et al, 1999;Muir et al, 1996), presumably due to differences in POPs in their prey. All three techniques were combined by Herman et al (2005) to qualitatively examine the dietary specializations of eastern North Pacific killer whale populations. An additional approach-POP ratios-can be used to assess regional sources of POPs transferred to predators from their prey (Calambokidis and Barlow, 1991;Krahn et al, 1999;Muir et al, 1990).…”

Cultural transmission of tool use by Indo-Pacific bottlenose dolphins (Tursiopssp.) provides access to a novel foraging niche

“…Further, such samples are infrequently obtained or unfeasible due to their reliance on subject capture or mortality. In recent years, the analysis of fatty acids (FAs) has been shown to provide a powerful tool in diet studies [31][32][33]. The underlying premise is that FAs of consumed prey are deposited in a predictable manner into the adipose tissue of predators, thereby creating a unique profile of a number of FAs in various proportions, reflecting long-term diet [34].…”