MEPS 302:275-291 (2005)  -  doi:10.3354/meps302275

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

D. P. Herman1,*, D. G. Burrows1, P. R. Wade2, J. W. Durban2, C. O. Matkin3, R. G. LeDuc4, L. G. Barrett-Lennard5, M. M. Krahn1

1NOAA Fisheries, Northwest Fisheries Science Center, 2725 Montlake Boulevard East, Seattle, Washington 98112, USA
2NOAA Fisheries, Alaska Fisheries Science Center, 7600 Sand Point Way NE, Seattle, Washington 98115, USA
3North Gulf Oceanic Society, PO Box 15244, Homer, Alaska 99603, USA
4NOAA Fisheries, Southwest Fisheries Science Center, 8604 La Jolla Shores Drive, San Diego, California 92037, USA
5Vancouver Aquarium Marine Science Centre, Box 3232, Vancouver, British Columbia V6B 3X8, Canada

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.

KEY WORDS: Feeding ecology · Killer whale · Biopsy sampling · Stable isotopes · Fatty acids · Organochlorines · Pollutants · Pacific Ocean

Full text in pdf format