Blubber fatty acid composition of bowhead whales, Balaena mysticetus: Implications for diet assessment and ecosystem monitoring S.M. Budge a, ⁎, A.M. Springer b , S.J. Iverson c , G. Sheffield d , C. Rosa e a Department of Process Engineering and Applied Science, Dalhousie University, Halifax, NS, Canada B3J 2X4 b Institute of Marine Science, University of Alaska Fairbanks, Fairbanks, Alaska 99775, USA c Department of Biology, Dalhousie University, Halifax, NS, Canada B3H 4J1 d Alaska Department of Fish and Game, Fairbanks, Alaska, USA e North Slope Borough Department of Wildlife Management, Barrow, Alaska, USA article info abstract Article history: Received 13 February 2008 Accepted 17 February 2008 Fatty acids (FA) have a diversity of structures that are transferred with little modification through food webs, making them valuable in assessing diets of animals that cannot be directly observed feeding. Before using FA to estimate diets, it is necessary to evaluate variation in FA signatures within and among individuals of a given species. To begin assessing diets and foraging of western Arctic bowhead whales (Balaena mysticetus), we examined the FA in blubber of 64 bowheads taken in the spring and fall subsistence hunts in 1997–2002 at Barrow and Kaktovik, Alaska. We found no significant differences in FA characteristics of inner blubber layers taken from either duplicate samples on the dorsal surface, or between dorsal and ventral sites. Significant differences were found in the FA composition between inner and outer layers of blubber at the same body site. We also found age, season and year to have significant effects on FA composition; however, gender was not found to be significant. While the importance of the Beaufort Sea as a feeding ground of bowhead whales remains uncertain, our results indicate that adults and sub-adults foraged to some extent on different prey and that both age classes consumed copepods there in summer at sufficient levels to significantly alter their blubber FA profiles. Both of these findings correspond with dietary conclusions reached from the analysis of stomach contents. Furthermore, we found compelling evidence that yearly variation in bowhead FA reflect changes in FA compositions of phytoplankton at the base of the food web, probably in response to climate variation. Variability in phytoplankton-derived FA in blubber was correlated significantly with yearly mean values of the Pacific Decadal Oscillation. FA in bowhead whale blubber, therefore, might be used to monitor effects of climate change on lower trophic levels and production processes in the western Arctic. © 2008 Elsevier B.V. All rights reserved. Keywords: Foraging ecology Lipids Western Arctic 1. Introduction Fatty acids (FA) and FA signature analysis are becoming increasingly important tools in many ecological applications, and have been used as biomarkers to help describe trophic pathways in marine food webs and to assess foraging differences among predators (e.g., Iverson et al., 1997; Dahl et al., 2000; Hooker et al., 2001; Best et al., 2003; Budge et al., 2007). The technique works because most marine FA are synthesized by phytoplankton and other organisms at low trophic levels, FA have a wide variety of structures, and they undergo little biochemical change when passed up the food chain (Dalsgaard et al., 2003; Iverson, in press). Thus, it is possible to recognize FA in a predator's fat stores that were derived from their prey. Most applications of FA analysis are qualitative in nature, investigating spatial or temporal variations in diets among and within individuals or populations. More recently, a new technique, quantitative FA signature analysis (QFASA), has been developed (Iverson et al., 2004, 2007) in which quantitative estimates of diet are derived from FA signatures of predator and prey. FA analysis and QFASA are particularly useful in evaluating diets of species that cannot be directly observed feeding or which pose other research difficulties. For example, our knowledge of bowhead whale (Balaena mysticetus) diets in Alaska is derived from analyses of stomach contents of whales taken in the spring and fall subsistence harvests at villages in the Beaufort Sea (Barrow and Kaktovik), and indirectly from analyses of stable isotopes of baleen and other tissues from those animals (e.g., Hoekstra et al., 2002; Lowry et al., 2004; Lee et al., 2005). However, there are uncertainties associated with these methods. Many whales have nothing in their stomachs and the prey in those that do represent just the most recent feeding. Isotopes provide information on trophic level and general carbon source, but not on the taxonomic identity of the prey. Thus, the interpretations of results from these two methods do not always agree. Also, very little is known about diets outside of the Beaufort Sea (in the northern Bering Sea and Chukchi Sea), where bowheads spend much of the year. Journal of Experimental Marine Biology and Ecology 359 (2008) 40–46 ⁎ Corresponding author. Tel.: +1 902 494 6010; fax: +1 902 429 0219. E-mail address: Suzanne.budge@dal.ca (S.M. Budge). 0022-0981/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jembe.2008.02.014 Contents lists available at ScienceDirect Journal of Experimental Marine Biology and Ecology journal homepage: www.elsevier.com/locate/jembe