Differences in ratios of stable isotopes of nitrogen in long-finned pilot whales (Globicephala melas) in the western and eastern North Atlantic

Abstract

Naturally occurring nitrogen stable isotopes found in tissues have been shown to differ among animals feeding on various prey species and at different trophic levels. The ratio of 15N to 14N, expressed relative to atmospheric nitrogen, is compared for four types of tissues collected from long-finned pilot whales from three locations in the North Atlantic. The tissues were skin, muscle, blubber, and teeth, arranged in decreasing rates of biological turnover. The tissues with fastest turnover rates reflect the most recent diets. The ratios differed among tissues, reflecting possible changes in diet over time, and within tissues among the three geographic locations reflecting different dietary histories. Significant differences in ratios from skin, muscle, and blubber between animals from the eastern and western Atlantic suggest the whales are not feeding at the same trophic level. That is, there are more predator-prey relationships separating western Atlantic pilot whales and their primary production. Differences in the isotope rations for blubber, a lower turnover rate tissue, between whales from Cape Cod and the Mid-Atlantic Bight suggest that whales from these areas were feeding in different areas over the longer term. Different patterns of variability in nitrogen isotope ratios from pilot whale teeth among the three regions suggest potentially more complex, longer term movement patterns.