Fatty acid composition of common dolphin blubber

Abstract

Sixty-five fatty acids were quantified in the blubber of two closely related species of common dolphin (Delphinus delphis, D. capensis) from the coast of southern California. Dolphins were grouped according to gender, reproductive status, method of collection (gillnet vs. strand), and species. Blubber was collected from incidentally caught or dead-stranded dolphins at a mid-lateral site, caudal to the trailing edge of the dorsal fin. Blubber was divided horizontally into inner, middle and outer layers, lipid was extracted, and fatty acid methyl esters were prepared and analyzed using gas chromatography. Multivariate and univariate statistical analyses were employed, and all three layers were distinguishable from one another on the basis of fatty acid composition. In general, gradients in fatty acid content (mass %) were observed across the depth of the blubber, with 12 of the 15 most abundant fatty acids present in significantly different quantities in all three layers. Levels of monounsaturated fatty acids were greatest in the outer layer, while levels of saturated and polyunsaturated n-3 and n-6 fatty acids were greatest in the inner layer. In general, sexually mature animals showed a greater degree of fatty acid stratification than sexually immature dolphins. Degree of stratification was also greater in physically mature male dolphins, suggesting that differences in degree of stratification may be attributed to differences in diet. Classification and regression tree analysis (CART) resulted in the fewest misclassifications when dolphins were grouped by species, possibly indicating that these closely related animals forage on different prey species. CART analyses based on gender and reproductive status resulted in higher misclassification rates. In general, dietary fatty acids were selected as splitting criteria in CART analyses, further suggesting that the observed differences in fatty acid composition between the various groups of dolphins may be attributed to differences in diet.