BLUBBER FATTY-ACIDS OF FINBACK AND HUMPBACK WHALES FROM THE GULF OF ST-LAWRENCE

Possible differences in the diet or metabolism of sympatric finback and humpback whales in the Gulf of St. Lawrence were investigated through analysis of their blubber fatty acids. Free-ranging finback (Balaenoptera physalus, n = 19) and humpback (Megaptera novaeangliae, n = 10) whales were sampled through biopsy during summer 1991. The two species differed in the chemical composition and stable carbon isotope distribution of fatty acids extracted from their outermost blubber layer. Finback blubber was slightly but significantly richer in its relative proportions of 12:0, 13:0, i14:0, 17:0, 18:1 n9, 18:1 n7, and 20:0 (probability of difference greater than or equal to 99%), 18:2 n6, 18:0, and 19:0 (probability greater than or equal to 95%), and 16:1 n5 and 16:0 (greater than or equal to 90%). The stable isotope ratio of finback total fatty acids averaged -25.5 +/- 0.4 parts per thousand. Humpbacks contained relatively more i16:0, 18:1 n5, 20:5 n3, and 22:6 n3 (probability greater than or equal to 99%), 16:1 n7, i18:0, 20:4 n6, and 22:5 n3 (greater than or equal to 95%), and 20:4 n3 (>90%). Their fatty acid delta(13)C averaged -25.8 +/- 0.5 parts per thousand (different from finbacks with a probability of 95%). There was no significant difference between the two species in the relative proportions of 14:1, 14:0, i15:0, a15:0, 15:0, i17:0, a17:0, 17: 1, 20:1 n9, 20:1 n7, 22:1 n11, or 22.1 n9, which together made up one-third of total fatty acids. We used principal component and cluster analyses to integrate and visualize the differences in the chemometric data sets. The chemical and isotopic differences found in the present study are consistent with a slightly lower trophic position for humpbacks compared to finbacks in the Gulf of St. Lawrence, reflecting a difference in long-term, average diet.