ESR 6:259-271 (2009)  -  DOI: https://doi.org/10.3354/esr00163

ABSTRACT: North Atlantic right whales Eubalaena glacialis feed predominantly on Calanus finmarchicus Stage V copepods. Calanus possesses 2 classes of storage lipids, triacylglycerols (TAG) and wax esters (WE), the latter comprising 94% of total lipids. Most mammals are incapable of metabolizing WE and thus eliminate it in their feces. The objective of this study was to determine whether right whales are capable of metabolizing both TAG and WE. We compared the lipid composition of copepods collected during plankton tows (n = 64) over 2 summers (2006 and 2007) with the lipid composition of 24 right whale fecal samples collected synoptically in the Bay of Fundy. Using ingestion and defecation models, we estimated that an average right whale (40000 kg) ingests ~58000 g of WE d^–1 but eliminates only 250 g of WE, implying that right whales are assimilating over 99% (57765 g) of dietary WE. Lipids in the feces differed significantly from those of the diet. Copepod lipids were dominated by saturated fatty acid (FA) components 14:0 (14.73 ± 0.32 wt%) and 16:0 (8.99 ± 0.20 wt%), with monounsaturated and polyunsaturated components comprising the remainder. Long chain monounsaturated 20:1n-9 and 22:1n-11 dominated the fatty alcohol composition of copepods. Fecal lipid composition consisted primarily of saturated FA, many of which were absent in the copepods. These data suggest that right whales have evolved an unusual metabolic capability, such as specialized enzymatic machinery or a gut symbiont, which, unlike other mammals, enables them to utilize most of their WE-rich diet.

KEY WORDS: Eubalaena glacialis · Right whale · Lipid metabolism · Wax ester · Triacylglycerol · Calanus finmarchicus · Copepod · Feeding