Annual variation in the nutritional value of Stage V Calanus finmarchicus: implications for right whales and other copepod predators

Abstract

Stage V (C5) Calanus finmarchicus is a central prey item for animals feeding at several trophic levels in the Bay of Fundy, Canada, especially the highly endangered North Atlantic right whale Eubalaena glacialis. Here, we show that the energy and lipid content of C5 C. finmarchicus collected twice monthly (July to September) from the Grand Manan Basin exhibited significant variation over multiple years (2006 to 2010). Mean ± SD wet mass energy (6.77 ± 0.65 kJ g-1) was highest in 2007 and lowest in 2009 (5.82 ± 0.90 kJ g-1); lipid content followed the same pattern. Significant decreases in individual energy content were observed over the summer during 2006 and 2010. Lipid content was significantly correlated with energy content. Overall, energy content of copepods was 13% lower in 2009 than in 2006-2007, which could alter foraging patterns and activity budgets of predators such as the North Atlantic right whale and have implications for assessment of whale habitat based on models of energy requirements. Variation in C5 quality may be linked to annual changes in the lipid content of Bay of Fundy herring, which consume copepods and are in turn a main prey item of seabirds, fishes, and marine mammals. Our study emphasizes that variation in quality, not just quantity, of prey should be considered when formulating predator consumption models and in tracking trophic transfer.