Composition and energy contents of mature inshore spawning capelin (Mallotus villosus): Implications for seabird predators

1. Lipid levels of capelin are highest in late fall and lowest during the summer spawning season; protein levels are constant at 13–14% body wt throughout the year.

2. Ovid females contained significantly more lipid and protein and less water and had higher energy densities than males and spent females.

3. Surgically-removed egg masses made up 34.2 ± 10.3% female body wt and were very similar in composition and energy density to gravid females, differing from spent females and males in similar respects. Owing to the ovarian development of females, sexes differ in energy density only during the spawning season.

4. Sexes were similar in amino acid composition. Analysis of capelin and three other seabird forage species revealed that isoleucine levels were lower than minimum avian maintenance and growth requirements.

5. Implications for the foraging behaviour and food preferences of diving seabird predators (murres, puffins) are discussed