Energy densities of capelin (Mallotus villosus) and sand lance (Ammodytes americanus and Ammodytes dubius) during the summer in coastal Newfoundland

Forage species occupy the intermediate trophic level and mediate energy flow through marine food webs. In coastal Newfoundland, capelin (Mallotus villosus (Müller, 1776)) and Atlantic sand lance (Ammodytes americanus DeKay, 1842; Ammodytes dubius Reinhardt, 1837) are important forage fish during the summer when high abundances of predators (e.g., seabirds, piscivorous fish, whales) rely on them for energy. Samples were collected during 2020, 2023 and 2024 and we used bomb calorimetry to determine whether these prey types (capelin: gravid and spent females, partially spent males; sand lance: adult females [2020 only] and juveniles) differed in energy density (kJ/dry g; ED) and total energy (kJ/fish). In 2020, ED of adult female and juvenile sand lance did not differ but were lower than all capelin categories. ED of gravid and spent females and male capelin did not differ in 2020 and 2023, but gravid females were higher in 2024. Adult females had higher total energy than juvenile sand lance but both were lower than all capelin categories. Our findings indicate that more sand lance would be needed by predators to reach a fixed energy content per meal, but predator net energy gain would also be influenced by other fish density and distribution.