Calorimetry measurements of energy value of some Alaskan fishes and squids

Abstract

Food habits studies of marine mammals increase our understanding of the trophodynamic interrelationships of these predators within their ecosystem. In order to determine the energetic importance of specific prey in the diet and physiology of marine mammals, it is necessary to know the caloric density of these prey. Few data exist in the literature concerning the energy content of complete fish and squid bodies, especially noncommercial species which are usually eaten whole by Alaskan pinnipeds. In 1984, the National Marine Mammal Laboratory conducted a short-term study to obtain additional data on the total energy content of entire specimens of known and probable prey species. A total of 278 fish and squid specimens representing 20 species were collected in the Bering Sea and Gulf of Alaska during routine assessment surveys by the Alaska Fisheries Science Center. In addition, 10 squid specimens of three additional species caught in the North Pacific Ocean during 1981 and 1982 were included in this study. Total energy content of the entire fish or squid body was determined by bomb calorimetry after the specimens were thawed and weighed. Percent moisture and ash were also determined for each specimen. Energy values of dry mass, ash-free dry mass, and wet mass were calculated. Based on the energy content of ash-free dry mass, the fish and squid species analyzed in this study comprised five groups: 1) very high energy   ( = 7.7 kcal/g) species such as eulachon, Thaleichthys pacificus; 2) high energy ( = 6.6 kcal/g) species such as Pacific herring, Clupea pallasi, capelin, Mallotus villosus, and magistrate armhook squid, Berryteuthis magister; 3) medium energy content ( = 6.1 kcal/g) species such as northern rockfish, Sebastes polyspinis, and boreal clubhook squid, Onychoteuthis borealijaponica; 4) low energy density ( = 5.8 kcal/g) species such as walleye pollock, Theragra chalcogramma, and arrowtooth flounder, Atheresthes stomias; and 5) very low caloric density ( = 5.4 kcal/g) species such as Pacific cod, Gadus macrocephalus, and armorhead sculpin, Gymnocanthus galeatus.


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