Boreogadus saida (Hop & Tonn, 1998)

4.5 | Energy content of B saida View in CoL prey species

Energy content measurements on most species from our study generally corresponded well with findings from the literature ( Båmstedt, 1981; Norrbin & Båmstedt, 1984; Nowicki et al., 2023; Percy & Fife, 1981). Variations in energy content with season and body size have been found for various species. The energy content of the krill species T. inermis did not vary between winter and summer, but larger specimens had a higher energy content than smaller ones ( Nowicki et al., 2023). For another krill species, Meganyctiphanes norvegica , variation between summer and winter was found, with values of 22.71 and 24.60 kJ g 1 MD, respectively ( Nowicki et al., 2023). Energy contents decreased in winter (18.77 and 17.83 kJ g 1 MD) compared to summer (23.07 and 21.13 kJ g 1 MD) for both T. libellula and T. abyssorum , respectively ( Nowicki et al., 2023). Individuals of T. libellula larger than 30 mm were found to have a higher energy content compared to smaller individuals, but for individuals < 20 mm, there was no difference between size classes of T. libellula nor was there a difference with similar-sized T. abyssorum ( Nowicki et al., 2023) . This suggests that the energy content measurements we performed on T. libellula and T. abyssorum can be regarded as representative for the individuals ingested by the B. saida in our study.

In the growth rate model, the energy content of Calanus prey was based on measurements performed on C. hyperboreus . Size measurements performed on Calanus spp. from the stomachs suggest, however, that the stomach contents likely contained a majority of C. finmarchicus and/or C. glacialis . The energy contents of the three Calanus species may vary, largely because lipid contents depend on developmental stage, season, and region due to the different life cycles and distribution patterns of the three Calanus species (e.g., Graeve et al., 2005; Kattner et al., 1989; Kirkesaeter, 1978 in Båmstedt, 1981; Scott et al., 2000; Swalethorp et al., 2011). Although some studies indicate that the energy density or lipid content per weight unit can be similar among the three species ( Davies et al., 2012; Kohlbach et al., 2016), the smaller sizes indicate that energy content per individual would be less for C. glacialis and C. finmarchicus compared to C. hyperboreus .