Abstract
Atlantic salmon (Salmo salar) are a commercially and recreationally important species that are also an important indicator species for the North Atlantic pelagic ecosystem’s overall health. The populations of Atlantic salmon have declined since the 1980’s, and it is hypothesized that a decrease in prey quality may be one factor contributing to their decline. It is crucial that the energy density of the major prey species of Atlantic salmon are determined and explained with the use of proximate composition analysis (PCA). The accuracy of dry weight values was first confirmed to be not significantly different from the control via a freezing experiment, using Fundulus heteroclitus that mimics the commonly used procedure to store samples at sea. The three main Atlantic salmon prey species, M. villosus, G. fabricii, and Themisto sp.,displayed a strong correlation between energy density and percent dry weight, meaning percent dry weight is an excellent predicter of energy density. The average energy density of M. villosus was 6.57kJ/g and was significantly higher inside fjords, in the year 2016, in fall, at higher latitudes, and for larger lengths. The average energy density of G. fabricii was 5.46kJ/g and was significantly higher inside fjords, in the year 2017, in spring, at lower latitudes, and for larger lengths. Themisto sp. had an average energy density of 5.39kJ/g and was significantly higher outside fjords, in the year 2017, at lower latitudes, and with larger lengths. The data suggest that Atlantic salmon can maximize energy gain inside fjords for M. villosus and G. fabricii and shift to Themisto sp. when outside of fjords, because these three major forage species exhibited a higher energy density in those respective habitats. Additionally, Atlantic salmon would gain more energy by concentrating feeding efforts on G. fabricii during the spring and shift to targeting M. villosus in the fall.