Foraging ecology of nearshore fishes in the Gulf of Alaska

Abstract

The survival of juvenile marine fishes, which support commercial fisheries and provide a prey resource, is often dependent on conditions in protective and nearshore habitats. We examined the trophic interactions of several juvenile fishes in the nearshore Gulf of Alaska (GOA) including Pacific cod (Gadus microcephalus), saffron cod (Eleginus gracillis), walleye pollock (Gadus chalcogrammus), Pacific sand lance (Ammodytes hexapterus), Pacific herring (Clupea pallasii), rockfish (Sebastes spp.) and greenlings (Hexagrammos spp.). We used fatty acid (FA) and stable isotope (SI) markers to evaluate foraging ecology and the potential for competition among age-0 fish species in broad east (134°W – 136°W) and west (149°W – 153°W) regions of the GOA. Sampling efforts were greater in the west GOA, so many of our findings were focused in that region. In the west GOA, FA and SI markers indicated that Pacific cod and saffron cod usually shared similar diets, potentially leading to competition for resources. Also in the west GOA, we found evidence that Pacific cod and walleye pollock both relied to similar extents on calanoid copepods during summer. Juvenile sand lance and herring were much smaller than the other species and had diets that contrasted with all other species. In both the east and west GOA, rockfish were present in two distinct size classes with the smaller size feeding at a lower trophic level than all other fish species in the study. The smaller rockfish likely consumed mainly calanoid copepods. Throughout the east and west GOA, greenling and rockfish typically consumed prey with a very different lipid source than the other juvenile fish. In addition, we noted few consistencies in FA and SI markers between the east and west, except in rockfish diets. Overall, we found a complex relationship within the nearshore fish communities in the east and west GOA that showed substantial variation across bays, seasons and subareas.