• Diets of four eelpout species (genus Lycodes) in the U.S. Beaufort Sea based on analyses of stomach contents and stable isotopes of nitrogen and carbon

      Apsens, Sarah J.; Norcross, Brenda; Iken, Katrin; Mueter, Franz; López, Andres (2017-12)
      Eelpouts of the genus Lycodes are an abundant group of demersal fishes in the U.S. Beaufort Sea. Currently eelpout diet and the exact role of eelpouts in the Arctic food web are poorly understood. Additionally, if and how eelpouts avoid intra- and interspecific competition for resources is unknown. In this study, diets of four common Beaufort Sea eelpout species were analyzed with respect to along-shelf (longitude) gradients, across-shelf (depth) gradients, and ontogeny (fish body length) to determine diet composition and patterns of resource partitioning. Diets of the four most numerous eelpout species were analyzed using a combination of stomach contents and nitrogen and carbon stable isotope analyses: Adolf's Eelpout Lycodes adolfi, Canadian Eelpout L. polaris, Archers Eelpout L. sagittarius, and Longear Eelpout L. seminudus. Nitrogen stable isotopes of fish tissue were analyzed to determine trophic level and carbon stable isotopes to determine if origin sources of carbon in food web pathways of eelpout diets differed among species. Fishes were collected in the central (2012) and eastern (2013 and 2014) Beaufort Sea in August and September as part of the U.S.-Canada Transboundary program. Prey groups Polychaeta, Amphipoda, Isopoda, Ophiuroidea, and Copepoda composed a large proportion of the diet by percent weight for all four species of Lycodes, but their relative contributions differed among the species examined. This study indicated that eelpouts feed almost exclusively on benthic prey and avoid interspecific competition by occupying different habitat space and having different diets. Intraspecific similarity in diet composition was low suggesting these fish have diverse diets even among individuals of the same species. Fish length was associated with changes in diet composition for L. adolfi and L. sagittarius, but not L. polaris and L. seminudus. Longitude and depth were correlated with shifts in diet composition for L. sagittarius, but not the other three species. Lycodes polaris occupied a lower trophic level than the other three eelpout species based on nitrogen stable isotope values. Despite differences in the across-shelf distribution between L. polaris and the three deep-water eelpout species, carbon sources of diet were indistinguishable among the four eelpout species. Ecological information on abundant Arctic fish species like eelpouts is needed for long-term ecosystem monitoring, which is especially important in light of pronounced climate changes and increased human activities in the Arctic.
    • Spatial patterns, environmental correlates, and potential seasonal migration triangle of Arctic cod (Boreogadus saida) distribution in the Chukchi and Beaufort seas

      Forster, Caitlin; Norcross, Brenda; Mueter, Franz; Seitz, Andrew; Longerwell, Elizabeth (2019-05)
      Arctic Cod (Boreogadus saida) is a key forage fish species in the Arctic marine ecosystem and provides a critical energetic link between lower and upper trophic levels. Despite its ecological importance, spatially explicit studies synthesizing Arctic Cod distribution across a multitude of research efforts previously have not been conducted in the western portion of its range. I used spatial generalized additive models (GAM) to map the distribution of Arctic Cod by size class and relative to environmental variables. I compiled demersal trawl data from 21 research cruises conducted from 2004 to 2017 in the Chukchi and Beaufort seas, and investigated size-specific patterns in distribution to infer movement ecology of Arctic Cod as it develops from juvenile to adult life stages. High abundances of small, juvenile Arctic Cod (<70 mm total length) in the northeastern Chukchi Sea and western Beaufort Sea were separated from another region of high abundances in the eastern Beaufort Sea, near the US and Canadian border, suggesting possible population structure in the Pacific Arctic. In both the Chukchi and Beaufort seas, large, adult Arctic Cod (>130 mm total length) were found offshore and spatially segregated from small and medium (71-130 mm total length) fish, indicating an ontogenetic offshore movement of Arctic Cod as it matures. Relating environmental correlates to Arctic Cod abundance demonstrated that temperature and salinity were related to juvenile distribution patterns, while depth was the primary correlate of adult distribution. Furthermore, a comparison of spring and summer 2017 abundances of Arctic Cod in the southern Chukchi Sea, from the Bering Strait to Cape Lisburne found low abundance in the spring when compared to the summer. Differences in Arctic Cod abundance at different times of year suggest that Arctic Cod migrate seasonally, potentially following patterns of biological production in the Chukchi Sea. Arctic Cod migration may follow a classical 'migration triangle' route between nursery grounds as juveniles, feeding grounds as subadults, and spawning grounds as adults, in relation to ice cover and seasonal production in the Chukchi Sea. The analysis presented here is necessary to address federally mandated research requirements, which include improving understanding of stock structure and resolving essential fish habitat (EFH) for different life stages, as well as to gain better general understanding of the role of Arctic Cod in the Pacific Arctic.
    • Subsistence salmon fishing in Beaufort Sea communities

      Cotton, Shelley S.D.; Carothers, Courtney; Craighead George, John (2012-12)
      Environmental change, combined with observations of increasing numbers of salmon in subsistence fisheries, has generated a need for more information about salmon use, abundance, and distribution in the Arctic. Ethnographic research was conducted in Barrow and Nuiqsut, Alaska, in 2010 and 2011 with 41 active fishermen and elders. Salmon catches were perceived to be increasing; however, perceptions about changing salmon abundance were mixed. While pink salmon (Oncorhynchus gorbuscha) and chum salmon (O. keta) have been observed in subsistence fisheries in the central North Slope region for over 50 years, only within the last 10 to 20 years has local use of these resources begun to increase. In this region, salmon are less important as a subsistence resource compared to whitefish species (Coregonus spp.). However, many fishermen participating in the Elson Lagoon gill net fishery near Barrow have begun to target salmon. Harvest estimates for this fishery in 2011 indicated that chum salmon and pink salmon catches comprise the majority of all fish caught (42% and 23%, respectively). Chinook salmon (O. tshawytscha) have been increasingly targeted, but catches are generally low. While sockeye salmon (O. nerka) numbers were perceived to have increased on the North Slope, catches of this species are rare. Only a few stray coho salmon (O. kisutch) have been captured in this region. Informants identified new stream systems where salmon are present and spawning, suggesting possible distribution shifts. Fishermen in both communities reported developing knowledge of salmon and are increasing their use of salmon as a subsistence resource.