• Physical environmental and biological correlates of otolith chemistry of Arctic marine fishes in the Chukchi sea

      Gleason, Christine Marie; Norcross, Brenda; Brown, Randy; Horstmann-Dehn, Larissa; Trefry, John; Christie, David (2012-08)
      Life history movement patterns in marine fishes can be determined by otolith chemistry if environmental variables are reflected in the otoliths. Arctic cod (Boreogadus Saida), Arctic staghorn sculpin (Gymnocanthus tricuspis), and Bering flounder (Hippoglossoides robustus) are abundant Arctic fishes in the Chukchi Sea with overlapping distributions. Physical environmental data, demersal fishes, bottom seawater, and sediment interface seawater samples were collected from the Chukchi Sea Offshore Monitoring in Drilling Area (COMIDA) cruise on July 30, 2009 and the Russian American Long-term Census of the Arctic (RUSALCA) cruise from September 3 to 30, 2009 in the Chukchi Sea. Magnesium (Mg), strontium (Sr), barium (Ba), and calcium (Ca) were measured with an inductively coupled plasma mass spectrometer (ICP-MS) on the most recent growth edge of otoliths and in whole fish blood, as well as Ba in bottom and sediment interface seawater. Environmental variables and fish age correlated with Arctic cod and Arctic staghorn sculpin otolith signatures while only environmental variables correlated with Bering flounder signatures. Elemental correlations were not always consistent for the variables tested among species. The complexity of this multi-element tool suggests otolith chemistry may not be useful to determine life history movement patterns of these demersal Arctic fishes in offshore waters.
    • 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.