Rockfish trophic relationships in Prince William Sound, Alaska, based on natural abundances of stable isotopes

Rockfish trophic relationships in Prince William Sound, Alaska, based on natural abundances of stable isotopes

T.C. Kline Jr.

Rockfish trophic relationships in Prince William Sound, Alaska, based on natural abundances of stable isotopesThis is part of Biology, Assessment, and Management of North Pacific Rockfishes
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Description

About two dozen rockfish species coexist within Prince William Sound (PWS). According to ecological theory these species should reduce competition by minimizing diet overlap. This was verified by using ecological metrics based on the natural abundance of carbon and nitrogen stable isotopes. Carbon source dependency was based on a regional carbon isotope gradient whereas trophic level was based on trophic enrichment of 15N. There was a gradient in carbon source dependency among rockfish slope, pelagic, and demersal eco-groups. Pelagic rockfishes had the greatest dependency on Gulf of Alaska (GOA) derived carbon. Within demersal rockfishes, copper rockfish were most dependent on PWS derived carbon. Rockfishes did not respond to a strong pulse in GOA subsidies, like forage groups, confirming that their stable isotope composition reflected relatively longer time-integration. Yelloweye and quillback rockfish shifted concordantly in carbon source dependency but separated in terms of relative trophic level. Relative trophic level (TL), based on the nitrogen isotope value of a herbivorous copepod for reference TL = 2.0, ranged from 3.2 (juveniles) to 5.1 (shortspine thornyhead). Another slope species, the shortraker rockfish, had the second highest TL = 4.9. Dark rockfish was the lowest adult TL = 3.6. Alternative nonlethal sampling for isotope values using blood is possible given normalization of the data for lipid isotope effects.

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