RECYCLING OF ELEMENTS TRANSPORTED UPSTREAM BY RUNS OF PACIFIC SALMON .2. DELTA-N-15 AND DELTA-C-13 EVIDENCE IN THE KVICHAK RIVER WATERSHED, BRISTOL BAY, SOUTHWESTERN ALASKA

Biota deltaN-15 and deltaC-13 values (deviations from recognized isotope standards from Iliamna Lake (a major anadromous sockeye salmon (Oncorhynchus nerka) nursery lake supporting peak-year runs > 10 million) and several other anadromous-salmon-free lakes in the Kvichak River watershed, Bristol Bay, southwestern Alaska, were compared to determine the significance of marine-derived nitrogen (MDN) delivered by returning adult salmon. Biota In Iliamna Lake had higher deltaN-15 compared with control lakes, verifying a mixing model correlating deltaN-15 with MDN. Periphyton deltaN-15 values reflected localized input from populations of spawning salmon. Juvenile sockeye MDN varied in response to escapement size, suggesting the importance of large escapements >10 million) for maintaining a predominantly MDN lacustrine N pool. Other resident fishes showed shifts in deltaN-15 between years of high and low escapement. The dual-isotope approach, using deltaN-15 and deltaC-13 together, suggested that fish production is primarily dependent on limnetic primary and secondary production. The dual-isotope approach indicated that the coast range sculpin (Cottus aleuticus) was the only fish with an appreciable dietary component consisting of salmon eggs or emergent fry.