Values of δ15N and δ13C (the per mil deviation from the recognized isotope standard) from biota of a southeastern Alaska stream (Sashin Creek) that receives an annual run of 30 000 anadromous pink salmon (Oncorhynchus gorbuscha) were measured to determine sources of nitrogen (N) and carbon (C). Marine-derived nitrogen (MDN) is the predominant source of N for food webs found in the lower 1200 m of the stream which, due to a waterfall, is the only portion of the stream available to salmon returning to spawn. Comparable spawning section biota were enriched by about 5 per mil relative to the salmon-free control section, corresponding to the difference between 0 and 100% MDN in a mixing model. Food webs of resident rainbow trout (O. mykiss), at the outlet of one of the source lakes, Sashin Lake, have very low δ13C, suggesting the importance of a respired C pool in the lake. The source of C in the remainder of the stream is C fixation by autochthonous producers and marine organic C (within the salmon spawning section). Resident fishes in the salmon spawning section depend on MDN and some of the C delivered by the annual run of returning salmon.

Biota δ15N and δ13C values (deviations from recognized isotope standards) from lliamna 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 lliamna Lake had higher δ15N compared with control lakes, verifying a mixing model correlating δ15N with MDN. Periphyton δ15N 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 δ15N between years of high and low escapement. The dual-isotope approach, using δ15N and δ13C 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.

Physical and biological variables affecting juvenile Pacific herring (Clupea pallasi) in Prince William Sound (PWS) from 1995 to 1998 were investigated as part of a multifaceted study of recruitment, the Sound Ecosystem Assessment (SEA) program. Though more herring larvae were retained in eastern PWS bays, ages‐0 and ‐1 herring used bays throughout PWS as nursery areas. Water transported into PWS from the Gulf of Alaska (GOA) contributed oceanic prey species to neritic habitats. Consequently, variations in local food availability resulted in different diets and growth rates of herring among bays. Summer food availability and possible interspecific competition for food in nursery areas affected the autumn nutritional status and juvenile whole body energy content (WBEC), which differed among bays. The WBEC of age‐0 herring in autumn was related to over‐winter survival. The limited amount of food consumption in winter was not sufficient to meet metabolic needs. The smallest age‐0 fish were most at risk of starvation in winter. Autumn WBEC of herring and winter water temperature were used to model over‐winter mortality of age‐0 herring. Differences in feeding and energetics among nursery areas indicated that habitat quality and age‐0 survival were varied among areas and years. These conditions were measured by temperature, zooplankton abundance, size of juvenile herring, diet energy, energy source (GOA vs. neritic zooplankton), WBEC, and within‐bay competition.

Plankton populations in Prince William Sound, Alaska, exhibited pronounced seasonal, annual and longer‐period variability in composition and standing stock in response to physically influenced differences in nutrient availability, and possibly currents that modify local biomass by exchanges with water from the bordering Gulf of Alaska. During springs in which early, strong physical stratification developed, intense, short‐lived phytoplankton blooms occurred. These blooms had relatively short residence times in the water column. In contrast, during springs in which slower, weaker stratification developed, phytoplankton blooms were prolonged and took longer to peak. These slower blooms prolonged the period of phytoplankton production, prolonged interaction with the springtime grazing community and led to the incorporation of more organic matter into pelagic food webs. A coupled biological‐physical simulation of plankton production was used to examine the implications of seasonally varying air and mixed‐layer temperatures, surface winds and incident light on the timing, duration, annual production and standing stock of plankton. Our modelling results reproduced the observed characteristics of the springtime production cycle, and the magnitude of zooplankton stocks for the period 1992–97 but not for 1981–91. These results suggest that for most of the 1990s, bottom‐up influences on nutrient supplies controlled levels of primary consumers, whereas for the 11 years before that, other unknown factors dominated this process. We present the results of a comprehensive, multiyear study of relationships between plankton and physical limitations, and a retrospective analysis of earlier conditions to explore the possible causes for these differences.

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