Alaska Fishery Research Bulletin Issues, Vol.4 No. 2 - Winter 1997

Age-Structured Analysis of Pacific Herring from Norton Sound, Alaska

Erik H. Williams and Terrance J. Quinn II - Vol. 4(2):87-109. 1997.

For many exploitable Pacific herring Clupea pallasi stocks in Alaska, age-structured assessment models are used to forecast the abundance of returning herring. The purpose of this study was to develop such a model for Norton Sound herring. Commercial catch and sampling data for Norton Sound herring were obtained from the Alaska Department of Fish and Game. Natural mortality estimates were obtained from analysis of life history parameters. Initial starting values for the age-structured model were obtained from cohort analysis. Better results were obtained when age-composition data for age 10 and older were pooled into a plus group. A parametric bootstrap analysis using a beta distribution by incorporating variability from the age-composition residuals provided standard errors of the estimates. The analysis suggested that aerial surveys underestimated actual biomass in the early 1980s. However, a sensitivity analysis suggested that higher natural mortality in those years could have produced similar results. The fit of this model to the data was comparable to that obtained with age-structured assessments of other Alaska herring stocks. We believe this model can be used as a stock-assessment tool for management of Norton Sound herring.

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Literature Compilation on Tagging Red King Crabs in Alaska from Initial Efforts in 1954 through 1969

William E. Donaldson - Vol. 4(2):110-119. 1997. No Abstract.

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Consequences to Juvenile Sockeye Salmon and the Zooplankton Community Resulting from Intense Predation

J. P. Koenings and G. B. Kyle - Vol. 4(2):120-135. 1997.

Stocking of juvenile sockeye salmon Oncorhynchus nerka into nonanadromous lakes at levels comparable with juvenile densities in anadromous lakes supporting natural sockeye salmon populations effected up to a 90% reduction in zooplankton biomass. The zooplankton communities subsequently became resistant to predation as the vulnerable Daphnia, Diaptomus, and ovigerous Cyclops were virtually eliminated and the more agile (nonovigerous) Cyclops and smaller Bosmina persevered and became predominant. Relying on a standing crop of zooplankton that was severely depressed by intense grazing the previous season, juvenile sockeye salmon experienced at least a 3-fold reduction in numbers and biomass between fry and smolt stages from the previous year. Our experimental results confirmed our empirical findings that, in rearing-limited lakes, smolt biomass production becomes a function of zooplankton biomass. Once restructured by excessive predation, some zooplankton communities were unresponsive or slow to respond to either reduced grazing pressure and/or to subsequent nutrient treatment. This delayed recovery of overgrazed zooplankton populations reduced growth and survival (rearing efficiency) for ensuing cohorts. In response, Frazer Lake sockeye salmon populations fell far below replacement, the dominant-year run segment collapsed, and the amplitude of high versus low return per spawner ratios increased. In contrast, less damaged zooplankter populations responded to nutrient treatments, leading to a 3-fold increase in fry-to-smolt survival and a 6- to 20-fold increase in smolt biomass. The degree to which juvenile sockeye salmon foraging decreases biomass levels and changes the species composition of the zooplankton community ultimately determines the duration of zooplankton recovery and lowered sockeye salmon production.

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Trophic-Level Responses to Nutrient Treatment of Meromictic and Glacially Influenced Coghill Lake

J. A. Edmundson, G. B. Kyle, S. R. Carlson, and P. A. Shields - Vol. 4(2):136-153. 1997.

Prior to a 1990-1994 run decline, Coghill Lake consistently produced the highest single-system sockeye salmon Oncorhynchus nerka catches in Prince William Sound. Although limnological and juvenile fisheries data are not available before the run declined, we hypothesized that sockeye salmon fry produced from 3 consecutive years of high escapements (1980-1982) might have overgrazed the zooplankton forage base and reduced the lake's sockeye salmon rearing capacity. In 1993 the Exxon Valdez Oil Spill Trustee Council approved and helped fund a nutrient enrichment stock restoration project for Coghill Lake to mitigate the oil-damaged fishery resources. During 4 years of nutrient enrichment (1993-1996), the seasonal mean phosphorus concentration increased 22%, algal biomass of mainly genera edible by zooplankton increased 220%, and the standing stock (density) of the prevalent zooplankton (Cyclops) increased 117% compared to pre-enrichment years (1988-1992). The sockeye salmon population averaged 263,604 smolts before enrichment compared to 940,411 during treatment. This increased smolt production is attributed to increases in primary and secondary production because the number of smolts produced per spawner also increased during enrichment. The trophic-level responses to nutrient enrichment in meromictic, glacially influenced Coghill Lake were similar to those observed for other clearwater holomictic and meromictic lakes treated in Alaska.

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Early Marine Residence, Growth, and Feeding by Juvenile Salmon in Northern Cook Inlet, Alaska

Lawrence L. Moulton - Vol. 4(2):154-177. 1997.

Juvenile salmon were captured in June and July 1993 with a surface townet in the northern portion of Cook Inlet, a glacially turbid estuary. Hydroacoustic sampling indicated that most fish targets were in the top 2 m of the water column. Many salmon juveniles, particularly chinook Oncorhynchus tshawytscha, sockeye O. nerka, and coho O. kisutch, moved rapidly out of the sampling area, although residence in northern Cook Inlet extended into mid July. Chum salmon O. keta were more abundant than any other salmon species in northern Cook Inlet, and by July were widely distributed throughout the study area. Diets of juvenile salmon in June were similar to those reported in other studies, calanoid copepods, fish larvae, and other zooplankton being abundant in stomachs. Chum salmon, followed by pink salmon O. gorbuscha, fed most intensively. Drift insects were an important part of chum salmon diets in June and predominated the diet of all species in July. Heavy feeding on drift insects demonstrated by all juvenile salmon was probably a response to high turbidities reducing feeding efficiency and effecting a near-surface orientation. Apparent growth in chum salmon juveniles was within the reported range for other regions. During July, both chum and pink salmon juveniles rearing in northern Cook Inlet achieved growth rates and conditions comparable to those of nearby Prince William Sound, which is not glacially occluded.

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Salmon Stocks at Risk: What's the Stock and What's the Risk?

Harold J. Geiger and A. J. Gharrett - Vol. 4(2):178-180. 1997.

Fisheries managers and fisheries population biologists and geneticists have 2 big problems when talking about salmon stocks at risk: disagreement about what a stock is, and too little to go on about what is at risk. We recommend leaving the word stock to fisheries managers, with the traditional emphasis on groups of fish managed as a unit. We recommend reserving the word deme to mean a smaller-scaled stable population of interbreeding salmon, with the emphasis on genetic discreteness. We hope maintaining this distinction can help promote a freer discussion of fluctuations in run sizes and help direct more attention to biological issues, like the underpinnings of sustainable fish production. Second, we want to turn the question around from "are stocks at risk?" to "what is at risk?" We conclude that if concrete services that humans enjoy from salmon populations were fairly evaluated against activities that put those services at risk, sustainability is undervalued.

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Incidence of Thermally Marked Pink and Chum Salmon in the Coastal Waters of the Gulf of Alaska

Edward V. Farley, Jr., and Kristen Munk - Vol. 4(2):181-187. 1997.

A Gulf of Alaska research cruise during July and August 1996 provided ocean recoveries of 698 juvenile pink Oncorhynchus gorbuscha and 350 chum O. keta salmon thermally marked during incubation at Alaskan and Canadian hatcheries. We obtained the recoveries from 2,343 pink and 1,695 chum salmon examined for thermal marks. The marked salmon migrated westerly; those released from southeastern Alaska hatcheries were caught as far west as Cape Puget and Cape Hinchinbrook, whereas pink salmon released from Prince William Sound hatcheries were found as far west as Mitrofania Island. Our results indicate that a modest research sampling program can collect sufficient numbers of thermally marked salmon for detailed studies of the growth and development of individual salmon stocks.

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