Alaska Fishery Research Bulletin Issues, Vol.1 No. 2 - Winter 1994

Differences Between Inseason and Postseason Stock Composition Estimates for Sockeye Salmon in Gillnet Catches in 2 Districts in Southeast Alaska and in the Stikine River, 1986 to 1989

Kathleen A. Jensen - Vol. 1(2):107-124. 1994.

Linear discriminant function analysis of sockeye scale patterns was used to estimate stock compositions of sockeye salmon Oncorhynchus nerka catches in U.S. and Canadian fisheries that harvest Stikine River stocks. Inseason and postseason estimates were made for U.S. gillnet fisheries in Southeast Alaska Districts 106 and 108 and Canadian gillnet fisheries in the Stikine River. Inseason analysis worked well in 1986, 1987, and 1988, but did not work well in 1989. Most differences between inseason and postseason estimates during 1986 to 1988 were not of practical significance; i.e., management actions based on inseason estimates would have been the same had they been based on postseason estimates. Differences were numerically small, generally <1,000 fish. The season total differences in stock-specific catch estimates ranged from 0.0% to 7.1% in District 106. In 1989 weekly differences were of practical significance and were numerically large, ranging from 12 to 7,882 fish. Season differences in District 106 ranged from 3.2% for transboundary Stikine fish to 28.7% for Nass/Skeena fish. In 1989 use of average historical proportions would have resulted in better stock composition estimates than the inseason analysis did. All practical differences were also statistically significant using log-likelihood ratio analysis with alpha = 0.05.

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On the Discrimination of Sockeye and Chinook Salmon in the Kenai River Based on Target Strength Determined with 420 kHz Dual-Beam Sonar

Douglas M. Eggers - Vol. 1(2):125-139. 1994.

The feasibility of using target strength to discriminate between upstream migrating salmon was examined by computer simulation of the expected sampling distribution of mean target strength for a variety of sampling regimes and mixed populations of Kenai River sockeye Oncorhynchus nerka and chinook O. tshawytscha salmon. The simulations were based on empirically derived parameters for underlying Rayleigh probability distribution for square root of the backscattering cross section and length-frequency distributions observed for Kenai River sockeye and chinook salmon. Computer simulation experiments were conducted to examine (1) the effect of target-strength measurement rate on ability to discriminate fish, (2) whether it was possible to discriminate sockeye and chinook salmon species or age classes of chinook salmon, and (3) the consistency of model predictions and observed target-strength distributions of migrating salmon in the Kenai River. Simulated target-strength distributions were consistent with observed target-strength distributions. Although with high sampling rates it was possible to discriminate certain mixed populations of sockeye and chinook salmon, it was not possible to discriminate between sockeye and chinook salmon with the sampling rates achieved in the Kenai River. Because of high within-fish variability in target strength and low between-fish differences in mean target strength, target strength cannot be used by itself to discriminate between fish in the Kenai River.

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Lingcod Fishery Monitoring in Southeast Alaska

David A. Gordon - Vol. 1(2):140-152. 1994.

Lingcod Ophiodon elongatus have recently become an important commercial fish species in Southeast Alaska. The fishery began in 1987 and occurs along the outer coast of northern Southeast Alaska. Dinglebar gear is the primary gear used in the directed fishery. Lingcod are also caught incidentally in significant amounts in the longline and salmon troll fisheries. The Alaska Department of Fish and Game has monitored the fishery through dockside samples, skipper interviews, and onboard observer trips since 1988. Catch per unit effort is lowest during the summer months. Average length of lingcod caught in the directed dinglebar fishery from 1988-1992 was 81 cm, and lingcod caught in the longline fisheries while targeting other species averaged 91 cm. The largest male lingcod sampled from the directed fishery was 95 cm and the largest female was 127 cm. Male lingcod are caught at a higher rate than females from March through May. Peak spawning occurs in February. Size at which >50% of the female lingcod sampled were mature was 83 cm. Lingcod may shrink up to 8 cm when held in slush-ice.

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Nutrient Treatment of 3 Coastal Alaskan Lakes: Trophic Level Responses and Sockeye Production Trends

Gary B. Kyle - Vol.1(2):153-167. 1994

Three coastal oligotrophic lakes with variable interannual production of sockeye salmon Oncorhynchus nerka were treated with additions of fertilizer to increase zooplankton biomass for the purpose of producing more numerous and larger smolts. Nutrient additions increased primary production (chlorophyll-a) by as much as 500% and resulted in a sustained higher level of zooplankton biomass than before treatment. Zooplankton biomass increased from 40% to 700% after nutrient treatment in the 3 lakes. For the 2 lakes in which data were available, sockeye smolt biomass increased from 50% to 250%, and in the third lake the mean weight of age-1 smolts increased by 35%. For all 3 lakes subsequent adult sockeye production increased. The phosphorus loading rates for these lakes exceeded that of treated coastal lakes in Canada by 2-5 times; however, the oligotrophic status of these lakes was not altered. The sustained high production of zooplankton and the consistent production of larger or more abundant smolts indicated that the higher phosphorus loading rates for these Alaskan lakes were advantageous to rearing sockeye salmon fry.

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A Lightweight, Inclined-Plane Trap for Sampling Salmon Smolts in Rivers

Gary L. Todd - Vol.1(2):168-175. 1994.

The design and use of an inclined-plane trap is described for capturing salmon smolts in medium to large (5-60 m3·sec-1) rivers of Alaska. The trap was designed to minimize fish scale loss and mortality, be lightweight yet durable, minimize debris loading, be readily moved by 2 people, and be easily transported by a small river boat or helicopter. The tapered design allows traps to be stacked inside one another when being transported. This trap style has been in use since the early 1980s in small clearwater streams and large glacial rivers of southcentral Alaska. Catch efficiencies from mark-and-recapture tests have exceeded 10% for a single trap. The highest daily catch to date for 1 trap occurred in June 1994 when 96,979 sockeye salmon Oncorhynchus nerka smolts were caught in the Kasilof River.

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We Don't Do Allocation

Paul Krasnowski - Vol.1(2):176-178. 1994. No Abstract.

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Tanner Crab Survival in Closed Pots

Al Kimker - Vol.1(2):179-183. 1994.

Lost and delinquent commercial and sport fishing gear has gained public notoriety recently because of documented waste of fish and shellfish resources. Shellfish and groundfish pots have contributed to the problem. Although escape mechanisms have been developed to allow egress of captured species from pots, imprecise release time of these devices has generated debate exacerbated by inexact estimates of the survival of captured species. To gain information on Tanner crab Chionoecetes bairdi survival in pots, we captured large, adult male Tanner crabs and held them in cod pots in the outer portion of Kachemak Bay, Alaska. The pot tunnels were secured shut so the crabs had no chance to escape. No external source of food was provided. The pots were pulled periodically over a 119d period. A total of 52 (39%) of the original 132 crabs died during the experiment.

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Compensatory Feeding Capacity of 2 Brachyuran Crabs, Tanner and Dungeness, After Starvation Periods Like Those Encountered in Pots

J. M. Paul, A. J. Paul, and Al Kimker - Vol.1(2):184-187. 1994.

Food usage rates were measured in 2 brachyuran species, Tanner crab Chionoecetes bairdi and Dungeness crab Cancer magister, following starvation periods of 0, 30, 60, and 90 d. F-tests indicated that there was no compensatory feeding. Food usage rates within species were similar among the 4 test groups, regardless of the length of starvation. Food usage rates were approximately 0.4% body weight per day for Tanner crabs and 1.0% for Dungeness crabs. Neither species markedly increased its consumption rate to compensate for the nutritional deficits. Starvation periods as short as 30 d negatively affected survival of both species under laboratory conditions.

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