Alaska Fishery Research Bulletin Issues, Vol.3 No. 1 - Summer 1996

Spot Shrimp Growth in Unakwik Inlet, Prince William Sound, Alaska

Al Kimker, Wayne Donaldson, and William R. Bechtol - Vol.3(1):1-8. 1996.

Commercial shrimp harvests from the pot fishery in Prince William Sound, Alaska, averaged 2.9 metric tons (mt) annually prior to 1979. Catches increased rapidly after 1978, 110 mt being harvested in 1986. Little was known about adult spot shrimp Pandalus platyceros, which composed the bulk of these harvests. To obtain life history information the Alaska Department of Fish and Game marked 10,168 spot shrimp with streamer tags during 1983-1986. A total of 1,061 tags were recovered, 206 of these being repeat recoveries. The maximum time at liberty was 1,562 d, during which time the shrimp grew 11.5 mm. Mean annual growth was 3.1 mm for the 477 recoveries that molted between recaptures. Data on time at liberty and size at tagging and recapture for individual shrimp were fit to a von Bertalanffy growth equation. Results indicated that shrimp 28.5 to 41.5 mm carapace length were 3 to 7 years old, representing 5 age classes. Combined with previous studies that indicated the juvenile stage of spot shrimp lasts at least 2 years, lifespans of spot shrimp in Prince William Sound probably exceed 7 years. This longevity is much greater than previously assumed and emphasizes the need for more conservative management.

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Abundance of the Chinook Salmon Escapement in the Taku River, 1989 to 1990

Keith A. Pahlke and David R. Bernard - Vol. 3(1):9-20. 1996.

An interagency study was conducted to estimate, through mark-recapture methods, the abundance of large (greater than or equal to 660 mm MEF), spawning chinook salmon Oncorhynchus tshawytscha in the Taku River in 1989 and 1990. Fish were captured with fish wheels from May through July in the lower river at Canyon Island in Southeast Alaska. All fish were marked with back-sewn spaghetti tags, and some were additionally fitted with radiotags. Chinook salmon recaptured in Canadian tributaries showed that fish bound for the Nahlin River generally passed Canyon Island first, those bound for the Nakina River passed next, and fish bound for Tatsatua and Kowatua Rivers passed last. The 1984 year class predominated samples in both 1989 and 1990. Little or no size- or sex-selective sampling among larger fish was evident in samples taken from tributaries. Because many recaptured fish had lost their spaghetti tags, the marked population used for estimating abundance was defined as only those fish with radiotags that had been tracked to their spawning grounds. Recapture proportions were similar among tributaries. Abundance of large fish was estimated at 40,329 (SE = 5,646) for 1989 and 52,142 (SE = 9,326) for 1990. Estimates of abundance from aerial surveys of the Taku River were considerably smaller than estimates from mark-recapture experiments in both 1989 and 1990, a trend repeated in studies at other transboundary rivers in later years.

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Relative Effects of Mixed Stock Fisheries on Specific Stocks of Concern: A Simplified Model and Brief Case Study

Denby S. Lloyd - Vol.3(1):21-31. 1996.

An algebraic model is presented that allows comparison of changes in total catch, stock-specific catch, and stock-specific harvest rate for various fisheries harvesting the same stock of concern under conditions of change in the stock's abundance. The model operates without detailed estimates of each fishery's complete stock composition and without ongoing assessment of each component stock's biomass or population size. Rather, observations or assumptions of the proportional contribution (rho sub x) of the stock of concern to each fishery's total catch, combined with presumptions of change in that stock's abundance (theta sub x), are sufficient to illustrate proportional changes in catch and harvest rate under management prescriptions for constant harvest rate and for constant total catch. Results indicate that mixed stock fisheries, especially those with low rho sub x from a particular stock, are only slightly affected by and exert very small influence upon changes in abundance of that stock, even if total harvests remain constant. In contrast, single stock fisheries with high rho sub x are more directly affected by and exert more substantial influence upon changes in the stock's abundance. Because the presence of other stocks in a mixed stock fishery dilutes its relationship to any stock in particular, such a fishery may not need to be managed nearly so precisely as another fishery for which a common stock supports the bulk of the harvest.

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Relative Effects of Mixed Stock Fisheries on Specific Stocks of Concern: Application to Fixed Escapements and Norton Sound Chum Salmon

Denby S. Lloyd - Vol. 3(1):32-44. 1996.

An algebraic model relating annual changes in harvest rate and catch of various fisheries to the percent of total catch in each fishery contributed by a particular stock is examined to explore implications pertaining to harvest sharing and related escapements. Results indicate that mixed stock fisheries, especially those in which the stock of concern composes a small proportion of the total catch, tend to achieve much of their proportional responsibility for fixed escapement without adjustment of total catch. More terminal fisheries with high contributions from a particular stock must adjust total harvests to achieve similar responsibility. Adjusting total catch of mixed stock fisheries to fully achieve a strict proportional sharing of escapement comes at a cost of many times the number of fish forfeited from the harvest compared to the number of fish added to the stock's escapement. Such additions to the escapement are often insubstantial. Harvest adjustments in single stock fisheries, however, provide a 1-fish benefit to the escapement for each fish forfeited from the harvest, and often such contributions compose a substantial portion of the total escapement objective. Implications for Norton Sound chum salmon Oncorhynchus keta escapements are explored for the South Peninsula June mixed stock fishery compared to more terminal fishing in Norton Sound.

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Can Alaska Balance Economic Growth with Fish Habitat Protection? A Legislator's Perspective

Drue Pearce - Vol. 3(1):45-48. 1996. No Abstract.

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Can Alaska Balance Economic Growth with Fish Habitat Protection? A Biologist's Perspective

Kenneth E. Tarbox and Terry Bendock - Vol. 3(1):49-53. 1996. No Abstract.

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Microscale Abundance of Copepod Nauplii Prey of Larval Fishes in a Glaciated Fiord Measured with a 50-mL Sampler

A. J. Paul and J. M. Paul - Vol. 3(1):54-58. 1996.

Copepod nauplii were collected with a 50-mL sampler in 1995 to examine the microscale spatial heterogeneity of copepod nauplii in the immediate hunting territory of larval fish. The study was done in a glaciated fiord during the spring hatching period for walleye pollock Theragra chalcogramma. From mid April through mid May 50-mL water samples taken at 5- and 10-m depths contained, on average, 0.2-1.0 copepod nauplii 150-350 mm long. By 15 May the average sample counts were typically 1.0-4.0 nauplii at 5 m and 0.4-2.0 at 10 m deep. Based on previous literature values, copepod nauplii in Resurrection Bay exhibited sufficient abundance in these microscale samples to support walleye pollock larvae.

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Aspects of Sockeye Smolt Production in the Egegik River System of Bristol Bay, Alaska

Patrick C. Martin and Denby S. Lloyd - Vol. 3(1):59-63. 1996.

In Becharof Lake a significant positive correlation was found between the total number of sockeye salmon Oncorhynchus nerka, primarily age 1. and age 2., produced by brood year and the proportion of older holdover parr (age 2.) produced by the subsequent brood year. This suggests possible density-dependent effects of grazing pressure by large numbers of parr that reduce the food available to fry in subsequent years, which in turn causes a higher proportion of parr from subsequent brood years to have a longer freshwater residence. Recent, large spawning escapements may affect the rearing capacity of Becharof Lake and thereby reduce the subsequent production of smolts and return of adult sockeye salmon to the Egegik River.

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