Alaska Fishery Research Bulletin Issues, Vol.2 No. 2 - Winter 1995

Coded Wire Tagging Studies of Chinook Salmon of the Unuk and Chickamin Rivers, Alaska, 1983-1993

Keith A. Pahlke - Vol. 2(2):93-113. 1995.

From 1983 through 1988 wild juvenile Chinook salmon Oncorhynchus tshawytscha were tagged with coded wire tags: 20,531 young-of-year and 42,475 smolts on the Unuk River and 30,501 smolts on the Chickamin River. From 1985 through 1993 a total of 296 Unuk River and 208 Chickamin River tags were recovered from fisheries and escapements. Among-year estimates of smolt populations at the time of tagging ranged from 142,000 to 510,000 fish, and fractions of the juvenile populations tagged annually ranged from 1.0 to 6.5%. Recoveries indicated the 2 stocks rear primarily in the inside waters of southern Southeast Alaska and are available for harvest over their entire oceanic life cycle. Exploitation rates on the Unuk River stock ranged from 14 to 24% overall and from 8 to 22% by the commercial troll fleet, the primary harvester. Chickamin River exploitation rates ranged from 27 to 50% overall and from 17 to 40% by the commercial troll fleet. No area or time strata were identified as the major harvester of the 2 stocks. Distribution and harvest of the stocks were similar to those of Ketchikan-area hatcheries, which have brood stocks developed from those 2 stocks. Age composition of the escapement was similar to other Southeast Alaska chinook stocks: almost all males were age 1.1 to 1.4 and most females were age 1.3 and 1.4.

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Updated Length-Based Population Model and Stock-Recruitment Relationships for Red King Crab in Bristol Bay, Alaska

J. Zheng, M. C. Murphy, and G. H. Kruse - Vol.2(2):114-124. 1995.

A length-based population model for Bristol Bay red king crab Paralithodes camtschaticus was updated and applied to abundance and catch data from 1968 to 1994. The updated model has fewer parameters and assumes constant natural mortality over length and 2 levels of natural mortality over time for males and 3 levels for females. A nonlinear least squares approach was used to estimate abundance, recruitment, and natural mortality. We added confidence intervals for the abundance estimates with a bootstrap percentile method. Natural mortality was estimated to be 4 to 5 times higher in the early 1980s than during other periods. The observed population abundances were well fitted by the updated model. Confidence intervals for legal male abundance were narrower than for mature female abundance. The stock-recruitment data estimated from the updated length-based model provided a good fit to both general and autocorrelated Ricker models. However, recruitment estimates were lower and the relationships were slightly more depensatory than in the previous model.

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Population Model Suggests New Threshold for Managing Alaska's Togiak Fishery for Pacific Herring in Bristol Bay

Fritz Funk and Katherine A. Rowell - Vol. 2(2):125-136. 1995.

The threshold biomass for fisheries on Pacific herring Clupea pallasi that spawn near Togiak, in Bristol Bay, Alaska, was reviewed based on the data collected in the decade following threshold harvest policy initiation in 1987. The current threshold of 31,752 mt (35,000 tons), below which fishing is precluded, was found to be too low. This threshold had been set at 25% of the spawning biomass during a period that included substantial harvests. A threshold set at 25% of the average unfished biomass (AUB) is widely used in other herring fisheries along the Pacific coast. A 1,000-year simulation of abundance was used to determine AUB under several possible spawner-recruit relationships and sets of stock-assessment data. Four alternative age-structured assessment (ASA) models fit to the available data for Togiak herring under different sets of assumptions were used to represent the uncertainty in the stock-assessment data. A large discrepancy between abundance trends from aerial surveys and trends apparent in age-composition data resulted in a large amount of uncertainty about past biomass levels in the ASA model, which was reflected in the AUB estimates. Ricker and empirical spawner-recruit models fit to the information from the ASA analysis were used to simulate density-dependent effects on recruitment. The uncertainty in the basic population dynamics data provoked a wide range of AUB estimates under different sets of assumptions. AUB estimates ranged from approximately 159,000 to 433,000 mt, and the resulting thresholds ranged from approximately 40,000 to 108,000 mt. Based on this information, we recommend that the Togiak threshold be raised to at least 45,000 to 50,000 mt, pending further resolution of the discrepancies between abundance trends from aerial surveys and abundance trends from age compositions. Setting thresholds at 25% of AUB only rarely triggered fishery closures and these fishery closures produced very little reduction in long-term average yield.

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Epizootics of Infectious Hematopoietic Necrosis Virus in an Enhanced Population of Sockeye Salmon Oncorhynchus nerka Smolts at Chenik Lake, Alaska

Jill E. Follett and Tamara O. Burton - Vol. 2(2):137-142. 1995.

Infectious hematopoietic necrosis virus (IHNV) epizootics in emigrating sockeye salmon Oncorhynchus nerka smolts occurred in the spring of 1991 and 1992 at Chenik Lake in Southcentral Alaska. The lake historically supported a natural run of sockeye salmon, but lake stocking was initiated following a substantial population decline. An estimated 32,000 smolts in 1991 and 42,000 smolts in 1992 emigrated from the lake, which was substantially less than the 1.0-1.4 million smolts expected. IHNV was isolated f rom both moribund and apparently healthy smolts. Though smolt mortality was attributed to IHNV, other factors also may have contributed to the reduced numbers. Stressful environmental conditions and high fish density may have precipitated the disease outbreaks. In 1993, smolt abundance was less than expected but IHNV was not isolated. Management plans for the Chenik Lake system include maintaining current escapement levels at 10,000 adults and reducing stocking to between 1.0 and 1.5 million fry.

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Thermal Mark Technology for Inseason Fisheries Management: A Case Study

Peter Hagen, Kristen Munk, Benjamin Van Alen, and Bruce White - Vol. 2(2):143-155. 1995.

Effective management of wild and hatchery salmon stocks in Alaska requires rapid and accurate determination of each component in commercial mixed stock catches. Marking 100% of the hatchery fish with thermally induced bands on their otoliths can potentially reduce uncertainty in the management of mixed stock fisheries, this premise being the subject of our investigation. In 1992 and 1993, adult hatchery pink salmon Oncorhynchus gorbuscha that had been thermally marked by prescribed water temperature manipulation in Gastineau Hatchery passed through commercial fisheries on their return to this Southeast Alaska hatchery. In 1993 we processed otoliths that had been collected from the fisheries in 1992. We also applied an inseason recovery plan to process otoliths from the 1993 run; from a random sample of 400 heads collected from each of 5 commercial and 3 experimental fisheries, 100-150 otoliths were subsampled and examined within 24 h to provide managers with inseason estimates of composition. Later, additional otoliths were processed to increase precision around the estimates and to develop quality control criteria. A total of 3,870 heads from the 1993 fisheries were collected, from which 952 otoliths were processed inseason and 1,359 postseason. The final precision, based on the 95% confidence intervals, fell within ±2% of the point estimate for each fishery. The accuracy of detecting marked otoliths was determined by planting 17 known marked otoliths into samples processed for the inseason estimate. All planted otoliths were correctly identified. Personnel were trained to process and read otoliths as part of this project. Their progress was evaluated through samples containing both known marked and known unmarked otoliths and by determining between-reader agreement. The results confirmed the importance of training and indicated that, when learning to detect thermal mark patterns, individual skill development varies. We found thermal mark recovery in this study to be a timely and cost-effective tool for managing mixed stock fisheries.

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Marine Factors in the Production of Salmon: Their Significance to the Pacific Salmon Treaty

Jev Shelton and Jeffery P. Koenings - Vol. 2(2):156-163. 1995. No Abstract.

Measurements from 64 mature male red king crabs Paralithodes camtschaticus were made in carapace length (CL) and chela height (CH) before and after they molted in the laboratory. Increases in chela height for adult males 72-143 mm CL averaged 3.2 mm (SD = 1.5) at molting, but claw growth was not correlated to initial CH. At all carapace lengths examined there were individuals with both relatively large and small CH/CL ratios. After molting, CH/CL ratios increased in 28%, decreased in 25%, and stayed the same in the remaining 47% of the males. Among mature males, large or small claws relative to CL seemed to be an individual trait that was retained through the molt.

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Bulletin is Now on the Internet

Marla Trollan and Kurt Savikko - Vol. 2(2):168. 1995.
(No Abstract) Full Editorial:

Readers of the Alaska Fishery Research Bulletin may be interested to know that the journal's abstracts are now available on the Internet, and the entire journal may be online in 1997 or 1998, at which time paper production may be gradually phased out. The journal's abstracts are found in the Alaska Department of Fish and Game (ADF&G) web site, along with the guide to authors and editorial policy. The department's general/statewide information page provides a link to listings of publication titles organized by issue and by species group, and to which the abstracts are linked.

The ADF&G web site also provides other useful scientific and general information about Alaska's wildlife and fisheries. The site is about a year old but is really just beginning to evolve; considerable expansion is planned over the coming year. Commercial fisheries information has led the way with scientific report and publication listings, current and historical statistical data, and program descriptions. Similar information is being developed for sport fisheries and wildlife.

The web site structure blends the organization of the agency with subject categories. For example, the Commercial Fisheries Management and Development Division was primarily divided by management region. Beneath this level, the following subject areas were defined: species & fisheries, programs, publications, regulations, general divisional information & frequently asked questions, staff listings & contacts, and permits, licenses and forms. The other divisions are expected to develop similar structures. Statewide and general information include a departmental overview, photo gallery, drawings of Alaska's fish, and links to other relevant sites.

At this time, specific commercial fisheries information now available includes salmon and herring forecasts with prior-year fishery overviews; fishery regulations and policies; current (inseason) and historical salmon catch statistics; descriptions of tag-otolith, pathology, and limnology programs; overview of herring fisheries in Alaska; species descriptions; and commercial fisheries system codes (used in fish tickets, Intent to Operate Reports, and Commercial Fisheries Operator Annual Reports). Department reports are also listed by series: Informational Leaflets, Technical Data Reports, Technical Fishery Reports, Regional Information Reports, Fishery Research Bulletins, and Special Publications. Future additions to the site will include such things as Intent to Operate and Catcher/Seller forms, a variety of fishery-related maps, permit information, inseason shellfish catch statistics, salmon enhancement and mariculture production information, and fishery news releases and management plans.

The site is accessed as follows: http://www.adfg.alaska.gov. Individuals wishing to find salmon catch statistics, for example, would first access ADF&G's home page, select the Commercial Fisheries Management and Development link, next select the Statewide & General Information link (regional links could also be selected for area-specific information), and finally select the Salmon link under the Finfish Species and Fisheries heading.

Note: PDF file may contain outdated website URLs.

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