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Alaska Fishery Research Bulletin Issues, Vol.12 No. 2 - Winter 2007
Geographic Distribution, Depth Range, and Description of Atka Mackerel Pleurogrammus monopterygius Nesting Habitat in Alaska
Robert R. Lauth, Scott W. McEntire, and Harold H. Zenger Jr. — Vol. 12(2):165–186. 2007.
Understanding the spatial and bathymetric extent of the reproductive habitat of Atka mackerel Pleurogrammus monopterygius is basic and fundamental information for managing and conserving the species. From 1998 to 2004, scuba diving and in situ and towed underwater cameras were used to document reproductive behavior of Atka mackerel and to map the geographic and depth ranges of their spawning and nesting habitat in Alaska. This study extended the geographic range of nesting sites from the Kamchatka Peninsula to the Gulf of Alaska, and extended the lower depth limit from 32 to 144 m. Male Atka mackerel guarding egg masses were observed during October—indicating that the duration of the nesting period in Alaska is more protracted than in the western Pacific. Results from this study also suggest that nearshore nesting sites constitute only a fraction of the nesting habitat and that there is no concerted nearshore spawning migration for Atka mackerel in Alaska. Nesting sites were widespread across the continental shelf and found over a much broader depth range than in the western Pacific. Nesting habitat was invariably associated with rocky substrates and water currents; however, smaller-scale geomorphic and oceanographic features as well as physical properties of the rocky substrate were variable between different island groups and nesting sites. Water temperatures for nesting sites ranged from 3.9°C to 10.5°C. Water temperatures within nesting sites varied little and did not appear to be limiting the upper or lower depth boundaries of nesting. Results from dive transects showed significantly fewer egg masses above 20 m water depth. Other possible factors limiting the upper or lower depth limit of nesting sites are discussed.Full Article (PDF 4,330 kB)
Historical and Current Abundance Estimation
Briana H. Witteveen, Kate M. Wynne, and Terrance J. Quinn II — Vol. 12(2):187–196. 2007.
A photo-identification, mark–recapture study was conducted on a feeding aggregation of humpback whales Megaptera novaeangliae in the waters of eastern Kodiak Island between June and September 2002. Historically, a portion of this population was targeted in a local commercial whale fishery. The fishery was conducted in eastern Kodiak Island out of Port Hobron, Alaska, between 1926 and 1937 and resulted in the removal of nearly 1,600 humpback whales. An estimated 157 (95% confidence interval: 114, 241) whales were in the study area in 2002 based on the Schnabel maximum likelihood estimator (MLE) for closed populations. The Schnabel MLE of abundance in 2002 and historic catch values were used to back-calculate the historical abundance trend in the study area between 1925 and 2002 using a delay-difference model with a density dependent recruitment function. Historical abundances were calculated both prior to commercial whaling in 1925 and immediately post-whaling in 1938. Estimated abundance within the study area just prior to commercial whaling was 343 (331, 376). Immediately following the cessation of whaling in 1938, estimated abundance within the study area was 27 (14, 61). Results from this study show the Port Hobron whale fishery likely had a significant impact on the local humpback whale population.Full Article (PDF 490 kB)
Parasites of the Fishes of Alaska and Surrounding Waters
Adam Moles — Vol. 12(2):197–226. 2007.
The published records of parasites of freshwater and marine fishes of Alaska and the surrounding seas through 2006 are summarized. Fish hosts are listed alphabetically, providing a single, convenient source of information on the known parasites of Alaskan fishes. Of the 601 species of fish believed to inhabit the waters of Alaska, parasites are herein listed for 89 species. Information from 135 published studies spanning over a century of work are consolidated to assist both biologists and future investigators in parasite identification.Full Article (PDF 302 kB)
Estimating Southeast Alaska Tanner Crab Abundance Using Pot Survey and Commercial Catch Data
Jie Zheng, Janet M. Rumble, and Gretchen H. Bishop — Vol. 12(2):227–242. 2007.
A catch–survey analysis was developed for 11 Tanner crab stocks in Southeast Alaska. The models were applied to pot survey and commercial catch data time series ranging from 1999–2005 to 1978–2005, depending on the availability of data for each stock. The models fit the pot survey data very well for 9 out of 11 stocks. The models estimated absolute abundance for mature and legal males and relative abundance for mature females. The trends of absolute male abundance estimates differed among some stocks, and there was no a consistent pattern of male recruitment to the model for all 11 Tanner crab stocks. Mature male abundance and recruitment to the model declined during recent years for several stocks. Although legal harvest rates have been lower during the recent 10 years than for the previous period, overall harvest rates are still very high for some stocks.Full Article (PDF 1,498 kB)
Seasonal Marginal Growth on Otoliths of Seven Alaska Groundfish Species Support the Existence of Annual Patterns
Daniel K. Kimura, Delsa M. Anderl, and Betty J. Goetz — Vol. 12(2):243–251. 2007.
The Alaska Fisheries Science Center’s Age and Growth Program has been collecting qualitative otolith edge growth data for many of the principal species that it ages. The edge-type data collected are coded on a scale from 0 to 5, in an attempt to categorize the characteristics of the outermost growth zone of the otolith for the month of capture. Edge growth classification data can be subject to biases when age readers are looking for a particular pattern of growth. However, analysis of edge-type data can be used to determine the apparent strength and timing of seasonal growth patterns, and thus provides a weak form of age validation. We develop a simple model that allows us to estimate the signal strength and timing of otolith edge growth using standard nonlinear least squares. We do this by combining edge codes so that they are concentrated into two distinct categories: category 1 which represents an otolith with a full increment of opaque growth or a translucent zone on the edge (with perhaps a hint of new opaque growth), or category 3 which represents an otolith which has substantial growth, 1/4 to 1/2 of the previous year’s otolith growth, on its edge. Because the remaining categories (2 and 4) contained relatively few observations, categories 1 and 3 can be treated using a logit-like transformation, and then modeled with a cosine function. This model appeared to capture a strong seasonal trend in edge-type growth in 7 species for which reasonable amounts of data were available. These results support that the growth rings found in many Alaska groundfish are generally annual marks, but do not validate that conventional ages from otolith ring counts for any of these species are accurate.Full Article (PDF 657 kB)
Evaluation of the Macroscopic Staging Method for Determining Maturity of Female Walleye Pollock Theragra chalcogramma in Shelikof Strait, Alaska
Kresimir Williams — Vol. 12(2):252–263. 2007.
Macroscopic or visual staging is the primary method for determining maturity status of walleye pollock Theragra chalcogramma stocks in the Gulf of Alaska and the Bering Sea, although its accuracy has not been established. To address this, maturity data and samples were taken during several annual spawning surveys of pollock conducted in Shelikof Strait, Gulf of Alaska. Comparison of histological and macroscopic staging methods on 126 ovary samples resulted in a 25% misclassification rate, with 75% of these misclassifications reclassified into the adjacent stages. Misclassifications were most common among developing stages 2 and 3, and the prespawning stage 4. Paired readings of female pollock maturities were made at sea during the surveys, with readers disagreeing on classification stage in 36% of 411 observations. Reader disagreements were most common between stages 3 and 4 (11.4%), stages 4 and 5 (5.8%) and stages 7 and 8 (4.8%). Errors made across the boundaries of stages 3 and 4 as well as stages 2 and 8 can impact the estimates of length at 50% maturity and consequently the spawning stock biomass. These types of errors were observed in the histological validation process, but due to the very low incidence of stages 3 and 8 in the survey population (1.8% and 0.4%, respectively), the contribution of these potential errors to maturity assessments can be considered small.Full Article (PDF 783 kB)
Maturity of Female Northern Rockfish Sebastes polyspinis in the Central Gulf of Alaska
Elizabeth Chilton — Vol. 12(2):264–269. 2007.
The northern rockfish Sebastes polyspinis (Taranetz and Moiseev in Taranetz, 1933) is the second most important commercial rockfish species caught in the Gulf of Alaska. Current estimates of northern rockfish age and length at 50% maturity from the annual Gulf of Alaska stock assessment are based on macroscopic evaluations of a relatively small sample size collected in 1996. This study determined the maturity stage of female northern rockfish using histological techniques from 157 samples over a 2-year period. Estimated age at 50% maturity for female northern rockfish in the central Gulf of Alaska is 8 years and estimated length at 50% maturity is 310 mm. The maturity estimates presented in this study indicate that female northern rockfish mature at a younger age and smaller size than previously reported.Full Article (PDF 308 kB)
Growth of Female Red King Crabs Paralithodes camtshaticus from Kodiak, Alaska, during Pubertal, Primiparous, and Multiparous Molts
Bradley G. Stevens and Katherine M. Swiney - Vol. 12(2):270–277. 2007.
Growth models for red king crabs Paralithodes camtschaticus typically apply increments based strictly on size and sex, but growth of female red king crabs depends on their specific life history stage and previous reproductive history. Over a period of 5 years, we held female red king crabs in the laboratory for periods up to 4 years, during which we recorded growth for 77 crabs that molted at least once, and some that molted 2 or 3 times, for a total of 121 different molting events. Molts (and data) were classified as being pubertal (i.e., the molt to maturity), primiparous, or multiparous. During their pubertal molt, female red king crabs grew an average of 18.2%, primiparous crabs grew an average of 6.7% and multiparous crabs grew an average of 3.6%. Relationships between premolt and postmolt size differed significantly between molting types. As a result, female crabs of a given size would have different molt increments depending on their reproductive history. Length of captivity did not affect the molt increment at a specific life history stage, i.e. during the primiparous molt; molt increments for females that molted within 6 months of capture were similar to those that molted after an additional year in captivity. Molt increments for multiparous crabs were essentially identical to those reported previously for tagged females. Models of red king crab growth, recruitment, and reproductive output could be significantly improved by considering both the size of female crabs and their reproductive history.Full Article (PDF 282 kB)
A Workshop on Mechanisms Affecting Year-Class Strength Formation in Snow Crabs Chionoecetes opilio in the Eastern Bering Sea
Gordon H. Kruse, Albert V. Tyler, Bernard Sainte-Marie, and Douglas Pengilly - Vol. 12(2):270-277. 2007.
A group of specialists on subarctic crab biology and fisheries participated in a workshop to discuss stage-specific recruitment processes of snow crab Chionoecetes opilio populations. The goal was to develop from experience with North Pacific and North Atlantic stocks a comprehensive set of hypotheses on the physical and biotic factors that may contribute to the variation in year-class success of the snow crab stock in the eastern Bering Sea. Participants identified 15 life history stages and associated survival and productivity processes. Some of the processes deemed to be most critical include match of hatching larvae with adequate densities of suitable prey, advection (or retention) of larvae to nursery areas suitable for settlement, predation by Pacific cod Gadus macrocephalus and other predators, and cannibalism of newly settled juveniles by older, larger snow crab juveniles. A comprehensive set of hypotheses is intended to serve as a vehicle by which to direct future field and laboratory research programs to better understand snow crab population and fishery dynamics.Full Article (PDF 358 kB)
Trends in Area-Weighted CPUE of Pacific Sleeper Sharks Somniosus pacificus in the Northeast Pacific Ocean Determined from Sablefish Longline Surveys
Dean L. Courtney and Michael F. Sigler — Vol. 12(2):292–316. 2007.
The deepwater Pacific sleeper shark Somniosus pacificus is an opportunistic predator in the northeast Pacific Ocean. Their life history and distribution are poorly understood, and changes in their relative abundance or distribution could have direct and indirect effects on the ecosystem. There are no directed fisheries or surveys for Pacific sleeper sharks in Alaskan marine waters; consequently, abundance estimation is limited to indirect methods. We analyzed Pacific sleeper shark incidental catch (bycatch) from sablefish longline surveys conducted on the upper continental slope of the eastern Bering Sea, Aleutian Islands, and Gulf of Alaska between the years 1979 and 2003. Our objectives were to estimate trends in Pacific sleeper shark relative abundance and their statistical significance. A total of 1,565 Pacific sleeper sharks were captured by sablefish longline surveys between the years 1979 and 2003 with a sample effort of 19.7 million hooks. Area (km2) weighted catch per unit effort (CPUE) of Pacific sleeper sharks was analyzed from standardized sablefish longline surveys between the years 1982 and 2003 with bootstrap 95% confidence intervals as an index of relative abundance in numbers. Within the limited time series available for hypothesis testing, area-weighted CPUE of Pacific sleeper sharks increased significantly in the eastern Bering Sea between the years 1988 and 1994 and in the Gulf of Alaska between the years 1989 and 2003, but also decreased significantly in the Gulf of Alaska in 1997. The increasing trend in the Gulf of Alaska was driven entirely by one region, Shelikof Trough, where most (54%) Pacific sleeper sharks were captured. Increasing trends in area-weighted CPUE of Pacific sleeper sharks in the eastern Bering Sea and Shelikof Trough are consistent with previous analyses of fishery-dependent and fishery-independent data from the northeast Pacific Ocean and with evidence of a climatic regime shift that began in 1976 and 1977. Whether increasing trends in area-weighted CPUE of Pacific sleeper sharks from sablefish longline surveys represent an increase in the relative abundance of Pacific sleeper sharks at the population level or just reflect changes in local densities is unknown because of caveats associated with computing area-weighted CPUE of Pacific sleeper sharks from sablefish longline surveys and because of a lack of information on the life history and distribution of Pacific sleeper sharks.Full Article (PDF 839 kB)
AFRB: Editor's Note
Doug Eggers - Vol. 12(2):323. 2007.
(No Abstract) Full Editorial:
After a run of 13 years, the Alaska Department of Fish and Game, Division of Commercial Fisheries is ceasing publication of the Alaska Fishery Research Bulletin. This is the final issue. In 1994, the AFRB evolved from the Fishery Research Bulletin monograph series into the current peer-reviewed journal, publishing articles, issues and perspectives, notes and letters on fisheries research by state, federal and university scientists. Regretfully, current budget and staffing issues make it impossible to continue publishing the AFRB. All issues of the AFRB will continue to be available online.
Doug Eggers, Editor