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Status of the Gulf of Alaska sablefish (Anoplopoma fimbria) resource in 1983. Alaska Department of Fish and Game Informational Leaflet 235.

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Abstract

Available sources of information on sablefish biology and the Gulf of Alaska sablefish fishery are reviewed and harvest recommendations are presented. A U.S. longline fishery for sablefish has existed in the Gulf of Alaska since the early 1900's. Gulf-wide catches escalated rapidly during the 1960's when the Japanese distant water fleet developed. Total Gulf of Alaska harvests peaked in 1972 at 36,199 metric tons and began to decline, with recent annual harvests at about 9,000 metric tons. The U.S. longline fishery traditionally fished only in the eastern Gulf of A1 aska, but is currently expanding westward. Foreign sabl efish harvests are currently restricted to the central and western Gul f of Alaska. Recent developments in sablefish aging techniques using "break and burn" methods describe very slow growth in adult sablefish. The slow growth rates imply that large sablefish are much older than previously calculated, with maximum ages frequently exceeding 40 years. A much lower natural mortality rate of 0.11 is estimated from the new growth information, substantially less than previous estimates of 0.2. Sablefish recruitment appears to be characterized by long periods of relatively low recruitment between very strong year classes. Because these periods of low recruitment may exceed 10 years, maintaining large number of older fish in the population may be critical to reproductive success. Electrophoretic studies of sablefish genetics indicate that there is some degree of spatial segregation of Gulf of Alaska sablefish stocks. However some tagging studies indicate substantial movements of Si sh, with small fish (< 66 cm) tending to move north and westward and larger fish moving south and eastward. Trends in sablefish abundance are derived from Japanese longline fishery statistics, a Gulf-wide U.S.-Japanese longline survey, pot indexing in Southeastern Alaska, and port sampling of the U.S. longline fleet in Southeastern Alaska. Sablefish stock biomass appears to be increasing in abundance throughout the Gulf, largely a result of the recruitment of the strong 1977 year class. Subsequent year classes have not been strong. A new stock production model which allows for increases in fishing power indicates that MSY is probably lower than calculated in previous models. Estimates of stock size are derived from stock production model parameters and from area- swept in a Bering Sea trawl survey, combined with comparative longline-trawl sampling in the Aleutian area. Yield-per-recruit analyses indicate that size limi ts wi 11 not increase the yield or landed value from the sablefish fishery. Population parameter estimates are used in an age and sex-structured simulation model to determine "equilibrium yields" (EY) which will maintain constant biomass from 1984-1991. However because of uncertainty in the parameter estimates, it is recommended that equilibrium yield (EY) calculated by other means be applied to the Gulf of Alaska. Optimum yield (OY) are recommended to remain at 75% of the EY, or 9,473 metric tons for the entire Gulf sf Alaska. A new method of spatial allocation of the Gulf-wide OY is presented, based on the spatial distribution of biomass estimated in the U. S.-Japanese longline survey. KEY WORDS: sablefish, stock status, age, growth, migration, Gulf of Alaska, longline fishery, equilibrium yield, mortality, maximum sustained yield, yield-per-recruit.
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... The sablefish fishery is located around the North Pacific Rim -as far west as the Japanese coast, up to Cape Navarin in the northern Bering Sea, throughout the Aleutian Islands and the GOA, and as far south as Baja California (Hart, 1973;Kodolov, 1968;Sasaki, 1985;Wolotira et al., 1993). Most of the catch comes from Alaskan waters (Heifetz and Fujioka, 1991), with the largest concentrations of sablefish in the GOA found in the central and eastern Gulf (Hanselman et al., 2014b; Table 3), corresponding with their principal spawning grounds (Funk and Bracken, 1984). Adult sablefish are semi-demersal and have been observed within 1 m of the sea floor (Krieger, 1997) in deep waters on the outer shelf and the continental slope, and in coastal fjords at depths of 200-1000 m (Allen and Smith, 1988;Kendall and Matarese, 1987;Mason et al., 1983;McFarlane and Beamish, 1983), though most fish have been observed between 300 and 700-m depths (Maloney and Sigler, 2008). ...
... Sablefish recruitment appears to be characterized by long periods of relatively low levels between very strong year-classes (Funk and Bracken, 1984). In the annual assessment for sablefish stock in Alaska, which treats sablefish in both the GOA and the eastern Bering Sea as a single stock, recruitment is defined as the number of age-2 sablefish entering the assessment model (Hanselman et al., 2014b). ...
... For a typical marine fish stock, the two primary factors affecting recruitment are the level of adult spawning and the ecological processes influencing egg-torecruit survival. For sablefish, the level of adult spawners seems to be a secondary factor (Hanselman et al., 2014b), as spawning success appears to be highly dependent on favorable environmental conditions, coincident with the availability of a spawning population size above some unknown critical level (Funk and Bracken, 1984). Thus, it seems likely that sablefish recruitment is driven primarily by ecosystem processes. ...
... Fujioka & H. Zenger, 1995, NOAA, pers. comm.), 1977(Bracken 1983), 1980, 1984 Beginning in 1985, juvenile sablefish (age-1 and 2) have been tagged and released in a number of bays and inlets in southeast Alaska, ranging from Ketchikan to Juneau. Following reports of high catch rates in recent years, tagging efforts have expanded to several areas of the CGOA, however, St. John Baptist Bay (SJBB) outside of Sitka on Baranof Island is the only area to have been sampled annually since 1985 and to have consistently had juvenile sablefish. ...
... Sablefish natural mortality has been estimated to be about 0.1 (Funk and Bracken 1984;Johnson and Quinn 1988). In the 2016 assessment, estimating natural mortality was revisited with a prior CV of 10% to propagate more uncertainty in the model. ...
Technical Report
Full-text available
Moderate changes to the assessment methodology were implemented for the 2021 sablefish SAFE. Previously, for the 2020 SAFE, model 16.5_Cont was used as the assessment model. However, increasing retrospective patterns in recent recruitment estimates were persistent as new data were added to the model. Since 2017, maximum Acceptable Biological Catch (ABC) projections based on model 16.5_Cont using the North Pacific Fishery Management Council’s (NPFMC) tier 3 FMP B40% harvest control rule (HCR) had been deemed unreliable for sablefish due to overly optimistic population growth forecasts. For the 2021 SAFE, multiple model updates are being proposed, including refinements to the biological inputs, new selectivity and catchability parametrizations, and improved data reweighting approaches, all of which have helped to address retrospective patterns. The sablefish assessment authors explored a number of alternative models using a thorough model development exercise (Appendix G) and a new model configuration was developed (Appendix 3H). The final proposed model for the 2021 SAFE, 21.12_Proposed_No_Skip_Spawn, resolves the recruitment estimation issues associated with model 16.5_Cont, while maximum ABC projections are once again deemed adequate for the basis of management advice.
... The published natural mortality estimates for sablefish in the Gulf of Alaska range from 0.10 (10%) (Sigler et al. 2001, Funk and Bracken 1984, and Johnson and Quinn 1988 to 0.22 (22%) (Low et al. 1976). The current National Marine Fisheries Service (NMFS) stock assessment for the Gulf of Alaska uses a rate of 0.10 (10%). ...
... M is assumed to be 0.1 in the analyses presented based on estimates produced by Funk and Bracken (1984). In a recent assessment, Haist et al. (2001) considered values of M from 0.08 to 0.1 to encompass the range reported in assessments throughout the northeast Pacific. ...
Article
1 The Regional Information Report Series was established in 1987 to provide an information access system for all unpublished divisional reports. These reports frequently serve diverse ad hoc informational purposes or archive basic uninterpreted data. To accommodate timely reporting of recently collected information, reports in this series undergo only limited internal review and may contain preliminary data; this information may be subsequently finalized and published in the formal literature. Consequently, these reports should not be cited without prior approval of the author or the Division of Commercial Fisheries.
... Canadian researchers report age determinations up to 55 years (McFarlane and Beamish 1983). A natural mortality rate of M=0.10 has been assumed for previous sablefish assessments, compared to M=0.112 assumed by Funk and Bracken (1984). Johnson and Quinn (1988) used values of 0.10 and 0.20 in a catch-at-age analysis and found that estimated abundance trends agreed better with survey results when M=0.10 was used. ...
... Juvenile sablefish are pelagic and at least part of the population inhabits shallow near-shore areas for their first one to two years of life (Rutecki and Varosi 1997 (Bracken 1983(Bracken ), 1980(Bracken , 1984(Bracken , and 1998 year classes in southeast Alaska, the 1997 and 1998 year classes in Prince William Sound (W. Bechtol, ADFG, pers. ...
Article
Full-text available
Relative to last year's assessment, we made the following substantive changes in the current assessment. Input data: Relative abundance and length data from the 2008 longline survey, relative abundance and length data from the 2007 longline and trawl fisheries, and age data from the 2007 longline survey and longline fishery were added to the assessment model. Model changes: When moving to a sex-specific model in 2007, the number of selectivity parameters was greatly increased. These parameters were estimated with high correlation and low precision. For this year we use simpler selectivity functions and link some selectivity curves to improve parameter estimation without greatly affecting model fit or trends. We show two steps to a recommended model that reduces the total parameters by thirteen with minimal effects on the overall model fit. A CIE review is planned for Spring 2009. Assessment results: The fishery abundance index was up 5% from 2006 to 2007 (the 2008 data are not available yet). The survey abundance index decreased 2% from 2007 to 2008 and follows a 14% decrease from 2006 to 2007. Relative abundance in 2008 is 3% lower than 2000, and is at an all-time low for the domestic longline survey. Spawning biomass is projected to be similar from 2008 to 2009, and begin declining through 2012. We also include results from a study to test for sablefish cannibalism pots in the Fishery section and the results from a gear experiment in Appendix 3C.
... A natural mortality rate of M = 0.10 has been assumed for previous sablefish assessments, compared to M = 0.112 assumed by Funk and Bracken (1984). Johnson and Quinn (1988) used values of 0.10 and 0.20 in a catch-at-age analysis and found that estimated abundance trends agreed better with survey results when M = 0.10 was used. ...
Technical Report
Full-text available
2020 update of the Alaskan sablefish stock assessment.
... Stock assessments of Alaskan sablefish have generally assumed that natural mortality is about 0.1. For example, Funk and Bracken (1984) assumed M=0.112, with subsequent assessments assuming M=0.1 until 1999. From 1999 to 2003 natural mortality was estimated at about 0.1 but analysis of the Bayes posterior distribution of M in 2004 ( Sigler et al. 2004) showed that these estimates were not well-supported. ...
Article
To evaluate the potential of increasing yield in the Gulf of alaska sablefish (Anoplopoma fimbria) fishery with a minimum size limit, a modified yield per recruit analysis was used to explore trends in yield, equilibrium biomass, reproductive potential, and economic value. The Gulf of Alaska sablefish catch quotas are apportioned to the fixed- and trawl-gear fisheries in the approximate amounts of 86.1% and 13.9%, respectively. The traditional yield per recruit model was modified to incorporate age-specific selectivity rates for each gear type and to compute yield from the combination of the two fisheries. The model also incorporated a discard mortality on undersized fish. With no discard mortality, yield per recruit increases with increasing size limits. However, the increases are significant only at high fishing mortality rates (greater than 0.20). With discard mortality, yields decrease with increasing size limits. Equilibrium biomass and the egg production index increase with increasing size limits, both with and without discard mortality, but the increases are negligible with discard mortality. The effects of a minimum size limit on gross and net value are similar to those on yield, with and without discard mortality, except that the fishing mortality rates that maximize net value are substantially less than those that maximize yield and gross value. As the fishing mortality rate for Gulf of Alaska sablefish is low (0.13), it was concluded that minimum size limits would be ineffective and could even be a detriment because of discard mortality.
Article
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5.1 Executive Summary 5.1.1 Summary of major changes Relative to the September preliminary assessment, we made the following substantive changes in the current assessment. Input data: Relative abundance and length data from the 1999 longline survey and 1999 longline fishery and length data from the 1998 longline fishery were added to the assessment model. Assessment results: Sablefish abundance increased during the mid-1960’s due to strong year classes from the late 1950’s and 1960’s. Abundance subsequently dropped during the 1970’s due to heavy fishing; catches peaked at 56,988 mt in 1972. The population recovered due to exceptional year classes from the late 1970’s; spawning abundance peaked again in 1987. The population then decreased because these exceptional year classes are dying off. The survey abundance index increased 10% in numbers and 5% in weight and the fishery abundance index increased 11% in weight from 1998 to 1999. These increases follow decreases from 1997 to 1998, so that relative abundance in 1999 is similar to 1997. Exploitable and spawning biomass are projected to increase 3 and 1%, respectively, from 1999 to 2000. Alaska sablefish abundance now appears low and stable. This is a change from previous assessments where abundance appeared low and slowly decreasing. Further years data are needed to confirm that abundance has stabilized. ABC recommendation and decision analysis: A simple Bayesian analysis was completed by examining the effect of uncertainty in natural mortality and survey catchability on parameter estimation. A decision analysis was completed using the posterior probability from the Bayesian analysis to determine what catch levels likely will decrease abundance. The decision analysis indicates that a yield of about 17,000 mt most likely will keep spawning biomass the same and has only a 20% probability of reducing 2004 spawning biomass to less than 90% of 2000 spawning biomass. Based on this result, we recommend a 2000 ABC of 17,000 mt for the combined stock, a 7% increase from the 1999 ABC of 15,900 mt. The maximum permissible yield from an adjusted F40% strategy is 17,200 mt. Regional ABC recommendation: A 5-year exponential weighting of the survey abundance index in weight (relative population weight or RPW) by region was used to apportion the combined ABC to regions, resulting in the 2 following apportionments: Bering Sea 1,384 mt, Aleutian Islands 2,446 mt and Gulf of Alaska 13,170 mt, which is further apportioned Western 1,928 mt, Central 5,921 mt, West Yakutat 1,890 mt, and East Yakutat / Southeast 3,431 mt. Members of the fishing industry have asked us to show how fishery and survey information could be combined to produce an alternate apportionment of ABC; see section 5.8.7.
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