Alaska Groundfish Research Articles

Modeling in an integrated ecosystem research framework to explore recruitment in Gulf of Alaska groundfish – Applications to management and lessons learned

The Gulf of Alaska Integrated Ecosystem Research Program (GOAIERP) supported multi-disciplinary analyses integrating physical and biological oceanography and modeling to examine how the environment influences survival and recruitment of early life stages of select commercially and ecologically important groundfish species. Recruitment is an important component of population variability, and understanding the processes influencing recruitment is central to fishery management and ecosystem planning. Determining the relative impact of advection and the environmental conditions experienced during transport between spawning and nursery areas is an inherently interdisciplinary problem. It requires consideration of physical and lower trophic level environments in concert with early life history dynamics. Here we discuss how Eulerian ecosystem models and Lagrangian Individual-Based Models for groundfish were integrated within the framework of an interdisciplinary observational program. Metrics (e.g. regionally-based averaged water temperature, integrated primary production, probability of juvenile settlement) were derived from model outputs as proxies for recruitment success. The recruitment indices were then correlated to estimated recruitment from stock assessments. Using the GOAIERP as a case study, we discuss the value that modeling can add to a field program and fisheries management planning, the challenges faced, and steps that can be taken to maximize program success. Coordination of model development, experimentation, and field sampling is necessary but can be challenging. Consideration of the appropriate sequence during data analyses and model development is critical. Careful consideration must be given to ensure that data collected in the field will inform, improve, or validate models. Sufficient time must be allocated within the program to incorporate field data collected during the program and mechanistic understandings into the models. Model outputs should be designed to have utility to management decisions and value to regional stakeholders. Collectively, the studies in this modeling program provide insight as to how models might be used to better understand recruitment processes and lead to recommendations to support the integration of ecosystem models into fisheries management.

Why are catches in mixed fisheries well below TAC?

In major mixed stock fisheries of the United States, the actual catch is well below the total allowable catch (TAC). In recent years, only 20–30% of the TAC is caught in the US West Coast non-whiting fishery, whereas 60–80% of the TAC is caught in the Gulf of Alaska groundfish trawl fishery. Possible explanations for the underutilization are (1) lack of infrastructure, (2) lack of market demand, and (3) low quota limits on some species restricting the ability to harvest other species. Using species by species data on catch, TAC and lease price for species under Individual Transferable Quotas, we evaluate the support for these hypotheses. The results suggest that rebuilding plans, under a strict timeline, ultimately created many of the choke species on the West Coast and reduced processing infrastructure, such that the fishery still struggles with low quota utilization even after stocks have been rebuilt. In comparison, the Gulf of Alaska has not had a history of rebuilding plans and generally has higher utilization. The results suggest that rebuilding plans intended to increase sustainable harvest have been successful at increasing abundance but have been unsuccessful at rebuilding the fishery.

Climate effects and bottom‐up controls on growth and size‐at‐age of Pacific halibut (Hippoglossus stenolepis) in Alaska (USA)

AbstractPacific halibut (Hippoglossus stenolepis) are an ecologically, commercially, and culturally important Alaskan groundfish species. Commercial harvest of halibut dates back to the late 19th century and has been managed by the International Pacific Halibut Commission (IPHC) since 1921. IPHC surveys have revealed declining trends in survey biomass in multiple regions and region‐specific declines in mean size‐at‐age (size‐at‐age) over the past two decades (>50% in some areas). Changes in size‐at‐age can arise from a variety of physical, ecological, sampling, and fishery effects, including size‐dependent fishery or predation mortality, alteration in growth from variability in prey quality or quantity, and changes in temperature‐dependent metabolic demands. Here, we develop and apply a bioenergetics model for halibut using survey‐based diet and temperature data for Alaska to evaluate potential environmental drivers of size‐at‐age. In general, juvenile (<40 cm fork length) foraging rates were highest in the Gulf of Alaska concomitant with higher potential growth and elevated basal metabolic demands during warm summer conditions. In contrast, adult (40–120 cm FL) potential growth was highest in the Eastern Bering Sea, potentially reflecting lower metabolic costs and higher rates of prey consumption in that region. We additionally find evidence for interannual variation in potential growth, with a higher frequency of reduced growth potential in the last decade, particularly in the Eastern Bering Sea in 2015 and 2016 for both juvenile and adult halibut. These results suggest the potential for patterns in size‐at‐age to arise from trophic and environmental constraints that collectively limit growth in some regions and years.

Spatiotemporally explicit model averaging for forecasting of Alaskan groundfish catch.

Fisheries management is dominated by the need to forecast catch and abundance of commercially and ecologically important species. The influence of spatial information and environmental factors on forecasting error is not often considered. I propose a forecasting method called spatiotemporally explicit model averaging (STEMA) to combine spatial and temporal information through model averaging. I examine the performance of STEMA against two popular forecasting models and a modern spatial prediction model: the autoregressive integrated moving averages with explanatory variables (ARIMAX) model, the Bayesian hierarchical model, and the varying coefficient model. I focus on applying the methods to four species of Alaskan groundfish for which catch data are available. My method reduces forecasting errors significantly for most of the tested models when compared to ARIMAX, Bayesian, and varying coefficient methods. I also consider the effect of sea surface temperature (SST) on the forecasting of catch, as multiple studies reveal a potential influence of water temperature on the survival and growth of juvenile groundfish. For most of the preferred models, inclusion of SST in the model improved forecasting of catch. It is advisable to consider both spatial information and relevant environmental factors in forecasting models to obtain more accurate projections of population abundance. The STEMA method is capable of accounting for spatial information in forecasting and can be applied to various types of data because of its flexible varying coefficient model structure. It is therefore a suitable forecasting method for application to many fields including ecology, epidemiology, and climatology.

The last cowboys: keeping open access in the Aleut groundfish fishery of the Gulf of Alaska

As the North Pacific Fishery Management Council prepared to rationalize the Gulf of Alaska groundfish trawlers under the guise of bycatch management beginning in 2012, a social impact assessment investigated the fishery’s operations, stresses, dependencies, and desires of the primarily local Aleut (Unangan) fleets and families in the Western Gulf villages of King Cove and Sand Point, Alaska. This article describes the historical development of the local trawl fleet, their unique status in the fishery, and their rationale for their near universal rejection of a community protection measure. For these small coastal communities, the keys to success are competition, diversification into many fisheries, and supporting their communities through local hire and investment. Aleut fishermen feared that the impending neoliberal chapter would erase their history and traditions, remove competition, reallocate quota away from those that built the fishery and made it successful, diffuse fishermen’s support of their home communities, and undermine what it means to be Aleut. This fear is compounded by ecological changes affecting marine species abundances in the Gulf of Alaska.

Characteristics and discard mortality of octopus bycatch in Alaska groundfish fisheries

Octopus are caught incidentally in several US federally-managed trawl, longline, and pot fisheries in Alaska. The majority caught are giant Pacific octopus Enteroctopus dofleini. Recent changes in fisheries management in Alaska have resulted in the creation of an octopus species complex with annual catch limits, leading to increased interest in management and catch accounting for this data-poor assemblage. This study characterized the incidental octopus catch in Alaska groundfish fisheries and the mortality rate of octopus caught and discarded at sea. Onboard fisheries observers collected data on octopus weight, sex, and condition at discard in a variety of Alaska groundfish fisheries from 2006 to 2011. A field study aboard a commercial pot-fishing vessel examined delayed mortality resulting from the capture process in giant Pacific octopus during routine pot fishing. Octopus incidental catch varied widely in size and condition at capture for various fishing gear types. Vessels fishing using pot gear captured larger octopus than vessels using longline or trawl gear. Initial condition at capture was best in pot gear, with over 90% of octopus discarded from pot vessels alive in excellent condition. Octopus taken in trawl gear had the highest immediate mortality rate, with 68–94% dead or injured at discard. Giant Pacific octopus held for 24–60h following pot capture showed no signs of delayed mortality or decline in condition. These results suggest that assuming 100% mortality of discarded octopus may overestimate fishing impacts.

Using smooth sheets to describe groundfish habitat in Alaskan waters, with specific application to two flatfishes

In this analysis we demonstrate how preferred fish habitat can be predicted and mapped for juveniles of two Alaskan groundfish species – Pacific halibut (Hippoglossus stenolepis) and flathead sole (Hippoglossoides elassodon) – at five sites (Kiliuda Bay, Izhut Bay, Port Dick, Aialik Bay, and the Barren Islands) in the central Gulf of Alaska. The method involves using geographic information system (GIS) software to extract appropriate information from National Ocean Service (NOS) smooth sheets that are available from NGDC (the National Geophysical Data Center). These smooth sheets are highly detailed charts that include more soundings, substrates, shoreline and feature information than the more commonly-known navigational charts. By bringing the information from smooth sheets into a GIS, a variety of surfaces, such as depth, slope, rugosity and mean grain size were interpolated into raster surfaces. Other measurements such as site openness, shoreline length, proportion of bay that is near shore, areas of rocky reefs and kelp beds, water volumes, surface areas and vertical cross-sections were also made in order to quantify differences between the study sites. Proper GIS processing also allows linking the smooth sheets to other data sets, such as orthographic satellite photographs, topographic maps and precipitation estimates from which watersheds and runoff can be derived. This same methodology can be applied to larger areas, taking advantage of these free data sets to describe predicted groundfish essential fish habitat (EFH) in Alaskan waters.

Comparative methods for evaluating climate change impacts on the foraging ecology of Alaskan groundfish

Comparative methods for evaluating climate change impacts on the foraging ecology of Alaskan groundfish

DNA-based identification methods of prey fish from stomach contents of 12 species of eastern North Pacific groundfish

Stomach content analysis of eastern North Pacific groundfish has been conducted routinely by researchers interested in understanding trophic interactions between key predator species and their prey. Identification of prey by traditional morphological methods has limitations however, due to the loss of identifiable characters from digestion and morphological similarities between taxa. Furthermore, some forage fish (e.g., osmerids, ammodytids, and juvenile gadids), common prey of Bering Sea and Gulf of Alaska groundfish, are difficult to distinguish because of their slender or fusiform shape, disarticulating easily during digestion. DNA-based identification methods were developed to differentiate among 18 fish species, some that are found at depths greater than 200m, from four taxonomic families: Ammodytidae and Osmeridae (forage fish), Pleuronectidae (flatfish), and Gadidae (gadid fish). Polymerase chain reaction (PCR) amplification of a 739 basepair section of mitochondrial DNA cytochrome c oxidase I and an 862 basepair section of mitochondrial DNA cytochrome b was followed by restriction digest assays and resulted in species level resolution for 16 of 18 species of interest. PCR restriction digest assays applied to fish prey from stomach contents of groundfish indicated the presence of several target species, eulachon (Thaleichthys pacificus), walleye pollock (Gadus chalcogrammus), searcher (Bathymaster signatus), rock sole (Lepidopsetta bilineata), yellowfin sole (Limanda aspera) and either Bering flounder (Hippoglossoides robustus) or flathead sole (H. elassodon). The PCR restriction digest protocols improved the identification rate of predated fish from stomach contents compared to identification by conventional taxonomic methods alone, and DNA sequence analysis further resolved identification of unknown prey fish samples.

The frequency and quantity of Alaskan groundfish catcher-vessel landings made with and without an observer

Abstract Faunce, C. H., and Barbeaux, S. J. 2011. The frequency and quantity of Alaskan groundfish catcher-vessel landings made with and without an observer. – ICES Journal of Marine Science, 68: 1757–1763. The North Pacific Groundfish Observer Programme (NPGOP) is one of the largest on-board fishery-monitoring programmes in the world, and the data are used extensively for both in- and post-season management of fisheries. Within certain limits, Alaskan fishers determine when and where to carry observers. There may be an incentive to fish differently during observed trips because (i) observed trips carry higher costs than unobserved trips, and (ii) bycatch quanta for quota deduction are estimated by applying bycatch rates from observed trips to retained catches on unobserved trips. Such differences may be manifest through the skewed deployment of observers among fisheries, i.e. a deployment effect, and through unrepresentative activities by fishers when an observer is on board, i.e. an observer effect. Despite long-standing concerns expressed over the NPGOP's 40-year history, evidence of deployment and observer effects have been based largely on anecdotal information. In 2008, database changes allowed a comparison of industry landing reports for trips with and without an observer. A deployment effect was evidenced by significant deviations from the expected landing ratios between observed and unobserved trips, and linear mixed-effect models revealed differences in the landed weight and evidence for an observer effect within two of five fisheries examined.

An assessment of vulnerability in Alaska groundfish

Federal fishery management rules in the United States have recently changed, necessitating an examination of which fish stocks require annual catch limits and how appropriate stock complexes are formed. We used an analytical approach termed productivity–susceptibility analysis (PSA) to analyze the vulnerability of federally managed Alaska groundfish stocks to overfishing. The focus of the effort was non-target stocks that have limited data available for determining stock status and vulnerability. The PSA approach was originally created to assess risks to bycatch in Australian trawl fisheries and compares productivity attributes (e.g. life-history traits) to factors that determine a stock's susceptibility to fishing impacts, producing a combined score indicative of a stock's relative vulnerability to overfishing. We used a form of the PSA developed by a working group from the U.S. National Marine Fisheries Service specifically for use in assessing vulnerability in federally managed fisheries. Alaska groundfish displayed a wide range of vulnerability scores, and this result was mainly due to variability in productivity scores. Susceptibility scores varied less than productivity scores and were centered on an intermediate value. The inclusion of target stocks in the PSA was valuable for assessing the relative vulnerability of the non-target stocks. Sensitivity analyses indicated that PSAs respond differently to changes in attribute scores depending on their initial conditions, and managers should be careful in interpreting changes in PSA results when stocks are re-evaluated.

Introduction: Origins and Settlement of the Indigenous Populations of the Aleutian Archipelago

Introduction: Origins and Settlement of the Indigenous Populations of the Aleutian Archipelago Dixie West (bio), Dennis O’Rourke (bio), and Michael H. Crawford (bio) Keywords Aleutian Islands, Indigenous Peoples, Colonization, Contact, Biology [Correction] The series of papers in this special issue of Human Biology use an interdisciplinary approach to address regional questions and to integrate disparate Aleutian data into a broad, synthetic effort. The contributors leverage decades of data on Aleut origins, biogeography, and behavior through integration of molecular analyses, linguistics, archaeology, and ethnography. This research explores the origin and colonization of the Aleutian archipelago, communication and the extent of prehistoric cultural exchange among Aleut subgroups, ethnographic information as applied to human biological variation, metric and genetic variation among Aleut groups, and prehistoric dietary reconstruction. The Aleutian archipelago, composed of eastern, central, and western islands, extends 1,800 km between the North American and Asian continents and divides the northern Pacific Ocean from the Bering Sea. Volcanic in origin and formed during the early Tertiary, the archipelago is composed of more than 200 islands divided into six groups, separated by ocean passes. The climate is maritime and is characterized by foggy and cloudy weather, frequent rain and winds, and often cold but not severe annual temperatures. The Aleutians form the southern boundary for the most biologically and commercially important region of the Pacific—the Bering Sea. Until recently, this area was a rich ecotone that supported abundant populations of large marine mammals, ocean fisheries, thick kelp forests, complex near-shore ecosystems and intertidal zones, spawning streams, and a highly diverse avian fauna pivotal to the adaptations and survival of the human groups who, in the past, peopled the islands of the archipelago. However, the Aleutians, once considered one of the richest island ecosystems in the world, have been undergoing considerable biotic turnover (Estes and Duggins 1995). Population densities of marine mammals and some economical fish have dramatically declined, and the once thick kelp forests have decreased (Committee on the Alaska Groundfish Fishery and Steller Sea Lions 2003; Trites et al. 1999). In contrast, Aleutian waters have witnessed increases in sea urchin, pollack, and [End Page 481] shark populations, species that were historically uncommon in this ecosystem (Estes et al. 1998; Springer 1999). This biotic restructuring has occurred over a short time period and carries socioeconomic consequences and lessons for local inhabitants—and the world community, especially if rapid global warming is the cause (Estes et al. 1998). The Aleutian Islands define the southern margin of Beringia, across which much of the early peopling of the Americas occurred, and present a 9,000-year record of human occupation in the east and a record of more than 3,000 years in the west. Current research suggests that these prehistoric human inhabitants had minimal interactions with populations outside the archipelago, with any new interactions commencing from the Alaska Peninsula. These remote islands preserve the critical cultural and biological information of peoples who settled, adapted, and thrived in a subarctic maritime world. The historical record of the Aleut peoples, like many other Native Americans, is one of exploitation and decimation resulting from disease and warfare. During the 18th century, the arrival from Russia of sea otter hunters, followed by Russian Orthodox missionaries, had a drastic effect on Aleutian populations and their hunter-gatherer culture, economy, and maritime environment (Tikhmenev 1978). Upon contact, the native population declined rapidly; by 1831 only 16 islands were inhabited by an estimated 2,000 natives (Sekora 1973). This initial historical period has provided the richest reservoir of ethnographic data (Berkh 1974; Black 1984; Lantis 1970; Liapunova 1996; Veniaminov 1984), which largely focus on Aleuts living on the eastern islands. A second devastating blow to Aleut culture occurred in 1943, when the Imperial Japanese Navy bombed Dutch Harbor in the eastern Aleutians and captured Kiska and Attu islands to the west. Naval weather observers on Kiska and Attuans were relocated to prisoner-of-war camps in Hokkaido, Japan, where less than half of them survived. The American military relocated Aleuts living in nine villages on six islands to evacuation camps in southeast Alaska for 3 years, where over 10% died. In the best interests of the United States, American...

Managing non‐target, data‐poor species using catch limits: lessons from the Alaskan groundfish fishery

Abstract The 2006 reauthorisation of the Magnuson‐Stevens Fishery Conservation and Management Act requires annual catch limits for all target and non‐target species within federally managed fisheries in the United States. In Alaska, both target and non‐target species in the Alaska groundfish fisheries have been managed using catch limits since the early 1990s. Non‐target species that are caught incidentally in a fishery require monitoring to ensure that the population is not negatively impacted by commercial fishing. Resource assessment scientists have been challenged with obtaining sufficient data to recommend an acceptable catch level for management of these species. This paper reviews three case studies where a catch limit is determined for non‐target species when certain data are limited: (1) varying levels of biomass and catch data for all species within a species group or complex; (2) adequate catch data but no biomass data; (3) emerging target fishery of data‐poor species, plus an example of how a complex of ecosystem component species is managed.

Aspects of the Biology and Species Composition of Skates (Rajiformes) from Insular Waters of Southeastern Alaska

Key words: Raja rhina, Bathyraja, reproduc-tive biology, sex ratio, size composition, speciescomposition, Clarence Strait, Dixon Entrance,Gulf of AlaskaDirect and indirect fishing pressure on skates(Order: Rajiformes) has resulted in populationdeclines of exploited stocks and considerableshifts in size structure and species compositionof skate assemblages (Walker and Hislop 1998;Dulvy and others 2000; Rogers and Ellis 2000;Frisk and others 2002). Fishing mortality isespecially deleterious to many skate speciesbecause of their k–selected life history traits,including slow growth, late ages at maturity,and low fecundity (Holden 1974; Cailliet andGoldman 2004). Large skate species are morelikely to exhibit these life history patterns andare therefore typically more susceptible toexploitation than smaller species (Dulvy andReynolds 2002; Ellis and others 2005).Incidental catch of skates is substantial inseveral Gulf of Alaska groundfish fisheries suchas cod longline, halibut longline, and flatfish

Potential Benefits of Coastal Ocean Observing Systems to Alaskan Commercial Fisheries

In this article we attempt to illustrate the potential benefits to Alaskan commercial fisheries expected from enhancements to the Alaska Ocean Observing System (AOOS) through changes in fishery management strategies. In particular we show how the use of improved AOOS data in research, stock assessment, and ultimately fisheries management has the potential to result in significant benefits in the Bering Sea and Gulf of Alaska groundfish and Kodiak king crab fisheries. We show through a case study approach that information such as might be provided by an enhanced AOOS could conceivably contribute over $600 million in additional annual revenue in Alaska's groundfish fishery. In addition we estimate that had the information from such a system been available in the 1970s and 1980s the Kodiak king crab stock collapse could have been avoided and $60 million in annual revenues generated. Benefit estimates (as measured by revenue increases) are based on the assumptions that when better data is delivered those data will be integrated into stock assessment models; when better data are integrated into the models the new data will actually improve the reliability of the models; and when the reliability of the models is improved predictions will be accepted by managers or industry members.

Population impacts of endangered short-tailed albatross bycatch in the Alaskan trawl fishery

We conduct a decision analysis that explores the effects of trawl-related fishery mortality on achieving the population recovery goals for the US federally-endangered short-tailed albatross (Phoebastria albatrus), proposed by the US Fish and Wildlife Service. A population model is constructed and its parameters estimated using data on counts of the numbers of albatross chicks and eggs at Torishima Island, Japan, where 83% of the world’s population of this species is found. Bayesian inference is used to assign probabilities to alternative plausible rates of fishing mortality and as the basis for population projections with different levels of trawl mortality to determine their effects on achieving the population recovery goals. The analyses of the impact of trawl mortality on the Torishima short-tailed albatross population suggests that exceeding the current expected incidental take in the Alaskan groundfish trawl fishery, two in any 5-year period, by as much as a factor of 10 would have little impact on when the proposed recovery goals for the species are achieved. A quantitative approach that addresses uncertainty, such as that outlined in this study, could aid the process to evaluate allowable limits in light of species recovery goals by addressing both take limits and recovery goals within the same framework.

Determining spatial and temporal overlap of an endangered seabird with a large commercial trawl fishery

Spatial and temporal overlap between the short-tailed albatross Phoebastria albatrus, an endangered species, and the Alaskan groundfish trawl fleet is of concern because of the potential for incidental mortality. Due to the small size of this albatross population (ca. 2000 birds) and their wide-ranging foraging behavior, opportunistic sightings contribute the majority of the data on their distribution. In contrast, detailed information exists on fishing effort. In this study, 2 methods were used to predict albatross distributions: (1) bounded interpolation of sightings and (2) distance to the 1000 m isobath. The fishery was grouped into 5 sectors based on fish processing mode and predomi- nant product type. Locations and durations of observed trawls were associated with the predicted albatross densities and overlap was quantified using 2 metrics. Spatial and temporal overlap of alba- trosses and the trawl fleet was influenced by the assumptions used to infer albatross distribution and also differed among trawl sectors depending on the metric used to calculate overlap. The sectors with the highest and lowest overlap changed seasonally. In general, overlap scores were lowest in winter and spring due to both low trawl effort (in winter) and low albatross sightings (winter and spring). Relative effort in trawl sectors, in addition to proximity to high predicted albatross densities, con- tributed to overlap rankings such that some sectors with greater effort in areas with lower predicted albatross density had higher overlap scores than sectors with less effort in areas with high predicted albatross densities.

Comparative habitat associations in juvenile Pacific cod and other gadids using seines, baited cameras and laboratory techniques

Pacific cod are commercially and ecologically important in the North Pacific, currently ranking 2nd in tonnage and value landed in the Alaskan groundfish fishery. To date, few studies have focused on the habitat requirements of Pacific cod, and as a result, our understanding of their ecology has largely been borrowed from better-studied gadid species, especially Atlantic cod. In July–Aug 2006, we used field and laboratory techniques to explicitly examine habitat associations of Pacific cod and two co-occurring gadids, saffron cod ( Eleginus gracilis) and walleye pollock ( Theragra chalcogramma), in coastal areas around Kodiak Island, AK. Pacific cod were the most abundant gadid in seine collections, followed by saffron cod and walleye pollock respectively. Small Pacific cod (3.5–7.5 cm TL) were most highly associated with Laminaria and eelgrass beds but moved into open habitats at larger sizes i.e., > 8.0 cm TL. Baited cameras indicated that the majority of juvenile Pacific cod were nearshore in August ( i.e., ≤ 4.5 m), but schools were also seen in deeper (6.0–13.5 m), unstructured habitats. In contrast, age-0 saffron cod were almost exclusively restricted to eelgrass beds ( Zostera marina) (3.5–13.0 cm) as were later year-classes i.e., 18–50 cm. Pollock were highly variable in their distribution, and were almost absent from the nearshore in late August. In 2 m experimental aquaria, Pacific and saffron cod chose macrophyte habitats under increased predation risk but also associated with these habitats at larger scales ( i.e., c. 10 m tank) in the absence of a predator. Our results indicate both distinct differences and parallels between Pacific and Atlantic cod that will guide future process-oriented habitat research in both species.

Alaska red king crab: A relatively intractable target in a multispecies trawl survey of the eastern Bering Sea

The success with which Alaska's groundfish stocks have been managed is not matched by management of its crab stocks, several of which have been declared overfished. It is unlikely that all species will be sampled equally well in a generic, multispecies trawl survey with a uniform distribution of sampling effort. We evaluated the relative sampling tractability of six species targeted by the eastern Bering Sea stock assessment survey conducted annually by the U.S. National Marine Fisheries Service to see if there were differences that might explain the dichotomy in management success observed for groundfish and crabs. Using relative niche breadth, Green's Index of spatial patchiness, heterogeneity of variance and abundance-estimate precision, we analyzed 22 years of survey data to conclude that three major crab species, red king crab ( Paralithodes camtschaticus), snow crab ( Chionoecetes opilio) and Tanner crab ( Chionoecetes bairdi), were less tractable than three major fish species, walleye pollock ( Theragra chalcogramma), Pacific cod ( Gadus macrocephalus) and yellowfin sole ( Pleuronectes asper). In particular, our analysis established red king crab as the species for which abundance-estimate precision, niche breadth and sampling efficiency were lowest, patchiness was highest and heterogeneity of variance was the most severe. As a consequence, Bering Sea multispecies sampling is not likely to achieve the same degree of abundance-estimation success for red king crab as it might for other crab or fish species.

Using multi-species surplus production models to estimate ecosystem-level maximum sustainable yields

We used time series of biomass and catches for the major commercial groundfish stocks in the Eastern Bering Sea/Aleutian Islands region and in the Gulf of Alaska to compute annual surplus production for 1977–2004. Annual surplus production and average annual biomass were aggregated across stocks within each region to examine the relationship between total surplus production and total aggregated biomass. We fit two surplus production models (Graham-Schaefer and Pella-Tomlinson) to the observed relationships to estimate maximum multi-species surplus production (equivalent to maximum sustainable yield) of the groundfish complexes in these ecosystems. Maximum multi-species surplus production was estimated to be approximately 2.5 × 10 6 t in the Bering Sea/Aleutian Islands and 330 × 10 3 t in the Gulf of Alaska. These point estimates were smaller than the sum of single-species MSY proxies from recent stock assessments, and estimates for the Gulf of Alaska were much smaller than earlier estimates that were used to specify optimum yield ranges for the Gulf of Alaska groundfish complex. Therefore, optimum yield ranges for the Gulf of Alaska may need to be re-assessed to reflect more recent conditions. We further estimated the effects of environmental variability on annual surplus production using correlations and generalized surplus production models with environmental covariates. Results suggest that surplus production in the Bering Sea may be lower during conditions associated with the positive phase of the Pacific Decadal Oscillation, which is characterized by warmer temperatures, reduced ice, and reduced wind mixing over the shelf. Similarly, surplus production on the Gulf of Alaska shelf was lower during years with warm bottom temperatures coupled with low salinities in late winter. If maximum multi-species surplus production varies as a result of environmental variability, optimum yield ranges for the groundfish complexes in these ecosystems should take such fluctuations into account.