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Results from this study suggest that small-scale variability in the Alaska Coastal Current (ACC) and competition between juvenile pollock and capelin are potential mechanisms affecting the distribution and abundance of fishes in the Gulf of Alaska (GOA). Fish distributions in Barnabus Trough, off the east coast of Kodiak Island, were assessed using acoustic data collected with a calibrated echosounder during August–September 2002 and 2004. Trawl hauls were conducted to determine the species composition of the fish making up the acoustic backscatter. Oceanographic data were collected from moorings, conductivity–temperature–depth (CTD) probes, trawl-mounted microbathythermographs (MBT) and expendable bathythermographs (XBT). National Centers for Environmental Prediction (NCEP) reanalysis data were used to assess area winds, and information on regional transport was derived from current meters deployed on moorings north and south of Kodiak Island. The distribution of water-mass properties and fish during 2002 showed variability at the temporal scale of weeks. Juvenile pollock (age-1 and age-2) were initially most abundant in warm, low-salinity water on the inner shelf, whereas capelin were distributed primarily on the outer shelf in cool, high-salinity waters. During a 2-week period juvenile pollock distribution expanded with the offshore expansion of warm, low-salinity water, and capelin abundance in outer-shelf waters decreased. We hypothesize that wind-driven pulsing of the ACC resulted in increased transport of warm, low-salinity water through the study area. In 2004, warm, low-salinity water characterized the inner shelf and cool, high-salinity water was found on the outer shelf. However, the distribution of water-mass properties did not show the weekly scale variability observed in 2002. Area winds were consistently toward the southwest during 2004, such that we would not expect to see the wind-driven pulsing of ACC water that occurred in 2002. Age-1 and age-2 pollock were not observed in Barnabus Trough in 2004. Instead, the midwater acoustic backscatter was composed of capelin mixed with age-0 pollock, and these capelin were not restricted to the outer-shelf waters, but were found primarily in warm, low-salinity inner-shelf waters that had been previously occupied exclusively by age-1 and age-2 pollock. We suggest that this is consistent with inner-shelf waters being preferred foraging habitat for juvenile pollock and capelin. Further study of the mechanisms linking climate change with variability in the ACC is needed, as are studies of the potential for competition between juvenile pollock and capelin.

Acoustic trawl surveys were conducted in 2000 and 2001 in two troughs located off the eastern coast of Kodiak Island in the Gulf of Alaska as part of a multiyear, multidisciplinary experiment to examine the influence of environmental conditions on the spatial distribution of adult and juvenile walleye pollock (Theragra chalcogramma) and capelin (Mallotus villosus). Continuous underway sea surface temperature samples and water column profiles collected in 2000 and 2001 showed the presence of a sharp shelf-break front in Chiniak Trough and a mid-trough front in Barnabas Trough. At distances

In a search for ocean conditions potentially affecting the extent of Pacific hake (Merluccius productus) feeding migrations, we analyzed data collected in 1995 and 1998 by the National Marine Fisheries Service on abundance and distribution of hake (by echo integration), intensity and distribution of alongshore flow (from acoustic Doppler current profiler), and temperature (conductivity–temperature–depth profiles). Our results show that Pacific hake are associated with subsurface poleward flow and not a specific temperature range. Temporal and spatial patterns characterize both hake distribution and undercurrent characteristics during the two years of this study. We suggest that poleward flow in this area defines adult hake habitat, with flow properties aiding or impeding the poleward migration of the population. We conclude that although physical processes may not directly affect fish production, they may be the link between large-scale ocean–atmosphere variability and pelagic fish distribution.

This paper provides a retrospective analysis of the relationship of physical oceanography and biology and recruitment of three Eastern Bering Sea flatfish stocks: flathead sole (Hippoglossoides elassodon), northern rock sole (Lepidopsetta polyxystra), and arrowtooth flounder (Atheresthes stomias) for the period 1978–1996. Temporal trends in flatfish production in the Eastern Bering Sea are consistent with the hypothesis that decadal scale climate variability influences marine survival during the early life history period. Density-dependence (spawning stock size) is statistically significant in a Ricker model of flatfish recruitment, which includes environmental terms. Wind-driven advection of flatfish larvae to favorable nursery grounds was also found to coincide with years of above-average recruitment through the use of an ocean surface current simulation model (OSCURS). Ocean forcing of Bristol Bay surface waters during springtime was mostly shoreward (eastward) during the 1980s and seaward (westerly) during the 1990s, corresponding with periods of good and poor recruitment. Distance from shore and water depth at the endpoint of 90-day drift periods (estimated time of settlement) were also found to correspond with flatfish productivity.

A review of oceanographic and climate data from the North Pacific and Bering Sea has revealed climate events that occur on two principal time scales: a) 2–7 years (i.e. El Nino Southern Oscillation, ENSO), and b) inter-decadal (i.e. Pacific Decadal Oscillation, PDO). The timing of ENSO events and of related oceanic changes at higher latitudes were examined. The frequency of ENSO was high in the 1980s. Evidence of ENSO forcing on ocean conditions in the North Pacific (Nino North conditions) showed ENSO events were more frequently observed along the West Coast than in the western Gulf of Alaska (GOA) and Eastern Bering Sea (EBS). Time series of catches for 30 region/species groups of salmon, and recruitment data for 29 groundfish and 5 non-salmonid pelagic species, were examined for evidence of a statistical relationship with any of the time scales associated with Nino North conditions or the PDO. Some flatfish stocks exhibited high autocorrelation in recruitment coupled with a significant step in recruitment in 1977 suggesting a relationship between PDO forcing and recruitment success. Five of the dominant gadid stocks (EBS and GOA Pacific cod, Pacific hake and EBS and GOA walleye pollock) exhibited low autocorrelation in recruitment. Of these, Pacific hake, GOA walleye pollock and GOA Pacific cod exhibited significantly higher incidence of strong year classes in years associated with Nino North conditions. These findings suggest that the PDO and ENSO may play an important role in governing year-class strength of several Northeast Pacific marine fish stocks.

We review the application of multispecies models as tools for evaluating impacts of fishing on marine communities. Four types of model are identified: descriptive multispecies, dynamic multispecies, aggregate system, and dynamic system models. The strengths and weaknesses of multispecies models and their ability to evaluate the causal mechanisms underlying shifts in production are examined. This comparison provides a basis for assessing the benefits of each modelling approach as a tool for evaluating impacts of fishing in marine ecosystems. Benefits of multispecies models include: improved estimates of natural mortality and recruitment; better understanding of spawner–recruit relationships and of variability in growth rates; alternative views on biological reference points; and a framework for evaluating ecosystem properties. Populations are regulated by competition (food limitation), predation, and environmental variability. Each factor may influence different life-history stages, locally or regionally. However, most multispecies models address only a subset of these factors, often aggregated over functionally different species or age groups. Models that incorporate the important interactions at specific stages and scales will be necessary if they are to continue to supplement the information provided by single-species models. 2000 International Council for the Exploration of the Sea

Hypotheses concerning the decline of Steller sea lions in the Gulf of Alaska (GOA) were evaluated based on comparison of data to three other ecosystems that had similar environmental and commercial fishery characteristics. We focus on examining the effects of commercial pinniped harvest, commercial fisheries, and environmental changes. Of the four pinniped species included in this study, only the Steller sea lion population has exhibited a sharp decline in population number. Comparative analysis indicated that the Gulf of Alaska pinniped population has not experienced any unique large-scale perturbations compared to the other ecosystems. Commercial pinniped harvest occurred in all four ecosystems. The history of harvest was shortest for GOA Steller sea lions and the numbers taken were lower than in the Barents Sea and Benguela Current ecosystems. Exploitation rates, though only calculated for years when both harvest numbers and total population size were available, also indicated that the Steller sea lion...

A separable catch-age stock assessment model that accommodates predation mortality is applied to the Gulf of Alaska walleye pollock (Theragra chalcogramma) assessment. Three predators are incorporated in the model: arrowtooth flounder (Atheresthes stomias), Pacific halibut (Hippoglossus stenolepis), and Steller sea lion (Eumetopias jubatus). The effect of these predators is examined by defining the predation mortality as a type of fishery. The model is used to quantify changes in the relative fit to the survey, fishery, and predator data when the assumption of constant natural mortality is relaxed. Specifically, we examine the effect of assumptions regarding the functional feeding response, residual naturaly mortality, and uncertainty in predator biomass on stock assessment. Total natural mortality rates (including predation) tended to be higher than estimated from life history characteristics of the stock. Models that did not account for uncertainty in natural mortality underestimated uncertainty in current stock biomass by as much as 20%. Our results indicate that independent estimates of survey selectivity, additional food habits data, and estimates of the feeding responses of predators to different prey densities are all needed to improve our ability to develop stock assessment models that address ecosystem concerns. 2000 International Council for the Exploration of the Sea

A major reorganization of the North-east Pacific biotatranspired following a climatic ‘regime shift’ in the mid1970s. In this paper, we characterize the effects ofinterdecadal climate forcing on the oceanic ecosys-tems of the NE Pacific Ocean. We consider the con-cept of scale in terms of both time and space withinthe North Pacific ecosystem and develop a conceptualmodel to illustrate how climate variability is linked toecosystem change. Next we describe a number of re-cent studies relating climate to marine ecosystem dy-namics in the NE Pacific Ocean. These studies havefocused on most major components of marine ecosys-tems – primary and secondary producers, forage spe-cies, and several levels of predators. They have beenundertaken at different time and space scales. How-ever, taken together, they reveal a more coherentpicture of how decadal-scale climate forcing may affectthe large oceanic ecosystems of the NE Pacific. Finally,we synthesize the insight gained from interpretingthese studies. Several general conclusions can bedrawn.1 There are large-scale, low-frequency, and some-times very rapid changes in the distribution of atmo-spheric pressure over the North Pacific which are, inturn, reflected in ocean properties and circulation.2 Oceanic ecosystems respond on similar time andspace scales to variations in physical conditions.3 Linkages between the atmosphere/ocean physicsand biological responses are often different across timeand space scales.4 While the cases presented here demonstrateoceanic ecosystem response to climate forcing, theyprovide only hints of the mechanisms of interaction.5 A model whereby ecosystem response to specifiedclimate variation can be successfully predicted will bedifficult to achieve because of scale mismatches andnonlinearities in the atmosphere–ocean–biospheresystem.INTRODUCTIONIn this paper, we characterize the effects of interde-cadal climate forcing on the oceanic ecosystems of theNE Pacific Ocean. Our approach is first to reflect on anumber of recent studies relating climate to marineecosystem dynamics. These studies have focused onmost major components of marine ecosystems – pri-mary and secondary producers; primary, secondary andtop-level predators. They have been undertaken atdifferent time and space scales. However, taken to-gether they begin to reveal a more coherent picture ofhow decadal-scale climate forcing may affect the largeoceanic ecosystems of the NE Pacific. We then syn-thesize the insight gained from these studies with whatwe know about atmospheric and oceanic physics andhow they affect these marine ecosystems.Of particular importance to this paper is the con-cept of scale. Ricklefs (1990) defines scale as thecharacteristic distance or time associated with varia-tion in natural systems. He goes on to make threeimportant points about why the concept of scale is soimportant to developing an understanding of ecosys-tem structure and dynamics. Every process and pattern has a temporal andspatial extent.

NOAA's Fisheries Oceanography Coordinated Investigations (FOCI) contributes information to help forecast year-class strength of walleye pollock (Theragra chakogrammu) in the Gulf of Alaska. Quantitative estimates of recruitment are obtained from models of stock assessment and stock projection employing information supplied by FOCI. To generate its information, FOCI convenes specialists in marine biology, physical and fisheries oceanography, meteorology, and statistics to assemble and analyse relevant biological and physical time series with respect to recruitment and processes hypothesized to influence fish survival. Statistical methods encompass linear and nonlinear regression, stochastic simulation modelling, transfer function time series modelling, and tree-modelling regression. The current database consists of 31 years of data, and analyses have identified factors that affect ocean stratification and circulation during spring and summer of the fish's birth year as being important to recruitment. A conceptual model of the recruitment process serves as the framework for a recruitment forecast scheme. A stochastic mathematical simulation model of the conceptual model produces similarities between simulated and observed recruitment time series. FOCI has successfully forecast recruitment observed over the past several years.

A series of age-specific life tables for walleye pollock (Theragra chalcogramma) in the western Gulf of Alaska was compiled for the 1980-91 year classes. The life tables were utilized to perform an exploratory key factor analysis to examine the timing of critical periods in the recruitment process, evidence of densitydependence at different stages and trends in mortality rates. Early larval mortality was significantly correlated with generational mortality (In recruitshpawning biomass), but patterns in juvenile mortality also were similar to generational mortality and in some years were clearly dominant in determining the fate of a cohort. Density-dependent mortality, based on the correlation between mortality and initial abundance, was indicated only for the late larval to early juvenile stage. Time trends were marginally significant for juvenile mortality. It is speculated that the observed increase in juvenile mortality is associated with increasing abundance of arrowtooth flounder. Weaknesses in the data base are discussed; these along with the short time series involved make our conclusions tentative and subject to further study. We hypothesize that pollock recruitment levels can be established at any life stage depending on sufficient supply from prior stages, a type of dynamics which can be termed supply dependent multiple life stage control.

Considerable progress has been made in understanding physiological responses of marine organisms to climate change (Portner and Farrell, 2008; Somero, 2011) and in projecting future responses of individual species (Chown and Gaston, 2008; Helmuth, 2009). Key to this understanding are findings that indicate that multiple climate-related and non-climate-related stressors interact in their impacts on marine organisms, and that physiological responses to these stressors can be highly variable across species and life-history stages.

A number of international treaties and conventions have been developed to aid in addressing ocean issues that affect multiple jurisdictions and countries. Many of these focus either primarily on marine resources or involve them in some fashion. Exploring and strengthening synergies between these treaties and conventions would be extremely beneficial for providing increased value, better coordination, and improved focus and facilitation of the development of key priorities (Robinson et al., 2005). The following discussion includes only a subset of the larger body of international conventions and treaties.

In marine ecosystems, rising atmospheric CO2 and climate change are associated with concurrent shifts in temperature, circulation, stratification, nutrient input, oxygen content, and ocean acidification, with potentially wide-ranging biological effects. Population-level shifts are occurring because of physiological intolerance to new environments, altered dispersal patterns, and changes in species interactions. Together with local climate-driven invasion and extinction, these processes result in altered community structure and diversity, including possible emergence of novel ecosystems. Impacts are particularly striking for the poles and the tropics, because of the sensitivity of polar ecosystems to sea-ice retreat and poleward species migrations as well as the sensitivity of coral-algal symbiosis to minor increases in temperature. Midlatitude upwelling systems, like the California Current, exhibit strong linkages between climate and species distributions, phenology, and demography. Aggregated effects may modify energy and material flows as well as biogeochemical cycles, eventually impacting the overall ecosystem functioning and services upon which people and societies depend.

A stochastic age-structured bioeconomic simulation model was developed as a tool for evaluating economic returns to a fishery from alternative harvest policies. The model, which was applied to the Gulf of Alaska walleye pollock (Theragra chalcogramma) fishery, combines the dual goals of protection of the base stock and efficient use of the public resource into an explicit objective function. This paper presents the results of several experiments in which the simulation model is used to examine the sensitivity of the optimum harvest strategy estimates to alternative definitions of risk and assumptions regarding recruitment. Alternative definitions of risk consider assumptions about stock productivity, threshold biomass, economic factors, and hybrid formulations. The bioeconomic extension of the population dynamics model is used to quantify differences in the estimates of optimum fishing mortality obtained from the different risk definitions. Model results demonstrate that estimates of optimal fishing mortality and economic return to the fishery are sensitive to the specific definition of risk used to manage the fishery. The recruitment assumption turned out to be more important to optimum harvest strategy estimates than did risk definitions.

A central and classic question in ecology is what causes populations to fluctuate in abundance. Understanding the interaction between natural drivers of fluctuating populations and human exploitation is an issue of paramount importance for conservation and natural resource management. Three main hypotheses have been proposed to explain fluctuations: (i) species interactions, such as predator–prey interactions, cause fluctuations, (ii) strongly nonlinear single-species dynamics cause fluctuations, and (iii) environmental variation cause fluctuations. We combine a general fisheries model with data from a global sample of fish species to assess how two of these hypothesis, nonlinear single-species dynamics and environmental variation, interact with human exploitation to affect the variability of fish populations. In contrast with recent analyses that suggest fishing drives increased fluctuations by changing intrinsic nonlinear dynamics, we show that single-species nonlinear dynamics alone, both in the presence and absence of fisheries, are unlikely to drive deterministic fluctuations in fish; nearly all fish populations fall into regions of stable dynamics. However, adding environmental variation dramatically alters the consequences of exploitation on the temporal variability of populations. In a variable environment, (i) the addition of mortality from fishing leads to increased temporal variability for all species examined, (ii) variability in recruitment rates of juveniles contributes substantially more to fluctuations than variation in adult mortality, and (iii) the correlation structure of juvenile and adult vital rates plays an important and underappreciated role in determining population fluctuations. Our results are robust to alternative model formulations and to a range of environmental autocorrelation.

The cold-temperate regions of the North Pacific and North Atlantic oceans, from about 40°N latitude to the Arctic fronts, support large and productive fisheries ( 1 ), particularly in the northernmost regions: the Bering Sea in the Pacific and the Barents Sea in the Atlantic. The two main near-bottom fish species in the Bering and Barents seas are walleye pollock ( Gadus chalcogrammus ) and Atlantic cod ( G. morhua ), respectively. In the past decade, the two species have responded differently to ocean warming. These response patterns appear to be linked to a complex suite of climatic and oceanic processes that may portend future responses to warming ocean conditions.

The impact of climate on fisheries is highly variable, indirect, and complex. Several dominant themes related to climate change and fisheries are considered in some of the chapters in this volume (Chapters 2, 3, and 6), including: complex interactions, formation of patterns over large-scales, high variability over small-scales, and the desirability of forecasting tools. This chapter discusses how these themes are focal issues in many of the world's seas, including the northeast Pacific Ocean. The chapter identifies how established climate-fish links often deteriorate with time, and underscore the role of regime shifts and switches of climatic controlling factors.

Hollowed, A. B., Barange, M., Ito, S-I., Kim, S., Loeng, H., and Peck, M. 2011. Effects of climate change on fish and fisheries: forecasting impacts, assessing ecosystem responses, and evaluating management strategies. – ICES Journal of Marine Science, 68: 984–985.