Pacific Cod Research Articles

Integrating seabird dietary and groundfish stock assessment data: Can puffins predict pollock spawning stock biomass in the North Pacific?

AbstractInformation on the annual variability in abundance and growth of juvenile groundfish can be useful for predicting fisheries stocks, but is often poorly known owing to difficulties in sampling fish in their first year of life. In the Western Gulf of Alaska (WGoA) and Eastern Bering Sea (EBS) ecosystems, three species of puffin (tufted and horned puffin, Fratercula cirrhata, Fratercula corniculata, and rhinoceros auklet, Cerorhinca monocerata, Alcidae), regularly prey upon (i.e., “sample”) age‐0 groundfish, including walleye pollock (Gadus chalcogramma, Gadidae) and Pacific cod (Gadus microcephalus, Gadidae). Here, we test the hypothesis that integrating puffin dietary data with walleye pollock stock assessment data provides information useful for fisheries management, including indices of interannual variation in age‐0 abundance and growth. To test this hypothesis, we conducted cross‐correlation and regression analyses of puffin‐based indices and spawning stock biomass (SSB) for the WGoA and EBS walleye pollock stocks. For the WGoA, SSB leads the abundance of age‐0 fish in the puffin diet, indicating that puffins sample the downstream production of the WGoA spawning stock. By contrast, the abundance and growth of age‐0 fish sampled by puffins lead SSB for the EBS stock by 1–3 years, indicating that the puffin diet proxies incoming year class strength for this stock. Our study indicates connectivity between the WGoA and EBS walleye pollock stocks. Integration of non‐traditional data sources, such as seabird diet data, with stock assessment data appears useful to inform information gaps important for managing US fisheries in the North Pacific.

Effects of feeding differentially enriched Artemia nauplii on the survival, growth, fatty acid composition, and air exposure stress response of Pacific cod (Gadus macrocephalus) larvae

The ability of enriched live food, such as Artemia, to improve the growth performance of Pacific cod (Gadus macrocephalus) larvae during larviculture has yet to be fully established. Thus, the effects of feeding differentially enriched Artemia to Pacific cod larvae were investigated here, specifically the effects on the survival, growth, fatty acid composition, and air exposure stress response of the larvae. Three different commercial Artemia enrichment emulsion oils were used: commercially available enrichment 1, 2, and 3, referred to as ER1, ER2, and ER3, respectively. Although ER2-treated Artemia contained the most eicosapentaenoic acid (EPA) and ER3-treated Artemia contained the most docosahexaenoic acid (DHA) and highly unsaturated fatty acid (HUFA), the ER1 enrichment improved overall survival, growth, and survival after air stress test to the greatest extent in larval Pacific cod. Furthermore, the levels of DHA and HUFA observed in larvae fed the ER1 diet were higher than the respective concentrations of these nutrients observed in larvae fed the other diets. Thus, under the experimental conditions applied in the present study, ER1 provided Artemia with DHA and EPA ratio of 4.1 for early feeding of Pacific cod larvae.

Application of the Gadidae Fish Processing Waste for Food Grade Gelatin Production

Waste from fish cutting (heads, swim bladders, fins, skin, and bones) is a high-value technological raw material for obtaining substances and products with a wide range of properties. The possibility of using waste from cutting fish of the Gadidae family: the Alaska pollock (Gadus chalcogrammus) and the Pacific cod (Gadus macrocephalus), processed in the coastal zone, is scientifically substantiated. In this work, a technology has been developed for processing accumulated waste from fish cutting in order to obtain fish gelatin, which is characterized by high protein content (more than 80.0%) and a full set of essential and nonessential amino acids. We studied the quality of fish gelatin obtained from wastes from cutting the fish of the Gadidae family. The possibility of using fish gelatin as a component of fish products is shown; the dose of its introduction into the fish products is substantiated. The data obtained made it possible to recommend the use of fish processing waste products as a gelling component and a source of amino acids in multicomponent food systems.

Is the protected Atlantic cod (Gadus morhua) population in Gilbert Bay, Labrador, nearing a tipping point?

Abstract The Gilbert Bay Marine Protected Area (MPA), Labrador, was created in 2005 to protect a resident, locally adapted population of Atlantic cod and its habitat. Twenty years of monitoring has shown a 90% decline in this bay‐cod population since the creation of the MPA. The decline of large commercial‐sized cod in the bay was accompanied with increases in the abundance of other fish species, including rock cod (Gadus macrocephalus ogac), sculpin (Myoxocephlalus scorpius), and winter flounder (Pseudopleuronectes americanus), suggesting loss of strong top‐down community control. These changes suggest a positive feedback mechanism leading to a fish community tipping point, which could severely impact the recovery potential of the protected Atlantic cod population in the MPA. We suggest that managers should be including this possibility in their management decisions for the Gilbert Bay MPA.

Estimating fine‐scale movement rates and habitat preferences using multiple data sources

AbstractFisheries scientists and managers must track rapid shifts in fish spatial distribution to mitigate stakeholder conflict and optimize survey designs, and these spatial shifts result in part from animal movement. Information regarding animal movement can be obtained from selection experiments, tagging studies, flux through movement gates (e.g. acoustic arrays), fishery catch‐per‐unit effort (CPUE), resource surveys and genetic/chemical markers. However, there are few accessible approaches to combine these data types while accounting for spatially correlated residual patterns. We therefore discuss a movement model involving diffusion (random movement), taxis (movement towards preferred habitat) and advection (passive drift following ocean currents). We specifically outline how these movement processes can be fitted to data while discretizing space and time and estimating non‐linear habitat preferences using environmental layers as well as spatial process errors. Finally, we introduce an R package, ATM, by fitting the model to bottom trawl survey, longline fishery and tagging data for Pacific cod (Gadus macrocephalus, Gadidae) in the Bering Sea during winter/summer seasons from 1982 to 2019. Combining data types predicts an increasing proportion of cod residing in the northern Bering Sea from 2013 to 2019, and estimates are informative in a recent stock assessment model. We fit sensitivity analyses by dropping tag, survey or fishery data, and this analysis shows that tagging data are necessary to identify diffusion rates, while survey data are informative about movement among biogeographic strata. This “hybrid” species distribution model can help explain poleward movement, project distributions under future climate conditions and evaluate alternative tag‐deployment scenarios to optimize tagging designs.

Aging Pacific cod (Gadus macrocephalus) from otoliths using Fourier‐transformed near‐infrared spectroscopy

AbstractFor decades, age‐structured stock assessments have been a key component to managing fishery resources worldwide. Fisheries management systems have been under increasing demand to generate a greater volume and quality of age estimates. Traditional aging techniques, which require physical preparation followed by microscopic examination of fish otoliths, are labor‐intensive, expensive, and inherently subjective among individual analysts, making repeatability and precision a challenge. Here we investigated an innovative approach to aging fish from their otoliths using Fourier‐transformed near‐infrared spectroscopy and partial least squares regression models. Models were fit to and validated on spectra and used to microscopically estimate ages of Pacific cod from three years of fishery‐independent otolith data out of the Bering sea. Calibrated and validated models for each year, as well as on an ensemble of the three years, yielded high precision for the multiyear model (R2 = 0.869, RMSE = 0.614, PA = 63%, CV = 7.412), and independent year models (R2 = 0.844–0.891, RMSE = 0.555–0.615, PA = 65%, CV = 6.313–6.775). These metrics of model performance were highly comparable to precision from the traditional microscopic aging approach (R2 = 0.763–0.869, RMSE = 0.639–0.737, PA = 63%–70%, CV = 5.671–6.698). In all cases, a two‐sided Kolmogorov–Smirnov test showed no significant difference between reference and model estimated age distributions. Our results illustrate how Fourier‐transformed near‐infrared spectroscopy can be utilized on otoliths to predict age estimates with substantially greater efficiency, good precision, high repeatability, and no loss in data integrity compared to the traditional microscopic method for aging Pacific cod.

Estimating spatiotemporal availability of transboundary fishes to fishery‐independent surveys

Abstract Taxa can expand beyond historical scientific survey footprints and into new areas with different survey protocols as they move to track their preferred climate. In global groundfish fisheries, for example, scientists estimate population dynamics within the spatial extent of a fishery‐independent survey using an index known as a design‐based estimator. Observed changes in species distribution in recent years suggest that some groundfish are moving beyond the spatial extent of single surveys. We must intercalibrate disparate data that cover a larger spatial extent to maintain our ability to accurately index populations as their availability to historical surveys changes. We combine US and Russian data from the northern, eastern and western Bering Sea to understand the proportion of fish biomass within the extent of the eastern survey (‘availability’). Surveys are within close proximity to each other, but with different sampling protocols (hence catch a different proportion of local densities, termed ‘sampling efficiency ratio’). We use Alaska pollock Gadus chalcogrammus, Pacific cod Gadus macrocephalus and Alaska plaice Pleuronectes quadrituberculatus as case studies to calculate survey efficiency ratios and two area‐swept estimators, termed local and conventional, to summarize groundfish biomass over various spatial scales across the Bering Sea. We estimated variation in spatial availability of transboundary stocks to the eastern Bering Sea (EBS) survey. In 2017, the most recent available year of survey coverage that included all three Bering Sea regions, estimated availability in the EBS of pollock biomass was ~33%, cod biomass was ~27% and plaice biomass was ~26%, down from ~58%, ~71% and ~30%, respectively, in 2010. Synthesis and applications. This is the first study to provide an empirical way to combine Russian and US data in the Bering Sea to assess changes in the availability of groundfish biomass, which, in turn, will alter the interpretations and values of population indices used in regional management. We recommend leveraging this approach using existing global fishery‐independent datasets that span different spatiotemporal footprints to monitor transboundary stocks, and as a template to initiate international cooperation on the assessment of spatial availability of stocks common to multiple countries.

Rapid identification of cod and oil fish components based on loop-mediated isothermal amplification

Establishing rapid and correct detection methods to identify cod fish species is very important to promote labels correction and control fraud behavior. This study developed a systematic method mainly using visible loop-mediated isothermal amplification (LAMP) to identify cod and oil fish that are commonly found from the Chinese market. Specific primer sets were designed based on the Cytb gene of each species, and four primer sets were found to successfully achieve very high specificity in identifying the corresponding targeting species, including Gadus morhua, Gadus macrocephalus, Theragra chalcogramma and two oilfish species (Ruvettus pretiosus and Lepidocybium flavobrunneum), respectively. The discrimination of Merluccius australis, Dissostichus eleginoides and Anoplopoma fimbria can be realized by a two-step method with only LAMP or qPCR. The relatively systematic primers and methods explored in this study can be successfully applied against the serious mislabels and adulterations in cod fish market.

Rapid and Reliable Assessment of Fish Physiological Condition for Fisheries Research and Management Using Fourier Transform Near-Infrared Spectroscopy

Measuring fish population responses to climate change requires timely ecological information, warranting innovative approaches to data collection in fisheries research and management. Fourier transform near-infrared (FT-NIR) spectroscopy is a promising tool to efficiently and cost-effectively obtain multiple types of fisheries data including fish physiological health and energetics that can provide indicators of stock status and environmental change. We tested the applicability of FT-NIR spectroscopy to determine fish physiological state and condition by developing calibration models for morphometric indices of body condition [Fulton’s K and hepatosomatic index (HSI)], biochemical measurements of tissue composition (lipid content and energy density), and a nucleic acid-based index of recent growth (RNA:DNA) of juvenile Pacific cod (Gadus macrocephalus). Calibration models had the best predictive ability for lipid content followed by HSI and energy density, whereas spectral data had weak relationships with Fulton’s K and RNA:DNA. For lipid content, energy density, and HSI, informative spectral regions were primarily associated with carbon-hydrogen bonds in lipid molecules. Additionally, FT-NIR spectroscopy calibration models better predicted lipid content than morphometric measurements that are often used as proxies for measuring energy reserves, indicating that FT-NIR spectroscopy might serve as a more informative index of body condition and energy stores than other rapid methods. Efficient sample analysis by FT-NIR spectroscopy can supplement traditional metrics of body condition and be especially useful for ensuring the availability of monitoring data in support of fisheries research and management.

Molecular characterization and expression profiles of two interleukin genes IL-8 and IL-10 in Pacific cod (Gadus macrocephalus)

During the early development of the Pacific cod, high mortality due to viral infection is observed. To demonstrate the immune responses activated in Pacific cod during this critical period, two cytokines, the proinflammatory cytokine interleukin-8 (IL-8) and the anti-inflammatory cytokine interleukin-10 (IL-10), were identified and characterized in this study. The cDNA of IL-8 was 1047 bp in length, containing an ORF of 297 bp that encoded a 98 aa protein, whereas the IL-10 cDNA sequence consisted of 856 bp that harbored a 537 bp ORF encoding a 178 aa protein. Pairwise comparison and phylogenetic analysis of the two genes clearly demonstrated their close relationships with their counterparts in the Atlantic cod. Constitutive expression was detected in eight tested tissues; the transcription of both genes was observed during the critical period of the early developmental stage in Pacific cod, and their expression levels dramatically increased following poly I:C stimulation of larvae at 12 days post-hatching (dph). Taken together, these results suggested that IL-8 and IL-10 may be involved in the inflammatory responses of Pacific cod.

Life without ice: Perceptions of environmental impacts on marine resources and subsistence users of St. Lawrence Island

The Bering Strait region is undergoing rapid environmental change linked to reductions in the extent and seasonal availability of sea ice. The goal of the present study was to assess the impacts that environmental change and loss of sea ice has had on marine subsistence resources and resource users in the communities of St. Lawrence Island (SLI), Alaska. The broader research design was multidisciplinary in order to document any shifts in the abundance and health of key marine subsistence species, while recording people's perceptions of changing environmental conditions in their lifetime. The present study focuses on the perceived social and material effects of climate change on SLI residents. To capture human perceptions and experiences, open ended interviews were conducted during three weeks in April and May 2019, during which time 25 SLI residents were interviewed. Four main themes were assessed: 1) key marine resources for SLI communities, 2) perceptions about changes in key resources, 3) community responses to change, and 4) the future of the subsistence way of life in these communities. Interviews were transcribed, coded for themes, and analyzed using MAXQDA software. Results indicate the four most discussed marine resources were Pacific walruses (Odobenus rosmarus divergens), seals, crabs, and fish. The largest changes observed in these resources included: decreased walrus harvests and limited access with increased hunting effort; an increase in the abundance of Hanasaki crab (Paralithodes brevipes) and limited crab harvests due to lack of shorefast ice; and increasing abundances of walleye pollock (Gadus chalcogrammus) and Pacific cod (Gadus macrocephalus). SLI residents utilize a broad range of edible marine flora and fauna, and at times, eat less desirable prey items due to scarcity of preferred species. Lastly, most informants that discussed the future of a subsistence way of life, were concerned future generations will be harvesting and eating less subsistence resources. Due to environmental changes, and most specifically loss of sea ice, SLI communities may have to diversify the species that they harvest to continue maritime subsistence practices, or may turn to consuming more terrestrial and domestic sources of protein if available. To better understand resource availability and to manage for a changing ecosystem, resource managers and policy makers may: 1) anticipate a need for conducting stock assessments for king and Hanasaki crabs at regular intervals, 2) anticipate a need for conflict resolutions, mitigation frameworks, or agreements if commercial fishing vessels encroach on space and resources traditionally used by SLI subsistence users, and 3) take an active approach in obtaining authorizations for the harvest of currently protected marine mammals, which may be needed to ensure food security and consumption of historically traditional foods from the local environment.

Seasonal migratory patterns of Pacific cod (Gadus macrocephalus) in the Aleutian Islands

BackgroundPacific cod (Gadus macrocephalus) is an ecologically important species that supports a valuable commercial fishery throughout Alaska waters. Although its life history includes seasonal movement for spawning and feeding, little is known about its movement ecology. Here, we present results from the first study to use pop-up satellite archival tags (PSATs) to track the within-year movements of Pacific cod to understand their potential seasonal movement patterns within the Aleutian Islands. This study was part of a cooperative research project; tagging was conducted onboard commercial vessels during the winter fishing season while Pacific cod were aggregated to spawn in the central Aleutian Islands.ResultsOf the 36 PSATs deployed, we were able to obtain movement data from 13 Pacific cod that were at liberty between 60 and 360 days. We determined that three tagged Pacific cod were predated on by marine mammals and three were recaptured by the commercial fishery. Geolocation models were produced for four migrating individuals. Eight Pacific cod moved to a productive foraging ground near Seguam Island located 64 to 344 km from their release site and presumed spawning ground within a few weeks of their release. These movements indicate that some Pacific cod in the Aleutian Islands undergo seasonal migration. Three Pacific cod remained near their release locations (within 50 km) for more than 75 days suggesting the existence of partial migration in the population. Two Pacific cod undertook larger movements (378 and 394 km) during which they swam over deep passes and crossed several management boundaries highlighting the potential connectedness of Pacific cod throughout the Aleutian Islands.ConclusionsThis study provided important initial insights into the seasonal movement patterns of Pacific cod in the Aleutian Islands. Most tracked Pacific cod (77%) undertook migrations in the middle of March (64–394 km) from their winter spawning areas to summer foraging areas, but a few individuals remained in their capture location suggesting a partial migration strategy. Their ability to cross deep passes that were previously seen as potential barriers to movement has expanded our understanding of population connectivity.

Long-Term Variability of Piscivorous Fish in China Seas Under Climate Change With Implication for Fisheries Management

Due to persistent fishing expansion in the China Seas over the past six decades, fisheries resources have been over-exploited; as a result, exploited fish have become smaller in size and younger in age. Marine piscivorous fish constituted a large portion of Chinese fisheries catch, long-term variability of which has rarely been investigated despite intense fishing pressure and climate change. In this study, we attempt to identify their responses to climate change and fishing activities and to provide scientific basis for sustainable exploitation of these resources. Seven taxa from pelagic to demersal species inhabiting either cold-water or warm-water were selected to represent the piscivorous fish assemblage in the China Seas. Total catch of these piscivorous fish in the China Seas increased during the early 1990s, stabilizing around 1.2 million tons after 1997. Principal component analysis (PCA) showed evident interannual-decadal variabilities in the catch of these fish with step changes around 1985/86 and 1997/98. Individual taxa, however, showed different trends in catches with sharks, rays, and lizardfishes manifesting downward trends while Pacific cod, eels, and hairtail increasing. Common dolphinfish and Japanese-Spanish mackerel increased largely in the 1990s but declined slightly during the 2000s. Although there were temporal overlaps between climate change and fishing variabilities, results of gradient forest analyses indicated that fishing effort imposed the most important influence on piscivorous fish. And among all climate variables explored in this study, sea surface temperature (SST) especially that of the East China Sea, had greatest impacts on variations in piscivorous fish catch, which may have been gradually exacerbated by the continued high fishing intensity. In addition, significant changes were identified in the life history traits in the species we evaluated, such as reduced average body sizes and truncated age compositions, strongly indicating the effect of fishing. We therefore advocate precautionary fishery practices under climate change.

Tidally Induced Temporal Variations in Growth of Young‐of‐the‐Year Pacific Cod in the Yellow Sea

AbstractThe Yellow Sea is the southern limit of the distribution of Pacific cod (Gadus microcephalus), and the Yellow Sea Cold Water Mass (YSCWM) provides an appropriate over‐summering habitat for this species. Tidal current is the major component of the Yellow Sea hydrodynamic system, and its periodic variations influence the local ecological conditions and related ecosystems, particularly in the YSCWM, which is stratified in summer. To investigate the influence of tidal currents on Pacific cod growth, otolith daily increment in young‐of‐the‐year (YOY) Pacific cod in the Yellow Sea was analyzed in 2017. These data were integrated with a simulated tidal current using a multi‐scenario time‐delay analysis. This showed that: (1) the otolith daily increment exhibited a strong signal similar to the fortnightly tidal variation; (2) there was a lag of ∼8 days between the highest growth rate induced by the tidal current variation and monthly spring tide; and (3) the influence of the tidal current on otolith daily growth was stronger after migration of the cod into the YSCWM, particularly during the settlement stage. Given the stratified ocean structure during the over‐summering period, enhanced tidal mixing during the fortnightly spring tide would improve the exchange of nutrients and oxygen within the YSCWM, and lead to a delayed response of otolith growth due to feeding/digestion and subsequent growth. Therefore, variations in the tidal current have a marked positive ecological effect on the growth of YOY Pacific cod, and ultimately on the YSCWM ecosystem.

A Dynamic Stress-Scape Framework to Evaluate Potential Effects of Multiple Environmental Stressors on Gulf of Alaska Juvenile Pacific Cod

Quantifying the spatial and temporal footprint of multiple environmental stressors on marine fisheries is imperative to understanding the effects of changing ocean conditions on living marine resources. Pacific Cod(Gadus macrocephalus), an important marine species in the Gulf of Alaska ecosystem, has declined dramatically in recent years, likely in response to extreme environmental variability in the Gulf of Alaska related to anomalous marine heatwave conditions in 2014–2016 and 2019. Here, we evaluate the effects of two potential environmental stressors, temperature variability and ocean acidification, on the growth of juvenile Pacific Cod in the Gulf of Alaska using a novel machine-learning framework called “stress-scapes,” which applies the fundamentals of dynamic seascape classification to both environmental and biological data. Stress-scapes apply a probabilistic self-organizing map (prSOM) machine learning algorithm and Hierarchical Agglomerative Clustering (HAC) analysis to produce distinct, dynamic patches of the ocean that share similar environmental variability and Pacific Cod growth characteristics, preserve the topology of the underlying data, and are robust to non-linear biological patterns. We then compare stress-scape output classes to Pacific Cod growth rates in the field using otolith increment analysis. Our work successfully resolved five dynamic stress-scapes in the coastal Gulf of Alaska ecosystem from 2010 to 2016. We utilized stress-scapes to compare conditions during the 2014–2016 marine heatwave to cooler years immediately prior and found that the stress-scapes captured distinct heatwave and non-heatwave classes, which highlighted high juvenile Pacific Cod growth and anomalous environmental conditions during heatwave conditions. Dominant stress-scapes underestimated juvenile Pacific Cod growth across all study years when compared to otolith-derived field growth rates, highlighting the potential for selective mortality or biological parameters currently missing in the stress-scape model as well as differences in potential growth predicted by the stress-scape and realized growth observed in the field. A sensitivity analysis of the stress-scape classification result shows that including growth rate data in stress-scape classification adjusts the training of the prSOM, enabling it to distinguish between regions where elevated sea surface temperature is negatively impacting growth rates. Classifications that rely solely on environmental data fail to distinguish these regions. With their incorporation of environmental and non-linear physiological variables across a wide spatio-temporal scale, stress-scapes show promise as an emerging methodology for evaluating the response of marine fisheries to changing ocean conditions in any dynamic marine system where sufficient data are available.

Fine-scale variability in otolith chemistry: Application to the life history analysis of Pacific cod (Gadus macrocephalus) in the Yellow Sea

The Yellow Sea is the southwestern limit of the distribution of Pacific cod (Gadus macrocephalus), a typical cold water and commercially important fish in the North Pacific. The catch of Pacific cod in the Yellow Sea has increased gradually in recent years, and has received substantial attention. To explore the use of otolith chemistry in the characterization of different spawning grounds and crucial life history events, a total of 60 specimens of Pacific cod were obtained from October 2016 to August 2017. The contents of barium (Ba) and strontium (Sr) in otoliths from the core to the edge along the ventral side were determined using laser ablation-inductively coupled plasma-mass spectrometry. Based on hierarchical cluster analysis (HCA), the specimens were assigned to two groups based on the ratio of Ba:Ca at the core. The various patterns of core-to-edge Ba:Ca inferred using a linear mixed-effect (LMM) model suggested differences in the spawning ground environments for Pacific cod in the Yellow Sea, and step changes found in the Sr:Ca ratio, and a corresponding check observed in otolith images suggest that the settlement of Pacific cod occurred approximately 80–120 days after hatching. The nature of the data prevents firm conclusions being drawn from the data available at present, but the significant differences in certain elements among individuals and the association with crucial life history events in Pacific cod are noteworthy.

Community-level economic impacts of a change in TAC for Alaska fisheries: A multi-regional framework assessment

A marine heatwave caused the total biomass of Gulf of Alaska (GOA) Pacific cod to plummet by 67% from 2015 to 2018. Based on the results from GOA Pacific cod stock assessment model, the North Pacific Fishery Management Council cut the GOA Pacific cod total allowable catch (TAC) by 80% in 2018. This study uses a 10-region multi-regional social accounting matrix model to compute the economic impacts of the cod fishery disaster on the six borough and census areas (BCAs) in Southwest Alaska plus effects on the other four regions. We consider both the negative effects of the reduction in the cod harvest and the offsetting effects from an observed increase in the price of the fish to calculate the “net” economic impacts. This study found that the offsetting effects from the price increase are significant; the reduction in total regional output in the rest of the United States is 15% less severe if effects of the price changes are taken into account. Furthermore, the region suffering the largest impacts on total seafood industry output (Aleutians East Borough) from the reduced TAC is not necessarily the region where the largest total regional impact occurs (rest of the U.S.).

Contrast of warm and cold phases in the Bering Sea to understand spatial distributions of Arctic and sub-Arctic gadids

The influence of climate on the dynamics of Arctic gadids is of increasing interest, particularly as research and survey effort expands in the Pacific Arctic. Understanding species-specific thermal tolerance may inform models of species distribution and projections of available habitat and also clarify implications of warming for ecological communities. Analyzing shifts in species distribution in warm and cold periods, this study considers the effects of a warming climate on the distribution of two keystone Arctic gadids (polar cod, saffron cod) and two commercially important sub-Arctic gadids (walleye pollock, Pacific cod). Shifts in distribution were used to derive temperature tolerance thresholds and to project how these species might react to a warming Arctic. Significant shifts were noted in comparisons of warm (2002–2005, 2014–2016, 2017–2018) and cold (2006–2013) periods. Sub-Arctic species expanded and contracted their range as environmental conditions shifted. In contrast, Arctic species appeared constrained, such that population densities increased or decreased within the same core geographic area. Additionally, species with a demersal life history were able to tolerate a wider range of thermal conditions. These results provide important insights on relative thermal tolerance of each species, differential influence of temperature on pelagic versus demersal life histories, and depth as thermal refuge. This study demonstrates both the need to understand the spatial response of fish to changing ocean conditions in polar regions and the utility of distributional analyses to inform that effort.

Modern specialized fishery of sea fish in the western Bering Sea

The shelf and continental slope of the western Bering Sea, being among the most productive areas of the Far-Eastern Seas of Russia, became exploited by commercial fishery half a century ago, after introduction of 200-mile exclusive economic zones in 1977 and relocation of the Russian fishing fleet from the eastern Bering Sea to its western part. In 2010-2019, about 20 % of the total catch of sea fish in the Far-Eastern basin (excluding pacific salmons) were caught in the West Bering Sea fishery zone. Among the fishery districts of the Russian Far East, this area is currently the 1st one by annual catch of pacific cod, grenadiers, sculpins and sablefish, 2nd— by catch of walleye pollock, halibuts and skates, 3rd— by catch of rockfishes, and 4th— by catch of pacific herring and flounders. Features of specialized fishery in the West Bering Sea fishery zone in 2010-2019 are clarified. Now 48 types of the specialized fishery can be distinguished here, while 96.3 % of the average annual landing is provided by the following 8 most important types: walleye pollock midwater trawl fishery (77.8 % of mean annual catch); pacific herring midwater trawl fishery (6.1 %); pacific cod bottom longline fishery (4.7 %); walleye pollock Danish seine fishery (2.7 %); grenadiers bottom longline fishery (2.4 %), pacific cod Danish seine fishery (0.9 %); squids bottom trawl fishery (0.9 %); and pacific cod bottom trawl fishery (0.8 %). All these types of fishery are highly specialized and portion of the target objects in the catches ranges from 76 to 96 % (according to official statistics), while the by-catch accounted as 4-24 %. The is no specialized fishery on such objects as rockfishes, arrowtooth and kamchatka flounders, and sablefish in the West Bering Sea fishery zone, but they are landed as by-catch. The fishery statistics with the data sorting to specialized fishery and by-catch can be used quite effectively for the stocks assessment and determining acceptable level of their exploitation, with recommendations for fishery regulation, including evaluation the possible level of non-specialized by-catch.

Modern state of stocks for demersal and pelagic fishes on the shelf of Olyutorsky-Navarin area

Stocks of demersal and pelagic fish species are assessed for the bottom layer over the outer shelf and upper continental slope between Cape Olyutorsky and Cape Navarin (northwestern Bering Sea) on the data of bottom trawl survey conducted aboard RV Professor Levanidov over the isobaths 20-400 m in the summer of 2019. The total biomass of demersal fish in the surveyed polygon was estimated as 682,262 t; the portion of pacific cod was 51.50 %, arrowtooth flounder — 9.80 %, great sculpin — 9.64 %, rock sole — 4.60 %, alaska skate — 4.57 %, flathead flounders — 2.56 %, yellow irish lord — 2.30 %, and < 2 % for other species. The total biomass of pelagic fish species in the bottom layer was estimated as 759,639 t (species-specific coefficients of catchability were used); the portion of adult walleye pollock was 85.12 %, its juveniles — 9.94 %, pacific herring — 4.67 %, and other pelagic species — 0.27 % in sum. Mean ratios of the species stock between the surveyed polygon and other areas of the northwestern Bering Sea, as the Gulf of Anadyr and the deeper continental slope (below 400 m), were evaluated using the data of bottom trawl surveys conducted in 2005-2017. Some species as yellow irish lord, saffron cod, pacific halibut, arrowtooth flounder, great sculpin, kamchatka flounder, rock sole, and aleutian skate distributed mostly within the polygon and their mean biomass in the outside areas varied from 0.5 % to 69.2 % relative to the biomass in the polygon surveyed in 2019. On the contrary, the portions of pacific cod, greenland halibut, alaska skate, and walleye pollock were larger outside the polygon — from 102.9 to 190.4 %, and almost entire stocks were in the outside areas for alaska plaice, flathead flounders, and pacific herring — from 533.4 % to 1380.5 % relative to the biomass accounted within the polygon. The stocks assessed in 2019 reflected both the state of populations and their spatial and bathymetric redistribution, mostly because of the St. Lawrence Cold Water Pool shrinkage at the bottom of the Gulf of Anadyr. The stocks fluctuations are reasoned mainly by natural factors, rather than fishery impact.