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The degree to which walleye pollock (Gadus chalcogrammus , hereafter pollock) move between the US and Russian zones of the Bering Sea is a key source of uncertainty for fisheries management. To study transboundary migrations across the US–Russia maritime boundary and explore how climate variability might influence these migrations, four seafloor-mounted echosounder moorings were deployed from July 2019 to August 2020 in the northwestern Bering Sea. The observations indicated that a substantial amount of pollock moves between the US and Russia seasonally, with a period of southeast movement into the US as winter as sea ice forms and northwest movement into Russia in early summer as waters warm. Over the deployment period, 2.3-times more pollock backscatter moved into the US zone in fall and winter than exited the subsequent spring and summer. We hypothesize that the difference in the net movement between regions was driven by pollock moving farther into Russia during the historically warm conditions at the start of deployment period and reduced northwest return migration the following summer when temperatures were relatively cooler. This supports the hypothesis that temperature affects pollock distribution, and that continued warming will lead to a larger proportion of the stock in Russian waters. [ABSTRACT FROM AUTHOR]

The purpose of this research was to explore the impact of collagen peptides derived from cod (Gadus) skin on H2O2-induced 2BS senescence cells. The senescence model induced by H2O2 was established to determine the cell proliferation rate, ROS level, cell apoptosis, and peroxidase content after the intervention of the optimal dose of collagen peptides. Collagen peptides effectively suppressed apoptosis in 2BS senescence cells, substantially decreasing ROS and MDA levels. Furthermore, SOD and CAT activities were significantly elevated. In summary, collagen peptides have demonstrated a significant capacity to impede the process of cellular senescence in 2BS cells through the reduction of oxidative stress and apoptosis. [ABSTRACT FROM AUTHOR]

Recent summer surveys of the northeastern Chukchi Sea found pelagic fishes were dominated by large numbers of age-0 Arctic cod (Boreogadus saida , Gadidae) and walleye pollock (Gadus chalcogrammus , Gadidae), while adult fishes were comparatively scarce. The source and fate of these young fishes remain unclear, as sampling in this region is impeded by seasonal ice cover much of the year. Seafloor-mounted echosounders were deployed at three locations in the northeastern Chukchi Sea from 2017 to 2019 to determine the movement and seasonal variability of these age-0 gadids. These observations indicated that the abundance of pelagic fishes and community composition on the Chukchi Sea shelf were highly variable on seasonal time scales, with few fish present in winter. Tracking indicated that fish movements were strongly correlated with local currents. Fishes were primarily displaced to the northeast in summer and fall, with periodic reversals towards the southwest driven by changes in regional wind patterns. The flux of fishes past the moorings indicated that the prevailing northward currents transport a large proportion of the age-0 pelagic fishes present on the Chukchi shelf in summer to the northeast by fall, leading to relatively low abundances of age-1+fishes in this environment. [ABSTRACT FROM AUTHOR]

The phylogeographic analysis of Gadus chalcogrammus from the Asian part of the range (the western part of the Bering Sea, the Sea of Okhotsk and the Sea of Japan, the Pacific waters of the Kuril Islands and Kamchatka) based on data on the polymorphism of the mtDNA control region fragment (D-loop, 526 bp) was performed for the first time using large-scale material (1162 individuals from 38 samples). The obtained results indicate the existence of two large groups in the surveyed water area: one is localized in the western part of the Bering Sea, and the other is formed by samples from the Sea of Japan and the Sea of Okhotsk and from the Pacific waters of the Kuril Islands and Kamchatka. An unusually low level of polymorphism in the mtDNA control region of Gadus chalcogrammus was revealed, which was also previously found in G. macrocephalus and is probably due to similar microevolutionary processes that took place in the past in both species. [ABSTRACT FROM AUTHOR]

Summary: Gadus morhua, Gadus chalcogrammus and Melanogrammus aeglefinus represent the most frequently found Gadiformes species on Chinese market. While the phenotypic similarities and the absence of morphological features after production process make the visual identification a challenging task, paving the way for species mislabelling. The present study aimed to develop a novel one‐step triplex high‐resolution melting (HRM) analysis for rapid authentication of G. morhua, G. chalcogrammus and M. aeglefinus, targeting the mitochondrial cytochrome coxidase I, cytochrome b and NADH dehydrogenase subunit 2 genes, respectively. Results highlighted high specificity of the designed primers for each species. The triplex HRM assay allowed the full discrimination among G. morhua, G. chalcogrammus and M. aeglefinus, with high levels of confidence. Methodology validation succeeded on commercial products, proving the suitability of the one‐step triplex HRM assay for rapid identification of G. morhua, G. chalcogrammus and M. aeglefinus. [ABSTRACT FROM AUTHOR]

The North Pacific marine heatwave of 2014–2016 (nicknamed "The Blob") impacted marine ecosystems from California to Alaska, USA, with cascading effects on fisheries and fishing communities. We investigated the effects of this anomalous ocean warming on early life stages of walleye pollock (Gadus chalcogrammus) in the Gulf of Alaska. In spring of 2015, pollock larvae were caught at record low levels relative to a 30‐year time series. Survival rates were low during the summer, and by late summer, numbers were further reduced, with very low abundances of juvenile (age‐0) pollock. Our analyses suggested multiple mechanisms for this decline: (a) Low‐saline conditions may have impacted egg buoyancy and survival; (b) population densities of zooplankton nauplii may have been too low to support first‐feeding larvae; (c) body condition of age‐0 pollock was poor and a bioenergetics model indicated that reduced quality of zooplankton prey, coupled with warmer temperatures, increased the ration required for positive growth by up to 19%, at a time when prey abundance was likely reduced. Thus, walleye pollock experienced a cascade of poor conditions for growth and survival through early life stages, resulting in the near disappearance of the 2015 year class in the population by the end of their first year. These impacts differ from previous warm years and emphasize the importance of looking beyond simple temperature–abundance relationships when predicting species responses to climate warming. [ABSTRACT FROM AUTHOR]

Drift of propagules occurs within many populations inhabiting flow fields. This affects the number of propagules that rejoin their source population (recruitment) and plays a role in adaptive spatial redistribution. We focus on the cause and consequence of interannual variation in geographic distribution of population density among five cohorts of young‐of‐the‐year (age‐0) juvenile walleye pollock Gadus chalcogrammus in the western Gulf of Alaska (GOA). The coastal GOA is a wind‐driven advective system. Walleye pollock spawn during spring and their eggs and larvae drift southwestward; by late summer, age‐0 juveniles are variously distributed over the shelf. We found that high population densities of age‐0 juveniles (ca. 6 months old) near the southwestward exit of the Alaska Coastal Current from the GOA corresponded with high abundance of larvae from the major spawning area upstream, but did not translate into high abundance at older ages. Further, offshore and upwelling‐favorable winds were associated with the high downstream abundance and presumed export. In contrast, downwelling‐favorable (northeasterly) wind during and shortly after spawning (April–May) was associated with high recruitment at age 1. Finally, we found that recruitment also increased with apparent retention of age‐0 juveniles in favorable habitat upstream near the main spawning area. We hypothesize that wind‐related retention in superior upstream habitat favors recruitment. Our results argue for including wind‐driven transport in future walleye pollock recruitment models. We encourage more work on the juvenile stage of marine fishes aimed at understanding how transport and species‐specific habitat suitability interact to affect population response to large‐scale forcing. [ABSTRACT FROM AUTHOR]

Climate change in Arctic and sub-Arctic seas is leading to rapid changes in the dispersal potential of marine organisms. In Alaskan waters, loss of sea ice and salinity changes associated with warming may have a strong effect on the distribution and survival of eggs and larvae of key fish species at the Pacific–Arctic interface, such as polar cod (Boreogadus saida) in the Chukchi Sea and walleye pollock (Gadus chalcogrammus) in the northern Bering Sea. We conducted laboratory experiments to investigate how changes in ontogeny and salinity influenced the buoyancy and survival of eggs and larvae of these and two other gadids (Pacific cod, Gadus macrocephalus and saffron cod, Eleginus gracilis). Polar cod egg density varied among family groups, but eggs were more buoyant than those of walleye pollock overall. Eggs of both species followed a typical pattern of increasing density early in development. After hatching, polar cod and walleye pollock larvae were similar in density, and were notably more buoyant than the larvae of species with demersal eggs (Pacific cod and saffron cod). Larvae of the two Arctic species (polar cod and saffron cod) were less sensitive to salinity challenges than the sub-Arctic gadids, but polar cod became more sensitive at 6 weeks post-hatch. These results highlight possible adaptations of polar cod to ensure that their eggs are positioned under or near ice after spawning so that larvae hatch in productive surface waters during ice break-up. A comparison of modeled seawater densities to egg densities during the post-spawning period suggests that walleye pollock eggs would only be in contact with seasonal sea ice on the northern edge of their distribution at latitudes above ~ 63 °N. The synergic effects of environmental variables on vertical distribution of eggs and their survival potential will be important biogeographic mechanisms to consider with climatic warming and continued loss of sea ice. [ABSTRACT FROM AUTHOR]

Introdução: A polaca do Alasca, considerada a espécie de pescado marinho mais capturada mundialmente, é importada pelo Brasil como filés congelados. Apresenta uma fauna parasitária própria, porém a presença desses parasitos na musculatura pode causar implicações na segurança alimentar e repugnância. Objetivo: Este trabalho teve como objetivos investigar e relatar a presença de grupos parasitários em amostras comerciais de filés congelados de polaca do Alasca, considerando o potencial de risco à saúde humana e métodos de controle. Método: Foram analisadas 44 amostras de filés congelados de polaca do Alasca coletadas do comércio varejista da região metropolitana de São Paulo e as formas larvares foram isoladas por dissecção e observadas em microscópio estereoscópico e óptico. Resultados: Foram encontrados 133 parasitos mortos em 68% das amostras. Os cestódeos da ordem Trypanorhyncha foram detectados com maior frequência (88%), seguidos de nematódeos do grupo dos anisaquídeos (Anisakidae/Raphidascarididae) (11%) e acantocéfalo (1%). Dentre eles, os anisaquídeos apresentam potencial zoonótico, se ingeridos vivos, e alergênico mesmo após processamento térmico. Conclusões: Trata-se do primeiro relato da presença de formas parasitárias em amostras comerciais de filés de polaca do Alasca e os resultados alertam para a necessidade de melhorias com relação às boas práticas na cadeia produtiva e de maior atenção sobre o potencial alergênico relacionado ao consumo desses parasitos nos filés de peixes congelados.

The contents of 1056 stomachs were included in a trophic‐guild analysis to document separation amongst 16 groundfish species inhabiting Pacific herring Clupea pallasii and walleye pollock Gadus chalcogrammus nursery fjords in Prince William Sound, Alaska and to determine the relative contribution of C. pallasii and G. chalcogrammus to that separation. A total of five multi‐species feeding guilds and one outlier species were determined through multivariate analyses. Major gradients of trophic separation spanned from invertebrates (mostly shrimps, crabs and unidentified decapods) to fishes (mostly unidentified fishes, C. pallasii and G. chalcogrammus) a pattern that was influenced by intra and interspecific differences in predator lengths. While C. pallasii and G. chalcogrammus were important to the overall guild structure, within‐guild similarities were consistently highest due to unidentified fishes. In general, larger predators consumed the largest C. pallasii and G. chalcogrammus, with the smaller‐on‐average predators consuming smaller C. pallasii and fewer or smaller G. chalcogrammus. Regardless of guild inclusion, groundfishes primarily consumed pre‐recruit C. pallasii and G. chalcogrammus (i.e., younger than age 3 years fishes), which has the potential to negatively influence recruitment of these forage fishes to the adult, spawning population. [ABSTRACT FROM AUTHOR]

Walleye pollock (Gadus chalcogrammus) is one of the popular fish species in Korea and known to frequently harbor anisakid nematodes. Despite many papers regarding walleye pollock having been published, there is no information on the prevalence and distribution of anisakid nematodes from walleye pollock in Korean waters. We investigated 716 walleye pollock caught from Goseong, the East Sea of the Korean Peninsula during May 2015-December 2016. In total, 1,085 nematodes were collected and subsequently identified by PCR-RFLP analysis of internal transcribed spacer region of ribosomal DNA. The prevalence and mean intensity of anisakid nematodes was 63.6% (68/107) and 4.4 larvae/fish (297/68) in samples of 2015, and 21.5% (131/609) and 6.0 larvae/fish (788/131) in samples of 2016. The most abundantly isolated anisakid nematode was Anisakis simplex (Rudolphi, 1809) (73.5%, 798/1,085), followed by Contracaecum osculatum (Rudolphi, 1802) (3.1%, 34/1,085), Hysterothylacium aduncum (Rudolphi, 1802) (2.9%, 31/1,085), Anisakis pegreffii (Campana-Rouget and Biocca, 1955) (1.4%, 15/1,085), and a hybrid genotype (0.4%, 4/ 1,085). The mitochondrial DNA cox2 gene sequences of randomly selected A. simplex showed the highest similarity (99.5%-98.8%) with those from chub mackerel (Scomber japonicus) in Japan or from chum salmon (Oncorhynchus keta) in Korea. The mtDNA cox2 gene sequences of C. osculatum showed the highest similarity (99.0%) with those from bearded seals in Japan. All of these results give us clues to the geographical distribution, migration route and prey items of walleye pollock caught off Korea. Further extensive analyses will be necessary to get more information on the biology of Korean walleye pollock. [ABSTRACT FROM AUTHOR]

Differences in zooplankton populations in relation to climate have been explored extensively on the southeastern Bering Sea shelf, specifically in relation to recruitment of the commercially important species walleye pollock (Gadus chalcogrammus). We addressed two research questions in this study: (i) Does the relative abundance of individual copepod species life history stages differ across warm and cold periods and (ii) Do estimated secondary production rates for copepods differ across warm and cold periods? For most copepod species, warmer conditions resulted in increased abundances in May, the opposite was observed in colder conditions. Abundances of smaller-sized copepod species did not differ significantly between the warm and cold periods, whereas abundances of larger-sized Calanus spp. increased during the cold period during July and September. Estimated secondary production rates in the warm period were highest in May for smaller-sized copepods; production in the cold period was dominated by the larger-sized Calanus spp. in July and September. We hypothesize that these observed patterns are a function of temperature-driven changes in phenology combined with shifts in size-based trophic relationships with primary producers. Based on this hypothesis, we present a conceptual model that builds upon the Oscillating Control Hypothesis to explain how variability in copepod production links to pollock variability. Specifically, fluctuations in spring sea-ice drive regime-dependent copepod production over the southeastern Bering Sea, but greatest impacts to upper trophic levels are driven by cascading July/September differences in copepod production. [ABSTRACT FROM AUTHOR]

Baseline surveys of offshore pelagic fishes in the eastern Chukchi Sea in 2012 and 2013 found that age-0 Arctic cod (Boreogadus saida) dominated the pelagic fish community in summer, with relatively few adults present in the region. Since this time, drastic changes in the ocean-atmosphere-ice feedback loop have led to continued warming, further reducing ice cover, and increased northward transport has led to an increase in Pacific-origin waters on the Chukchi shelf in summer. To examine potential bottom-up effects of these environmental changes on pelagic fishes in this rapidly changing environment, we extended a time series of large-scale acoustic-trawl surveys with additional surveys in 2017 and 2019. Age-0 Arctic cod were the most abundant pelagic fish in all four survey years, comprising 68–93% of fish abundance. However, age-0 walleye pollock (Gadus chalcogrammus), which were scarce (<0.1% of fishes) and confined to the southern Chukchi in 2012 and 2013, were present in high abundance (>21% of fish abundance) throughout the Chukchi shelf in 2017 and 2019. Age-0 Arctic cod were substantially more abundant in 2017 than in other years, possibly due to increased survivorship of larvae under warm conditions. Unlike in 2017, Arctic cod and pollock were spatially separated in 2019 due to enhanced transport, with Arctic cod primarily present in the northeastern portion of the survey area, which was characterized by cool surface and bottom temperatures. The substantial increase in abundance of age-0 pollock in recent years suggests that environmental conditions now allow this species to extend its northern range into the southern and central Chukchi Sea, at least on a seasonal basis. The changes in abundance and species composition of pelagic fishes in the 2012–2019 time series are tightly coupled to recent changes in sea ice, temperature, and the increasing transport of Bering Sea waters through Bering Strait into the Chukchi Sea. Given that the environment is expected to experience further warming and increased transport, these northward shifts in species distribution are likely to persist in the future. [ABSTRACT FROM AUTHOR]

Changes to physical and chemical oceanographic structure can lead to changes in phytoplankton biomass and growth, which, in-turn, lead to variability in the amount of energy available for transfer to higher trophic levels (e.g., forage fish). In general, age-0 (juvenile) walleye pollock ( Gadus chalcogrammus ) have been shown to have low fitness (determined by energy density and size), in warm years compared to average or cold years in the southeastern Bering Sea. Contrary to these findings, the year 2007 was a cold year with low fitness of age-0 pollock compared to the transition year of 2006 (transitioning from warm to cold conditions) and cold years, 2008–2011. In late summer/early fall (mid-August through September), significantly lower surface silicic acid concentrations coupled with low phytoplankton production and chlorophyll a (Chl a ) biomass were observed in 2007 among 2006–2012 ( P <0.05). We postulate that the low silicic acid concentrations may be an indication of reduced surface nutrient flux during summer, leading to low primary productivity (PP). The nutrient replenishing shelf/slope water exchange that occurred during late October–February (2006–2007) indicates that deep-water nutrient/salinity reserves for the start of the 2007 growing season were plentiful and had similar concentrations to other years (2006–2012). The spring bloom magnitude appeared to be slightly below average, and surface silicic acid concentrations at the end of the spring bloom period in 2007 appeared similar to other years in the middle domain of the southeastern Bering Sea. However, during summer (June–August) 2007, high stratification and the low number of storm events resulted in low flux of nutrients to surface waters, indicated by the low surface silicic acid concentrations at the end of summer (mid-August through September). Surface silicic acid may be useful as an indicator of surface nutrient enrichment (and subsequent PP) during summer since other macronutrients (e.g. nitrate) are usually near or below detection limits at this time, and diatoms are generally scarce during summer. Surface silicic acid concentration was also positively associated with the size of juvenile fish (age-0 pollock weight and length). This reinforces the theory that nutrient availability and primary productivity are important to energy allocation for higher trophic levels during summer, and possibly provides links between stratification and wind mixing, surface nutrient input, PP and juvenile fish size and condition. [ABSTRACT FROM AUTHOR]

Euphausiids are an important component of the eastern Bering Sea marine ecosystem. We synthesized information on the ecological roles of two species, Thysanoessa raschii , which predominates over the Middle and Inner Shelf Domains, and Thysanoessa inermis , which predominates over the Outer Shelf Domain. Although estimates of euphausiid biomass across the shelf are not well constrained, we estimated that, between April and July, 2004–2010, euphausiid biomass was 3.08–5.25 g C m −2 on the outer shelf and 1.95–3.92 g C m −2 on the middle shelf. Modeled estimates of euphausiid production, for spring and summer combined, varied between 0.043 g C m −2 d −1 and 0.051 g C m −2 d −1 , depending on location, with a mean of 0.048 g C m −2 d −1 . Recently reported field measurements of annual primary production over the southeastern Bering Sea in 2008–2009 vary between 0.06 and 6.65 g C m −2 d −1 , with a mean of 1.262 g C m −2 d −1 ±2.049 g C m −2 d −1 in spring and summer combined, a level sufficient to support euphausiids, at least on an annualized basis. Walleye pollock ( Gadus chalcogrammus, hereafter pollock) is the single most important consumer of euphausiids over the eastern Bering Sea shelf. We estimated that pollock consumed between 0.0042 and 0.019.7 g C m −2 d −1 of euphausiids, depending on year, with a mean of 0.011 g C m −2 d −1 in summer averaged over 1999–2009. This consumption is equivalent to between 17% and 29% of summer euphausiid production, depending on location. Over the period for which data were available (2004–2012), we observed a strong negative relationship between euphausiid biomass as determined in acoustic surveys and pollock biomass as estimated in the eastern Bering Sea pollock stock assessment ( r 2 =0.82). During this time period, sea-surface temperature was the second strongest predictor of euphausiid biomass, ( r 2 =0.63). However, for the period 2004–2010, bottom temperature ( r 2 =0.94) was the strongest predictor, followed by pollock biomass from the pollock stock assessment ( r 2 =0.82), and sea-surface temperature ( r 2 =0.81). Mean pollock density in the acoustic surveys was not a powerful predictor of euphausiid biomass during either period. In spatially explicit multiple regression analyses for the periods 2004–2012 and 2004–2010 those formulations that included sea-surface and bottom temperatures as well as survey estimates of pollock had the greatest explanatory value. However, when either or both temperature terms were dropped, the explanatory value of the models dropped considerably. When pollock biomass was dropped from the models, there was little change in explanatory value compared to the full model. Euphausiid production and pollock consumption data coupled with a negative relationship between euphausiid biomass and stock assessment estimates of pollock biomass indicate a top-down predation effect. However, strong negative relationships between euphausiid biomass and water temperatures indicate the influence of a bottom-up mechanism. The apparent differences in these results may relate to the different spatial and temporal scales used to assess the pollock biomass used in the analyses. Alternatively, euphausiid biomass may be strongly controlled during a restricted portion of the year, such as spring, if critical food needs are not met in some years. We lack the data necessary to resolve these alternative hypotheses. [ABSTRACT FROM AUTHOR]

The performance of midwater trawls used during acoustic surveys for walleye pollock ( Gadus chalcogrammus ) was estimated using a novel method of combining acoustic and catch information. Direct comparisons of acoustic and catch derived density showed a poor correlation between the two ( r 2 = 0.07), suggesting this discrepancy might be in part due to trawl performance. Trawl efficiency and selectivity were determined by comparing acoustically derived fish density within the trawling volume with catch-based density in a modeling framework. Additional factors thought to potentially influence trawl performance, consisting of environmental conditions including water temperature, bottom and fishing depth, variables relating to survey methodology including survey vessel, codend liner, and the time of day when trawling occured, and fish population characteristics including spawning state and condition factor were evaluated in the models. Incorporating efficiency and selectivity parameters resulted in improved model fits, as did the addition of explanatory variables. Efficiency was found to be associated with the proportion of spawning fish in the catch, water temperature, and the time of day, while selectivity appeared to be influenced by condition factor and the survey vessel used. The acoustic-catch modeling approach confers advantages of making available large historic datasets where acoustic data was collected during trawling and providing sufficient contrasts in parameters of interest not easily achieved with direct trawl performance experiments. [ABSTRACT FROM AUTHOR]

We used genetic techniques to identify gadids (cods) to species in the Pacific Arctic during a time of substantial physical change in the marine ecosystem between 2012 and 2019. The dominant fish species in the Chukchi Sea is Arctic Cod (Boreogadus saida); however, other gadids such as Saffron Cod (Eleginus gracilis), Pacific Cod (Gadus macrocephalus) and Walleye Pollock (Gadus chalcogrammus) have been observed. Two aims in this study were to evaluate the accuracy of at sea morphological identification (which can be difficult for juveniles) with genetic species identification and to document potential variation in species composition and distribution of gadids in the Pacific Arctic in response to changing environmental conditions. Microsatellite and mtDNA genetic results revealed that most B. saida collected in the Chukchi Sea in 2012 and 2013 were correctly identified at sea. Conversely, genetic results from samples collected in 2017 and 2019 revealed a large number of G. chalcogrammus and some G. macrocephalus and E. gracilis that were initially identified at sea as B. saida. The majority of misidentification occurred between B. saida and G. chalcogrammus. This study indicates a northward shift of G. chalcogrammus and B. saida during warmer conditions. In addition, juvenile Polar Cod (A. glacialis), which is not typically found in the Chukchi Sea and was not identified at sea, was genetically detected on 3 hauls on the northern Chukchi Shelf, outside of its documented distribution. Accurate species identification, especially during a time of changing marine landscapes, is not only important for survey abundance estimates but for downstream analyses as well. This emphasizes the value of implementing strategies for correct identification of the gadid species to better capture and monitor responses to varying and likely changing conditions. Our results provide strong evidence of distributional shifts and range expansions of gadid species in the Arctic, which may be the result of changing climactic conditions. [ABSTRACT FROM AUTHOR]

To identify the factors that influence the growth rate of flathead flounder Hippoglossoides dubius in Funka Bay, Japan, we studied temporal changes in the growth of this species and its prey from 1989 to 2012. The lowest growth rate of H. dubius was recorded in the 1995 year-class, which had experienced severe hypoxia between 1995 and 1997. However, the highest growth rate was recorded in the 2007 year-class, which had experienced hypoxia between 2009 and 2011. In 2000 and 2001, small-sized flounder (<200 mm TL) from the 1995 year-class were feeding on mysidaceans, whereas those from other year-classes fed on small Ophiura spp. (<9 mm in disc diameter) in 2009, 2011, and 2012. Small Ophiura spp. were more abundant in 2007 and 2011 than in 2002 and 2003. Successful recruitment of Ophiura spp. took place between 2007 and 2011 and cohorts from these years could tolerate hypoxia. This suggests that food availability improved under hypoxic conditions, which led to improved growth in small flounders. Large flounders (≥200 mm TL) from all year-classes fed on prickleback fishes (Stichaeidae) and walleye pollock Gadus chalcogrammus juveniles. The growth of large flounders was enhanced by an increase in the abundance of Stichaeidae fishes and G. chalcogrammus juveniles. [ABSTRACT FROM AUTHOR]

Ursvik et al. compared the complete mitochondrial DNA (mtDNA) genome sequences of Walleye Pollock (Gadus ( = Theragra) chalcogrammus) from the Pacific Ocean with a pair of fish from an isolated population of Norwegian pollock in the Barents Sea. They concluded that the Norwegian population was recently introduced from the Pacific. We test this hypothesis within a temporal framework provided by a phylogeographic analysis of complete genomes from the pollocks' sister species, Atlantic Cod (Gadus morhua), and their divergence 3.5 mya. Pollock have a coalescent ancestor 189 ± 25 kya. The two Norwegian fish have a common ancestor 87 ± 7 kya, which suggests an ancient origin rather than a recent human-mediated introduction. Mitochondrial genomic biodiversity in pollock antedates the most recent glacial cycle. The clade structure of the whole-genome tree indicates that previously described single-locus mtDNA haplotypes and haplogroups are typically paraphyletic. [ABSTRACT FROM AUTHOR]