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Changes to Earth's climate affect organisms globally; in marine systems, these impacts are seen through warming water temperatures, ocean acidification, hypoxia and frequent marine heatwaves. These effects may lead to the movement of species to more favourable conditions. While climate‐driven movement is well studied at the adult stage, how the early life stages of marine fish will respond to future variability is less clear. Many fish species are constrained by specific spawning locations or phenology. Spawning in certain locations allows for local retention of offspring, while precise timing can facilitate transport of offspring to nursery locations through seasonal circulation patterns. Our research investigates how changing oceans impact the location and timing of spawning of Bering Sea groundfishes over the next century. We used ROMS SST and SSS model output and NOAA survey data in species distribution models to hindcast and project distributions and centre of gravity for eggs and larvae of six groundfish species. Our analyses found that most of our study species exhibit flexible geography. However, the speed and direction of egg and larval movement did not track the speed and direction of their respective thermal niches. Hence, the projected distributional patterns of adult stages may be limited by their early life stages. This response is likely to be mirrored globally by other species with planktonic eggs and larvae. These results indicate that life history considerations are critical for the management of commercially important species, as effects on early life stages are strongly connected to the success or failure of adult populations. [ABSTRACT FROM AUTHOR]

Abstract Between 2001 and 2013 the southeastern Bering Sea alternated between multi-year periods of relatively warm (2001–2005) and relatively cold (2007–2013) years. Adult Flathead Sole Hippoglossoides elassodon in the southeastern Bering Sea shift their spatial distribution pattern in relation to bottom water temperature indicating the importance of the thermal environment in determining fish habitat. The objective of this study was to infer Flathead Sole spawning area in the southeastern Bering Sea in May from ichthyoplankton surveys of their eggs using generalized additive models to assess how warm (2002, 2003, and 2005) and cold (2008, 2009, 2010, and 2012) years affected the location of their spawning site. Three mechanisms through which temperature could affect egg distribution were investigated: 1) additively, assuming a similar effect of temperature across the spatial domain, 2) as a spatially variable term, assuming that the effect of temperature changes across locations, and 3) as a threshold effect on the spatial distribution of eggs, assuming the distribution of eggs changes abruptly in relation to the annual average temperature. The model including temperature as a spatially variable effect had the smallest AIC score and therefore was chosen as the best fit. This model showed that the effect of temperature on egg density varied across the study area and indicated a northeastward expansion of the spawning site as temperature increased. The area of expansion may correspond with the outer reach of a cold-water mass (called the cold pool) that extends in the Bering Sea middle domain during late spring and summer, and forms as a result of the previous winter ice coverage. Flathead Sole are known to avoid temperatures colder than 2 °C that is also used as the boundary for the cold pool, thus spawning fish may have moved relative to the spatial extent of the cold pool. [ABSTRACT FROM AUTHOR]

Understanding how fish distributions may change in response to environmental variability is important for effective management of fish populations, as predicted climate change will likely alter their habitat use and population dynamics. This research focused on two commercially-and ecologically-important flatfish species in the eastern Bering Sea (EBS), Greenland halibut (Reinhardtius hippoglossoides) and Pacific halibut (Hippoglossus stenolepis), which may be especially sensitive to climate-induced shifts in habitat due to strong seasonally and ontogenetically variable distributions. We analysed data from fishery-dependent and fishery-independent sources to determine how environmental variability influenced habitat use, thus gaining a uniquely comprehensive range of seasonal and geographic coverage of each species' distribution. Greenland and Pacific halibut exhibited strong and contrasting responses to changes in temperature on the shelf, with catches decreasing and increasing, respectively, beyond 1 °C. The effect of temperature was not as prominent along the slope, suggesting that slope habitats may provide some insulation from shelf-associated environmental variability, particularly for Greenland halibut. With warming, Greenland halibut exhibited more of a bathymetric shift in distribution, while the shift was more latitudinal for Pacific halibut. Our results suggest that habitat partitioning may, in part, explain differences in Greenland and Pacific halibut distributions. This research adds to our understanding of how the distributions of two fish species at opposite extremes of their ranges in the EBS – Greenland halibut at the southernmost edge and Pacific halibut at the northernmost edge - may shift in relation to a changing ocean environment. [ABSTRACT FROM AUTHOR]

The Bering Sea responds rapidly to atmospheric perturbations and over the past several decades has experienced extreme variability in both its physical and biological characteristics. These changes can impact organisms that inhabit the region, particularly marine fishes, as normal current patterns to which reproductive habits are tuned can be disrupted, which, in turn, may influence recruitment and population dynamics. To understand the influence of ocean circulation on groundfish recruitment in the eastern Bering Sea, we examined transport along and across the Bering Slope derived from 23 years (1982–2004) of simulations from a Regional Ocean Modeling System (ROMS) ocean circulation model. We expected that changes in the strength and position of the Bering Slope Current (BSC) would affect recruitment in selected species (Pacific cod, walleye pollock, Greenland halibut, Pacific halibut, and arrowtooth flounder), and that circulation features along and across the shelf edge would be strongly influenced by atmospheric forcing. Variability in along-shelf transport at three transects along the path of the BSC, cross-shelf transport across the 100 and 200 m isobaths, and transport through Unimak Pass were examined. Strong seasonal and interannual variations in flow were observed, with transport typically highest during fall and winter months, coinciding with timing of spawning activity in the five species. Significant correlations were found between transport, BSC position, and groundfish recruitment. Pacific cod, in particular, benefitted from decreased along-shelf and on-shelf flow, while Pacific halibut recruitment increased in relation to increased on-shelf transport through southern canyons. The results of this study improve our understanding of variability in circulation and associated effects on groundfish recruitment in the eastern Bering Sea. [ABSTRACT FROM AUTHOR]

Abstract: Environmental variability is increasingly recognized as a primary determinant of year-class strength of marine fishes by directly or indirectly influencing egg and larval development, growth, and survival. Here we examined the role of annual water temperature variability in determining when and where walleye pollock (Theragra chalcogramma) spawn in the eastern Bering Sea. Walleye pollock spawning was examined using both long-term ichthyoplankton data (N=19 years), as well as with historical spatially explicit, foreign-reported, commercial catch data occurring during the primary walleye pollock spawning season (February–May) each year (N=22 years in total). We constructed variable-coefficient generalized additive models (GAMs) to relate the spatially explicit egg or adult catch-per-unit-effort (CPUE) to predictor variables including spawning stock biomass, season, position, and water temperature. The adjusted R 2 value was 63.1% for the egg CPUE model and 35.5% for the adult CPUE model. Both egg and adult GAMs suggest that spawning progresses seasonally from Bogoslof Island in February and March to Outer Domain waters between the Pribilof and Unimak Islands by May. Most importantly, walleye pollock egg and adult CPUE was predicted to generally increase throughout the study area as mean annual water temperature increased. These results suggest low interannual variability in the spatial and temporal dynamics of walleye pollock spawning regardless of changes in environmental conditions, at least at the spatial scale examined in this study and within the time frame of decades. [Copyright &y& Elsevier]

The spatial dynamics of species are the result of complex interactions between density-independent and density-dependent sources of variability. Disentangling these two sources of variability has challenged ecologists working in both terrestrial and aquatic ecosystems. Using a novel spatially explicit statistical model, we tested for the presence of density-independent and density-dependent habitat selection in yellowfin sole (Limanda aspera) in the eastern Bering Sea. We found specificities in the density-dependent processes operating across ontogeny and particularly with gender. Density-dependent habitat expansion occurred primarily in females, and to a lesser degree in males. These patterns were especially evident in adult stages, while juvenile stages of both sexes exhibited' a mix of different dynamics. Association of yellowfin sole with substrate type also varied by sex and to a lesser degree with size, with large females distributed over a wider range of substrates than males. Moreover, yellowfin sole expanded northward as cold subsurface waters retracted in summer, suggesting high sensitivity to arctic warming. Our findings illustrate how marginal habitats can play an important role in buffering density-dependent habitat expansion, with direct implications for resource management. Our spatially explicit modeling approach is effective in evaluating density-dependent spatial dynamics, and can easily be used to test similar hypotheses from a variety of aquatic and terrestrial ecosystems. [ABSTRACT FROM AUTHOR]

Acoustic survey data were used to estimate the abundance and distribution of age-0 walleye pollock and zooplankton near the Pribilof Islands, Bering Sea, nursery area at two time periods in two consecutive years: the beginning of August, and mid-September, of 1996 and 1997. The 1996 pollock year class ultimately produced a large adult cohort in the eastern Bering Sea, while the 1997 year class produced a below-average adult cohort. Acoustic densities of age-0 pollock were significantly lower in August – and declined more strongly from August to September – in 1997 than in 1996, indicating that the trend to adult cohort strength was already set by August. Diet composition analyses revealed that age-0 pollock ate a much higher proportion of euphausiids in 1997 than in 1996, despite lower acoustic abundance of euphausiids in 1997. We infer that in 1996, age-0 pollock experienced greater feeding success by August, with high concentrations of copepods available for smaller fish to consume, and high concentrations of euphausiids available for larger individuals. In 1997, age-0 pollock had lower body condition in August and may have been limited by the availability of small (<2 mm) copepods. Bioenergetic modeling of prey consumption did not indicate a likelihood that age-0 pollock would begin to deplete euphausiids until late August in 1996, and not at all between August and mid-September in 1997. [ABSTRACT FROM AUTHOR]

Life‐history traits of individuals in marine populations exhibit large sources of variability. In marine fish, variation of individual size at a given age has three main components: (1) spatial, correlated with the location in which individuals are caught, (2) temporal, correlated with the time when individuals are caught, and (3) generational, correlated with the year of birth of the examined individuals. These variations, if present, have practical implications for individual fitness as well as for sampling, survey design, and population assessment. Disentangling these variations and understanding their sources is hard, given the potentially correlated nature of their effects on individual traits. This study examines the size‐at‐age relationship of the Bering Sea Pacific cod, an economically and ecologically important groundfish. We used extensive records spanning 1994 to 2016 (inclusive) of 25,213 observations of both environmental variables and catch, lengths, and ages. We found that the average size of individuals of the same age could differ up to 7 cm. Notably, we found that the cohort composition of the sampled population explained >75% of the year effect and that individuals caught in the northwest and shallower portion of the sampling area were on average 5 cm smaller than individuals caught in the southern and deeper portion. We further found that northwest movement of young cod (age 1–5) as a result of warming places individuals in areas where we predict them to have smaller size at age. Smaller and less conditioned individuals are less fecund and may not be able to perform long migrations to return to their distant spawning grounds. Both the spatial distribution and water temperature experienced by Pacific cod in the Bering Sea are changing, and this study provides a mechanism for how these changes affect Pacific cod life‐history traits and individual fitness. [ABSTRACT FROM AUTHOR]

Pacific cod ( Gadus macrocephalus ) is an economically and ecologically important species in the southeastern Bering Sea and Aleutian Islands, yet little is known about the spawning dynamics of Pacific cod in these regions. To address this knowledge gap, we applied a gross anatomical maturity key for Pacific cod to describe temporal and spatial patterns of reproductive status over three winter spawning seasons: 2005, 2006, and 2007. Maturity status of female Pacific cod was assessed by fishery observers during sampling of commercial catches and used to construct maps showing spawning activity in the Bering Sea and Aleutian Islands. Most spawning activity was observed on the Bering Sea shelf and Aleutian Island plateaus between 100 and 200 m depth. Data for those days when a high percentage of spawning stage fish were observed were used to identify areas with concentrations of spawning fish. Spawning concentrations were identified north of Unimak Island, in the vicinity of the Pribilof Islands, at the shelf break near Zhemchug Canyon, and adjacent to islands in the central and western Aleutian Islands along the continental shelf. The spawning season was found to begin in the last days of February or early March and extend through early to mid-April. Variation in spawning time (averaging ~10 days between years) may have been associated with a change from warm (2005) to cold (2007) climate conditions during the study period. Our information on Pacific cod spawning patterns will help inform fishery management decisions, models of spawning and larval dispersal and the spatial structure of the stock. [ABSTRACT FROM AUTHOR]