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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]

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

According to the nursery size hypothesis, flatfish recruitment is constrained by nursery area. Thus, if resource selection models can be shown to accurately predict the location and geographic extent of flatfish nursery areas, they will become important tools in the management and study of flatfish population dynamics. We demonstrate that some resource selection models derived previously to predict the presence and absence of juvenile flatfishes near shore were applicable to the broader continental shelf. For other age-species groups, derivation of new models for the continental shelf was necessary. Our study was conducted in the western Gulf of Alaska (GoA) during October 2011 on four groups of age-0 juvenile flatfishes: Pacific halibut ( Hippoglossus stenolepis ), arrowtooth flounder ( Atheresthes stomias ), northern rock sole ( Lepidopsetta polyxystra ), and flathead sole ( Hippoglossoides elassodon ); and three groups of age-1 juvenile flatfishes: northern rock sole, flathead sole, and yellowfin sole ( Limanda aspera ). Sampling occurred at 33 sites across the continental shelf. Fish were collected using a 3-m beam trawl, and a midwater trawl. Environmental data were collected on sediment composition and water temperature and depth. Many of the age-species groups co-occurred in the Shumagin and Barnabus sea valleys; however, age-0 arrowtooth flounder occurred at more locations than other juveniles, perhaps due to a relatively broad tolerance of environmental conditions and to the utilization of midwater habitat. Thus, the large nursery area of arrowtooth flounder may be one reason why they are currently the most abundant GoA flatfish. In fact, among all species, mean recruitment at age 3 increased with the percent occurrence of age-0 juveniles at the 33 sites, a proxy for relative nursery area, in accordance with the nursery size hypothesis, suggesting that mean recruitment among GoA flatfishes is structured by nursery size. [ABSTRACT FROM AUTHOR]

Abstract: This study provides a retrospective analysis of the relationship between physical oceanography, biology and recruitment of three Eastern Bering Sea flatfish stocks: flathead sole (Hippoglossoides elassodon), northern rock sole (Lepidopsetta polyxystra), and arrowtooth flounder (Atheresthes stomias) during the period 1978–2005. Stock assessment model estimates of recruitment and spawning stock size indicate that temporal patterns in productivity are consistent with decadal scale (or shorter) patterns in climate variability, which may influence marine survival during the early life history phases. Density-dependence (through spawning stock size) was statistically significant in a Ricker stock-recruit model of flatfish recruitment that included environmental terms. Wind-driven advection of northern rock sole and flathead sole larvae to favorable nursery grounds was found to coincide with years of above-average recruitment. Ocean forcing of Bristol Bay surface waters during springtime was mostly on-shelf (eastward) during the 1980s and again in the early 2000s, but was off-shelf (westerly) during the 1990s, corresponding with periods of good and poor recruitment, respectively. Finally, the Arctic Oscillation was found to be an important indicator of arrowtooth flounder productivity. Model results were applied to IPCC (Intergovernmental Panel on Climate Change) future springtime wind scenarios to predict the future impact of climate on northern rock sole productivity and indicated that a moderate future increase in recruitment might be expected because the climate trends favor on-shelf transport but that density-dependence will dampen this effect such that northern rock sole abundance will not be substantially affected by climate change. [Copyright &y& Elsevier]

Two similar appearing congeners, Hippoglossoides robustus (Bering flounder) and H. elassodon (flathead sole), inhabit the Bering Sea and are harvested together during the commercial fishery. In order to establish more precise overfishing limits, the annual spawning biomass must be estimated. Spawning biomass is modelled using the best estimate of the age and length at which 50% of the stock is expected to reach maturity (A 50, L 50). The major objective of this study was to establish the first maturity estimates for Bering flounder. Females matured at a similar age for Bering flounder (A 50, 9 years) and flathead sole (A 50, 10 years). However, the body length at which females matured was significantly smaller for Bering flounder (L 50, 238 mm) compared to flathead sole (L 50, 320 mm). The difference in the length-at-maturity was probably caused by growth differences, which significantly differed between species. The distribution and spawning locations of both species in the eastern Bering Sea survey area was related to the prevailing seawater temperatures and Bering flounder occurred in significantly colder water than flathead sole. The association between cold and the distribution of Bering flounder suggests that this species may be particularly vulnerable to periods of extended sea warming. [ABSTRACT FROM AUTHOR]

The general warming of the eastern Bering Sea (EBS) and the wide range of abundance exhibited by several eastern Bering Sea flatfish motivated an examination of how density-dependent and density-independent factors may influence the spatial distributions of EBS flatfish. In this study, EBS trawl survey data from 1982 to 2006 were used to examine how temporal changes in the distributions of six flatfish species groups [yellowfin sole ( Limanda aspera), rock sole ( Lepidopsetta sp.), flathead sole ( Hippoglossoides sp.), Alaska plaice ( Pleuronectes quadrituberculatus), arrowtooth flounder ( Atheresthes sp.), and Greenland turbot ( Reinhardtius hippoglossoides)] are related to temporal changes in the location of the ‘cold pool’ (bottom water < 2°C), and how the area occupied by flatfish are related to the cold pool and population abundance. Rock sole and flathead sole distributions have generally moved northwest since 1982 and are significantly correlated with the movement of the cold pool, whereas arrowtooth flounder avoid the cold pool and their area occupied is inversely related to the size of the cold pool. The area occupied by arrowtooth flounder and rock sole are also significantly related to stock abundance. Multivariate statistical models indicate that the location of rock sole is more strongly related to stock abundance than to the cold pool, whereas the area occupied by arrowtooth flounder is more strongly related to the area of the cold pool rather than abundance. The temperatures occupied by several flatfish stocks indicate a substantial variability in suitable temperatures. These results suggest that a complex suite of density-dependent and density-independent factors may determine the response of EBS flatfish spatial distributions to increasing temperatures. [ABSTRACT FROM AUTHOR]

Considerable attention has been devoted to contaminants (mainly PCBs and mercury) in subsistence foods (particularly fish) from various parts of the world. However, relatively little attention has been devoted to examining mercury levels in a full range of subsistence foods from a particular region. While managers and scientists compute risk based on site-specific data on contaminant levels and consumption rates, a first step in making risk decisions by subsistence peoples is knowledge about the relative levels of mercury in the foods they eat. This study examined levels of mercury in subsistence foods (edible components) from several islands in the western Aleutians of Alaska, including algae (4 species), invertebrates (9 species), fish (15 species) and birds (5 species). Samples were gathered by both subsistence hunters/fishers and by scientists using the same equipment. Another objective was to determine if there were differences in mercury levels in subsistence foods gathered from different Aleutian islands. We tested the null hypotheses that there were no interspecific and interisland differences in mercury levels. Because of variation in distribution and the nature of subsistence hunting and fishing, not all organisms were collected from each of the islands. There were significant and important differences in mercury levels among species, but the locational differences were rather small. There was an order of magnitude difference between algae/some invertebrates and fish/birds. Even within fish, there were significant differences. The highest mean mercury levels were in flathead sole (Hippoglossoides elassodon, 0.277 ppm), yellow irish lord (Hemilepidotus jardani, 0.281 ppm), great sculpin (Myoxocephalus polyacanthocephalus, 0.366 ppm), glaucous-winged gull (Larus glaucescens, 0.329 ppm) and its eggs (0.364 ppm), and pigeon guillemot (Cepphus columba, 0.494 ppm). Mercury levels increased with increasing weight of the organisms for limpets (Tectura scutum), and for 11 of the 15 fish species examined. Nine of the 15 fish species had some samples over the 0.3 ppm level, and 7 of 15 fish had some samples over 0.5 ppm. For birds, 95% of the pigeon guillemot muscle samples were above the 0.3 ppm, and 43% were above 0.5 ppm. While health professionals may argue about the risk and benefits of eating fish, and of eating alternative protein sources, the public should be provided with enough information for them to make informed decisions. This is particularly true for subsistence people who consume large quantities of self-caught foods, particularly for sensitive sub-populations, such as pregnant women. We argue that rather than giving people blanket statements about the health benefits or risks from eating fish, information on mean and maximum mercury levels should also be provided on a wide range of subsistence foods, allowing informed decisions, especially by those most at risk. [Copyright &y& Elsevier]

Abstract: Increasingly there is a need to assess the contaminant levels in fish as indicators of the health and well-being of both the fish and their consumers, including humans. This paper examines the levels of arsenic, cadmium, chromium, lead, manganese, mercury, and selenium in the kidney, liver, and muscle of great sculpin and flathead sole from Adak Island in the Aleutian Islands, Alaska. Both species are consumed by the local Aleuts and others. There were significant differences in the levels of heavy metals as a function of tissue for both fish species; the liver of sculpin and sole generally had the highest levels of most metals, except for arsenic, lead, and selenium. Sole had significantly higher mean levels of arsenic in kidney (32,384 vs. 531ppb, wet weight), liver (18,954 vs. 2532ppb), and muscle (19,452 vs. 1343ppb) than did sculpin. Sole also had higher mean levels of cadmium (230 vs. 63ppb), lead (1236 vs. 48ppb), mercury (150 vs. 107ppb), and selenium (5215 vs. 1861ppb) in kidney than did sculpin. There were significant correlations among weight and length measurements for both species. However, except for mercury, there were few significant correlations among tissue types for most metals. Only mercury and manganese levels were significantly correlated with size for sculpin (but not for sole). Levels of arsenic, lead, and mercury may pose a risk to predators that consume them, and arsenic and mercury may pose a risk to human consumers. [Copyright &y& Elsevier]

Data collected from an annual groundfish survey of the eastern Bering Sea shelf from 1975 to 2002 were used to estimate biomass and biodiversity indexes for two fish guilds: flatfish and roundfish. Biomass estimates indicated that several species of flatfish (particularly rock sole, arrowtooth flounder, and flathead sole), several large sculpins (Myoxocephalus spp.), bigmouth (Hemitripterus bolini), and skates (Bathyraja spp.) had increased. Declining species included several flatfish species and many smaller roundfish species of sculpins, eelpouts (Lycodes spp.), and sablefish (Anoplopoma fimbria). Biodiversity indexes were calculated by using biomass estimates for both guilds from 1975 through 2002 within three physical domains on the eastern Bering Sea shelf. Biodiversity trends were found to be generally declining within the roundfish guild and generally increasing within the flatfish guild and varied between inner, middle, and outer shelf domains. The trends in biodiversity indexes from this study correlated strongly with the regime shift reported for the late 1970s and 1980s. [ABSTRACT FROM AUTHOR]

Data from ichthyoplankton surveys conducted in 1972 and from 1977 to 1999 (no data were collected in 1980) by the Alaska Fisheries Science Center (NOAA, NMFS) in the western Gulf of Alaska were used to examine the timing of spawning, geographic distribution and abundance, and the vertical distribution of eggs and larvae of flathead sole (Hippoglossoides elassodon). In the western Gulf of Alaska, flathead sole spawning began in early April and peaked from early to mid-May on the continental shelf. It progressed in a southwesterly direction along the Alaska Peninsula where three main areas of flathead sole spawning were indentified: near the Kenai Peninsula, in Shelikof Strait, and between the Shumagin Islands and Unimak Island. Flathead sole eggs are pelagic, and their depth distribution may be a function of their developmental stage. Data from MOCNESS tows indicated that eggs sink near time of hatching and the larvae rise to the surface to feed. The geographic distribution of larvae followed a pattern similar to the distribution of eggs, only it shifted about one month later. Larval abundance peaked from early to mid-June in the southern portion of Shelikof Strait. Biological and environmental factors may help to retain flathead sole larvae on the continental shelf near their juvenile nursery areas. [ABSTRACT FROM AUTHOR]

Female flathead sole Hippoglossoides elassodon maturity appears not to be area dependent since the total length ( LT) at which 50% were mature ( LT50) was similar for the central Gulf of Alaska (333 mm) and south-eastern Bering Sea (320 mm) areas. Likewise the age at which 50% were mature ( A50) was similar in the south-eastern Bering Sea (9·7 years) and central Gulf of Alaska (8·7 years). The timing of female flathead sole spawning may also be similar between areas. Batch or serial spawning was indicated for flathead sole. Female flathead sole grew at a similar rate in both the Gulf of Alaska and Bering Sea. In contrast, males grew faster in the Bering Sea than in the Gulf of Alaska. Males grew more slowly than females in both areas after 5 years of age, and reached a smaller maximum LT. The growth of both sexes was similar during 1993 and 1996 in the Gulf of Alaska. [ABSTRACT FROM AUTHOR]

An underwater video system is under investigation by the National Marine Fisheries Service for use in studying the capture efficiency of a survey bottom trawl’s footrope in diverse habitats commonly sampled during surveys. This system utilizes a 50-watt quartz halogen light since most survey stations are at depths greater than natural light can penetrate for low-light camera use. One potential shortcoming to this approach is that the light emitted might alter fish behaviour and thereby bias estimates of escapement. The light effect on escapement was examined by attaching the video system onto a trawl fitted with an auxiliary capture bag to retain those fish which would have otherwise escaped beneath. A paired towing experiment (unlit vs. lit) was conducted to test the hypothesis that there is no effect on capture proportion due to the addition of artificial light. ANOVA was used to test for the effect both fish length and water depth had on escapement. Since neither length nor depth were significant, a paired t test (α=0.05) was used to test the null hypothesis. For five of the six species examined, we found no effect of the light on fish escapement. Only flathead sole (Hippoglossoides elassodon) showed a statistically significant difference in capture proportion due to artificial light, the proportion decreasing by 0.0698. [ABSTRACT FROM PUBLISHER]

In fiathead sole (Hippoglossoides elassodon) growth was linearly related to energy consumption (J g−1 day−1 ) at 4°C by the following equation: growth (%bw day−1) =0.006 (consumption J g−1 ) −0.130; r2 =0.80. Growth was independent of size for fish between 1 and 350g when growth was expressed as a function of consumption in Jg−1 day−1. Maintenance ration determined in feeding - growth experiments was 21.7 J g−1 day −1 at 4.0°C.Minimum estimates for daily ration to achieve growth rates observed in the Bering Sea were ∼0.4 to 6.2%bw day−1, depending on fish size and prey energy content. These rations are three to 50 times higher than previous existing consumption estimates but well within the capacity of the species. [ABSTRACT FROM PUBLISHER]