Northern Rock Sole Research Articles

Biological Characteristics of the Great Sculpin Myoxocephalus polyacanthocephalus (Cottidae) from Pacific Waters off the Kuril Islands and Southeastern Kamchatka in Autumn Period

The spatial distribution, size-sex composition, feeding of Myoxocephalus polyacanthocephalus and accompanying species in the Pacific waters off the northern Kuril Islands and southeastern Kamchatka in the autumn period are considered. In August–November 1997, this species was represented in catches by individuals with a length of 30-89 (on average 47.8 ± 0.5) cm and a body weight of 300–11000 (2321 ± 90) g. Females dominated over males; the sex ratio was 1.2 : 1.0. The relationship between the body weight and length of great sculpin is described by the exponential equation: W = 0.0031FL3.446 (R2 = 0.935). The food spectrum of great sculpin includes fish (56.2% of the diet), mainly the walleye pollock Gadus chalcogrammus and Atka mackerel Pleurogrammus monopterygius (19.9 and 11.9%, respectively); fish processing wastes (19.6%), mainly heads of Atka mackerel (12.2%); as well as decapods (18.6%), mainly the snow crab Chionoecetes opilio (14.1%). As great sculpin grow, decapods are replaced by fish in the diet and walleye pollock is replaced by Atka mackerel and Liparidae. The size and sex composition and feeding patterns of great sculpin as well as the species composition of the accompanying species differed in some parts of the surveyed area. The co-occurrence of great sculpin with walleye pollock and the northern rock sole Lepidopsetta polyxystra was 100%.

Functional foraging habits and dietary overlap of yellowfin sole (Limanda aspera) and northern rock sole (Lepidopsetta polyxystra) in a coastal nursery of the Bering Sea: suppl. table

Functional foraging habits and dietary overlap of yellowfin sole (Limanda aspera) and northern rock sole (Lepidopsetta polyxystra) in a coastal nursery of the Bering Sea: suppl. table

Functional foraging habits and dietary overlap of yellowfin sole (Limanda aspera) and northern rock sole (Lepidopsetta polyxystra) in a coastal nursery of the Bering Sea

Functional foraging habits and dietary overlap of yellowfin sole (Limanda aspera) and northern rock sole (Lepidopsetta polyxystra) in a coastal nursery of the Bering Sea

Evaluating the impact of climate and demographic variation on future prospects for fish stocks: An application for northern rock sole in Alaska

Climate-enhanced stock assessment models represent potentially vital tools for managing living marine resources under climate change. We present a climate-enhanced stock assessment where environmental variables are integrated within a population dynamics model assessment of biomass, fishing mortality and recruitment that also accounts for process error in demographic parameters. Probability distributions for the impact of the associated environmental factors on recruitment and growth can either be obtained from Bayesian analyses that involve fitting the population dynamics model to the available data or from auxiliary analyses. The results of the assessment form the basis for the calculation of biological and economic target and limit reference points, and projections under alternative harvest strategies. The approach is applied to northern rock sole (Lepidopsetta polyxystra), an important component of the flatfish fisheries in the Eastern Bering Sea. The assessment involves fitting to data on catches, a survey index of abundance, fishery and survey age-compositions and survey weight-at-age, with the relationship between recruitment and cold pool extent and that between growth increment in weight and temperature integrated into the assessment. The projections also allow for an impact of ocean pH on expected recruitment based on auxiliary analyses. Several alternative models are explored to assess the consequences of different ways to model environmental impacts on population demography. The estimates of historical biomass, recruitment and fishing mortality for northern rock sole are not markedly impacted by including climate and environmental factors, but estimates of target and limit reference points are sensitive to whether and how environmental variables are included in stock assessments and projections.

Latitudinal variation in the growth and condition of Juvenile flatfishes in the Bering Sea

The Bering Sea spans a wide latitudinal range, connecting with the temperate North Pacific Ocean to the south and the arctic Chukchi Sea to the north. Climate change has rapidly and significantly altered Bering Sea ecosystem dynamics. The biomass of predominantly boreal marine species have increased in the subarctic northern Bering Sea following recent record-high water temperatures across the shelf. Among those species are two commercially-important flatfishes: yellowfin sole (Limanda aspera; YFS) and northern rock sole (Lepidopsetta polyxystra; NRS). In this study, the Bering Sea was divided latitudinally into three areas – north, central, and south – to assess the implications of a northward shift or expansion of juvenile flatfish habitat on production potential. The growth, diet, and condition of juveniles were compared among areas from 2016 to 2018. Summer bottom temperatures in the Bering Sea in 2016 and 2018 were anomalously warm, but 2017 temperatures were closer to the 2010–2018 average. Prey availability does not appear to be a limiting habitat factor across the Bering Sea. Juveniles of both species grow faster in length and to greater length-at age in the south. The morphometric-based condition of juvenile YFS appears to be better in the northern Bering Sea, while that of juvenile NRS also improves towards the north. Condition increased from 2016 to 2017, but then decreased slightly from 2017 to 2018. Although the results suggest larger size and faster growth of juveniles are associated with warmer bottom temperatures, there is also indication that growth and condition of juvenile flatfish may not continue to increase if current high temperatures persist in their habitat. Exploratory habitat models show that the condition of juvenile YFS may be negatively influenced by temperature. Negative effects on growth and energy storage may set in as the upper thermal physiological tolerance of each species is approached. The critical temperature maxima for each species is unknown, but it may be lower for the cold-adapted YFS than for NRS, implying that YFS may be less buffered against effects of climate warming.

Greater exposure of nearshore habitats in the Bering Sea makes fish early life stages vulnerable to climate change

Marine fish species with complex life cycles undergo ontogenetic changes in their physiological and habitat requirements. Therefore, predicting how warming ocean conditions are likely to impact fish populations requires size-(age-) and habitat-specific analyses. We determined the habitat exposure and scope of adaptability of 4 shelf-oriented flatfish species in the Bering Sea to projected climate-driven warming. We quantified present day and end-of-century habitat exposure based on hindcasts and forecasts of regional ocean circulation models and quantified fish adaptability based on changes in depth distribution and from published thermal tolerances of northern rock sole Lepidopsetta polyxystra, yellowfin sole Limanda aspera, Alaska plaice Pleuronectes quadrituberculatus, and flathead sole Hippoglossoides elassodon. These 4 species complete their life cycle within the Bering Sea shelf but have different depth preferences and thermal tolerances throughout ontogeny. We found that species or size ranges that occupy the inner shelf, such as northern rock sole, yellowfin sole, and Alaska plaice, are exposed to higher seasonal variability compared to outer shelf species. While these inner shelf species are likely adapted to large seasonal changes in temperature, the future range of seasonal variability was projected to exceed their thermal tolerances. Therefore, we expect species that reside inshore during part of their life cycle and have high temperature sensitivity and limited mobility to be particularly vulnerable to climate change.

Contrasting the variability in spatial distribution of two juvenile flatfishes in relation to thermal stanzas in the eastern Bering Sea

Abstract Groundfish species in the Bering Sea are undergoing pronounced changes in spatial distribution and abundance due to warming ocean temperatures. The main drivers of interannual variability in this ecosystem are the alternating warm and cold thermal stanzas. Yellowfin sole (Limanda aspera; YFS) and northern rock sole (Lepidopsetta polyxystra; NRS) are commercially-valuable flatfishes in the Bering Sea and are among the most dominant groundfish species there in numbers and biomass. We examined the variability in the spatial distribution and abundance of juvenile NRS and YFS in relation to the ice and temperature conditions associated with warm-cold thermal shifts from 1982 to 2017. The goal was to assess the implications of the fluctuating thermal environment for Bering Sea flatfish production. We found ice cover and bottom temperature indices in the preceding 1 to 3 years to be the best predictors of NRS juvenile distribution. In contrast, these indices were not significantly correlated with YFS juvenile distribution, which could be an artifact of their relatively low availability to sampling. A warm stanza, as the Bering Sea is currently in, is expected to favor high numbers of NRS juveniles and the northward expansion of their distribution.

Environmentally driven forecasts of northern rock sole (Lepidopsetta polyxystra) recruitment in the eastern Bering Sea

AbstractNorthern rock sole recruitment in the eastern Bering Sea has been hypothesized to (a) depend on wind‐driven surface currents linking spawning and nursery areas, (b) be density‐dependent, and (c) be negatively impacted by cold bottom temperatures over a large nursery area during the first summer of life. A suite of models was developed to test these hypotheses. Data included 32 years of recruitment and spawning biomass estimates derived from a stock assessment model and wind and temperature indices customized to the environmental exposure of age‐0 northern rock sole in the eastern Bering Sea. The predictive ability of the models was evaluated, and the models were used to forecast recruitment to age‐4 for recent year classes which are poorly retained by the standard multi‐species bottom trawl survey gear. Models which included wind and temperature indices performed better than a naïve forecast based on the running mean. The best‐performing model was a categorical model with wind and temperature thresholds, which explained 49% of the variation in recruitment. Ricker models performed more poorly than models without a spawning biomass term, providing no evidence that recruitment is related to stock size. The models forecast higher recruitment for the most recent year classes (2015–2018) than for prior year classes with observed poor recruitment (2006–2013). These environment‐based recruitment forecasts may improve recruitment estimates for the most recent year classes and facilitate study of the effects of future climate change on northern rock sole population dynamics.

How “The Blob” affected groundfish distributions in the Gulf of Alaska

AbstractWe investigated the distributional shifts of groundfish in response to anomalous ocean conditions, particularly the recent anomalously warm period (2014–2016; “The Blob”), based on data from ten Gulf of Alaska bottom trawl surveys conducted by the Alaska Fisheries Science Center during 1996–2015. Six groundfish species were considered: Pacific cod (Gadus macrocephalus), arrowtooth flounder (Atheresthes stomias), walleye pollock (Gadus chalcogrammus), Pacific ocean perch (Sebastes alutus), northern rock sole (Lepidopsetta polyxystra), and southern rock sole (Lepidopsetta bilineata). Ontogenetic differences were examined by dividing data for each fish species into size classes. Our study demonstrated that after accounting for size‐specific depth preferences, the spatial responses of groundfish to anomalous ocean conditions differed by species and foraging guild in the central Gulf of Alaska. Pacific cod and arrowtooth flounder showed similar responses to ocean warming, but different responses to cooling. In general, Pacific cod moved to deeper depths in warmer years and moved to shallower depths in colder years. Arrowtooth flounder also moved deeper in warmer years. However, in colder years, large arrowtooth flounder (>40 cm) shifted toward shallower depths while smaller‐sized fish shifted toward deeper depths. In warmer years, large pollock (>30 cm) moved to deeper waters while smaller pollock (10–20 cm) moved to shallower waters. Pacific ocean perch exhibited an opposite response to thermal changes in habitat compared with Pacific cod and arrowtooth flounder. They moved deeper in colder years, but there was no clear change in depth as a function of size in response to warmer habitat.

Availability of yellowfin sole Limanda aspera to the eastern Bering Sea trawl survey and its effect on estimates of survey biomass

Availability of yellowfin sole Limanda aspera to the National Marine Fisheries Service eastern Bering Sea trawl survey, rather than trawl sampling efficiency, is proposed as the primary reason for relatively high annual variability of biomass estimates in this region, including most recently, a 48% increase from 2015 to 2016. The main hypothesis presented here is that temperature-mediated differences in the timing of spring-summer spawning migrations to unavailable nearshore spawning grounds, affect survey biomass estimates. Colder bottom temperatures delay both migrations and spawning, causing higher proportions of mature individuals to reside in the unavailable nearshore grounds at the time of annual survey (June–July). Indicators of this scenario include decreases of mature fish proportions and decreases in mean overall fish lengths during colder years when biomass was less than expected. Further evidence includes differences in spatial distribution between warm and cold years, and spatial shifts away from nearshore areas between early June and July–August sampling during which catch per unit effort (CPUE) increased and proportion of females increased. That neither of these spatial shifts nor temperature-CPUE relationships occurred for northern rock sole Lepidopsetta polyxystra, a species of similar morphology and abundance, and overlapping spatial distribution, suggests that temperature-mediated trawl sampling efficiency was not a major contributing factor for yellowfin sole. We have also found a positive relationship between survey biomass estimates and survey start times, reinforcing that availability is a function of timing. The addition of survey start time to the catchability (q) parameter within the current stock assessment model significantly improved model fits to abundance data.

Recent Data on Northern Rock Sole Lepidopsetta polyxystra from the Northwestern Part of the Bering Sea

The features of the biology and spatial distribution of northern rock sole Lepidopsetta polyxystra are described based on the analysis of samples from bottom trawlings in the northwestern part of the Bering Sea at depths of 57−440 m in June–August 1996–2001.

Razmerno-vozrastnaya struktura dvukhlinejnoj kambaly Lepidopsetta polyxystra u YUgo-Vostochnoj Kamchatki v 2003-2016

Razmerno-vozrastnaya struktura dvukhlinejnoj kambaly Lepidopsetta polyxystra u YUgo-Vostochnoj Kamchatki v 2003-2016

Seasonal, interannual, and spatial patterns of community composition over the eastern Bering Sea shelf in cold years. Part II: ichthyoplankton and juvenile fish

AbstractClimate-mediated oceanographic changes have led to protracted periods of above- or below-average water temperatures over the eastern Bering Sea shelf since the early 2000s. Ecosystem components, from phytoplankton to marine birds, have shown dichotomous responses to these temperature stanzas. Understanding within-stanza responses is fundamental to modelling efforts that project ecosystem responses under future climate scenarios. This study describes fish communities associated with Walleye Pollock during the age-0 period and also examines within-stanza homogeneity of assemblages. Spatial patterns of assemblage structure are compared with pre-defined ecoregions and environmental indices are assessed to determine potential mechanisms that delineate species assemblages. Walleye Pollock, rockfishes, Sand Lance, and Northern Rock Sole contributed to spring assemblages in every year. Assemblages were delineated by across-shelf gradients in 2008 and 2010 while 2009 assemblages showed less spatial structure. In summer, the diversity of fish assemblages increased across years but early-stage juvenile Walleye Pollock represented a small portion of the total abundance in 2009. Environmental gradients were related to fish assemblages, but patterns were along-shelf in 2008 and across-shelf in 2010. In fall, late-stage juvenile Walleye Pollock dominated the catch in 2008, but did not typify any assemblage in 2009. Overall, patterns of assemblage structure were not consistent with pre-defined ecoregions. Assemblage structure in 2009 was unique and indicates that within-stanza variability may complicate modelling projections based on ecosystem-level responses to climate changes.

Biological features of common fish species in Olyutorsky-Navarin region and the adjacent areas of the Bering Sea: 3. Righteye flounders (Pleuronectidae)

Biological features of the seven abundant commercial species—the Pacific halibut Hippoglossus stenolepis, the Greenland halibut Reinhardtius hippoglossoides, the Alaska plaice Pleuronectes quadrituberculatus, the northern rock sole Lepidopsetta polyxystra, the yellowfin sole Limanda aspera, the flathead sole Hippoglossoides elassodon, and the Bering flounder H. robustus (Pleuronectidae)—have been studied for a 20-year period (1995−2015). These species are present in the northwestern Bering Sea in the summer–autumn season; they form the gatherings in Olyutorsky-Navarin region. The size-weight spectra of the fish caught by different fishing gear has been analyzed, the peculiarities of the linear growth and the weight gain, as well as the spawning period and scale and the spawning conditions, have been described. The largest halibut specimens have been registered in the bottom setlines and gill nets, while flounders were in snurrevad catches; the smallest specimens have been observed in trawl catches. The abundant year-class in most of the studied species is seen well on the long-term plots of the fish size spectra and is tracked by the decrease of their biological parameters. The species that demand vast growing grounds (Pacific halibut, Alaska plaice, northern rock sole, and yellowfin sole) are characterized by a smaller average body size of the fish sampled in the coastal waters due to the prevalence of the young specimens in this area.

The potential effects of pre-settlement processes on post-settlement growth and survival of juvenile northern rock sole (Lepidopsetta polyxystra) in Gulf of Alaska nursery habitats

Early life history traits in marine fish such as growth, size, and timing of life history transitions often vary in response to environmental conditions. Identifying the potential effects of trait variation across life history stages is critical to understanding growth, recruitment, and survival. Juvenile northern rock sole (Lepidopsetta polyxystra) were collected (2005, 2007, 2009–2011) from two coastal nurseries in the Gulf of Alaska during the early post-settlement period (July–August) to examine variation in early life history traits in relation to water temperature and juvenile densities in nurseries as well as to evaluate the potential for carry-over effects. Size-at-hatch, larval growth, metamorphosis size and timing, and post-metamorphic and recent growth of juveniles were quantified using otolith structural analysis and compared across years and sites. Additionally, traits of fish caught in July and August were compared for evidence of selective mortality. Post-metamorphic and recent growth were related to temperatures in nurseries as well as temperatures during the larval period, indicating a direct influence of concurrent nursery temperatures and a potential indirect effect of thermal conditions experienced by larvae. Correlations between metamorphic traits and fish size at capture demonstrated that interannual variation in size persisted across life history stages regardless of post-settlement growth patterns. No evidence of density-dependent growth or growth-selective mortality were detected during the early post-settlement period; however, differences in hatch size and metamorphosis timing between fish collected in July and August indicate a selective loss of individuals although the pattern varied across years. Overall, variation in size acquired early in life and temperature effects on the phenology of metamorphosis may influence the direction of selection and survival of northern rock sole.

Elevated CO2 does not exacerbate nutritional stress in larvae of a Pacific flatfish

AbstractMultiple aspects of climate change are expected to co‐occur such that ocean acidification will take place in conjunction with warming and a range of trophic changes. Previous studies have demonstrated that nutritional condition plays a significant role in the responses of invertebrates to ocean acidification, but similar studies have yet to be conducted with marine fishes. In this study, we examined the potential interactive effects of elevated CO2 levels and nutritional stress on the growth and development of northern rock sole (Lepidopsetta polyxystra). Separate experiments examined the effects of these two environmental stressors during the pre‐flexion (3–31 days) and post‐flexion (31–87 days) larval stages. In both stages, the larval feeding regime has a much larger impact on growth rates than did the CO2 level, and there was no observed interaction between stressors. By 31 days post‐hatch, larvae in the high‐feeding treatment were 84.2% heavier than the fish in the low‐feeding treatments, but there was no significant effect of CO2 level on body size or condition. While overall growth rates were faster during the pre‐flexion stage, the effects of food limitation were greater for post‐flexion larvae undergoing metamorphosis, with the high‐feeding treatment fish being 3.3 times as heavy as fish in the low‐feeding treatments. These results have important implications for understanding the impacts of the multi‐faceted nature of climate change on population productivity of commercial fish species in the North Pacific.

Histological changes in gonads of rock sole <i>Lepidopsetta polyxystra</i> during its life cycle

Histological changes in gonads of rock sole <i>Lepidopsetta polyxystra</i> during its life cycle

Reproductive cycle and the scale of gonad maturity for rock sole <i>Lepidopsetta polyxystra</i>

The gonad maturity scale for rock sole Lepidopsetta polyxystra is presented in tabular form. Its reproductive cycle is described on the base of histological studies and analysis of seasonal occurrence of the species individuals with gonads at certain stages of maturity, in comparison with dynamics of the gonad-somatic index. Four phases are determined in the reproductive cycle. The first phase continues until the start of sexual cells maturing in the age 4-5 years (maturity stages I and II) - these juvenile fish live in the coastal shallow waters and are practically absent in trawl catches. Other three phases repeat annually. During the second phase, the rock sole gonads restore after previous spawning (stage VI) and begin the maturing for the next one (stage III, with yolked oocytes appearance in female gonads). This phase continues 8-9 months, usually from March to November-December and associates with active feeding when fish refill their energetic losses. The third phase is the time of fast maturing of gonads (stage IV, with active yolk producing and accumulation in oocytes and mass forming of spermatozoids) during wintering, when accumulated energetic resources are transformed to maintenance of the reproductive system. This phase starts from the moment of divergence between the reserve and reproductive funds of sexual cells in female gonads and continues 2-3 months. The fourth phase is the spawning (maturity stage V). It continues 1.0-1.5 months, usually with the peak of spawning in April.

Habitat quality of the coastal southeastern Bering Sea for juvenile flatfishes from the relationships between diet, body condition and prey availability

The distribution and body condition of juvenile northern rock sole (NRS), Lepidopsetta polyxystra, and yellowfin sole (YFS), Limanda aspera, were studied in relation to prey availability across the coastal shelf at the Alaska Peninsula boundary of the eastern Bering Sea (EBS) to assess spatial variability in habitat quality. Juveniles of ≤20cm and adults of ≥30cm total length were collected from bottom trawl catch samples at stations located 10 to 120km from the Alaska Peninsula coast, and in bottom depths of 28 to 85m. Stomach contents and stable isotopes of carbon and nitrogen from muscle tissue were analyzed to describe diet composition. The quantity and quality of prey did not significantly affect the distribution of juvenile NRS and YFS. Spatial mismatch between the diet composition and the infauna prey assemblage suggested that prey availability was not limiting across the area, allowing fish to select for prey, presumably to maximize net energy gain. The body condition of juvenile NRS was higher in the eastern section of the area (Bristol Bay) – where they shared spatial and dietary niches with juvenile YFS, than in the west section (Unimak Island) where juvenile YFS were largely absent. A difference in body condition suggests that habitat quality may be higher in Bristol Bay. For NRS, stomach contents and stable isotopes in muscle tissue indicated an ontogenetic diet shift from amphipods to polychaetes from juvenile to adult stages. In contrast, for YFS, amphipods seemed to remain the primary prey and polychaetes the least important prey from juvenile to adult stage. Given that the high prey availability found in this south coastal area of EBS extends to areas across the EBS shelf, favorable habitat for juvenile flatfishes should be extensive. However, much of this potential juvenile habitat is underutilized by NRS, which were mainly limited to Bristol Bay and the Alaska Peninsula, whereas YFS did extend north over 500km from Bristol Bay along the inner shelf domain (≤50m deep). Abiotic factors, particularly ocean currents and water temperature, may be more significant than prey availability in the spatial distribution of juveniles. Thus, changes in the hydrographic and thermal regime of the EBS are likely to impact juvenile flatfish distribution and habitat productivity.

Differential patterns of divergence in ocean drifters: Implications for larval flatfish advection and recruitment

In an effort to better understand the physics of the eastern Bering Sea shelf current as it relates to flatfish advection to favorable near-shore areas, sets of multiple, satellite-tracked, oceanic drifters were released in 2010, 2012 and 2013. The release sites and dates were chosen to coincide with known spawning locations for northern rock sole (Lepidopsetta polyxystra) and known time of larval emergence. The drifters were drogued 5-each at 20 and 40m in 2010 and 2012, and 4 at 40m and 2 at 20m in 2013. The locations of drifters were used to calculate divergence over a 90-day period that corresponds to the larval pelagic duration of Bering Sea shelf northern rock sole. Results indicate that there are alternating periods of positive and negative divergence with an overall trend toward drifter separation after 90days, roughly the end of the rock sole planktonic larval period. Examination of the drifter behavior at the hourly scale indicates that semi-daily tidal forcing is the primary mechanism of drifter divergence and convergence. Field observations of early-stage northern rock sole larval distributions over the same period indicate that predominant oceanographic advection is northerly over the continental shelf among preflexion stages, though juveniles are predominantly found in nursery areas located ~400km eastward and inshore. Evidence from drifter deployments suggests that behavioral movements during the postflexion and early juvenile larval phases that optimize eastward periodicity of tidal cycles is a viable mechanism to enhance eastward movement of northern rock sole larvae to favorable nursery grounds. A regional ocean modeling system (ROMS) was implemented to track the different rates of dispersion in simulations both with and without tidal forcing, and was used to estimate effective horizontal eddy diffusion in the case of both isobaric (fixed-depth) and Lagrangian (neutrally buoyant) particles. The addition of tidal forcing had a pronounced effect on horizontal eddy diffusion, increasing its value by a factor of five in the case of fixed-depth floats, as compared with a factor of two in the case of neutrally buoyant floats. Further, the incorporation of diurnal vertical behavior in phase with favorable (on shelf) tides transported the “larvae”~400km within 40days of their release date. Empirical drifter data coupled with model evidence suggest that semi-diurnal tidal forcing is the primary mechanism of eastward advection over the Bering Sea shelf, and larval observational data suggest that northern rock sole larvae can maximize their eastward transport to nursery grounds by synchronizing their vertical movements to tidal periodicity during the postflexion stage.