Northern Rock Sole Lepidopsetta Polyxystra 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%.

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.

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.

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.

Specific features of ecology of the clownfin sculpin Artediellus camchaticus Gilbert et Burke, 1912 (Pisces: Scorpaeniformes: Cottidae) in the Pacific waters near Kamchatka and Kuril Islands

Specific features of ecology of the clownfin sculpin Artediellus camchaticus (Cottidae) in the Pacific waters off the southeastern Kamchatka and northern Kuril Islands are provided. Main habitation area of this relatively rare and small species of sculpins with maximal length 19 cm and body weight to 50 g is waters of the lower part of the shelf with near-bottom temperatures 0–2 °С, where it most frequently occurred with walleye pollock Theragra chalcogramma and northern rock sole Lepidopsetta polyxystra. Smallest individuals stay mainly in bathymetric interval 151–250 m, while relatively large – mainly on smaller and greater depths. Clownfin sculpin is benthophage, main food objects of which (over 98% by weight) are amphipods and polychaetеs. Catch rates and occurrence of clownfin sculpin in the Pacific waters off the southeastern Kamchatka and northern Kuril Islands are subjected to some interannual, seasonal, and diurnal dynamics.

Specifics of the distribution of commercial fishes in the northwestern Bering Sea

Data of trawling censuses (1996–2005) are used to analyze the specifics of the distribution of commercial fishes present in the northwestern Bering Sea in summer and autumn and forming accumulations in the waters of the Olyutorsky-Navarin region. Areas with maximum fish density usually have a temperature range of 2.4–4.0°C in near-bottom water layers; they are observed in the same localities, with some interannual variation: in the middle shelf, with depths of 50–160 m southwest of Cape Navarin to Cape Khaiidin and between the Dezhneva Bay and Expeditsii Bay, and in waters of the continental slope adjacent to the first area, with depths over 270 m. The accumulations on the shelf mainly consist of such commercial species as the Alaska pollock Theragra chalcogramma, Pacific cod Gadus macrocephalus, saffron cod Eleginus gracilis, northern rock sole Lepidopsetta polyxystra, Alaska plaice Pleuronectes quadrituberculatus, and righteye flounders of the genus Hippoglossoides (H. robustus and H. elassodon); on the continental slope, they consist mainly of the Greenland halibut Reinhardtius hippoglossoides and Pacific halibut Hippoglossus stenolepis. The recorded density of fish in the Olyutorsky-Navarin region was the highest in 2004–2005 and the lowest in 1999, 2001, and 2002. This variation was determined mainly by the interannual variation in the fishing for cods (Gadidae), which reflected the emergence of abundant generations and migration activity in fishes of this family, as well as from differences in the efficiency of fishing gear. Fishing for many species can and should be performed simultaneously; special attention should be paid to the coastal areas of the Olyutorsky-Navarin region, where considerable fish resources (such as the saffron cod, Pacific halibut, and other righteye flounders) are present.

Polychaete worm tubes modify juvenile northern rock sole Lepidopsetta polyxystra depth distribution in Kodiak nurseries

We have observed inter-annual variability in the depth distribution of juvenile northern rock sole Lepidopsetta polyxystra on their nursery grounds around Kodiak Island, Alaska. This study evaluates whether this variability is a response to inter-annual changes in the availability of habitat created by polychaete tubes; principally Sabellides sibirica. We suspect that worm tubes constitute an alternative refuge and/or feeding habitat for juvenile flatfish. Accordingly, we hypothesized that during years of low worm abundance, fish would concentrate in the shallows (<10m depth) where they find refuge from predation, but would move to greater depths (>15m, where the worms occur) during years when the worms were abundant. Using data on worm abundance and fish density over 5yr, we tested this hypothesis at 2 Kodiak nursery embayments. Whether worms were abundant in a given year or embayment had no influence on overall fish abundance, however, worm abundance did influence juvenile flatfish depth distributions. At Holiday Beach, where worms tended to be scarce, fish were typically concentrated in shallow water. However, during the 1year when worms were abundant, fish were concentrated in deeper water. At Pillar Creek Cove, where worms are more regularly found, fish tended to concentrate in deeper water, the exception being the one year when worms were nearly absent. Regression analysis for both sites and all years indicated that the percent of fish occupying shallow water (<10m) decreased with increasing worm abundance. When worms were prevalent, fish were most commonly found on bottom with sparse to moderate worm cover, but avoided bottom where the worms were so dense as to form a ‘turf’. These results demonstrate that the geographic and inter-annual variation in worm tube abundance has significant influence over the distribution of juvenile northern rock sole.

Predation of hatchery-cultured juvenile red king crabs (Paralithodes camtschaticus) in the wild

The ecologically and commercially important red king crab (Paralithodes camtschaticus) is depleted throughout much of the North Pacific and thought to be recruitment-limited, making it an appropriate candidate for stock enhancement efforts. Information on predation of newly settled red king crabs in nearshore habitats is needed to assess the feasibility of large-scale releases. We tethered hatchery-cultured red king crabs of two sizes (range: 1.75–4.08 mm carapace width) in the field for 24 h trials in July and September 2011 and used underwater video cameras to identify predators and predation susceptibility. We identified hermit crabs (Pagurus spp.), Alaskan ronquil (Bathymaster caeruleofasciatus), Arctic shanny (Sticheus punctatus), northern rock sole (Lepidopsetta polyxystra), and kelp greenling (Hexagrammos decagrammus) as predators. Survival did not vary by body size or deployment month; however, small crabs were consumed sooner than large crabs. Most predation events occurred in daylight hours, with the exception of Alaskan ronquil. Our results suggest stock enhancement efforts should consider predator assemblages when developing release strategies. Future studies should investigate spatial variation in predation pressure at multiple locations on broad temporal scales to optimize release strategies and understand population-level effects.

On the seasonal pattern of formation of opaque zone on otoliths of the northern rock sole Lepidopsetta polyxystra of the Pacific shelf of Kamchatka and the Northern Kurils

On the seasonal pattern of formation of opaque zone on otoliths of the northern rock sole Lepidopsetta polyxystra of the Pacific shelf of Kamchatka and the Northern Kurils

Effects of natural and anthropogenic disturbance on polychaete worm tubes and age-0 flatfish distribution

ABSTRACT: Tubes of the ampharetid polychaete Sabellides sibirica are a prominent yet spatiallyvariable habitat feature in shallow-water flatfish nurseries around Kodiak, Alaska, USA. Juvenileflatfish associate with the edges of worm tube regions but seldom use the dense ‘turf-like’ wormbeds that sometimes form on the bottom in the late summer. The present study used a fine-scaleanalysis (2 to 3 m) to examine how juvenile flatfish distribution changed with worm tube hetero-geneity, i.e. density and patchiness. Using a video sled, 8 transect lines (~250 m each) were repeat-edly surveyed from late summer to mid-winter in a worm tube region of Pillar Creek Cove, half ofwhich were experimentally disturbed using simulated trawl gear. Results indicated that juvenileflatfish (mainly northern rock sole Lepidopsetta polyxystra) increasingly use patches of bare sub-strate as worm tube densities increase. However, the simulated trawl disturbance resulted in aunique kind of patchiness, typified by long, thin exposed regions of bare substrate referred to as‘combing’. Unlike natural patches, evidence of combing disappeared 2.5 mo after the initial distur-bance, whereas natural patches persisted throughout the entire study. Flatfish abundance in-creased in trawl-disturbed worm tube beds for only a short period (2 d), possibly due to episodicforaging opportunities rather than physical changes in habitat. These results indicate that wormtube habitat is provisionally resilient to disturbance, and its heterogeneity (density, patchiness, andpatch type) is an important component of habitat quality for juvenile flatfish in Alaska.KEY WORDS: Coastal habitats · Benthic recovery · Patchiness · Habitat heterogeneity · Northernrock sole

Growth and distributional correlates of behavior in three co-occurring juvenile flatfishes

We explored whether anti-predator behavior and intrinsic growth are co-evolved traits in 3 co-occurring juvenile flatfish species: English sole Pleuronectes vetulus, Pacific halibut Hippoglossus stenolepis and northern rock sole Lepidopsetta polyxystra. English sole are risk prone, adopting behavior that renders them more vulnerable to predation, while northern rock sole are more risk averse. Pacific halibut are risk sensitive and modulate behavior to match per- ceived threats. We hypothesized that risk-taking behavior and intrinsic growth rate would be pos- itively correlated in these species. We examined the willingness of each species to feed, both in the presence and absence of risk, and in separate experiments we measured their intrinsic growth rates under a range of temperatures. As predicted, risky behavior in English sole was accompa- nied by high intrinsic growth, while risk aversion in rock sole was accompanied by low growth. Pacific halibut confounded predictions, combining moderate risk-taking behavior with high growth. Lastly, we examined the depth distribution of each species. We expected English sole would be restricted to the shallows (<5 m), where predators are less common, while rock sole would have a deeper distribution, being better able to co-exist with predators. Halibut were expected to present an intermediate depth distribution. Again, English sole and rock sole con- formed to predictions, while Pacific halibut confounded them by having a deeper depth distribu- tion, comparable to that of rock sole. We suspect that the behavioral plasticity of Pacific halibut, combined with refuging behavior and well-developed escape capabilities, may allow them to have both high intrinsic growth as well as the ability to coexist with the predators. Thus, our results provide only partial support for our hypothesis that behavior and growth are co-evolved traits that together control the distribution of juvenile flatfishes across predation gradients.

Contrasting Maturation and Growth of Northern Rock Sole in the Eastern Bering Sea and Gulf of Alaska for the Purpose of Stock Management

AbstractThe primary purpose of this study was to provide commercial fishery managers with the age‐ and length‐at‐maturity information about northern rock sole Lepidopsetta polyxystra needed for them to set a sustainable overfishing limit and evaluate the precision of the two predictors of maturity. The estimated length at which 50% of eastern Bering Sea female northern rock sole matured (L 50) was 309 mm, which was significantly smaller than that for Gulf of Alaska females. We determined that the differences in L 50 between populations were probably the result of differences in the rate of female growth. Growth was significantly faster in the Gulf of Alaska than in the eastern Bering Sea during 1996 and 1999. However, by 2007 the growth rates were similar between these areas. The variability in growth was correlated with seawater temperature. There were also differences in the age at which 50% of the females matured (A 50) between the populations in the eastern Bering Sea (9 years) and the Gulf of Alaska (7 years). In contrast, within the eastern Bering Sea, females maintained a similar A 50 over several years, which indicates that age is the most reliable predictor of maturity for northern rock sole.Received April 8, 2011; accepted August 11, 2011

Effect of nursery habitat on density-dependent habitat selection in juvenile flatfish

Nursery habitats contribute significantly to adult recruitment of marine fish, but the density of juveniles that they can support depends in part on conspecific interactions among juveniles. Density-dependent habitat selection (DDHS) was compared in the laboratory using two species of age-0 yr flatfish: 1) English sole Pleuronectes vetulus, which utilizes estuarine nurseries at high densities and 2) northern rock sole Lepidopsetta polyxystra, which occurs at lower densities in coastal nurseries and is known to exhibit DDHS. The pattern of DDHS was hypothesized to be similar in both species, but to initiate at higher densities and be less responsive to predation risk in English sole. Trials were conducted over eight density treatments (0.4, 0.8, 1.5, 3.0, 6.1, 12.2, 18.6, and 23.8 fish m − 2 ), both with and without predation risk, and offered fish equal access to a preferred sand habitat and a less-preferred gravel habitat. Rock sole showed typical DDHS by increasing percentage use of the gravel habitat as conspecific density increased, with DDHS initiated at about 1.5 fish m − 2 . English sole showed no DDHS: there was no relationship between percentage use of gravel habitat and conspecific density. Predation risk caused rock sole to significantly decrease gravel usage across all densities, but did not significantly change habitat selection for English sole. These results suggest that each species may be behaviorally adapted to the conspecific density and predation risk of their respective nursery habitats, and correspond well with the comparatively risk-prone behaviors of English sole. The relationship between nursery habitat and density-dependent behavior may be further understood by studies integrating factors such as turbidity, food resources and ontogeny.

A Simple Biomass‐Based Length‐Cohort Analysis for Estimating Biomass and Fishing Mortality

AbstractA biomass‐based length‐cohort analysis (LCA) was examined for its performance in estimating total stock biomass and fishing mortality (F) for a population in equilibrium. We compared two LCA methods—(1) a numbers‐based LCA that relies on catch numbers at length as input data and (2) a new biomass‐based LCA that relies on catch biomass at length—by applying both to simulated data that generally followed characteristics of Pacific chub mackerel Scomber japonicus in Korean waters. We investigated the effects of using two length aggregation methods, two data simulation methods, and three expressions of weight growth (i.e., exponential growth over the length increment of the analysis, arithmetic mean growth, and geometric mean growth). Biomass and F were estimated from the new model and compared with those estimated from the numbers‐based LCA model. A sensitivity analysis was performed to understand which aspect of the model parameters controlled the results. Sensitivity to estimates of terminal F was also examined. Results of the analysis showed that the allometric power coefficient β was the most important model parameter and that sensitivity of biomass‐based LCA to terminal F was similar to that of numbers‐based LCA. Monte Carlo simulation was used to evaluate the equilibrium assumption and to calculate confidence intervals for biomass estimates. We applied the biomass‐based LCA model to data for northern rock sole Lepidopsetta polyxystra in the eastern Bering Sea. A comparison of biomass‐based LCA population biomass estimates with northern rock sole research survey biomass estimates showed good agreement between the two types of estimates. The biomass‐based LCA described in this study is unique in that it incorporates growth explicitly into the estimation procedure, which can be useful under data‐deficient situations when simple length composition data and estimates of total catch biomass from just one sampling year are the only available data.

Quantifying thermal effects on contemporary growth variability to predict responses to climate change in northern rock sole (Lepidopsetta polyxystra)

Understanding the causes of contemporary variation in growth rates can offer insights into the likely consequences of climate change for growth and recruitment of coastal marine fishes. We examined the growth dynamics of age-0 northern rock sole ( Lepidopsetta polyxystra ) over four years in three nurseries at Kodiak Island, Alaska, USA. Following the settlement period, fish were sampled monthly (July–October) with a 3 m beam trawl at fixed-position transects. Postsettlement sizes were positively related to temperatures during the spawning and larval periods, suggesting environmental control of spawning or settlement timing. Summer growth on the nursery grounds varied significantly among sites and years (mean size 32.8–63.1 mm in mid-September), with the Holiday Beach site consistently supporting the fastest growth rates. Contrary to expectations of density dependence and thermal regulation, nursery ground growth rates were not significantly correlated with fish density or water temperatures. The minor contribution of thermal variation to growth rates appears related to the conservative growth strategy and low thermal sensitivity of northern rock sole. These results suggest that climate changes influencing spawning time and larval growth may have larger impacts on first-year growth and recruitment of this species than temperature effects on the growth of nursery-resident juveniles.

Indirect predator effects on age-0 northern rock sole Lepidopsetta polyxystra: growth suppression and temporal reallocation of feeding

Field observations reveal that age-0 northern rock sole avoid feeding during daylight hours, instead, concentrating their feeding at dusk. Laboratory studies demonstrate these fish to be extremely risk averse in their behavior relative to predators. We hypothesized that dusk feeding may be an adaptation to mitigate the conflict between feeding and predator avoidance, which if unre- solved, could negatively affect not only short term survival, but growth as well. We designed experi- ments to examine firstly, whether growth of juvenile northern rock sole is suppressed by the percep- tion of chronic predation risk, and secondly, whether growth suppression is alleviated by allowing fish to feed at dusk. Replicate groups of 15 fish were grown in the presence or absence of predators (2 walleye pollock) and given access to food under either daylight or dusk conditions over a 6 wk period. Flatfish growth was independently and negatively influenced by both predator presence and daylight conditions; fish fed in daylight in the presence of predators lost weight, while those fed under dusk conditions in the absence of predators grew faster. These results are consistent with our hypothesis that dusk feeding is a behavior that mitigates effects of predation, not only upon survival, but also upon growth. Further, if predator abundance influences growth, as suggested by our data, indirect predator effects such as growth suppression may significantly influence the quality of nurs- ery habitats that differ in predator abundance.

Adaptive coloration, behavior and predation vulnerability in three juvenile north Pacific flatfishes

Adaptive color change in flatfish has long been of interest to scientists, yet rarely studied from an ecological perspective. Because color change can take a day or so in some species, movement between sediments with differing color or texture may render fish more conspicuous to predators. We conducted laboratory experiments to test the following hypotheses related to adaptive color change in flatfish: 1) fish which do not cryptically match sediment will be more vulnerable to predation, 2) fish will reduce activity and bury to minimize conspicuousness when on a sediment they mismatch, and 3) fish will choose a sediment they match when given a choice. Experiments were conducted using three co-occurring north Pacific juvenile flatfishes: English sole Parophrys vetulus, northern rock sole Lepidopsetta polyxystra and Pacific halibut Hippoglossus stenolepis. As per expectations, juvenile flatfish were more vulnerable to visual predators when they mismatched sediment. Mismatched fish tended to behave differently than fish which matched the sediment. Rather than burying and becoming inactive, they became more active and less likely to bury, perhaps contributing to their predation vulnerability. This increased activity may have represented search for better matching sediment, a stress response, or conspicuousness-related density dependent behavior. Fish which had acclimated to light colored sediment preferred light over dark sediment in choice trials. In contrast, fish acclimated to dark sediment demonstrated no preference. These experiments demonstrate that adaptive coloration is an integral part of the flatfish detection minimization strategy and that movement between habitats can increase risk of predation.

Presence of larger flatfish modifies habitat preference by Age-0 northern rock sole Lepidopsetta polyxystra

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 342:227-238 (2007) - doi:10.3354/meps342227 Presence of larger flatfish modifies habitat preference by Age-0 northern rock sole Lepidopsetta polyxystra Clifford H. Ryer1,*, Allan W. Stoner1, Mara L. Spencer1, Alisa A. Abookire2 1Fisheries Behavioral Ecology Program, Alaska Fisheries Science Center, NOAA Fisheries, Hatfield Marine Science Center, Newport, Oregon 97365, USA 2Alaska Fisheries Science Center, NOAA Fisheries, Kodiak Laboratory, 301 Research Court, Kodiak, Alaska 99615, USA *Email: cliff.ryer@noaa.gov ABSTRACT: Essential fish habitat (EFH) is poorly defined for the early stages of most commercially important species. Age-0 flatfish making summer use of shallow coastal embayments around Kodiak Alaska distribute themselves according to a variety of bottom features. Both field and laboratory studies indicate that the numerically dominant species, northern rock sole Lepidopsetta polyxystra and Pacific halibut Hippoglossus stenolepis, demonstrate an affinity for seafloor with emergent structure: algae, shell, worm-tubes, etc. We conducted field manipulations, in which bivalve shell was scattered on the seafloor along 100 m transects, with the goal of examining movements of juvenile flatfish in response to these habitat alterations. In the first manipulation, contrary to expectations, Age-0 flatfish emigrated from the shell-enhanced seafloor, producing fish densities that were lower than on adjacent un-enhanced bottom. In comparison, larger flatfish, predominantly Age-1+ rock sole Lepidopsetta spp., increased in abundance on shell-enhanced bottom. Small flatfish may have moved to avoid larger flatfish. The manipulation was repeated at another site with similar physical features, but where large flatfish abundances are generally lower. This time, Age-0 flatfish densities were greater on the shell-enhanced bottom than on adjacent un-enhanced bottom. Again, large flatfish were more abundant on the shell bottom, but they were nearly an order of magnitude less abundant than in the first manipulation. In a subsequent laboratory experiment, Age-1 northern rock sole demonstrated stronger affinity for shell bottom than did Age-0 northern rock sole. In another experiment, Age-0 northern rock sole moved to avoid aggregations of larger conspecifics as well as other species of large flatfish. We conclude that these Age-0 flatfish, predominantly northern rock sole, perceive larger fish as predators and/or competitors, with habitat quality degraded by their presence. These results demonstrate that habitat quality for juvenile fish is influenced by biotic factors as well as by physical characteristics of habitat. KEY WORDS: Habitat complexity · Habitat quality · Rock sole · Pacific halibut · Predator-prey interactions · Competitive interactions · Essential fish habitat · Indirect predation effects Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 342. Online publication date: July 24, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.

Density-dependent habitat selection in marine flatfish: the dynamic role of ontogeny and temperature

Changes in habitat use with increasing conspecific density are well-documented, but such patterns are likely to be dynamic over the lifespan of the organism and responsive to changes in the environment. In the laboratory, we examined how habitat selection was mediated by ontogeny (6, 8 and 12 mo) and temperature (4 and 9°C) in 2 juvenile, marine flatfish species: Pacific halibut Hip- poglossus stenolepis and northern rock sole Lepidopsetta polyxystra. In a set of initial trials at 9°C, groups of same-aged juvenile flatfish (6, 8 or 12 mo) of either halibut or rock sole were given the choice of 2 habitats—fine sand (preferred) and coarse gravel (unpreferred)— at 1 of 6 densities (0.4 to 12.2 fish m -2 ). A second set of trials was conducted at 4°C using 8 mo juvenile fish of both species over the same range of densities. At 9°C, density-dependent habitat selection was observed among all treatment groups. As juveniles increased in age in the 9°C treatments, both species began occu- pying the less-preferred gravel habitat at lower densities. However, at 4°C, density-dependent habi- tat selection varied between species. Sand habitat supported higher densities of juvenile Pacific hal- ibut at 4°C whereas no change was observed in northern rock sole. Juvenile Pacific halibut activity was also lower than rock sole at 4°C, suggesting that competitive interactions (e.g. interference, ter- ritoriality etc.) and/or physiological demands of halibut is sufficiently reduced at this temperature to increase the carrying capacity of the preferred habitat. Together, these results indicate that temper- ature, ontogeny and density interact to yield unique habitat selection patterns in fish, mechanisms that may be important in area-abundance relationships.