Pacific Halibut Research Articles

Reducing elasmobranch bycatch: Laboratory investigation of rare earth metal and magnetic deterrents with spiny dogfish and Pacific halibut

Spiny dogfish ( Squalus acanthius) comprises a significant unwanted bycatch on demersal longlines set for halibut and cod in shelf waters of the east and west coasts of North America. In this laboratory study, attacks on baits were tested in the presence of two different rare earth materials (neodymium–iron–boride magnets and cerium mischmetal) believed to deter elasmobranch catch. Experiments were made with spiny dogfish and with Pacific halibut ( Hippoglossus stenolepis) in pairwise tests of the rare earth materials and inert metal controls. Dogfish attacked and consumed baits tested with cerium mischmetal at a lower frequency than controls. Times to attack the baits were significantly higher in the presence of mischmetal, as were numbers of approaches before first attack. The time differential between mischmetal and control treatments and the number of baits consumed converged with increasing food deprivation (1 h, 2 d, and 4 d), but treatment differences were always significant. Cerium mischmetal appeared to be irritating to dogfish and may disrupt their bait detection and orientation abilities. Magnets also appeared to irritate dogfish but provided no protection for baits in feeding trials. Pacific halibut showed no reaction whatsoever to the rare earth magnets or cerium mischmetal. Mischmetal, therefore, may be useful in reducing spiny dogfish bycatch in the halibut fishery. Disadvantages in using mischmetal in commercial operations are expense, hazardous nature, and relatively rapid hydrolysis in seawater.

Halibut mitochondrial genomes contain extensive heteroplasmic tandem repeat arrays involved in DNA recombination

BackgroundHalibuts are commercially important flatfish species confined to the North Pacific and North Atlantic Oceans. We have determined the complete mitochondrial genome sequences of four specimens each of Atlantic halibut (Hippoglossus hippoglossus), Pacific halibut (Hippoglossus stenolepis) and Greenland halibut (Reinhardtius hippoglossoides), and assessed the nucleotide variability within and between species.ResultsAbout 100 variable positions were identified within the four specimens in each halibut species, with the control regions as the most variable parts of the genomes (10 times that of the mitochondrial ribosomal DNA). Due to tandem repeat arrays, the control regions have unusually large sizes compared to most vertebrate mtDNAs. The arrays are highly heteroplasmic in size and consist mainly of different variants of a 61-bp motif. Halibut mitochondrial genomes lacking arrays were also detected.ConclusionThe complexity, distribution, and biological role of the heteroplasmic tandem repeat arrays in halibut mitochondrial control regions are discussed. We conclude that the most plausible explanation for array maintenance includes both the slipped-strand mispairing and DNA recombination mechanisms.

Homing and summer feeding site fidelity of Pacific halibut ( Hippoglossus stenolepis) in the Gulf of Alaska, established using satellite-transmitting archival tags

A total of 48 adult Pacific halibut were tagged in the Gulf of Alaska using Pop-up Archival Transmitting (PAT) tags. Fish were tagged during 2005 while on their summer feeding grounds and the tags programmed to release from their host fish (pop-up) exactly 365 days after deployment, thus providing a full year's environmental data (depth, temperature, and light levels) as well as each fish's location the summer after tagging. Nine tags were recovered by the commercial fleet substantially in advance of their pop-up dates, eight prematurely released from their host fish, and six failed to report to satellites on their programmed date. For halibut that escaped the fishery and whose tags broadcast reliable endpoint locations ( n = 23) or were recaptured by the commercial fishery close to their pop-up date ( n = 2), 80% were located within 20 km of their initial tagging location after 1 year at liberty. Depth records confirmed that most of these fish ( n = 15; 60% of all tag recoveries) had actively homed to their summer grounds after spending winter in deep water at the shelf edge, as opposed to simply remaining near their tagging location throughout time at liberty. The rate of site fidelity observed here is further corroborated by an ongoing Passive Integrated Transponder (PIT) tagging study, suggesting that summer site fidelity and homing are likely to be general characteristics across recruited ages, as well as being interannually persistent. Homing provides a strong mechanism to establish and maintain population substructure, and high rates within a population have implications for ongoing research, interpretation of historical fishery trends, and conceptual models of population structure.

A revision of Entobdella Blainville in Lamarck, 1818, with special emphasis on the nominal (type) species “Entobdella hippoglossi (Müller, 1776) Blainville, 1818” (Monogenea: Capsalidae: Entobdellinae) from teleost flatfishes, with descriptions of three new species and a new genus

Species of Entobdella Blainville in Lamarck, 1818, from skin (less commonly gills) of teleost flatfishes and occasionally from round-bodied teleosts are reviewed, with special reference to the nominal (type) species “Entobdella hippoglossi (Müller, 1776) Blainville, 1818” (Monogenea: Capsalidae: Entobdellinae) and to E. pugetensis Robinson, 1961. In the late 20th century the following 5 species were synonymised with E. hippoglossi: E. brattstroemi Brinkmann, 1952; E. curvunca Ronald, 1957; E. rosaceus Crane, 1972; E. squamula (Heath, 1902) Johnston, 1929; E. steingroeveri (Cohn, 1916) Johnston, 1929. We have shown that E. brattstroemi and E. squamula are valid, E. curvunca is a synonym of E. hippoglossi and E. rosaceus and E. steingroeveri are species inquirendae. Specimens of E. steingroeveri, first described in 1916 by Cohn, have been re-examined. Parasites from the Pacific Ocean on Hippoglossus stenolepis Schmidt, 1904 (Pacific halibut) and Eopsetta jordani (Lockington, 1879) (Petrale sole) (Pleuronectiformes: Pleuronectidae) and parasites geographically isolated in the Atlantic Ocean on H. hippoglossus (Linnaeus, 1758) (Atlantic halibut) and Reinhardtius hippoglossoides (Walbaum, 1792) (Greenland halibut) (Pleuronectiformes: Pleuronectidae) have all been regarded as E. hippoglossi. We confirm that E. hippoglossi sensu stricto is a parasite of the Atlantic halibut, but is accompanied on the same host by a second entobdelline species, E. vanbenedeni n. sp. It differs from the type species, E. hippoglossi in the anatomy of the distal region of the vagina and in the number, distribution and shape of papillae on the ventral surface of the haptor. Parasites from H. stenolepis are morphologically similar to E. hippoglossi on H. hippoglossus (no second species has been found on H. stenolepis), but differences in the number and shapes of haptor papillae support proposal of the parasites from H. stenolepis as a distinct species, E. stenolepis n. sp. Our anatomical studies of these parasites, with the exception of E. pugetensis, have revealed a cluster of several seminal receptacles opening into the ovo-vitelline duct. Previous reports of a single seminal receptacle in E. stenolepis (as E. hippoglossi) and E. steingroeveri are erroneous. Furthermore, reports of the vagina opening proximally into the alleged single seminal receptacle are also incorrect; direct and indirect evidence suggests that in all these parasite species, including E. pugetensis, the vagina opens proximally into the vitelline reservoir. Entobdella squamula from Paralichthys californicus (Ayers, 1859) (California flounder) (Pleuronectiformes: Paralichthyidae) differs from E. stenolepis, E. hippoglossi and E. vanbenedeni in the relative lengths of the accessory sclerites and anterior hamuli. Parasites originally identified as E. squamula from Hippoglossina macrops Steindachner, 1876 (Bigeye flounder) (Pleuronectiformes: Paralichthyidae), caught off the coast of Chile by the Lund University Chile Expedition (1948 – 49), differ from E. squamula in the shapes of the accessory sclerites and are regarded as a new species, E. brinkmanni n. sp. E. aegyptiacus Amer, 1990 must be regarded as a species inquirenda. A key to the 7 valid species of Entobdella recognised by us is included. Entobdella pugetensis differs in the following ways from all other species of Entobdella: the parasite is found on gills (less commonly on skin) of Atheresthes stomias (Jordan & Gilbert, 1880) (Arrowtooth flounder) (Pleuronectiformes: Pleuronectidae); the penis sac has a thick, possibly muscular, wall; the vagina is a relatively wide, short, straight tube with a conspicuous opening; no seminal receptacles have been observed; there are no papillae on the ventral surface of the haptor. We regard these distinctions as sufficient to erect a new genus, Branchobdella n. gen. to accommodate B. pugetensis n. comb. Assimilation of spermatophores in skin-parasitic Entobdella spp. and in the gill parasite B. pugetensis is discussed.

Comparative characteristics of the diet of Pacific halibut Hippoglossus stenolepis from different areas of the northwestern part of the Pacific Ocean

Food composition of Pacific halibut Hippoglossus stenolepis has been considered in three areas of the northwestern Pacific: in the western part of the Bering Sea, in Pacific waters off the northern Kuril Islands and southeastern Kamchatka, and waters off the southern Kuril Islands. The main food items in all studied regions were shrimp, cephalopods, and fish. It has been noted that fish offal plays a considerable role in the feeding of H. stenolepis in the western part of the Bering Sea. Changes in food composition in relation to fish growth, depth of catch, and sex of individuals have been analyzed; and differences in the composition of food items consumed by H. stenolepis in different parts of the studied areas have been considered.

Mercury in fishes of Alaska, with emphasis on subsistence species

In the north, the presence of mercury (Hg) in food leading to chronic exposure is a scientific, economic and political issue. Guidelines have been established for the safe consumption of fish containing Hg, however, adherence to these guidelines must be weighed against the health benefits of consuming fish, such as from the omega-3 polyunsaturated fatty acids, vitamins and minerals. Alaskan Natives generally consume much more fish than the national average. This review summarizes and synthesizes the significant amount of data that has been generated on Hg in Alaska fish, particularly those consumed by Alaskans. Also included are a review of the benefits of eating fish, human health concerns relating to Hg toxicity and various risk assessment guidelines for food consumption. Emphasis was placed on methylmercury (MeHg), the most toxic form to humans. Hg concentrations were examined in 17 freshwater fish species and 24 anadromous and marine fish species, for a total of 2,692 specimens. For freshwater fish the greatest database was on northern pike (Esox lucius). For anadromous and marine fish the greatest database was on Pacific halibut (Hippoglossus stenolepis) and the five species of Pacific salmon (Oncorhynchus spp.). Overall, most fish had muscle Hg concentrations of < or =1 mg kg(-1) (wet wt.), within the USFDA's Action Level and Alaska's guideline for safe concentrations of MeHg in edible fish. Pacific salmon, the most commonly consumed fish group, had exceptionally low (< or =0.1 mg kg(-1)) Hg concentrations. Pacific halibut muscle Hg content was less than 0.3 mg kg(-1). Northern pike, a piscivorous (fish-eating) and long-lived fish, contained the highest muscle Hg values, often exceeding the state's guidelines for food consumption. A discussion of the safe consumption level for pike is included.

Evaluation of Video Technology for Monitoring of Multispecies Longline Catches

AbstractAt‐sea catch monitoring of the Alaskan longline fishery for Pacific halibut Hippoglossus stenolepis is insufficient. The International Pacific Halibut Commission (IPHC) conducted studies in 2002 and 2004 comparing catch composition data from electronic monitoring (EM) systems to those of at‐sea observers. The EM systems use automated data loggers linked to digital video cameras, a transducer on shipboard hydraulic systems, and a global positioning system receiver. The goal of both studies was to determine whether EM technologies could provide precise and verifiable catch composition data on commercial longline vessels to supplement and complement the data collected by fisheries observers. The EM video analyst's catch data were similar to the observers' data in the 2002 study; however, the video analyst recorded fewer fish for 7 of the 17 species categories investigated. In 2004, the IPHC employed EM technology in another study incorporating recommendations from the 2002 study, including improved camera configurations. The video analyst's data showed increased agreement with the observer data. However, the observers recorded slightly fewer individuals of some species categories, opposite the findings of the 2002 study. This change suggests that incorporating the technology recommendations enhanced the video analyst's accuracy relative to the observer data. Our analysis also highlights the fact that data provided by human observers have their own suite of errors and that the comparisons between EM and observers have no absolute standard of reference. The findings indicate that EM technology can effectively address the lack of catch composition data in the Pacific halibut and other hook‐and‐line fisheries in Alaska.

A biomonitoring plan for assessing potential radionuclide exposure using Amchitka Island in the Aleutian chain of Alaska as a case study

With the ending of the Cold War, the US and other nations were faced with a legacy of nuclear wastes. For some sites where hazardous nuclear wastes will remain in place, methods must be developed to protect human health and the environment. Biomonitoring is one method of assessing the status and trends of potential radionuclide exposure from nuclear waste sites, and of providing the public with early warning of any potential harmful exposure. Amchitka Island (51° N lat, 179° E long) was the site of three underground nuclear tests from 1965 to 1971. Following a substantive study of radionuclide levels in biota from the marine environment around Amchitka and a reference site, we developed a suite of bioindicators (with suggested isotopes) that can serve as a model for other sites contaminated with radionuclides. Although the species selection was site-specific, the methods can provide a framework for other sites. We selected bioindicators using five criteria: (1) occurrence at all three test shots (and reference site), (2) receptor groups (subsistence foods, commercial species, and food chain nodes), (3) species groups (plants, invertebrates, fish, and birds), (4) trophic levels, and (5) an accumulator of one or several radionuclides. Our major objective was to identify bioindicators that could serve for both human health and the ecosystem, and were abundant enough to collect adjacent to the three test sites and at the reference site. Site-specific information on both biota availability and isotope levels was essential in the final selection of bioindicators. Actinides bioaccumulated in algae and invertebrates, while radiocesium accumulated in higher trophic level birds and fish. Thus, unlike biomonitoring schemes developed for heavy metals or other contaminants, top-level predators are not sufficient to evaluate potential radionuclide exposure at Amchitka. The process described in this paper resulted in the selection of Fucus, Alaria fistulosa, blue mussel ( Mytilus trossulus), dolly varden ( Salvelinus malma), black rockfish ( Sebastes melanops), Pacific cod ( Gadus macrocephalus), Pacific halibut ( Hippoglossus stenolepis), and glaucous-winged gull ( Larus glaucescens) as bioindicators. This combination of species included mainly subsistence foods, commercial fish, and nodes on different food chains.

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.

Fisheries management in practice: review of 13 commercially important fish stocks

This paper comparatively reviews several commercially important fish stocks, their state and their management in various regions of the world including Japanese anchovy, Bay of Biscay anchovy, North Sea sandeel, North Sea herring, Icelandic cod, Barents Sea cod, South African cape hakes, sockeye salmon, chinook salmon, southern bluefin tuna, Pacific halibut, Greenland halibut and Patagonian toothfish. The reviewed fish stocks are systemized in three categories: (1) stock properties and status; (2) management structure and objectives; and (3) management advice. We gather evidence to outline qualities of management regimes that are recommended and highlight those that most often fail. Robust management, biological limits (reference points), implementation and consensus are critical points that separate successful and unsuccessful management regimes. We evaluate each fish stock’s management performance relative to its management objectives and current conservation issues. Furthermore, we point out the importance of stakeholder involvement in fisheries management as well as the problems that international fisheries commissions face through examples from the case studies. Management successes tended to be single-nation and single-stock fisheries with capacity control and clear stakeholder involvement. Fisheries with fleet overcapacity, unclear objectives and illegal activity characterized the case studies with management problems.

Short-term forecasting of halibut CPUE: Linear and non-linear univariate approaches

In the present paper, two univariate forecasting techniques were tested to evaluate the short-term CPUE capacity forecast for Pacific halibut, Hippoglossus stenolepis (Pleuronectidae). The first methodology, based on the Box–Jenkins approach (autoregressive integrated moving average models [ARIMA models]), assumes a linear relationship between the time series data. The second methodology, using artificial neural network models (ANNs), enables highly non-linear processes to be modelled. The best results from a seasonal ARIMA model indicated that one non-seasonal autoregressive term combined with a non-seasonal moving average term and a seasonal moving average term was suitable to explain a variance level of 32.6% in the validation phase, providing statistically acceptable but insufficiently satisfactory estimations. The configuration of the best ANN model (three autoregressive terms in the input layer and five neurons in the hidden layer) provided a significant improvement in the independent validation phase (91% of the variation explained), indicating a clear non-linear relationship between variables. Modelling of the abundance indices is a useful tool for understanding the dynamics of populations and may enable short-term quantitative recommendations for fisheries management to be made.

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.

Evaluating Network Analysis Indicators of Ecosystem Status in the Gulf of Alaska

This is the first study on the emergent properties for empirical ecosystem models that have been validated by time series information. Ecosystem models of the western and central Aleutian Islands and Southeast Alaska were used to examine indices of ecosystem status generated from network analysis and incorporated into Ecopath with Ecosim. Dynamic simulations of the two ecosystems over the past 40 years were employed to examine if these indices reflect the dissimilar changes that occurred in the ecosystems. The results showed that the total systems throughput (TST) and ascendancy (A) followed the climate change signature (Pacific decadal oscillation, PDO) in both ecosystems, whereas the redundancy (R) followed the inverse trend. The different trajectories for important species such as Steller sea lions (Eumetopias jubatus), Atka mackerel (Pleurogrammus monopterygius), pollock (Theragra chalcograma), herring (Clupea pallasii), Pacific cod (Gadus macrocephalus) and halibut (Hippoglossus stenolepis) were noticeable in the Finn cycling index (FCI), entropy (H) and average mutual information (AMI): not showing large change during the time that the Stellers sea lions, herring, Pacific cod, halibut and arrowtooth flounder (Atheresthes stomias) increased in Southeast Alaska, but showing large declines during the decline of Steller sea lions, sharks, Atka mackerel and arrowtooth flounder in the Aleutians. On the whole, there was a change in the emergent properties of the Aleutians around 1976 that was not seen in Southeast Alaska. Conversely, the emergent properties of both systems showed a change around 1988, which indicated that both systems were unstable after 1988.

RADIONUCLIDES IN MARINE FISHES AND BIRDS FROM AMCHITKA AND KISKA ISLANDS IN THE ALEUTIANS: ESTABLISHING A BASELINE

Amchitka Island (51degrees N lat, 179 degrees E long) was the site of three underground nuclear tests from 1965-1971. There have been no substantive studies of radionuclides in marine fishes and birds in the area since the mid-1970's. In this study, levels of 60Co, 52Eu, 90Sr, 99Tc, 129I, 137Cs, and the actinides (241Am, 238Pu, 239,240Pu, 234U, 235U, 236U, and 238U) were studied in ten marine fish species (including Pacific Cod Gadus macrocephalus and Pacific Halibut Hippoglossus stenolepis) and five marine bird species (including Glaucous-winged Gulls Larus glaucescens, Tufted Puffins Fratercula cirrhata, and Common Eider Ducks Somateria mollissima) from Amchitka. The same species were collected at a reference site, Kiska Island (52 degrees N lat; 177 degrees E long), about 130 km west of Amchitka. Each sample was a composite of edible muscle from five or more individual fish or birds of similar size (+/-15%) from the same sampling station. The null hypotheses of no differences among species or between Amchitka and Kiska were tested. Most analytic results were below the minimum detectable activity (MDA), even when 1,000 g sizes and 72 h counting times were used. The only radionuclides detected above the MDA were 137Cs, 241Am, 239,240Pu, 234U, 235U, and 238U. There were significant differences in 137Cs as a function of species, but not location, for top predatory fishes. Of the fishes, eight of ten species had 137Cs values above the MDA for some samples; only one bird, Glaucous-winged Gull, had 137Cs values above the MDA. The highest concentrations of 137Cs were in Dolly Varden [Salvelinus malma, 0.780 (Bq kg(-1) wet weight)] and Pacific Cod (0.602 Bq kg(-1)). In aggregate for any actinides, 73 of 234 (31%) composites for fish were above the MDA, compared to only 3 of 98 (3%) for birds. 234U and 238U, radionuclides that are primarily natural in origin, were routinely detected in these biological samples, but there were no significant differences in mean concentrations between Amchitka and Kiska. The concentrations of all radionuclides examined at Amchitka are similar to those of other uncontaminated Northern Hemisphere sites, and are lower than those reported for fishes and birds from the Irish Sea in the vicinity of the Sellafield nuclear reprocessing facility, an area with known contamination.

Relative predation vulnerability of three juvenile (Age-0) North Pacific flatfish species: possible influence of nursery-specific predation pressures

Pleuronectid flatfish are generally thought to utilize stereotypical anti-predator behavior to reduce encounters with potential predators. In this study, we tested the relative vul- nerability of 3 juvenile (Age-0) flatfish species to predation under controlled laboratory conditions. Predators consumed significantly more English sole Parophrys vetulus than either Pacific halibut Hippoglossus stenolepis or northern rock sole Lepidopsetta polyxystra in clear water (0 nephelo- metric turbidity units, NTU), suggesting differing anti-predator strategies and/or capabilities. In con- trast to halibut and rock sole, which remained buried and inactive, English sole were often observed actively moving about. As a result, English sole were encountered more frequently by predators than the other 2 species, suggesting that they were more conspicuous to the predators. This was further evidenced by a higher frequency of stalk encounters for English sole, whereby the predators detected and approached them prior to prey flushing. However, as an estuarine-dependent species, English sole are generally exposed to lower densities of predators in an environment that tends to be highly turbid. When similar trials were conducted at higher turbidity (18 NTU), predation rates on English sole decreased to rates comparable to that for halibut and rock sole in clear water (0 NTU). Although English sole appeared more vulnerable to predation, their behavior may have evolved in response to, and be mitigated by, the turbid nature of the estuarine nursery environments to which they recruit, where predation pressure is significantly reduced in comparison to open coastal habitats.

Divergent foraging strategies of three co-occurring north Pacific flatfishes

Despite facing similar constraints imposed by the environment, significant variation in life history traits frequently exists among species generally considered to comprise a single ecological guild. For juvenile flatfishes, constraints on foraging activity include variation in light and prey availability, as well as predation risk. This paper describes the visual constraints on, and divergent foraging strategies of three co-occurring north Pacific flatfish species, northern rock sole (Lepidopsetta polyxystra), Pacific halibut (Hippoglossus stenolepis), and English sole (Pleuronectes vetulus). Visual foraging abilities measured in the laboratory decreased rapidly below 10−4 μmol photons·m−2 s−1, and were similar among species. Despite similar sensory constraints, field sampling in August 2004 at a Kodiak Island nursery site (Holiday Beach, 57o41.2′ N, 152o27.7′ W) identified species differences in diets, diel foraging patterns, and within-nursery depth distributions. Northern rock sole and English sole fed primarily on bivalve siphons and polychaetes, whereas mysids dominated the diets of Pacific halibut. Northern rock sole were geographically the most widespread but feeding activity was temporally restricted to the dusk period. Pacific halibut were rare in shallow depths (<5 m) and fed most intensively prior to dusk. English sole fed throughout the daylight hours and were abundant only in the shallowest (<5 m) habitats. These differences in diets, foraging times, and habitat use appear related to previously documented species-specific behavioral characteristics as well as general spatial (increasing with depth) and temporal (increasing during foraging activity) variations in predation risk. At one extreme, the conservative behavioral strategy of northern rock sole may permit use of a broader range of foraging habitats, whereas English sole may be restricted to shallow water by limited behavioral responses to predation threat. These observations demonstrate that the appearance of habitat partitioning is not due to differences in sensory ability, but reflects multi-faceted, species-specific responses to the ecological tradeoffs between foraging and predation risks.

Ecosystem models show combined effects of fishing, predation, competition, and ocean productivity on Steller sea lions (Eumetopias jubatus) in Alaska

Steller sea lions (Eumetopias jubatus) increased in the eastern portion of their range while declining in the Gulf of Alaska and Aleutian Islands from the late 1970s to late 1990s. We constructed ecosystem models of the central and western Aleutians and of southeast Alaska to simultaneously evaluate four hypotheses explaining sea lion dynamics: killer whale (Orcinus orca) predation, ocean productivity, fisheries, and competition with other species. Comparisons of model predictions with historical time series data indicate that all four factors likely contributed to the trends observed in sea lion numbers in both ecosystems. Changes in ocean productivity conveyed by the Pacific Decadal Oscillation influenced the abundance trajectory of several species. Fishing could have affected the ecosystem structure by influencing the abundance of Atka mackerel (Pleurogrammus monopterygius) in the Aleutians and Pacific herring (Clupea pallasii) in southeast Alaska. Pacific halibut (Hippoglossus stenolepis) in the Aleutians and arrowtooth flounder (Atheresthes stomias) in southeast Alaska appear to impede sea lion population growth through competitive interactions. Predation by killer whales was important when sea lions were less abundant in the 1990s in the Aleutians and in the 1960s in Southeast Alaska, but appear to have little effect when sea lion numbers were high.

Wounding and reflex impairment may be predictors for mortality in discarded or escaped fish

The goal of this study was to test the hypothesis that wounding and reflex impairment, measures of fish condition, could be used to predict mortality in flatfish and roundfish that had been towed in a net in the laboratory. The extent of fish wounding resulting from net abrasion was measured with computer analysis of green fluorescence that occurred when fluorescein was retained in wounds and illuminated with ultraviolet light. Reflex impairment was measured in free swimming fish 5 min after towing by observing orientation, and startle responses to visual and mechanical stimuli. Wounding was related to mortality in walleye pollock, a species that was sensitive to net abrasion, but not in other less sensitive species. Wounding may not predict mortality associated with environmental factors and combinations of stressors in fishing, as the effects of these factors can change without corresponding changes in the extent of wounding. Reflex impairment in walleye pollock, sablefish, northern rock sole, and Pacific halibut was significantly related to mortality in biphasic relationships described by sigmoid curves ( y = a / ( 1 + e − ( x − x 0 / b ) ) ) . Measurement of reflex impairment may be a powerful tool for expanding the scope and replication of fishing experiments in the field and for comparing bycatch mortality among various fishing practices and fisheries.

Time course of osmoregulatory, metabolic, and endocrine stress responses of Pacific halibut following a 30-min air exposure

Summary Endocrine, metabolic and osmoregulatory changes in Pacific halibut upon capture and at intervals following a 30-min air exposure were measured. Concentrations of cortisol, sodium, and chloride in plasma and serum peaked two hours after the stressor. Thirty minutes after a 30-min air exposure concentrations of glucose in plasma had increased significantly from levels obtained immediately after the stressor and remained elevated for up to 4 h. Plasma lactate was also elevated 30 min after the stress treatment and lactate concentrations increased significantly at each subsequent sampling interval, 2 and 4 h. There was a significant linear increase in plasma lactate for fish sampled from 1.5 to 6.5 h after capture. Incidence of delayed mortality was low; of 22 experimentally stressed animals only one died over a 10-day monitoring period. These data illustrate the difficulties in using single time-point plasma indices of stress to assess condition of animals after capture since the time-course of physiological changes associated with the stress response vary with parameter measured and may take hours to be fully expressed.

Temperature affects activity and feeding motivation in Pacific halibut: Implications for bait-dependent fishing

Laboratory experiments were conducted to test the hypothesis that temperature (2–10 °C) and recent feeding history (1–14 days food deprivation) influence the activity and feeding motivation of Pacific halibut ( Hippoglossus stenolepis). Activity was examined before and after presentation of a chemical cue prepared from squid ( Loligo opalescens). Spontaneous activity in 2 °C was essentially zero and increased with temperature. Searching behavior increased with cue introduction in all treatments and search intensity was closely correlated with temperature. Food deprivation did not significantly affect either pre- or post-cue activity. The number of baits located, attacked and consumed increased with temperature, and the times required to accomplish those behaviors decreased significantly with temperature. In most cases, very slow responses occurred at 2 °C, differences between 4 and 6 °C were small and not significant, and times were shortest in 10 °C. Temperature did not have a significant effect on latency in attack or bait handling time, and feeding history had no significant effects on any of the timed measures. These results indicate a large potential impact of temperature on Pacific halibut catchability in longline surveys. Stock size could be significantly underestimated in a cold season or cold year and in deep water environments where temperatures are low.