Pacific Halibut Research Articles

What are we protecting? Fisher behavior and the unintended consequences of spatial closures as a fishery management tool

Spatial closures like marine protected areas (MPAs) are prominent tools for ecosystem-based management in fisheries. However, the adaptive behavior of fishermen, the apex predator in the ecosystem, to MPAs may upset the balance of fishing impacts across species. While ecosystem-based management (EBM) emphasizes the protection of all species in the environment, the weakest stock often dominates management attention. We use data before and after the implementation of large spatial closures in a North Pacific trawl fishery to show how closures designed for red king crab protection spurred dramatic increases in Pacific halibut bycatch due to both direct displacement effects and indirect effects from adaptations in fishermen's targeting behavior. We identify aspects of the ecological and economic context of the fishery that contributed to these surprising behaviors, noting that many multispecies fisheries are likely to share these features. Our results highlight the need either to anticipate the behavioral adaptations of fishermen across multiple species in reserve design, a form of implementation error, or to design management systems that are robust to these adaptations. Failure to do so may yield patterns of fishing effort and mortality that undermine the broader objectives of multispecies management and potentially alter ecosystems in profound ways.

Determination of mercury in fish otoliths by cold vapor generation inductively coupled plasma mass spectrometry (CVG-ICP-MS)

A method based on cold vapor generation inductively coupled plasma mass spectrometry (CVG-ICP-MS) has been developed for determination of inorganic mercury, Hg(II), and total mercury in fish otoliths. Sodium borohydride (NaBH4) was used as the only reducing agent and its concentration was optimized across an acidity gradient to selectively reduce Hg(II) without affecting methylmercury, CH3Hg(I). Inorganic Hg was quantitatively reduced to elemental mercury (Hg0) with 1×10−4% (m/v) NaBH4. CH3Hg(I) required a minimum of 0.5% (m/v) NaBH4 for complete reduction. Increasing the HCl concentration of solution to 5% (v/v) improved the selectivity toward Hg(II) as it decreased the signals from CH3Hg(I) to baseline levels. Potassium ferricyanide solution was the most effective in eliminating the memory effects of Hg compared with a number of chelating and oxidizing agents, including EDTA, gold chloride, thiourea, cerium ammonium nitrate and 2-mercaptoethylamine chloride. The relative standard deviation (RSD) was less than 5% for 1.0μgL−1 Hg(II) solution. The detection limits were 4.2 and 6.4ngL−1 (ppt) for Hg(II) and total Hg, respectively. Sample dissolution conditions and recoveries were examined with ultra-pure CaCO3 (99.99%) spiked with Hg(II) and CH3HgCl. Methylmercury was stable when dissolution was performed with up to 20% (v/v) HCl at 100°C. Recoveries from spiked solutions were higher than 95% for both Hg(II) and CH3Hg(I). The method was applied to the determination of Hg(II) and total Hg concentrations in the otoliths of red emperor (CRM 22) and Pacific halibut. Total Hg concentration in the otoliths was 0.038±0.004μgg−1 for the red emperor and 0.021±0.003μgg−1 for the Pacific halibut. Inorganic Hg accounted for about 25% of total Hg indicating that Hg in the otoliths was predominantly organic mercury (e.g., methylmercury). However, as opposed to the bioaccumulation in tissues, methylmercury levels in otoliths was very low suggesting a different route of uptake, most likely through the deposition of methylmercury available in the water.

Temporal and Ontogenetic Variability in Trophic Role of Four Groundfish Species—Walleye Pollock, Pacific Cod, Arrowtooth Flounder, and Pacific Halibut—around Kodiak Island in the Gulf of Alaska

AbstractChanges in trophic position estimates of commercial fishery catches are used as an ecosystem‐based indicator for sustainability, but often these estimates do not incorporate species‐specific seasonal feeding dynamics and ontogenetic diet changes. Using stable isotope analysis, we obtained a fine‐scale resolution of ontogenetic and temporal (interannual and seasonal) variations in the trophic roles of four commercially and ecologically important groundfish species in the Gulf of Alaska: walleye pollock Theragra chalcogramma, Pacific cod Gadus macrocephalus, arrowtooth flounder Atheresthes stomias, and Pacific halibut Hippoglossus stenolepis. For each groundfish taxon, the nitrogen stable isotope signature (δ15N) increased with total length. In contrast, the lipid‐normalized carbon stable isotope signature (δ13C′) significantly varied with size‐class only for walleye pollock. There were species‐specific differences in trophic position; adult Pacific cod fed at the highest trophic position, and walleye pollock fed at the lowest trophic position. Walleye pollock also had the lowest δ13C′, indicating a mainly pelagic diet, while Pacific halibut and Pacific cod had the highest δ13C′, indicating a mostly benthic diet. Interannual differences in trophic position were detected for each species. Pacific cod, arrowtooth flounder, and Pacific halibut fed at a significantly lower trophic position in 2003 than in 2001, 2002, or 2004. All species had a significantly lower average δ13C′ (i.e., a more benthic diet) in 2001 and a higher average δ13C′ (a more pelagic diet) in 2003. Pacific cod, Pacific halibut, and walleye pollock had a significantly more pelagic diet in the summer. Walleye pollock, arrowtooth flounder, and Pacific halibut showed a significantly more benthic diet in the fall, which probably corresponded with their seasonal migrations. Temporal variations in stable isotope signatures were observed but were relatively small (<1.25‰). Length‐based ontogenetic diet shifts, however, were much larger (up to 6‰) and must be considered when trophic position is used as an ecosystem indicator of sustainability.

Use of Veterinary Ultrasound to Identify Sex and Assess Female Maturity of Pacific Halibut in Nonspawning Condition

AbstractUltrasound was used for sex identification and female maturity assessment of Pacific halibut Hippoglossus stenolepis ranging from 64‐ to 144‐cm fork length collected during their nonspawning period (boreal summer) in the central and eastern Gulf of Alaska. Ultrasonic sex identification employed inspection of gross morphology and gonadal morphometrics, the latter involving determination of gonad length (maximum posterior gonad extent [MPGE]) and testing for difference between sexes. Morphometric analysis was refined further for females by removing ovaries, macroscopically determining maturity status, and comparing MPGE and proportional ovarian length (POL) among maturity stages. Ultrasonically determined gross morphology was sufficient to achieve accurate sex identification in even the smallest individuals examined. Ovaries were rounded anteriorly with no apparent internal structure, whereas testes were sickle‐shaped with characteristic internal structure formed by the junctures between testicular lobes. Maximum posterior gonad extent was significantly greater for females but did not provide accurate sex determination because values overlapped considerably between sexes; 80% of all fish (n = 147) exhibited MPGE within the range of overlap. Values of both MPGE and POL overlapped considerably between mature and immature females, but threshold values were identified for both metrics above which all individuals were mature. Only for POL was a lower threshold apparent, below which all individuals were immature. Considering MPGE and POL simultaneously suggested a possible means for identifying first‐time spawners and may warrant additional investigation.Received January 13, 2011; accepted June 2, 2011

Alaskan flatfishes on the German market: part 1: identification by DNA and protein analytical methods

North Pacific flatfishes are gaining increased popularity on the German market. Isoelectric focusing of sarcoplasmic proteins and PCR-based DNA analysis were applied to identify fillets of nine Alaskan Flatfish species: Artheresthes stomias (Arrow-tooth flounder), Limanda aspera (Yellowfin sole), Isopsetta isolepis (Butter sole), Lepidopsetta bilineata (Southern rock sole), Lepidopsetta polyxystra (Northern rock sole), Hippoglossus stenolepis (Pacific halibut), Hippoglossoides elassodon (Flathead sole), Platichthys stellatus (Starry flounder), and Glyptocephalus zachirus (Rex sole). Characteristic protein patterns were obtained for raw fillets of several species. Reactivity of flatfish DNA against five pairs of primers was tested, amplifying segments of the mitochondrial cytochrome b, cytochrome oxidase subunit I, 16S rRNA gene, as well as the nuclear parvalbumin gene. Amplicons of the cytochrome b gene were sequenced and used for single-strand conformation polymorphism analysis. The survey of deep-frozen commercial yellowfin sole fillets resulted in the detection of 17% of the fillets being mislabelled; Northern rock sole, butter sole and flathead sole had been used as substitutes.

Analysis of match–mismatch between commercial fishing periods and spawning ecology of Pacific halibut (Hippoglossus stenolepis), based on winter surveys and behavioural data from electronic archival tags

Abstract Loher, T. 2011. Analysis of match–mismatch between commercial fishing periods and spawning ecology of Pacific halibut (Hippoglossus stenolepis), based on winter surveys and behavioural data from electronic archival tags. – ICES Journal of Marine Science, 68: 2240–2251. The fishery for halibut (Hippoglossus stenolepis) in the eastern Pacific is closed during the boreal winter, roughly corresponding to the seasonal spawning of the species. Opening and closing dates for each season are stipulated annually based on economics and biology. Historical surveys and data from electronic tags are analysed to assess the extent to which recent closures have encompassed the annual spawning cycle of the species, as defined by migration to offshore spawning sites, active spawning, and return to feeding areas. These were assessed by calculating mean maximum daily depth profiles for fish exhibiting seasonal migration, calculating the date-specific proportions of the tagged population either migrating to or resident on their feeding or spawning grounds, and examining the temporal distribution of spent and running fish in historical surveys along with evidence of spawning contained in high-resolution tag data. The data indicate that fishery closures over the past 20 years have been consistently too short to protect the entirety of a migration period that begins as early as September and is not substantially completed until May. Additionally, some recent season openings have encroached on the active spawning season. Failure to fully protect spawning migrations may allow seasonal interception fisheries, and the selective removal of early and late spawners could cause changes in stock demographics, restrict effective spawning, and influence long-term stock productivity, especially in the face of environmental variability.

Use of Fish Hydrolysates and Fish Meal Byproducts of the Alaskan Fishing Industry in Diets for Pacific White Shrimp Litopenaeus vannamei

AbstractWe determined the suitability of four fish hydrolysates and two fish meals (Pacific halibut Hippoglossus stenolepus and arrowtooth flounder Atheresthes stomias; all derived from byproducts of the Alaskan fishing industry) as replacements for menhaden fish meal in shrimp diets. A control diet (30% crude protein; 8.5% crude lipid) was produced with menhaden meal (13% of diet). Experimental diets were manufactured by using each hydrolysate or fish meal to replace 50% of the menhaden meal on an isonitrogenous basis. Each diet was fed to Pacific white shrimp Litopenaeus vannamei in an outdoor, zero‐water‐exchange system for 8 weeks. Final weight, survival, feed efficiency, and growth rate were compared among treatments by analysis of variance. The final weights and growth of Pacific white shrimp fed two of the hydrolysates (one acidified to pH 3.8 and left in a liquid state; the other acidified, then neutralized to pH 6.5 and drum‐dried) and the two fish meals were not different from those of shrimp fed the control diet. Shrimp that were given the other two hydrolysates (one acidified to pH 3.8 and then drum‐dried; the other hydrolyzed [but not acidified] and then drum‐dried) had lower final weights and growth than shrimp fed the control diet. These data indicate that the two fish meals and two of the hydrolysates in this trial can replace 50% of menhaden meal in diets for shrimp, although there is some loss of growth potential in some cases. The lack of a diet effect on feed efficiency indicates that the growth differences were mostly the result of differences in feed intake rather than nutritional quality.

Constant proportion harvest policies: Dynamic implications in the Pacific halibut and Atlantic cod fisheries

Overfishing, pollution and other environmental factors have greatly reduced commercially valuable stocks of fish. In a 2006 Science article, a group of ecologists and economists warned that the world may run out of seafood from natural stocks if overfishing continues at current rates. In this paper, we explore the interaction between a constant proportion harvest policy and recruitment dynamics. We examine the discrete-time constant proportion harvest policy discussed in Ang et al. (2009) and then expand the framework to include stock-recruitment functions that are compensatory and overcompensatory, both with and without the Allee effect. We focus on constant proportion policies (CPPs). CPPs have the potential to stabilize complex overcompensatory stock dynamics, with or without the Allee effect, provided the rates of harvest stay below a threshold. If that threshold is exceeded, CPPs are known to result in the sudden collapse of a fish stock when stock recruitment exhibits the Allee effect. In case studies, we analyze CPPs as they might be applied to Gulf of Alaska Pacific halibut fishery and the Georges Bank Atlantic cod fishery based on harvest rates from 1975 to 2007. The best fit models suggest that, under high fishing mortalities, the halibut fishery is vulnerable to sudden population collapse while the cod fishery is vulnerable to steady decline to zero. The models also suggest that CPP with mean harvesting levels from the last 30 years can be effective at preventing collapse in the halibut fishery, but these same policies would lead to steady decline to zero in the Atlantic cod fishery. We observe that the likelihood of collapse in both fisheries increases with increased stochasticity (for example, weather variability) as predicted by models of global climate change.

Age and growth of the Pacific halibut Hippoglossus stenolepis and the size-age composition of its catches in the North-Western part of the Pacific Ocean

The results of investigation are discussed on age and growth of the Pacific halibut Hippolglossus stenolepis, as well as size-age composition of its catches in three regions of the North-Western Pacific—in Navarin area of the Bering Sea, in Pacific waters on the Northern Kurils and south-eastern Kamchatka, of the Southern Kurils—from the end of the last century. The growth rate of Pacific halibut is similar in all three regions in spite of their considerable geographic remoteness. No significant differences in the growth rate of males and females in these regions, as well as no significant interannual differences in growth of specimens caught in Pacific waters off the Northern Kurils and south-eastern Kamchatka in 1996–2000, are found. Comparison of the present-day size-age composition and that in the beginning-middle of the last century revealed their considerable similarity.

Genetic Sex Identification and the Potential Evolution of Sex Determination in Pacific Halibut (Hippoglossus stenolepis)

The discovery of genetic markers linked to physiological traits in wild populations is increasingly desired for ecological and evolutionary studies, as well as to inform management decisions. However, identifying such markers often requires a large investment of both time and money. Serendipitously, in a recent microsatellite survey, we discovered three out of 16 microsatellite loci that were correlated to the female sex in Pacific halibut (Hippoglossus stenolepis). These three loci were screened in 550 Pacific halibut to determine their accuracy at identifying sex. Genetic assignment successfully identified sex in 92% of individuals from sample collections spanning 3,000 km and 9 years. All but two of 287 females had one copy of a characteristic allele for at least one of the three microsatellite loci, resulting in consistent heterozygote excess in females. This pattern is consistent with the hypothesis that females are the heterogametic sex in Pacific halibut, which thus may have a different sex-determination pattern than the closely related Atlantic halibut (Hippoglossus hippoglossus). A rapid divergence of sex-determining mechanisms could be either a cause or consequence of speciation between Pacific and Atlantic halibut. In either case, the ability to genetically identify sex in individual Pacific halibut provides a new tool for ecological studies, fisheries management, and insight into the evolution of sex determination in flatfish.

Seasonal abundance and distribution of pelagic and demersal fishes in southeastern Alaska

We quantified seasonal and interannual variability of pelagic and demersal fishes available to marine predators in southeastern Alaska focusing on prey of the Steller sea lion ( Eumetopias jubatus). Estimates of abundance were determined from echo integration mid-water trawl and demersal longline surveys. The dominant species were walleye pollock ( Theragra chalcogramma) (average biomass 9057 t), Pacific hake ( Merluccius productus) (1715 t), Pacific herring ( Clupea pallasii) (1176 t), Pacific halibut ( Hippoglossus stenolepis) (average catch rate 524 kg per 1000 hooks), Pacific cod ( Gadus macrocephalus) (177 kg per 1000 hooks), sablefish ( Anoplopoma fimbria) (120 kg per 1000 hooks), and sandpaper skate ( Bathyraja interrupta) (26 kg per 1000 hooks). Of these species, seasonal differences in species abundance were detected for walleye pollock ( p = 0.03), Pacific cod ( p = 0.001) and sablefish ( p < 0.001) with walleye pollock the most abundant and widespread species year-round. Herring, hake, and juvenile (120–350 mm) and adult (>350 mm) pollock are pelagic species. Adult and juvenile pollock and hake were found in open water, while herring, young-of-the-year (<120 mm) and the smallest juvenile pollock were found in bays. Herring of all ages concentrate in dense schools. Pollock and hake form scattered layers throughout open water with juvenile pollock shallower than adult pollock and adult pollock shallower than hake. Halibut, sablefish, skates, Pacific cod and arrowtooth flounder are demersal species; sablefish were deeper than the other demersal species. These seasonal and annual changes in prey availability affected prey selection of sea lions which shifted their diet in response.

Dispersal and behavior of Pacific halibut Hippoglossus stenolepis in the Bering Sea and Aleutian Islands region

Currently, it is assumed that eastern Pacific halibut Hippoglossus stenolepis belong to a single, fully mixed population extending from California through the Bering Sea, in which adult halibut disperse randomly throughout their range during their lifetime. However, we hypothesize that hali but dispersal is more complex than currently assumed and is not spatially random. To test this hypo thesis, we studied the seasonal dispersal and behavior of Pacific halibut in the Bering Sea and Aleutian Islands (BSAI). Pop-up Archival Transmitting tags attached to halibut (82 to 154 cm fork length) during the summer provided no evidence that individuals moved out of the Bering Sea and Aleutian Islands region into the Gulf of Alaska during the mid-winter spawning season, supporting the concept that this region contains a separate spawning group of adult halibut. There was evidence for geographically localized groups of halibut along the Aleutian Island chain, as all of the individuals tagged there displayed residency, with their movements possibly impeded by tidal currents in the passes between islands. Mid-winter aggregation areas of halibut are assumed to be spawning grounds, of which 2 were previously unidentified and extend the species' presumed spawning range ∼1000 km west and ∼600 km north of the nearest documented spawning area. If there are indeed inde- pendent spawning groups of Pacific halibut in the BSAI, their dynamics may vary sufficiently from those of the Gulf of Alaska, so that specifically accounting for their relative segregation and unique dynamics within the larger population model will be necessary for correctly predicting how these com- ponents may respond to fishing pressure and changing environmental conditions.

Physiological responses of Pacific halibut, Hippoglossus stenolepis, to intracoelomic implantation of electronic archival tags, with a review of tag implantation techniques employed in flatfishes

Management of Pacific halibut (Hippoglossus stenolepis), a long-lived flatfish, is complicated by possible ontogenic and sex-specific variation in migration. Archival tags promise the ability to help uncover long-term movement patterns at the individual level, if the tags can be retained and recovered from healthy fish. We examined fifteen individuals (69–90 cm fork length) for long-term physiological response to intracoelomic implantation of three types of archival tags: fully internal, internal with right angle protruding light stalk, and internal with straight protruding light stalk. Tags represented 0.05–0.16% of initial fish weights. Fish were reared at 10.8 ± 1.1°C for 59 weeks post-surgery. One fish died after 39 weeks from thermal stress unrelated to the surgical procedure. Temporal variation in behavior of tagged fish was indistinguishable from that of controls (n = 15 tagged, 5 controls). Treatment and control-group fish grew at similar rates. No tag expulsion or physiological response was evident in the individual that died at 39 weeks, but nine of eleven individuals dissected at the end of 59 weeks had developed internal responses. These responses ranged from deposition of fibrous protein and/or calcitic material on tag surfaces to partial or full tag encapsulation in either the visceral peritoneal layer (fully-internal tags) or the intestinal mesenteries (stalk-bearing tags). The responses were within the range reported for other pleuronectids implanted with tags of similar configuration and may have implications for design and interpretation of long-term tagging studies. Encapsulation may reduce the probability of tag recoveries even in the absence of tag expulsion, especially in species eviscerated at sea.

Using food web model results to inform stock assessment estimates of mortality and production for ecosystem-based fisheries management

Examining food web relationships for commercially important species enhances fisheries management by identifying sources of variability in mortality and production that are not included in standard single-species stock assessments. We use a static mass-balance model to evaluate relationships between species in a large marine ecosystem, the coastal Gulf of Alaska, USA. We focus on food web relationships for four case-study species: Pacific halibut ( Hippoglossus stenolepis ), longnose skate ( Raja rhina ), walleye pollock ( Theragra chalcogramma ), and squids (order Teuthoidea). For each, we present the species’ position within the food web, evaluate fishing mortality relative to predation mortality, and evaluate diet compositions. We find that high trophic level (TL) species, whether commercially valuable (halibut) or incidentally caught (skates), have mortality patterns consistent with single-species assessment assumptions, where fishing mortality dominates natural mortality. However, assessments for commercially valuable (pollock) or incidentally caught (squids) mid-TL species can be enhanced by including food web derived predation information because fishing mortality is small compared with high and variable predation mortality. Finally, we outline food web relationships that suggest how production of species may change with diet composition or prey availability.

A risk–benefit analysis of wild fish consumption for various species in Alaska reveals shortcomings in data and monitoring needs

Northern peoples face a difficult decision of whether or not to consume wild fish, which may contain dangerous levels of contaminants such as methylmercury (MeHg), but which also offer a number of positive health benefits, and play an important role in rural household economies. Here, new methods for developing consumption advice are applied to an existing data-set for methylmercury (MeHg) levels in Alaskan fish. We apply a quantitative risk–benefit analysis for eight freshwater, saltwater and anadromous fish species, using dose–response relationships to weigh the risks of MeHg bioaccumulation against the benefits of omega-3 fatty acids (EPA and DHA) toward cardiovascular and neurodevelopmental health endpoints. Findings suggests that consumption of many of the fish species reviewed here, including northern pike, Pacific Halibut, and arctic grayling, may lead to increased risk of coronary heart disease and declines in infant visual recognition memory. However, we also identify significant variation among regions, among studies within the same region, and also within studies, which make it difficult to craft consistent consumption advice. Whereas salmon consistently shows a net-benefit, for instance, data for arctic grayling, pike, sablefish, and some halibut are all too imprecise to provide consistent recommendations. We argue for more detailed local-scale monitoring, and identification of possible thresholds for increased risk in the future. We caution that MeHg and omega-3 FA are just two variables in a complicated calculus for weighing the risks and benefits of locally-available and culturally-significant foods, and argue for future work that takes both a place-based and plate-based approach to diet and contamination.

The Economic Impact of Saltwater Sportfishing Harvest Restrictions in Alaska: An Empirical Analysis of Nonresident Anglers

AbstractSaltwater sportfishing is a popular activity for visitors to Alaska. In this paper, a stated‐preference model of saltwater sportfishing participation is used to generate estimates of the changes in participation resulting from changes in harvest limits for three primary recreational target species in Alaska saltwater fisheries: Pacific halibut Hippoglossus stenolepis, Chinook salmon Oncorhynchus tshawytscha, and coho salmon O. kisutch. These estimates are then used in a state‐level computable general equilibrium (CGE) model to generate estimates of the economic impacts of harvest policies. We find that the impacts of changes in nonresident anglers' expenditures are smaller than those from a social accounting matrix model and that many of the impacts from an increase in expenditures leak out of state owing to Alaska's heavy dependence on imports of goods and services from the rest of the United States. Moreover, changes to harvest limits appear to have a small effect on the Alaska economy, at least in comparison with the overall size of that economy.

Identification of skate nursery habitat in the eastern Bering Sea

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 403:243-254 (2010) - DOI: https://doi.org/10.3354/meps08424 Identification of skate nursery habitat in the eastern Bering Sea Gerald R. Hoff* NOAA, National Marine Fisheries Service, Alaska Fisheries Science Center, 7600 Sand Point Way NE, Seattle, Washington 98115, USA *Email: jerry.hoff@noaa.gov ABSTRACT: Identification of habitat used for skate egg deposition has been rarely studied or reported worldwide. Four nursery sites for the Alaska skate Bathyraja parmifera, 2 for the Aleutian skate B. aleutica and 2 for the Bering skate B. interrupta were identified along the upper continental slope in the eastern Bering Sea. All sites were located near undersea canyons from 145 to 380 m depth in relatively flat sandy to muddy bottom habitat. Bottom temperatures were relatively constant throughout the year, varying from 3.7 to 4.6°C. Egg case densities varied between nursery sites and were encountered at the Alaska skate nursery in Bering Canyon at densities greater than 800000 eggs km–2. Based on egg case composition, sites were predominantly used by a single skate species for egg deposition; however, up to 6 skate species used the habitat commonly. Seasonal sampling indicated that sites were continuously occupied throughout the year, and embryo length composition showed multiple cohorts developing simultaneously. Data from bottom trawl surveys suggest juvenile skates occupy habitats different than nursery sites. The movement of juvenile skates out of nursery habitat after hatching may lessen predation by common predators such as the Pacific cod Gadus macrocephalus and the Pacific halibut Hippoglossus stenolepis. KEY WORDS: Elasmobranch · Skate · Reproduction · Egg case · Undersea canyon · Nursery · Alaska Full text in pdf format PreviousNextCite this article as: Hoff GR (2010) Identification of skate nursery habitat in the eastern Bering Sea. Mar Ecol Prog Ser 403:243-254. https://doi.org/10.3354/meps08424 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 403. Online publication date: March 22, 2010 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2010 Inter-Research.

Isotopic Correlation (δ18O versus δ13C) of Otoliths in Identification of Groundfish Stocks

AbstractThe management of many marine fish stocks suffers from a lack of genetic data or insignificant genetic differentiations, particularly for the commercially important groundfish along the U.S. Pacific coast. In this study, we investigated a large number of otoliths of various groundfish species from the coasts of Washington and Oregon and analyzed them for stable oxygen (18O/16O, or δ18O) and carbon isotope ratios (13C/12C, or δ13C). The isotopic results and correlation of δ18O versus δ13C of Pacific hake Merluccius productus, sablefish Anoplopoma fimbria, Pacific halibut Hippoglossus stenolepis, and Pacific cod Gadus macrocephalus indicated that most of the groundfish we examined had two or more spawning stocks or subpopulations; the only tested species that might belong to a single coastwide stock was yelloweye rockfish Sebastes ruberrimus. Compared with genetic methods of stock identification, the isotopic signatures of otoliths have distinct advantages in determining (1) a time series to separate the different life stages of marine fish and (2) the oceanographic and environmental conditions to which fish are exposed. Thus, stable isotopic signatures in otoliths appear to be an alternative for marine fish stocks when there is little genetic differentiation between populations or no genetic data are available.

The role of flatfishes in the organization and structure of the eastern Bering Sea ecosystem

We evaluated the role of flatfishes in the organization and structure of the eastern Bering Sea ecosystem using the Ecopath/Ecosim approach. As basic input data for the Ecopath/Ecosim model, we used estimates of biomass from bottom trawl surveys and age-structured population models, production/biomass (P/B) ratio, consumption/biomass (Q/B) ratio, diet composition (DC), and fisheries harvests for each component of species or species groups. We estimated the trophic level of each component, niche overlaps among flatfishes, and the impacts of competition and predation on flatfish species in the eastern Bering Sea ecosystem. Based on those estimates, we developed the tropho-dynamic structure of the ecosystem, and the model was used to simulate ecological effects of fishery exploitation patterns. No single flatfish species appeared to have a profound and uniquely important role in the organization and structure of the ecosystem. Instead, the most important component among the guild of flatfish species appeared to be yellowfin sole Pleuronectes asper, which had greater biomass than other flatfish and a relatively diverse diet among the small flatfish species. Pacific halibut Hippoglossus stenolepis, Greenland turbot Reinhardtius hippoglossoides, and arrowtooth flounder Atheresthes stomias were important keystone predators in the eastern Bering Sea ecosystem together with some groups of marine mammals and sea birds. Intra flatfish complex cannibalism was not observed, however, substantial diet overlaps were common in the flatfish guild system.

Incorporating ecosystem forcing through predation into a management strategy evaluation for the Gulf of Alaska walleye pollock (Theragra chalcogramma) fishery

An emerging goal of national and international fisheries management organizations is the development of an ecosystem-based approach to fisheries management. The mechanisms determining changes in an ecosystem and their impacts on marine populations are not well established for most species, but the expectations of managers are that these impacts should be accounted for when selecting management strategies. Predation is an important component of ecosystem dynamics, and predator–prey functional responses can be used to represent predation in multi-species population dynamics models. The predators of walleye pollock, Theragra chalcogramma, in the Gulf of Alaska include arrowtooth flounder (Atheresthes stomias), Pacific cod (Gadus macrocephalus), and Pacific halibut (Hippoglossus stenolepis). Management strategy evaluation is used to examine the impact of changes over time in natural mortality-at-age related to trends in predator abundance on the performance of the current management strategy for the fishery for walleye pollock in the Gulf of Alaska. The current management strategy is evaluated under nine scenarios which capture uncertainty regarding the predator–prey functional relationship and the level of future fishing mortality on the predators. The current management strategy, which ignores the possibility of changes over time in natural mortality, kept the spawning biomass high relative to the target level and had a low risk of fishing mortality exceeding the overfishing limit, due to low catches relative to the total biomass.