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1.
In 2003, the Alaska walleye pollock industry reported product quality issues attributed to an unspecified parasite in fish muscle. Using molecular and histological methods, we identified the parasite in Bering Sea pollock as Ichthyophonus. Infected pollock were identified throughout the study area, and prevalence was greater in adults than in juveniles. This study not only provides the first documented report of Ichthyophonus in any fish species captured in the Bering Sea, but also reveals that the parasite has been present in this region for nearly 20 years and is not a recent introduction. Sequence analysis of 18S rDNA from Ichthyophonus in pollock revealed that consensus sequences were identical to published parasite sequences from Pacific herring and Yukon River Chinook salmon. Results from this study suggest potential for Ichthyophonus exposures from infected pollock via two trophic pathways; feeding on whole fish as prey and scavenging on industry‐discharged offal. Considering the notable Ichthyophonus levels in pollock, the low host specificity of the parasite and the role of this host as a central prey item in the Bering Sea, pollock likely serve as a key Ichthyophonus reservoir for other susceptible hosts in the North Pacific.  相似文献   

2.
Walleye pollock is the second most extensively fished species in the world. The major fishing grounds include the Bering and Okhotsk Seas. Large-scale fishing started in the 1960s and continues to date with average annual landings over this 50-year period of 1.5 million tons. Yet over this period catches were characterized by considerable volatility. This volatility makes rational management of stock and planning of annual fishing activities difficult. The changes in annual catches correlate with the changes in the biomass of walleye pollock. Existing data suggest a close link between climate change in the northern Pacific and biomass, which allows quantitative estimates of future trends in the biomass, and consequently annual catch, of walleye pollock. Cooling of the northern Pacific is expected to increase the biomass in the Sea of Japan and decrease it in the Bering Sea and Sea of Okhotsk. The opposite is predicted to occur if the northern Pacific experiences warming.  相似文献   

3.
Information on the annual variability in abundance and growth of juvenile groundfish can be useful for predicting fisheries stocks, but is often poorly known owing to difficulties in sampling fish in their first year of life. In the Western Gulf of Alaska (WGoA) and Eastern Bering Sea (EBS) ecosystems, three species of puffin (tufted and horned puffin, Fratercula cirrhata, Fratercula corniculata, and rhinoceros auklet, Cerorhinca monocerata, Alcidae), regularly prey upon (i.e., “sample”) age-0 groundfish, including walleye pollock (Gadus chalcogramma, Gadidae) and Pacific cod (Gadus microcephalus, Gadidae). Here, we test the hypothesis that integrating puffin dietary data with walleye pollock stock assessment data provides information useful for fisheries management, including indices of interannual variation in age-0 abundance and growth. To test this hypothesis, we conducted cross-correlation and regression analyses of puffin-based indices and spawning stock biomass (SSB) for the WGoA and EBS walleye pollock stocks. For the WGoA, SSB leads the abundance of age-0 fish in the puffin diet, indicating that puffins sample the downstream production of the WGoA spawning stock. By contrast, the abundance and growth of age-0 fish sampled by puffins lead SSB for the EBS stock by 1–3 years, indicating that the puffin diet proxies incoming year class strength for this stock. Our study indicates connectivity between the WGoA and EBS walleye pollock stocks. Integration of non-traditional data sources, such as seabird diet data, with stock assessment data appears useful to inform information gaps important for managing US fisheries in the North Pacific.  相似文献   

4.
Ecosystem‐based fisheries management requires the development of physical and biological time series that index ocean productivity for stock assessment and recruitment forecasts for commercially important species. As recruitment in marine fish is related to ocean condition, we developed proxies for ocean conditions based on sea surface temperature (SST) and biometric measurements of chum salmon (Oncorhynchus keta) captured in the walleye pollock (Gadus chalcogrammus) fishery in the eastern Bering Sea in three periods (July 16–30, September 1–15 and September 16–30). The main purpose of this paper was to evaluate Pacific salmon (Oncorhynchus spp.) growth as a possible indicator of ocean conditions that, in turn, may affect age‐1 walleye pollock recruitment. Marine growth rates of Pacific salmon are the result of a complex interplay of physical, biological and population‐based factors that fish experience as they range through oceanic habitats. These growth rates can, therefore, be viewed as indicators of recent ocean productivity. Thus, our hypothesis was that estimated intra‐annual growth in body weight of immature and maturing age‐4 male and female chum salmon may be used as a biological indicator of variations in rearing conditions also experienced by age‐0 walleye pollock; consequently, they may be used to predict the recruitment to age‐1 in walleye pollock. Summer SSTs and chum salmon growth at the end of July and September explained the largest amount of variability in walleye pollock recruitment indicating that physical and biological indices of ocean productivity can index fish recruitment.  相似文献   

5.
We investigated the distributional shifts of groundfish in response to anomalous ocean conditions, particularly the recent anomalously warm period (2014–2016; “The Blob”), based on data from ten Gulf of Alaska bottom trawl surveys conducted by the Alaska Fisheries Science Center during 1996–2015. Six groundfish species were considered: Pacific cod (Gadus macrocephalus), arrowtooth flounder (Atheresthes stomias), walleye pollock (Gadus chalcogrammus), Pacific ocean perch (Sebastes alutus), northern rock sole (Lepidopsetta polyxystra), and southern rock sole (Lepidopsetta bilineata). Ontogenetic differences were examined by dividing data for each fish species into size classes. Our study demonstrated that after accounting for size‐specific depth preferences, the spatial responses of groundfish to anomalous ocean conditions differed by species and foraging guild in the central Gulf of Alaska. Pacific cod and arrowtooth flounder showed similar responses to ocean warming, but different responses to cooling. In general, Pacific cod moved to deeper depths in warmer years and moved to shallower depths in colder years. Arrowtooth flounder also moved deeper in warmer years. However, in colder years, large arrowtooth flounder (>40 cm) shifted toward shallower depths while smaller‐sized fish shifted toward deeper depths. In warmer years, large pollock (>30 cm) moved to deeper waters while smaller pollock (10–20 cm) moved to shallower waters. Pacific ocean perch exhibited an opposite response to thermal changes in habitat compared with Pacific cod and arrowtooth flounder. They moved deeper in colder years, but there was no clear change in depth as a function of size in response to warmer habitat.  相似文献   

6.
Larval and early juvenile fishes were sampled from the eastern Bering Sea (EBS) shelf from 2001 to 2005, and in 2007. Data from these collections were used to examine spatial and temporal patterns in species assemblage structure and abundance. The years 2001–2005 were unusual because the EBS water temperature was ‘warm’ compared with the long‐term mean temperature. In contrast, 2007 was a ‘cold’ year. The abundance of the five most numerous taxa at 12 stations common to all years sampled (1996–2005, 2007) were significantly different among years. Larval and early juvenile stage Theragra chalcogramma (walleye pollock), a commercially important gadid, were by far the most abundant fish in all years. Bottom depth alone best explained assemblage structure in most years, but in others, bottom depth and water column temperature combined and percent sea‐ice coverage were most important. Abundance of T. chalcogramma larvae increases with water column temperature until 5°C and then becomes level. Higher abundances of Gadus macrocephalus (Pacific cod) larvae occur in years with the greatest percent sea‐ice cover as indicated by GAM analysis. Larvae of Lepidopsetta polyxystra (northern rock sole) increase in abundance with increasing maximum wind speed, but decrease at a later date during the last winter storm. The data are consistent with the hypothesis that oceanographic conditions, specifically water temperature and sea‐ice coverage, affect the spatial and temporal pattern of larval abundances. In general, ichthyoplankton species assemblages can be important early indicators of environmental change in the Bering Sea and potentially other subarctic seas as well.  相似文献   

7.
Interannual variability in growth of walleye pollock, Theragra chalcogramma, was examined. Adult walleye pollock were collected from the central Bering Sea (Aleutian Basin) from 1978 to 1999. Average fork lengths were found to be approximately 47 cm during the 1970–80s, this increased to 56 cm in the late 1990s. Age was determined for 4805 individuals using the otolith break and burn method. Ages ranged from 5–23 years and the year classes of 1978 and 1989 were dominant in the 1980s and the 1990s, respectively. Fish had significantly larger length-at-age in the 1990s compared to the 1970–80s, and interannual variability in age–length relationship was clearly observed. Taking into consideration a recent decrease of the walleye pollock biomass in the central Bering Sea, density-dependent growth was supported as one possibility of the growth variability. At the same time, we could not rule out the possibility that oceanographic variability affected the growth of walleye pollock in the area.  相似文献   

8.
I examined the age, growth, maturity, mortality, and body condition of walleye pollock, Theragra chalcogramma, in the northeastern Japan Sea (northern Japan Sea population) and evaluated their resilience to exploitation. Walleye pollock were collected in pre-spawning (October 1991-1995) and post-spawning (April 1990-1996) seasons. Estimated ages ranged from 3 to 18 years for both sexes. A von Bertalanffy growth model showed that females had longer asymptotic fork length (460 mm) than males (425 mm). Fifty percent of females and males were mature at 348 mm (4.6 years) and 322 mm (3.9 years), respectively. The instantaneous natural mortality rate was estimated to be 0.22. These life-history traits in the northern Japan Sea population were compared to those in the Bering Sea, the Gulf of Alaska, and the Japan Pacific populations. As a result, female walleye pollock in this population matured at small body sizes, grew rapidly toward small maximum sizes, and had short reproductive lifespans with low size-specific fecundity and poor body condition. Low prey availability and habitat temperatures are considered as a possible mechanism for the small maximum sizes in this population. The potential rate of population increase of both the northern Japan Sea population and other pollock populations tended to be lower than other exploited populations of non-viviparous marine fishes, suggesting potentially lower resilience to exploitation in this population and walleye pollock populations in general.  相似文献   

9.
Populations of several species of marine birds and mammals in the Bering Sea and Gulf of Alaska have been declining since the mid-1970s, with numbers of one, the Steller sea lion (Eumetopias jubatus) , so depressed it was listed as threatened under the Endangered Species Act in spring 1990. All of the declining populations depend to an important extent on walleye pollock (Theragra chakogramma) for food, although they eat numerous other species as well. In contrast, certain animals that compete with pollock for common prey have been increasing in abundance. All of these changes could be related through food web connections mediated by pollock. Pollock is also important to people–it presently supports the largest single-species commercial fishery in the world, in large part because of its great biomass, which has averaged about 15 × 106t in the Bering Sea over the past 15 years. Pollock consume an inordinate proportion of the pelagic production in the Bering Sea, which further supports the conclusion that it is a key species in the ecosystem. However, there are conflicting hypotheses about the importance of the roles played by pollock as predator and prey, and about the effect that changes in pollock abundance might have on biomass yield at higher trophic levels.  相似文献   

10.
ABSTRACT: Stocks of walleye pollock Theragra chalcogramma collected from: (i) the Sea of Japan (off Rebun Island and Kumaishi); (ii) the Pacific coast (off Shikabe and eastern Hokkaido); and (iii) Nemuro Strait off Hokkaido, northern Japan, were examined for anisakid nematodes during December 1999 to February 2000, and the prevalence and abundance of Anisakis simplex and Contracaecum osculatum larvae were compared among the various sampling sites for fish of the same size and age. Anisakis simplex was generally more abundant than C. osculatum . Infection by A. simplex varied between the aforementioned stocks of walleye pollock as well as within stocks, whereby fish from off Rebun Island and Nemuro Strait were infected the most, followed by those from off the Pacific coast and Kumaishi. Infection by C. osculatum differed between the host stocks, and C. osculatum was the most abundant among the fish from Nemuro Strait. The infection variations seemed to be due to differences in host growth rate, host feeding habit, and the distribution of marine mammal final hosts. The results indicate that these two larval nematodes are useful biological indicators for the population study of walleye pollock in Japanese waters.  相似文献   

11.
Acoustic survey data were used to estimate the abundance and distribution of age-0 walleye pollock and zooplankton near the Pribilof Islands, Bering Sea, nursery area at two time periods in two consecutive years: the beginning of August, and mid-September, of 1996 and 1997. The 1996 pollock year class ultimately produced a large adult cohort in the eastern Bering Sea, while the 1997 year class produced a below-average adult cohort. Acoustic densities of age-0 pollock were significantly lower in August – and declined more strongly from August to September – in 1997 than in 1996, indicating that the trend to adult cohort strength was already set by August. Diet composition analyses revealed that age-0 pollock ate a much higher proportion of euphausiids in 1997 than in 1996, despite lower acoustic abundance of euphausiids in 1997. We infer that in 1996, age-0 pollock experienced greater feeding success by August, with high concentrations of copepods available for smaller fish to consume, and high concentrations of euphausiids available for larger individuals. In 1997, age-0 pollock had lower body condition in August and may have been limited by the availability of small (<2 mm) copepods. Bioenergetic modeling of prey consumption did not indicate a likelihood that age-0 pollock would begin to deplete euphausiids until late August in 1996, and not at all between August and mid-September in 1997.  相似文献   

12.
Eastern Bering Sea pollock have two distinctly different stable spawning grounds—along the shelf and in the eastern and central Aleutian Islands between 400 and 500 m water columns. Pollock spawning behavior supports the hypothesis that the shelf and deepwater “basin” spawning pollock are completely independent reproductive stocks. Deepwater pollock inhabit the shelf and, once mature at age 5–6 years, migrate from the shelf onto the continental slope into the Zhemchug, Pribilof, and Bering canyons by the end of winter. Bering Sea pollock recruitment and year class abundance have high annual variability, but there are no clear relationships between pollock year class strength and water temperature, ice distribution or survival on early ontogenesis stages (eggs and larvae). Young-of-the-year fish survival varies dramatically during winter supporting the hypothesis that the Bering Sea pollock recruitment and strength of year class have high annual variability depending on young-of-the-year fish survival during winter. The annual change of physical oceanography condition, productivity and species composition of zooplankton community are associated with great differences in pollock seasonal migrations and distribution, reproduction, survival of recruits at early stages of development and finally with abundance of year classes and total biomass. Implementation of ecosystem-based fishery management most important for application of pollock research both of Russian national program and on base of International Agreements.  相似文献   

13.
Abstract. Pacific flatfish from North American and Japanese coastal waters regularly manifest skin tumours. Those are generally papillomas, which develop from primary inflammatory nodules (vascularized nodules) on fish of a few months's age. Inside the epidermal part of the tumour slightly dedifferentiated malpighian cells change to rounded enlarged cells showing evidence of considerable degeneration (vacuolization and destruction of the cell organelles). These 'X-cells', which compose the major part of the mature tumour, always remain characteristically separated from the surface, from the basal lamina, and from each other, by non-enlarged 'enyelope cells'.
Oval, similarly degenerate cells also occur in the tumour stroma, especially in the nodule-like pre-papillomatous stages and here they originate apparently from fibroblasts.
In the Atlantic, on the other hand, skin papillomas and other neoplastic skin growths occur relatively infrequently. The skin papillomas of Atlantic flatfish are considerably less complex. They belong to the relatively simple type which predominates in fishes in general–hyperplastic epidermal papillae which are supported and natured by branched folds of the dermal tissue (stroma).
Considering the close relationship between the Pacific and Atlantic flatfishes, the distinctive structure of the skin tumours of Pacific fish is considered to be due probably to the influence of a specific virus.  相似文献   

14.
We review the stock assessment strategies and management procedures for walleye pollock Theragra chalcogramma in Japan. In Japan, walleye pollock is classified into 4 stocks. Because biological data, fishing conditions, etc. are different for each stock, the stocks are assessed by different methods. Harvest strategies aiming at stock recovery are proposed for the Northern Japan Sea stock and the Nemuro Strait stock, which are currently in poor condition. For the Japanese Pacific stock and the Southern Okhotsk Sea stock, which are in good condition, harvest strategies for current fishery operations are proposed. In Japan, fisheries co-management has traditionally been carried out, and in recent years a total catch limitation system called the total allowable catch, a resource recovery plan, and a resource management plan have also been implemented. Although a plan is devised that accounts for the stock conditions of walleye pollock, it is also necessary to consider socioeconomic factors, ecosystem factors, and so on. However, we consider that the main focus of stock management for walleye pollock will still be maintaining fishing pressure at an appropriate level, which includes regulating fish size and price during the fishing season.  相似文献   

15.
An important element in the U.S. management of fisheries in the North Pacific is the existence of Community Development Quotas (CDQs) which grant community corporations the right to fish in many fisheries off the coast of Alaska. The eastern Bering Sea pollock fishery is the largest of these fisheries, with 10 % of the quota allocated to CDQs. The CDQ program evolved from a partial catch share program that existed from 1992 to 1999 within a limited-entry fishery to a full catch share program with separate spatial rights. In this paper I examine the temporal and spatial uses of CDQ rights and how these uses have changed since the implementation of catch shares throughout the fishery. I also discuss the dispersion of CDQ royalties since the program’s inception and examine the prices of CDQ fishing rights from 1992 to 2005 when data on quota value were reported to the government. I compare quota prices to information about walleye pollock fishing and examine the evolving use of CDQ rights. The use of the CDQ right has changed from extending the season to enabling fishing in otherwise closed areas during the season. The number of vessels fishing with CDQ rights has declined substantially, with all pollock CDQ fishing now done by at-sea processors.  相似文献   

16.
Epidermal hyperplasia consisting of discrete translucent raised outgrowths of cells were observed on the skin of walleye, Stizostedion vitreum vitreum (Mitchill), during their spawning period in the spring. The cells constituting the hyperplastic growths were limited to the epidermal layer, and were associated with surface budded, 120-nm-diameter, retrovirus-like particles located in the expanded intercellular spaces. These tumour-like growths were distinct from the other virus-associated skin lesions of walleye including dermal sarcoma, lymphocystis disease and herpesvirus-associated hyperplasia. Lesions could be differentiated by careful observation in the field and comparison of portions of each growth by histologic and electron microscopic observations.  相似文献   

17.
The southwestern Pacific coast of Hokkaido is the main spawning ground for the Japanese Pacific stock of walleye pollock Theragra chalcogramma. A commercial gillnet fishery targeting spawning adult pollock in this area mainly operates from October to January to coincide with the migration of adult pollock from the feeding ground. Given the results of acoustic surveys, and changes in the proportion of the monthly total catch that was monthly walleye pollock caught by the commercial gillnet fishery, it is thought that the timing of walleye pollock spawning migration to the Donan area varies among years and that the pollock catch of the gillnet fishery clearly reflects changes in pollock abundance in this area. A time series of interannual variability in catch data from 1980 to 2005 suggested that adult pollock migrated and concentrated on their spawning ground later in the 1980s and after 2000 than in the 1990s. Such decadal-scale shifts are presumably caused by climatic changes (e.g., in water temperature) in the Oyashio region. These shifts affect the gillnet fishery through differences in monthly unit prices of pollock and changes in the formation of fishing grounds. These scientific findings can aid the establishment of rules for more efficient walleye pollock resource management under the total allowable catch system.  相似文献   

18.
Concern about impacts of climate change in the Bering Sea prompted several research programs to elucidate mechanistic links between climate and ecosystem responses. Following a detailed literature review, Hunt et al. (2011) (Deep‐Sea Res. II, 49, 2002, 5821) developed a conceptual framework, the Oscillating Control Hypothesis (OCH), linking climate‐related changes in physical oceanographic conditions to stock recruitment using walleye pollock (Theragra chalcogramma) as a model. The OCH conceptual model treats zooplankton as a single box, with reduced zooplankton production during cold conditions, producing bottom‐up control of apex predators and elevated zooplankton production during warm periods leading to top‐down control by apex predators. A recent warming trend followed by rapid cooling on the Bering Sea shelf permitted testing of the OCH. During warm years (2003–06), euphausiid and Calanus marshallae populations declined, post‐larval pollock diets shifted from a mixture of large zooplankton and small copepods to almost exclusively small copepods, and juvenile pollock dominated the diets of large predators. With cooling from 2006–09, populations of large zooplankton increased, post‐larval pollock consumed greater proportions of C. marshallae and other large zooplankton, and juvenile pollock virtually disappeared from the diets of large pollock and salmon. These shifts in energy flow were accompanied by large declines in pollock stocks attributed to poor recruitment between 2001 and 2005. Observations presented here indicate the need for revision of the OCH to account for shifts in energy flow through differing food‐web pathways due to warming and cooling on the southeastern Bering Sea shelf.  相似文献   

19.
The nutritional quality of 13 commercial fish meals (10 from pollock, two from salmon, and one from cod) made from by-products of the Alaska fish processing industry was determined in diets for the marine fish Pacific threadfin Polydactylus sexfilis . Pelleted feeds were manufactured containing these meals as complete replacement of a low-temperature processed Norwegian fish meal (control). These feeds were fed to triplicate tanks of fish at the facilities of the Oceanic Institute, Hawaii for a period of 9 wk. At the end of the trial, the final weight, feed efficiency, protein efficiency ratio and survival data were subjected to ANOVA procedures. The performance parameters of the fish fed the white fish meals (pollock and cod) were not significantly different from the control. Of the two salmon meals, one promoted good growth and efficiency and one did not. It is concluded that the nutritional quality of Alaska white (pollock and cod) fish meals is equivalent to that of the low-temperature Norwegian fish meal and are of suitable quality for inclusion in commercial feeds for Pacific threadfin.  相似文献   

20.
Between 1988 and 1993, 12 satellite-tracked buoys were deployed in four eddies in the south-eastern Bering Sea. Our success in finding eddies resulted from placing buoys in high concentrations of walleye pollock (Them-gra chalcogramma) larvae. We utilize data from hydro-graphic surveys, satellite-tracked buoys and moored current meters to describe the eddies. Small (< 25 km diameter) eddies likely transit along the slope of the eastern Bering Sea every 45–60 days. In previous studies such small features were not observed because their size fell within typical separation of hydrographic stations and the weak sea surface temperature gradients are not resolved by satellite-borne infrared imagery.  相似文献   

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