bluuebunny/crossref_metadata_2025 huggingface dataset:
Ubiquitous eddies of the eastern Bering Sea and their coincidence with concentrations of larval pollock
Authors: SCHUMACHER J. D. , STABENO P. J.
Published: October 2007

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.
Relationships between temperature and landing patterns in the southern Labrador and eastern Newfoundland inshore cod fishery
Authors: CHEN XIAO HONG , SHELTON PETER A. , BATH ALISTAIR J.
Published: October 2007

The temporal pattern of cod landings in the inshore trap fishery off the east coast of Newfoundland and Labrador is examined in this study. Unlike previous studies which have been broad scale or of a localized nature, this analysis looks at variations within fishing seasons and among fishing areas in trap landings. A significant relationship between water temperature and the weekly pattern is demonstrated. Significant spatial patterns in weekly landings are described and related to longshore differences in the seasonal variation in temperature.
Decadal‐scale regime shifts in the large marine ecosystems of the North‐east Pacific: a case for historical science
Authors: FRANCIS ROBERT C. , HARE STEVEN R.
Published: October 2007

There are two fundamental ways of doing science: the experimental‐predictive and the historical‐descriptive. The experimental‐predictive approach uses the techniques of controlled experiment, the reduction of natural complexity to a minimal set of general causes, and presupposes that all times can be treated alike and adequately simulated in the laboratory. The historical‐descriptive approach uses a mode of analysis which is rooted in the comparative and observational richness of our data, is holistic in its treatment of systems and events, and assumes that the final result being studied is unique, i.e. dependent or contingent upon everything that came before. We suggest that one of the real difficulties we have in understanding ecosystem properties is our inability to deal with scale, and we show how historical science allows us to approach the issue of scale through the interpretation of pattern in time and space. We then use the techniques of the historical‐descriptive approach to doing science in the context of our own and other research on climate change and biological production in the North‐east Pacific Ocean. In particular, we examine rapid decadal‐scale shifts in the abundance and distribution of two major components–salmon and zooplankton ‐ of the large marine ecosystem of the North‐east Pacific, and how they relate to similar shifts in North Pacific atmosphere and ocean climate. We conclude that they are all related, and that climate‐driven regime shifts, such as those we have identified in the North‐east Pacific, can cause major reorganizations of ecological relationships over vast oceanic regions.
Predicting the dispersion of sprat larvae (Sprattus sprattus (L.)) in the German Bight
Authors: BARTSCH JOACHIM , KNUST RAINER
Published: October 2007

Sprat (Sprattus sprattus (L.)) larval dispersal in the German Bight is predicted with a model system consisting of two three‐dimensional circulation models and a three‐dimensional transport model. Horizontal distribution data for specific length classes of larvae, obtained from field surveys carried out in the German Bight during summer 1991, are used as initial conditions for the starting points of the tracers in the transport model. Sprat larval distributions are predicted and are compared with distributions of the appropriate length class of larvae observed during a subsequent cruise about 3 weeks later. The predicted larval (tracer) distributions compare favourably to observed larvae distributions in the inner model areas but not in the areas close to the coast. Factors contributing to inaccurate predictions are uncertainties in horizontal and vertical larval distributions as well as the model grid resolution, which is too coarse in coastal areas.
Simulated carrying capacities of fish in Norwegian fjords
Authors: VANES ANNE GRO VEA SAL , AKSNES DAG , FOSSÅ JAN HELGE , GISKE JARL
Published: October 2007

The influence of oceanographic and meteorological conditions and topography on the carrying capacity of organisms in coastal areas of western Norway is investigated by field studies and dynamic modelling. Published data on Calanus finmarchicus, the dominant species in the zooplankton biomass of west Norwegian coastal waters, demonstrate a strong gradient, with high densities at the outer coastal areas and lower densities at the innermost localities. This gradient spans several orders of magnitude. A similar tendency is found in the data from pelagic trawling and from beach seine catches, and simulation modelling indicates that fish production depends on zooplankton availability. According to the model, the carrying capacity level of fish production is high in the outer areas and decreases with distance from the outer coast according to the decrease in advected biomass of zooplankton. The simulations indicate that while growth prospects for individuals at lower trophic levels vary with the distance from the coast, potential for growth seems largely unaffected by the distance from the coast for the sublittoral piscivores (e.g. cod). This indicates that, for immigration of a new sublittoral piscivore to a habitat, it does not matter whether the habitat is situated close to the outer coast or far from it. A consequence for stock enhancement may be that a small‐scale release of sublittoral piscivores will be equally productive in most coastal areas, while the outcome of a large‐scale release will be strongly dependent on distances from the coast. The outcome may be high, but variable, in the outer areas and low, but probably more constant in the innermost areas, provided that releases of juvenile, sublittoral, piscivorous fish do not result in a fish stock density in excess of the carrying capacity level.
The global distribution of wind‐induced upwelling
Authors: XIE LIUSEN , HSIEH WILLIAM W.
Published: October 2007

The global distribution of wind‐induced upwelling at the base of the surface Ekman layer has been computed from the COADS monthly wind stress from 1950 to 1988. In contrast to previous studies where the Ekman transport equations became invalid near the Equator, this paper computed upwelling right to the equator by incorporating friction in the surface transport equations. Comparing the seasonal changes in the equatorial upwelling between the Atlantic and the Pacific, we found that the Atlantic had the larger magnitude change while the Pacific had the larger latitudinal shift. The anomalous wind‐induced upwelling/downwelling associated with El Niño were computed over several latitudinal bands in the Pacific by compositing the data from six El Nino events. By plotting the July zonally averaged upwelling anomalies in the Pacific in a latitude‐time contour plot, we found northward phase propagation at about 3.5° latitude per decade in the low latitudes, a feature not found in the January upwelling. Long‐term upwelling trends were computed and their potential influence on fisheries are discussed.
Differences in food availability for Japanese sardine larvae between the frontal region and the waters on the offshore side of Kuroshio
Authors: NAKATA K. , ZENITANI H. , INAGAKE D.
Published: October 2007

The availability of food for larvae of the Japanese sardine, Sardinops melanostictus, was investigated in the Kuroshio frontal region and the waters on the offshore side of the Kuroshio, the Pacific coast of central Japan, in March 1990 and 1991, respectively. Food availability was assessed by changes in biomass and production of nauplii and small copepods, and RNA/DNA ratios of the larvae during about 2.5 days (the frontal region) or 3 days (the offshore waters) of tracking a drifter released in a pitch of the larvae. The biomas of the nauplii tended to increase with time in the frontal region and to decrease in the waters on the offshore side of the Kuroshio during the drifter tracking periods. The production of small copepods including nauplii in the waters on the offshore de of the kuroshio was 14% of that in the frontal region. The sum of the mean food requirements of the carnivorous macrozooplankters and sardine larvae was 11% of the production of small copepods including nauplii in the frontal region, compared with 136% in the waters offshore of the Kuroshio. The RNA/DNA ratios of postlarvae smaller than 8 mm in the frontal reqion were significantly higher than those in the waters on the offshore side of the Kuroshio (P < 0.001) It is considered that the food availability for sardine larvae was relatively high in the frontal region and low in the waters on the offshore side of the Kuroshio. The food availability for the larvae probably deteriorated with the offshore shift of the main spawning ground from the frontal region to the waters on the offshore side of the Kuroshio in the latter half of the 1980s.
Spatial and temporal changes in the groundfish assemblages on the north‐east Newfoundland/Labrador Shelf, north‐west Atlantic, 1978–1991
Authors: GOMES MANUEL C. , HAEDRICH RICHARD L. , VILLAGARCIA M. GUADALUPE
Published: October 2007

From 1978 to 1991, biomass and abundance have declined in members of the marine fish community on the Newfoundland‐Labrador Shelf. This decline was common to all commercial groundfish and to many noncommercial ones as well. Since about 1985, the biomass decline has been accompanied by major shifts in the geographic distribution of almost every species. Some species disappeared from inshore, others disappeared from the north, and others did both. Some species appear to have had major shifts in abundance (north to south or inshore to offshore) whereas other species exhibited a biomass decline in one area but maintained a rather uniform level in others. Multivariate analysis of groundfish survey data identified four groundfish assemblage areas on the shelf, i.e. areas characterized by a homogeneous faunal composition. Distribution patterns of the assemblages remained relatively stable from 1978 until 1987, but have entered a period of dramatic change since then. Changes in the distribution patterns of individual species anticipated changes at the community level. Intense exploitation of groundfish is the most likely explanation for the decline of fish biomass on the Newfoundland‐Labrador Shelf. The shifts in distribution observed, however, suggest that broad‐scale environmental effects may also be at work.
Oceanographic features that define the habitat of Pacific ocean perch, Sebastes alutus
Authors: SCOTT BETH
Published: October 2007

This study investigates the possibility that oceanographic features could have effects on the variations observed in the apparent abundance of a demersal rockfish, Pacific ocean perch, Sebastes alutus. Simultaneous monitoring of physical variables and indices of fish abundance was achieved by attaching oceanographic equipment to the fishing gear of commercial vessels and sampling the fish catch. It was found that perch prefer a temperature range from at least 4.8d̀C to 6.7d̀C and that their movement patterns are linked to the movement of these temperatures by coastal wind patterns. Perch prefer areas with steep bathymetry, characterized by turbulent activity due to interactions between the local bathymetry and tidal currents.
Effects of temperature, wind and spawning stock biomass on recruitment of Arcto‐Norwegian cod
Authors: OTTERSEN GEIR , SUNDBY SVEIN
Published: October 2007

Sea temperature has earlier been shown to have a large influence on the recruitment of Arcto‐Norwegian cod, Gadus morhua. We here hypothesize that this linkage is partly due to the direct effect of temperature on larval and juvenile growth. Secondly, temperature acts as a proxy for both biotic and abiotic factors influencing recruitment. Indices of abundance of early juvenile cod (2–3 months old), 0‐group cod (4–5 months old) and 3‐year‐old cod are analysed in more detail against the environmental temperature, wind stress components, wind‐induced turbulent energy and the spawning stock biomass. To deal with autocorrelation, non‐stationar‐time and nun‐normality, which complicate a statistical time series analysis, randomization and Box‐Jenkins methods are applied. In addition to the important effect of high sea temperature during the early life stage in forming strong year classes, the results show that the spawning stock biomass is nearly as important. Also, alongshore southerly wind stress anomalies during the period of pelagic drift (from April through summer) and offshore wind stress anomalies during egg and early larval stages (in April) act favourably on recruitment. The beneficial effect of southerly wind anomalies could he linked partly to high temperature, but the flux of zooplankton‐rich water from the Norwegian Sea into the feeding areas of the Barents Sea may also be increased. The favourable influence of offshore winds in April is less predominant and causal links are also less clear; possible explanations for this might be increased offshore spreading of eggs and early larvae, resulting in reduced risk of predation, and increased compensation inflow of intermediate Norwegian Sea water which, in this restricted period of time, has a high concentration of spawning copepods suitable as prey for the developing cod larvae.
On the variable subsurface environment of fish stocks in the Bering Sea
Authors: REED R.K.
Published: October 2007

Data from 1971 to 1993 are used to examine characteristics and variability of the subsurface temperature maximum in the Aleutian Basin of the Bering Sea. The temperature of this feature varies from ∼3.5g̀C to 4.6d̀C at depths of ∼150–400 m, and sigma‐t density is usually in the range 26.6–26.9. The variability is caused mainly by the absence or presence of inflow of warm, low‐density Alaskan Stream water through Amukta Pass. Thus the environment offish stocks is far from uniform.
It's about time: new beginnings and old good ideas in fisheries science
Authors: SHARP GARY D.
Published: October 2007

Views about aquatic resource management are changing, particulaly now that resource yields from world fisheries have been shown to be not only unsustainable, but steadily declining under conventional management practice. There is ample reason for re‐examination, and more pragmatic definitions of what is meant by sustainability There have nearly always been clear, reasonable means for making appropriate decisions that would have safeguarded most of the ocean's living resources, hut in general greed and lack of societal will, as articulated it national governmental levels, have promoted the present resource deterioration. I also posit that the underlying science in support of sustainable fisheries decision‐making has been responsible for a great proportion of this deterioration. Revitalization of fisheries science, indeed rehabilitating the affected fisheries, will he required to regain the losses in credibility of the agencies and of the underlying science. This will depend upon resumption of integrated environmental monitoring, more enlightened application of what is already known, and reconnection of the science to the several industries involved, i.e. fishing, processing and marketing. Management implemented at the market place may be one of the few remaining options to secure the sustainability of natural resources
A spatially explicit fitness‐based model of capelin migrations the Barents Sea
Authors: FIKSEN Ø. , GISKE J. , SLAGSTAD D.
Published: October 2007

The geographical distribution and production of the Barents Sea capelin (Mallotus villosus, Osmeridae) is modelled by the use of a state‐variable optimization technique (dynamic programming), where the main objective of individuals always is to maximize fitness, or total expected reproduction (RO), by selecting the most profitable habitats through time. Fitness is gained by successful reproduction (a function of size) during the spawning season on the breeding grounds off northern Norway. The environment (predators, temperature and zooplankton prey) is determined by a meteorologically forced circulation model for the year 1980, creating a spatial and seasonal fluctuation in the environment. Predation from cod is the main source of mortality, and the distribution of the cod (Gadus morhua) stock is assumed to vary with temperature. Growth is predicted from a bioenergetic model, incorporating the cost of swimming between feeding areas and spawning grounds. Field data of the capelin stock recorded during autumn cruises from 1979 is implemented at the start of the model, and then this stock is modelled through 1980 and the first months of 1981. Model predictions are compared with the observed distribution of capelin in autumn 1980. Habitat selection has consequences for the dynamics of the population and growth of individuals, demonstrating the importance of combining external (environmental) and internal (evolutionary) forcing to understand and predict the dynamics of fish populations. This study is the first application of dynamic programming to model the dynamics and ecology

of horizontal fish migration, and we suggest that the method may be developed into a useful tool for the management of short‐lived species.
Computer simulations of homeward‐migrating Fraser River sockeye salmon: is compass orientation a sufficient direction‐finding mechanism in the north‐east Pacific Ocean?
Authors: DAT CLAIRE G. , LEBLOND PAUL H. , THOMSON KEITH A. , INGRAHAM W. JAMES
Published: October 2007

Computer simulations were used to investigate whether compass orientation is a sufficient guidance mechanism for sockeye salmon migrating to the Fraser River from their ocean foraging grounds in the north‐east Pacific Ocean. Daily surface ocean currents, simulated by the ocean surface current simulations (OSCURS) model, were used to test the influence of currents on the return oceanic migration of Fraser River sockeye salmon. High seas tagging and coastal recover data of Fraser River sockeye salmon were used for the migration simulations. Surface currents were shown to increase the speed of the homeward‐migrating sockeye salmon, as well as to deflect the fish in a north‐eastward direction. In spite of ocean currents, all Fraser River sockeye salmon were able to reach their destination with a fixed direction and bioenergetically efficient swimming speed when migration was delayed until the last month at sea. Compass orientation alone was shown to be a sufficient direction‐finding mechanism for Fraser River sockeye salmon.
Sinking rate of loricae of some common tintinnid ciliates
Authors: SUZUKI TOSHIKAZU , TANIGUCHI AKIRA
Published: October 2007

Sinking rate of empty loricae of seven tintinnid species was measured in settling chambers. The sinking rates normalized for 3% NaCl solution at 20d̀C are 0.25‐2.08 m day‐1 for five hyaline loricae and 1.90 and 15.9 m day‐1 for two agglutinated loricae. Positive relationships between sinking rate and size of hyaline loricae such as volume, surface area and nominal diameter were established, which favour the practical estimation of sinking rate of empty loricae discarded by natural tintinnid populations by measuring size composition. The slower sinking rate of hyaline loricae, compared with that of diatoms, indicates their availability as indicators of particular water masses in the ocean. Loricae incorporated into faecal pellets of zooplankton and marine snow also indicate the origin of these sinking particles.
A comment on transfer efficiencies
Authors: BAUMANN MICHAEL
Published: October 2007

This paper discusses the validity of several assumptions in a recent publication on the primary production required to sustain the annual world fish catch of £120 million t. A transfer efficiency between trophic levels in aquatic ecosymms of 15% results in the primary production requirement of 2.6% of the total primary production to sustain the world fish catch, not 8% as reported from calculations with a transfer efficiency of 10%. The importance of accurate estimates of predation efficiency and trophic level is shown.
Species associations of epipelagic nekton of the North Pacific Ocean, 1978–1993
Authors: PEARCY WILLIAM G. , FISHER JOSEPH P. , ANMA GEN , MEGURO TOSHIMI
Published: October 2007

Strong latitudinal gradients in species composition were revealed by two‐way indicator species analysis (TWINSPAN) and detrended correspondence analysis (DCA) of 41 species of epipelagic fishes and squids in 513 gillnet collections by research vessels of Hokkaido University over a huge area of the northern North Pacific during the summers of 1978–1993. Salmonids inhabited northern subarctic water and skipjack tuna (Euthynnus pelamis) and flying squid (Ommastrephes bartrami) inhabited the region of the Subarctic Boundary, but distinct boundaries between species groups and sample groups were lacking, largely because abundant species, such as Pacific saury (Cololabis saira) and Pacific pomfret (Brama japonica), migrated across most of this region during the summer. Longitudinal differences were not pronounced, but some species, including Japanese sardine (Sardinops melanostictus) and Japanese anchovy (Engraulis japonicus), were only found in the western Pacific. Pacific saury was more common in the western Pacific, whereas sockeye salmon (Oncorhynchus nerka) was concentrated in the eastern Pacific. Interannual fluctuations in the latitude of species groups were most closely correlated with changes in sea surface temperatures. In the western Pacific, 1982, 1983, 1985, 1987‐88, and 1992‐93 were cool years when subarctic and transitional assemblages were found farther to the south than other years. Temperature and salinity at various depths were highly correlated with each other and with first‐axis DCA ordinations scores. Long‐term trends in community structure were not apparent during the 1.6 decades.
New data about communities of plankton and nekton of the far‐eastern seas in connection with climate‐oceanological reorganization
Authors: SHUNTOV V. P. , DULEPOVA E. P. , RADCHENKO V. I. , LAPKO V. V.
Published: October 2007

The present condition of the pelagic communities of the far‐eastern seas is considered. From the beginning of the 1990s, significant changes, caused by a replacement of the climate‐oceanological period, have occurred in the structure of plankton and nekton communities. The current situation is assumed to be the beginning of a period similar to one in the 1940s‐1960s.
Sea birds as proxies of marine habitats and food webs in the western Aleutian Arc
Authors: SPRINGER ALAN M. , PIATT JOHN F. , VLIET GUS VAN
Published: October 2007

We propose that ocean conditions of the Near Islands in the western Aleutian Arc mimic those of the shallow continental shelf of the eastern Bering Sea to the extent that the marine community, including assemblages of forage fishes and their avian predators, has distinctly coastal characteristics. In contrast, marine avifauna and their prey at neighbouring Buldir Island are distinctly oceanic. For example, at the Near Islands, the ratio of thick‐billed to common murres, Vria lomvia and U. aalge, is low and black‐legged kittiwakes, Rissa tridactyla, but not red‐legged kittiwakes, R. brevirostris, nest there. Diets of murres and kittiwakes are dominated by sand lance, Ammodytes hexapterus, an abundant coastal species. At Buldir Island, thick‐billed murres greatly outnumber common murres, red‐legged kittiwakes and black‐legged kittiwakes are both abundant, and diets of the birds consist primarily of oceanic squid and lantern‐fish (Myctophidae). This mesoscale difference in food webs is apparently a consequence of the local physiography. A broad escarpment on the Near physiographic block creates a comparatively expansive, shallow, shelflike habitat around the Near Islands, where a pelagic community typical of coastal regions flourishes. Buldir Island is the only emergent feature of the Buldir physiographic block, with little shallow water surrounding it and, apparently, little opportunity for other than oceanic species to exist. Patterns in the distribution of fishes, and thus of sea birds, throughout the Aleutian Islands might be largely explained by the presence or absence of shelf‐like habitat and the relationship between physical environments and food webs. In the larger context of fisheries oceanography, this model for the Aleutian Islands improves our ability to interpret physical and biological heterogeneity in the ocean and its relationship to regional community dynamics and trends in the abundance and productivity of individual species at higher trophic levels.
Survival and growth of sardine larvae in the offshore side of the Kuroshio
Authors: ZENITANI HIROMU , NAKATA KAORU , INAGAKE DENZO
Published: October 2007

After 1984 the major spawning of the Japanese sardine, Sardinops melanostictus, has been observed to occur in the offshore waters, where the survival of early‐stage larvae (4–10 mm in length) is questionable. The main objective of this study is to estimate the growth and survival rates of the early‐stage larval cohort in the offshore side of the Kuroshio Current.

A radar‐reflecting buoy with a surface drogue was launched to tag a patch of larvae, and the patch was traced for 3 days in March 1991. The survival rate of the early‐stage larval cohort was calculated from the change in density during the survey. The range of the instantaneous mortality rate was from 0.83 to 1.11 day, a survival rate of32‐44%day‐1.The mean density of the smaller larvae (4–6 mm in length) decreased more rapidly than that of the larger larvae (6–10 mm in length) during the sampling period.

The survival rate of the first‐feeding larvae in the offshore region seemed to be lower than that of the post‐flrst‐feeding larvae. However, the growth rates of the first‐feeding larvae's survivors in the region were higher than those of the post‐first‐feeding larvae's survivors. The first‐feeding larvae in the offshore region seemed to survive when the growth rate of the larvae was high.
Walleye pollock recruitment in Shelikof Strait: applied fisheries oceanography
Authors: KENDALL ARTHUR W. , SCHUMACHER JAMES D. , KIM SUAM
Published: October 2007

Fisheries‐Oceanography Coordinated Investigations (FOCI) is a National Oceanic and Atmospheric Administration (NOAA) research programme seeking to understand recruitment processes of commercially exploited Alaskan fishes. The FOCI is mainly comprised of scientists at the Pacific Marine Environmental Laboratory and the Alaska Fisheries Science Center who study both the biotic and abiotic environment, including processes within larval patches through integrated field, laboratory, and modelling studies. The initial focus of studies was walleye pollock (Theragra chakogramma) spawning in Shelikof Strait, Gulf of Alaska. The choice of this population for our research was based on development of a large fishery and the substantial variation in recruitment that was observed in the late 1970s and early 1980s. Also, the early life history of this population is quite predictable and restricted both temporally and spatially. Walleye pollock spawn consistently in a small part of Shelikof Strait in early spring from which a large patch of eggs and later larvae is produced. In most years this concentration of larvae drifts to the south‐west through the strait during April and May. Large numbers of larvae are often found in eddies which frequent the area and we have observed improved feeding conditions for larvae, in as opposed to out of eddies. We have found that first‐feeding larvae have higher survival rates during calm periods, rather than in storms, and that in many years recruitment is largely set by the end of the larval period, although in some years age‐0 juvenile mortality is also important. FOCI now generates information that is being used for management of this resource.
The plankton of Shelikof Strait, Alaska: standing stock, production, mesoscale variability and their relevance to larval fish survival
Authors: NAPP JEFFREY. M. , INCZE LEWIS S. , ORTNER PETER B. , SIEFERT DEBORAH L. W. , BRITT LISA
Published: October 2007

Physically‐mediated variations in production, standing stock and distribution of plankton have a significant impact on the growth and survival of larval fishes in Shelikof Strait. We integrate descriptions of mechanisms that control the distribution and regional production of planktonic organisms with mechanisms that influence survival of early life history stages of marine fish, especially the locally abundant walleye pollock, Theragra chalcogramma.

The timing of the spring phytoplankton bloom is more variable than the regular appearance of pollock larvae, and is affected by variability in the winter to spring storm season transition, stratification in the Alaska Coastal Current (ACC), and cloudiness. The spring bloom occurs first in the ACC, fuelling local production of copepod nauplii, the main prey item of early larval pollock. Shelikof Strait zooplankton standing stock is higher in the ACC than the surrounding Coastal Water (CW) throughout the spring. This is the result of local production as well as regional production which occurs upstream of the strait. Mesoscale features associated with the ACC (fronts, meanders, and eddies) determine the distribution of plankton through physical convergence, and reduced dispersion and transport. Evidence for enhancement of planktonic production in these features is lacking. Thus the ACC plays a strong role in determining plankton production, standing stock, and distribution in the Shelikof region.

The strength of the relationship among plankton, planktonic production, larval pollock growth and survival, and fisheries recruitment is variable. The plankton is only one of several key variables that affect eventual recruitment to the pollock fishery.
Physical transport of young pollock larvae (Theragra chalcogramma) near Shelikof Strait as inferred from a hydrodynamic model
Authors: HERMANN ALBERT J. , RUGEN WILLIAM C. , STABENO PHYLLIS J. , BOND NICHOLAS A.
Published: October 2007

An advective model was used to simulate the drift of larval walleye pollock (Theragra chalcogramma) over a 40‐day period (late April through early June) near Shelikof Strait, Alaska. This model was used: (i) to assess how much of the observed change in larval positions during that period can be explained by transport at fixed depth; (ii) to demonstrate that observed change can be related to mean large‐scale meteorological forcing; and (iii) to investigate accumulation of larvae in specific areas near the coast. Based on availability of larval and circulation data, three years were studied: 1988, 1989 and 1991. Velocity fields generated from a hydrodynamic model driven by winds and runoff were used to advect particles seeded in accordance with observed larval distributions in late April of each year. The modelled larvae were tracked at 40 m depth, corresponding to the mean depth of sampled larvae and the depth of neutrally buoyant drifters employed in field studies. Specific features observed in late May larval surveys were reproduced by the model, such as the accumulation of larvae in a shoal area downstream of the strait. Differences among the modelled years include extensive flushing of larvae to the south‐west in 1988 and 1991, vs. limited flushing in 1989. These differences appear related to the mean large‐scale atmospheric pressure patterns for April‐May of those years.
Observed patches of walleye pollock eggs and larvae in Shelikof Strait, Alaska: their characteristics, formation and persistence
Authors: STABENO PHYLLIS J. , SCHUMACHER JAMES D. , BAILEY KEVIN M. , BRODEUR RICHARD D. , COKELET EDWARD D.
Published: October 2007

Using observations from 38 ichthyoplankton surveys conducted near Shelikof Strait, Alaska between 1979 and 1992, we characterized the horizontal distribution and spatial patchiness of the early life stages of walleye pollock (Theragra chalcogtamma). Lloyd's index of patchiness ranged from 3.9‐6.1 for eggs and 3.9–16.2 for larvae. This index was size (age) dependent: low for eggs, high for newly hatched larvae, then decreasing through late larval stage. By the early juvenile stage, patchiness increased as pollock began to school. The percentage of larvae in a patch (defined as the percentage of larvae present at stations where larval counts exceeded the mean by one standard deviation during the given survey) varied greatly (26–92%). Larval distributions were used to deduce physical mechanisms responsible for patches. Three categories of patches were identified: those created by interaction of larvae with time‐dependent currents, those in the vicinity of Sutwik Island, and those associated with eddies. Simulation experiments were utilized to examine processes influencing patch formation and the role of larval swimming. Between 5 and 6 weeks after hatching, larvae have swimming abilities that enable them to maintain a patch already created by physical mechanisms.
Walleye pollock egg distribution and mortality in the western Gulf of Alaska
Authors: BRODEUR RICHARD D. , PICQUELLE SUSAN J. , BLOOD DEBORAH M. , MERATI NAZILA
Published: October 2007

We examine the distribution and mortality of walleye pollock (Theragra chakogramma) eggs in the western Gulf of Alaska. Most pollock eggs were found in mid‐water, with low proportions in the neustonic and epibenthic layers during all years of sampling. A silhouette camera towed through a high egg density region provided new information on small‐scale spatial distributions and provided density estimates at two depth layers similar to those of depth‐discrete net sampling. Annual egg production curves and natural mortalities were estimated for 1987‐92 based on the abundance of several cohorts relative to their production rate. Production during 1989 and 1990 was lower than in the other four years but 1988 was the only year to show markedly different (higher) mortality than the rest. Fertilization rate was generally very high (>99%) but several collections early in the season contained a substantial fraction of unfertilized eggs. Invertebrate egg predation was mainly due to euphausiids and was variable among locations and years. Egg cannibalism by adult pollock on the spawning grounds was inconsequential (< 1% for all years) compared to invertebrate predation.
Mortality of larval walleye pollock Theragra chalcogramma in the western Gulf of Alaska, 1988–91
Authors: BAILEY KEVIN M. , PICQUELLE SUSAN J. , SPRING STELLA M.
Published: October 2007

Mortality rates of larval walleye pollock Theragra chakogramma were estimated from larval survey data from 1988 to 1991. Mortality estimates were based on cohort‐specific losses between occupations of survey grids. Interannually, estimates of early feeding stage larval mortality rates ranged over an order of magnitude, from 0.045–0.43 day‐1, and declined sharply with age. There is some evidence that mortality rates of early feeding larvae tend to be negatively correlated with temperature and postively correlated with wind mixing.
A review of the distribution, ecology and population dynamics of age‐0 walleye pollock in the Gulf of Alaska
Authors: BRODEUR RICHARD D. , WILSON MATTHEW T.
Published: October 2007

This review paper synthesizes published research and unpublished data on the abundance and distribution patterns, ecology and population dynamics of walleye pollock (Theragra chalcogramma) during their first year of life (age‐0) in the Gulf of Alaska. Distribution patterns have been described using mainly trawl catches, but recently, acoustic methodology has been employed, especially in examining vertical distributions. Although age‐0 pollock are found throughout the Gulf, the highest catches occurred west of Kodiak Island. Pollock are pelagic for at least their first 6 months of life but show an ontogenetic increase in depth distribution superimposed on a pronounced diel vertical migration at a larger size. Daily growth rates are variable depending on year, season and area, and growth generally ceases during the winter. The diet of age‐0 pollock shifts from mainly copepods in early juveniles to euphausiids by fall, with epibenthic organisms becoming important during the winter months. Feeding occurs mainly at night in surface waters. Age‐0 pollock are most frequently associated with gelatinous zooplankton (medusae) and older pollock. Many predators on age‐0 pollock have been identified; the most important are arrowtooth flounder (Atheresthes stomias), adult pollock, puffins (Fratercula spp.), murres (Una spp.), harbor seals (Phoca vitulina richardsi) and Steller sea lions (Eumetopiasjubatus). Modelling provides some insight into the population dynamics of these juveniles and environmental conditions which interannually affect their survival. These results are discussed relative to the importance of age‐0 pollock in the recruitment of this species and to their role in the pelagic ecosystem.
Cohort survival patterns of walleye pollock, Theragra chalcogramma, in Shelikof Strait, Alaska: a critical factor analysis
Authors: BAILEY KEVIN M. , BRODEUR RICHARD D. , HOLLOWED ANNE B.
Published: October 2007

A series of age‐specific life tables for walleye pollock (Theragra chalcogramma) in the western Gulf of Alaska was compiled for the 1980‐91 year classes. The life tables were utilized to perform an exploratory key factor analysis to examine the timing of critical periods in the recruitment process, evidence of density‐dependence at different stages and trends in mortality rates. Early larval mortality was significantly correlated with generational mortality (In recruits/spawning bio‐mass), but patterns in juvenile mortality also were similar to generational mortality and in some years were clearly dominant in determining the fate of a cohort. Density‐dependent mortality, based on the correlation between mortality and initial abundance, was indicated only for the late larval to early juvenile stage. Time trends were marginally significant for juvenile mortality. It is speculated that the observed increase in juvenile mortality is associated with increasing abundance of arrowtooth flounder. Weaknesses in the data base are discussed; these along with the short time series involved make our conclusions tentative and subject to further study. We hypothesize that pollock recruitment levels can be established at any life stage depending on sufficient supply from prior stages, a type of dynamics which can be termed supply dependent multiple life stage control.
Change in chum salmon (Oncorhynchus keta) stomach contents associated with fluctuation of pink salmon (O. gorbuscha) abundance in the central subarctic Pacific and Bering Sea
Authors: TADOKORO KAZUAKI , ISHIDA YUKIMASA , DAVIS NANCY D. , UEYANAGI SHOJI , SUGIMOTO TAKASHIGE
Published: October 2007

The abundance and stomach contents of salmonids (Oncorhynchus spp.) and the biomass of prey organisms were examined in the central subarctic Pacific and Bering Sea in the summer of 1991 and 1992. Salmonids were caught by surface longline using the same level of fishing effort. Chum (O. keta) and pink (O. gorbuscha) salmon were the predominant species, representing 44% and 36% sof the total catch (n = 1275) in 1991. In 1992, chum salmon composed 85% of the total catch (n = 603), but the catch of pink salmon decreased to 1% of the total catch due to the odd/even year fluctuation of Asian pink salmon abundance in the study area. It was found that chum salmon changed their dominant diet from gelatinous zooplankton (pteropods, appendicular‐ians, jellyfishes, chaetognaths, polychaetes and unidentified materials) in 1991, when pink salmon were abundant, to a diet of crustaceans (euphausiids, cope‐pods, amphipods, ostracods, mysids and decapods) in 1992, when pink salmon were less abundant. Local crustacean biomass (wet weight; mg m‐3) had significant negative correlation with the CPUE (catch number per 30 hachi) of pink salmon in 1991 (r = ‐0.586; P = 0.026) and that of chum salmon in 1992 (r =–0.616; P = 0.014). There may be a limitation in the available prey resource for production of salmonids.
Decadal variation in the trans‐Pacific migration of northern bluefin tuna (Thunnus thynnus) coherent with climate‐induced change in prey abundance
Authors: POLOVINA JEFFREY J.
Published: October 2007

Northern bluefin tuna, Thunnus thynnus, apparently spawn only in the western Pacific and a portion of the juveniles migrate to the eastern Pacific. During the past decade, catches of northern bluefin in the eastern Pacific have declined. One possible cause for this decline, proposed by bluefin stock assessment studies, is a decline in the proportion of bluefin that migrate out of the western Pacific. This hypothesis is examined with several indices of the relative abundance of bluefin tuna in the western and eastern Pacific. These indices suggest a decline in the proportion of bluefin migrating to the eastern Pacific since 1977. This period of reduced bluefin migration coincides with a period when a prey of bluefin, Japanese sardine, Sardinops melanosticta, were abundant off Japan. It is hypothesized that in years when sardines are abundant off Japan, a higher proportion of bluefin stay in the western Pacific compared with years when sardines are scarce. Currently, the adun‐dance of sardines off Japan is declining. If this decline continues, this hypothesis predicts an increase in bluefin migrating north of Hawaii and into the eastern Pacific.
Feeding success and survivorship of Arctic cod larvae, Boreogadus saida, in the Northeast Water polynya (Greenland Sea)*
Authors: MICHAUD JOSÉE , FORTIER LOUIS , ROWE PETER , RAMSEIER RENÉ
Published: October 2007

We tested the hypothesis that enhanced feeding success and survivorship of Arctic cod larvae in the Northeast Water polynya (Greenland Sea) are associated with high densities of their zooplankton prey in areas of low sea ice concentration. From late May to early August 1993, first‐feeding yolk‐sac larvae (6.5–8.5 mm long) were collected primarily along the coast and over shallow banks in the polynya, whereas post yolk‐sac larvae (8.5–14 mm) were more uniformly dispersed over the sampling area. Arctic cod larvae < 14 mm fed almost exclusively on copepod nauplii (74% of total prey number) and copepod eggs (16%). Feeding success was defined as the residuals of the regression of the number of prey ingested against larval length. Nauplii density varied from 9600 to 731300 nauplii m‐2(equivalent to 0.16 to 12.2 nauplii 1‐1) but, contrary to our hypothesis, seldom limited the feeding success of Arctic cod larvae. Water temperature was the best predictor of feeding success in larvae of all sizes. First‐feeding success and survivorship were low for larvae hatched before mid‐July, and improved thereafter as surface temperatures increased in the open waters of the polynya. There was no relationship between feeding success and irradiance or wind. Assuming a fixed spawning season, it is concluded that a larger fraction of the newly hatched larvae would experience adequate temperatures in years when the polynya opens early. Based on this conclusion, we propose that the timing of the opening of polynyas is a critical determinant of year‐ class strength in Arctic cod, a key species in the Arctic food web.
Alternative models of climatic effects on sockeye salmon, Oncorhynchus nerka, productivity in Bristol Bay, Alaska, and the Fraser River, British Columbia
Authors: ADKISON MILO D. , PETERMAN RANDALL M. , LAPOINTE MICHAEL F. , GILLIS DARREN M. , KORMAN JOSH
Published: October 2007

We compare alternative models of sockeye salmon, Oncorhynchus nerka, productivity (returns per spawner) using more than 30 years of catch and escapement data for Bristol Bay, Alaska, and the Fraser River, British Columbia. The models examined include several alternative forms of models that incorporate climatic influences as well as models not based on climate. For most stocks, a stationary stock‐recruitment relationship explains very little of the interannual variation in productivity. In Bristol Bay, productivity covaries among stocks and appears to be strongly related to fluctuations in climate. The best model for Bristol Bay sockeye involved a change in the 1970s in the parameters of the Ricker stock‐recruitment curve; the stocks generally became more productive. In contrast, none of the models of Fraser River stocks that we examined explained much of the variability in their productivity.
Concentration of pelagic organisms at mesoscale fronts in the western subarctic Pacific: small fish on long waves
Authors: ROGACHEV K. A. , SALOMATIN A. S. , CARMACK E. C.
Published: October 2007

Acoustical backscatter observations conducted off the Kuril Straits (Boussole and Vries Straits) in the western subarctic Pacific show increased concentrations of mesopelagic fish (suspected to be fish of the family Myctophidae) associated with long (4–40 km), high‐amplitude (about 100 m) internal waves. Such wave packets are thought to be generated by tidally driven flows through the deep Kuril Island straits. Because myctophids are a small, subarctic fish that must remain in cold waters, it is assumed that their increased concentration is due to an ability to sense flow direction and take advantage of the horizontal flow convergence in these long waves. Because vertical motions in waves are weak, small fish can easily maintain their preferred depth of habitat, and their concentrations tend to increase along horizontal convergence lines formed by wave orbital velocities.
Temperature as a possible factor in the increased abundance of American lobster, Homarus americanust during the 1980s and early 1990s
Authors: DRINKWATER K. F. , HARDING G. C. , MANN K. H. , TANNER N.
Published: October 2007

Through most of the geographical range of the American lobster, Homarus americanus, from Newfoundland to the Middle Atlantic Bight, catches reached new historical maxima or near maxima in the late 1980s or early 1990s. Because of the high exploitation rates, this increase in landings is believed to reflect increased recruitment. Previous studies have shown that increased lobster landings in certain areas were linked to rising sea temperatures. This paper examines the hypothesis that the increased landings during the 1980s and early 1990s were temperature induced. When temperature‐dependent regressions of lobster landings, developed by earlier authors, were extended to the present they failed to predict the sharp rise in landings during the 1980s. In addition, the increase in lobster landings is shown to have occurred over a larger spatial scale than coherent temperature fluctuations. These results, together with an exploratory correlation analysis between sea temperatures and lobster landings, lead to the conclusion that the increase in lobster catches in the 1980s was not linked to changes in ocean temperatures.