bluuebunny/crossref_metadata_2025 huggingface dataset:
Long‐term variability in zooplankton biomass in the subarctic Pacific Ocean
Authors: BRODEUR RICHARD D. , WARE DANIEL M.
Published: October 2007

Zooplankton collections from the subarctic Pacific were analyzed from two periods (1956–1962 and 1980–1989). In this report, we document: 1) a positive correlation between the intensity of winter winds and subsequent summer zooplankton biomass in the subarctic gyre within these periods; and 2) a doubling of zooplankton biomass and a similar increase in pelagic fish and squid abundance between these two periods of time. Some possible explanations for these changes are considered.
Environmental influences on the recruitment of Newfoundland/Labrador Cod*
Authors: HELBIG J. , MERTZ G. , PEPIN P.
Published: October 2007

This paper investigates possible linkages between the environment and year‐class success of Newfoundland/ Labrador cod. Aspects of the physical environment relevant to recruitment are reviewed and the current knowledge of the patterns of spawning and larval occurrence is summarized. A critical review of investigations aimed at correlating recruitment with climactic fluctuations is made and concludes that these studies have been largely fruitless. A series of numerical simulations of particle drift are presented to investigate the potential importance of storms and to try to identify nursery grounds. These simulations suggest that Labrador Shelf eggs and larvae are segregated from Grand Banks eggs and larvae. Favorable storm tracks appear to be required for significant numbers of eggs and larvae to reach the bays of Northeast Newfoundland.
Size‐dependent predation on marine fish larvae by Ctenophores, Scyphomedusae, and Planktivorous fish
Authors: COWAN JAMES H. , HOUDE EDWARD D.
Published: October 2007

Size‐dependent predation rates on marine fish larvae by the ctenophore Mnemiopsis leidyi, scyphomedusa Chrysaora quinquecirrha, and planktivorous fish Anchoa mitchilli were estimated via experiments in 3.2 m3 me‐socosms. Predation rates on larvae of the goby Gobio‐soma bosci were estimated in relation to 1) length of larval prey, 2) presence or absence of alternative < 1 mm zooplankton prey, and 3) a predator‐prey interaction between the scyphomedusa and ctenophore. The consumption rate of larvae by the three predators generally declined as larval length increased. The ctenophore ate fewer (1.0 d‐1 per predator) larvae than did the medusa (7.8 d‐1 per predator) or bay anchovy (4.0 d‐1 per predator), but it consumed larvae in all size classes tested (3.0–9.5 mm SL). Predation by bay anchovy and the medusa was more size‐dependent: 3.0–5.0 mm larvae were most vulnerable. Fewer larvae were eaten by the ctenophore and bay anchovy when zooplankton alternative prey was available, but predation on larvae by the medusa was not influenced by alternative zooplankton prey. Consumption rate of fish larvae by the medusa was reduced 20–25% when the ctenophore was present as its alternative prey. An encounter‐rate model was developed and its parameters estimated from the experimental results. Model simulations indicated that the relationship between larval size and vulnerability is dependent on size, swimming speed, and behavior of both predators and larvae, and that bigger or faster‐growing fish larvae are not always less vulnerable to predation.
Changes in body growth of northern fur seals from 1958 to 1974: density effects or changes in the ecosystem?
Authors: TRITES ANDREW W. , BIGG MICHAEL A.
Published: October 2007

Analysis of morphometric measurements collected from northern fur seals (Callorhinus ursinus) between 1958 and 1974 suggests a periodicity in growth rates and physical condition that may reflect underlying, large‐scale environmental changes. The data further suggest that fur seals attained larger body sizes as the breeding population on the Pribilof Islands declined over this 16‐year period. These conclusions are based on changes observed in the mean body size and condition index of mature females, changes in the annual growth rates of immature females, and changes in male and female growth curves. Interpreting annual changes in physical growth is complicated by inconsistencies in sampling between years and by large natural variations in body mass and body length within years. Commercial fisheries may influence the abundance of prey, and alter the physical growth of pinnipeds, but other physical and biological factors are probably more important determinants. Changes in body length and mass are useful indicators of per capita prey abundance and offer useful insights into conditions experienced by fur seals. Unfortunately, it is not possible to determine whether changes observed in growth are due entirely to changes in population density or whether they reflect changes in the ecosystem, or some combination of both.
Acoustic observations of fish schools and scattering layers in a Kuroshio warm‐core ring and its environs
Authors: AOKI ICHIRO , INAGAKI TADASHI
Published: October 2007

Biological sound scattering characteristics in a frontal region between warm and cold waters were examined at the southern edge of a Kuroshio warm‐core ring off Sanriku, the northeast coast of Japan. The scattering strength was low in the surrounding cold water and high in the warm‐core ring. The depth and thickness of sound‐scattering layers changed in accordance with the vertical structure of the water mass during the day or at night. Intense, thick scattering layers were observed on the warm‐water side of the front and farther inside the warm‐core ring. Fish schools were distributed in the mixed layer warmer than 17°C at depths of 10‐30m above the scattering layers on the warm‐water side of the front.
Considerations of stock structure of yellowfin tuna (Thunnus albacares) in the Indian Ocean based on fishery data
Authors: NISHIDA TSUTOMU
Published: October 2007

Yellowfin stock structure in the Indian Ocean was studied by using industrial tuna longline fishery data. Three types of test variables were used to detect stock structure, i.e., CPUE, age‐specific CPUE, and coefficient of variation for size. Time‐series data of test variables were compiled for six sub‐areas that were arranged by dividing the whole region systematically along longitude lines every 20 degrees. Then time‐series data were smoothed by moving averages, and regressed by simple models. Patterns of time‐series trends were graphically and statistically compared to classify homogeneous sub‐area groups. Two assumptions were (a) that homogeneous stocks exist longitudinally and overlap in adjacent waters, and (b) that test variables within homogeneous sub‐area groups are equally affected, and hence patterns of the time‐series trends are similar. After graphical screening for significant sub‐area groups, analysis of covariance was applied to test homogeneity of regression parameters representing patterns of the time‐series trends. By classifying homogeneous sub‐area groups, stock structures were determined at the P <0.05 and P <0.50 levels. The P<0.50 level was recognized as a useful criterion for ‘weak’ test variables since masked or vague structures at the P <0.05 level were likely cleared at this level in many cases. Results of this study and past stock structure studies were reviewed and compared. It was concluded that there are two major and two minor stocks of yellowfin tuna. The two major stocks (the western and the eastern) are located at 40o‐90oE and 70o‐130oE respectively. The minor stocks are the far western and the far eastern stocks (the latter possibly being a part of the Pacific stock), which are located westward of 40oE and eastward of 110oE respectively. Neighboring stocks are intermingled in adjacent waters.
Hydrography and spatial variability in the size distribution of phytoplankton along the Kurile Islands in the western subarctic Pacific Ocean
Authors: TAGUCHI SATORU , SAITO HIROAKI , KASAI HIROMI , KONO TOKIHIRO , KAWASAKI YASUHIRO
Published: October 2007

Spatial variability in the size distribution of the phytoplankton community along the Kurile Islands, in the western subarctic Pacific Ocean, was investigated in terms of chlorophyll a concentrations in August and September, 1990. Analysis of dynamic height relative to 1,500 db and temperature–salinity diagrams at 50 m depth revealed five major oceanographic regions in this study area. The characteristic hydrography was clearly related to the surface distribution of chlorophyll a concentrations. As a warm core ring originating from the Kuroshio water was cooled by the surrounding water and meteorological conditions, its physical, chemical, and biological characteristics changed. Dominant picoplankton were replaced by a 10‐2 μm size fraction in the warm core ring. In the Oyashio region, physical structures were less variable but concentrations of chlorophyll a were most variable and cells larger than 10 μn dominated. An anticlockwise eddy found in the Oyashio water showed the highest concentration of chlorophyll a. In the Okhotsk region, the chlorophyll standing stock was small with a low percentage of cells larger than 10 μm in spite of high nitrate concentrations. Along the Kurile Islands and Hokkaido Island, the surface mixed layer was not well defined; surface nitrate concentrations were relatively high, and the chlorophyll standing crop was also high with low percentages of picoplankton. The spatial heterogeneity in the dominance of cells larger than 10 μm in phytoplankton assemblages seems to be clearly associated with the effect of nitrate availability determined by water structure.
δ13C‐δ15N values as indicators of trophic position and competitive overlap for Pacific salmon (Oncorhynchus spp.)
Authors: WELCH DAVID W. , PARSONS TIMOTHY R.
Published: October 2007

Analysis of δ13C and δ15N isotope values for five species of Pacific salmon indicate that they form a trophic hierarchy on the high seas. On the basis of an analysis of these stable isotope ratios, chinook salmon feed at the upper end of the food chain and pink salmon at the lower end, in the sequence pink → sockeye → coho → chinook, with chinook and pink salmon separated by ca. 0.8 of a trophic level. Chum salmon occupy a peculiar position, with low δ13C values and high δ15N values, possibly reflecting an unusual diet that includes large amounts of gelatinous zooplankton (salps, ctenophoi;s, and medusae). Chum appear to occupy a unique trophic position, at a trophic level nearly as high as that of chinook but at the end of a different branch of the food chain. If true, the potential for trophodynamic competition with other salmon species is small. Our results suggest that the greatest potential for trophodynamic competition occurs within the pink‐sockeye‐coho grouping. A similar analysis, restricted to five stocks of North American sockeye, shows that four widely separated stocks have similar heavy isotope compositions but that the separation between these stocks is still statistically significant. The Chilko stock is strikingly different, however, suggesting that it is located in the central Gulf of Alaska, a region of intense upwelling. Circumstantial evidence supporting the possibility that the Chilko and other sockeye stocks are geographically separated within the Gulf of Alaska is reviewed.
The distribution of cod (Gadus morhua) in relation to temperature and oxygen level in the Gulf of St. Lawrence
Authors: D'AMOURS DENIS
Published: October 2007

Bottom temperature and oxygen level were measured in the northern Gulf of St. Lawrence during a ground‐fish trawl survey held in August and September 1991. Cumulative relative frequencies of temperature and oxygen level and cumulative relative frequencies of temperature x cod and oxygen X cod were computed with consideration of the random stratified sampling scheme. A total of 84‐3% of temperature x cod frequency cumulated from 2oC to 4oC, but only 25% of the frequency of temperature alone cumulated from 2oC to 4oC. At an oxygen level of 3.4 mg/1, only 2.6% of the oxygen X cod frequency had cumulated, while 24.3% of the cumulative frequency of oxygen alone was already observed at the same oxygen level. A comparison of the cumulative relative frequencies of temperature and of temperature X cod indicates that cod choose intermediate temperatures in the available range. A comparison of the cumulative relative frequencies of oxygen and of oxygen x cod indicate that cod avoid water with an oxygen level below 3.4 mg/1. This oxygen level is known to cause physiological stress in captivity. Data from the stations with oxygen levels ± 3.4 mg/1 were ignored, and the cumulative relative frequency of temperature was recomputed. As a result, the avoidance of cold water by cod was emphasized: 23% of the cumulative frequency of temperature alone was below 2oC, and 47.8% was above 4oC, in contrast to 17.2% and 57.5%, respectively, prior to removal of data from hypoxic stations.
Predation on walleye pollock (Theragra chakograrnma) eggs and yolk‐sac larvae by pelagic crustacean invertebrates in the western Gulf of Alaska
Authors: BAILEY KEVIN M. , BRODEUR RICHARD D. , MERATI NAZILA , YOKLAVICH AND MARY M.
Published: October 2007

Immunological detection of yolk protein was used to assess predation by pelagic amphipods (gammarid and hyperiid), mysids, and euphausiids on eggs and yolk‐sac larvae of walleye pollock Theragra chalcogramma during 1988 and 1989. Consumption estimates were made on the basis of frequency of positive immunoassays, assay detection times (gut clearance time), predator abundance, and spatial overlap of predators and prey. From our results gammarid amphipods and euphausiids were important predators on eggs and yolk‐sac larvae, respectively. Gammarid amphipods alone consumed about 14% of the standing stock of pollock eggs in 1989. These results were compared with those from clearance rate experiments of predators feeding on pollock eggs in 300‐1 bags. In general, clearance rate estimates of egg consumption were lower than those determined from gut contents.
Cod spawning in relation to physical and biological cycles of the northern North–west Atlantic
Authors: MYERS R. A. , MERTZ G. , BISHOP C. A.
Published: October 2007

All the available, reliable cod (Gadus morhua) spawning data for the northern North–west Atlantic (the Grand Banks of Newfoundland, the Labrador and West and East Greenland Shelves) have been analysed to update older, often unpublished, reports of spawning dates. The derived spawning times are examined for latitudinal trends and it is shown that no consistent, general pattern exists. The spawning dates are compared with seasonal cycles of plankton abundance, ocean temperature, water column stability and oceanic transport. The latitudinal trends in spawning dates and timing of the plankton peak are found not to correspond.
The use of satellite imagery to direct research ship sampling operations
Authors: BROWN R. M. , DENMAN K. L. , BORSTAD G. A. , PARKS J. R.
Published: October 2007

Oceanographic processes on the continental shelf adjacent to Vancouver Island are energetic, highly variable and dominated by eddies, upwelling jets and shelfbreak baroclinic instabilities. Consequently, areas of enhanced planktonic production are patchy and ever‐changing, making them difficult to study and map from ship. We have developed a technique for transmitting interpreted thermal AVHRR satellite imagery to research ships, where we use the imagery to direct CTD sampling lines, acoustic Doppler current profiling and deployment of drifting buoys. The AVHRR satellite images are geo‐referenced, masked and interpreted to produce a contoured sea surface temperature field in the area of interest. The contour field image is transferred between personal computers equipped with matching facsimile subsystems. The compressed image is transmitted via HF radio link or Inmarsat. The preprocessing of the image ashore provides for significant data compression and allows for operational use of the image to direct research of fishing within 12 h of the satellite pass.
The North Atlantic turbine: views of production processes from a mainly North Atlantic perspective
Authors: WYATT T. , JENKINSON I. R.
Published: October 2007

A brief account is given of the ‘agricultural hypothesis’, the key studies which led to its replacement by the ‘grazing hypothesis’, and early models of the classical planktonic food chain. The budgetary problems posed by these views led to interest in the roles of dissolved and particulate components of planktonic ecosystems, and to discovery of the ‘microbial loop’. The balance between these alternative pathways is seen to reflect processes at the interface between hydrodynamics and ecology.
Variations in food abundance for Japanese sardine larvae related to the Kuroshio meander
Authors: NAKATA KAORU , HADA AKIO , MATSUKAWA YASUO
Published: October 2007

Long‐term fluctuations of chlorophyll a concentration, and abundance of herbivorous or omnivorous small copepods during the spawning season of the Japanese sardine, Sardinops melanosticta, were examined in relation to the types of Kuroshio meander. The purpose was to clarify the influence of the meander on the production of food organisms for the sardine larvae and their survival in the Pacific coastal region of central Japan. During an A‐type meander of the Kuroshio, when the offshore and inshore movements of the Kuroshio path were small except at the beginning of the meander, the surface chlorophyll a concentration in the coastal region was lower than that during a non‐A‐type meander with frequent and prompt fluctuations of the Kuroshio path. The abundance of small copepods was also low during the A‐type meander except in the subsequent spring just after the beginning of an A‐type meander, but often high during the non‐A‐type meander. Prompt fluctuations of the Kuroshio path during the non‐A‐type meander probably cause local upwellings which stimulate primary and secondary production near the Kuroshio, and may enhance the survival of the sardine larvae. On the contrary, the quasi‐stationary state of an A‐type meander may be unfavourable for the production of phytoplankton and nauplii of herbivorous or omnivorous small copepods, and therefore the survival of the sardine larvae becomes poor.
Comparative analysis of ichthyoplankton sampling gear for early life stages of walleye pollock (Theragra chalcogramma)
Authors: SHIMA MICHIYO , BAILEY KEVIN M.
Published: October 2007

Comparative gear tows were conducted during the summers of 1987–1990 in the Gulf of Alaska. Efficiencies of four types of ichthyoplankton sampling gear were compared with respect to total catch and size distribution of larval fish. Fish were sampled using the bongo net (333 and 505 μm mesh), 1 m Tucker net, 3 m Tucker net and the Methot frame net. Results indicate that the bongo and the 1 m Tucker nets caught similar numbers and size distribution of fish. The larger 3 m Tucker and Method frame nets caught a larger size class of fish but a smaller total catch. Although there was a slightly significant diel difference in total catch detected in the smaller nets, no diel differences in size distribution of fish caught were detected for any of the nets.
Fishery development in the eastern North Pacific: a natural‐cultural system perspective, 1888–1976
Authors: DEIMLING ELISABETH A. , LISS WILLIAM J.
Published: October 2007

Commercial fishery landings data spanning almost a century were examined from three regions within the eastern North Pacific: north‐central California, Oregon‐Washington, and Southeast Alaska. Fisheries in each region developed differently because each region had unique species, community trophic composition, and other community parameters related to differences in physico‐chemical characteristics. Fisheries also began at different times in each region. Despite differences, overall patterns of landings were similar among regions. A ‘fishing‐up’ sequence occurred in each region that included seaward expansion of the fishery and diversification of taxonomic composition of landings. Mean annual landed weights of several very desirable taxa fished continuously from the early years of the fisheries initially increased, peaked, then declined. These patterns are similar to those found in studies of long‐term fishery development in the Great Lakes. Other patterns of landings over time common to each region were: exclusions of particular taxa in more recent time periods; predominance of pelagic species; and shifts in trophic composition away from predominance of taxa at high trophic levels. In two regions there were initial increases, then declines in mean annual weights of total landings. Similarities in these patterns among regions that differ greatly in terms of physico‐chemical characteristics suggest the overwhelming importance of common cultural parameters. Management suggestions are made based on the common patterns of commercial fishery development.
Simulating the dispersion of vertically migrating sprat larvae (Sprattus sprattus (L.)) in the German Bight with a circulation and transport model system
Authors: BARTSCH JOACHIM , KNUST RAINER
Published: October 2007

A model system consisting of two three‐dimensional circulation models and a three‐dimensional transport model is used to simulate the dispersal of sprat larvae (Sprattus sprattus (L.)) in the German Bight. A Northwest European shelf sea model simulates the currents of the North Sea and provides sea surface elevation data for the open boundaries of the German Bight circulation model. The German Bight circulation model has a horizontal grid resolution of 2.75 km and a vertical resolution of 5 m except for the bottom layer. The driving forces of the circulation models are the M2‐tide, six‐hourly time‐dependent wind stress and air pressure fields as well as monthly climatological density fields. The simulated currents serve as input to the transport model. The model area, grid size and the vertical resolution of the transport model are in accordance with the German Bight circulation model. The transport model simulates advection and diffusion using a Monte Carlo method. Furthermore it incorporates a simulation of active vertical movement of the larvae. The vertical migration pattern is dependent on the time of day and size of the larvae and is based on field data from the German Bight. Horizontal larvae distribution data, gained from two out of five field surveys carried out in the German Bight during spring and summer 1991, are used as initial values for the starting points of the tracers in the transport model. Simulated tracer distributions are compared with larval distributions observed during subsequent cruises about 3 weeks later. Discrepancies and similarities between tracer and larval distributions are discussed.
Eulerian views of layered water currents, vertical distribution of some larval fishes, and inferred advective transport over the continental shelf off North Carolina, USA, in winter
Authors: GOVONI JOHN J. , PIETRAFESA LEONARD J.
Published: October 2007

Currents that effect the shoreward transport of the larvae of estuarine‐dependent fishes spawned in winter in Onslow Bay, North Carolina, USA, were driven by winds and pressure gradients, and influenced by the Gulf Stream. Aside from storms, winds over the continental shelf in Onslow Bay blew predominantly alongshore with velocities approaching 14 m s‐1 during February and March 1986, and January and February 1989. Water masses and currents observed at two current‐meter moorings, one at mid‐shelf and the other on the outer shelf, reflected the onshore (or offshore) advection of interior water in compensation for the offshore (or onshore) advection of wind‐driven surface water. Winds and currents reversed direction approximately every 4 to 6 days. The larvae of Atlantic menhaden, Brevoortia tyrannus, spot, Leiostomus xan‐thurus, and Atlantic croaker, Micropogonias undulatus, were most abundant in 17–19oC and 20–21oC water of the outer shelf and Gulf Stream fronts. There was little indication of diel vertical migration; larval Atlantic menhaden were most abundant in mid‐ and surface water, while spot and Atlantic croaker were most abundant in mid‐ and deep water. Given this distribution, the inferred advective transport of larvae was at times onshore, but at other times it was offshore. Within a spawning season, the prevalence of either reciprocation could determine the number of larvae that reach coastal inlets.
Relationships among yellowfin and skipjack tuna, their prey‐fish and plankton in the tropical western Indian Ocean
Authors: ROGER CLAUDE
Published: October 2007

Stomach contents of yellowfin (Thunnus albacares) and skipjack (Katsuwonus pelamis) tuna caught by trolling and purse seining in the tropical western Indian Ocean, together with those of the prey‐fish found in their stomachs, have been analysed. Epipelagic fish are the main prey of these tunas, whereas no vertically migrating fish, which inhabit subsurface layers at night, have been found in their stomachs. These tunas are thus considered day‐feeders. Purse‐seine‐caught tunas, which belong to large schools, have a much higher number of prey‐fish in their stomachs than tunas caught by trolling on small schools. Similarly, prey‐fish from purse‐seine tunas have a much higher number of plank‐tonic prey in their stomachs than those from troll‐caught tunas. Therefore, these tunas adopt a wandering strategy in small schools when food resources are scarce and form large schools when they are abundant. The planktonic organisms found in the stomachs of prey‐fish are described by taxa and sizes; they represent the fraction of the planktonic biomass actually supporting the stock of tuna. Size ratios between the three links tuna‐prey‐fish‐plankton are very high, suggesting that these tunas benefit from a short food chain which is probably efficient from the energetic point of view.
The influence of ocean climate on coastal plankton and fish production
Authors: ROBINSON CLIFFORD L. K.
Published: October 2007

This study evaluates the influence of oceanic variability on plankton and fish production in a coastal upwelling system off southern Vancouver Island, British Columbia, Canada. A trophodynamics model is used to hind‐cast plankton and fish production as estimated by empirical seasonal patterns in upwelling, sea surface temperature, solar radiation, and by biomasses of Pacific hake (Merluccius productus) and Pacific herring (Clupea pallasi). Simulation results indicate that interannual and longer‐term variability in coastal plankton production occurs, and that the patterns are primarily determined by the dynamics in the initiation and intensity of coastal upwelling. Fish properties are greatly influenced by zooplankton, with simulated hake production being correlated with summer euphausiid production, and measured herring condition being correlated with autumn zooplankton production. An evaluation of transfer efficiencies indicates that interannual variability in the diatom‐to‐fish transfer is high (CV = 78%), with the majority of this variability occurring in the diatom‐to‐zooplankton component of the transfer. Seasonal dynamics of the diatom‐to‐zooplankton transfer result from the effects of upwelling on diatom production, and subsequent trophodynamic phasing with copepods and euphausiids.
Is there a role of ocean environment in American and European eel decline?
Authors: CASTONGUAY MARTIN , HODSON PETER V. , MORIARTY CHRISTOPHER , DRINKWATER KENNETH F. , JESSOP BRIAN M.
Published: October 2007

American eel (Anguilla rostrata) recruitment has declined dramatically, in parallel with that of European eel (Anguilla anguilla). Since both species spawn in the Sargasso Sea and migrate as larvae to continental waters, the coincidence in recruitment failure implies an Atlantic‐wide cause, due perhaps to ocean climate. There is indirect evidence that the Gulf Stream has weakened in the 1980s. A slower Gulf Stream could interfere with larval transport and generate observed patterns of declining abundance of American eel only in northern North America and relatively uniform declines of European eel throughout Europe. While specific causes are still unclear, these data indicate a threat to both species and to their commercial fisheries.
A review of temperature and oxygen tolerance studies of tunas pertinent to fisheries oceanography, movement models and stock assessments
Authors: BRILL RICHARD W.
Published: October 2007

Detailed data on the physiological abilities and habitat requirements of some tuna species have now been collected. Laboratory and field studies show tunas are not strictly prisoners of their own thermoconserving mechanisms, but have rapid and extensive control over the efficacy of their vascular countercurrent heat exchangers. Skipjack tuna (Katsuwonus pelamis) are, therefore, probably not forced out of formerly suitable habitats as they grow because of the potential for overheating, as formerly thought. Because of their thermoregulatory abilities, bigeye tuna (Thunnus obe‐sus) apparently can exploit food resources well below the thermocline by minimizing rates of heat loss when in cold water, and then maximizing rates of heat gain from the environment during brief upward excursions into the warmer mixed layer.

Widely cited estimates of limiting oxygen levels, based on estimated metabolic rates at minimum hydrostatic equilibrium swimming speeds, are not accurate because tunas have exceptionally high oxygen demands even at slow speeds. High metabolic rates, even at slow swimming speeds, most likely result from the high osmoregulatory costs engendered by tunas' large thin gills and/or their other adaptations for achieving exceptionally high maximum metabolic rates. Recent laboratory research and modelling efforts suggest the capacity of tunas' cardiorespiratory systems to deliver oxygen at extraordinarily high rates was evolved to allow rapid recovery from strenuous exercise, rapid digestion, and high rates of gonadal and somatic growth, not high sustained cruising speeds. The rate at which reduced ambient oxygen levels prolong the time required for tunas to recover from strenuous exercise appears to be a good index of habitat suitability, with respect to oxy‐een.
Simulation of juvenile sockeye salmon (Oncorhynchus nerka) migrations in the Strait of Georgia, British Columbia
Authors: PETERMAN RANDALL M. , MARINONE SILVIO G. , THOMSON KEITH A. , JARDINE IAN D. , CRITTENDEN ROBERT N. , LEBLOND PAUL H. , WALTERS CARL J.
Published: October 2007

Previous research has documented two main migratory routes of juvenile sockeye salmon (Oncorhynchus nerka) through the Strait of Georgia, British Columbia, Canada, and large interannual variability in marine survival rates of the Chilko Lake stock. Simulation models were used to explore the influence of surface currents on the migratory route of juvenile sockeye salmon (smolts) through the Strait of Georgia. We used a model of downstream migration to generate daily numbers of Chilko Lake sockeye salmon smolts entering the Strait of Georgia, based on daily counts of smolts leaving the rearing lake. A numerical hydrodynamic model (driven by surface wind, tide, and Fraser River discharge) hindcasted surface currents in the Strait of Georgia on a 2 km × 2 km grid. A smolt migration model simulated fish moving through the Strait with different compass‐oriented migratory behaviours (i.e. swimming speed and directional orientation) within the time‐varying surface advection field. Results showed that surface currents within the Strait of Georgia can affect the migratory route of sockeye salmon smolts in spite of their large size (8 cm). Wind is the forcing mechanism primarily responsible for determining which migratory route would be used. Under prevailing wind conditions (i.e. toward the north‐west), most sockeye salmon smolts would use the eastern migratory route; however, relatively brief south‐eastward wind events (lasting about 2 days) would force most smolts into the western migratory route. Given the heterogeneity of food for salmon within the Strait, we hypothesize that wind‐driven variability in the annual proportion of smolts that use the western and eastern migratory routes in the Strait of Georgia affects early marine survival rates of Fraser River sockeye salmon.
Match/mismatch predictions of spawning duration versus recruitment variability
Authors: MERTZ G. , MYERS R. A.
Published: October 2007

According to the match/mismatch hypothesis, larval fish survival and eventual recruitment is dependent on the offset time between the peaks of abundance of larvae and their planktonic prey. A rudimentary larval food supply model is developed to determine the dependence of food availability on the mismatch between peaks. The model predicts that recruitment variability should increase as spawning duration decreases, a result which is moderately supported by an analysis of Atlantic cod (Gadus morhua) data.
Recruitment variability and oceanographic stability
Authors: MYERS RANSOM A. , PEPIN PIERRE
Published: October 2007

We examine the hypothesis that recruitment is more variable in populations on isolated offshore banks than nearby shelf populations. Recruitment of cod (Gadus morhua) and American plaice (Hippoghssoides plates‐soides) on Flemish Cap is more variable than in any comparable population. Recruitment of haddock (Melanogrammus aeglefinus) on Rockall Bank is also more variable than in surrounding populations. These results are confirmed both by estimates obtained by virtual population analysis and by research surveys. Recruitment of haddock and herring (Clupea harengus) on Georges Bank is also more variable than in surrounding populations; however, the results for two other groundfish populations, cod and yellowtake flounder (Limanda ferruginae), on Georges Bank are ambiguous. We conclude that marine fish populations on isolated banks are more variable than those on nearby shelf regions.
Influence of a Sargassum forest on the spatial distribution of water flow
Authors: KOMATSU TERUHISA , MURAKAMI SHIN‐ICHI
Published: October 2007

The influence of a Sargassum forest on the spatial distribution of water flow generated by waves and tidal currents was investigated. Water flow was measured horizontally and vertically by using plaster balls at a Sargassum forest in Saiki Bay facing the Bungo Channel, on the Pacific Coast of Kyushu Island, Japan, from 7 to 9 March 1989 during the luxuriant growth season of Sargassum species. Plaster balls were deployed at several depths at stations placed with horizontal scales of 10–100 m. Wet weight loss of plaster balls immersed in the field for 50 h was converted to the speed of steady flow (named intensity of water motion) that brought the equivalent loss in a tank experiment. The results clarified that the spatial distribution of water flow showed good correlation with that of the standing crop of Sargassum forest, and that the intensity of water motion was appreciably diminished in the Sargassum forest. We also discuss ecological implications of the reduction in water flow within the Sargassum forest for the growth and settlement of Sargassum species.
Plankton abundance and size structure in the northern North Pacific Ocean in early summer
Authors: ODATE TSUNEO
Published: October 2007

Phyto‐ and zooplankton abundance and size structure were investigated in the northern North Pacific Ocean (37.0–49.5oN along 180o longitude) during June of 1987. The area between 41.5oN and 47.5oN was expected to be abundant in phytoplankton since both water column stability and nutrient availability were favourable for phytoplankton growth. Actual phytoplankton abundance was, however, low between 41.5oN and 45.5oN. In particular, abundance of net phytoplankton (>10μm) was low although picophytoplankton (<2 μm) was abundant between 41.5oN and 43.5oN. The zooplankton community between 41.5oN and 45.5oN was characterized by a large amount of net zooplankton and a small amount of microzooplankton. This situation may be best explained by top‐down control; that is, net zooplankton grazing suppressed net phytoplankton and microzooplankton abundance. The diminished microzooplankton promoted the increase of picophytoplankton. Because planktivorous Pacific saury were abundant between 40.0oN and 41.0oN, it is further speculated that the low biomass of net zooplankton south of 41.0oN resulted from feeding by Pacific saury. The reduced grazing pressure of net zooplankton may have enhanced the growth of net phytoplankton and microzooplankton in this region.
Distribution and abundance of South‐west Atlantic anchovy spawners (Engraulis anchoita) in relation to oceanographic processes in the southern Brazilian shelf
Authors: LIMA IVAN D. , CASTELLO JORGE P.
Published: October 2007

The reproductive environment of the South‐west Atlantic anchovy, Engraulis anchoita, in the southern Brazilian coast was investigated using maritime weather reports from the US National Climatic Center. These reports were summarized to yield seasonal distributions of sea surface temperature, wind stress and Ekman transport for 2‐month segments of the seasonal cycle. The vertical oceanographic structure and dynamics were studied using temperature and salinity data collected from oceanographic cruises. The seasonal distribution and biomass of South‐west Atlantic anchovy spawners were estimated by acoustic surveys. Anchoita spawns intensively off southern Brazil during winter and early spring when the Ekman transport is directed onshore, and the combined effects of freshwater run‐off and the flow of cold water near the bottom result in a strong vertical stability over the continental shelf. During this season, primary production peaks due to nutrient input from Sub‐Antarctic waters and freshwater run‐off. These conditions would avoid dispersal of eggs and larvae offshore and favour the production and maintenance of fine‐scale food particle aggregations required for successful first feeding of newly hatched larvae. In summer, the conditions are almost reversed and anchoita spawners are virtually absent from the area. Thus, the spawning strategy of anchoita in southern Brazil seems to be tuned in a way to optimize larval retention, minimize exposure to turbulent mixing and take advantage of enhanced plankton productivity.
Modelling advection of cod eggs and larvae on the Newfoundland Shelf
Authors: DAVIDSON FRASER J. M. , DEYOUNG BRAD
Published: October 2007

We investigate interannual variations in dispersion for the drift and retention of cod eggs and larvae on the Newfoundland Shelf using a two‐dimensional Lagrangian tracking model. The velocity field for the drift model is obtained from a diagnostic calculation of objectively analysed density data. Time‐dependent currents are generated using an inertial‐current slab model driven by observed winds. Eggs and larvae are treated as passive drifters seeded in a dispersion model of the Newfoundland Shelf region. We identify favourable and unfavourable zones of retention on the Newfoundland Shelf. We show that northerly, shelf‐break spawning locations are more favourable than southerly shelf‐break spawning locations for northern cod, (Gudus morhua, in NAFO divisions 2J3KL).
A structured approach to using biological and environmental parameters to forecast anchovy recruitment
Authors: COCHRANE K. L. , HUTCHINGS L.
Published: October 2007

Simulation studies have indicated that a valuable increase in mean annual yield could be achieved in the South African anchovy, Engraulis capensis, fishery if below‐average recruitment could be forecast at the start of the fishing season, 6 months before recruitment can he reliably measured. This paper reports on initial investigations into biological and environmental indicator‐ which could be used to make such forecasts. Valid estimates of recruitment strength in the species are available from 1985 to 1992 and the environmental and biological indicators of interest have been monitored for periods starting from between 1984 and 1988, to the present. Most of the data were obtained from monitoring on anchovy spawner biomass surveys which have been undertaken each November since 1984.

A conceptual model of the factors influencing the recruitment process was constructed and the available data were examined for empirical evidence of the importance of each event included in the model. Fluctuations in copepod biomass and production on the spawning grounds, the incidence of oocyte atresia in adult females, the incidence of southerly winds at Cape Point and the distance offshore of the 16°C isotherm at Cape Columbine were associated with fluctuations in anchovy recruitment. It is suggested that particular attention should be paid to monitoring of these variables to investigate further these associations. If persistent relationships are found, it may be possible to construct an expert system to forecast recruitment from observed values of these variables at the start of a fishing season. A preliminary set of three decision rules is presented.
Winter distribution and movements of northern Atlantic cod (Gadus morhua) along the Newfoundland—Labrador continental shelf edge derived from observations on commercial trawlers
Authors: WROBLEWSKI J. S. , KULKA D. W. , NARAYANAN S. , OAKE A. M. , COLLIER A. G. , MCGRATH B. D.
Published: October 2007

Catch‐effort data recorded by observers aboard commercial trawlers fishing the Newfoundland‐Labrador continental shelf during the winters of 1980–1991 were used to define the distribution and movements of pre‐spawning and spanning Atlantic cod, Gadus morhua. Although cod were widely distributed over the outer continental shelf in the months of January to April, commercial concentrations were consistently located in three areas along the shelf edge. These three areas, constituting only 16% of the 190000 km2 fishing ground for northern cod, were centred north‐east of Belle Isle Bank, north‐east of Funk Island Bank, and between Funk Island Bank and the northern Grand Bank Tow positions with catch rates 5000 kg h‐1 were plotted on a weekly basis to define movements of cod schools during the winters of 1986–1988. It was assumed that change in the collective position of trawlers taking large quantities of cod reflected shoal movements. Analyses indicate that cod moved southeast along the shelf edge in January and February of each year, crossing from NAFO Division 2J into 3K Each March, cod in Division 3K apparently moved northwest against prevailing ocean currents into the Hamilton Bank region of 2J. These movements do not appear to be a direct response to ocean temperature or pack ice conditions, although cod moving along the shelf break were generally in bottom waters of 24°C. We suggest these patterns reflect the migratory behaviour of pre‐spawning and spawning cod.
Horizontal distribution and seasonal variability of the epipelagic chaetognath Sagitta elegans in relation to hydrography in the western subarctic Pacific Ocean
Authors: TERAZAKI MAKOTO , SAITO HIROAKI , KASAI HIROMI , KONO TOKIHIRO , KAWASAKI YASUHIRO , TAGUCHI SATORU
Published: October 2007

The spatial distribution and seasonal variability of epipelagic chaetognaths along the Kurile Islands and off south‐east Hokkaido, in the western subarctic Pacific Ocean. were investigated during the period from May 1990 to October 1992. Sagitta elegans was the dominant species among the epipelagic chaetognaths in the study area. Juvenile S. elegans were distributed mainly along the path of the mixed water which was determined by the acceleration potential anomaly (APA) at the iso‐pycnal density surface of 26.6 σθ. The location of the path of The mixed water meandered around cyclonic and anticyclonic eddies. Catches of S. elegans were made at temperatures ranging from 4.5 to 22.2d̀C. The juvenile distribution, however, was mostly restricted to between 1 and 4d̀C of the potential temperature determined at the isopycnal density surface of 26.6 σθ. Variability in the juvenile abundance within the path of the mixed water could be caused by predation rather than by food limitation because microzooplankton, which are known to he prey for juveniles, were abundant enough to meet the food requirements of juveniles in the study area. Adults occurred in spring (April‐May) and young individuals (juvenile and stage 1) were abundant in summer (June‐July), when a strong thermocline developed. The main spawning period appears to be during April‐May, with a possible second spawning period in the autumn.
Variation in the condition factors of California pelagic fishes and associated environmental factors
Authors: PARRISH RICHARD H. , MALLICOATE DONNA L.
Published: October 2007

Time series of condition factors for mackerel, Scomber japonicus, jack mackerel, Truchurus symmetricus, and northern anchovy, Engraulis mordax, stocks in the Southern California region were compared with time series of oceanographic indices to develop hypotheses concerning physical environmental forcing of the population dynamics and energetics of small pelagic fishes. Mackerel and jack mackerel condition factor time series showed decade‐scale variation, whereas those of anchovy showed coherent fluctuations for 1 to 2 years. Mackerel, and to a lesser extent jack mackerel, condition factors were correlated with proxy indices of alongshore advection (sea level), offshore advection (Ekman transport), ambient temperature (shore station temperature), and ambient salinity (shore station salinity). The condition factor of anchovy was much less correlated with environmental variables. Multiple regression analyses which included sea level, upwelling and salinity proxies explained 80% (33%) of the variance in the annual (monthly) condition factor of mackerel. The first‐order variation in condition factors of mackerel and jack mackerel suggests that they are responding to very large‐scale perturbations of the California Current system which are at least partially described by variations in sea level. The population size of mackerel is apparently also responding to these large‐scale perturbations, making it difficult to isolate environmental dependence of condition factors from density dependence. The second‐order variation is more regional in nature and unexpectedly it appears to be associated with upwelling in the Baja California region.
A century and a half of change in the climate of the NE Pacific
Authors: WARE D.M.
Published: October 2007

Spectral analysis of twenty‐one climate records indicates that NE Pacific temperatures and winter wind stress have fluctuated at four dominant time scales in this century: 2–3 years (quasi‐biennial oscillation), 5–7 years (El Nin̈o‐Southern Oscillation, ENSO), 20–25 years (bidecadal oscillation, BDO), and a poorly resolved, very‐low‐frequency (VLF) oscillation with a 50–75 year period. Forty‐four per cent of the low‐frequency variability in British Columbia air temperatures is associated with the strength of the Aleutian Low pressure system in winter. Only 42% of the ‘strong’ and 25% of the ‘moderate’ ENSO events in this century have produced large warm anomalies off BC. Interactions between the ENSO, bidecadal and very‐low‐frequency oscillations produce a pattern of alternating warm and cool climate states, with major warnings every 50 to 75 years. Since 1850 there have been seven warm periods, lasting an average of 11.4 years, and six cool periods lasting an average of 10.8 years. Sharp transitions from cool to warm climate states (as in 1977/78) occur when warming phases of the BDO and VLF oscillations coincide. Recent evidence suggests that the BDO may originate in either the tropical or the subtropical North Pacific. The NE Pacific has experienced a major warming since 1978. A long‐range forecast suggests that the BDO and VLF oscillations peaked in 1989 and are currently in a cooling phase. Consequently, coastal temperatures should moderate for the rest of this century. A transition to the next cool climate state could occur about the year 2001. The forecast for moderating temperatures could begin the first phase of the recovery of the southern BC coastal chinook and coho salmon and herring stocks, which are currently at low abundance levels.