bluuebunny/crossref_metadata_2025 huggingface dataset:
Response of the Southern California current system to the mid‐latitude North Pacific coastal warming events of 1982–1983 and 1940–1941
Authors: SIMPSON JAMES J.
Published: October 2007

The large‐scale structure of the California Current during the 1982–1983 mid‐latitude North Pacific coastal warming event showed several persistent (> 16 months), anomalous conditions: positive sea surface temperature anomalies (1–2.5oC), depression of the inshore thermocline by as much as 50 m greater than normal, anomalous high inshore steric heights (˜ 1.05 dyn. m) compared with normal values, anomalous high sea levels (˜ 25 cm), positive subsurface temperature anomalies (3–4oC), negative salinity anomalies (0.1‐0.3%), positive dissolved oxygen anomalies (0.5‐1.5 ml/1), and negative inshore nutrient anomalies. The magnitudes of the subsurface anomalies generally are much larger than those of the surface anomalies. The cross‐shelf length scales of the subsurface anomalies vary between 300 and 500 km. During this same period, pronounced negative sea surface temperature anomalies (2–3oC) developed in the central mid‐latitude North Pacific. The characteristic diagrams and sign reversals in the salinity, oxygen, and nutrient anomalies are consistent with enhanced onshore transport of Pacific subarctic water from the offshore California Current. The source of this water is primarily from the west‐northwest. The subsurface anomalies were produced dynamically by a depression of the inshore thermocline, which, at least in part, resulted from convergence of mass at the coastal boundary. The surface anomalies, however, were produced by a combination of dynamical and local thermodynami‐cal processes. Observed anomalous atmospheric forcing, as reflected in the 700 mb height anomaly and in negative upwelling indices, is consistent with enhanced onshore transport from offshore California Current. All the data support the conclusion that the expansion and intensification of the Aleutian Low and the decrease in strength of the North Pacific High produced an anomalous basin‐wide atmospheric circulation that, coupled directly with the large‐scale wind‐driven oceanic circulation, produced a major component of the North Pacific coastal warming response observed during 1982–1983. Nearly identical mid‐latitude atmospheric forcing and oceanic responses were observed during the 1940–1941 analog event. Anomalous phytoplankton and zooplankton distributions also were observed, and fish catch during this period decreased by about 40%, with nearshore pelagic species particularly affected. Not only was the abundance of single species affected, but also the community structure (i.e., rank order of abundance) was changed in response to the changing environmental conditions. The biological response appears to have been driven by the increased static stability, deeper thermocline, and reduced nutrient concentrations, which, in turn, resulted from the anomalous atmospheric circulation.
A review: Walleye pollock in the North Pacific–how much difference do they really make?
Authors: SPRINGER ALAN M.
Published: October 2007

Populations of several species of marine birds and mammals in the Bering Sea and Gulf of Alaska have been declining since the mid‐1970s, with numbers of one, the Steller sea lion (Eumetopias jubatus), so depressed it was listed as threatened under the Endangered Species Act in spring 1990. All of the declining populations depend to an important extent on walleye pollock (Theragra chakogramma) for food, although they eat numerous other species as well. In contrast, certain animals that compete with pollock for common prey have been increasing in abundance. All of these changes could be related through food web connections mediated by pollock. Pollock is also important to people–it presently supports the largest single‐species commercial fishery in the world, in large part because of its great biomass, which has averaged about 15 × 106t in the Bering Sea over the past 15 years. Pollock consume an inordinate proportion of the pelagic production in the Bering Sea, which further supports the conclusion that it is a key species in the ecosystem. However, there are conflicting hypotheses about the importance of the roles played by pollock as predator and prey, and about the effect that changes in pollock abundance might have on biomass yield at higher trophic levels.
A context for recruitment correlations: why marine fisheries biologists should still look for them
Authors: TYLER A. V.
Published: October 2007

In many cases when ecologists want to investigate a process, they often look for the best system on which to conduct the research, “best” meaning that the possibility of discovering mechanisms is optimized or made easier in some way. In fisheries we do it backwards. The species and system are given to us by economics, and we then fly in the face of the difficult circumstances to find mechanisms that are elusive anyway. These difficult circumstances constitute in some sense the first set of statistical problems. Using examples from the Northeast Pacific, I review the characteristics of cohort time series that make some species more tractable; propose a conscious process of conceptualization to assist in the formulation of clear, germane hypotheses; highlight the contrast between modeling in the sense of statistical fitting versus simulation models of processes; explore how the first round of models integrates with the second round of planning for new data collection at sea and in the lab; and, finally, propose how to judge success in terms of an operational approach.
The Fraser River plume: some preliminary observations on the distribution of juvenile salmon, herring, and their prey
Authors: JOHN MICHAEL A. ST. , MACDONALD J. STEVENSON , HARRISON PAUL J. , BEAMISH RICHARD J. , CHOROMANSKI EDWARD
Published: October 2007

Zooplankton and fish densities in the southern Strait of Georgia were observed to coincide with variations in surface salinities resulting from the outflow of the Fraser River. Vertical net hauls in the euphotic zone revealed that copepods, amphipods, and euphausiids were significantly more abundant per m3 in the brackish estuarine plume (surface salinities ‐ 10–15 ppt) when compared to the area covered by the freshwater of the Fraser River plume (0–10 ppt) and the region of the Strait of Georgia (25–30 ppt) unaffected by the outflow of the Fraser River.

The estuarine and riverine plumes had significantly higher fish densities (adult and juvenile herring, and juvenile salmonids [excluding chinook]) than the Strait of Georgia region, with no significant differences in densities of juvenile chinook salmon observed between regions. The highest catches of juvenile salmonids were at the boundary between the estuarine plume and the Strait of Georgia. Zooplankton found in the stomach contents of both adult and juvenile herring suggested that the herring were filter‐feeding on the zooplankton in the estuarine plume. Juvenile salmonids fed primarily on small unidentifiable juvenile fish. The existence of increased densities of prey items in the estuarine plume is proposed to be the primary mechanism resulting in increased residence time in this region by outmigrating juvenile salmonids. Utilization of aggregated zooplankton could lead to increased salmonid growth rates and therefore to enhanced survival of individuals utilizing the Fraser River plume environment.
The influence of ocean currents on latitude of landfall and migration speed of sockeye salmon returning to the Fraser River
Authors: THOMSON K. A. , INGRAHAM W. J. , HEALEY M. C. , LEBLOND P. H. , GROOT C. , HEALEY C. G.
Published: October 2007

We hypothesize that the interannual variability of the Northeast Pacific Ocean circulation affects the latitude of landfall and migration speed of adult sockeye salmon (Oncorhynchus nerka) returning to the Fraser River. The Ocean Surface Current Simulations (OSCURS) model was used to simulate the return migration paths of compass‐orientated sockeye for two years: 1982, which had a weak Alaska Gyre circulation and low Northern Diversion Rate (defined as the percentage of sockeye returning around the north end of Vancouver Island instead of the south end); and 1983, with a strong circulation and high northern diversion rate. The majority of model sockeye made landfall further north in 1983 than in 1982. The difference in landfall between 1983 and 1982 depended on the migration start position, swim speed, direction of orientation, and migration start date. The currents assisted the shoreward migration of sockeye starting from south of 55o N and impeded the migration of sockeye starting from further north. The simulation results were consistent with our hypothesis and suggest that the effects of the Northeast Pacific currents must be included in sockeye migration models. We propose a conceptual model for the prediction of the Northern Diversion Rate that includes Blackbourn's (1987) temperature‐displacement model, enhanced to include the effects of currents during the ocean phase of migration, and the use of two predictive formulas for the coastal phase of migration: the formula of Xie and Hsieh (1989) for sockeye approaching Vancouver Island directly from the ocean, and a yet‐to‐be‐developed formula for sockeye approaching from within the Coastal Downwelling Domain directly to the north of Vancouver Island.
Recent changes in the trophic structure of the Black Sea
Authors: ZAITSEV YU. P.
Published: October 2007

During the past few decades, the Black Sea has been subjected to various human impacts that have led to changes in the ecology of this inland sea. River runoff has introduced high levels of certain heavy metals and other toxic substances as well as detergents. Ship traffic has led to the introduction of new species, and fishing pressures have also altered the ecology of the area.

This paper reviews major ecological changes over the past 40 years. An increase in nutrients has caused eutrophication, with outbursts of phytoplankton blooms and changes in the species composition of these algae. Small‐sized zooplankton species and gelatinous zooplankton have become more common, while many of the herbivorous copepods have decreased in abundance or have disappeared. The introduction of the predatory ctenophore Mnemiopsis leidyi in the 1980s has had significant impact on the plankton community and has led to a sharp decline in anchovy stocks. Decreased water transparency has led to a loss of macrophytic algae, except in shallow waters, and to a subsequent decline in the zoobenthos associated with this flora. Eutrophication has also led to decreased oxygen concentrations in the near‐bottom water due to large amounts of decomposing phytoplankton, and regions of hypoxia and anoxia now appear on the shelf, with consequent reduction in benthic populations of invertebrates and demersal fish. The numbers of fish species harvested commercially have fallen from 26 to 5, but the total catch has increased, owing to increases in abundance of small fish (e.g., sprat) and horse mackerel, and to increased fishing effort.
Sampling error resulting from depth‐dependent plankton distributions and current differentials in a two‐layered system
Authors: ANDERSON JOHN T. , WEBSTER IAN T.
Published: October 2007

We evaluate a source of error observed in standard ichthyoplankton bongo tows in which volumes of water filtered did not result in increased catches of red‐fish. Our analyses demonstrate that, under conditions where redfish larvae are distributed in surface waters in a two‐layered system, current differentials between surface and subsurface layers resulted in biased, standardized estimates of larval abundances as a result of filtering varying amounts of subsurface waters. Analysis of standard survey results on Flemish Cap demonstrated that this source of bias was limited to the May‐June period, after waters became stratified and before redfish passed from the larvae to pelagic juvenile stage. Correcting for this source of sampling bias wIII result in more accurate absolute estimates of ichthyoplankton abundance, and we estimate that variation (CV) for replicate samples may be reduced by 10%.
Are tidal fronts good recruitment areas for herbivorous copepods?
Authors: UYE SHIN‐ICHI , YAMAOKA TORU , FUJISAWA TOSHIRO
Published: October 2007

Horizontal distributions of phytoplankton biomass and numerical abundance of copepod nauplii were investigated across a tidal front in the northern part of Bungo Channel, the Inland Sea of Japan, in May and June 1988. The frontal area was characterized by abrupt changes in subsurface (3 m deep) temperature and salinity, and by an increased standing stock of phytoplankton. The density of copepod nauplii was lower in the frontal area than in adjacent stratified and mixed areas. The population egg production rate of a predominant copepod species (Paracakmus sp.) was higher due to elevated fecundity on an individual basis in response to increased chlorophyll concentrations, in the frontal zone. However, the frontal population was subjected to higher mortality, probably due to predation by carnivores that were mainly accumulated passively within the area. From these facts, we conclude that tidal fronts are not always good areas for recruitment of herbivorous copepods, although fronts give rise to high standing stocks of phytoplankton.
Remote sensing and geographical information systems: Their past, present and future use in global marine fisheries
Authors: SIMPSON JAMES J.
Published: October 2007

Historically, the fishing community (e.g., fishermen, resource managers) has used remotely sensed products either in the form of direct Automatic Picture Transmission (APT) reception on a ship or FAX charts transmitted from land‐based stations. Both these products have severe limitations within the context of near real‐time support/management of an operational fishery. Moreover, relatively little use of geographical information systems (GIS) technologies has been made by either the fishing industry, fishery resource managers, or by the general oceanographic community. This latter omission is unfortunate because GIS has the potential to overcome two long‐standing problems associated with satellite‐directed fisheries: 1) the absence of information due to clouds; and 2) the general lack of support for nonpelagic fisheries. This report gives the background, motivation, and essential design elements for use of a combined remote sensing/geographical information system (RS/GIS) in an operational fishery and illustrates how a combined RS/GIS approach can be used to mitigate some of the traditional limitations in satellite‐directed fisheries. Finally, an attempt is made to provide some possible directions this new technology may take during the 1990s.
The effect of environment on puerulus settlement of the western rock lobster (PanuUrus cygnus) in Western Australia
Authors: CAPUTI NICOLAVITO , BROWN RHYS S.
Published: October 2007

The level of puerulus settlement has proven to be a reliable predictor of the recruitment to the western rock lobster (Panulirus cygnus) fishery three and four years later. It is generally accepted that the early larval stages are moved offshore by wind‐driven surface currents. Previous studies have shown that coastal sea level, used as an indicator of the strength of the Leeuwin Current flowing down the west coast of Australia, was positively related to the level of puerulus settling on the inshore reefs after a 9‐ to 11‐month larval life. In this paper a significant relationship is also demonstrated between winter/spring storms, which are usually associated with onshore westerly winds, and the level of puerulus settlement (multiple correlation of 0.83, R1= 0.68, n = 22). Rainfall from coastal localities was used as an index of the storms. The residuals from this relationship showed a significant positive autocorrelation. The autocorrelation was incorporated into the relationship by using time series analysis with a transfer function model and a first‐order autocorrelation (R2= 0.76).

The possible relationship between storms and the Leeuwin Current and their effect on the puerulus settlement are considered, and the potential for the environmental variables to bias or obscure the spawning stock recruitment relationship is discussed.
Influences of mean advection and simple behavior on the distribution of cod and haddock early life stages on Georges Bank
Authors: WERNER FRANCISCO E. , PAGE FRED H. , LYNCH DANIEL R. , LODER JOHN W. , LOUGH R. GREGORY , PERRY R. IAN , GREENBERG DAVID A. , SINCLAIR MICHAEL M.
Published: October 2007

Results of a modeling study designed to explore the influences of physical advection and certain biological mechanisms on the distribution of cod (Gadus morhua) and haddock (Melarwgrammus aeglefinus) early life stages on Georges Bank are described. Using a late‐winter/early‐spring 3‐D circulation field driven by the M2 tidal current, mean wind stress and Scotian Shelf inflow, we examine the distribution of cod and haddock larvae spawned on the Northeast Peak of the Bank. The sensitivity to a March‐April baroclinic field is also explored. Results indicate that larvae remaining in the surface Ekman layer are generally advected off‐bank. However, downwelling associated with Ekman layer convergence near the shelf break provides a mechanism for larvae to exit from the off‐bank surface drift. Larvae below the surface layer are transported south‐westward along the southern flank of Georges Bank and are retained on the Bank if their position immediately upstream of the Great South Channel is shoalward of (roughly) the 70 m isobath. Within the Great South Channel region and between the 50 and 70 m isobaths, retention can depend on the phase of the tide. Spawning shoalward of the 50 m isobath on the Northeast Peak greatly increases the chances of retention. These results apply to passive larvae and to those with specified vertical distributions and migration based on observations. Directional on‐bank swimming at rates of 0.5 to 1 body length per second would substantially enhance shoalward displacement, resulting in larval distributions during the first 2 months that are consistent with field observations.
Does water temperature determine year class strength in New Zealand snapper (Pagrus auratus, Sparidae)?
Authors: FRANCIS MALCOLM P.
Published: October 2007

The abundance of 1+ snapper(Pagrus auratus)was estimated by trawl surveys and was found to vary 17‐fold over 7 years. There was a strong positive correlation between year class strength and autumn (April‐June) sea surface temperature during the 0+ year, with the latter explaining 94% of the variability in year class strength. The underlying mechanism is unknown, but three hypotheses relating snapper growth and survival to temperature are discussed. The strengths of the 1991 and 1992 year classes are predicted to be below average and extremely weak, respectively.
A study of spring‐and autumn‐spawned herring (Clupea harengus L.) larvae in the Norwegian Coastal Current during spring 1990
Authors: FOSSUM P. , MOKSNESS E.
Published: October 2007

An intensive sampling program for yolk‐sac herring larvae and microzooplankton was carried out in the main spawning area of Norwegian spring‐spawning herring during March to April 1990 (between 62o and 63o30'N) to estimate their hatching period and the abundance of copepod eggs and nauplii. Additional investigations were carried out in the Skagerrak area during January‐March and on the Norwegian Shelf in May to study the otolith microstructure of the herring larvae. In May both autumn‐ and spring‐spawned herring larvae were found in the samples from the Norwegian Shelf. They were easily distinguished by differences in otolith microstructure. The pattern in increment widths in the otoliths of the autumn‐spawned larvae indicated that these larvae had not been transported through the Skagerrak area, but more likely were carried directly from the northern North Sea across the Norwegian Trench and into the Norwegian Coastal Current system. The calculated hatching of the spring‐spawned larvae sampled in May occurred significantly later than the observed hatching over the spawning grounds. The results suggest a mismatch between the abundance of first‐feeding herring larvae and their prey organisms, resulting in a higher survival of those herring larvae hatching during the latest part of the spawning period. This coincides with a general increase towards the middle of April in the abundance of prey organisms, from 1 to 4 1_1. There were no differences in otolith microstructure among spring‐spawned herring larvae sampled on the shelf in May, indicating that these larvae originated from the same cohort and were well mixed throughout the whole shelf area.
Distribution and abundance of two species of codlet (Teleostei, Bregmacerotidae) larvae from the south‐eastern Brazilian Bight
Authors: MATSUURA YASUNOBU , GARCIA ANA CLAUDIA DE SILVA , KATSURAGAWA MARIO , SUZUKI KAZUKO
Published: October 2007

Two species of codlet (Bregmacerotidae) larvae were collected during nine survey cruises conducted in the south‐eastern Brazilian Bight between 23oS and 30oS in 1985‐91. Of 4846 codlet larvae collected during nine cruises, 99.2% were identified as Bregmaceros canton and only 0.8% were B. athanticus. The two species were more abundant during winter in the neritic region (60–135 m depth). Vertical distribution of codlet larvae was studied using the BIOMOC net, and vertical profiles of temperature/salinity and chlorophyll a concentration were recorded by CTD and fluorescent sonde. Only 9.0% of larvae were collected in the upper 30 m and 91.0% were found deeper (> 40 m). The depths of highest density of larvae bore a close relationship to the subsurface chlorophyll maximum layer. Some B. canton larvae were found in the upper 30 m layer at night, but no larva was found during the day. Water temperatures where B. canton larvae occurred ranged from 16 to 23oC, but most larvae were found at 18–20oC and in salinities of 35.5–36.5 psu.
Preparation of hatchery—reared chum fry for life at sea: osmoregulation dynamics
Authors: ZAPOROZHEC O. M. , ZAPOROZHEC G.V.
Published: October 2007

The development of saltwater tolerance was studied in chum fry reared in the Malkinsky hatchery (central Kamchatka, 200 km from the Sea of Okhotsk). Hypo‐osmoregulatory ability of fry was assessed by dynamics of plasma sodium concentration, 24 and 48 h after their transfer from fresh water to seawater (30%o), and by fry survival in seawater of 40%o salinity. Complete osmoregulation function in young chum was developed in seawater only in late June, despite their earlier development of silver body color and fairly high migration activity. No correlation was found between the weight of fish and their osmoregulatory abilities. The reasons for late smoltification of hatchery‐reared chum have not yet been clearly defined. One explanation might be the combined effect of low nocturnal temperatures and considerable daily fluctuations in temperature (more than 8oC) during the period of egg incubation (in fall), as well as during smoltification of chum juveniles (spring‐early summer). Data on the osmoregulatory ability of chum smolts could be useful in forecasting their survival in the early marine period of life.
Occurrence of an exceptional catch of pelagic juvenile lingcod (Ophiodon elongatus) off Point Reyes, California
Authors: ADAMS PETER B. , RALSTON STEPHEN , LAIDIG THOMAS E.
Published: October 2007

An exceptionally large catch of pelagic juvenile lingcod (Ophiodon elongatus) was made just offshore of Point Reyes, California in 1990. Results of 678 midwater trawls from annual surveys from 1983 to 1990 show that pelagic juvenile lingcod have a strong nearshore distribution and were most abundant in the Gulf of the Farallones, with a mean abundance of 5.0 per trawl. Otoliths from fish taken in the large catch were used to estimate parameters of a log‐transformed Gompertz growth model, which was then used to calculate hatch dates. Hatching peaked around 24 March and ranged from 10 March to 19 April, implying a January‐February spawning season for lingcod off central California. The large catch was associated with an anticyc‐lonic eddy which would lead to water being trapped near the coast; convergence of fish associated with the eddy may have been due to either physical or biological effects.
Sperm whales associated with Gulf Stream features off the north‐eastern USA shelf
Authors: WARING GORDON T. , FAIRFIELD CAROL P. , RUHSAM CYNTHIA M. , SANO MARGARET
Published: October 2007

Marine mammal surveys were conducted during sum Mer 1990 and 1991 in shelf‐edge and off‐shelf waters between Cape Hatteras and Georges Bank. Sperm whales were the most frequently sighted large whale in both years, constituting 27.9% and 12.7% of total sightings in 1990 and 1991, respectively. Sighting rates of sperm whales that were within a 9.3 km buffer (5 n.m.) of the Gulf Stream north wall were not significantly different (x2= 2.86, P > 0.05) from those within the Gulf Stream during 1990. In 1991, however, significantly more (x2= 51.0, P < 0.05) sightings were associated with shelf‐edge areas where warm core rings were located.
Causes of spatio‐temporal variation in the patchiness of larval fish distributions: differential mortality or behaviour?
Authors: FRANK KENNETH T. , CARSCADDEN JAMES E. , LEGGETT WILLIAM C.
Published: October 2007

We studied age‐ and size‐related patterns in the patchiness of distributions of larval capelin (4–21 mm TL) on the Newfoundland Grand Bank. The distribution of yolk‐sac larvae was highly contagious, and was consistent with the distribution of spawning capelin. Lloyd's patchiness index declined fivefold from the yolk‐sac (4–6 mm) to the small post‐yolk‐sac (9–11 mm) stage. The patchiness index then increased steadily and by 2.5‐fold through the medium (14–16 mm) and large (19–21 mm) post‐yolk‐sac stages. This increase in patchiness was accompanied by a steady increase in the strength of the correlation between the abundance of larvae and of the edible zooplankton, and between the centre of mass of the larval and zooplankton vertical distributions through these length classes. In an attempt to distinguish between the alternative hypotheses of differential mortality or behavioural aggregation as the cause of the changes in larval capelin patchiness observed, we compared these changes with changes in the patterns of vertical migration, patchiness, and correlation with food abundances in a co‐occurring, non‐schooling zooplanktivore, Sagitta ekgans. Sagitta vertical migration and correlations between predatodprey abundance were similar to those observed in capelin. However, patchiness indices calculated for Sagitta were similar to the lowest values observed for capelin larvae. We conclude that the initial decline in patchiness observed in small larvae was due primarily to advection and diffusion away from the spawning site. The subsequent increase in larval patchiness, which did not occur in the non‐schooling Sagitta, was attributed to active behaviours of the larvae in response to the vertical and horizontal distributions of their prey. The implications of these findings for the interpretation of larval early life history are discussed.
Effects of a changing windfield on cod stocks of the North Atlantic
Authors: DICKSON R. R. , BRANDER K. M.
Published: October 2007

This paper reviews the impacts of climatic change on six North Atlantic cod stocks during the present century – at Iceland, Greenland, Labrador, Faroes, the Barents Sea and the Baltic. Though the relevant changes in each region can all be set in the context of the same slow shifts in the large–scale Atlantic windfield, the mechanism and scale of the response is varied, operating through changes in the interstock exchange of larvae by ocean currents, direct effects of windiness on stratification, direct and indirect effects on environmental temperature and, in the special case of the Baltic, via the effects of westerly wind events on the inflow/ stagnation cycle of the Baltic Deeps. In certain places and times, these climatic influences have constituted the dominant control on the success of a stock.
Tintinnid ciliates as indicator species of different water masses in the western North Pacific Polar Front
Authors: KATO SATOSHI , TANIGUCHI AKIRA
Published: October 2007

Distributions of 10 dominant tintinnid taxa and groups in the western North Pacific Polar Frontal Zone or the Sanriku Waters were analysed on T‐S‐Plankton diagrams to estimate their values as indicator species of water masses. Because it is difficult to identify the origin of water by conventional T‐S analysis in areas such as this where three currents such as the warm Kuroshio, the Tsugaru Warm Current and the cold Oyashio are converging, reliable indicator species can be of great help in identification of the water masses. Normal cells of tintinnids with a soft body together with empty loricae were plotted separately on T‐S diagrams. Because empty loricae of most species were distributed over wider ranges of temperature and salinity, or empty loricae might remain suspended in a particular water mass for a fairly long time, tintinnid species including empty loricae were recognized as reliable indicator species. Because contrastingly different tintinnid faunas were derived from the Kuroshio and the Oyashio, water masses originating from both currents were clearly traced by the indicator species as would be expected. Furthermore, by employing the appropriate indicator species defined on the T‐S‐Plankton diagram, it was also possible to identify the most similar pair of water masses, i.e. the Tsugaru Warm Current and mixture of the Kuroshio and the Oyashio, which cannot be identified by conventional T‐S analysis.
What controls the distribution of the coccolithophore, Emiliania huxleyi, in the North Sea?
Authors: HOLLIGAN PATRICK M. , GROOM STEPHEN B. , HARBOUR DEREK S.
Published: October 2007

Satellite data show that the distribution of Emiliania huxleyi in the North Sea is characterized by considerable spatial patchiness as well as large annual differences in abundance within any particular area. The causes of this variability are largely unknown, and therefore unpredictable, reflecting a paucity of information on the ecophysiology of the species.
Photosynthesis characteristics of the phytoplankton in the Celtic Sea during late spring
Authors: PLATT TREVOR , SATHYENDRANATH SHUBHA , JOINT IAN , FASHAM MICHAEL J. R.
Published: October 2007

During a three‐week cruise to the Celtic Sea in late spring, the photosynthesis characteristics of the phytoplankton were followed at a single, nominal station. Observations were made on size–fractionated samples as well as on whole samples. The properties of the small (<1 μm fraction) and large (>1 μm fraction) differed with respect to the parameters aB (initial slope) and PBm (assimilation number) of the photosynthesis‐light curve and to the dependence of these parameters on environmental covariables. These differences account for some of the difficulty in explaining fluctuations in properties of unfractionated samples. Optical analysis leads to a method for estimation of photic depth, with high confidence, for days on which underwater irradiance measurements were not available. The shape of the vertical profile of photosynthetic pigments changed in a systematic way throughout the cruise. The implications for calculation of water‐column primary production are discussed. In the Celtic Sea, during late spring, use of a non‐spectral model assuming uniform water column for computation of primary production will lead to differences of up to 20% compared with the results of a fully spectral model that admits vertical stratification.
Diatom demography in winter – simulated by the Lagrangian Ensemble method
Authors: WOODS JOHN , BARKMANN WOLFGANG
Published: October 2007

According to Sverdrup's (1953) model of the spring bloom, phytoplankton biomass decreases in winter when the mixed layer depth exceeds the critical depth. We have used a one‐dimensional mathematical model integrated by the Lagrangian Ensemble method to simulate a population of diatoms during the winter between two growing seasons off the Azores. The model allows us to diagnose the demographic changes in the simulated diatom population from a variety of perspectives. The total population falls to a minimum of 70 million diatoms m‐2 at the end of February. The vertical distribution of the population dynamics is first analysed in terms of daily Eulerian averages over 1 m depth intervals. Growth starts in February when the diurnal thermocline becomes shallower than 50 m, but while the mixed layer is still 200 m deep. The natural mortality has a minimum in winter because it is reduced (in the model) with temperature and population density. Eulerian analysis suggests that in winter, diatoms have a life expectancy of more than 3 months, so a significant number will survive the months of December, January and February when there is very little growth. Losses to grazing are negligible in winter. Lagrangian analysis shows how an individual diatom responds to its changing ambient environment caused by variation in depth (due to turbulent mixing) and the diurnal and seasonal changes in the photosynthetically active radiance. The different trajectories followed by the thousands of plankton particles simulated by the model produce diversity in growth rate ranging over several orders of magnitude, so care has to be taken in statistical analysis.

The paper ends with a re‐assessment of the value of the critical depth and compensation depth as predictors for onset of the spring bloom. The compensation depth was computed by Eulerian averaging over 1 m depth inter‐vals each day. For 1 month after the vernal equinox the compensation depth follows the ascent of the mixed layer as it rises from a depth of 100 m to 40 m. Lagrangian analysis reveals that this is due to the photo‐adaptation better matching the ambient irradiance experienced by diatoms in the mixed layer compared with those at the same depth in the seasonal thermo‐cline. By mid‐April the spring bloom has already ad‐vanced so far that self shading influences the compensation depth, which then rises into the mixed layer. We conclude that Sverdrup's criterion is not useful for predicting changes in the diatom population simulated by our model.
Generation of a phytoplankton maximum in a grazing‐extended logistic model
Authors: ROTHSCHILD B. J. , PATRICK E. V.
Published: October 2007

The cause of variability in the vertical distribution of phytoplankton has been a subject of considerable interest, particularly in the development of various ‘global change’ scenarios. The classic two‐layer explanation for the phytoplankton maximum form of vertical variability derives from physical considerations: a switching in the sign of production owing to a stepwise reduction in irradiance with increasing depth. This paper shows how quasi‐periodicity in the vertical distribution of phytoplankton and the special case of a ‘maximum’ can arise from zooplankton grazing. To show this we employ the dynamics of the grazing‐extended logistic model.
Alternative methods for the estimation of immigration to the Icelandic cod stock
Authors: SHEPHERD J. G. , POPE J. G.
Published: October 2007

Periodic migrations offish from Greenland are known to have augmented the Icelandic cod stock on many occasions during the last 50 y. These immigrations have been observed both in the catch‐at‐age compositions, and through tagging experiments. Two new and independent methods for estimating the extent of immigration have been developed, based on (a) analysis of weight‐at‐age data; (b) comparison of virtual population analyses for a restricted range of ages and the full range of ages in the available data. Both methods confirm recent strong immigration of the 1973 and 1984 year classes, but also suggest that significant immigration was a fairly regular event throughout the 1970s, and also occurred in 1985. It appears that immigration is quite strongly correlated with the year‐class strength at Greenland, and that between 20% and 60% of the Greenland fish eventually return to rejoin the Icelandic stock.
Stock'related changes in biological parameters of the Icelandic summer'Spawning herring
Authors: JAKOBSSON J. , GUØMUNDSDÓTTIR A. , STEFÁNSSON G.
Published: October 2007

During the period 1960–1992 the stock size of Icelandic summer‐spawning herring varied from about 300 000 t in the early 1960s to just above 10000 t in the early 1970s. Since then the stock size has increased to about 400 000 t in 1992. Examination of the mean weight at age and length at age as well as condition factor of the herring revealed that these parameters have fluctuated slightly, but without a trend, over a wide range of stock abundance, but increased when the stock was at extremely low level of stock abundance. Examination of the stock‐recruitment relationship revealed that there were clear positive signs of increased recruitment at high stock levels. Similarly there were signs that the recruitment level was greatly affected by the cold period 1964–1971. Comparison of the VPA stock estimates and acoustic stock estimates indicated that the natural mortality is in the range of 0.1‐0.15.
Statistical analyses of intra‐ and interspecific density effects on recruitment of chub mackerel and sardine in Japan
Authors: KISHIDA TATSU , MATSUDA HIROYUKI
Published: October 2007

Density effects of chub mackerel, Scomber japonicus, and sardines, Sardinops melanosticta, on the recruitment strength of each species were examined by multiple regression analyses of year‐class strengths and stock abundances or catch statistics compiled over nearly 30 y. The two species have become successively dominant in the pelagic fish assemblage in Japanese waters during the last few decades. Results suggested that both sardines and chub mackerel played suppressive roles on sardine recruitment (P < 0.01), and it seemed that such inhibition was brought about mainly by the dominant species of the two. A direct density effect on chub mackerel recruitment by either species was not clear, but analyses indicated that both species produced delayed density effects on chub mackerel year‐class strengths (P < 0.01). Year‐class strengths of chub mackerel were highly dependent upon annual egg production, which in turn was apparently affected by the stock abundance of the two species over the previous 2 or 3 y. Delayed intraspecific density effects on egg production seemed to operate strongly until the late 1970s. After the sardine stock increased significantly (i.e. 1980s), however, the per capita annual egg production of chub mackerel did not recover in spite of a decrease in the stock size, possibly owing to the delayed density effects of the sardine stock.
The ecological impact of the Great Salinity Anomaly in the northern North‐west Atlantic
Authors: MERTZ G. , MYERS R. A.
Published: October 2007

In a number of recent papers Cushing has advocated that the Great Salinity Anomaly (GSA), which entered the northern North Atlantic in the early 1970s, adversely affected the recruitment of a number of deep‐water fish stocks of this ocean. Cushing envisages that a temperature anomaly accompanying the GSA slowed and/or delayed growth in the spring phytoplankton bloom which sequentially affected zooplankton growth and fish recruitment. We test a number of hypotheses relating to Cushing's picture, focusing on the waters of the West Greenland, Labrador and Newfoundland Shelves. We find that, south of Greenland waters, there were no significant temperature anomalies corresponding to the GSA. In addition we show that stability of the shelf waters increased during the GSA, casting doubt on the contention that the phytoplankton bloom was delayed by retardation of the spring stabilization of the water column due to the influence of cold water. Our analysis indicates that the food chain coupling of environment to recruitment (climate to phytoplankton to zooplankton to fish) is not strong in the study region.
Physical and biological consequences of a climate event in the central North Pacific
Authors: POLOVINA JEFFREY J. , MITCHUM GARY T. , GRAHAM NICK E. , CRAIG MITCHELL P. , DEMARTINI EDWARD E. , FLINT ELIZABETH N.
Published: October 2007

Climatic changes over the North Pacific which began in the mid 1970s, peaked in the early 1980s, and ended by the late 1980s, appear to have altered productivity at various trophic levels in the marine ecosystem in the central North Pacific. The climatic change resulted in increased mixed layer depth and the frequency of deep mixing events, particularly during January‐March. A number of biological time series for species ranging from primary to apex levels in the North‐western Hawaiian Islands, show corresponding declines in productivity of 30–50% from the early 1980s to the present. We hypothesize that during the early 1980s, increased mixing due to the climate event resulted in greater nutrient input into the euphotic zone and ultimately increased ecosystem productivity. Productivity over a range of trophic levels declined when the climate event ended.
Interannual variability in coastal Washington Dungeness crab (Cancer magister) populations: larval advection and the coastal landing strip
Authors: McCONNAUGHEY ROBERT A. , ARMSTRONG DAVID A. , HICKEY BARBARA M. , GUNDERSON DONALD R.
Published: October 2007

Substantial and unexplained variations in abundance characterize US west coast populations of Dungeness crab,Cancer magister.It is likely that this variability reflects oceanic advection of larvae given the dynamics of the California Current system, the protracted (4–5 months) pelagic larval phase and the restrictive nature of juvenile habitat requirements. We compare 40 years of Ekman transport vectors during January‐May (1947– 1986) with time‐lagged and stratified commercial landings for coastal Washington (1951–1990). Persistent landward and net northward flow characterized the circulation of near‐surface waters during the larval periods studied. A mechanism for progressive seaward transport of larvae through ontogeny, as proposed by others, was not apparent. Overall, above‐ (below‐) average year classes were associated with relatively weak (strong) northward transport and, to a lesser degree, strong (weak) landward transport. Based on these analyses and in consideration of the prevailing coastal circulation, we propose that the relative magnitude of C.magisterjuvenile recruitment and, hence, incoming year class strength, reflects: (1) the proportion of larvae retained within a relatively narrow (≤ 15 km) and heterogeneous ‘coastal landing strip’, (2) the availability of suitable substrate within the coastal landing strip at time of settlement and (3) the magnitude of downstream advective losses (export) of larvae from the California‐Oregon‐Washington coastal system. Based on a consideration of the physics of the California Current system and the larval biology of the species, significant linkage of Dungeness crab populations along the west coast of North America is likely.
Modelling the transport of particles in the North Sea with reference to sandeel larvae
Authors: BERNTSEN JARLE , SKAGEN DANKERT W. , SVENDSEN EINAR
Published: October 2007

The transport of particles representing sandeel larvae in the North Sea is simulated with a three‐dimensional circulation model for the years 1976 to 1990. A great year‐to‐year variability in drift patterns is demonstrated. The results may explain some of the observed differences in recruitment between the main sandeel areas in the North Sea. In the northern sandeel area it seems that strong year classes are unlikely if the retention due to unfavourable currents is poor, and that a high retention in the summer may favour a good year class. In the southern sandeel area no clear coupling between year class strength and larval drift is found, possibly because the retention always seems large enough for a potentially good year class. For more quantitative use of such models in relation to sandeel recruitment, more biological knowledge is obviously needed on larval vertical distribution and timing of sandeel hatching and settling.
Transport of larvae and juvenile fish into central and northern Norwegian waters
Authors: BJØRKE HERMAN , SAETRE ROALD
Published: October 2007

The distribution of juvenile fish in Norwegian waters in spring and summer provides evidence that some of these are transported into Norwegian coastal waters from spawning grounds outside the ecosystems which comprise the central and northern Norwegian coast, the Barents Sea and the Spitsbergen area. The relevant species are capelin (Mallotus villosus Müller), haddock (Melanogrammus aeglefinus L.), herring (Clupea hareri' gus L.) and saithe (Pollachius virens L.). A substantial part of the saithe and haddock stock along the central and northern Norwegian coast is considered to be recruited from spawning grounds in the northern North Sea. A contribution of these species from the spawning grounds around the Faeroe Islands and west of Scotland may also occur in some years. Herring from the northern North Sea are found scattered off the Norwegian coast north to 70oN. It seems likely that pelagic species such as capelin and herring are transported by the prevailing currents from Iceland.
Distribution and reproduction of the planktonic copepod, Calanus pacificus, off southern California during winter‐spring of 1992, relative to 1989–91
Authors: MULLIN MICHAEL M.
Published: October 2007

Abundance and production of eggs by female Calanus pacificus off southern California were assessed in February and April, 1992, together with biomass of chlorophyll and abundance of larval anchovy. Because 1992 was an anomalous year as a result of a Californian El Nino, the patterns were compared with analogous data for 1989‐91. Female Calanus were much less abundant in both February and April of 1992 than in the earlier years, and the anomalies were negatively related to temperature anomalies, but the biomass of chlorophyll and per capita egg production were anomalously low only in February. The horizontal distribution of female Caianus was similar to that of chlorophyll in winter, but was more efficient (in the sense of permitting more complete utilization of the available chlorophyll) in April, 1992, than in the earlier springs. The abundances of larval anchovy were positively correlated with the reproduction of the Calanus population in 1992 and in the earlier years, but the larvae were poorly distributed with respect to Calanus spawning, in both 1992 and the earlier years, to take best advantage of the resulting nauplii as food.
On the relationship between the Oyashio front and saury fishing grounds in the north‐western Pacific: a forecasting method for fishing ground locations
Authors: YASUDA ICHIRO , WATANABE YOSHIRO
Published: October 2007

The relationships between fishing ground locations of Pacific saury (Cololabis saira) and the two Oyashio fronts, the offshore front between 146oE and 155oE and the coastal Oyashio intrusion, before the saury fishing season, were examined using data from 1971 to 1991. Interannual geographical shifts of both the offshore Oyashio front and saury fishing grounds had a dominant interdecadal fluctuation. In years when the offshore front shifted north (south), the fishing grounds were formed relatively nearshore (offshore). When the offshore front shifted north, the fishing grounds were formed further nearshore in years the coastal Oyashio intrusion extended south. When the offshore front shifted south, on the other hand, the southward extension of the coastal intrusion did not necessarily cause formation of coastal fishing grounds. These results showed that locations of the fishing grounds depend not only on local and instantaneous oceanographic environments around the fishing grounds, but also on oceanographic conditions over an extensive range of the Oyashio area. This might indicate that the ecology of the saury's northward migration, through mixed water regions between the Kuroshio and Oyashio fronts in spring and summer, has a close relation to the shift of the offshore Oyashio front over a time range of months. A practical forecasting method for locations of saury fishing grounds is proposed based on the oceanography before the fishing season.