Does Le Danois Bank (El Cachucho) influence albacore catches in the Cantabrian Sea?

This study explores the relationship between a seamount located in the Cantabrian Sea known as Le Danois Bank (El Cachucho fishing ground), the first offshore Marine Protected Area (MPA) in Spain, and the Spanish albacore (Thunnus alalunga) surface fishery that operates during the summer and autumn months. The geographical distribution of catch per unit effort (CPUEs), expressed by number, showed that August and September were the months with the highest catches in the El Cachucho area, however, annual variability existed. Nominal CPUE series obtained from both logbook data and fishing interviews revealed that higher CPUEs were achieved inside the MPA during some fishing seasons, but there was no consistency in the data, since spatial and temporal variability were shown. The spatial distribution of monthly CPUE data was characterized by means of geostatistical analysis. Albacore schools tended to aggregate in mesoscale patches of similar dimensions but the location of these aggregations was non-stationary both in space and time. This supports the hypothesis that albacore are not randomly spatially distributed, but that they concentrated in certain areas where they find suitable conditions of food availability.     

Effect of the mesoscale hydrographic features on larval fish distribution across the shelf break of East China Sea

Surveys of fish larvae and oceanographic conditions were conducted along transects across the shelf break region in the East China Sea (ECS) in May 2001. The objective of this study was to investigate the distribution and assemblages of fish larvae across the shelf break region and their relationships to mesoscale hydrographic features. There was a warm surface streamer from the Kuroshio which extended toward the shelf region of the ECS; concurrently, we observed the intrusion of the less saline shelf water into the subsurface layer towards the offshore. In all 66 taxa (65 families and 1 order) of larvae were collected by oblique net tows using a bongo net, the larval fish density and number of families sampled were lower in the low-temperature area. Based on cluster analysis and environmental factor, two larval fish assemblages were identified: off-shelf/Kuroshio and shelf break. In shelf break assemblage, Auxis spp. and Diaphus spp. were abundant in the warm surface streamer. In contrast, Maurolicus japonicus, Synagrops spp., Bregmaceros sp. and Champsodon spp. were found in the off-shelf region where the offshore intrusion of less-saline water occurred. This different pattern of the horizontal distribution would reflect vertical distribution of the larvae in the water column. Moreover, copepod nauplii density was higher in the upper layer of the shelf region. Thus, dynamic interactions between the Kuroshio and shelf waters at the frontal boundary are concluded to potentially affect larval fish transport and prey availability.     

Numerical simulation of a mesolow over a Gulf Stream filament

A three-dimensional mesoscale numerical model is used to investigate mesoscale circulation over a Gulf Stream filament. Two numerical experiments are performed with different initial uniform ambient wind speeds (U=0.1 m s^–1, 3.5 m s^–1 and 7 m s^–1) for a typical winter day. It is found that for both low and moderate winds, a closed mesoscale circulation forms over the Gulf Stream filament. When the Gulf Stream filament was removed, the model did not predict a mesoscale circulation. The modeled circulation over the filament is in agreement with the observations, suggesting that the atmospheric circulations over the filaments may be an important mechanism in the U.S. East Coast cyclogenesis.     

Bowhead whales feed on plankton concentrated by estuarine and tidal currents in Academy Bay,Sea of Okhotsk

Academy Bay in the Sea of Okhotsk is an important summertime feeding ground for pelagic-feeding Bowhead whales (Balaena mysticetus) in the western subarctic North Pacific. The present work combines satellite observations with physical (CTD, currents, tides) and biological (zooplankton sampling) measurements. Data obtained aboard the RV Lugovoe in August–September 2003 and July–August 2004 show dense populations of zooplankton (such as copepods Calanus glacialis, Pseudocalanus sp., pteropods Limacina helicina, and chaetognaths Sagitta sp.) that are concentrated by physical mechanisms within this critically important ecosystem. We show that near-bottom, cold water intrusions from the northern Sea of Okhotsk associated with the estuarine circulation advect arctic herbivorous calanoids (Calanus glacialis) and mollusks Limacina helicina into the region.     

DDT,PCB and benzo(a)pyrene levels in white croaker (Genyonemus lineatus) from southern California

In 1978 the California Department of Fish and Game carried out a major, independent sportfishing survey in southern California. The results of that survey indicated that approximately one million angler-trip hours per year were spent fishing and that one in three fish caught was a white croaker (Genyonemus lineatus). There was no attempt by the Department of Fish and Game to determine the disposition of caught fish. We conducted a subsequent survey in 1980 which included 12 popular sportfishing sites in the Los Angeles area. Our results also indicated that one in three fish caught was a white croaker. In addition our survey showed that 82% of the sportfishermen ate the white croaker they caught and the median consumption was 14.8 g day^?1 person^?1. White croaker were then sampled by hook-and-line from 11 of the 12 survey sites plus two control sites and analysed for PCB, DDT and BaP. Median PCB levels ranged from 0.014 to 0.41 mg wet kg^?1; median DDT from 0.059 to 7.5 mg wet kg^?1 and BaP was below detectable limits of 1 ng for all sites.     

Chlorinated hydrocarbons in lower continental slope fish collected near the Farallon Islands,California

During December, 1985, Dover sole (Microstomus pacificus) were collected at water depths of 500 and 1000 m and sablefish (Anoplopoma fimbria) were collected at a water depth of 1000 m in the vicinity of former low-level radioactive and chemical munition disposal sites located near the Farallon Islands, California. Liver tissues were analysed for chlorinated hydrocarbons by gas chromatography with electron capture detection (GC/ECD). Chlorinated hydrocarbons (DDTs and PCBs) were detected in all fish. Concentrations of total DDTs and PCBs in livers of Dover sole and sablefish were as high as, or higher than, those recently reported for the same species collected in heavily contaminated coastal waters of Southern California. The presence of DDTs (up to 9 μg g⁻¹, wet wt) and PCBs (up to 7 μg g⁻¹, wet wt) in fish livers may indicate extensive contamination of the coastal waters or bottom sediments in the vicinity of the Farallon Islands. Even though the definitive sources of the chlorinated hydrocarbons detected in the Dover sole and sablefish are not known, the relative proximity of the former chemical munition disposal sites indicates that these areas may be a potential source of one or both of these contaminants.     

Dynamics of a Prorocentrum minimum bloom along the northern coast of Sinaloa,Mexico

To investigate the relative importance of mesoscale physical events, such as upwellings and physical and chemical variables during an algae bloom of Prorocentrum minimum, 25 sampling sites were established offshore of the Navachiste Lagoon Complex on the east side of the Gulf of California. Samples were analyzed for phytoplankton concentration, water chemistry, and temperature during November 1999, January, March, April, May, and August 2000. Satellite imagery of sea surface temperature (SST) for April 2000 was processed to obtain a synoptic view of the area during the extraordinary bloom of P. minimum in the open waters of the Gulf of California. The bloom was associated with change of oceanographic conditions from moderate winds to calm period, temperature increase and high nitrate (NO₃⁻-N) and ammonia (NH₄⁺-N) content in the offshore waters. Depletion of these nutrients during the bloom suggests that this species uses both types of nitrogen substrates. Cysts in the northernmost sampling stations in January and March indicate that upwelling water, rich in nitrates, also carried a seed stock population of P. minimum. SST patterns in the satellite imagery suggest wind-forcing as the responsible mechanisms triggering the algal bloom offshore of the Navachiste Lagoon Complex.     

Numerical simulations of mesoscale variability in the Straits of Florida

The circulation in the Straits of Florida is dominated by the throughflow of the Florida Current, as modified by tidal flows, responses to atmospheric cold front and extratropical cyclone (easterly wave and tropical cyclone) passages in winter (summer), and intrinsic mesoscale variability due to instabilities of the Florida Current front and jet system. Monthly meanders of the Florida Current, persistent oceanic fronts associated with the Florida Current’s baroclinic jet, and frontal eddies shed weekly by the Florida Current are the primary mesoscale features. A limited area model (Princeton Ocean Model: POM) is implemented to cover the Straits of Florida with a curvilinear grid that resolves the mesoscale structure, especially where the baroclinic flow is locked to steep topography in a 90 degree bend of the Straits. Florida Current cyclonic frontal eddies are spawned spontaneously, grow as they translate downstream, interact with shelf waters, and exhibit the same space-time attributes that characterize their observed counterparts, as evidenced by satellite imagery, shipboard synoptic mapping, coastal HF radar, and moored time series. Here, a deeper understanding is attempted for the frontal eddy kinematics and dynamics by examining, for example, their sensitivity to model parameter values, synoptic versus monthly atmospheric forcing, and other determinants of the flow. The mean flow shears are concentrated along the shelfbreak, where these frontal eddies are trapped, favoring the formation of the eddies by mean flow instabilities. In particular, it is found that the Florida Current frontal eddies exist independent of the wind-forcing considered (i.e., no winds, monthly winds, and synoptic (but not mesoscale) winds); however, they are modulated by the synoptic wind-forcing. Nevertheless, intriguingly, the frontal eddies have the same weekly time scale as the weather cycle.     

The vertical distribution of maraena whitefish (Coregonus maraena) early juveniles in different times of day in a newly created oligotrophic lake

Diel vertical distribution of strictly pelagic juvenile (23–47 mm total length) maraena whitefish Coregonus maraena (Bloch, 1779) was repeatedly investigated in spring primarily using hydroacoustics in the artificial post-mining Most Lake in the Czech Republic. At the same time, an ichthyoplankton trawl was used to identify acoustical targets. During the day, fish performed extensive shoaling behaviour in depths between 2 and approximately 40 m and were not accessible for trawling. By evening, with decreasing light intensity, shoals started to disintegrate and at night fish were relatively homogeneously distributed in the water column from the surface down to a depth of 40 m. Juvenile maraena whitefish could be caught by trawl as the only fish species at night. Shoaling behaviour started again approximately 1.5 h before sunrise. The data showed steep decreases in fish density between the two surveys in spring which indicates significant mortality of early juvenile coregonids as a result of poor availability of zooplankton in a highly oligotrophic post-mining lake.     

A Survey of Precipitation-Induced Atmospheric Cold Pools over Oceans and Their Interactions with the Larger-Scale Environment

Pools of air cooled by partial rain evaporation span up to several hundreds of kilometers in nature and typically last less than 1 day, ultimately losing their identity to the large-scale flow. These fundamentally differ in character from the radiatively-driven dry pools defining convective aggregation. Advancement in remote sensing and in computer capabilities has promoted exploration of how precipitation-induced cold pool processes modify the convective spectrum and life cycle. This contribution surveys current understanding of such cold pools over the tropical and subtropical oceans. In shallow convection with low rain rates, the cold pools moisten, preserving the near-surface equivalent potential temperature or increasing it if the surface moisture fluxes cannot ventilate beyond the new surface layer; both conditions indicate downdraft origin air from within the boundary layer. When rain rates exceed \(\sim\) 2 mm h\(^{-1}\), convective-scale downdrafts can bring down drier air of lower equivalent potential temperature from above the boundary layer. The resulting density currents facilitate the lifting of locally thermodynamically favorable air and can impose an arc-shaped mesoscale cloud organization. This organization allows clouds capable of reaching 4–5 km within otherwise dry environments. These are more commonly observed in the northern hemisphere trade wind regime, where the flow to the intertropical convergence zone is unimpeded by the equator. Their near-surface air properties share much with those shown from cold pools sampled in the equatorial Indian Ocean. Cold pools are most effective at influencing the mesoscale organization when the atmosphere is moist in the lower free troposphere and dry above, suggesting an optimal range of water vapor paths. Outstanding questions on the relationship between cold pools, their accompanying moisture distribution and cloud cover are detailed further. Near-surface water vapor rings are documented in one model inside but near the cold pool edge; these are not consistent with observations, but do improve with smaller horizontal grid spacings.     

Early contamination of European flounder (Platichthys flesus) by PCDD/Fs and dioxin-like PCBs in European waters

Contamination levels and profiles of 7 polychlorinated-p-dioxins, 10 polychlorinated furans (PCDD/Fs) and 12 dioxin-like polychlorinated biphenyls (dl-PCBs) were investigated in juvenile European flounder (Platichthys flesus) captured in different nursery areas in the northeastern Atlantic coast across its geographical distribution range. The toxic equivalent concentrations (WHO-TEQ_fish) were also determined in order to evaluate which P. flesus population was more exposed to dioxin-like toxicity. Juveniles caught in the Sørfjord (Norway) showed the lowest WHO-TEQ_fish concentration (0.052 pg WHO-TEQ_fish g⁻¹ wet weight) whereas the highest value was observed in fish from the Wadden Sea (The Netherlands; 0.291 pg WHO-TEQ_fish g⁻¹ ww), mainly due to the greater contribution of 2,3,7,8-tetrachlorodibenzo-p-dioxin, the most toxic congener. Nonetheless, when comparing the results with existent tissue residue-based toxicity benchmarks, no adverse effects resulting from PCDD/Fs and dl-PCBs are expected to occur in flounder from the studied systems.     

Inorganic carbon dynamics during northern California coastal upwelling

Coastal upwelling events in the California Current System can transport subsurface waters with high levels of carbon dioxide (CO₂) to the sea surface near shore. As these waters age and are advected offshore, CO₂ levels decrease dramatically, falling well below the atmospheric concentration beyond the continental shelf break. In May 2007 we observed an upwelling event off the coast of northern California. During the upwelling event subsurface respiration along the upwelling path added ∼35 μmol kg⁻¹ of dissolved inorganic carbon (DIC) to the water as it transited toward shore causing the waters to become undersaturated with respect to Aragonite. Within the mixed layer, pCO₂ levels were reduced by the biological uptake of DIC (up to 70%), gas exchange (up to 44%), and the addition of total alkalinity through CaCO₃ dissolution in the undersaturated waters (up to 23%). The percentage contribution of each of these processes was dependent on distance from shore. At the time of measurement, a phytoplankton bloom was just beginning to develop over the continental shelf. A box model was used to project the evolution of the water chemistry as the bloom developed. The biological utilization of available nitrate resulted in a DIC decrease of ∼200 μmol kg⁻¹, sea surface pCO₂ near ∼200 ppm, and an aragonite saturation state of ∼3. These results suggest that respiration processes along the upwelling path generally increase the acidification of the waters that are being upwelled, but once the waters reach the surface biological productivity and gas exchange reduce that acidification over time.     

A study case of bioluminescence potential dynamics in the Delaware Bay with observations and modeling

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Chemical and isotopic prediction of aquifer temperatures in the geothermal system at Long Valley, California

Temperatures of aquifers feeding thermal springs and wells in Long Valley, California, estimated using silica and Na-K-Ca geothermometers and warm spring mixing models, range from 160/dg to about 220°C. This information was used to construct a diagram showing enthalpy-chloride relations for the various thermal waters in the Long Valley region. The enthalpy-chloride information suggests that a 282 ± 10°C aquifer with water containing about 375 mg chloride per kilogram of water is present somewhere deep in the system. That deep water would be related to 220°C Casa Diablo water by mixing with cold water, and to Hot Creek water by first boiling with steam loss and then mixing with cold water. Oxygen and deuterium isotopic data are consistent with that interpretation. An aquifer at 282°C with 375 mg/kg chloride implies a convective heat flow in Long Valley of 6.6 × 10⁷ cal/s.     

A model study of spin-down and circulation in a cold water dome

A three-dimensional prognostic hydrodynamic model in cross sectional form is used to examine the influence of bottom friction, mixing and topography upon the spin-down and steady-state circulation in a cold water bottom-dome. Parameters characteristic of the Irish Sea or Yellow Sea cold water domes are used. In all calculations, motion is induced by specifying an initial temperature distribution characteristic of the dome, and an associated along frontal flow. The spin-down of the dome is found to be influenced by the coefficient of bottom friction, with a typical time scale of order 10 days, and in general to be independent of the chosen initial vertical profile of along frontal flow. However, in the case in which the along frontal flow is such that the near bed velocity is zero, then bottom stress is also zero, and there is no appreciable spin-down. Calculations showed that the formulation of viscosity and diffusivity had a greater effect upon the steady-state circulation than topography, suggesting that background mixing of tidal origin is important. The lack of topographic influence was due mainly to the formulation of the initial conditions which were taken to be independent of topography. The steady-state circulation was characterized by a cyclonic flow in the surface region, with an anti-cyclonic current near the bed, where frictional effects produced a bottom Ekman layer and an across frontal flow. This gave rise to vertical circulation cells in the frontal region of the dome with prevailing downwelling motion inside the dome. A detailed analysis of the dynamic balance of the various terms in the hydrodynamic equations yielded insight into the processes controlling the steady-state circulation in cold water domes. Responsible Editor: Phil Dyke     

Food-web manipulation of drinking water reservoirs with salmonids: vertical distribution of prey and predator

In a novel biomanipulation experiment salmonids were used as a tool to improve water quality. The manipulation was initiated in spring 2000 as a response to non-point sources of phosphorus in a drinking water reservoir in Saxony, Germany. Salmonids (brown trout, Salmo trutta forma lacustris) were chosen as predators as the reservoir has a large hypolimnic water body and surface temperatures rarely exceed 20 °C. The vertical distributions of prey fish and brown trout were analysed with a fleet of vertical gill nets set in the pelagic zone of the reservoir. Consumption of brown trout was estimated by means of a bioenergetic model and the diet analyses of the trout. While the dominant planktivore (roach, Rutilus rutilus) was caught almost exclusively in the epilimnion during the stratification period trout were caught mainly below a depth of 10 m. Diet analysis revealed that the trout performed vertical migrations to consume food in the epilimnic layer, as an important food component were adult terrestrial and aquatic insects. The amount of fish in the food increased strongly with the size of the brown trout. The consumption estimate suggested that the trout had consumed 2-3% of the total roach stock during the study period (May-November 2000) of the first year of biomanipulation. We conclude that in general salmonids are suitable for food-web manipulation in deep reservoirs, but the stocked fish should be as large as possible (> 300 mm) and the proportion of large trout (> 500 mm) should be as high as possible.     

Migration de la truite lacustre (Salmo trutta lacustris L.) dans le Léman et ses affluents

A total of 2588 adult migratory brown trout (Salmo trutta lacustris) have been tagged from 1964 to 1974 on their spawning sites, in tributaries of the western part of Lake Geneva (Switzerland). Most of the fish (96.2%) recaptured during spawning seasons in the following years have been found in the same river where they had previously been caught. Most tagged fish recaptured by fishermen were found in the western part of the Lake, near their home rivers. This tendency is very strong in autumn and winter. It still remains highly significant in spring and summer.

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Dédié à Wolfgang Geiger     

Effects of surface drag on low-level frontogenesis within baroclinic waves

Using a three-dimensional nonhydrostatic mesoscale numerical model (MM5), the evolution and structures of baroclinic waves with and without surface drag in case of dry and moist atmosphere are simulated, with special emphases on the effects of surface drag on the low-level frontal structure and frontogenesis. There are two different effects of surface drag on the low-level frontogenesis in the dry case. On one hand, the surface drag weakens the low-level frontogenesis and less inclined to develop the baroclinic wave due to the dissipation. But on the other hand, the surface drag induces a strong ageostrophic flow, which prolongs the low-level frontogenesis and finally leads to the enhancement of cold front. Compared with the no surface drag case, the surface drag increases the frontal slope espe- cially in the boundary layer, where the front is almost vertical to the surface, and then enhances the prefrontal vertical motion. All these conclusions expanded the analytical theory of Tan and Wu (1990). In the moist atmosphere, the influence of surface drag on frontal rainbands is also obvious. The surface drag weakens the convection, and reduces the energy dissipation near the surface when the initial relative humidity is relatively weak. At this time, the confluence induced post-frontal updrafts moves across the cold front and reinforces the prefrontal convection, which is beneficial to the maintenance of the rainband in cold sector. Given the enhancement of relative humidity, the moist convection domi- nates the low-level frontogenesis while the retardation of surface drag on energy dissipation is not obvious, therefore the effects of surface drag on the low-level frontogenesis and precipitation are re- duced.     

Inter- and intra-annual patterns of Ulva prolifera green tides in the Yellow Sea during 2007-2009, their origin and relationship to the expansion of coastal seaweed aquaculture in China

The large green-tide events that occurred in the Yellow Sea in 2008 (3489 km²) and 2009 (4994 km²) are shown to be novel events preceded only once by a much smaller event in 2007 (82 km²). The blooms originated in the coastal area of Jiangsu province and spread north-east towards the Shandong Peninsula. The blooms grew at different rates and mesoscale variability in surface winds explained the differences in the spatial and temporal patterns of blooms in 2008 and 2009. The 2009 bloom was tracked to its origin immediately offshore of extensive intertidal flats between Yancheng and Nantong where recent rapid expansion of Porphyra aquaculture has occurred. We review published hypotheses which have been advanced to explain the occurrence of blooms and in light of our findings, we conclude that the accumulation and disposal of waste Ulva prolifera from Porphyra aquaculture rafts is the most likely cause of the blooms.