bluuebunny/crossref_metadata_2025 huggingface dataset:
Sorption of atrazine, 2,4‐D, nitrobenzene and pentachlorophenol by urban and industrial wastes
Authors: Wu Q. , Blume H. ‐P. , Rexilius L. , Fölschow M. , Schleuss U.
Published: March 2003

This study was carried out to investigate the sorption properties of man‐made soil developed from sewage sludge, municipal wastes, brick and mortar debris, harbour sludge, sand fills, fly ash, and wastes from coking plants and coal mines. The composition of organic matter in the samples was analysed, and the sorption isotherms of four reference chemicals (nitrobenzene, atrazine, 2,4‐D, pentachlorophenol) were determined. Fly ash, which contains up to 89% of its carbon as Black Carbon, showed a strong affinity to all four chemicals. For the other waste materials, a strong correlation between the logarithm of the Freundlich adsorption constant, Kf, and the logarithm of organic carbon, Co, was established (r = 0.85–0.96). This holds for the non‐ionic nitrobenzene and also, within a certain pH range depending on the pKa of the compound, for the three ionizable organic compounds (atrazine: pH > 4; 2,4‐D: pH > 5; PCP: pH > 6). At pH near the pKa value the sorption is sensitive to pH. There were no statistically significant differences between the waste materials and the natural soils in the relations between logKf and logCo for either ionic or non‐ionic chemicals. This result suggests that the method devised for estimating the sorption of organic chemicals in natural soils based on their content of organic carbon is equally valuable for the waste materials, with the exception of fly ash which contains a large amount of Black Carbon.
Changes in organic matter, nitrogen, phosphorus and cations in soil as a result of fire and water erosion in a Mediterranean landscape
Authors: Gimeno‐García E. , Andreu V. , Rubio J. L.
Published: March 2003

Fire affects large parts of the dry Mediterranean shrubland, resulting in erosion and losses of plant nutrients. We have attempted to measure these effects experimentally on a calcareous hillside representative of such shrubland. Experimental fires were made on plots (4 m × 20 m) in which the fuel was controlled to obtain two different fire intensities giving means of soil surface temperature of 439°C and 232°C with temperatures exceeding 100°C lasting for 36 min and 17 min. The immediate and subsequent changes induced by fire on the soil's organic matter content and other soil chemical properties were evaluated, together with the impact of water erosion.

Seven erosive rain events, which occurred after the experimental fires (from August 1995 to December 1996), were selected, and on them runoff and sediment produced from each plot were measured. The sediments collected were weighed and analysed. Taking into account the variations induced by fire on the soil properties and their losses by water erosion, estimates of the net inputs and outputs of the soil system were made. Results show that the greatest losses of both soil and nutrients took place in the 4 months immediately after the fire. Plots affected by the most intense fire showed greater losses of soil (4077 kg ha−1) than those with moderate fire intensity (3280 kg ha−1). The unburned plots produced the least sediment (72.8 kg ha−1). Organic matter and nutrient losses by water erosion were related to the degree of fire intensity. However, the largest losses of N‐NH4+ and N‐NO3– by water erosion corresponded to the moderate fire (8.1 and 7.5 mg N m−2, respectively).
Modelling the solid–solution partitioning of organic matter in European forest soils
Authors: Lofts S. , Simon B. M. , Tipping E. , Woof C.
Published: March 2003

The processes controlling the solid–solution partitioning of organic matter in soils are central to understanding carbon cycling in terrestrial ecosystems, yet are poorly understood at present. We studied the partitioning of soil organic matter between solid and solution in batch titrations of 12 soil samples from three European forests in a range of climates. We also examined the release of soil organic matter on repeated leaching. The partitioning was simulated using a model that pictures the pool of potentially mobile organic matter to consist of fractions of differing solubilities. Desorption of organic matter was then effected by an increase in the electrical charge of the organic molecules due to their chemical reactions with other soil components.

The model could simulate the partitioning of organic matter in all the soils using two parameters describing the amounts of soil organic matter in each fraction. The release of organic matter on repeated leaching was reasonably well described. The model predicted that dissolved organic matter should have become more hydrophilic with depth in the soil, due to the retention of more hydrophobic components in the upper horizons. This accorded with observed compositions of the soil organic matter. The model also showed that at the ambient pH of the soils, only a small proportion of the potentially mobile organic matter (comprising fulvic acids and hydrophilic moieties) was involved in partitioning to the solution.
A new sampling technique to monitor concentrations of CH4, N2O and CO2 in air at well‐defined depths in soils with varied water potential
Authors: Kammann C. , Grünhage L. , Jäger H. ‐J.
Published: March 2003

A new sampling technique for measuring the concentrations of trace gases (CH4, CO2 and N2O) in the soil atmosphere from well‐defined depths is described. Probes are constructed from silicone tubing closed with silicone septa on both ends, thereby dividing an inner air space from the outer soil atmosphere without a direct contact. The gas exchanges between the inner and outer atmosphere only by diffusion through the walls of the silicone tube. Tests revealed that the gases N2O, CO2 and CH4 in the enclosed space reached 95% equilibrium with the surrounding atmosphere at 20°C within 7 h or faster. The probe measurements are reproducible: the standard deviation of samples taken from 26 probes stored in the laboratory atmosphere equalled that of a standard gas. The probes can easily be constructed and installed at specified depths in the soil.

The method has the following advantages compared with other methods that use spaces with holes in them for gas exchange: (i) the silicone probe enables trace gases to be sampled in wet soils, including ones that are waterlogged or temporarily saturated; (ii) the sampling itself does not create low pressure and hence does not create mass flow in the soil matrix from undefined depths; and (iii) the probe can be made to take samples of gas of any required size. The silicone probes did not show ageing effects during 18 months of use in the field in a mineral soil under grass. The probes yielded comparable results: three probes inserted at 5 cm depth in a uniformly treated 100‐m2 plot provided nearly identical average trace gas concentrations within the measurement period.
Influence of soil strength on root growth: experiments and analysis using a critical‐state model
Authors: Kirby J.M. , Bengough A.G.
Published: March 2003

Roots grow thicker in compacted soil, even though it requires greater force for a large object to penetrate soil than it does for a small one. We examined the advantage of thickening in terms of the stresses around a root penetrating with constant shape, rather than the stresses around an expanding cylinder or sphere, as has been studied previously. We combined experiments and simulations of the stresses around roots growing in compacted soils. We measured the diameter of pea roots growing in sandy loam and clay loam at four different densities, and the critical‐state properties of the soils. At a penetration resistance of about 1 MPa the diameter of the roots in the sandy loam was about 40% greater than that at 0.7 MPa, and at 2 MPa it was about 60% greater. In the clay loam, there was less thickening – about 10% greater at 1 MPa and about 20% greater at 1.5 MPa. The maximum axial stresses were predicted using a critical‐state finite‐element model to be at the very tip of the root cap. When there was friction between the root and the soil, shear stresses were predicted with smaller values at the tip than just behind the tip. When the interface between the soil and the root was assumed to be frictionless, there were by definition no shear stresses. In the frictionless case the advantage of root thickening on relieving peak stress at the root tip was diminished. The axial and shear stresses were predicted to be smaller in the clay loam than in the sandy loam and may explain why the roots did not thicken in this soil although its resistance to penetration was similar. Our results suggest that the local values of axial and shear stresses experienced by the root near its tip may be as important in constraining root growth as the total penetration resistance.
Pollution of carbonate soils in a Mediterranean climate due to a tailings spill
Authors: Simón M. , Dorronsoro C. , Ortiz I. , Martín F. , Aguilar J.
Published: March 2003

The retention walls in a pond containing the residues from the pyrite mine of Aznalcóllar (southern Spain) broke open on 25 April 1998, spilling approximately 6 × 106 m3 of polluted water and toxic tailings, which affected some 55 km2. Drying and aeration of the tailings resulted in oxidation, forming an acidic solution with high pollutant contents, the effects of which were studied in a calcareous soil. The infiltration of this solution markedly affected only the first 12 mm of the soil, where strong acidification caused the weathering of the carbonates, and where the fine mineral particles were hydrolysed. The SO42− ions in the acidic solution precipitated almost entirely at this depth, forming gypsum, hydroxysulphates and complex sulphates. The Fe3+ ions also precipitated there, mainly in amorphous or poorly crystallized forms, adsorbing to As, Sb, Tl and Pb dissolved in the acidic solution. The Al3+ ions, though partly precipitating in the acidic layer, accumulated mostly where the soil pH exceeded 5.5 (12–14 mm in depth). They did so primarily as amorphous or poorly crystallized forms, adsorbing to Cu dissolved in the acidic solution. The Zn2+ and Cd2+ ions accumulated mainly at pH > 7.0 (19–21 mm in depth), being adsorbed chiefly by clay mineral. After 15 months, only the first 20 mm of the soil were acidified by the oxidation of the tailings and most of the pollutants did not penetrate deeper than 100 mm. Consequently, the speed of the cleanup of the toxic spill is not as important as a thorough removal of tailings together with the upper 10 cm of the soil.
Modelling soil pore characteristics from measurements of air exchange: the long‐term effects of fertilization and crop rotation
Authors: Schjønning P. , Munkholm L. J. , Moldrup P. , Jacobsen O. H.
Published: March 2003

Long‐term cultivation of soils for arable crops and without application of organic manure is thought to reduce the soil quality for crop production. We studied the porosity of two sandy loam soils from organic dairy farms with a ley cropping system and compared them with a conventionally managed dairy farm growing arable crops only and an arable soil receiving only mineral fertilizers, respectively. Saturated hydraulic conductivity, water retention characteristics, air diffusivity and air permeability were determined in the plough layer of the soil.

The soil of one of the organic dairy farms contained many more earthworm burrows and had a significantly larger hydraulic conductivity than the counterpart soil of the conventionally managed dairy farm. In other respects, these two soils were much alike. The soil of the other organically managed dairy farm was less dense and had a larger volume of pores > 30 μm than the arable soil receiving only mineral fertilizers. A tube model was used to combine the air exchange measurements in a description of the soil pores. The pore system of the mineral fertilized soil consisted of continuous arterial pores with only a small volume of blocked and marginal pores embedded in the soil matrix next to the arterial pores. The porosity of the counterpart organic dairy farm soil had a considerable volume of blocked and especially marginal pores. The complexity of the latter was considered beneficial for local aeration in the soil and for derived soil properties such as fragmentation on tillage.
Uncertainty analysis for pedotransfer functions
Authors: Minasny B. , Mc Bratney A. B.
Published: March 2003

Both empirical and process‐simulation models are useful in predicting the outcome of agricultural management on soil quality and vice versa, and pedotransfer functions have been developed to translate readily available soil information into variables that are needed in the models. The input data are subject to error, and consequently the transfer functions can produce varied outputs. A general approach to quantifying the resulting uncertainty is to use Monte Carlo methods. By sampling repeatedly from the assumed probability distributions of the input variables and evaluating the response of the model, the statistical distribution of the outputs can be estimated. Methods for sampling the probability distribution include simple random sampling, the sectioning method, and Latin hypercube sampling. The Latin hypercube sampling is applied to the quantification of uncertainties in pedotransfer functions of soil strength and soil hydraulic properties. Hydraulic properties predicted using recently developed pedotransfer functions are also used in a model to analyse the uncertainties in the prediction of soil‐water regimes in the field. The uncertainties of hydraulic properties in soil‐water simulation show that the model is sensitive to the soil's moisture state.
Increases in pH and soluble salts influence the effect that additions of organic residues have on concentrations of exchangeable and soil solution aluminium
Authors: Mokolobate M. S. , Haynes R. J.
Published: March 2003

It has been suggested that additions of organic residues to acid soils can ameliorate Al toxicity. For this reason the effects of additions of four organic residues to an acid soil on pH and exchangeable and soil solution Al were investigated. The residues were grass, household compost, filter cake (a waste product from sugar mills) and poultry manure, and they were added at rates equivalent to 10 and 20 t ha−1. Additions of residues increased soil pH measured in KCl (pH(KCl)) and decreased exchangeable Al3+ in the order poultry manure > filter cake > household compost > grass. The mechanism responsible for the increase in pH differed for the different residues. Poultry manure treatment resulted in lower soil pH measured in water (pH(water)) and larger concentrations of total (AlT) and monomeric (Almono) Al in soil solution than did filter cake. This was attributed to a soluble salt effect, originating from the large cation content of poultry manure, displacing exchangeable Al3+ and H+ back into soil solution. The considerably larger concentrations of soluble C in soil solution originating from the poultry manure may also have maintained greater concentrations of Al in soluble complexed form. There was a significant negative correlation (r = −0.94) between pH(KCl) and exchangeable Al. Concentrations of AlT and Almono in soil solution were not closely related with pH or exchangeable Al. The results suggest that although additions of organic residues can increase soil pH and decrease Al solubility, increases in soluble salt and soluble C concentrations in soil solution can substantially modify these effects.
Predicting carbon content in illitic clay fractions from surface area, cation exchange capacity and dithionite‐extractable iron
Authors: Kahle M. , Kleber M. , Jahn R.
Published: March 2003

We used the specific surface area (SSA), the cation exchange capacity (CEC) and the content of dithionite‐extractable iron (Fed) to predict the content of organic carbon in illitic clay fractions of topsoils from loess. We determined SSA (BET‐N2 method) and CEC of clay fractions after removing organic C or reducing oxides or both. The CEC and the SSA of the carbon‐ and oxide‐free clay fraction explained 56% and 54% of the variation in C content, respectively. The Fed content of the clay fractions was strongly and negatively related to the C content, and with the SSA of the carbon‐free clay fraction it predicted C content almost completely (R2 = 0.96). The results indicate that the amount of cations adhering to the silicate clay minerals and the size of the silicate mineral surface area are important properties of the mineral phase for the storage potential of C. The reason for the negative relation between iron oxides and C content remains unclear.
Phosphorus uptake by rice from soil that is flooded, drained or flooded then drained
Authors: Huguenin‐Elie O. , Kirk G. J.D. , Frossard E.
Published: March 2003

To investigate the mechanisms by which rice plants growing in alternately flooded and drained soils absorb soil phosphate, we grew rice in moist, flooded and flooded then moist soils, and compared the measured uptake of phosphorus (P) with that calculated using a mathematical model of uptake allowing for solubilization by various means. The theory and equations for the model are given, together with a method for solving diffusion equations near roots in a root system of increasing density. The diffusion coefficients and buffer powers of P in the soil under the different water regimes are measured by following diffusion of P to a resin sink, and the parameters describing solubilization are estimated from previously published results. In all the water regimes studied, the plants relied upon solubilization for most of their P. The roots were not mycorrhizal, as they will often not be in intermittently flooded soils. In the flooded soil, uptake was three times that in the moist soil, and was consistent with solubilization by acidification caused by roots as a result of oxidation of iron and imbalance between the intake of cations and anions. In the moist soil, the uptake was consistent with solubilization by excretion of organic anions from the roots. In the flooded then moist soil, uptake declined sharply as the soil dried because P became immobilized in the soil. However, the final uptake was similar to that in the continuously moist soil, indicating that some of the immobilized P was re‐solubilized by roots, possibly by excretion of organic anions.
Summer habitat affinities of estuarine fish in US mid‐Atlantic coastal systems
Authors: MONACO  , WEISBERG  , LOWERY
Published: March 2003

Fisheries management strategies based on habitat protection require definitive assessment of fish habitat affinities, but most habitat association information is based on disparate data from multiple sampling strategies. Habitat affinities were quantitatively defined using consistently collected data with a 16‐m high‐rise otter trawl at 314 Virginian Province (US) sites from 1990 to 1993. Catch rates and field‐recorded salinity, depth, sea bed type, and geography (coastal system) associated with each trawl were analysed. Habitat affinity was quantified by comparing the concentration of fish in a particular habitat with the prevalence of that habitat. Fishes exhibited a specific habitat affinity even though they occurred across a range of environmental gradients. Fish were most associated with salinity (14 of 19 species/life‐stage groups had a significant affinity for at least one salinity zone). Three‐quarters of the flatfish displayed an affinity for a selected sea bed type; the same percentage of sciaenids had an affinity for a particular salinity zone.
Fishing impacts and the degradation or loss of habitat structure
Authors: Turner S. J. , Thrush S. F. , Hewitt J. E. , Cummings V. J. , Funnell G.
Published: March 2003

The wider effects of fishing on marine ecosystems have become the focus of growing concern among scientists, fisheries managers and the fishing industry. The present review examines the role of habitat structure and habitat heterogeneity in marine ecosystems, and the effects of fishing (i.e. trawling and dredging) on these two components of habitat complexity. Three examples from New Zealand and Australia are considered, where available evidence suggests that fishing has been associated with the degradation or loss of habitat structure through the removal of large epibenthic organisms, with concomitant effects on fish species which occupy these habitats. With ever‐increasing demands on fish‐stocks and the need for sustainable use of fisheries resources, new approaches to fisheries management are needed. Fisheries management needs to address the sustainability of fish‐stocks while minimizing the direct and indirect impacts of fishing on other components of the ecosystem. Two long‐term management tools for mitigating degradation or loss of habitat structure while maintaining healthy sustainable fisheries which are increasingly considered by fisheries scientists and managers are: (1) protective habitat management, which involves the designation of protected marine and coastal areas which are afforded some level of protection from fishing; and (2) habitat restoration, whereby important habitat and ecological functions are restored following the loss of habitat and/or resources. Nevertheless, the protection of marine and coastal areas, and habitat restoration should not be seen as solutions replacing conventional management approaches, but need to be components of an integrated programme of coastal zone and fisheries management. A number of recent international fisheries agreements have specifically identified the need to provide for habitat protection and restoration to ensure long‐term sustainability of fisheries. The protection and restoration of habitat are also common components of fisheries management programs under national fisheries law and policy.
Sri Lankan reservoir fishery: a case for introduction of a co‐management strategy
Authors: Amarasinghe U. S. , De Silva S. S.
Published: March 2003

The inland fisheries of Sri Lanka are essentially artisanal on most of the reservoirs in the country. The annual inland fish production declined dramatically after 1990, when state patronage for the development of the inland fisheries was discontinued for 4 years. This decline was shown to be a result of growth overfishing of the two dominant cichlid species which accounted for over 90% of landings. This was a result of using small mesh ( < 6.9 cm) gillnets in the absence of the State‐sponsored monitoring procedure in the fishery after 1990. This indicates that it is necessary to monitor inland fisheries management in Sri Lanka through a centralized authority in the current situation. However, in some Sri Lankan reservoirs, fishing communities can be categorized as ‘organized’ because they collectively make decisions to define procedures for the rational exploitation of the fishery resources. In reservoirs with ‘organized’ fishing, the communities themselves have developed mechanisms to regulate the landing sizes of dominant cichlid fish species through community‐based fisheries management strategies. In such reservoirs, over‐exploitation of fish stocks was not evident, even after 1990, when state‐sponsored monitoring procedures were suspended. Based on these observations, an alternative approach is recommended for the management of Sri Lankan reservoir capture fisheries in which the Government and resource‐users have equal responsibilities in the management of the resources.
Finnish lake fisheries and conservation of biodiversity: coexistence or conflict?
Authors: Salmi P. , Auvinen H. , Jurvelius J. , Sipponen M.
Published: March 2003

The conservation of biodiversity in aquatic habitats has become an increasingly important challenge in the management of water resources. In addition to the complexity of the lake fishery and the management structure, the popularity of gill net fishing, in particular, has brought problems when re‐establishing populations of Arctic charr, Salvelinus alpinus (L.), collecting genetically sustainable numbers of spawners of the land‐locked salmon, Salmo salar m. sebago (Girard), and increasing the population of the Saimaa ringed seal, Phoca hispida saimensis (Nordq.) to a sustainable level in the Vuoksi watercourse, south‐east Finland. The attitudes towards protection among the users and other interested parties vary. In order to enhance the coexistence of the lake fishery and endangered species over large water areas, improved institutional linkages are needed among the local, regional and governmental levels of the fragmented decision‐making regime. Environmental interests should also be integrated into the communication structure.
Differences in head shape of the European eel, Anguilla anguilla (L.)
Authors: Proman J. M. , Reynolds J. D.
Published: March 2003

Differences in eel, Anguilla anguilla (L.), head shape were the result of greater increases in head width, rather than changes in head length. The ratio of head width:total length (HW:TL) increased significantly (t‐test, P < 0.05) from the glass‐yellow eel stage. Cultured yellow eels were exclusively narrow headed (mean HW:TL = 0.027, range = 0.023–0.032), while wild yellow eels displayed an array of head shapes (mean HW:TL = 0.033, range = 0.023–0.046). Therefore, broad heads (HW:TL 0.033) occurred only among wild yellow eels sampled and may have resulted from diet. Cultured yellow eels consumed only small pellet material. Of wild yellow eels stomachs containing food, 78% of broad‐headed eels consumed large and/or hard‐bodied organisms (e.g. beetles, fish, molluscs and Notonecta sp.), while 83% of narrow‐headed eels consumed exclusively small/soft‐bodied prey (e.g. amphipods and chironomids).
Can fishermen allocate their fishing effort in space and time on the basis of their catch rates? An example from Spermonde Archipelago, SW Sulawesi, Indonesia
Authors: Pet‐Soede C. , Van Densen W.L.T. , Hiddink J.G. , Kuyl S. , Machiels M.A.M.
Published: March 2003

Spatial and temporal patterns in catch rates and in allocation of fishing effort were analysed for the coastal fishery in Spermonde Archipelago, Indonesia, to assess whether fishermen can optimise their strategy from catch information, or whether they fish under great uncertainty and merely minimise risks. On average 517 fishing units operated in the 2800 km2area, catching 21 t fish day−1. Major gear categories were hook and line (59% of total effort and 5% of total catch), and lift nets (16% of total effort and 70% of total catch). The size of individual resource spaces varied with gear type and was smaller in unfavourable weather conditions. Although spatial patterns in catch rates at the scale of the whole archipelago were evident, fishermen could not differentiate between locations, as catch variance within their individual resource spaces was high relative to the contrasts in spatial patterns. The aggregated distribution of fishing effort in Spermonde must be explained by factors such as the small scale of operations, rather than fish abundance.
Potential impact of climate warming on recreational fishing opportunities for Atlantic salmon, Salmo salar L., in Newfoundland, Canada
Authors: Dempson J. B. , O'Connell M. F. , Cochrane N. M.
Published: March 2003

Potential impacts of climate warming on recreational fishing opportunities were addressed by assessing the frequency and extent that Atlantic salmon, Salmo salar L., rivers in Newfoundland have been closed over a 25‐year period (1975 to 1999) because of warm water temperatures and low water levels. On average, approximately 28% of all salmon rivers were temporarily closed annually, with over 70% affected in some years. This has resulted in a loss of 35–65% of the potential fishing days available in some salmon fishing areas with the collective 1995 to 1999 period being impacted the most over the past two decades. Geographically, west and south‐west coastal rivers were affected less from environmental closures than east and some south coast fishing areas. A trend for increased closures of rivers related to environmental reasons could reduce the economic importance of the recreational salmon fishery and also make it more difficult to assess the status of Atlantic salmon stocks, which is a requirement for conservation of the resource.
Effectiveness of four methods for tagging juveniles of farm‐reared gilthead sea bream, Sparus aurata, L.
Authors: Sánchez‐Lamadrid A.
Published: March 2003

This study tested different tags for each size of farm‐reared gilthead sea bream, Sparus aurata L. juveniles, used in enhancement programmes. The following tags were tested: dye mark, fingerling tag, opercular tag, anchor tag A (filament diameter of 1.20 mm) and anchor tag B (0.85 mm). Tag/mark retention, wounds produced by the tag, ease of application, ease of detection and cost were examined. Epidermal dye marks had poor retention and detection rates. Of the tags tested, retention was greater for the anchor tag A (80–100%) after 7 months; anchor tag B showed a retention rate of only 20% after 3 months. The fingerling tag had a retention rate of 27.5% after 12 months. The opercular tag had a retention rate of 44% after 20 days but fractured the opercular bone in many cases. Tag incisions and wounds persisted in some fish for the duration of the experiment.
A comparison of catchment based salmonid habitat survey techniques in three river systems in Northern Ireland
Authors: O'CONNOR W. C. K. , KENNEDY R. J.
Published: March 2003

Three survey techniques, a fully quantitative, multivariate study; a shorter or truncated fully quantitative method and a Geographical Information System (GIS) based, semi‐quantitative, survey technique, were developed to assess in‐river salmonid habitats on a catchment wide basis. These methods were tested and compared on three river systems in Northern Ireland: the Blackwater, the Bush and the Main. The research indicated that the fully quantitative method generated an accurate habitat database but required a high investment in time and resources to complete. The truncated survey approach often produced an inaccurate habitat database. The semi‐quantitative technique generated a more accurate habitat dataset with greater productivity and efficiency for the resources invested in the survey.
The relationship between stock and catch and the effect of bait on catch as determined for a UK recreational catch and release fishery
Authors: SMITH P. A.
Published: March 2003

Abstract Twelve anglers fishing in a UK navigation canal for a total of 42 h caught 567 fish, mainly gudgeon, Gobio gobio (L.) (n=306) and roach, Rutilus rutilus (L.) (n=253) at an average catch rate of 13.4 fish angler‐h−1 or 128.5 g angler‐h−1. The species and size of fish caught were compared with the numbers determined by depletion estimates at six sections of canal using micromesh seine netting. Fifty four percent of fish caught in the net were < 60 mm FL. Gudgeon (60–99 mm) were over‐represented in the anglers' catches whilst roach (60–99 mm) were under‐represented. The size distribution of roach and gudgeon caught by anglers using two types of bait (small maggots and chironomid larvae) was examined and smaller fish were found to be caught using the latter.
Variations in the drift of larval cod (Gadus morhua L.) in the Baltic Sea: combining field observations and modelling
Authors: Voss RÜdiger , Hinrichsen Hans‐Harald , John Mike ST
Published: March 2003

Coupled three‐dimensional (3‐D) physical oceanographic modelling and field sampling programmes were carried out in May 1988 and August 1991 to investigate the potential drift of larval cod (Gadus morhua L.) in the Bornholm Basin of the Baltic Sea. The goals were to predict the transport of cod larvae, thus aiding the identification of physical processes influencing larval retention/dispersal. Numerical simulations were performed using a 3‐D eddy‐resolving baroclinic model based on the Bryan–Cox–Semtner code adapted for the Baltic Sea. Within the Bornholm Basin, the model was initialized with ground truth data of physical parameters obtained on the research cruises, and all simulations were forced with actual wind data. Outside the basin, generalized hydrographic features of the Baltic Sea were utilized by incorporation of simulated hydrographic fields from previous model runs typical for the time periods considered. Larval drift was simulated either by incorporation of passive drifters, or as the initial horizontal distribution of larvae implemented into the model. Drift model simulations of larval transport agreed relatively well with field observations. The influence of variations in the vertical distribution on a smaller scale, i.e. vertical deviations of ± 6 m from the observed mean centre of mass, on the drift was examined, revealing no significant differences in the drift of larvae depending on their vertical distribution. The different wind forcing during the investigated time periods was linked to a retention situation in May 1988 and to a dispersal situation in August 1991. Finally, observed spatial distribution patterns of 1‐group cod based on Baltic Young Fish Surveys (BYFS) were compared with their predicted transport in the larval phase and examined with respect to recruitment.
On the use of Lloyd’s index of patchiness
Authors: Bez N.
Published: March 2003

Lloyd’s index of patchiness, and to a lesser extent, of mean crowding, are often applied to (fish or ichthyoplankton) densities, although they were designed for use with counts of individuals. The consequences of this erroneous application are described with examples. Alternative statistics are presented for application to densities. Like the mean crowding, these statistics are robust against zeroes and cannot be considered as spatial statistics.
Anomalous conditions in the south‐eastern Bering Sea, 1997: nutrients, phytoplankton and zooplankton
Authors: Stockwell Dean A. , Whitledge Terry E. , Zeeman Stephan I. , Coyle Kenneth O. , Napp Jeffrey M. , Brodeur Richard D. , Pinchuk Alexei I. , Hunt George L.
Published: March 2003

Anomalies in the regional weather over the south‐eastern Bering Sea during spring and summer of 1997 resulted in significant differences in nutrient availability, phytoplankton species composition, and zooplankton abundance over the continental shelf as compared with measurements in the 1980s. Calm winds and the reduction of cloud cover in spring and summer produced a very shallow mixed layer in which nitrate and silicate were depleted after an April diatom bloom. High submarine light levels allowed subsequent phytoplankton growth below the pycnocline and eventual depletion of nitrate from the water column to depths of 70 m or more. Thus, total new production during 1997 may have exceeded that of previous years when nitrate was not depleted below the pycnocline. A bloom of the coccolithophorid, Emiliania huxleyi, was observed in early July in the warm, nutrient‐depleted waters over the middle and inner shelf. Emiliania huxleyi concentrations reached 4.5 × 106 cells L–1 by September, and the bloom persisted through the autumn. There was evidence for increased abundance of some species of copepods in 1997 as compared with data from the middle domain in June 1981. The abundance of adult and juvenile euphausiids in 1997 was statistically similar to values measured in 1980 and 1981. However, near‐surface swarms were rarely observed on the inner shelf in August–September 1997. Lack of euphausiid availability in the upper water column may partially explain the August–September mass mortality of planktivorous short‐tailed shearwaters (Puffinus tenuirostris) observed on the inner shelf.
The influence of mesoscale ocean processes on anchovy (Engraulis encrasicolus) recruitment in the Bay of Biscay estimated with a three‐dimensional hydrodynamic mode
Authors: Allain G. , Petitgas P. , Lazure P.
Published: March 2003

The relationship between anchovy (Engraulis encrasicolus) recruitment in the Bay of Biscay and environmental variables during their planktonic phase (March to July) was investigated from 1986 to 1997. Meteorological variables (wind and temperature) are forcing effects on the sea, but they are not thought to be processes that govern larval survival directly. Food‐web dynamics are believed to be more closely linked to larval survival and are related to the physical vertical water column structure. Therefore, we used a three‐dimensional (3D) hydrodynamic model to characterize three major physical mesoscale processes affecting vertical structure in south‐east Biscay: stratification, upwelling and river plume extent. Indices were estimated from the model outputs to characterize and quantify the space/time evolution of these structures during the period March to July. A multiple linear regression analysis was then used to analyse hierarchy in the explanatory power of the physical indices. Coastal upwelling and shelf stratification breakdown indices were the most significant explanatory variables, with positive and negative effect on recruitment, respectively. A model with these two indices explains 75% of the recruitment variability of anchovy observed in the period 1987–96.
Relationship between spatial distribution of the Patagonian stock of Argentine anchovy, Engraulis anchoita, and sea temperatures during late spring to early summer
Authors: Hansen J. E. , Martos P. , Madirolas A.
Published: March 2003

The relative abundance of adult Argentine anchovies (Engraulis anchoita) and the thermal structure of the sea between 41° and 45°30′S during four research surveys were compared. Acoustic data were collected while making parallel transects along which CTD (conductivity, temperature, depth) stations were regularly distributed. Anchovy abundance was related to both the sea surface temperature and the stratification of the water column, as classified according to the φ parameter of stability (Simpson, 1981). Regarding the whole water column, the sea temperatures where adult anchovies were recorded ranged from 8.5 to 16.5°C, but anchovy echo traces from waters above 14°C were obtained mainly at night. The sea surface temperature bounds for anchovy distribution were 11 and 17°C, with a preferential range between 12.5 and 16°C, but no absolute value of sea surface temperature was found to be most favourable for the species. The highest fish abundances were related to sharp thermal gradients, either horizontally recorded in frontal zones (≈ 0.02°C or more per km) or vertically associated to the occurrence of a thermocline (stability > 10 J m–3). Sea fronts seemed to be the axes for the distribution of anchovy shoals, and the annual changes in the positions of the fronts seemed to be followed by analogous changes in the locations of the main anchovy concentrations. Within thermally stratified areas and during the daytime, anchovies apparently preferred the thermocline layer or the layer immediately above that, although a few fish shoals were located below the thermocline.
The influence of oxygen saturation on the distributional overlap of predator (cod, Gadus morhua) and prey (herring, Clupea harengus) in the Bornholm Basin of the Baltic Sea
Authors: Neuenfeldt Stefan
Published: March 2003

Environmental heterogeneity can create boundary conditions for the co‐occurrence of marine predators and their prey. If one or both are spatially constrained by their tolerance to environmental variables, then spatial differences in the availability of possible habitats define the volume of distributional overlap. Cod (Gadus morhua L.) and its prey, herring (Clupea harengus L.), in the vertically stratified Bornholm Basin of the Baltic Sea are presented as an example. A non‐linear model was used to estimate oxygen avoidance thresholds for both species. Herring avoided oxygen saturation levels below 50%, while cod tolerated oxygen saturation down to 16%. The threshold of 50% oxygen saturation, below which cod could not encounter its prey, herring, was applied to a time series of vertical oxygen profiles from the centre of the Bornholm Basin to estimate the size of the overlap volume during the winter period from 1958 to 1999. Dependent on the oxygenation of the deep‐water, the overlap volume varied between 57 km3 and 250 km3.
Length and sex‐specific associations between spiny dogfish (Squalus acanthias) and hydrographic variables in the Bay of Fundy and Scotian Shelf
Authors: Shepherd Travis , Page Fred , Macdonald Bruce
Published: March 2003

The associations between spiny dogfish (Squalus acanthias) and hydrographic variables (temperature, salinity and depth) were examined in the Bay of Fundy and Scotian Shelf from 1970 to 1998. Data were obtained from standard groundfish bottom trawl surveys. Dogfish sex affected habitat associations. Males were found to occupy bottom water of significantly higher salinities and depths than that occupied by females. Length also significantly affected habitat associations. Smaller dogfish occupied relatively deep, high salinity bottom water compared with larger dogfish. Overall, the occupied temperatures, salinities and depths were significantly different from those which were available. Dogfish occupied warmer temperatures along a narrow range (6.62–9.19°C) compared with those which were available (1.57–9.35°C). Occupied salinity (32.70–34.43 ppt) and occupied depth (88.62–184.66 m) were also distributed along a narrower range than available salinity (32.16–34.79 ppt) and available depth (55.00–218.10 m). Sex‐specific, length‐specific and overall environmental preference by dogfish may bias traditional `offshore' groundfish surveys while large scale changes in hydrographic parameters may alter dogfish distribution and their interactions with other marine fauna.
Application of a habitat‐based model to estimate effective longline fishing effort and relative abundance of Pacific bigeye tuna (Thunnus obesus)
Authors: Bigelow Keith A. , Hampton John , Miyabe Naozumi
Published: March 2003

A new habitat‐based model is developed to improve estimates of relative abundance of Pacific bigeye tuna (Thunnus obesus). The model provides estimates of `effective' longline effort and therefore better estimates of catch‐per‐unit‐of‐effort (CPUE) by incorporating information on the variation in longline fishing depth and depth of bigeye tuna preferred habitat. The essential elements in the model are: (1) estimation of the depth distribution of the longline gear, using information on gear configuration and ocean currents; (2) estimation of the depth distribution of bigeye tuna, based on habitat preference and oceanographic data; (3) estimation of effective longline effort, using fine‐scale Japanese longline fishery data; and (4) aggregation of catch and effective effort over appropriate spatial zones to produce revised time series of CPUE. Model results indicate that effective effort has increased in both the western and central Pacific Ocean (WCPO) and eastern Pacific Ocean (EPO). In the WCPO, effective effort increased by 43% from the late 1960s to the late 1980s due primarily to the increased effectiveness of effort (deeper longline sets) rather than to increased nominal effort. Over the same period, effective effort increased 250% in the EPO due primarily to increased nominal effort. Nominal and standardized CPUE indices in the EPO show similar trends – a decline during the 1960s, a period of stability in the 1970s, high values during 1985–1986 and a decline thereafter. In the WCPO, nominal CPUE is stable over the time‐series; however, standardized CPUE has declined by ∼50%. If estimates of standardized CPUE accurately reflect relative abundance, then we have documented substantial reductions of bigeye tuna abundance for some regions in the Pacific Ocean. A decline in standardized CPUE in the subtropical gyres concurrent with stability in equatorial areas may represent a contraction in the range of the population resulting from a decline in population abundance. The sensitivity of the results to the habitat (temperature and oxygen) assumptions was tested using Monte Carlo simulations.
Recent advances in understanding the circulation and hydrography of the East China Sea
Authors: Lie Heung‐Jae , Cho Cheol‐Ho
Published: March 2003

The physical oceanography of the East China Sea (ECS) has been studied extensively through comprehensive observing programmes conducted in the 1990s, allowing clarification of the major oceanographic processes involved in establishing the hydrography and circulation. An overview of the general circulation and hydrography in the ECS is given here, mainly based on the new observational results and with special attention to the Kuroshio bifurcation north‐east of Taiwan and south‐west of Kyushu and the major currents in the outer continental shelf. A new schematic circulation pattern of the ECS is sketched using these observations. The oceanographic conditions and fisheries environments of the ECS are not only seasonally variable because of the response of the basin to the seasonally varying atmospheric conditions, but also spatially and temporally complicated because of the wide spectrum of phenomena that coexist with various scales.
Identification of Atlantic bluefin tuna (Thunnus thynnus) stocks from putative nurseries using otolith chemistry
Authors: Rooker Jay R. , Secor David H. , Zdanowicz Vincent S. , De Metrio Gregorio , Relini Lidia Orsi
Published: March 2003

Chemical signatures in the otoliths of teleost fishes represent natural tags that may reflect differences in the chemical and physical characteristics of an individuals' environment. Otolith chemistry of Atlantic bluefin tuna (Thunnus thynnus) was quantified to assess the feasibility of using these natural tags to discriminate juveniles (age 0 and age 1) from putative nurseries. A suite of six elements (Li, Mg, Ca, Mn, Sr and Ba) was measured in whole otoliths using solution‐based inductively coupled plasma mass spectrometry. Otolith chemistry of age‐1 T. thynnus collected from the two primary nurseries in the Mediterranean Sea and western Atlantic Ocean differed significantly, with a cross‐validated classification accuracy of 85%. Spatial and temporal variation in otolith chemistry was evaluated for age‐0 T. thynnus collected from three nurseries within the Mediterranean Sea: Alboran Sea (Spain), Ligurian Sea (northern Italy), and Tyrrhenian Sea (southern Italy). Distinct differences in otolith chemistry were detected among Mediterranean nurseries and classification accuracies ranged from 62 to 80%. Interannual trends in otolith chemistry were observed between year classes of age‐0 T. thynnus in the Alboran Sea; however, no differences were detected between year classes in the Tyrrhenian Sea. Age‐0 and age‐1 T. thynnus collected from the same region (Ligurian Sea) were also compared and distinct differences in otolith chemistry were observed, indicating ontogenetic shifts in habitat or elemental discrimination. Findings suggest that otolith chemistry of juvenile T. thynnus from different nurseries are distinct and chemical signatures show some degree of temporal persistence, indicating the technique has considerable potential for use in future assessments of population connectivity and stock structure of T. thynnus.