bluuebunny/crossref_metadata_2025 huggingface dataset:
Calculation of nitrogen mineralization and leaching in fallow soil using a simple dynamic model
Authors: Mary B. , Beaudoin N. , Justes E. , Machet J. M.
Published: March 2003

Simple models describing nitrogen processes are required both to estimate nitrogen mineralization in field conditions and to predict nitrate leaching at large scales. We have evaluated such a model called LIXIM, which allows calculation of nitrogen mineralization and leaching from bare soils, assuming that these are the dominant processes affecting N in bare soil. LIXIM is a layered, functional model, with a 1‐day time step. Input data consist of frequent measurements of water and mineral N contents in soil cores, standard meteorological data and simple soil characteristics. The nitrate transport is simulated using the ‘mixing‐cells’ approach. The variations in N mineralization with temperature and moisture are accounted for, providing calculation of the ‘normalized time’. An optimization routine is used to estimate the actual evaporation and the N mineralization rates that provide the best fit between observed and simulated values of water and nitrate contents in all measured soil layers.

The model was evaluated in two field experiments (on loamy and chalky soils) including treatments, lasting 9–20 months. The water and nitrate contents in soil were satisfactorily simulated in both sites, and all treatments, including a 15N tracer experiment performed in the loamy soil. In the chalky soil, the calculated water balance agreed well with drainage results obtained in lysimeters and independent estimates of evaporation. At both sites, N mineralization was reduced by the incorporation of crop residues (wheat or oilseed rape straw); the amounts of nitrogen immobilized varied between 20 and 35 kg N ha−1. In the treatments without crop residues, the mineralization rate followed first‐order kinetics (against normalized time) in the loamy soil, and zero‐order kinetics in the chalky soil. In the latter soil, the mineralization kinetics calculated in situ were close to the kinetics measured in laboratory conditions when both were expressed against normalized time.
Interactions of allophane with humic acid and cations
Authors: Yuan G. , Theng B. K. G. , Parfitt R. L. , Percival H. J.
Published: March 2003

Allophanic soils are known to accumulate organic matter, but the underlying mechanism is not well understood. Here we have investigated the sorption of humic acid (HA) by an allophanic clay in the presence of varied concentrations of either CaCl2 or NaCl as background electrolytes. Both the HA and the clay were separated from New Zealand soils. Much more HA was sorbed in CaCl2 than in NaCl of the same ionic strength. Apparently Ca2+ ions were more effective than Na+ ions in screening the negative charge on HA. In CaCl2 the HA molecule might also assume a more compact configuration than in NaCl. In the presence of CaCl2 sorption increased, reached a maximum, and then declined as the concentration of HA in solution was increased. This behaviour was not observed in NaCl where sorption showed a gradual and steady increase with HA concentration. We propose that ligand exchange occurs between the surface hydroxyl groups of allophane and the carboxylate groups of HA. As a result, the allophane–HA complex acquires negative charges, requiring the co‐sorption of extraneous cations (Ca2+ or Na+) for charge balance. The Ca2+ co‐sorbed can attract more HA to the complex possibly by a cation‐bridging mechanism, giving rise to a maximum in sorption. The decline in sorption beyond the maximum may be ascribed to a decrease in the concentration of free Ca2+ ions through binding to HA molecules in solution. The increase in supernatant pH may be attributed to a ligand exchange reaction between the surface hydroxyls of allophane and the carboxylate groups of HA, and proton binding to the allophane–HA complex.
A mathematical model of root uptake of cations incorporating root turnover, distribution within the plant, and recycling of absorbed species
Authors: Darrah P. R. , Staunton S.
Published: March 2003

Understanding the movement of cations in soil, particularly trace metals, is required in many applications such as phytoremediation and pollution control. A dynamic mechanistic model has been developed to describe the long‐term root uptake of a surface‐applied, strongly adsorbed, pollutant metal cation, such as radiocaesium, from soil. It consists of two submodels. The first calculates uptake per unit root length at a local scale over a root's lifetime, for various initial conditions. The second calculates cumulative uptake at a whole‐plant scale for the entire rooting depth as a function of time. The model takes into account the renewal of roots which are considered to have a limited lifetime. Root density may be a function of soil depth and a proportion of roots need not contribute to uptake. Recycling from decaying, or grazed, roots and shoots is considered.

Simulations show that removal of cations from soil is exaggerated unless some recycling by roots or shoots is considered or the entire root length does not contribute to uptake. Because of root turnover, uptake is not rapidly limited by diffusive flux of the cation from the bulk soil solution to the solution–root interface. Uptake is very sensitive to root architecture and plant physiology.
Single‐ and dual‐porosity modelling of multiple tracer transport through soil columns: effects of initial moisture and mode of application
Authors: Kätterer T. , Schmied B. , Abbaspour K. C. , Schulin R.
Published: March 2003

We investigated the effect of initial moisture contents and mode of application on the displacement of multiple conservative tracers through undisturbed columns of a Humic Gleysol. Bromide was applied at the soil surface and chloride was injected at 5 cm depth. The columns were irrigated with deuterium‐enriched water. A dual‐porosity model and two single‐porosity models were calibrated separately to Br– and Cl– elution curves in the two columns.

Elution curves were almost identical for Br– and Cl– under initially wet conditions, whereas the displacement of Br– was faster than that of Cl– in the initially dry column, indicating rapid transport with preferential flow. Only the dual‐porosity model described the long‐tailing breakthrough of Cl– in the initially dry column adequately. The parameter values giving acceptable fits for ‘Br dry’ were not compatible with the description of the three other elution curves, which could be adequately modelled with a single set of parameter values.

The estimated set of common parameters was validated by comparing with the elution curves of deuterium water, nitrate and sulphate, as well as with resident tracer concentrations at four depths. The results showed that solutes can be displaced much faster when applied at the surface of initially dry soil than when applied to wet soil or when resident in the soil matrix. The simulation results suggest that solute transport under initially dry conditions was governed by preferential flow of infiltration water through macropores by‐passing the matrix due to shrinkage cracks and water repellence of matrix surfaces.
Three‐dimensional trajectories of 60Co‐labelled earthworms in artificial cores of soil
Authors: Capowiez Y. , Renault P. , Belzunces L.
Published: March 2003

Information on earthworm burrowing behaviour is scarce and therefore the evolution of the macroporosity related to earthworm activities is still poorly known. We have designed a new apparatus, ‘Colonne Gamma’, to follow the three‐dimensional trajectories of radio‐labelled earthworms in artificial cores of soil. Earthworms are radio‐labelled by injecting into their coelomic cavity a small source of 60Co (volume 0.1 mm3, intensity 13.5 μCi). The emission of gamma rays is recorded by three detectors carried by a disc that oscillates vertically around the soil core where the earthworm is introduced. We have also developed a deterministic model to estimate the positions of the 60Co source from the number of gamma rays received by each detector during an oscillation. Numerical experiments showed that the uncertainties of estimates were less than 3 mm for each coordinate. To validate the results, we tracked the trajectory (one position every 4 minutes) of a radio‐labelled earthworm for 1 week and compared it with the skeleton of the macroporosity obtained by computer assisted tomography of the same soil core. There was a general qualitative agreement between the trajectory and the skeleton. Moreover, based on the precise study of the successive positions of the earthworm we could distinguish two different kinds of activities in the trajectory: displacement and digging events. The ‘Colonne Gamma’ apparatus therefore has great potential for studies of the ecology and the behaviour of earthworms.
Fate of microbial residues in sandy soils of the South African Highveld as influenced by prolonged arable cropping
Authors: Amelung W. , Lobe I. , Du Preez C. C.
Published: March 2003

Long‐term cultivation of former grassland soils results in a significant decline of both living and dead microbial biomass. We evaluated the effect of duration of cropping on the preservation of fungal and bacterial residues in the coarse‐textured soils of the South African Highveld. Composite samples were taken from the top 20 cm of soils (Plinthustalfs) that have been cropped for periods varying from 0 to 98 years in each of three different agro‐ecosystems in the Free State Province. Amino sugars were determined as markers for the microbial residues in bulk soil and its particle‐size fractions. Long‐term cultivation reduced N in the soil by 55% and the contents of amino sugars by 60%. Loss rates of amino sugars followed bi‐exponential functions, suggesting that they comprised both labile and stable fractions. With increased duration of cropping the amino sugars attached to silt dissipated faster than those associated with the clay. This dissipation was in part because silt was preferentially lost through erosion, while clay particles (and their associated microbial residues) remained. Erosion was not solely responsible for the reduction in amino sugar concentrations, however. Bacterial amino sugars were lost in preference to fungal ones as a result of cultivation, and this effect was evident in both silt‐ and clay‐sized separates. This shift from fungal to bacterial residues was most pronounced within the first 20 years after converting the native grassland to arable cropland, but continued after 98 years of cultivation.
Seasonal and between‐year variations of fish populations in the middle Thames estuary: 1980–1989
Authors: ARAUJO  , BAILEY  , WILLIAMS
Published: March 2003

Fish samples collected at the cooling water intake screens of West Thurrock power station located 35.5 km downstream of London Bridge on the Thames estuary during the decade 1980–1989 were analysed. Seasonal and long‐term changes in the abundance of the 15 most numerous fish species and in several fish community parameters were analysed. The majority of species were highly seasonal in their distribution and abundance. Species diversity was lower in the summer (May–August) compared with spring/winter (October–February). Evidence of long‐term changes in species diversity and community structure over the decade is presented. The changes were consistent with a period of relative stability (1980–1984) followed by a period of change (1985–1989) and may reflect a deterioration in water quality in the second quinquennium. It is argued that the monitoring of fish communities in estuaries should be based on a multi‐metric approach as no single indicator alone can describe the complex community structure.
Effects of forestry clear‐cutting on numbers and sizes of brook trout, Salvelinus fontinalis (Mitchill), in lakes of the Mastigouche Wildlife Reserve, Québec, Canada
Authors: BÉRUBÉ  , LÉVESQUE
Published: March 2003

Brook trout, Salvelinus fontinalis (Mitchill), angling data, collected between 1971 and 1991, were analysed before, during, and after logging operations for 20 lakes located within 200 m of a clear‐cutting area and 16 reference lakes undisturbed by logging. The mean weight of catches by anglers remained unchanged over the three periods, while catches per unit of effort (CPUE) and biomass per unit of effort (BPUE) decreased, respectively, by 18% and 22% after clear‐cutting. These changes reflected a significant modification in population dynamics probably caused by logging operations. Results indicated that the negative impacts on aquatic fauna were felt more strongly on water bodies located in watersheds where deforestation was more severe; CPUE was inversely correlated with a cumulative cutting index (CI) developed from physiographic parameters. An increasing interannual trend of the spring‐flood discharge in the order of 8% was noted. It was hypothesized that this increase might damage spawning and nursery habitats, hence affecting recruitment and offering a possible part of the explanation for the variations in fishing success. The cause‐to‐effect links and the mechanisms associated with changes affecting fish populations following deforestation remain to be clarified.
Genetic population structure of goldsinny wrasse, Ctenolabrus rupestris (L.), in Norway: implications for future management of parasite cleaners in the salmon farming industry
Authors: SUNDT R. C. , JØRSTAD K. E.
Published: March 2003

The application of goldsinny wrasse, Ctenolabrus rupestris (L.), as parasite cleaners in the salmon farming industry has led to transport of live wrasse between regions in Norway. Owing to the operation of salmon farms, some of the transferred wrasse escape from the salmon net pens and can therefore mix and potentially interbreed with the local populations. The genetic effects of such interbreeding are unknown and information about the genetic population structure of this species in Norwegian inshore waters is needed to evaluate the potential effects. A genetic study based on polymorphic tissue enzymes was therefore carried out. Four of the 35 protein coding loci screened were polymorphic at the 99% level, and only two at the 95% level. The allele frequencies of the IDDH‐1*; PGM‐1*; GPI‐1* and GPI‐2* loci were compared in wrasse samples (1442 specimens) collected at 12 localities. Significant differences were found for PGM‐1* among the samples collected at two inner fjord localities. Significant differences at the IDDH‐1*, PGM‐1* and GPI‐2* loci were found when data from a sample of transferred wrasse caught in southern Norway were compared with local wrasse in the recipient areas.
A low‐budget and versatile radiotracking system
Authors: COHEN M. A.
Published: March 2003

Abstract Radiotracking equipment was constructed for a study of the black piranha, Serrasalmus rhombeus (Linneaus), in the 2.6‐km‐long oxbow lake Coco Cocha, South‐East Peru, during the dry season of 1995. Twenty, 2.5‐g transmitters were constructed with a range in air of 300 m and a longevity of approximately 2 months. Detection was accomplished by a collapsible 250‐g Yagi and a modified AOR™ AR8000 scanner. This was achieved on a budget of less than $1000. Despite initial problems with transmitter reliability, nearly 400 h were spent on the lake over a 5‐month period and useful range and activity data were collected.
Influence of environmental factors on the density and biomass of stocked brown trout,Salmo truttaL., parr in brooks affected by intensive forestry
Authors: JUTILA E. , AHVONEN A. , LAAMANEN M.
Published: March 2003

Abstract The influence of environmental factors on the density and biomass of stocked brown trout,Salmo truttaL., parr was studied in brooks subjected to intensive forestry in the Isojoki river basin, western Finland. Multivariate regression analysis showed that 69% of the variation in the population density of parr was determined by five variables: (1) mean water depth; (2) the abundance of pools; (3) stony bottom substrates with stones sized between 2 and < 10 cm in diameter; (4) undercut banks; and (5) the percentage of shading by trees. Correspondingly, 57% of the variation in the biomass of parr was determined by three variables: (1) mean water depth; (2) the abundance of pools; and (3) benthic vegetation. Dredging of the brooks and forest ditching had the most harmful consequences for the nursery habitats of brown trout parr. Measures for the rehabilitation of brown trout production in these brooks are discussed.
Response of resident brown trout, Salmo trutta L., and rainbow trout, Oncorhynchus mykiss (Walbaum), to the stocking of hatchery‐reared brown trout
Authors: Weiss S. , Schmutz S.
Published: March 2003

Two strains of hatchery‐reared adult brown trout, Salmo trutta L., [208–334 mm total length (TL); n=  591] were individually marked and released into a limestone stream. The estimated survival after one month (86%; n=  508) was comparable to that for resident brown trout and rainbow trout, Oncorhynchus mykiss (Walbaum), (89%; n=  771), but declined to 14% (n=  83) after 8 months compared with 52% (n=  451) for resident trout. The movement of resident trout out of stocked stretches was higher (14%) than from control sites (5%), but the population size in both individual sites and the overall study area were unaffected. The growth of resident brown trout was unaffected by stocking, but rainbow trout showed lower growth rates in stocked versus unstocked stretches both one and 8 months after stocking (P <  0.002).
Water use and conservation for inland aquaculture ponds
Authors: Boyd C. E. , Gross A.
Published: March 2003

The general hydrological equation, inflow = outflow ± change in storage, can be used to make accurate estimates of water use by ponds for inland aquaculture projects. The primary inflows are precipitation, runoff and regulated water additions. The main outflows are evaporation, seepage, overflow after storms and intentional discharge. Water conservation measures such as maintaining storage capacity in ponds equal to the normal, maximum daily precipitation, reduction in seepage beneath dams and through pond bottoms, fish harvest without draining ponds, and water re‐use are discussed. Even with the implementation of water conservation measures, pond aquaculture is a water‐ intensive endeavour which consumes more water per unit of area than irrigated agriculture. However, the value of aquacultural production per unit of water used greatly exceeds that of irrigated agriculture. Reduction in effluent volume is the most effective water saving means, and not only reduces water consumption but also reduces the pollution potential of pond aquaculture.
Aquaculture–agriculture systems integration: an Australian prospective
Authors: Ingram B. A. , Gooley G. J. , McKinnon L. J. , De Silva S. S.
Published: March 2003

The concept of integrating aquaculture with irrigated farming systems was evaluated in three projects in the Goulburn–Murray Irrigation District (GMID) in south‐eastern Australia. (1) Semi‐intensive cage culture trials using silver perch, Bidyanus bidyanus (Mitchell), were undertaken in a range of irrigated farming systems: irrigation supply channels; groundwater supplies; and on‐farm storage dams. Survival and growth of fish under these conditions were comparable to fish reared in conventional aquaculture ponds. However, poor water quality at some sites reduced survival and growth. (2) A study was undertaken to assess the feasibility of the cage culture of silver perch and rainbow trout, Oncorhynchus mykiss (Walbaum), in three irrigation water storage reservoirs. Conditions within each reservoir, particularly water quality, wind and wave action, and cage fouling, varied considerably, and influenced fish growth and survival. (3) Mariculture trials were undertaken in two saline groundwater evaporation basins, which were part of an integrated agriforestry and salt reclamation system. The species tested included two oyster, two prawn and nine fish species. Some species exhibited exceptional survival and growth rates under trial conditions. These projects indicate that the concept of integrating aquaculture with existing irrigated farming systems has the potential to enhance productivity, water use efficiency and overall environmental sustainability in the GMID.
The fishery of the Ea Kao reservoir, southern Vietnam: a fishery based on a combination of stock and recapture, and self‐recruiting populations
Authors: Phan P. D. , De Silva S. S.
Published: March 2003

The present paper describes the fishery of the Ea Kao reservoir in south Vietnam. Historical data on the total production and total numbers of fish stocked were available from 1983 to 1996, and this information, together with the results of monthly monitoring of the fishery from June 1996 to December 1998, was used in the present study. A number of gears are used in the Ea Kao fishery, the most important being gill, lift and integrated nets, and beach seines. The fishery of Ea Kao is based on the annual stocking of advanced fry/early fingerlings of 0.3–1.0‐g bighead carp, Hypophthalmichthys nobilis (Richardson), silver carp, Hypophthalmichthys molitrix (Cuvier & Valenciennes) and rohu, Labeo rohita Hamilton, as well as the self‐recruiting indigenous species Toxabramis houdemeri Pellegrin and two exotic species, i.e. Nile tilapia, Oreochromis niloticus (L.), and common carp, Cyprinus carpio L. On average, the regularly stocked species contribute to 78% of total production, which has been around 400–450 kg ha−1 in the last few years. The monthly peak catches of stocked species tend to coincide with the rainy season from May to October and the catches of self‐recruiting species peak between February and April. A significant relationship (P < 0.001) exists between the stocking density in year n (SD, n ha−1) and the yield of stocked fish in year n+ 1 (Y, kg ha−1):
Population genetic studies of hilsa shad, Tenualosa ilisha (Hamilton), in Bangladesh waters: evidence for the existence of separate gene pools
Authors: Rahman M. , Nævdal G.
Published: March 2003

Hilsa shad, Tenualosa ilisha (Hamilton), in Bangladesh is found in inland rivers, estuaries and the marine environment, throughout the year, but the peak catch period is during upstream migration. Tissue (white muscle, liver, brain) samples (total 640 specimens) were collected from three different localities, representing marine, brackish and fresh water, during the monsoon in the summer of the years 1993–1996 to identify genetic markers and study the population structure of this species. The samples were analysed by starch gel electrophoresis and isoelectric focusing, and stained for 15 enzymes and general muscle proteins. Only phosphoglucomutase, aspartate amino transferase, esterase and unidentified muscle proteins were found to be polymorphic. The allele frequencies for the samples collected in the marine environment deviated from corresponding samples from freshwater and estuarine localities, indicating that hilsa shad in Bangladesh waters comprise more than one gene pool.
Escaped farmed salmon, Salmo salar L., in the Glenarm River, Northern Ireland: genetic status of the wild population 7 years on
Authors: Crozier W. W.
Published: March 2003

A previous study described genetic changes in a wild Atlantic salmon, Salmo salar L., population resulting from the spawning of escaped farmed salmon in the Glenarm River, Northern Ireland, in 1990. This study reports an extension of the original investigation with a further follow‐up sample that was taken from the river in 1997 to assess the genetic status of the wild population two generations after the original hybridization between the wild population and the farmed strain. Overall genetic variation across eight polymorphic allozyme loci indicated that the wild population remains significantly different from the pre‐escape population and from the immediate post‐escape population, the presence of an allele not having been previously detected in this population (GPI‐1,2*140), suggesting that further incursion(s) of farmed salmon may have taken place.
Estuarine fishes in two large eastern Australian coastal rivers—does prawn trawling influence fish community structure?
Authors: West R. J. , Walford T. R.
Published: March 2003

Fish communities were sampled quarterly over a 2‐year period at sites along the estuarine gradient of two large coastal rivers, the Richmond and Clarence, located in eastern Australian (NSW). A total of 175 582 fish from 73 species was captured, with two species making up 65% of this total. Many fish species of economic importance in local coastal waters were captured, predominantly as juveniles. Multivariate analysis revealed three significantly different groupings of sites corresponding to the marine, brackish and tidal‐freshwater zones of the two rivers. The two rivers were remarkably similar in terms of overall abundance and diversity of fish, and structuring of fish communities, despite a large‐scale and intensive prawn trawling industry operating on the Clarence River. Dependency of fishes on estuarine habitats and the distribution of some of the dominant fish species in relation to estuarine gradients are discussed.
Patterns of drift and power station entrainment of 0+ fish in the River Trent, England
Authors: Carter K. L. , Reader J. P.
Published: March 2003

Entrainment of 0+ riverine fish (mostly pelagic cyprinids) by a power station intake, and down‐river drift over a nearby weir, followed the same pattern, occurring throughout the year and being greatest during the night in the first weeks of life (i.e. in summer), reaching a peak shortly after dusk. Entrainment and drift of benthic species, and of fish older than 0+, were negligible. Mortality following entrainment was 100%. Impingement of fish on the intake screens was negligible, probably because individuals larger than the screen mesh were able to escape the intake current. The species composition and length‐frequencies of the drifting fish, but not their overall abundance, showed some variation with distance from the river margin. It is argued that the fish vulnerable to entrainment are those 0+ individuals which are dispersing in the river by drifting.
Length‐based Beverton and Holt spawning stock biomass per‐recruit‐models, with application to theLates stappersii(Boulenger) stock in Lake Tanganyika
Authors: Munyandorero J.
Published: March 2003

Two kinds of length‐based Beverton and Holt spawning stock biomass per‐recruit (SSB/R)‐models are presented. The first allows the computation of the absolute value ofSSB/R. The second estimates the index ofSSB/R, also called ‘relativeSSB/R’. Both models are extensions of the original age‐based Beverton and HoltSSB/R‐models. TheSSB/Rand its index can be assessed with reference to variations in the exploitation characteristics. These models were applied to theLates stappersii(Boulenger) stock in Lake Tanganyika using fishing mortality as the independent variable. They produce an absolute value ofSSB/Rof 12.95 g, representing 22.4% of that of the ‘virgin’ stock for the 1993–1994 equilibrium‐fishing regime. This level is indicative of an unsafe state of the stock in question. Moreover, the SSB forL. stappersiiseems to be fragile under increased fishing pressure as, for example, doubling or tripling the current fishing regime would reduce the currentSSB/Rby 57.3 and 77.4%, respectively. In general, the use of length‐based Beverton and HoltSSB/R‐models is handicapped by underlying hypotheses and sub‐models which are restrictive.
Diel variation in the seagrass ichthyofaunas of three intermittently open estuaries in south‐eastern Australia: implications for improving fish diversity assessments
Authors: Griffiths S. P.
Published: March 2003

Diel variation in the ichthyofaunas associated with Zostera capricorni Ascherson was investigated in three intermittently open estuaries in the Illawarra region, New South Wales. Each estuary showed differing diel shifts in fish assemblages, which appeared to be related to estuary size. In the largest estuary (Lake Illawarra) significantly more species were caught during the night than the day for all months. In contrast, there was little diel variation in the fish assemblages at Werri Lagoon and Shellharbour Lagoon, although many species were only caught during the night at both estuaries. The distinct diel changes at Lake Illawarra was thought to be attributable to the relatively deep channels adjacent to the seagrass beds which are better habitats for larger fishes compared with the shallow sand bars without deep channels throughout the two smaller estuaries. The composition of fish species within the three estuaries were significantly different, although each assemblage was characterised by large numbers of small‐sized fish (<100 mm FL) indicating the importance of intermittently open estuaries as fish habitats. It was concluded that night sampling provided a more complete picture of the ichthyofaunas associated with Z. capricorni. As a result, inclusion of night sampling in fish diversity assessments would increase the chance of catching diurnally rare species and therefore attain a better representation of the true community structure.
Comparison of exploited and unexploited yellow perch Perca flavescens (Mitchill) populations in Nebraska Sandhill lakes
Authors: Paukert C. P. , Willis D. W.
Published: March 2003

Exploitation can have a pronounced effect on fish populations. Yellow perch, Perca flavescens (Mitchill), populations in Nebraska Sandhill lakes were sampled in 1998 and 1999. Three of the 29 lakes containing yellow perch have been closed to fishing for at least 10 years. Unexploited yellow perch populations had fast growth rates, but age structure was similar to exploited populations. For unexploited lakes combined, mortality and condition were not different from exploited lakes. However, one unexploited lake, Marsh Lake, had the fastest growth, highest proportion of older fish and highest condition of all populations sampled. This lake had low interspecific competition and high invertebrate abundance, which likely resulted in fast growth and high condition. However, size structure and growth were also related to lake productivity. Although exploitation may affect yellow perch populations, other factors (food availability, predators and lake productivity) also play an important role in structuring these populations. Regardless, these results indicate the potential of yellow perch in Nebraska Sandhill lakes given no exploitation.
Use of GIS to predict effects of water level on the spawning area for smelt, Retropinna retropinna, in Lake Taupo, New Zealand
Authors: ROWE D. K. , SHANKAR U. , JAMES M. , WAUGH B.
Published: March 2003

A GIS model of the littoral bathymetry and substrate composition of Lake Taupo was created using ArcInfo. Littoral substrates were mapped by aerial photography and confirmed by ground‐truthing. Water depths were determined by echosounding linked to a differential GPS. These data were imported into ArcInfo where a 3D GIS model was used to calculate the total area of smelt, Retropinna retropinna Richardson, spawning habitat (i.e. clean sand between depths of 0.5–2.5 m) at each of five lake levels. There was little change in area over the first 50 cm below the natural maximum lake level, but spawning habitat decreased rapidly over the next 1.4 m such that a 30% reduction occurred at the natural minimum level. Anecdotal information on inter‐annual variations in lake level and smelt abundance supported the notion that high lake levels in spring result in high recruitment of smelt. The GIS model also predicted effects of lake level change on areas of macrophyte cover and on other littoral substrates, and could be used to assess effects of lake level changes on the habitats of other biota.
Assessing the abundance and distribution of eggs of sardine, Sardinops sagax, and round herring, Etrumeus whiteheadi, on the western Agulhas Bank, South Africa, using a continuous, underway fish egg sampler
Authors: LINGEN C.D. VAN DER , CHECKLEY JR  , BARANGE  , HUTCHINGS  , OSGOOD
Published: March 2003

A continuous, underway fish egg sampler (CUFES) was employed to assess the abundance and distribution of eggs of both sardine, Sardinops sagax, and round herring, Etrumeus whiteheadi, on the Western Agulhas Bank, South Africa, during September 1996. Samples were collected while underway along six inshore/offshore transects, and at stations along the transects. Volumetric estimates of egg density (eggs m−3) from on‐station CUFES samples were highly correlated with both volumetric and areal (eggs m−2) estimates of egg density from samples collected from CalVET net hauls at these stations, demonstrating the validity of this novel sampling technique. Sardine and round herring eggs were encountered in a band running parallel to the coast and extending from 10 to 30 nautical miles offshore to the shelf edge, and highest egg densities were associated with strong north‐west‐flowing currents in the region of the shelf edge. Collecting samples while underway increased the precision of the estimate of mean egg density for sardine eggs but not for round herring eggs. The use of CUFES in obtaining a fine‐scale resolution of sardine egg distribution, and as a tool for stock assessment, are discussed.
Simulations of the Black Sea pelagic ecosystem by 1‐D, vertically resolved, physical–biochemical models
Authors: OGUZ TEMEL , DUCKLOW HUGH W. , MALANOTTE‐RIZZOLI PAOLA , MURRAY JAMES W.
Published: March 2003

The present paper summarizes the results of several simulations of the central Black Sea pelagic food web using three different 1‐D, physical–biochemical, water column process models. The most simplified, five‐compartment version is used to explore the robust biological features of the ecosystem and the role of upper‐layer physics on the evolution of the euphotic zone biological processes. The other models, introducing additional biological complexities, show how these biologically structured models become more capable of simulating intensified subsurface summer production, more dynamic plankton structure arising after the increasing role of gelatinous carnivores in the ecosystem during the 1980s, and fairly sophisticated nitrogen cycling in the water column.
Modelling the dispersal of larval Japanese sardine, Sardinops melanostictus, by the Kuroshio Current in 1993 and 1994
Authors: HEATH M. , ZENITANI H. , WATANABE Y. , KIMURA R. , ISHIDA M.
Published: March 2003

Acoustic Doppler current profiler (ADCP) data collected during routine monitoring surveys of the distribution and abundance of Japanese sardine larvae (Sardinops melanostictus) off the Pacific coast of Japan in February 1993 and 1994 were used to construct stationary average flowfields for three levels in the upper 100 m in each year. No large‐scale meanders in the path of the Kuroshio Current were present in either year, but the axis of the current was closer to the coast in 1993 than in 1994. The flowfields were used to drive a particle‐tracking model representing the dispersal of sardine eggs and larvae. Particles were released in accordance with the observed distribution of eggs, and their positions tracked for up to 40 days. In 1993, the model indicated that ≈ 50% of the egg production was carried north‐eastwards out of the survey area into the area of the NW Pacific referred to as the Kuroshio Extension Zone. In contrast, only 5% of the egg production was exported to the Extension Zone in 1994, the remainder being retained in Japanese coastal waters. The consequences of the different dispersal patterns are discussed in relation to subsequent recruitment to the sardine stock. Based on commercial catch data, survival of the 1993 year class was 15% of that for the 1994 class. Hence, the results indicate that export of larvae to the Kuroshio Extension cannot in itself lead to successful recruitment.
Searching for sensitivity in the life history of Atlantic menhaden: inferences from a matrix model
Authors: Quinlan  , Crowder
Published: March 2003

We used modified Leslie matrix models to explore the life history of Atlantic menhaden (Brevoortia tyrannus). By examining the sensitivity of long‐term population growth rates to changes in vital rates, we identified those life history components which can cause large population level responses. Our models subdivide the first year of life into five stages (eggs, early larvae, late larvae, juveniles, and ‘peanuts’ or subadults), and population growth rate responds most strongly to changes in juvenile and late larval stages. The relative ranking between these stages is dependent on the magnitude of mortality during the prejuvenile stages relative to juvenile mortality. An examination of low‐level model parameters indicates that the population growth rate is influenced by the growth and mortality rates during the time when young‐of‐the‐year menhaden are gaining access to and residing in the estuaries. Sensitivity to changes in many adult metrics, such as fishing mortality, were relatively low. We conclude that a better understanding of biotic and abiotic factors that influence the late larval and juvenile stages will further our understanding of population dynamics in this species.
The 1882 tilefish kill — a cold event in shelf waters off the north‐eastern United States?
Authors: MARSH ROBERT , PETRIE BRIAN , WEIDMAN CHRISTOPHER R. , DICKSON ROBERT R. , LODER JOHN W. , HANNAH CHARLES G. , FRANK KENNETH , DRINKWATER KEN
Published: March 2003

A mass mortality of `warm‐water' tilefish in the Middle Atlantic Bight between April and August of 1882 suggests an episode of extreme cold in the shelf waters off the north‐eastern United States. This cooling is hypothesized to be a consequence of enhanced equatorwards transport of cold water in the Labrador Current, coincident with a minimum in the North Atlantic Oscillation (NAO) index during the early 1880s.

Although there is little direct evidence for this historical event, an analogue for the 1880s cooling is found in the 1960s, at the most recent NAO‐index minimum. Post‐1945 observations in the Middle Atlantic Bight / Gulf of Maine region reveal changes in winter baroclinic circulation between cool and warm decades, with greater equatorward penetration of south‐westwards flow along the shelf‐edge during the cool 1960s. Over the period 1934–77, the NAO is found to account for 17% of the interannual variance in Labrador Current transport around the Grand Banks.

Proxy evidence for the cold episode of the early 1880s is sought. Records of bottom temperature in the Middle Atlantic Bight region are reconstructed using stable oxygen isotopic analysis on the annual bands of shells of a bivalve mollusc (Arctica islandica) and an empirical model of covariability with local air temperature. The result is confirmation of the presence of anomalously cold water during the early 1880s.
Spatial variability in red sea urchin (Strongylocentrotus franciscanus) recruitment in northern California
Authors: Morgan Lance E. , Wing Stephen R. , Botsford Louis W. , Lundquist Carolyn J. , Diehl Jennifer M.
Published: March 2003

To better understand the spatial distribution of recruitment in the northern California red sea urchin (Strongylocentrotus franciscanus) population, we sampled size distributions at each of 12 locations in 1995 and 1996, two of those locations in 1994, and 5 of those locations in 1997. An index of recent recruitment in these size distributions and an estimate of density of recent recruitment reflect a similar spatial pattern of recruitment. This pattern appears to be determined by the effect of coastal circulation on larval delivery during relaxation of upwelling, and not the result of the positive effect of the adult spine canopy on juvenile survival. Recent recruitment of red sea urchins in northern California is higher in areas more frequently subjected to onshore and poleward flow during relaxation of upwelling. These results are consistent with a mechanism by which alongshore spatial variability in southward, offshore flow during upwelling winds allows larvae to maintain latitudinal position, whereas flows during event‐scale relaxations in upwelling winds serve to distribute settling larvae alongshore, favouring areas north of promontories. The consequent spatial pattern of red sea urchin settlement varies from year to year, and there are not yet sufficient data to demonstrate the degree to which this spatial pattern in recruitment determines a spatial pattern in fishable adult abundance.
Life cycle of Crangon crangon in the North Sea: a simulation of the timing of recruitment as a function of the seasonal temperature signal
Authors: Temming Axel , Damm Ulrich
Published: March 2003

The brown shrimp C. crangon supports a large commercial fishery in British, Belgian, Dutch, German and Danish waters. It produces eggs throughout the year with two seasonal peaks in summer and winter, respectively. Uncertainty exists with regard to the relative importance of the two egg production seasons for the mass invasion of juvenile recruits of 10–20 mm length in May/June, which is the dominant seasonal signal in the German and Dutch Wadden Sea, and which is presumed to grow into the exploitable stock by the autumn, causing the typical rise of commercial catches at that time of the year. A simulation model was developed that predicts the daily abundance of juvenile recruits attaining a given length, typically in the range of 10–20 mm. The model uses: (i) experimental data on the development times of eggs and larvae and the growth rates of juveniles; (ii) field data on the seasonal temperature cycle in different years (1986, 1992 and 1993 or mean conditions) and areas (German and Dutch Wadden Sea) of the North Sea; and (iii) a calculated index of the relative seasonal egg production intensity of adult C. crangon. Predictions of the simulations are compared with field observations on the seasonal occurrence of juvenile recruits in the German and Dutch Wadden Sea. Using temperature data from German waters, in the simulations peak recruitment was predicted to occur 1–2 months later than that observed in the field. However, if seasonal temperature data from Dutch waters were used, the predicted time of the first mass occurrence of recruits matched the field observations more closely. Simulations revealed that the first mass invasion of juveniles originates almost entirely from the winter egg production. It was also found that the simulated recruitment is condensed into a peak, which is narrower after a cold winter.
Comparison of euphausiid population size estimates obtained using replicated acoustic surveys of coastal inlets and block average vs. geostatistical spatial interpolation methods
Authors: Romaine Stephen J. , Mackas David L. , Macaulay Michael C.
Published: March 2003

Because of their intense patchiness, euphausiid spatial distributions and stock sizes are often assessed using echosounder surveys. However, statistical error bars appropriate for individual survey results are not well known. We quantified these by examining the statistical repeatability of acoustic estimates of total euphausiid biomass within two enclosed fjords adjoining the Strait of Georgia, British Columbia. Within each inlet, paired and replicated `mirror image' zig‐zag survey tracks provided sets of closely spaced backscatter profiles along the survey lines. Local stock density (biomass per unit area) was calculated by vertical integration across the euphausiid scattering layer. Total inlet population size was then estimated by horizontal interpolation and integration of the local measurements, both by block averaging and by geostatistical interpolation (kriging). By assuming no change in true population biomass over the short time interval separating replicate surveys, we could then estimate statistical precision by analysis‐of‐variance comparison among replicate survey grids. For the partial surveys (one or the other half of the mirror‐image paired grid) multiplicative error bars were about a factor of 1.5 for Jervis Inlet and 1.7 for Saanich Inlet. Use of the full surveys (both parts of the mirror‐image pair, roughly doubling the number of measurements in each estimate) reduced the error to about factor of 1.35 for Jervis but only to about 1.65 for Saanich. Statistical precision was similar for the block average vs. kriging interpolation and integration methods, however, kriging provided additional useful information about spatial pattern within the inlets.
A spatial model of population dynamics of the early life stages of Japanese sardine, Sardinops melanostictus, off the Pacific coast of Japan
Authors: Suda Maki , Kishida Tatsu
Published: March 2003

We constructed a numerical model reproducing the transport, survival and individual growth of the early life stages of Japanese sardine, Sardinops melanostictus, off the Pacific coast of Japan during 1978–93. The causes of early life stage mortality, including the influence of the effects of the spatial relationship between the spawning grounds and the Kuroshio on the mortality rate, were investigated. Survival and transport from egg stage to 60 days after spawning were modelled daily in a 1 × 1 degree mesh cell and individual growth in the period was modelled in each region (Kuroshio, Inshore, Offshore and Transition regions). Individual growth and survival from 60 to 180 days after spawning were modelled daily in the Transition region. Environmental data were taken from outside the model system. Our simulation indicates that survival variability in the larval stage (5–25 mm in standard length) is the key factor in determining the year‐class strength. The simulation revealed that strong year classes occurred with good survival in the spawning ground and whilst entrained in the Kuroshio current being transported to the main feeding grounds in the Transition region. The simulation also indicated that survival rates in 1988–93 were low in the Inshore, Kuroshio and Offshore regions, which depressed the year‐class strength during that period.
Can ingested cyanobacteria be harmful to the signal crayfish (Pacifastacus leniusculus)?
Authors: Lirås Vibeke , Lindberg Magdalena , Nyström Per , Annadotter Heléne , Lawton Linda A. , Graf Brigitte
Published: March 2003

1. A sample of adult signal crayfish were taken from a pond with a hepatotoxic bloom of the benthic cyanobacterium Oscillatoria sancta. Cyanobacteria were found in the stomachs of thirty‐one out of thirty‐two crayfish examined.

2. To examine the effect of hepatotoxic cyanobacteria on crayfish a 14‐day feeding trial was carried out with thirty‐six animals. There were three treatments: (i) hepatotoxic and (ii) non‐toxic Planktothrix agardhii; and (iii) crayfish pellets as a control.

3. High‐performance liquid chromatography (HPLC) showed that microcystins (the toxins of P. agardhii) had accumulated in the hepatopancreas of 50% of the animals in the toxic treatment.

4. The cyanobacteria did not appear to have any negative impact on the crayfish. All crayfish survived, remained motile and ate throughout the experiment.

5. During the experiment blood samples were taken and the total number of haemocytes counted. At the end of the experiment glucose concentration and relative wet weight of the hepatopancreas were measured. No differences between crayfish fed on toxic and non‐toxic P. agardhii and the controls were found.

6. The fact that microcystin accumulates in the crayfish hepatopancreas indicates that the toxin may be transferred further up the food chain.