bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of prolonged arable cropping on lignin compounds in sandy soils of the South African Highveld
Authors: Lobe I. , Du Preez C. C. , Amelung W.
Published: March 2003

The preservation of plant residues is important for sustainable arable cropping. Lignin is a marker for plant residues in soils. We have investigated influences of the length of cultivation on the dynamics of lignin. Composite samples were taken from the top 20 cm of soils that have been cropped for periods varying from 0 to 98 years in each of three different agro‐ecosystems in the Free State Province of South Africa. Lignin‐derived phenols were determined in the <2 µm (clay), 2–20 µm (silt), 20–250 µm (fine sand) and 250– 2000 µm (coarse sand) size separates. With increasing length of cultivation, the concentration of such phenols decreased to 36% of that in the grassland. The lignin contents as proportions of the total carbon did not change during cultivation, suggesting that there was no selective enrichment of lignin moieties as C was lost as a result of cultivation. The loss rate constants of lignin concentrations in particle‐size fractions increased in the order clay (0.17 year−1) ≤ silt (0.18 year−1) < fine sand (0.20 year−1) < coarse sand (0.22 year−1). Increasing ratios of phenolic acids to aldehydes in bulk soil, silt and fine sand fractions with increasing length of cultivation indicated that side chains were being oxidized. The ratios in the silt fraction, however, decreased after 10–20 years. We attribute this to a loss of lignin together with silt by wind erosion, resulting in a rejuvenation of lignin compounds in the remaining silt‐sized pools of C.
Depletion of soil phosphorus as assessed by several indices of phosphorus supplying power
Authors: Yli‐ Halla M. , Hartikainen H. , Väätäinen P.
Published: March 2003

This study attempts to clarify the advantages and shortcomings of various laboratory tests that are used to characterize the status and dynamics of soil phosphorus (P). We analysed a set of soil samples differing in P status for inorganic P fractions, water‐soluble P (Pw60) and bicarbonate‐extractable P (POlsen) both before and after a pot experiment in which soil was depleted. Their P exchange characteristics were determined by Q/I plots, fitted by a modified Langmuir equation, and the supplying power was further assessed by extracting soil samples with various amounts of water. The sensitivity of the P tests in assessing the decrease in inorganic reserves of P was expressed using a response index that was defined as the ratio between the decrease in inorganic P and the decrease in soil P test value. For POlsen, the index ranged from 6 to 11 and for Pw60 from 10 to 26. Desorption curves obtained by extracting soil samples with different amounts of water indicate increased buffering power and that large reserves of P were released from soil in weak solutions (P < 0.030 mg l−1) around soil particles. Although the constants of the Langmuir equation responded reasonably well to the changes in reserves of P in the soil, the results suggest caution is needed in the quantitative interpretation of the constant Q0 (instantly labile P) of the Langmuir equation.
A re‐interpretation of ‘Aluminium solubility mechanisms in moderately acid Bs horizons of podzolized soils’ by Gustafsson et al.
Authors: Farmer V. C. , Lumsdon D. G.
Published: March 2003

Gustafsson et al. in a recent paper in this Journal reported the effects of adding HCl, AlCl3 and Si(OH)4 on the pH and concentrations of Al and Si in 1:1 soil:solution systems at three different temperatures, using samples of soil from an allophanic Bs horizon. Contrary to their conclusions, their observations are compatible with Al in the soil solution being in equilibrium with a proto‐imogolite allophane; it is neither necessary nor even plausible to postulate a hypothetical Al hydroxide. Concentrations of 0.2–0.4 mm Si in the equilibrated solutions at pH 5 could arise from an amorphous silica, probably phytoliths. They cannot come from the allophane.
An appraisal of stocking strategies in the light of developing country constraints
Authors: Cowx I. G.
Published: March 2003

Stocking, transfer and introduction of fish are commonly used to mitigate loss of stocks, enhance recreational or commercial catches, restore fisheries, or to create new fisheries. However, many stocking programmes are carried out without definition of objectives or evaluation of the potential or actual success of the exercise. The present paper describes a strategic approach to stocking aimed at maximizing the potential benefits. A protocol is discussed which reviews factors such as the source of the fish, the stocking density, the age and the size of fish at stocking, the timing of stocking, and the mechanism of stocking. Finally, the effects of social, cultural and economic constraints on the potential outcome of stock enhancement programmes are discussed.
Restriction of the circulation of small pleasure boats on the rivers of Wallonia, Belgium
Authors: Érard P. G. , De Bast B.
Published: March 2003

The regional authorities of the Walloon Region in the south of Belgium have regulated the circulation of pleasure boats, and kayaks in particular, so as to limit the conflicts between different uses of rivers (e.g. nature conservation, recreational fishing and canoeing). The regulation was enacted in 1994, using the federal law of 1973 on nature conservation as its basis. It was made necessary by the recent and important development of river‐based recreational activities and by the need to protect the aquatic environment, the rivers, and the associated fauna and flora. The limitations were determined according to season, flow and time of the day. Authorized types of boat are described in the present study, and the conditions of access to the embarkation and disembarkation sites along the rivers are set out. The limitations to canoeing were settled according to the river classification. Minimum flow rates were determined for rivers where the necessity for protection was the highest because of the very high activity of rented kayaks and the risk of overcrowding the river. An information system allows the kayak operators and the sportsmen to be informed daily on the possibilities for canoeing.
Aspects of fisheries and water resources management in England and Wales
Authors: Hughes S. , Morley S.
Published: March 2003

Freshwater fish populations in England and Wales form an important resource with up to 2.2 million anglers involved in the recreational fishery. The resource consists principally of indigenous and naturalised cyprinids, and strongholds of species endangered elsewhere in Europe. Each component is under pressure from a range of sources including water abstraction and climate change. Water resources are under significant pressure and droughts in parts of England and Wales exposed the fragility of water supply systems. Climate change is a major concern, driving a re‐assessment of water supply yields. There are no objective methods available to predict changes in fish communities likely to arise from different water resource management options, except for simple systems. It is difficult to manage water resources using anything other than a precautionary approach. Accurate assessment of environmental requirements are required to strike the right balance between the needs of aquatic ecosystems and of economic efficiency.
Possibilities for the integration of fish farming into irrigation systems
Authors: Fernando C. H. , Halwart M.
Published: March 2003

Harvesting fish in irrigation systems, sometimes involving some form of husbandry or even culture, is a practice which dates back at least two millennia. Although seldom recorded, it seems to have been widespread in the tropics and subtropics, especially in rice fields. In the present century, improved management for land‐based crops and the demands for the successful raising of aquatic organisms were not generally compatible, but with the advent of integrated crop protection, this situation has changed drastically. Moreover, irrigation systems using stored or diverted water have increased exponentially during the past 50 years, but fish farming within these irrigated systems has not expanded equally, and therefore, there is now a huge potential for this integrated enterprise. A systematic approach to fish farming development at irrigation system level which will make this integration a viable enterprise is proposed. The whole range of aquatic habitats created by irrigation systems can be integrated with fish farming. Small and large irrigation reservoirs, the extensive network of irrigation canals, the irrigated fields themselves, as well as adjacent ponds or aquatic refuges of various sorts are all potential sites for nursing or grow‐out of fish. In many countries, there is now relatively easy access to fish seed, even in inland areas. Permanent water bodies should be stocked with a central pool of culture species harvested from short‐lived habitats which serve as nurseries. A flexible system of moving culture fish within the system of habitats should be feasible. For example, stocking material for reservoirs can be obtained from irrigated rice fields where the short maturation period of the crop only permits the harvest of fingerlings. If a pragmatic and flexible approach is made to use all habitats for fish production, there could be a year‐round supply of fish and a minimum wastage of stocks of cultured fish. The use of high‐yielding fish of good quality is essential for economic viability. In areas where a high diversity of fish with a requisite biomass of desirable species already exists, these indigenous fish can be harvested, but their yields may only be adequate for low‐income rural areas. Common carp, Cyprinus carpio L., has traditionally been a preferred cultured species. Tilapia are proposed as an alternative because these fish are cheap to raise, give high yields and are also quite palatable. Aside from economic revenues, this type of integration also involves ecological and social benefits. High densities of fish in irrigation systems enhance the yield of land crops, alleviate the pressure of terrestrial and aquatic pests, and lower the populations of vectors of diseases of man and domestic animals.
Efficiency of capture of tench, Tinca tinca L. by trammel nets of monofilament and multifilament net twine combinations
Authors: Balik İ. , Çubuk H.
Published: March 2003

Efficiencies of different trammel net types on capture of tench, Tinca tinca L. were investigated in Lake Beyşehir in Turkey between April 1998 and August 1999. Nets with an inner wall of monofilament and outer walls of multifilament (type A) were more efficient than the other net types (type B, monofilament inner and outer walls; type C, multifilament inner wall and monofilament outer walls; and D, multifilament inner and outer walls). Type A nets were 2.08, 1.79 and 1.08 times more effective than the types D, C and B for catching tench. Monofilament inner walls of trammel nets were on average 1.85 times more effective than multifilament inner walls. No significant difference in catching efficiency of monofilament and multifilament outer walls was found (P>0.05). The average size of tench caught in monofilament trammel nets was higher than those caught in multifilament trammel nets, although not significantly different.
Combining fishery prohibition with stocking of landlocked salmon,Salmo salarL.: an effort to gain bigger yield and individual size
Authors: Hyvärinen P. , Sutela T. , Korhonen P.
Published: March 2003

After stocking landlocked salmon,Salmo salarL., in Lake Änättijärvi, all fishing was prohibited for 18 months to provide time for the fish to establish and reach a larger size prior to capture. The potential benefit of the fishery prohibition was severely diminished by emigration of the stocked fish down the watercourse to other lakes. Only 19% of the recaptures of Carlin‐tagged individuals came from Lake Änättijärvi. Also, the CPUE of test fishing in Lake Änättijärvi indicated a steep decline in the density of stocked fish during the fishery prohibition period. The mean weight of landlocked salmon in the combined recaptures from Lake Änättijärvi and other lakes downstream was 660 g. When fishing was not prohibited, the corresponding mean weight at recapture was 442 g. It is recommended that landlocked salmon stocking should be carried out in lakes with relatively low fishing pressure.
Artisanal fisheries in urban reservoirs: a case study from Brazil (Billings Reservoir, São Paulo Metropolitan Region)
Authors: Minte‐Vera C. V. , Petrere Jr M.
Published: March 2003

Billings Reservoir is an urban reservoir located in the São Paulo Metropolitan Region. It supports 101 active artisanal fishermen. To describe this fishery, landings were recorded daily between February 1996 and January 1997 at Colônia (23° 50′ 57′′ S; 46° 40′ 02′′ W). In every landing, a data collector recorded catch, effort, fishing gears and fishing grounds. A total of 147 593 kg of fish were recorded in 3515 fishing trips. The exotic Nile tilapia, Oreochromis niloticus (L.), was the main species exploited (81.4% of the annual catches). Five other species were also targeted: the characid Astyanax eigenmaniorum (Cope) (13.0% of the annual catches); the erythrinid Hoplias aff. malabaricus (Block) (2.1%); the exotic cyprinid Cyprinus carpio L. (Campos & Fernández‐Yépez) (2.4%); the curimatid Cyphocharax modestus L. (1.1%); and the pimelodid Rhamdia sp. (0.1%). Two main groups of fishermen were discriminated using Principal Components Analysis; these were associated with the type of fishing gear and fishing strategies, i.e. those who exploited Nile tilapia with cast nets and beating gill nets, and those who exploited other species with set gill nets. Management and maintenance of this fishery should consider the positive top‐down effects that Nile tilapia could have in controlling eutrophication and also the social benefits.
Fishway entrance modifications enhance fish attraction
Authors: Bunt C. M.
Published: March 2003

Two Denil fishways on the Grand River, Ontario, were monitored annually since 1994 for activity by several dozen fish species. Fishway entrances were enlarged and repositioned approximately 2 m closer to the weir face, in areas where fish were attracted by weir discharge. These simple modifications resulted in increased attraction efficiency for pumpkinseed, Lepomis gibbosus (L.). After modifications, annual relative rate of recapture was 39% (95% confidence interval [CI]=32–46%), representing a 2.6–3‐fold increase in fishway use relative to pre‐modification conditions. Median daily recapture rates also increased significantly from 0% at both fishways to approximately 2%. These results suggest that fishway entrances should be located as close to a dam or weir face as possible, but velocity barriers from spillway or tailrace discharge must not compromise access.
Developing ecologically acceptable river flow regimes: a case study of Kielder reservoir and the Kielder water transfer system
Authors: Gibbins C. N. , Soulsby C. , Jeffries M. J. , Acornley R.
Published: March 2003

Kielder Reservoir and the Kielder water transfer scheme have been operational since the early 1980s. The hydro‐ecological changes that occur in the River North Tyne and the River Wear as a result of Kielder operations are highlighted and release policy changes designed to minimize impacts on salmonid fish are described. The Kielder Reservoir release regime results in sudden and marked changes in flow in the North Tyne. These changes affect the availability of suitable habitat for newly emerged 0+ Atlantic salmon Salmo salar L. and potentially lead to the drying out of areas used for spawning. Physical Habitat Simulation (PHABSIM) models suggest that the reservoir compensation flow provides adequate habitat for older 0+ fish but limits the availability of spawning habitat. A seasonally variable compensation and hydroelectric power (HEP) release regime that limits impacts and increases suitable spawning and 0+ habitat is described. Transfers of water to the River Wear result in short‐term changes in the abundance of certain invertebrate species, although there is no evidence that the river’s invertebrate fauna has been permanently altered. Consequently, it is unlikely that fish are affected indirectly by transfers through reductions in the abundance of their invertebrate prey. Transfers allow abstractions for potable and industrial water supply to continue without breaching the river’s statutory Minimum Maintained Flow (MMF). The PHABSIM models suggest that this augmentation helps avoid the loss of salmonid habitat during summer dry periods. Simulation of the impacts of some alternative regimes indicates that salmonid habitat could be increased further but at the expense of natural flow and habitat variation. Research findings do not suggest the need for changes to the transfer release regime.
Upstream passage of fish through a vertical‐slot fishway in an Australian subtropical river
Authors: STUART I. G. , BERGHUIS A. P.
Published: March 2003

The effectiveness of a vertical‐slot fishway on the Burnett River barrage for facilitating migration of fish was assessed. In 100 samples taken at the top and bottom of the fishway, over 52 000 fish representing 34 species were collected at a maximum rate of 4500 fish per day. In contrast, less than 2000 fish ascended the original pool‐and‐weir fishway in 128, 24 h samples at the top between 1984 and 1987. Juvenile size classes dominated the abundance of many species in the present study and fish between 24 and 930 mm in length ascended the vertical‐slot fishway. However, passage of small fish was restricted and for new fishways on tidal barriers a further reduction in head loss between pools is recommended. Importantly, the width of the vertical‐slots was too small for effective upstream passage of large Queensland lungfish, Neoceratodus forsteri (Krefft). The greatest diversity of fish species was found during low river flows. The findings suggest that vertical‐slot fishways with wide pools and low turbulence pass a diverse range of fish fauna present in subtropical coastal rivers.
An evaluation of tropical brush and vegetation park fisheries
Authors: WELCOMME R. L.
Published: March 2003

Brush and vegetation parks are common features of many tropical river fisheries. Areas of branches of certain tree and bush species combined with floating vegetation are placed in shallow, sheltered water so as to attract fish. They provide cover and spawning areas for many fish species. They are particularly rich trophically because of the abundance of epiphytic organisms, boring insects and molluscs on the submerged surfaces of the wood and the root systems, and because of the enriched bottom mud caused by decay of the woody material. Yields depend on the amount of woody material used and the age of the park. The economics of their operation can be complex and larger structures rely on a high degree of social organization for their installation and fishing. Fish parks are controversial in many areas, being viewed as an extractive method of fishing, a source of siltation and creator of social inequalities. However, when properly managed very high yields per unit area can be obtained and the structures can change from simple fish attracting devices to a form of aquaculture whereby net production from a river or lake can be increased.
Importance of instream cover for young masu salmon, Oncorhynchus masou, in autumn and winter
Authors: MIYAKOSHI Y. , HAYANO H. , OMORI H. , NAGATA M. , IRVINE J. R.
Published: March 2003

Densities of wild masu salmon, Oncorhynchus masou Brevoort, were investigated before (late‐September) and after (mid‐November) autumnal habitat shifts in a small river in Hokkaido, northern Japan. Abundance of instream cover habitat formed by coarse woody debris, submerged vegetation and undercut banks was quantified. Density of 1+ and older masu salmon was significantly correlated with cover abundance in autumn, although cover was not significant for density of 0+ fish, indicating that clear‐cut reaches were utilized by 0+ masu salmon in autumn. In early winter, densities of 0+ and 1+ and older masu salmon were both correlated with cover availability. These results suggest that the amount of cover habitat is an important regulator for densities of juvenile masu salmon during winter.
Developing co‐management in an artisanal gill net fishery of a deep hydro‐electric reservoir in Sri Lanka
Authors: NATHANAEL S. , EDIRISINGHE U.
Published: March 2003

Abstract Victoria, is a recently (1984) impounded, deep, hydro‐electric reservoir in Sri Lanka with an established commercial fishery. Participatory appraisal of the fishing community revealed decreasing reliance on fishing income with many fishermen moving away to supplementary occupations because of declining fish catches. Illegal fishing and theft of fishing gear resulting from open access, difficulties encountered in enforcing fisheries regulations and the need for fishermen to find alternative sources of income during low water levels are the major management problems. The top–down centralized management approach previously practised was ineffective in addressing any of these issues. Therefore, the possibilities and limitations for introducing co‐management as an alternative management strategy were discussed. Financial hardship coupled with perceived benefits through state sponsored welfare schemes caused a positive attitude change among fishermen, making them respond favourably to fishery management. Establishing a licensing system for controlled access, ensuring greater user‐group participation through equitable distribution of state sponsored benefits among members, attempting to enforce penalties for illegal fishing linked with surprise checks to enforce management regulations, and obtaining stakeholder perceptions regarding management issues are some of the recent steps taken by the Fishermen's Co‐operative Society which would positively contribute towards developing effective co‐management in this reservoir.
Invasion of the Black Sea by the ctenophore Mnemiopsis leidyi and recent changes in pelagic community structure
Authors: SHIGANOVA T. A.
Published: March 2003

A short synthesis of the present state of the ctenophore, Mnemiopsis leidyi, invasion in the Black Sea is given, together with a brief review of its status in other areas of the Mediterranean basin. The impact of M. leidyi on the main components of the pelagic community, mesozooplankton, ichthyoplankton and fish resources, based on published data and new field studies (1992–1997) are analysed. This assessment showed sharp fluctuations in the interannual abundance of M. leidyi. The main factors controlling the spatial distribution of M. leidyi were temperature and, to a lesser degree, salinity, whereas its abundance was controlled by food availability. An analysis of the main constituents of the pelagic ecosystem of the Black Sea before the M. leidyi outbreak showed that a reduction in numbers of planktivorous fishes, the main competitors of M. leidyi, could be a possible reason for the upsurge in abundance of M. leidyi. Following the increase of M. leidyi, there was a decline in the abundance and species diversity of ichthyoplankton and mesozooplankton. An assessment of data collected during the period 1992–1997 showed that the number of fish eggs and larvae and of zooplankton was negatively related to M. leidyi abundance. After the recent decrease of M. leidyi in the period 1995–1997, there has been an increase in abundance and diversity of fish eggs, fish larvae, and zooplankton, which together with an increased catch of planktivorous fish indicates that there has been a recovery of the ecosystem.
Lipid content of Calanus finmarchicus during overwintering in the Faroe–Shetland Channel
Authors: Jónasdóttir S.H.
Published: March 2003

Lipid class contents and composition of the copepodite stage CV and adult female Calanus finmarchicus were measured from the autumn to the spring along a transect crossing the Faroe–Shetland Channel. The data give a detailed vertical resolution of lipid content of C. fin‐marchicus before, during and after the time of diapause. In the deep water, where C. finmarchicus was in diapause, the wax ester (WE) content did not change between the autumn and spring with the exception of that of females, which showed a significant decrease in lipid content by March. The concentrations of lipids were lower and more variable in both CV and females in surface waters over the sampling period. In March, the lipid concentration of both CV and females decreased significantly with decreasing depth. The triacylglycerol (TAG) content of both CV and females was high in October at all depths but had almost disappeared by December. The TAG was either utilized during this time period or converted to WE. TAG was most prominent in October and again in February in copepods in the upper water column. A simple diagnostic model is presented that estimates how C. finmarchicus allocates energy reserves from lipids into various metabolic functions. The cost of diapause, molting, gonad formation and ascending from depth is estimated based on the time series data. The model indicates that the major portion of the stored lipid goes into gonad formation, in physical ascent and in basic metabolism during ascent, whereas maintenance of diapause and molting is not expensive in terms of lipid utilization.
Field calibration of the Optical Plankton Counter with respect to Calanus finmarchicus
Authors: Heath M.R. , Dunn J. , Fraser J.G. , Hay S.J. , Madden H.
Published: March 2003

Zooplankton in the Faroe–Shetland Channel and north‐western North Sea were sampled concurrently with a profiling serial net system and an Optical Plankton Counter (OPC) during January and March 1995. Calanus finmarchicus, together with a small proportion of Calanus helgolandicus (< 3% overall), made up > 75% of the zooplankton in the region, with C. finmarchicus being predominant below 500 m depth. Sensitivity analysis of the OPC data was carried out to determine the particle size range providing the highest correlation between the concentrations of stage CIV–CV and stage CVI C. finmarchicus estimated from net catches, and particle concentrations from the OPC. Significant correlations were obtained for particle size ranges that corresponded closely with microscopic measurements of the dimensions of copepodites. The highest correlations were obtained for stages CIV–CV in January.

According to the net sampling, the concentration of C. finmarchicus in January varied by at least four orders of magnitude over the survey region (< 0.05 to > 500 m−3), although only 4% of the samples contained > 100 m−3. When C. finmarchicus was present at concentrations of around 120 m−3, similar estimates of its abundance were obtained from the OPC data as from the net samples. At lower concentrations, the OPC increasingly overestimated the net catches, and the overestimate reached 40:1 at the detection limit of the nets (0.05 m−3). The average overestimate, taking into account the distribution of concentrations, was 2.5:1. This over‐estimate could not be wholly accounted for by the occurrence of other zooplankton species or potential errors associated with the OPC or net system, and the conclusion was that it arose mainly from the detection of detrital aggregates by the OPC. Thus, the OPC was effective at resolving the peak concentrations (> 100 m−3) of C. finmarchicus in the survey region, but was less effective at delineating the marginal areas of the distribution where C. finmarchicus was outnumbered by other similarly sized particles. Nevertheless, the results indicated that, with the application of calibration data such as described here, the OPC is a valuable tool for broad scale surveys of the spatial distribution of C. finmarchicus during the winter, when the animals are concentrated at depths > 500 m in areas such as the Faroe–Shetland Channel.
Physical oceanography of the North Carolina continental shelf during the fall and winter seasons: implications for the transport of larval menhaden
Authors: Werner  , Blanton  , Quinlan  , Luettich, Jr
Published: March 2003

The circulation over the continental shelf off the southern Middle Atlantic Bight (MAB) and northern South Atlantic Bight (SAB) is examined for the fall and winter periods. Observational data are compared with results from a three‐dimensional numerical model to identify the dominant processes on the shelf. By considering wind‐forcing, tides, and a specified upstream inflow (into the MAB), the observed and modelled flow fields are in close agreement in the mid‐ and inner shelf regions. The resulting larval drift indicates a seasonal dependence of transport pathways from spawning grounds to estuarine nursery areas for menhaden larvae and other offshore‐spawning estuarine‐dependent fish. Specifically, the physical oceanography of the MAB and SAB during the fall and winter months suggests a north‐to‐south shift in spawning areas providing recruits to the Carolina estuaries, in agreement with the observed migration of the spawning populations.
Diurnal variation in thermal environment experienced by salmonids in the North Pacific as indicated by data storage tags
Authors: Walker Robert V. , Myers Katherine W. , Davis Nancy D. , Aydin Kerim Y. , Friedland Kevin D. , Carlson H. Richard , Boehlert George W. , Urawa Shigehiko , Ueno Yasuhiro , Anma Gen
Published: March 2003

Eight temperature‐recording data storage tags were recovered from three salmonids in Alaska (pink and coho salmon and steelhead trout) and five chum salmon in Japan after 21–117 days, containing the first long‐term records of ambient temperature from Pacific salmonids migrating at sea. Temperature data imply diel patterns of descents to deeper, cooler water and ascents to the surface. Fish were found at higher average temperatures at night, with narrower temperature ranges and fewer descents than during the day. Fish tagged in the Gulf of Alaska were at higher temperatures on average (10–12°C) than chum salmon tagged in the Bering Sea (8–10°C). Chum salmon were also found at a wider range of temperatures (−1–22°C vs 5–15°C). This is probably related both to the different oceanographic regions through which the fish migrated, as well as species differences in thermal range and vertical movements. Proportions of time that individual fish spent at different temperatures seemed to vary among oceanographic regions. Steelhead trout may descend to moderate depths (50 m) and not be limited to the top few metres, as had been believed. Japanese chum salmon may seek deep, cold waters as they encounter warm surface temperatures on their homeward migrations. Temperature data from all fish showed an initial period (4–21 days) of day and night temperatures near those of sea surface temperatures, suggesting a period of recuperation from tagging trauma. A period of tagging recuperation suggests that vertical movement data from short‐term ultrasonic telemetry studies may not represent normal behaviour of fish. The considerable diurnal and shorter‐term variation in ambient temperatures suggests that offshore ocean distribution may be linked more to prey distribution and foraging than to sea surface temperatures.
Remotely sensed mesoscale oceanography and the distribution of Illex argentinus in the South Atlantic
Authors: Waluda C. M. , Rodhouse P. G. , Trathan P. N. , Pierce G. J.
Published: March 2003

In this study, we consider the influence of mesoscale oceanographic processes around the Falkland Islands (Islas Malvinas) in the South‐west Atlantic, during the period in which the commercial squid fishery for Illex argentinus operates. Spatially referenced fishery data and satellite‐derived advanced very high resolution radiometry (AVHRR) sea surface temperature (SST) data were examined using geographic information system (GIS) techniques. The distribution and relative abundance of I. argentinus in the Falkland Islands fishery was examined for the period 1989–96. Three consistent areas of high abundance were observed to the north‐east (shelf‐break region) and north‐west (shelf region) of the islands, and close to the northern coast of East Falkland. Areas of high sea surface temperature gradients (thermal gradients) extracted from remotely sensed satellite images were used as an indicator of mesoscale oceanographic activity and compared with the location of the fishery. I. argentinus were found to be associated with areas of thermal gradients, commonly seen at the interface of Falkland Current and Patagonian shelf waters. The techniques used in this analysis allow the overlay and analysis of physical oceanographic and fishery data with potential applications in fisheries management and operational fisheries oceanography.
Availability of horse mackerel (Trachurus trachurus) in the north‐eastern North Sea, predicted by the transport of Atlantic water
Authors: Iversen Svein A. , D. Skogen Morten , Svendsen Einar
Published: March 2003

One of the clearest relationships between a single marine climate variable and fisheries yield is found between the transport of Atlantic water into the North Sea in the winter and catches of horse mackerel (Trachurus trachurus L.) in the northern North Sea 6 months later. A three‐dimensional numerical model, the NORWegian ECOlogical Model system (NORWECOM), has estimated this inflow during the winter from 1976 to 2000, which is strongly correlated with the Norwegian fleet's catch of horse mackerel (r2 = 0.70) in the following autumn. It is hypothesized that a large influx of this relatively warm and nutrient rich water during the winter may support an early spawning of zooplankton and high biological production during the spring and summer. This might be the biological reason for a large fraction of the horse mackerel stock migrating into the North Sea during strong inflows.
Modelling the impact of the regulation of estuarine drift‐netting on the declared rod catch of Atlantic salmon	Salmo salarL. in the River Usk
Authors: Bowker  , Ferns  , Phillips  , Mawle
Published: March 2003

1. A novel method was used to determine if the statutory regulation of drift‐netting at the mouth of the River Usk in Wales was associated with a significant improvement in the stock and rod catch of salmon in the river upstream.

2. A linear regression model was constructed, in which the annual rod catch of salmon declared from the Usk between 1977 and 1988 was the dependent variable and the simultaneous annual catch declared from the nearby River Wye was the independent variable. The model was extrapolated to project the annual rod catches of salmon on the Usk, relative to the Wye, between 1989 and 1995.

3. The model accurately projected the actual rod catches declared from the Usk in 1989, 1990 and 1991. However, between 1992 and 1995 the declared catches deviated significantly (P≤ 0.05) from those projected by the model. The upsurge in rod catches declared after 1992 from the Usk, relative to the Wye was concomitant with the regulation of estuarine drift‐netting.

4. It was concluded that diminished estuarine exploitation had a beneficial impact on salmon angling success on the Usk. However, the utility of the model was restricted by inconsistencies in the methods used to generate the data, by changes in fishery management policies and by a lack of essential information on the interrelationships between catch, effort, stock and environmental conditions.
The fauna in the upper stony littoral of Danish lakes: macroinvertebrates as trophic indicators
Authors: Brodersen Klaus P. , Dall Peter C. , Lindegaard Claus
Published: March 2003

1. The macroinvertebrate fauna living on stones in the exposed stony littorals of thirty‐nine Danish lakes were examined by multivariate numerical methods. The data were derived from 125 semi‐quantitative samples and a species list of 126 taxa. The mean number of individuals per sample was 960, and among the most common taxa were Asellus aquaticus, Gammarus, Oulimnius, Tinodes, Cricotopus and Dicrotendipes.

2. The total number of species and fourteen individual taxa were positively correlated to mean depth of the lakes and eleven taxa were correlated to the total phosphorus concentration. The Shannon diversity was negatively correlated to the chlorophyll a concentration ([Chl a]).

3. Community patterns were examined by detrended correspondence analysis (DCA), and the relationship between species data and selected environmental variables was analysed by canonical correspondence analysis (CCA). Mean lake depth was found to be the strongest environmental variable in explaining the species data. The [Chl a] and Secchi depth also explained significant variation in the distribution of the stony littoral invertebrates. Wind fetch and relative exposure did not explain any variation in the faunal composition among sites.

4. The abilities of the macroinvertebrates to predict the lake trophic state, expressed as log ([Chl a]), were explored by means of weighted averaging (WA) regression and calibration. Two tolerance‐weighted WA models using inverse and classical regression for deshrinking are presented. The models were assessed by the root mean square error (RMSE) of prediction, using bootstrapping as cross validation, and by the correlation between observed and inferred log ([Chl a]). The model using inverse deshrinking had a RMSEboot = 0.41 and r2 = 0.63. By using classical regression, the predictability in the ends of the gradient was improved but the RMSE increased: RMSEboot = 0.46.

5. Although the factors determining faunal distribution patterns in the Danish lowland lakes were highly multivariate and difficult to disentangle, it seems reasonable to use the WA estimated species optima and tolerances to [Chl a] in a bio‐assessment model.
Plasticity of Daphnia magna life history traits in response to temperature and information about a predator
Authors: Sakwińska Olga
Published: March 2003

1. Exudates from predators often elicit early maturation in Daphnia, which may protect them from predation. Diel vertical migration (DVM) is also a predator‐avoidance device and affects life history traits because of the variable temperature experienced during migration. This study asks, therefore, how do these two effects interact and what are the net costs and benefits of the two defences combined?

2. Key life history features were studied in a two factorial life table experiment in a monoclonal cohort of Daphnia magna to quantify the costs of predator‐induced defences.

3. The costs of DVM, associated with low temperature, yielded a 30% decrease in the intrinsic rate of population increase. This was caused by later maturation and longer egg development time, despite a higher fecundity.

4. Chemical information that predators were present resulted in smaller, more numerous offspring, but had no significant effect on size and age at first reproduction. The costs of induction were therefore associated with smaller, and thus presumably lower quality, offspring.

5. Changes in life history induced by fish exudates were independent of the shifts caused by low temperature.

6. The measure of fitness chosen to assess the costs of induced defences is important because the costs often depend on the environment.
Does sediment resuspension have persistent effects on phytoplankton? Experimental studies in three shallow lakes
Authors: Ogilvie Brett G. , Mitchell Stuart F.
Published: March 2003

1. The persistence of effects of sediment resuspension on chlorophyll a, phytoplankton production and plant nutrients was examined by artificially resuspending sediment in enclosures in three shallow lakes and monitoring concentrations for 4–8 days. Realism was assessed by relating initial suspended solids concentrations to those observed during natural wind events.

2. Positive effects on the phytoplankton, persisting for at least 4–6 days were detected in eight of the nine experiments, and similar effects on nutrient concentrations were also common, although suspended solids had normally returned to control levels within 24 h

3. The phytoplankton during the periods of persistence was normally dominated by planktonic rather than benthic/meroplanktonic genera.

4. Several of the positive responses appeared to be associated with relief of nitrogen deficiency in the algae.

5. Persistent effects from previous resuspension events may cause baseline concentrations of phytoplankton and nutrients in shallow lakes to be overestimated and the effects of resuspension on phytoplankton and nutrients to be underestimated
Snail reaction to watercress leaf tissues: reinterpretation of a mutualistic ‘alarm’ hypothesis
Authors: Kerfoot W. C. , Newman R. M. , Hanscom Z.
Published: March 2003

1. Both emergent and submersed growth forms of the amphibious mustard watercress (Nasturtium officinale) contain appreciable concentrations of glucosinolate that deter feeding by a variety of aquatic grazers. Glucosinolate and myrosinase are stored separately in plant tissues, but undergo hydrolysis upon tissue damage to form characteristic isothiocyanates and nitriles.

2. Snails of the genus Physella readily consume yellowed, senescing leaves of watercress, yet are reluctant to attack fresh, green leaves. Laboratory behavioural studies confirm that these preferences are related to intrinsic properties of the leaves independent of periphyton concentrations. Snails are attracted to crushed yellow leaves, yet are actively repulsed by isothiocyanates liberated by crushed, green leaves, despite the higher nitrogen content of the green tissue.

3. The aversion response to crushed green leaves confirms reports by Haynes & Taylor (1984) and others that snails avoid crushed leaves of watercress. However, our interpretation of the interaction is distinctly different from theirs. Rather than a damaged plant signalling imminent danger to host periphyton grazers, the liberation of the compound 2‐phenylethyl isothiocyanate from damaged tissues acts as a deterrent that protects the plant against opportunistic herbivores, which include certain snail species.
Diel emigration and colonization responses of blackfly larvae (Diptera: Simuliidae) to ultraviolet radiation
Authors: Donahue William F. , Schindler David W.
Published: March 2003

1. Total counts of blackfly larvae densities over 30‐ and 57‐h periods in experimental channels during May of 1996 & 1997 indicate that ultraviolet radiation (UV; 290–400 nm) may be important in stimulating emigration.

2. Under experimentally controlled solar UV exposure, larval densities at dawn in UV‐shielded channels were 161% and 168% higher than in the UV‐exposed channels. Larval densities in UV‐exposed channels then decreased by 68.2% and 81.1% between dawn and early afternoon of the two days; density decreases in UV‐shielded channels were slight, and not statistically significant, during the same periods.

3. Larvae within UV‐exposed channels occupied shaded microhabitats during hours of intense solar radiation, suggesting that simuliid larvae can detect and respond to UV radiation over very short periods of time.

4. A cyclical pattern of UV‐induced emigration during hours of increasing solar flux (06.30–13.30) and net immigration in the hours of decreasing solar flux and at night emerged. Thus stream invertebrates may be very sensitive to environmental changes, resulting in either increased UV flux or decreased shading of streams. Diel cycles in invertebrate densities should be taken into account in research designs and sampling protocols in order to identify and interpret correctly results of both periodic surveys and experiments.
Leaf breakdown and associated macroinvertebrates in alpine glacial streams
Authors: Robinson Christopher T. , Gessner Mark O. , Ward J. V.
Published: March 2003

1. The relationship between macroinvertebrate assemblages and the breakdown of alder [Alnus viridis (Chaix), Dc.] leaves was examined by exposing leaf packs in four streams in an alpine glacial floodplain over 8 months. Although glacially fed, the four sites (pro‐glacial, glacial lake outlet, main channel, and a side‐channel with a mix of water sources) differed physically and contained different benthic communities.

2. Leaf breakdown and associated fungal properties differed widely among sites. Leaf decay rate varied by an order of magnitude (k ranged from 0.0029 to 0.0305 day–1), and was fastest at the lake outlet (< 20% leaf mass remaining by day 45) and slowest at the pro‐glacial site (> 75% remaining on day 45). Rapid processing at the lake outlet was because of the presence of Acrophylax zerberus Brauer, a shredding caddisfly.

3. There were few macroinvertebrate taxa at the pro‐glacial site (two to four taxa present in packs) and leaf breakdown was attributed primarily to micro‐organisms. Leuctra abundance in leaf packs was strongly correlated with fungal biomass but not with the sporulation activity of any specific aquatic hyphomycete. Other taxa, such as Baetis and chironomids, showed no relationship with any leaf characteristic, suggesting that leaf packs were used mainly as a habitat and not as a food resource.

4. The predatory stonefly Isoperla was significantly associated with the abundance of macroinvertebrate prey (Baetis, Chironomidae and Leuctra) in leaf packs at the main and side‐channel sites. The results indicate that leaf breakdown can vary widely in alpine lotic environments, reflecting site‐specific differences in habitat characteristics, and in macroinvertebrate and fungal composition.
Predation by longfin smelt (Spirinchus thaleichthys) on the mysidNeomysis mercedisin Lake Washington
Authors: Chigbu P. , Sibley T. H.
Published: March 2003

1. Longfin smelt and mysid samples collected in Lake Washington from 1988 to 1992 were examined, and historic data on smelt and mysid abundance were reviewed to assess the impacts of smelt predation on Neomysis mercedis. The feeding habits of smelt were also examined for differences between odd and even years, and seasonal and ontogenetic variations in smelt diet were described.

2. A reciprocal relationship in the abundance of 1+ smelt and Neomysis suggested that smelt regulate mysid abundance in the lake.

3. The proportion of smelt diet contributed by mysids was higher for less abundant year classes of smelt.

4. These results indicate that intraspecific competition for scarce mysids occurs in the even‐year classes of smelt.
Do xeric landscapes increase genetic divergence in aquatic ecosystems?
Authors: Thomas E. Perry , Blinn Dean W. , Keim Paul
Published: March 2003

1. Previous investigations of the ecological genetics among amphipods in south‐western U.S.A. suggested a xeric landscape promoted genetic divergence among passively dispersed freshwater invertebrates, thereby enhancing speciation events. We predicted that less divergence would occur among amphipod populations across similar geographic distances in mesic regions.

2. EightHyalella aztecapopulations were sampled along a 200‐km transect in western Oregon, U.S.A. Genetic distances among populations were estimated from randomly amplified polymorphic DNA (RAPD). Genetic analyses indicated much less divergence among Oregon populations than among Arizona populations in an arid environment.

3. Behavioural observations support the genetic data: Oregon populations exhibit little differentiation in swimming behaviour, whereasHyalellapopulations in Arizona exhibit extremes in swimming behaviour.

4. These results provide preliminary support for the hypothesis that a xeric landscape promotes genetic and behavioural divergence among amphipods. Many aquatic invertebrates classified as panmictic populations may encompass genetically distinct groups; those isolated by a xeric landscape are especially prone to diversification.