bluuebunny/crossref_metadata_2025 huggingface dataset:
Sampling fish communities in shallow lowland lakes: point‐sample electric fishing vs electric fishing within stop‐nets
Authors: PERROW M.R. , JOWITT A.J.D. , ZAMBRANO GONZÁLEZ L.
Published: November 2003

Fractional or point‐abundance sample (PAS) electric fishing was compared with conventional electric fishing within stop‐nets in several shallow, structurally complex, lowland lakes. The two methods tended to sample the fish community in different ways. PAS provided significantly higher total population estimates, partly as a result of the higher estimates for the dominant small fish (e.g. 0 + perch, Perca fluviatilis L.). Fish hidden by cover (macrophytes, branches, etc.) or substrate, such as eels Anguilla anguilla (L.) and ruffe Gymnocephalus cernuus (L.), were also sampled at a higher rate and for eel, this led to considerable variation in biomass estimates between the two methods. It is argued that PAS, rather than electric fishing within stop‐nets, provided more accurate estimates of fish population parameters and that PAS had several distinct advantages when used for qualitative and quantitative stock assessment, particularly in shallow lakes dominated by emergent and submerged vegetation.
Factors affecting the susceptibility of Irish soft‐water streams to forest‐mediated acidification
Authors: KELLY‐QUINN M. , TIERNEY D. , COYLE C. , BRACKEN J.J.
Published: November 2003

Hydrochemical sampling was carried out at forty seven sites on upland soft‐water streams in the eastern region of Ireland. The majority of sites were circum‐neutral during dry weather but became episodically acidic during heavy or prolonged rainfall. Sensitive sites were characterized by low alkalinity (< 200 μeq L–1) and low non‐marine hardness (< 120 μeq L–1) values and high levels of natural acidity (DTOC). These sensitive, naturally acidic waters were shown to be susceptible to acid inputs from forestry. The high acidity levels associated with some afforested catchments were attributed to inputs of sulphates, nitrates and hydrological factors.
Dynamics of upstream migration of the European eel, Anguilla anguilla (L.), in the Rivers Severn and Avon, England, with special reference to the effects of man‐made barriers
Authors: WHITE E. M. , KNIGHTS B.
Published: November 2003

The upstream migration of European eels, Anguilla anguilla (L.), was studied during 1991–1993 in the Rivers Severn and Avon using traps mounted on weir or sluice barriers. Only pigmented elvers and juvenile eels were trapped at the tidal limits, catches being equivalent to about 0.8% of the commercial glass eel catch in the lower estuary. First catches were made as temperatures rose above 10–11 °C. Pigmentation‐stage analyses and body size data indicated that estuarine migration was slow and that natural mortality was probably very high. Relatively more eels were trapped in the Severn compared with the Avon, but in both rivers the number of immigrants decreased rapidly upstream of the tidal limits, whilst the average size and age increased. The number and severity of weir and sluice barriers to be surmounted exerted a greater effect than distance alone. Recapture rates of marked eels were low (1–2%), implying variable migratory tendencies and/or high mortality. Mean migration rate in the non‐tidal rivers was 0.64 ± 0.6 km day–1 and some eels were not recaptured until one or two years after release. Speed of migration increased with temperatures above 15–16 °C. Relationships between migration dynamics, barriers and the scarcity of upriver stocks of eels and distorted population structures in the two rivers are discussed. Recommendations are made for the provision of passes and/or stocking to enhance migration and recruitment.
The reef fisheries surrounding the south‐west coastal cities of Madagascar
Authors: LAROCHE J. , RAZANOELISOA J. , FAUROUX E. , RABENEVANANA M. W.
Published: November 2003

The artisanal fishery in south‐west Madagascar, around the coastal cities of Morondava, Morombe and Tuléar, is particularly active. In the Morombe and Tuléar regions, fishing pressure focuses on coral formations close to landing sites and reef fish constitute the main part of the catch (Lethrinidae, Haemulidae, Siganidae). In Morondava, fishing is practised very close to the shore on sandy substrates, but also on offshore reef shallows. The catches are more diverse and made up of reef fish (Serranidae, Lutjanidae) and non‐reef species. Fishing from Morondava targets the highest trophic level of the coral reefs (piscivores/macroinvertebrate feeders: 87% of the catch) whereas in Tuléar and Morombe the higher fishing effort means that lower trophic levels are targeted to maintain catches. Despite the high fishing effort, especially around Morombe and Tuléar (standardizing fishing effort of 5200 hook h km–2 year–1 and of 12 300 hook h km–2 year–1, respectively), the catch per unit effort (CPUE) is still relatively high; it varies from 0.6 to 2 kg h‐1 per person over the whole zone and seems to be more linked to the fishing method used and to the degree of professionalism than to variations in the abundance of the resources surrounding the three cities. The relatively high CPUE can probably be explained by a continual immigration and/or recruitment on these fishing grounds. The fish originate from sectors that are far from towns and weakly exploited. A sociological study was carried out concurrently with the fishing survey and focused on present‐day transformations within the fishing community.
Effects of instream enhancement structures on brown trout, Salmo trutta L., habitat availability in a channelized boreal river: a PHABSIM approach
Authors: HUUSKO A. , YRJÄNÄ T.
Published: November 2003

Stream channel morphology and hydraulic conditions were measured before and after channel modification and boulder structure placements in a channelized boreal river to determine whether more favourable rearing habitat for brown trout, Salmo trutta L., was created. The assessment was performed using physical habitat simulation (PHABSIM) procedures based on summer and winter habitat preferences of brown trout for depth, velocity and substrate. The results showed that the availability of potential physical trout habitat can be increased in the study river at simulated low and moderate flow conditions by reconstruction of the river bed and placing instream boulder structures. The resulting diversity of depth and velocity conditions created a spatially more complex microhabitat structure. Improved habitat conditions were able to sustain a larger trout population. Hydraulic habitat models, like the PHABSIM framework, seem to be a suitable procedure to evaluate the benefits of physical habitat enhancement.
Experience of partnership models for the co‐management of Bangladesh fisheries
Authors: AHMED M. , CAPISTRANO A.D. , HOSSAIN M.
Published: November 2003

Failure in the past to ascertain responsible fishing practices and equitable distribution of benefits under traditional leasing systems has motivated the Bangladesh government to work in partnership with non‐governmental organizations (NGOs) and fishing communities in recent times. This paper discusses the operational approaches that were used to identify fishing people and create institutions for their increasing participation in local fisheries, and in making and enforcing resource use rules under various partnership arrangements. The group‐based empowerment strategies of NGOs; their role in securing for the beneficiaries the access rights to water bodies; the provision of credits and inputs for employment and income generation activities showed some practical evidence of the concept of the poor as managers of the fisheries resources. The policy issues involved in the rights of local community members to catch fish for subsistence are also discussed, as well as the challenges associated with the difficulties of reconciling differing government (GO) and nongovernment (NGO) organization priorities and points of view with regard to target group identification and levels of responsibilities.
Food availability and growth of the brook trout, Salvelinus fontinalis (Mitchill), in a French Alpine lake
Authors: CAVALLI L. , CHAPPAZ R. , BOUCHARD P. , BRUN G.
Published: November 2003

Plan Vianney lake, situated in the Oisans massif (French Alps) at an altitude of 2250 m, has a fish fauna composed of brook trout, Salvelinus fontinalis (Mitchell), and Artic charr, Salvelinus alpinus (L.). The present study examines the feeding behaviour of S. fontinalis in 1993–94 but also gives some data on S. alpinus. The brook trout represented 80% of the fish fauna of the lake. Dietary analysis showed that this species is an opportunistic feeder and revealed similarities in the trophic niches of S. fontinalis and S. alpinus and a low level of potentially available food resources. The annual growth of S. fontinalis was short and the growth rate was slow compared with other populations. Under these extreme conditions, female fish required several summers to replenish their reserves of energy and were only in condition to spawn once every 2 or 3 years. Although the fecundity of the population was low, it was sufficient to maintain the species in the lake which is not exploited.
Hydraulic and sedimentary characteristics of habitat utilized by Atlantic salmon for spawning in the Girnock Burn, Scotland
Authors: MOIR H. J. , SOULSBY C. , YOUNGSON A.
Published: November 2003

The Girnock Burn, a tributary of the River Dee, has been used as a monitoring site for Atlantic salmon, Salmo salar L., populations since 1966. The burn drains a catchment of 30 km2 and is a third order stream at the catchment outlet; its width ranges from 1 m in the headwaters to around 15 m in its lower reaches. During the period 1966–1996, the mean number of fish (average lengths; males = 0.64 m and females = 0.68 m) entering the burn for spawning averaged 126 (range 38–293) with a mean male:female ratio of 0.96 (range 0.58–1.66). Typically, 85% of the adults were 2‐sea winter fish. Redd counts in 17 spawning seasons showed that the number of redds constructed during the spawning season ranged from 13 to 141 with a mean of 79. Redds were generally 2–3 m long, 1–1.5 m wide and 0.2–0.3 m deep. Redd distributions showed that parts of the river were used more frequently for spawning than others. This paper describes the main physical characteristics of the river that influence spawning habitat. This characterization occurs at two scales; the overall Girnock system and individual river reaches. At the large scale, bed slope exerts a strong influence on spawning distribution by controlling the distribution of spawning‐calibre sediment. Additionally, river flow during the spawning period appears to have a significant influence on accessibility and the subsequent distribution of redds. At the reach scale, local hydraulic (depth, velocity and Froude number) and sedimentary (particle size distribution) variables were found to be increasingly important. Mean utilized depth, velocity and Froude number for 93 redds were 0.248 m, 0.536 m s–1 and 0.344, respectively. Samples of utilized sediment had a mean median particle size (D50) of 20.7 mm and a mean fines (particles < 1 mm diameter) content of 5.4%. It was suggested that the Froude number may be a useful single descriptor of hydraulic habitat, as it is dimensionless and is thus comparable between different sizes of river and fish species.
Variations in spawning ground area and egg density of the Japanese sardine in Pacific coastal and oceanic waters
Authors: WATANABE YOSHIRO , ZENITANI HIROMU , KIMURA RYO
Published: November 2003

The spawning ground of the Japanese sardine, Sardinops melanostictus (Schlegel), was distributed over the oceanic waters as well as the coastal waters along the Pacific coasts of western and eastern Japan during 1978–1992. The area of the spawning ground in the coastal waters on the continental shelf has ranged from 95 000 km2 in 1992 to 143 000 km2 in 1988, constituting 44–77% of the total area of the spawning ground. The area of the coastal spawning ground was relatively constant in spite of the large fluctuations in egg abundance, i.e. size of the spawning population, from 88 trillion (1987) to 668 trillion (1989) in the waters. Spawning adults seemed to extend over the coastal waters irrespective of the size of the spawning population. In contrast to the coastal waters, the spawning area in the oceanic waters offshore of the continental shelf increased from 31 000 km2 in 1978 to 183 000 km2 in 1988 and then shrank to 83 000 km2 in 1992, as a function of the spawning population size. The egg distribution density in the coastal waters stayed less than 6000 m−2 mo−1, but it reached as high as 27 400 m−2 mo−1 in the expanded spawning ground in the oceanic waters. The oceanic waters seemed to function as a reserve spawning ground for the sardine in years of extremely high spawning population.
The effect of seasonal anomalies of seawater temperature and salinity on the fluctuation in yields of small yellow croaker, Pseudosciaena polyactis, in the Yellow Sea
Authors: KIM SUAM , JUNG SUKGEUN , ZHANG CHANG IK
Published: November 2003

To include the effects of environmental factors on the production of small yellow croaker, Pseudosciaena polyactis Bleeker, in the Yellow Sea, we applied time series analysis to the commercial catch and salinity and temperature data for the period 1970 to 1988. Residuals from a weighted least‐squares regression of log‐transformed catches against year and month were calculated to remove not only seasonal factors but also long‐term trends in catches. The residuals of mean and standard deviation (SD) of temperature and salinity were calculated and used for autocorrelation, cross‐correlation and first‐order autoregression analysis (AR(1)) using maximum likelihood. The landings showed a decreasing pattern across years with a conspicuous seasonal cycle within years. Catch residuals showed a strong positive autocorrelation and a conspicuous time‐lagged cross‐correlation with the residuals of mean and SD of seawater temperature at 75␣m. AR(1) revealed that positive anomalies of mean temperature were associated with positive anomalies in the production of small yellow croaker with a one year time lag. The decrease in the residual of SD of temperature appears to be related to the high production 0.5–1.0 year later. The effect of salinity was negligible compared with that of temperature. Therefore, the warm spawning period and homogeneous temperature condition of previous years for young fish may cause the increase in the following year's yield of this fish species. When used to predict catches in 1989 and 1990, the AR(1) model explained 40% of the variances of the observed landings.
An individual based model of fish school reactions: predicting antipredator behaviour as observed in nature
Authors: VABØ RUNE , NØTTESTAD LEIF
Published: November 2003

An object‐orientated, two‐dimensional, cellular automata (CA) model is developed to describe and predict the schooling behaviour of fish in general, with Norwegian spring‐spawning herring, Clupea harengus L., being used as a case study. The CA model is applied to visualize internal school dynamics based on individual decision rules. Several antipredator strategies, such as split, join and vacuole, performed by schools during predator attack, are visualized in the model. The primary driving force of individual fish is based on simple attraction rules. The model includes stochastic elements which assume that individual herring do not have perfect information about their surroundings. Isolation of individual fish from a school during predator attack is also predicted by the model. The disruption of highly organized fish schools, followed by an attack on solitary herring individuals, may be an important tactic for predators feeding on schooling prey. The conceptual CA model identifies patterns and mechanisms both within and between schools that may be important in all schooling fish. Model simulations are compared with observed predator–prey interactions between killer whales, Orcinus orca L., and herring in northern Norway.
Distribution and settling of Japanese anchovy (Engraulis japonicus eggs at the spawning ground off Changjiang River in the East China Sea
Authors: ISEKI KAZUO , KIYOMOTO YOKO
Published: November 2003

Spatial patterns in the distribution and abundance of Japanese anchovy, Engraulis japonicus, eggs were studied from net surveys in the East China Sea in May 1991. Egg abundance was> 5 × 103 eggs (100 m3)−1 in the area off Changjiang River, where a large spawning ground was developed. The vertical distribution of living eggs showed a maximum concentration at the surface (40700 eggs (100 m3)−1) and rapidly decreased to ∼5000 eggs (100 m3)−1 at 14 m. Newly spawned eggs (stage I) were found throughout the water column but were most abundant near surface. Some eggs were morphologically identified as dead owing to their abnormal development and physical damage. In contrast to living eggs, no dead eggs were found at the surface and the concentrations were low to 21 m depth (40–64 eggs (100 m3)−1). The concentration increased markedly with increasing depth, reaching a maximum of 634 eggs (100 m3)−1 near the bottom (35 m). Dead eggs accounted for less than 0.3% of the total caught within 7 m of the surface and increased exponentially to 12% near the bottom.

The settling loss of dead anchovy eggs also was studied by employing sediment traps at the spawning ground. The downward flux of settling eggs was low (304–405 eggs m−2 day−1) at 15 and 20 m depths, but rapidly increased with increasing depth, reaching a maximum of 1622 eggs m−2 day−1 at 35 m (5 m above bottom). By comparing the egg flux at 20 m with the living eggs abundance in the upper 20 m, the settling loss of eggs was calculated as about 0.098 day−1. This probably represents the natural mortality of anchovy eggs caused by genetic abnormalities and incomplete fertilization.
Acoustic identification of isada krill, Euphausia pacifica Hansen, off the Sanriku coast, north‐eastern Japan
Authors: MIYASHITA KAZUSHI , AOKI ICHIRO , SENO KOUTARO , TAKI KENJI , OGISHIMA TAKASHI
Published: November 2003

In this study, the feasibility of identification and abundance estimation of isada krill, Euphausia pacifica, was examined using a two‐frequency (38 and 120 kHz) method. The acoustic survey and midwater trawling were conducted off the Sanriku coast, northern part of Honshu, Japan. In one pattern, the SV difference between the two frequencies was large, and in the other, the SV difference was small. These results were interpreted by scattering models, and showed that discrimination between isada krill and walleye pollock was possible.
Fluctuation in abundance of larval anchovy and environmental conditions in coastal waters off south‐western Taiwan as associated with the El Niño–Southern Oscillation
Authors: TSAI CHU‐FA , CHEN PEI‐YU , CHEN CHANG‐PO , LEE MING‐ANNE , SHIAH GUANG‐YAW , LEE KUO‐TIEN
Published: November 2003

Monthly abundance (CPUE) of larval anchovy in the coastal waters off south‐western Taiwan from 1980 to 1992 (156 months) fluctuated at intervals corresponding to the 4.3‐ and 2.2‐year cycles of the southern oscillation index (SOI). Also, CPUE was significantly correlated with sea surface temperature with a time lag of 3 months and nearly significantly to river flow with a time lag of 4 months, which in turn correlated with SOI at lags of 13–14 months (cross‐correlation and transfer function analyses). The results suggested the presence of linkage between recruitment of the larvae and ENSO episodes, perhaps through oceanographic and meteorological conditions that affect coastal upwelling and river discharge. The Kuroshio Current, which is the western extension of the North Equatorial Current, may be one of the important mechanisms of ENSO's teleconnections affecting local climate and fisheries in the western Pacific region.
Varying the timing of oyster transplant: implications for management from simulation studies
Authors: POWELL ERIC N. , KLINCK JOHN M. , HOFMANN EILEEN E. , FORD SUSAN
Published: November 2003

The transplanting of oysters from one ground to another is a common practice in the oyster industry. In Delaware Bay, for instance, oysters are typically transplanted from upper‐bay low‐salinity seed beds onto lower‐bay leased grounds for growth and conditioning before market. The higher salinity on the leased grounds, however, also favours higher losses to predation and disease. A coupled oyster–Perkinsus marinus–predator model was used to investigate how varying the timing of transplant affects the ultimate yield of Eastern oysters, Crassostrea virginica, in Delaware Bay. Simulations were run in which oysters were moved from seed beds to leased grounds in November, January, March, April and May. The number of market‐size (≥ 76 mm) adults available for harvest in the following July to November was compared for populations undergoing mortality from predation (crabs, oyster drills) and/or disease (Perkinsus marinus). In all simulations, the abundance of market‐size oysters declined between July and November. However, transplanting oysters in November resulted in the largest yield of market‐size oysters for all harvest times; transplanting in May resulted in the smallest yield. The autumn transplant allows oysters to benefit from the larger spring phytoplankton bloom over the leased grounds in the lower estuary. The effect of varying the season of transplant was most noticeable if oysters were harvested early (July or August). In all simulations, transplanting resulted in a higher abundance of market‐size oysters than direct harvest from the seed beds. Direct harvest would rarely be advantageous if the cost of transplant were insignificant and the relative rates of mortality were as stipulated. However, a May transplant is only moderately better than a direct harvest and the economic benefits of either option are likely to be determined by the cost of transplanting and the mortality associated with the process. In the same vein, the decision as to when to harvest relies on balancing the increased price obtained for oysters in the autumn with the increased loss owing to predation and disease. Awaiting an autumn harvest is clearly much riskier if the principal source of mortality is disease rather than predation, because disease mortality is concentrated on the market‐size oysters and is greatest in the autumn.
Daily and seasonal vertical migration rhythms in Daphnia
Authors: YOUNG STEPHEN , WATT PENELOPE
Published: November 2003

1. Clones of Daphnia longispina (O.F.M.), collected from ponds with different levels of predation, were monitored using video techniques in order to test the effects of temperature and visual cues on vertical migration behaviour.

2. Endogenous rhythms were found to have a part in the control of vertical migration in some clones but responses were highly variable.

3. Low temperature caused a marked increase in the amplitude of vertical migration in D. longispina, consistent with field studies.

4. Clones from ponds with fish predators had larger vertical migration amplitudes than clones from ponds with no fish, providing further evidence for the genetic basis of this mechanism.
Survival of caddis larvae in relation to their case material in a group of temporary and permanent pools
Authors: ZAMORA‐MUÑOZ CARMEN , SVENSSON BO
Published: November 2003

1. The occurrence of larvae of Limnephiluscoenosus and L. vittatus (Trichoptera) was recorded in 103 rock pools both before and after the dry periods in spring–summer (April–May and July–early August), when a great number of the pools dried out. In early spring, 84% of the pools sampled contained larvae of at least one of the species. Limnephilus coenosus larvae were present in a higher proportion of pools that later dried out than in the permanent ones, while L. vittatus larvae were predominantly found in permanent pools. Larvae of both species were found together in 31% of the inhabited pools.

2. Laboratory experiments, designed to elucidate differential survival under drought conditions, demonstrated that the organic cases of L. coenosus larvae held water more efficiently than did the mineral L. vittatus cases. Full‐grown (fifth instar) L. coenosus larvae also survived dry conditions better than did L. vittatus larvae. The higher survival of L. coenosus was due to a combination of drought‐resistant case material and a higher survival ability of the larvae themselves.

3. Limnephilus vittatus larvae were restricted by their low capability to withstand desiccation, although case material and food were available for L. vittatus larvae in all pools. Absence of case material and high‐quality food in many pools, however, restricted the presence of L. coenosus larvae, but this species did not suffer from heavy mortality because of desiccation and all pool populations of L. coenosus survived until pupation.

4. The differences in species composition in these temporary and permanent pools can be explained by the differential site selection by ovipositing females, as well as by larval survival. The intrinsically greater survival of L. coenosus larvae during drought, together with the water‐retaining properties of the cases, allowed this species to exploit stressful and risky habitats, such as temporary pools.
The nutrient budget of a small eutrophic loch and the effectiveness of straw bales in controlling algal blooms
Authors: KELLY L.A. , SMITH S.
Published: November 2003

1. A 1‐year intensive study of nutrient flows in Airthrey Loch, central Scotland, a small eutrophic [mean total phosphorus (TP) = 61.1 μg P l–1] well‐flushed freshwater body (area, 6.9 ha; mean depth, 1.85 m; volume, 1.274 × 105 m3; retention time, 0.44 yr), was undertaken.

2. The nutrient budget was dominated by large allochthonous P inputs, equivalent to an areal load to the loch of 8.56 kg P ha–1 yr–1, which occurred predominantly during winter. In the summer, when TP inputs were low, water column levels of TP still increased, as a result of aerobic P release from sediments.

3. Sorption experiments indicated potential for sediment P release at water P concentrations of up to 200 μg P l–1.

4. Aerobic release rate of P from sediments to the water column of Airthrey Loch was estimated to be of the order of 1 mg P m–2 day–1, and occurred during periods of elevated water column pH.

5. Straw bales placed in the loch to retard algal blooms were found not to have any demonstrable impact on algal concentrations observed during the study.
Mortality of Apatania fimbriata (Insecta: Trichoptera) during embryonic, larval and adult life stages
Authors: ENDERS GUDRUN , WAGNER RÜDIGER
Published: November 2003

1. Egg masses, oviposition site preferences, and abiotic and biotic factors causing mortality during embryonic, larval and adult life stages of Apatania fimbriata were studied. Laboratory investigations provided information on the temperature dependence of embryonic development, measured as an increase in egg volume.

2. A. fimbriata laid hemispherical egg masses, consisting of a transparent matrix containing a mean of 208 eggs. Egg masses were laid on stones situated just above the water surface in dark cavities in the stream bank.

3. Two hundred egg masses were mapped and individually monitored during embryonic development. There was no significant correlation between mortality during embryonic development and any of the abiotic parameters measured. First‐instar larvae of Osmylus fulvicephalus consumed developing eggs, and chironomids preyed on newly hatched larvae.

4. A mean of seventy‐two females emerged per metre of stream. Mortality during the 1993/94 life cycle was measured as a percentage of the potential number of eggs laid. Female mortality between emergence and oviposition was ≈ 80%. Eight per cent of individuals were lost during embryonic development. Larval mortality to emergence in 1994 was 11.3%. This indicates that the terrestrial life stage is probably decisive in the regulation of A. fimbriata populations.

5. Duration of embryogenesis at constant temperatures (4–20 °C) in the laboratory was described best by a negative exponential function. This species is cold stenothermal and there was no hatching success at 20 °C.

6. Egg volumes during embryonic development increased sigmoidally over time.
Periphyton dynamics in a floodprone prealpine river: evaluation of significant processes by modelling
Authors: UEHLINGER URS , BÜHRER HEINRICH , REICHERT PETER
Published: November 2003

1. Periphyton chlorophyll a was measured at weekly or 2 weekly intervals from October 1992 to March 1994 at four sites in a Swiss prealpine gravel bed river that was frequently disturbed by unpredictable spates.

2. To evaluate the dominant processes that control periphyton biomass, measured data were compared with a set of simulations from an empirical dynamic periphyton model. Different combinations of process hypotheses were systematically activated and deactivated in order to assess their importance.

3. The simplest model leading to an acceptable agreement with measured data employs a biomass‐dependent growth rate, a detachment rate directly proportional to discharge and biomass, and a catastrophic loss rate during bed moving spates. Terms describing light or temperature dependence had a minor effect on the model fit.

4. The model describes the temporal pattern of the periphyton biomass as a series of growth curves periodically truncated by spates. Within the uncertainties of the measurements, mainly caused by the spatial heterogeneity of periphyton, the biomass recovered along deterministic trajectories.

5. Sensitivity analyses with respect to model parameters and model structure showed that site‐specific model parameters could not be unequivocally determined, and that the model yields similar results with slightly different formulations of processes. This indicates that the data base with respect to periphyton biomass was too small for a unique identification of model details but that the main conclusions on the significance of processes did not depend on arbitrary choices of the model formulation.
Genetic differentiation among populations of Caridinazebra (Decapoda: Atyidae) in tropical rainforest streams, northern Australia
Authors: HUGHES J.M. , BUNN S.E. , HURWOOD D.A. , CHOY S. , PEARSON R.G.
Published: November 2003

1. Caridina zebra is a common atyid shrimp in some tropical rainforest streams in far north Queensland, Australia. Genetic variation at five allozyme loci was used to estimate the level of dispersal among populations of this species, within and between stream systems. Shrimps were sampled from nine streams in the Tully River catchment and two headwater streams in the adjacent Herbert River catchment in an area under consideration for extensive hydroelectric development.

2. High levels of genetic differentiation were recorded among most populations which suggests that, like other fully aquatic species, movement is limited to a very small spatial scale.

3. In the Tully catchment, populations of shrimp from streams with confluences at high altitude showed less genetic differentiation than those from streams which directly entered the lower river. Dispersal between the latter streams is clearly limited by the presence of large waterfalls and cascades.

4. Adjacent stream populations were often highly differentiated, despite their close proximity, suggesting that overland dispersal is unlikely. However, populations of shrimp in the two streams in the Herbert catchment were strikingly similar in genetic structure to those in adjacent headwater streams of the Tully. Such similarity may reflect relatively recent changes in drainage patterns.
Intraspecific stoichiometric variability and the ratio of nitrogen to phosphorus resupplied by zooplankton
Authors: CARRILLO P. , RECHE I. , CRUZ‐PIZARRO L.
Published: November 2003

1. An in situ experiment was carried out in a high‐mountain oligotrophic lake (La Caldera) to quantify the specific release rates of ammonium and phosphorus in different phases of the seasonal succession of plankton. The zooplankton community was dominated by the calanoid copepod Mixodiaptomus laciniatus.

2. The rates of release of N and P (from non‐detectable to 3.58 μg N mg–1 DW h–1 and from 0.26 to 2.29 μg P mg–1 DW h–1, respectively) and the N : P released ratio (not detectable to 4.77) fell within the range typical of oligotrophic lakes dominated by copepodite assemblages.

3. The values of the zooplankton N : P ratio (5 : 1 to 10 : 1 by weight) were lower than those established for other species of calanoids, and followed a well‐established pattern of seasonal variation from year to year with higher values after ice thaw and lower values as individual size increased (ontogenetic development).

4. The elemental composition of the zooplankton depended on individual size, while the released N : P ratio was inversely related to the N : P ratio of the food. This pattern conforms to the predictions of the homeostasis theory of Sterner (1990).

5. A feedback regulation was established between the stoichiometric composition of the zooplankton, their food and the released N : P ratio that can help explain changes in pelagic community structure during the ice‐free period.
Mesocosm experiments on the interaction of sediment influence, fish predation and aquatic plants with the structure of phytoplankton and zooplankton communities
Authors: BEKLIOGLU MERYEM , MOSS BRIAN
Published: November 2003

1. Little Mere, U.K., received large quantities of sewage effluent until 1991, when the effluent was diverted. Experiments, carried out in mesocosms in 1992 and 1993, were designed to predict the effects of: (i) reduced external nutrient loading; (ii) reduced internal loading from the sediment; and (iii) recolonization by fish of the better aerated water. Treatments included isolation of the water from the underlying sediment or exposure to the sediment (which lacked plants in 1992, but was covered by Potamogeton berchtoldii in 1993) crossed with different population densities of Rutilus rutilus in 1992 and of Perca fluviatilis in 1993.

2. Exposure to sediment (as opposed to isolation from it) resulted in no net change in the biovolumes of most major algal groups, but this masked major complementary effects on individual species. The experiments showed a decreasing influence of the sediment, between 1992 and 1993, in determining water chemistry, and an increasing pH between years but no increase in cyanophyte dominance. This had been anticipated because a lake upstream provides abundant inocula, and conditions in Little Mere after diversion of effluent were expected to favour cyanophytes.

3. Roach and perch additions to the mesocosms resulted in reductions in Daphnia populations but increases in numbers of small Cladocera and copepods. Plant‐associated Cladocera were unaffected by fish. The presence of submerged plants to some extent reduced fish predation effects on Daphnia hyalina.

4. The experimental results in general accurately predicted subsequent events in the open lake.
Effects of habitat structure on habitat use by Gammarus pulex in artificial streams
Authors: DAHL JONAS , GREENBERG LARRY
Published: November 2003

1. The influence of coarse substratum and flow, coarse substratum and food, and predation risk and flow on habitat use by Gammarus pulex was studied in three experiments conducted in artificial stream channels. Each stream channel consisted of a riffle and pool habitat.

2. Location of coarse substrata and food was manipulated by placing cobbles (coarse substratum) and leaf packs (food) in different habitats. Predation risk was varied by running experiments in the presence and absence of sculpins (Cottus gobio), and flow was varied by pumping water with one or two pumps.

3. In all experiments Gammarus were most abundant in pools but placement of cobbles in riffles increased use of the latter. An even greater percentage of Gammarus used riffles if leaf packs were also placed there. Decreased discharge and the presence of sculpins (Cottus gobio) also caused Gammarus to increase use of riffles. These data indicate that Gammarus is able to evaluate differences in habitat quality and respond accordingly.
Embryogenesis of Dinocras cephalotes, Perla grandis and P. marginata (Plecoptera: Perlidae) in different temperature regimes
Authors: FRUTIGER ANDREAS
Published: November 2003

1. Temperature dependence of embryogenesis of the three perlid stoneflies Dinocras cephalots, Perla grandis and P. marginata was investigated by means of incubation experiments. Special emphasis was laid on the effect of fluctuating temperatures and on intraspecific differences between populations from two different field sites in the Swiss prealps (i.e. River Necker and River Thur).

2. Dinocras cephalotes embryos develop between 6.3 and 26.6 °C. The lower threshold temperature is lower than has been reported for more northern populations (i.e. from England and Norway), indicating the existence of a latitudinal gradient. Perla grandis eggs only developed between 9.9 and 18.4 °C. In P. marginata, successful embryogenesis was observed between 9.9 and 18.4 °C, but not enough eggs were available to explore the threshold temperatures.

3. Embryogenesis of D. cephalotes and P. grandis was significantly faster at a 12/16 °C daily fluctuating temperature regime than at a constant 14 °C. However, no significant difference was found between the development under simulated field temperature regimes (with less distinct daily amplitudes) and constant temperatures.

4. D. cephalotes, hatching of eggs from the Necker population was much less synchronous than that in the Thur population. Since the Necker discharge regime is harsher than the Thur regime, it is possible that this asynchrony spreads the risk of destruction during bed‐moving floods.
Abundance and distribution within a guild of benthic stream fishes: local processes and regional patterns
Authors: TAYLOR CHRISTOPHER
Published: November 2003

1. Spatial patterns at regional and local scales were examined for evidence that species interactions can influence distribution and abundance within a guild of benthic fishes in upland streams of Oklahoma, U.S.A. Three groups of community patterns were examined: the species–area relationship, species–habitat associations, and interspecific associations.

2. The species–area relationship for riffle habitats was compared to a null species–area model based on random placement. The observed species–area curve was steeper resulting in less species per unit area in small streams than predicted by the null model.

3. Small, species‐poor streams had summed fish densities at least as high as larger, species‐rich streams, suggesting density compensation.

4. Several significant patterns of negative covariation were found among species at the regional scale, before and after statistically accounting for effects due to measured habitat variables.

5. For two of these negatively covarying taxa (Cottuscarolinae and Etheostomaspectabile), the influence of each species on the distribution of the other was evaluated experimentally in field enclosures varying in depth and current velocity. The sculpin C. carolinae caused a shift in habitat use by the darter E. spectabile, but no reciprocal shift was found.

6. These results indicate an agreement between local and regional patterns of distribution for C. carolinae and E. spectabile and suggest that biotic interactions can influence regional patterns of distribution for species within this guild.
Intraguild predation and species exclusions in amphipods: the interaction of behaviour, physiology and environment
Authors: DICK JAIMIE , PLATVOET DIRK
Published: November 2003

1. Data from field surveys, laboratory experiments and computer simulations of community dynamics revealed that a novel interaction among intraguild predation, physiological adaptation and environment may explain the complex distributions of two putatively competing aquatic amphipods.

2. Gammarus pulex and G. tigrinus both thrive in fresh and oligohaline waters in western Europe. However, the native European G. pulex excludes the invading North American G. tigrinus from freshwaters of relatively low conductivity, whereas the reverse occurs at higher conductivities. Additionally, there is much spatio‐temporal fluctuation in the patterns of coexistence of these species.

3. Laboratory experiments in The Netherlands and Ireland revealed that mutual predation of moulting individuals occurred frequently between these species. However, predation frequencies were differentially in favour of G. pulex under the ionic conditions to which this species is physiologically adapted (freshwater). On the other hand, predation was not differential under the ionic conditions to which G. tigrinus is physiologically adapted (oligohaline water).

4. A mathematical model, which extends the logistic equation to include mutual intraguild predation, simulated interactions over a range of values of relevant population parameters. This indicated that G. pulex would be excluded when balanced instantaneous rates of mutual predation were combined with the known greater reproductive output of G. tigrinus. However, this reproductive advantage is overcome by any relatively small bias in the instantaneous rate of predation favouring G. pulex, leading to the exclusion of G. tigrinus. This occurs even when the reproductive advantage to G. tigrinus is relatively large. Moreover, the model generated ‘switches’ in species dominance that are determined by the relative values of reproductive rate and mutual predation. The time taken to ‘switch’ may explain the transient periods of apparent coexistence of these species observed in the field.

5. The complex community dynamics of such species may thus be understood in terms of variation in the intensity of species interactions mediated by behavioural, physiological and environmental factors.
Regulation of algal biomass in a small lowland stream: field experiments on the role of invertebrate grazing, phosphorus and irradiance
Authors: KJELDSEN KARINA
Published: November 2003

1. Field experiments were undertaken in a small Danish lowland stream to study the role of invertebrate grazing, phosphorus concentration and irradiance in the regulation of benthic algal biomass on stones.

2. Algal biomass was regulated by invertebrate grazing. The gastropod Ancylus fluviatilis prevented algal biomass build up in early spring at a density of about 900 ind. m–2, and reduced algal biomass to very low levels during the algal growth period at a density of about 6000 ind. m–2. Grazing pressure therefore might regulate the magnitude of peak algal biomass in Gelbæk stream, a finding in agreement with earlier field observations.

3. As phosphorus enrichment to around 152 μg l–1 during the period when irradiance was not limiting did not result in any further increase in algal biomass, it can be concluded that algal growth in spring was not controlled by phosphorus limitation.

4. Algal biomass development differed significantly in a shaded and in a non‐shaded reach of the stream. Only very low algal biomass accumulation was evident in the shaded reach, while in the non‐shaded reach an algal biomass peak of about 800 mg chlorophyll m–2 was evident after 6 weeks of colonization. The shaded reach represented the light condition in Gelbæk stream after leaf proliferation of the overhead canopy and high bank vegetation. The findings therefore suggest that irradiance available to the algal community after shading from riparian vegetation prevents further algal biomass increase and hence determines the timing of peak algal biomass in the stream.

5. The irradiance experiment also suggests that if not regulated by invertebrate grazing or shading by an overhead canopy in the summer, then the magnitude of peak biomass in Gelbæk stream will be regulated by self‐shading in the algal community.

6. These field experiments support theories, derived from laboratory experiments and field studies, that regulation of algal biomass is a complex interaction of top‐down and bottom‐up mechanisms.
The effects of feeding regime on the growth and reproduction of the medicinal leech Hirudo medicinalis
Authors: DAVIES RONALD , McLOUGHLIN NATHAN
Published: November 2003

1. The feeding frequency, the size of meals, the number of meals required to attain reproductive maturity and the number of meals taken between iteroparous reproductive bouts were determined in the laboratory under optimal conditions for the medicinal leech Hirudo medicinalis fed exclusively on mammalian (bovine) blood. In addition the number of bouts of reproduction and the numbers of cocoons and hatchlings per cocoon produced were determined.

2. The average time for H. medicinalis to reach reproductive maturity at 20°C was 289 days, at an average wet biomass of 8143 mg with two–nine separate bouts of cocoon production. The number of meals to first reproduction was 8.9 (mean meal size of 3066.7 mg), with a significant correlation between total mass of blood ingested and the numbers of reproductive bouts and number of cocoons produced. Mean lifetime cocoon production per individual was 12.43, with 3.9 hatchlings per cocoon.

3. The significant positive relationships between ingestion, fecundity and developmental rate observed support the hypothesis that declining abundances of field populations of H. medicinalis are the result of lower available energy for growth, reflecting leeches now feeding predominantly on amphibian blood of lower energetic value than mammalian blood.
Possible impact of mild winters on zooplankton succession in eutrophic lakes of the Atlantic European area
Authors: ADRIAN RITA , DENEKE RAINER
Published: November 2003

1. We report on a long‐term study (1975–94) of water temperatures and plankton in a eutrophic lake (Heiligensee, Berlin, Germany). Using a phenomenological approach, we use historical data to infer how an increase in air temperature has influenced a natural zooplankton community.

2. Air temperatures in Berlin showed a significantly rising trend between 1975 and 1994. Mean winter air temperatures in the last 8 years always exceeded the long‐term mean.

3. A rising trend was also found for April water temperature, which increased significantly beginning in 1988–89. An increase of 2.58°C in the last 21 years was recorded using a linear model. A significantly decreasing trend was found in June but no trend was noted for the other summer months.

4. Phytoplankton composition shifted from a dominance of diatoms and cryptophytes during winter and spring in the 1980s towards a dominance of cyanobacteria in 1990–94.

5. The dominant zooplankton species in spring shifted in recent years from the large‐bodied Daphnia galeata to the smaller D. cucullata. Cyclops kolensis, previously the only invertebrate predator during winter, decreased in abundance while C. vicinus, usually present during spring and autumn, increased in abundance and was numerous during winter, a season passed in diapause in the earlier years.

6. Because direct and indirect temperature effects are species specific, we put forward the hypothesis that zooplankton species, rather than functional groups, are the nexus between environmental stress, such as rising air temperatures, and ecosystem changes.