bluuebunny/crossref_metadata_2025 huggingface dataset:
Fishery resources and economic gain in three mangrove areas on the south‐east coast of India
Authors: KATHIRESAN K. , RAJENDRAN N.
Published: March 2003

Abstract The fishery resources and fishing income in three different mangrove areas were evaluated. The mangrove‐rich area provided high catches of shellfish and finfish and yielded high fishery income, compared with the mangrove‐poor areas. Luxuriant mangrove areas supported a catch of 11 kg shellfish ha−1 day−1 and 4.5 kg finfish ha−1 day−1, corresponding with an economic gain of US$ 14 (Rs 603.7) day−1 for shellfish and US$ 3 (Rs 130.5) day−1 for finfish. The value of maintaining mangroves to ensure better fishery resources and to support coastal economies was identified. Management practices for conserving and enhancing mangroves and associated fishery resources are suggested.
Observations on the artisanal stake net fishery for shrimps in the Negombo Lagoon, Sri Lanka
Authors: Jayawardane P. A. A. T. , Perera H. A. R. E.
Published: March 2003

Abstract  The artisanal, stake net fishery for shrimp in the Negombo lagoon, Sri Lanka, was studied over 2 years. There are around 22 sites, at which 57–63 stake nets can be fixed, at sites close to the sea mouth of the Negombo lagoon. The estimated mean catch rates of the fishery were 23.21 and 26.19 kg per operation in 1998 and 1999, respectively. The estimated annual fish productivity from the fishery reduced from 240 t in 1998 to 215 t in 1999. Subadults of penaeid shrimps formed 82% of the stake net catch. The net monthly income per fishermen varied from Rs. 5000 to 33 200 (mean = 13 667). In the Negombo lagoon stake net fishery, a mechanism for equity sharing was formulated by the fishing community.
Mathematical models of population dynamics of the kelp Laminaria religiosa, with emphasis on temperature dependence
Authors: YOSHIMORI AKIRA , KONO TOKIHIRO , IIZUMI HITOSHI
Published: March 2003

Theoretical and numerical models were developed to investigate the effects of water temperature on the population dynamics of the kelp, Laminaria religiosa. The models describe seasonal changes in the biomass of kelp by calculation of growth and grazing rates of sea urchins, Strongylocentrotus nudus. Using the theoretical model, conditions were obtained to satisfy the statistical analysis of a relationship between water temperature and kelp harvests from a fishery census. The conditions require the negative second derivative of the growth rate with respect to temperatures, or the positive second derivative of the grazing rate. By using the numerical model, harvests of kelp were calculated for a change in water temperature over a given period. The period of a temperature change giving the maximum effects on the harvest was determined primarily by temperature dependence on the growth rate. Grazing by sea urchins had large effects on the harvest of kelp. A value of 104 was obtained for a ratio between harvests at the higher and the lower temperatures differing by ± 1∘C.
A spatial population dynamics simulation model of tropical tunas using a habitat index based on environmental parameters
Authors: Bertignac M. , Lehodey P. , Hampton J.
Published: March 2003

We are developing a spatial, multigear, multispecies population dynamics simulation model for tropical tunas in the Pacific Ocean. The model is age‐structured to account for growth and gear selectivity. It includes a tuna movement model based on a diffusion–advection equation in which the advective term is proportional to the gradient of a habitat index. The monthly geographical distribution of recruitment is defined by assuming that spawning occurs in areas where sea surface temperature is above 25°C. During the first 3 months of their life, simulated tunas are transported by oceanic currents, after which movement is conditioned by gradients in the habitat index. Independent estimates of natural mortality rates and population size from large‐scale tagging experiments carried out by the Secretariat of the Pacific Community are used in the simulations. The habitat index consists of components due to forage density and sea surface temperature, both of which are suspected to play major roles in determining tuna distribution. Because direct observations of forage are not available on a basin scale, we developed a submodel to simulate the surface tuna forage production (Lehodey et al., 1998). At present, only skipjack (Katsuwonus pelamis; a surface tuna species caught by purse seine and by pole‐and‐line) is considered, at a 1°‐square resolution and on a monthly climatological time series. Despite the simplicity of the model and the limitations of the data used, the simulation model is able to predict a distribution of skipjack catch rates, of the different fleets involved in the fishery, that is fairly consistent with observations.
Coupling of an individual‐based population dynamic model of Calanus finmarchicus to a circulation model for the Georges Bank region
Authors: MILLER CHARLES B. , LYNCH DANIEL R. , CARLOTTI FRANÇOIS , GENTLEMAN WENDY , LEWIS CRAIG V. W.
Published: March 2003

An individual‐based life history and population dynamic model for the winter–spring dominant copepod of the subarctic North Atlantic, Calanus finmarchicus, is coupled with a regional model of advection for the Gulf of Maine and Georges Bank. Large numbers of vectors, each representing individual copepods with elements for age, stage, ovarian status and other population dynamic variables, are carried in a computation through hourly time steps. Each vector is updated at each time step according to development rate and reproductive functions derived from experimental data. Newly spawned eggs are each assigned new vectors as needed. All vectors are subject to random mortality. Thus, both life history progression and population dynamics of C. finmarchicus are represented for the temperatures in the Gulf of Maine–Georges Bank region in the active season. All vectors include elements representing depth, latitude and longitude. This allows coupling of the population dynamics to the tide‐ and wind‐driven Dartmouth model of New England regional circulation. Summary data from the physical model are used to advance vectors from resting‐stock locations in Gulf of Maine basins through two generations to sites of readiness for return to rest. Supply of Calanus stock to Georges Bank comes from all of the gulf and from the Scotian Shelf. The top of the bank is stocked from western gulf basins; the North‐east Peak is stocked from Georges Basin and the Scotian Shelf. All sources contribute to stock that accumulates in the SCOPEX gyre off the north‐west shoulder of Georges Bank, explaining the high abundance recurrently seen in that region. There is some return of resting stock to Wilkinson Basin in the western gulf, but other basins must mostly be restocked from upstream sources to the north‐east.
New production in the equatorial Pacific: a coupled dynamical–biogeochemical model
Authors: STOENS A. , MENKES C. , DANDONNEAU Y. , MEMERY L.
Published: March 2003

A simple 3‐D biogeochemical model is coupled to a dynamical model forced by weekly winds deduced from ERS1 scatterometer data, to simulate new production in the equation Pacific from April 1992 to June 1995. The biogeochemistry is modelled as a nitrate sink modulated by chlorophyll, using nitrate/chlorophyll regressions derived from field data. The first simulation was carried out assuming that remineralization below the euphotic layer is totally controlled by sinking particles. In the second simulation, it is shown that the simulation of nitrate and new production by the biogeochemical model is improved, in comparison with field data, by adding an explicit dissolved organic nitrogen compartment. In the equatorial band, the model simulates a nitrate‐poor region (low new production) in the fresh warm pool separated from richer waters of the upwelling region by a salinity front. The zonal displacement of this salinity/nitrate front is associated with the El Niño–Southern Oscillation (ENSO). The modelled new production and physics, both in good agreement with the field data, represent useful tools for the study of skipjack tuna (Katsuwonus pelamis) forage distribution in the Pacific.
A model of the spring migration into the North Sea by Calanus finmarchicus overwintering off the Scottish continental shelf
Authors: Gallego A. , Mardaljevic J. , Heath M.R. , Hainbucher D. , Slagstad D.
Published: March 2003

A particle tracking model was used to investigate the annual spring invasion of the North Sea by Calanus finmarchicus copepodites which overwinter in deep water off the Scottish continental shelf. Flow fields generated by a hydrodynamic model (HDM) were used to simulate the advection of zero drag particles representing the copepods. Particles were released simultaneously from a regular lattice of start positions at a given depth (D1), and ascended at a fixed rate (dD/dt) until they reached a final depth (D2) in the surface layers. The proportion of particles reaching target areas in the northern North Sea was relatively insensitive to a moderate degree of variation (±20%) around chosen default values of the vertical migration parameters (D1, D2 and dD/dt), derived from field data. The inclusion of horizontal diffusion velocities and diel vertical migration in surface layers did not significantly affect the results. Sensitivity to wind direction was investigated by applying flow fields from HDM runs with different wind forcing scenarios. For the default vertical migration parameters, only north‐westerly winds resulted in particles entering the North Sea from release locations north of the Iceland–Scotland Ridge, where dense aggregations of overwintering copepods were encountered during field surveys. The particle tracking model predicted that the major routes for the spring Calanus invasion into the North Sea were the East of Shetland Atlantic Inflow and the Norwegian Trench Atlantic Inflow, which agreed with seasonal trends observed in Continuous Plankton Recorder data. Overall, despite its relative simplicity, particle tracking was confirmed as a robust tool to explore the causal mechanisms behind the annual invasion of the North Sea by C. finmarchicus emerging from diapause in the deep waters off the Scottish continental shelf.
Proximate composition of some north‐eastern Pacific forage fish species
Authors: Payne Susan A. , Johnson B. Alan , Otto Robert S.
Published: March 2003

To understand the relative dietary value of forage fish as prey in the Bering Sea and Gulf of Alaska, whole organisms of 13 species were analysed for proximate composition (protein, oil, ash and moisture content). Eulachon (Thaleichthys pacificus) were high in oil (total lipid) (16.8% to 21.4%) and low in moisture (64.6% to 70.8%). Oil in capelin (Mallotus villosus) ranged from 2.1% to 14.0%. Juveniles of walleye pollock (Theragra chalcogramma), Atka mackerel (Pleurogrammus monopterygius), Pacific herring (Clupea pallasii), and prowfish (Zaprora silenus) had low oil contents (< 1.8%) and high moisture contents (> 80.3%). Rankings of median proximate values illustrate the similarities. Surf smelt (Hypomesus pretiosus), rainbow smelt (Osmerus mordax), pricklebacks (Lumpenus spp.), Atka mackerel, Pacific sand lance (Ammodytes hexapterus) and Pacific sandfish (Trichodon trichodon) ranked high in median protein content (> 15.4%). Median ash content for all species ranged from 0.6% to 3.3%. Total wet mass caloric content (kcal g–1) was calculated for the four main species and a linear model was developed for caloric content as a function of moisture. The linear models (caloric content = b0 + b1 × moisture) were Pacific sand lance and Pacific sandfish (b0 = 7.82, b1 = – 0.09); eulachon (b0 = 7.97, b1 = – 0.08); and capelin (b0 = 9.70, b1 = – 0.11).
Variability in growth rates of larval haddock in the northern North Sea
Authors: GALLEGO  , HEATH  , BASFORD  , MACKENZIE
Published: March 2003

The large‐scale distribution of haddock (Melanogrammus aeglefinus) larvae in the northern North Sea was mapped in a grid survey carried out in late April 1996. A drifting buoy was deployed in the centre of one of the areas of concentration of larvae located off the east coast of the Shetland Isles, where intensive sampling was carried out for ≈ 10 days. Daily larval haddock growth variability, estimated from otolith microstructure analysis, was independent of the measured variability of the physical and biological environment of the larvae. The survey coincided with the onset of the spring plankton production bloom, and a likely explanation for the absence of environmental effects on larval growth was high food availability and larval feeding rates. Nevertheless, differences in growth were observed between cohorts, with larvae hatched later in the spring displaying higher growth at age than those hatched earlier. Particle‐tracking modelling suggested that differences in temperature history between cohorts, on their own or compounded by a potential interaction between temperature and the development of plankton production, may explain the higher growth rate of the larvae hatched later in the season.
Confirmation of the spawning area of the striped marlin, Tetrapturus audax, in the so‐called core area of the eastern tropical Pacific off Mexico
Authors: Armas Rogelio GonzÁlez , Sosa‐Nishizaki Oscar , RodrÍguez RenÉ Funes , PÉrez Victor AndrÉS Levy
Published: March 2003

We report the presence of striped marlin larvae in coastal waters of the mouth of the Gulf of California, collected during seven oceanographic cruises during 1990 to 1993. From 169 sampled stations, 30 produced a total of 68 larvae of 2.4–30.5 mm total length. Most of the larvae were about 3 mm, indicating a recent spawn. The sea surface temperature at the sampled stations ranged from 19.4°C to 32.0°C, but larvae were caught at stations with temperatures between 27.8°C and 31.5°C. These results clarify the existence of a spawning area of striped marlin in the eastern Pacific, located closer to the coast than previously believed, during several months of the year.
The zooplankton biomass in the Sea of Japan
Authors: Hirota Yuichi , Hasegawa Seizo
Published: March 2003

We examined seasonal, annual variation and horizontal distribution of zooplankton in the Sea of Japan from 1966 to 1990. Zooplankton was most abundant in the spring. The spring maximum appeared in February–March and in April–May in the southern and eastern parts of the study areas, respectively. In the summer and autumn, a secondary peak was most conspicuous in the eastern part. The difference between the estimated biomass at night and day was large in the spring and small in summer and autumn. The biomass in the offshore southern area peaked about every 3 years between 1966 and 1983, and increased abruptly in 1990. The density in the area north of 39°N or 40°N was high. Total biomass estimated in the upper 150 m layer in the Sea of Japan (106 km2) was 9.5 × 106 t in the daytime and 16.6 × 106 t at night.
Patterns in the spawning of cod (Gadus morhuaL.), sole (Solea soleaL.) and plaice (Pleuronectes platessaL.) in the Irish Sea as determined by generalized additive modelling
Authors: Fox  , O’Brien  , Dickey‐Collas  , Nash
Published: March 2003

Eleven ichthyoplankton cruises were undertaken covering most of the Irish Sea during the period February to June, 1995. To identify spawning localities and investigate temporal trends in egg production, the data on stage 1 A egg distributions of cod (Gadus morhua), plaice (Pleuronectes platessa) and sole (Solea solea) have been modelled using generalized additive models (GAMs). A two‐stage approach was adopted where presence/absence was firstly modelled as a binary process and a GAM surface subsequently fitted to egg production (conditional on presence). We demonstrate that this approach can be used to model egg production both in space and in time. The spawning sites for cod, plaice and sole in the Irish Sea were defined in terms of the probability of egg occurrence. For cod, we demonstrate that by integrating under predicted egg production surfaces, a cumulative production curve can be generated and used to define percentiles of production and thus delimit the extent of the spawning season. However, for plaice and sole, the surveys did not fully cover the spawning season and the limitations that this imposes on GAM modelling of these data are discussed. Comparison of the spawning sites in 1995 with historical data suggests that the locations of cod, plaice and sole egg production in the Irish Sea have probably remained relatively constant over the last 30 years.
Trends in coho marine survival in relation to the regime concept
Authors: Beamish  , Noakes  , Mcfarlane  , Pinnix  , Sweeting  , King
Published: March 2003

There was a synchronous and significant decrease in marine survival of coho salmon in the Strait of Georgia, Puget Sound, and off the coast from California to Washington after 1989. This large‐scale, synchronous change indicates that trends in coho marine survivals were linked over the southern area of their distribution in the north‐east Pacific, and that these linkages were associated with a common event. Indicators of large‐scale climate change (the Aleutian Low Pressure Index) and of recent regional climate change (the April flows from the Fraser River) also changed abruptly about the same time. The synchrony of trends in marine survival of aggregates of coho stocks from three distinct marine areas and trends in climate indices implies that climate/ocean changes can have profound impacts on the population dynamics of coho salmon. The trend towards low marine survival may persist as long as the trends in the climate indicators do not change.
Computer simulations of the effects of the Sitka eddy on the migration of sockeye salmon returning to British Columbia
Authors: Healey  , Thomson  , Leblond  , Huato Leonardo , Hinch  , Walters
Published: March 2003

The Sitka eddy is a mesoscale eddy, 300 km in diameter, that develops off SE Alaska in about one year in two. The eddy has surface currents exceeding 50 km day−1 and it has been suggested that the eddy could deflect migrating salmon to the south, thereby reducing the proportion of British Columbia (BC) sockeye salmon accessible to Alaskan fishers. We modelled its effects on the migration of sockeye salmon (Oncorhynchus nerka) returning to northern BC, using an individual‐based model to simulate migration paths, migration timing and metabolic costs of salmon with different migration behaviours. Except when their migration behaviour included positive rheotaxis, salmon that encountered the eddy had faster migration times and lower metabolic costs than those that did not. The least complex migration behaviour, compass orientation with no rheotaxis, was only slightly less efficient in metabolic terms than the optimal migration paths determined by dynamic programming. Our simulations show that the Sitka eddy itself does not deflect migrating salmon to the south or south‐east regardless of migration behaviour, but that by interrupting the normal northward flow of the Alaskan Current, the eddy could influence latitude of landfall of migrating salmon.
Relative contributions from exposed inshore and estuarine nursery grounds to the recruitment of stone flounder,Platichthys bicoloratus, estimated using otolith Sr:Ca ratios
Authors: Yamashita Yoh , Otake Tsuguo , Yamada Hideaki
Published: March 2003

In Sendai Bay, stone flounder larvae settle and spend their juvenile period in either shallow exposed inshore nursery grounds or estuarine nursery grounds. The purpose of this study is to examine the relative contributions of these two kinds of nursery grounds to the flounder population using otolith strontium:calcium ratios. Stone flounder juveniles were collected from both nursery grounds, and one‐ and two‐year‐old flounder were caught deeper in Sendai Bay. Sr and Ca content in the otoliths were measured by electron probe micro analysis. The Sr:Ca ratios in the otolith section corresponding to the early postsettlement period ranged from 3.06 to 3.85 for the exposed inshore areas with stable low temperature and high salinity conditions, and from 3.81 to 5.32 in brackish estuaries with high temperature and low salinity conditions but with large diel and tidal cyclical fluctuations. Values from an estuarine site with stable salinity ranged from 3.58 to 4.15 overlapping with both the above ranges. Rearing experiments supported our inference that the high otolith Sr:Ca ratios of juveniles inhabiting estuarine nursery grounds are attributable to higher temperature and physiological stress caused by the large diel temperature and salinity fluctuations within the estuaries. Estimation of the Sr:Ca ratio of recruited fish using the otolith section formed while in the nursery area showed that at least 20 out of 42 individuals examined originated from estuarine nursery grounds. The present study indicates that estuaries play an important role as nursery grounds for stone flounder, producing about half of the stock in spite of the small and restricted area compared with the wide expanse of the exposed inshore area.
Interannual variability in growth of walleye pollock, Theragra chalcogramma, in the central Bering Sea
Authors: Akira N. , Yanagimoto T. , Mito K. , Katakura S.
Published: March 2003

Interannual variability in growth of walleye pollock, Theragra chalcogramma, was examined. Adult walleye pollock were collected from the central Bering Sea (Aleutian Basin) from 1978 to 1999. Average fork lengths were found to be approximately 47 cm during the 1970–80s, this increased to 56 cm in the late 1990s. Age was determined for 4805 individuals using the otolith break and burn method. Ages ranged from 5–23 years and the year classes of 1978 and 1989 were dominant in the 1980s and the 1990s, respectively. Fish had significantly larger length‐at‐age in the 1990s compared to the 1970–80s, and interannual variability in age–length relationship was clearly observed. Taking into consideration a recent decrease of the walleye pollock biomass in the central Bering Sea, density‐dependent growth was supported as one possibility of the growth variability. At the same time, we could not rule out the possibility that oceanographic variability affected the growth of walleye pollock in the area.
Implications of interannual variability in euphausiid population biology for fish production along the south‐west coast of Vancouver Island: a synthesis
Authors: Tanasichuk R. W.
Published: March 2003

This is a synthesis of published and unpublished research on euphausiid and fish populations using the south‐west coast of Vancouver Island. Overall, the studies covered 1985–98, when there were two ENSO events and considerable variation in upwelling. The population biology of the dominant euphausiids (Thysanoessa spinifera, Euphausiapacifica) was monitored during 1991–98. The species abundance trends differed. Results of simple correlation analyses suggested that variations in temperature, salinity and upwelling do not explain variations in the abundance of larval or adult euphausiids, or in the abundance of portions of euphausiid populations on which fish feed. I found significant interannual variations in daily ration of the dominant planktivorous fish species, but euphausiids remained the most important prey. Pacific hake (Merluccius productus), the dominant planktivore, fed on larger (>17 mm) T. spinifera, even though the biomass of this part of the euphausiid biomass decreased by 75% between 1991 and 1997, but Pacific herring (Clupea pallasi) may have begun feeding on smaller E. pacifica. Therefore, any study of the relationship between fish production and krill biology must consider that part of the euphausiid biomass exploited by fish. In addition, some fish species and/or life history stages appeared to adapt to changes in euphausiid availability, while others did not. Such variation in adaptations also has to be described and considered to understand how changes in euphausiid biology affect fish productivity.
Spatial distribution and feeding habits of Pacific cod (Gadus macrocephalus) larvae in Mutsu Bay, Japan
Authors: Takatsu Tetsuya , Nakatani Toshikuni , Miyamoto Takanori , Kooka Kouji , Takahashi Toyomi
Published: March 2003

The spatial distributions and feeding habits of Pacific cod (Gadus macrocephalus) larvae, and the spatial distributions of copepod nauplii and copepodites, their main prey, were examined in Mutsu Bay from February to March during 1989–92. Yolk‐sac larvae were caught at 30–45 m depth at the bay mouth. Larvae without yolk were collected at 8–45 m depth at the bay mouth and the inner part of the bay, and large larvae were chiefly found in the bay. This geographical pattern in larval size may have been because of transport to the inner part of Mutsu Bay by the Tsugaru Warm Current. The dominant taxa of copepod nauplii and copepodites in the diet and the environment changed each year. Larvae fed mainly on abundant taxa in the environment, suggesting that larvae are opportunistic feeders. Nauplii and copepodites were abundant in the bay, especially in 1992. Copepodites were slightly more abundant in the diet of cod larvae in 1992 than in 1991, but this difference was smaller than in the environment. In addition, larvae with empty digestive tracts were scarce in 1991 and 1992. Prey concentrations in the bay in 1991 and 1992 seem to have been high enough to sustain most Pacific cod larvae.
Fisheries management based on ecosystem dynamics and feedback control
Authors: Matsuda Hiroyuki , Katsukawa Toshio
Published: March 2003

Recently, ecosystem management has become popular for forestry, agriculture and fisheries management. Carrying capacity and maximum sustainable yield for a particular species definitely depend on population sizes of other species in the same ecosystem. Natural stock fluctuations of sardine, anchovy and chub mackerel are well known examples of large, natural fluctuations. There is a negative correlation among their fluctuations. In accordance with the cyclic advantage hypothesis for replacement of pelagic fish species (Matsuda et al., 1992), we can predict the next dominant species, despite an uncertainty in the year of the next replacement. We recommend that commercial fisheries should switch their target to the next dominant species before the stock of the present dominant species collapses. Whilst total allowable catch (TAC) of the present dominant species can be as large as we can consume, TAC after the species collapses should be much smaller than the present catch level.
Biomass and taxonomic composition of micronekton in the western tropical–subtropical Pacific
Authors: Hidaka Kiyotaka , Kawaguchi Kouichi , Tanabe Toshiyuki , Takahashi Mio , Kubodera Tsunemi
Published: March 2003

The biomass distribution, community structure and species composition of the dominant micronektonic animals were determined in the western tropical Pacific, using day/night sampling from upper 200 m depth with a commercial midwater otter trawl in fall‐winter of 1994, 1995 and 1997. Night‐time micronekton biomass was significantly higher than daytime biomass except for a few cases. All the night‐time catches had similar taxonomic composition, dominated by myctophid fishes, small squids, shrimps and euphausiids. Night‐time micronekton biomass in the upper 200 m was assumed to be higher in the North Equatorial Counter Current than in the North Equatorial Current, reflecting the zooplankton biomass distribution which micronektons feed on at night. A total of 42 species of myctophid fishes, 34 species of squids, 27 species of shrimps and six species of euphausiids were collected. Community types of each dominant taxonomic group were classified by cluster analysis based on the species composition. A station located north of the subtropical convergence zone was distinct from other tropical stations south of the convergence zone, having significantly different species composition in three of the four dominant taxonomic groups (myctophids, squids and shrimps). The interaction between the larvae of commercially important fishes and micronektonic animals is discussed.
Relationships between zooplankton community structure and phytoplankton in two lime‐treated eutrophic hardwater lakes
Authors: Ghadouani Anas , Alloul Bernadette Pinel , Zhang Ying , Prepas And Ellie E.
Published: March 2003

1. North Halfmoon Lake and Lofty Lake (Alberta, Canada) were chosen for whole‐lake liming experiments as a new restoration technology to enhance calcite precipitation and reduce eutrophication. During a 3‐year study (1991–93) the relationships between zooplankton and phytoplankton were assessed, together with the effects of lime additions.

2. Zooplankton communities were numerically dominated by rotifers, while the major contribution to biomass was due to large filter‐feeding Daphnia during the first half of the summer season. In Lofty Lake, cladocerans made up to 93% of biomass, whereas in North Halfmoon Lake both cladocerans and calanoids were strongly represented.

3. Total zooplankton and cladoceran biomasses were inversely correlated with chlorophyll a (chl a). The same relationship was found between large Daphnia (≥ 1 mm) and chl a. These relationships suggest that the decline in Daphnia may have been caused by an increase in cyanobacteria biomass during bloom events.

4. There were minor changes in rotifer populations after liming; however, these changes have been caused by natural year‐to‐year variation rather than liming. In general, cladocerans showed an increase in body size and population biomass when pre and post‐treatment data were compared by means of ANCOVA. Statistical analysis showed that there were more cladocerans per unit of chl a after liming; however, further research is needed to relate these patterns unambiguously to the application of lime as a restoration technology.
Fatty acid biomarkers show dietary differences between dominant chironomid taxa in Lake Erken
Authors: Goedkoop  , Sonesten  , Markensten  , Ahlgren
Published: March 2003

1. In this field study, diatom‐specific and bacteria‐specific fatty acids were used as biomarkers to evaluate the differences in diet betweenChironomus plumosus (a spring‐emerging cohort) andC. anthracinus(an autumn‐emerging cohort), andProcladiusspp. Furthermore, total lipid content ofChironomuslarvae was analysed.

2. Individual dry mass of the spring cohort ofC. plumosusrapidly increased during spring and early summer. Surprisingly, the autumn‐emerging cohort showed remarkably little growth over the same time interval. The individual dry mass ofC. anthracinusinitially declined in early spring, but then increased during April and May.

3. Accumulation of the diatom‐specific fatty acid palmitoleic acid (16 : 1ω7) during spring was much higher inC. plumosus(> 3‐fold increase) than inC. anthracinus(1.5‐fold). Conversely, the bacterial indicatingisoform of septadecanoic acid (17 : 0i) was higher inC. anthracinusthan in the spring‐emerging cohort ofC. plumosus. This shows thatC. plumosusassimilates energy from the spring diatom bloom to a greater degree, whereasC. anthracinusfeeds more exclusively on detritus in the sediment.

4. Concentrations of 17 : 0iinProcladiuslarvae were 0.54 ± 0.13 mg g–1, i.e. consistently higher than for bothChironomustaxa, indicating that this predator gains a relatively high fraction of its energy through detrital pathways (from bacteria).

5. These results show that fatty acid biomarkers can be an appropriate tool to detect differences in larval diet between coexisting chironomid species, between two closely relatedChironomusspecies and between different cohorts.

6. The different feeding modes of bothChironomusspecies may be important for among‐lake distribution patterns, with filter‐feedingC. plumosusbeing dominant in relatively shallow lakes and deposit‐feedingC. anthracinusmore common in deeper lakes with stable stratifications. This conjecture was supported by a compilation of data from Lake Mälaren.
The role of shell strength in selective foraging by crayfish for gastropod prey
Authors: Brown K. M.
Published: March 2003

1. Four gastropods common in Wisconsin lakes, Amnicola limosa, Gyraulus parvus, Physella gyrina and Helisoma anceps, were exposed to predation by three crayfish congeners, Orconectes rusticus, O. propinquus and O. virilis in the laboratory to determine prey preference.

2. There were no differences in prey choice among the crayfish congeners, but there were clear differences in electivity for the different snail prey.

3. Crayfish had higher electivities for the thin‐shelled, plano‐spiral pulmonate Gyraulus parvus, despite its lower abundance in samples, than the thicker‐shelled prosobranch Amnicola limosa. Electivity for another plano‐spiral pulmonate, Helisoma anceps, was low, evidently because of its relatively thick shell and larger size. Amnicola limosa and the thin‐shelled pulmonate Physella gyrina (present at roughly the same relative abundance as Gyraulus parvus) were neither selected nor avoided.

4. Crayfish electivity appears to be a function of the resistance of shells to chipping by crayfish mandibles. Although different species are preferred, this is similar to the previously described selection of thin‐shelled species by sunfish.
Influence of hypolimnetic hydropeaking on the distribution and population dynamics of Ephemeroptera in a mountain stream
Authors: Céréghino R. , Lavandier P.
Published: March 2003

1. The Ephemeroptera assemblage of the River Oriège (Pyrenees, France) was studied up‐ and downstream of a hydroelectric power plant with hypolimnetic releases from a nearby high altitude reservoir. The life histories and larval growth of the six dominant species (Rhithrogena semicolorata, R. sp. gr. hercynia, R. kimminsi, Baetis alpinus, B. rhodani, Ephemerella ignita) were studied 700 m upstream (site A) and 700 and 3500 m downstream (sites B and C, respectively) of the power plant. Their drift patterns were studied at sites A and B.

2. The natural flow of the river was preserved when the plant was inoperative. During power generation, flow and temperature were the two main environmental factors modified. The natural flow in the river below the outlet may be enhanced several times a day from 1 to 11 m3 s–1 in summer and winter, and from 5 to 15 m3 s–1 during spring spates. During hydropeaking, the water was cooled in summer and slightly warmed in winter, but this was attenuated 3500 m downstream from the plant.

3. The density and biomass of the species studied at the three sites reflected both the impact of hydropeaking and the natural longitudinal zonation of the fauna. The lowest density and biomass was estimated at 700 m downstream from the plant (site B), consistent with a prominent role for hydropeaking. Site A showed constant mayfly drift caused by accidental dislodgement plus behavioural drift that was mainly nocturnal. Below the plant, the flushing action of peaking flows added to this a catastrophic drift, which was highest in autumn when the difference between natural and peak flows was greatest.

4. Environmental change caused only slight modifications in the life history patterns, affecting the hatching and/or emergence period and growth of several species. For instance, R. semicolorata grew through the winter below the outlet, when growth was slight upstream from the power plant. Under this kind of river regulation (natural discharge and temperature except during periods of power generation, and intermittent hydropeaking from a separate reservoir) modifications of the thermal regime had a minor effect on the population dynamics of mayflies, unlike hydraulic disturbances which strongly influenced the abundance and structure of the benthic community. Frequent (at least daily) high flow disturbances caused depletion of mayfly populations, despite daily renewal and colonization (drift) from undisturbed upstream locations.
Effect of primary producers on the heterotrophic metabolism of a stream biofilm
Authors: Roman Anna M. , Sabater Sergi
Published: March 2003

1. ,The influence of benthic algae on heterotrophic metabolism in a forested Mediterranean stream was investigated. Bacterial density and ectoenzymatic activities, as well as algal biomass (chlorophyll‐a) and metabolism (the rate of 14C incorporation), were measured during colonization over 60 days of artificial substrata (clay tiles) under light and dark conditions.

2. ,Chlorophyll‐a and the rate of 14C incorporation were significantly higher in light‐grown than in dark‐grown biofilms. Bacterial density and ectoenzymatic activity (especially β‐glucosidase) were also significantly higher in light‐grown biofilms.

3. ,Regressions of chlorophyll‐a and 14C incorporation values on the ectoenzymatic activities were significant. The slopes of regression lines obtained for dark‐grown biofilms were significantly higher than those obtained for light ‐grown biofilms.

4. ,The differences in the slope (of the regression lines) between dark and light‐grown biofilms suggest that the response of the heterotrophs is faster in biofilms with low algal biomass accrual and slows down when algal biomass is increased.

5. ,It is concluded that algal accumulation in the epilithic biofilm influences the use of organic matter by the heterotrophic community by increasing the amount of organic substrate available for bacteria.
Effects of physical refuges on fish–plankton interactions
Authors: Bertolo A. , Lacroix G. , Lescher‐Moutouš F. , Sala S.
Published: March 2003

1.Refuges that reduce fish‐induced mortality of zooplankton are considered to be key factors in controlling phytoplankton growth in lake ecosystems. In order to better understand the role of physical refuges for zooplankton on zooplanktivorous fish‐plankton relationships, an enclosure experiment was run in a mesotrophic lake. Even‐link systems (zooplankton and phytoplankton) and odd‐link systems (zooplanktivorous fish, zooplankton and phytoplankton) were established. We also established an odd‐link system with a physical refuge for zooplankton where fish predation was limited in the upper half of the enclosure.

2.Fish negatively affected density and mean body length of herbivorous zooplankton and total zooplankton, filtering rates with some intermediate effects in the presence of the refuge. A clear refuge effect was observed for the dominant herbivore, Ceriodaphnia. On the other hand, the refuge seemed to increase the vulnerability of those taxa that aggregated in upper layers of the water column. Grazing was thus reduced in both odd‐link systems.

3.The lack of significant correlation between nutrient availability and phytoplankton biomass in enclosures suggested a top‐down control of algal growth in our experimental systems. In both odd‐link systems (‘fish’ and ‘refuge’) phytoplankton biomass was significantly enhanced, and transparency was reduced in comparison with the even‐link system.
Patterns of distribution of macroinvertebrate families in rivers of north‐western Australia
Authors: Kay W. R. , Smith M. J. , Pinder A. M. , Mcrae J. M. , Davis J. A. , Halse S. A.
Published: March 2003

1. The northern half of Western Australia is a large, sparsely populated area with a climate that ranges from monsoonal in the Kimberley to arid in the Gascoyne and Pilbara regions. The aquatic invertebrate fauna is poorly known.

2. Fifty‐one sites located on 14 river systems were sampled three times between August 1994 and October 1995. A total of 90 taxa, most identified to family level, were collected. The fauna was dominated by insects, which constituted 74% of the total number of taxa collected.

3. Major habitats at each site were sampled separately and sites with more habitats tended to have a richer fauna. All habitats showed significant differences in taxonomic richness between regions. Family richness decreased with increasing latitude, being highest in the Kimberley region and lowest in the Gascoyne.

4. Despite the differences in taxon richness between regions, community composition of the aquatic invertebrate fauna at the family level did not differ greatly. Four major groups of sites were identified by cluster analysis, based on the invertebrate families present at each site, but differences between groups were small.

5. Significant temporal variation in taxon richness was found in channel habitat but not the three other habitats sampled (riffle, macrophyte, pool‐rocks). Community composition in channel habitat varied temporally among groups of sites identified by cluster analysis but the pattern was not consistent.
Habitat structure along channel‐unit sequences for juvenile salmon: a subunit‐based analysis of in‐stream landscapes
Authors: Inoue Mikio , Nakano S. H. Igeru
Published: March 2003

1. Habitat structure and habitat use by juvenile masu salmon, Oncorhynchus masou Brevoort, in small streams in northern Hokkaido, Japan, were examined by considering ‘subunits’ (patches within channel units) as structural elements of stream reaches.

2. Whole wetted channel surfaces of three study reaches were divided into 0.5 × 0.5 m quadrats, which were grouped into eight subunit types according to water depth and velocity, and substratum conditions by a cluster analysis. The subunit distribution showed a regular mosaic pattern corresponding to the channel‐unit sequence in each of the three reaches.

3. Juvenile masu salmon exhibited a strong preference for a subunit type characterized by greater depth and moderate current velocity (deep–moderate subunit; mean depth = 0.29 m; mean velocity = 0.19 m s−1). This subunit type usually occurred downstream of stretches with fast current. The preference of masu salmon for the deep–moderate subunit could be because of its usual spatial position in relation to other subunit types as well as to the characteristics of the subunit itself.

4. The results suggest that the value of a habitat is determined not only by the characteristics of the habitat itself, but also by those of adjacent habitats. Therefore, habitat use by stream fish should be studied in the context of the whole ‘in‐stream landscapes’.
Fish habitat preferences in large streams of southern France
Authors: Lamouroux Nicolas , Capra Hervé , Pouilly Marc , Souchon Yves
Published: March 2003

1. Relationships between fish and their habitat over whole geographic regions, which are evident from studies of many streams and species, can improve understanding of lotic communities and provide reliable management tools. Nevertheless, most habitat preference studies have been based on single sites, and confined to small streams and to game species.

2. Regional habitat preference models, based on local velocity, depth and roughness, were developed for twenty‐four species and their size classes commonly found in large European streams. Fish surveys were conducted in six large streams in southern France over an 8‐year period. To limit the influences of habitat variables other than those studied, we estimated fish preferences within each survey and averaged this information across surveys. Preferences were fitted with confidence intervals and their sensitivity to field uncertainty was evaluated.

3. Most species and size classes had significant preferences for local habitat conditions which were consistent across the region. Habitat preferences predominant in the region overall were not always observed at any one site, but habitat conditions preferred on average in the region were never actually avoided locally. These results support the use of regional preference models for fish and the development of similar models for other lotic groups whose sensitivity to local habitat conditions has been reported elsewhere.
Lake districts of north‐western Russia: identification of subregions based on analyses of hydrologic data
Authors: Gronskaya T. P.
Published: March 2003

1. There are more than 400 000 lakes in the north‐western part of European Russia. Data from 50 gauging stations (located on lakes with water surface area ≤ 400 km2), within the region, was used to identify regions that exhibit common hydrologic patterns.

2. Analyses of common hydrologic patterns permitted the division of the overall area into four regions within which lakes exhibit common hydrologic and limnologic features.
Optimum energy intake and gross efficiency of energy conversion for brown trout, Salmo trutta, feeding on invertebrates or fish
Authors: Elliott J.M. , Hurley M.A.
Published: March 2003

1. The chief objectives were to determine the daily optimum energy intake (COPT cal day−1) for growth and the gross efficiency (KG%) for converting energy intake into growth for brown trout, Salmo trutta. Energy budgets for individual fish were obtained from experiments with 292 trout (initial live weight 1–318 g) bred from wild parents, and kept at five constant temperatures (5, 10, 13, 15, 18 °C) and 100% oxygen saturation. Most trout (252) were fed over a period of 42 days on a fixed ration of shrimps, Gammarus pulex, the ration levels varying between zero and maximum, but 40 of the larger trout were fed to satiation on freshly‐killed sticklebacks (Gasterosteus aculeatus).  2. Energetics models developed in earlier studies on the same data were summarized briefly and were used to predict the relationship between the change in the total energy content of a trout (CG cal day−1) and its energy intake (CIN cal day−1), and hence to estimate COPT. The models were also used to predict the relationship between KG and CIN. In both comparisons, there was good agreement between observed values from the experiments and expected mean values predicted from the models. For trout feeding on invertebrates, COPT lay closer to the maximum, rather than the maintenance, energy intake. When the diet changed from invertebrates to fish, there was a marked increase in CIN, CG and KG.  3. For trout feeding on invertebrates, KG exceeded 30% within 7–11 °C, with a maximum KG of 31.8% at 8.9 °C. For piscivorous trout, KG exceeded 30% within 4–16 °C and 40% within 6.5–12 °C, with a maximum KG of 41.8% at 9.3 °C. These differences were discussed in relation to the results of previous workers, and the models used in the present study provided a method of exploring the limitations of the ‘K‐line’ hypothesis for the relationship between KG and CIN.
Leaf litter breakdown rates in boreal streams: does shredder species richness matter?
Authors: Jonsson Micael , Malmqvist Björn , Hoffsten Per‐Ola
Published: March 2003

1. Leaf litter breakdown rates were assessed in 23 boreal streams of varying size (first–seventh order) in central and northern Sweden.  2. Shredders were most abundant in small streams, while shredder species richness showed a hump‐shaped relationship with stream order, with most species in fourth order streams.  3. In a partial least‐squares regression analysis, year, water temperature, shredder species richness and shredder abundance were those factors correlating most strongly with leaf breakdown rates. Shredder species richness was more strongly correlated with leaf litter breakdown rates than shredder abundance, and shredder biomass showed no such correlation.  4. These data suggest that shredder species richness is an important variable in terms of leaf litter dynamics in streams.