bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of seasonal variations in meteorology and oceanography on the Brazilian sardine fishery
Authors: SUNYÉ PATRICIA S. , SERVAIN JACQUES
Published: March 2003

Seasonal variations in meteorological and oceanographic processes in the South Brazil Bight were studied to assess their influence on the Brazilian sardine Sardinella brasiliensis fishery. According to its environmental characteristics, the South Brazil Bight was divided into three sectors. The northern and southern sectors were similar during the spring and summer, showing areas of coastal upwelling and low rainfall rates. The middle sector was characterized by the presence of low‐salinity coastal waters in the inner shelf and by high rainfall. During autumn and winter, the middle and southern sectors were similar, both being under the influence of sub‐Antarctic waters. Multiple regression analyses showed significant correlation between environmental data and catches, although at a lower level in the northern sector (r2 = 0.57). In the middle and southern sectors, environmental data were highly correlated with the catches (r2 = 0.90 and 0.84). The sardine landings in the middle sector are principally affected by meteorological parameters, and in the south by oceanographic ones. In the middle sector, an inverse correlation between landings and rainfall is shown, while in the south, landings are positively correlated with salinity and sea temperature. The conclusion is that the seasonal landings of the Brazilian sardine within the South Brazil Bight are influenced by the distribution of less saline waters, the coastal waters and sub‐Antarctic waters.
Basin‐scale advection and population persistence of Calanus finmarchicus
Authors: BRYANT ANDREW D. , HAINBUCHER DAGMAR , HEATH MICHAEL
Published: March 2003

Advection of Calanus finmarchicus in the eastern North Atlantic was analysed using a particle‐tracking model based on the Hamburg Shelf Ocean Model (HAMSOM). Quasi‐static seasonal mean flowfields were simulated, archived and interpolated to represent a climatological‐mean annual cycle. Particles had a simple prescribed depth profile comprising deep overwintering, spring ascent, a shallow‐water phase followed by descent to overwintering depth. Export routes for C. finmarchicus from the model area were identified to the south of Greenland and to the north of the Lofoten Basin. Self‐sustaining overwintering areas were identified by observing how closely particles returned to their origins after one calendar year. Several such areas were found, notably in the Norway and Lofoten Basins, and in the Færoe–Shetland Channel. The particle tracking was run for up to 10 years to demonstrate persistence of these cycles. Known features of the winter and summer distributions of C. finmarchicus were reproduced by the model. The success of the HAMSOM in simulating both the shallow and deep circulation of the eastern North Atlantic and Norwegian Sea was critical to the identification of these spatio‐temporal cycles of C. finmarchicus.
Environmental and biological monitoring for forecasting anchovy recruitment in the southern Benguela upwelling region
Authors: PAINTING S. J. , HUTCHINGS L. , HUGGETT J. A. , KORRÛBEL J. L. , RICHARDSON A. J. , VERHEYE And H. M.
Published: March 2003

Environmental and biological sampling and monitoring have been carried out in the southern Benguela since 1988. The overall goal of this research is to investigate environmental factors affecting anchovy recruitment and to develop the ability to forecast anchovy recruitment from year‐to‐year using field data obtained during the spawning season (August to March). Sampling was conducted at three different temporal and spatial scales: during annual (November) broad‐scale hydro‐acoustic surveys to determine spawner biomass on the entire spawning ground and in the core transport and recruitment areas; during monthly surveys in the core spawning, transport and recruitment regions over two entire spawning seasons (1993/94 and 1994/95); and during weekly sampling (since 1995) along a single transect downstream from the spawning area. Annual surveys provide the best spatial coverage, but are inadequate for representing environmental conditions and anchovy spawning success over a prolonged season. Weekly sampling provides the best temporal coverage, but logistical constraints restrict information to a limited portion of the spawning area and a reduced number of variables. Monthly surveys provide intermediate coverage in time and space, but are expensive and labour‐intensive. Forecasting anchovy recruitment has been based on two different approaches: the establishment of empirical relationships, and the development of rule‐based expert systems. Forecasts from deterministic expert systems have compared well with final estimates of recruitment strength, and indicate that environmental and biological variables may be used in a structured way to forecast anchovy recruitment.
Circulation of the eastern North Atlantic and north‐west European continental shelf – a hydrodynamic modelling study
Authors: Hainbucher D. , Backhaus J.O.
Published: March 2003

As part of the interdisciplinary investigation of Calanus finmarchicus migrations between oceanic and shelf areas off north‐west Europe (the ICOS project), a three‐dimensional, prognostic baroclinic circulation model system, consisting of a coarse and a nested fine scale model, was constructed. The aim was to simulate the flow fields around Iceland, the Faroe Islands and the north‐west European continental shelf and slope, including the northern North Sea. The coarse scale model covered the northern North Atlantic and provided the far field flow to the finer scale model. The latter was initialized and forced with climatological seasonal (winter and spring) means of temperature, salinity, river run‐off, and other parameters necessary for the calculation of heat fluxes. Seasonal average simulations of flow and hydrographic conditions were performed, together with simulations of specific scenarios of uniform wind forcing from different directions. A feature common to all the results was a topographically guided northwards flow along the continental shelf edge, with a southwards counter‐flow in the vicinity of the Faroe–Shetland Channel. The extent and strength of the shelf edge current, of its counter flow, and of the re‐circulation cell in the northern North Sea, were dependent on the prevailing wind direction. The modelling results were consistent with the accepted circulation patterns in the area, and a comparison with field measurements in the Faroe–Shetland Channel showed that the main characteristics of the flow were well replicated, although the estimated strength of the slope current was somewhat less than in the field observations.
The South Atlantic Bight Recruitment Experiment: introduction and overview
Authors: Ortner  , Crowder  , Hoss
Published: March 2003

The South Atlantic Bight Recruitment Experiment (SABRE) brought together a interdisciplinary team of scientists to conduct research to enhance our understanding of the relationship between variation in environmental factors and the variable recruitment of ‘estuarine dependent’ fishes within the SAB. The project sought to develop a new fusion of government and academic scientists, each possessing unique skills, to address the difficult problem of recruitment variability in fishes. This fusion required the development of appropriate and at that time novel management and administrative strategies. SABRE initially focused on recruitment dynamics of Atlantic menhaden, Brevoortia tyrannus, in the South Atlantic Bight, but expanded over time to include several estuarine‐dependent species and much of the Middle Atlantic Bight as well. The project was conducted from 1991 to 1997 and resulted in a substantial improvement in our understanding of the life history and ecology of Atlantic menhaden and the potential constraints upon its recruitment. SABRE also contributed to our understanding of the physical oceanography of the western North Atlantic shelf and adjacent coastal inlets and the implications of physical dynamics upon the potential pathways for larval transport.
Diel vertical distribution of postflexion larval Citharichthys spp. and Sebastes spp. off central California
Authors: SAKUMA KEITH M. , RALSTON STEPHEN , ROBERTS DALE A.
Published: March 2003

The diel and spatial distributions of postflexion larval Citharichthys spp. and Sebastes spp. at 67 stations off central California were examined during March 1994 with a 10 m2 MOCNESS during 24 h sampling operations. At each station, a CTD profiler with an attached PAR sensor was deployed to measure temperature, salinity, σt, dynamic height, and ambient light levels at depth. Catches of C. sordidus, C. stigmaeus, unidentified Sebastes spp., and S. jordani were larger at night than during the day and crepuscular periods, probably because of net avoidance during the day and crepuscular periods, and (for Citharichthys spp.) vertical migration into the upper water column at night. C. sordidus and C. stigmaeus migrated vertically through the pycnocline on a diurnal cycle, while Sebastes spp. apparently remained in the mixed layer above the pycnocline at all times. No definitive patterns were observed between horizontal contours of temperature, salinity, and σt at depth and catches of any larvae. This was attributed to the relatively homogeneous spatial pattern in the water column above the pycnocline, where the majority of the fish occurred.
Interannual variation in the availability and utilization of euphausiids as prey for Pacific hake (Merluccius productus) along the south‐west coast of Vancouver Island
Authors: TANASICHUK
Published: March 2003

The species and size composition of euphausiids consumed by Pacific hake (Merluccius productus) along the south‐west coast of Vancouver Island were monitored during the 1989, 1990 and 1995–97 summer feeding seasons. Thysanoessa spinifera and Euphausia pacifica were the only euphausiid species eaten by hake. Hake persisted in selecting krill longer than 17 mm and consistently preferred T. spinifera, even though there was a substantial reduction in euphausiid abundance, a change in species composition and a shift in the size distribution to smaller individuals after the 1992–93 warm water years. The biomass of euphausiids available to hake after 1993 averaged 27% of that for 1991, the pre‐ENSO year, and was 12% of the 1991 value in 1996. Hake predation was not responsible for the reduction in euphausiid abundance, as it was already low at euphausiid sizes smaller than those eaten by hake.
Geographical variations in the trophic structure of the plankton community along a eutrophic–mesotrophic–oligotrophic transect
Authors: Uye S. , Iwamoto N. , Ueda T. , Tamaki H. , Nakahira K.
Published: March 2003

The geographical variations in trophic structure of the plankton community, as defined by total and relative carbon biomass of phytoplankton (PP), bacteria (BA), heterotrophic nanoflagellates (HNF), microzooplankton (MZ), and herbivorous (HNZ) and carnivorous net‐zooplankton (CNZ), were investigated along an inshore–offshore transect from the innermost part of Osaka Bay to the Pacific Ocean off Kii Channel, Japan, in June 1991. Based on physico‐chemical properties of the water and topographical features, the transect was divided into three trophic areas, i.e. eutrophic, mesotrophic and oligotrophic ones. The average carbon biomass of the total plankton community was highest (438 mg m−3) in the inshore eutrophic area, and declined steeply offshore (141 and 26.6 mg m−3 in the mesotrophic and oligotrophic areas, respectively). In the offshore oligotrophic area, the relative biomass of BA to PP and the relative biomass of small heterotrophs (i.e. BA, HNF and MZ) to the total heterotrophs were higher than in the other areas, indicating that the microbial food chain predominated. In the mesotrophic area, the biomass of HNZ (primarily copepods) was conspicuously high, even higher than that of PP, suggesting that the traditional grazing food chain prevailed. Because of this short food chain, a productive fishing ground is formed there. In the eutrophic area, the biomass of HNZ was much smaller relative to the enormous biomass of PP, indicating that a considerable amount of primary production was not utilized directly by the metazoan zooplankton. However, the relative contribution of the small heterotrophs to the total heterotrophs’ biomass was higher in this area, as in the oligotrophic area.
Decadal‐scale patterns in the relative year class success of sablefish (Anoplopoma fimbria)
Authors: King  , Mcfarlane  , Beamish
Published: March 2003

Climate–ocean regimes in the north‐east Pacific translate into decadal‐scale patterns in the relative success of sablefish (Anoplopoma fimbria). By combining estimates of year class abundance determined from commercial catches and research surveys for adults and juveniles, we were able to construct an index of year class success. Year classes from 1960 to 1976 were generally below average, with little indication of good year class success. The 1977 year class was exceptionally large and year classes from 1978 to 1990 were generally above average. Year classes following 1990 were generally below average. The periods with above‐average year classes were generally characterized by intense Aleutian Lows, above‐average frequency of south‐westerly winds and warmer coastal sea surface temperatures off the west coast of Vancouver Island. Decadal‐scale patterns in the production of sablefish suggest stability in long‐term periods of similar recruitment but different mean levels of productivity across periods. However, rapid shifts between periods remain unpredictable and therefore complicate the incorporation of decadal‐scale dynamics in management.
Interannual variability in stock abundance of the neon flying squid, Ommastrephes bartramii, in the North Pacific Ocean during 1979–1998: impact of driftnet fishing and oceanographic conditions
Authors: Yatsu Akihiko , Watanabe Tomowo , Mori Junta , Nagasawa Kazuya , Ishida Yukimasa , Meguro Toshimi , Kamei Yoshihiko , Sakurai Yasunori
Published: March 2003

Variability in catch‐per‐unit‐effort (CPUE) was examined for the autumn cohort of Ommastrephes bartramii collected with research driftnets during 1979–1998 along five longitudinal transects passing through the Subarctic, Transitional and Subtropical Domains in the North Pacific. CPUE was generally low during the period of intensive commercial driftnet fishing (1980–1992) and increased following the 1992 moratorium on the use of large‐scale driftnets. However, CPUE levels were low for the cohorts hatched in 1992 and 1996 (captured in subsequent years owing to a one‐year life of O. bartramii) that experienced low sea surface temperatures from hatching to recruitment. Among similar‐aged squid collected from 180° and 179°30′W in June, mantle lengths were significantly greater in 1997 than during 1995–96. These findings suggest that the driftnet fishery and sea surface temperatures from hatching to recruitment strongly affected stock abundance and possibly growth.
Observations on larval fish transport and retention on the Scotian Shelf in relation to geostrophic circulation
Authors: Reiss  , Panteleev  , Taggart  , Sheng  , DeYoung
Published: March 2003

We draw inferences about the dynamic processes responsible for the dispersal of ichthyoplankton on small marine banks using physical and biological data derived from static point‐estimates of water‐mass characteristics and ichthyoplankton collected concomitantly on the central Scotian Shelf. Where the density field evolves slowly and ageostrophic forcing is weak, the near‐surface geostrophic flow can be derived from hydrographic data using the dynamic height method modified for shallow seas. We assess our interpretations of larval distributions using simple particle tracking. The hydrography of the Scotian Shelf during November of 1997 was typical of late autumn, when density is determined by surface variation in salinity. Surface isopycnals generally paralleled isobaths, and there was no evidence of strong surface fronts. Sizes of larvae of pelagic origin (e.g. cod and hake) on Western Bank (sole spawning source) increased and became skewed towards larger animals (cod, 3–10 mm; hake, 5–15 mm) in water‐mass (Temperature and Salinity) space along isopycnals, consistent with gradual mixing and limited transport in the geostrophic flow (i.e. retention). Conversely, larvae of benthic origin (e.g. herring, 6–25 mm) were distributed across water‐mass space, consistent with multiple origins and substantial transport. Our results indicate that dispersal from small, low‐energy marine banks results from the interaction of spawning location, geostrophic currents and bathymetric steering, and requires neither convergence nor larval behaviour.
Influence of the marine abundance of pink (Oncorhynchus gorbuscha) and sockeye salmon (O. nerka) on growth of Ozernaya River sockeye
Authors: Bugaev V. F. , Welch D. W. , Selifonov M. M. , Grachev L. E. , Eveson J. P.
Published: March 2003

The length and weight of Russian sockeye (Oncorhynchus nerka) returning to the Ozernaya River (Kamchatka) was substantially reduced in years when the ocean abundances of Kamchatkan pink (O. gorbuscha) and sockeye salmon were high. We found that the density‐dependent reduction in sockeye growth on a per‐capita basis was greater for sockeye than for pink salmon. However, the overall effect of pink salmon abundance on sockeye growth was greater because of the higher numerical abundance of pink salmon. The strongest statistical relationships were found for sockeye from separate age groups; pooled data combining all age classes were statistically insignificant. We estimate that, if pink salmon were absent, the most strongly affected age group of sockeye salmon (2.1 males) would weigh twice as much at maturity than if pink salmon populations from eastern and western Kamchatka were both simultaneously at peak observed abundances. Trophic competition in the ocean between pink and sockeye salmon can therefore have a significant influence on the productivity of sockeye populations for the most strongly affected age groups. These effects are large enough that they should be explicitly considered in the management of salmon populations.
Fluctuation in the distribution of low‐salinity water in the North Equatorial Current and its effect on the larval transport of the Japanese eel
Authors: Kimura Shingo , Inoue Takashi , Sugimoto Takashige
Published: March 2003

Surface water in the North Equatorial Current (NEC) is composed of southern low‐salinity water diluted by precipitation to less than 34.2 psu and northern, high‐salinity tropical water greater than 34.8 psu. Analyses of 27‐year historical data, observed in winter and summer along the longitude 137°E by the Japan Meteorological Agency, shows that an obvious salinity front (34.5 psu) generated by the two water masses was usually located around 15°N. However, the salinity front has been moving northward during the past three decades. El Niño/Southern Oscillation (ENSO) affected salinity in the surface layer, while temperature changed in the middle layer. The salinity front sometimes moved southward, mainly south of 5°N, and the movement was well correlated with the southern oscillation index (SOI). Because precipitation at Yap (9.5°N, 138.1°E) fluctuated with SOI, this spike‐like southward movement of the salinity front was probably affected by reduction of low‐salinity water during El Niño in the north‐western Pacific Ocean. However, ENSO only induced such large southward movements of the salinity front when the time lag between the low precipitation and low SOI was short (within four months). This salinity front is quite important for long‐distance migrating fish such as the Japanese eel because the eels spawn just south of the salinity front in the NEC. This behaviour suggests that the movement of the salinity front associated with ENSO may control the success of larval transport from the spawning ground in the NEC to the nursery ground in East Asia. In fact, catch of the Japanese eel larvae in Japan was well correlated with fluctuation of SOI and the location of the salinity front, and lower catch occurred during El Niño. The salinity front has moved from 13°N to 17°N during the past three decades. Considering that conditions of larval transport are worse north of 15°N, we suggest that decadal‐scale linear decrease of glass eel catch during the past three decades also can be explained by the displacement of the salinity front.
Biophysical dynamics of western transition zones: a preliminary synthesis
Authors: Olson Donald B.
Published: March 2003

The nature of the western portions of the biogeographic temperate or transition zones in the North Pacific and North Atlantic is reviewed. The physical transport of nutrients and biomass into them from the Kuroshio and Gulf Stream as well as from the poleward sides are estimated. The conclusion is that the upwelling in the two western boundary currents makes the largest contribution to the nutrient and biomass fluxes into these transition zones. A conservative estimate of the amount of upwelled fluid is derived from absolute velocity sections in the Gulf Stream. The estimate suggests that upwelling into the euphotic zone exceeds 2 × 106 m3 s–1. This implies that upwelling in these western boundary currents matches or exceeds that in eastern boundary currents such as the California Current. The two western boundary regimes have very different poleward situations. The Oyashio extension flows parallel to the Kuroshio and is a deep current. The North Atlantic Shelf Front flow is to the west where it is ultimately entrained into the edge of the Gulf Stream. There does not seem to be any tendency for this to occur in the Kuroshio. Despite these differences in the northern and western boundaries, the two transition zones are similar with large amplitude meanders, anticyclonic rings and streamers dominating their physical structure. The physical features responsible for the transfer of materials from the boundary current extensions into the transition zones are similar in both systems. Ring formation contributes only ˜ 10% of the transfer, while ring‐induced streamers contribute 30%. The rest of the transport is contributed by branching of the boundary current front. Both currents have well developed secondary fronts consisting of subtropical surface water pulled into the transition zone.

Biologically, the upwelling in both western boundary currents leads to a biomass maximum along the boundary in both secondary producers (copepods) and in small pelagic fish. In the Kuroshio, the latter are the Japanese sardine, Sardinops melanostictus, that spawn in the Kuroshio and then enter the transition zone for the summer and fall months. In the Gulf Stream, the dominate species are menhaden, Brevoortia tyrannus and B. smithi. These species make use of the coastal environments of North America and although the adults spawn in the Gulf Stream, they are not thought to play a major role in the Slope Water, transition zone. The similar differences in the use of the Kuroshio and the Gulf Stream ecosystems occurs in the behaviour of bluefin tuna, squid and other large pelagics. The Gulf Stream system also lacks an equivalent to Pacific saury, Cololabis saira. The biology therefore is at least subtly different, with saury and sardines being replaced by mid‐water fish in the North Atlantic. A fuller comparison of the biology with quantitative methods in both systems should be encouraged.
Climate variability and marine survival of coho salmon (Oncorhynchus kisutch) in the Oregon production area
Authors: Koslow J. Anthony , Hobday Alistair J. , Boehlert George W.
Published: March 2003

Time series of adult recruitment for natural runs of coho salmon from the Oregon coastal region (1970–94) and marine survival of hatchery‐reared coho salmon from California to Washington (1960–94) are significantly correlated with a suite of meteorological and oceanographic variables related to the biological productivity of the local coastal region. These variables include strong upwelling, cool sea surface temperature (SST), strong wind mixing, a deep and weakly stratified mixed layer, and low coastal sea level, indicating strong transport of the California Current. Principal component analysis indicates that these variables work in concert to define the dominant modes of physical variability, which appear to regulate nutrient availability and biological productivity. Multiple regression analysis suggests that coho marine survival is significantly and independently related to the dominant modes acting over this region in the periods when the coho first enter the ocean and during the overwintering/spring period prior to their spawning migration. Linear relationships provided good fits to the data and were robust, capable of predicting randomly removed portions of the data set.
Assessing zooplankton advection in the Barents Sea using underway measurements and modelling
Authors: Edvardsen A. , Slagstad D. , Tande K. S. , Jaccard P.
Published: March 2003

The coastal shelf of northern Norway and the Barents Sea is highly advective and mainly affected by the North Atlantic Current and the Norwegian Coastal Current. The oceanographic conditions are an important factor for the spatial and temporal distribution of zooplankton in the region. To quantify zooplankton advection over the western border of the Barents Sea, a Scanfish/Optical Plankton Counter (OPC), Acoustic Doppler Current Profiler (ADCP), Multiple Opening and Closing Nets and Environmental Sampling System (MOCNESS), and hydrodynamic model were used. This study provides data from two time windows (June and July 1998) by continuous measurements between northern Norway and Bear Island. The zooplankton community structure was obtained by net tows and zooplankton abundance fields were mapped by an OPC counting zooplankton in the size range 0.7–14 mm equivalent spherical diameter. A simple zooplankton community structure was found with the copepod Calanus finmarchicus (CIII–CV) as the dominant species in this size fraction. Ocean currents were measured by a ship‐mounted ADCP and the residual currents were calculated by subtracting the tidal component obtained from a hydrodynamic model. Two measurements conducted in June and July 1998 shows a net eastward transport of water of 3.5 and 1.3 Sverdrup over the section. For the same two periods, zooplankton biomass transport is also positive towards east but varies by two orders of magnitude between the two measurements.
Seasonal heterotrophic flagellate and bacterial plankton dynamics in a large oligotrophic lake– Loch Ness, Scotland
Authors: Laybourn‐Parry Johanna , Walton Mark
Published: March 2003

1. Bacterial production in the 0–30 m water column of Loch Ness was measured using a dual labelling procedure with [3H] thymidine and [14C] leucine between May 1993 and June 1994. In most cases the uptake of the two labels did not covary, suggesting unbalanced growth. Rates of bacterial production varied from undetectable to 46.2 μg C l–1 day–1. Highest production coincided with the period of highest primary production, but carbon derived from this source was insufficient to meet the bacterial carbon demand, which was met by allochthonous humic inputs to the system.

2. Heterotrophic flagellate (HNAN) grazing rates, measured using fluorescently labelled bacteria, ranged between 10.3 and 24.5 bacteria cell–1 day–1 at temperatures between 5 and 15 °C. They removed up to 27% of the bacterial production per day.

3. Heterotrophic flagellate specific growth rates ranged from 0.043 to 0.093 h–1 between 5 and 15 °C, giving generation times of 7.4–16.1 h.

4. bacterial and HNAN abundances were not coupled, but the highest HNAN grazing impact related to a time of high bacterial productivity.
Effects of an invasive bivalve on the zooplankton community of the Hudson River
Authors: Pace Michael L. , Findlay Stuart E. G. , Fischer David
Published: March 2003

1. Previous studies documented that zebra mussels became abundant in the Hudson River during 1992 causing an 80–90% reduction in phytoplankton biomass. This study used intervention time series analysis of abundance, biomass and reproduction over the period 1987–95 to assess changes in zooplankton in response to the invasion.

2. Zebra mussels caused a size‐dependent decline in zooplankton. Microzooplankton, including tintinnid ciliates, rotifers and copepod nauplii all declined in 1992 and were scarce thereafter. Mean abundances of post‐naupliar copepods and of cladocerans were also lower following the invasion but these changes were not statistically significant (P > 0.05). Egg ratios and clutch sizes for the dominant cladoceran, Bosmina freyi, were not significantly related to zebra mussels, even though relatively low egg ratios were observed after the invasion.

3. The strong declines in microzooplankton were probably caused by direct zebra mussel predation. Estimated consumption rates by mussels were roughly equivalent to maximum microzooplankton growth rates.

4. The total biomass of zooplankton in the Hudson River declined by more than 70% following the invasion. Annual average zooplankton biomass was correlated with chlorophyll, but biomass per unit chlorophyll in the Hudson River was much lower than in lakes. The present study hypothesizes that this lower biomass reflects limitations by riverine flow and by predation during summer.
Primary nutrients and the biotic integrity of rivers and streams
Authors: Miltner Robert J. , Rankin And Edward T.
Published: March 2003

1. Controls to reduce loadings of primary nutrients to maintain biotic integrity in rivers and streams have not been widely implemented because the relation between nutrients and chlorophyll, and its consequences for higher trophic levels, is confounded in lotic ecosystems by their openness, the variable degree of nutrient limitation and by the effect of physical factors.

2. The relationship between primary nutrients and biotic integrity in rivers and streams was tested using biological, physical and chemical information collected since 1982 from similar locations in streams throughout Ohio using standard procedures.

3. There was a negative correlation between nutrients, especially total phosphorus, and biotic integrity. The deleterious effect of increasing nutrient concentration on fish communities in low order streams was detectable when nutrient concentrations exceeded background conditions (total inorganic nitrogen and phosphorus > 0.61 mg L–1 and 0.06 mg L–1, respectively).

4. These results suggest that the control of release of toxins and oxygen‐demanding wastes to rivers is insufficient to protect aquatic life, and confirm the importance of non‐point sources of pollution in catchment planning as well as the combined effect of habitat and riparian quality on nutrient assimilation.
Forestry impacts and the vertical distribution of stream invertebrates in south‐western Australia
Authors: Trayler K. M. , Davis J. A.
Published: March 2003

1. Vertical distributions of invertebrates (> 53 μm) were compared between two logged and two undisturbed headwater streams in south‐western Australia. The abundance and composition of invertebrates from core samples (4 cm diameter, 30 cm depth) were determined at intervals of 0–1 cm, 1–5 cm, 5–15 cm and 15–30 cm.

2. In addition to examining the effects of clearfell logging, this study provides the first description of the interstitial communities of Australian sandy streams. The interstitial fauna of the undisturbed streams were concentrated in the upper 5 cm of the bed and were numerically dominated by nematodes, a characteristic more typical of marine and lentic habitats than lotic systems.

3. The invertebrate community structure was substantially altered in the logged streams, with fewer taxa collected than in undisturbed streams. Invertebrate densities in the logged and undisturbed streams did not differ in the upper 5 cm of the bed, but, below this, densities were significantly lower in the logged streams. Increased sedimentation did not appear to be responsible for the differences in community structure between logged and undisturbed streams.

4. The impact of clearfell logging to the extent shown here has not previously been demonstrated in south‐western Australia. As a consequence it is strongly recommended that sampling of the benthic meiofauna is included in future biomonitoring protocols for the sandy streams of this region.
Development of vegetation and environmental conditions in an oligotrophic Danish lake over 40 years
Authors: Riis  , Sand‐jensen
Published: March 2003

1. Oligotrophic ‘Lobelia‐lakes’ are rare in Denmark. The few that have survived widespread eutrophication are in uncultivated sandy regions and are threatened by acidification and increased nutrient deposition from the atmosphere. Grane Langsø was considered the clearest lake in Denmark in the 1950s, when isoetids grew to 5.5 m depth and characeans covered the deepest part of the lake bottom at 11.5 m. The goal of the study reported here was to examine whether the lake has maintained this high quality by studying the development of macrophyte distribution and composition in relation to the changes in pH, nutrient conditions and transparency over the past 40 years.

2. Aquatic mosses now dominate the vegetation rather than rooted isoetids, probably as a result of acidification (summer median pH was 5.60 in 1958–1963 compared to 5.07 in 1976–1994). Along with a reduced median pH, annual pH fluctuations have increased from about 0.3 units 40 years ago to 0.9 units today.

3. The depth limit of isoetid species has declined markedly and Nitella flexilis, which previously dominated the dense bottom vegetation in the hypolimnion, has disappeared. These changes can be accounted for by reduced light penetration and an increased cover of filamentous green algae and mosses on the isoetid species.

4. The decline in light penetration was mainly caused by increased humic content following storm falls in 1981–84, but increased nutrient deposition may also have stimulated the growth of phytoplankton and filamentous green algae. The restricted macrophyte growth in the hypolimnion during summer can account for the change from oxygen supersaturation 40 years ago to anoxia today. The reduced light penetration has resulted in cooling of the hypolimnion, thereby increasing the stability and duration of thermal stratification. This increases the likelihood of anoxia in August–September. Profound changes in the plant community and in oxygen conditions have occurred, even though the decline of pH has been small and long‐term changes in nutrient concentration have been difficult to detect.
Intraspecific life history variation in the threatened Louisiana pearlshell mussel,Margaritifera hembeli
Authors: Johnson Paul D. , Brown Kenneth M.
Published: March 2003

1.Margaritifera hembeliis a threatened mussel limited to twenty‐two headwater streams in the Red River drainage in central Louisiana, USA. This study evaluated intraspecific variation in density, growth, size and age structure and shell morphology among several isolated populations. This study also identified the host fish and considered the role that host fish distribution played in determining mussel recruitment.

2. Mussels were aggregated in beds and average densities differed among streams. However, maximum mussel densities in beds were similar in all streams; the observed maxima were among the largest for monospecific mussel beds in North America, often exceeding 300 individuals m–2.

3. The maximum size reached by individuals differed among streams, but all size distributions were skewed towards larger individuals. A repeated measures analysis of tagged mussels in four populations, over a 2‐year period, indicated 2‐fold differences in growth rates among streams, and significant variation among years. Growth rates were not affected by local population density. Maximum ages reached, determined indirectly by comparing growth rates, varied from 45 to 75 years. A canonical discriminant analysis also revealed significant differences in shell morphology across populations.

4. Half of the populations showed evidence of recent recruitment, and these sites had fish assemblages dominated by the host fishNoturus phaeus(Taylor). Host fish abundance appeared more important than adult mussel density in explaining recruitment patterns.

5. Considerable intraspecific life history variation suggests that management strategies for this species should be stream‐specific, with emphasis on ensuring long‐term habitat stability.
Decomposition of standing litter of the freshwater emergent macrophyteJuncus effusus
Authors: Kuehn Kevin A. , Suberkropp Keller
Published: March 2003

1. Standing dead plant litter of emergent macrophytes frequently constitutes a significant fraction of the detrital mass in many freshwater wetland and littoral habitats. Rates of leaf senescence and decomposition of the emergent macrophyte Juncus effusus were examined in a small freshwater wetland in central Alabama, U.S.A. Juncus effusus leaves in the initial stages of senescence were tagged in random plant tussocks and monitored periodically to determine in situ rates of leaf senescence and death. Fully senescent leaves were collected, placed in litter bags, and suspended above the sediments to simulate standing dead decay conditions. Litter bags were periodically retrieved over 2 years and analysed for weight loss, litter nutrient contents (N, P), associated fungal biomass and fungal taxa.

2. Senescence and death of J. effusus leaves proceeds from the leaf tip to the base at an exponential rate. The rate of senescence and death of leaf tissue increased with increasing temperatures. Plant litter decomposition was slow (k = 0.40 yr–1), with 49% weight loss observed in 2 years. Both the nitrogen (N) and phosphorus (P) concentration (%) of litter increased during decomposition. However, the total amount of nitrogen (mg) in litter bags remained stable and phosphorus increased slightly during the study period.

3. Fungal biomass associated with plant litter, as measured by ergosterol concentrations, varied between 3 and 8% of the total detrital weight. Values were not significantly different among sampling dates (P > 0.05, ANOVA, Tukey). Fungi frequently identified on decaying litter were Drechslera sp., Conioscypha lignicola (Hyphomycetes), Phoma spp. (Coelomycetes), Panellus copelandii and Marasmiellus sp. (Basidiomycota).

4. These results support previous findings that plant litter of emergent macrophytes does not require submergence or collapse to the sediment surface to initiate microbial colonization and litter decomposition.
Hydraulic microdistribution patterns of larval fire salamanders (Salamandra salamandra salamandra) in the Weidlingbach near Vienna, Austria
Authors: Baumgartner N. , Waringer A. , Waringer J.
Published: March 2003

1. This study examined the longitudinal distribution of larval fire salamanders (Salamandra salamandra salamandra L.) in the Weidlingbach system, a first‐ to fourth‐order tributary of the Danube near Vienna, Austria. On the microhabitat scale, actual current velocities, Reynolds numbers and Froude numbers at larval locations were measured and larval positions mapped.

2. Larval densities were highest in shallow first‐ and second‐order tributaries where mean current speeds were less than 20 cm s−1, mean Reynolds numbers were less than 12 000 and mean Froude numbers were less than 0.30. Young larvae appeared on 26 April, fully grown larvae were observed from 11 May and larvae started metamorphosis from 27 June. Young adults left the brook between 26 August and 8 September. A severe flood on 25 May significantly reduced larval density, especially at sites near the source.

3. At a given sampling station young larvae favoured microhabitats exposed to only minor hydraulic stress. As larvae grew, they also colonized microhabitats with moderate current velocity (4–15 cm s−1). At sites with generally low discharge, larvae were distributed over a wider range of current velocities than at sites with higher discharge; at the latter, larvae were constricted to sheltered microhabitats.
Contribution of rotifers to the diet and fitness of Boeckella (Copepoda: Calanoida)
Authors: Couch Kyleigh M. , Burns Carolyn W. , Gilbert John J.
Published: March 2003

1. The calanoid copepods, Boeckella triarticulata Sars and Boeckella hamata Brehm, are major components of the freshwater zooplankton of New Zealand. It was not known whether these copepods ingest rotifers, nor whether the inclusion of rotifers in their diets might improve their fitness. The present study aimed to identify rotifer taxa which are eaten by each copepod species, and to examine the fitness consequences of the inclusion of one species of rotifer in the diet of B. triarticulata.

2. In feeding experiments using natural rotifer assemblages, both species of copepod ingested the rotifer Anuraeopsis fissa (0.4–4% of daily carbon intake), and B. triarticulata also ingested Polyarthra dolichoptera (6–30% of daily carbon intake) and Keratella cochlearis tecta (1% of daily carbon intake).

3. The contribution of rotifers to the fitness of adult female B. triarticulata was assessed by comparing survival and reproduction among five diets that contained varying densities of algae (Cryptomonas sp.) and/or Polyarthra dolichoptera (4 μg C L−1). Boeckella triarticulata produced fewer clutches on a rotifer‐only diet than on a solely algal diet, and addition of rotifers to a threshold algal diet did not affect copepod fitness relative to the solely algal diets. The present results suggest that Polyarthra at 4 μg C L−1 is not a high‐quality food for B. triarticulata.
Post‐European changes to the fluvial geomorphology of Bega catchment, Australia: implications for river ecology
Authors: Brierley Gary J. , Cohen Tim , Fryirs Kirstie , Brooks Andrew
Published: March 2003

1. Within a few decades of European disturbance in the mid‐nineteenth century, river character and behaviour were transformed in Bega catchment on the south coast of New South Wales, Australia. Ecological impacts of geomorphic changes to river structure and function throughout the catchment are assessed.

2. At the time of European settlement, many water courses in Bega catchment were discontinuous, with extensive swamps along middle and upper courses. Following a series of direct and indirect human impacts, channels became continuous in the middle and upper parts of the catchment, as extensive valley fills at the base of the escarpment were incised. Along the lowland plain, the channel widened by over 300%, fundamentally altering the relationship between the channel and its adjacent floodplain.

3. Geomorphic changes to river structure have modified habitat availability throughout Bega catchment. The impacts have been least pronounced in headwater streams, but have been dramatic along virtually all river courses beyond the base of the escarpment.

4. Changes in river structure have been directly related to altered riparian vegetation cover, and vice versa. As a consequence of changes to river structure, bed substrate calibre (and supply volume/rate) has been modified along most streams.

5. A series of indirect, secondary impacts have modified habitat viability along river courses. Lateral, longitudinal and vertical linkages within the river system have been altered, affecting the transfer of water, sediment, organic matter, nutrients and other biotic interactions.

6. These direct and indirect consequences of geomorphic changes in river structure suggest that ecologists need to adopt a longer‐term, catchment‐framed view of human disturbance to river ecosystems.

7. Effective, sustainable ecological rehabilitation of river courses is dependent on an understanding of geomorphic processes and determination of appropriate river structure at differing positions in catchments.
Allozyme diversity in brown trout (Salmo trutta) from Central Spain: Genetic consequences of restocking
Authors: Machordom A. , Garcåa‐Marån J. L. , Sanz N. , Almodçvar A. , Pla C.
Published: March 2003

1.  The brown trout (Salmo trutta) represents one of the main freshwater resources in Spain, but habitat alterations and overharvesting have contributed to the decline or disappearance of numerous natural populations. In addition, reinforcement programs of wild populations based on releases of hatchery reared fish of exogenous origin compromise the conservation of remnant native trout resources.

2.  We present allozymic data from Central Spain trout populations including stocked and unstocked populations. Although the levels of genetic variation observed were low and affected by hatchery releases (p = 18.23%, Ho= 3.39%), they were within the range observed in other European areas.

3.  The effective introduction of hatchery reared fish is genetically homogenising the populations in the studied area and disturbing the ancestral pattern of genetic variation that distinguishes the Tajo and Duero basins. Within the eight natural populations analysed, seven had alleles assigned to the foreign trout. The introgression in these populations, following the LDH‐5*90 allele frequency, ranged between 2% and 29.4%, but those values are not in concordance with the respective stocking effort undertaken in each population. Moreover, the release of hatchery‐reared fish does not solve the problems related to the reduced size of wild populations and their recruitment instability.
Life history and production of Paranephrops zealandicus in a forest stream, with comments about the sustainable harvest of a freshwater crayfish
Authors: Whitmore Nathan , Huryn Alexander D.
Published: March 2003

1. Life history and production were assessed for the crayfish Paranephrops zealandicus in three reaches of a headwater stream with a catchment of regenerating coniferous‐broadleaf forest in the south‐east of the South Island of New Zealand.

2. Crayfish density ranged from 3 to 4 m−2 in riffles and 4–12 m−2 in pools, depending on reach. Crayfish biomass (4–33 g AFDW m−2) and annual production (2–11 g AFDW m−2) were high compared with values reported elsewhere, while P:B ratio was low (0.33–0.43). This substantial production was dependent primarily upon high biomass rather than high growth rate.

3. The crayfish of this population rank amongst the longest lived and slowest growing ever recorded. Individuals estimated to be 16+ year of age were not uncommon. Females became reproductively active at 6+ year. Fewer than 4% of females carried eggs, and young remained attached to females for at least 15 months.

4. We propose that characteristics of this population are the consequence of a cool thermal regime (mean daily stream temperature = 7.0 °C, range 1.8–11.9 °C), and that low biomass turnover and poor reproductive rate precludes any sustainable commercial harvest of crayfish from streams in New Zealand with similar thermal regimes.