Large-scale, differential summer habitat use of three anadromous salmonids in a large river basin in Oregon, USA

The summer distribution of three juvenile anadromous salmonid species was compared in the mainstem sections and nine tributaries of the Upper South Umpqua River Basin, Oregon, USA. Chinook salmon, Oncorhynchus tshawytscha (Walbaum), was found at highest densities in the mainstem and mid-elevation tributaries. Coho salmon, O . kisutch (Walbaum), was essentially absent from the mainstem, but was found at high densities in the low-elevation tributaries. Steelhead trout, O . mykiss (Walbaum), was found in the mainstem and all nine tributaries; the highest densities of this species were in the upper mainstem reaches and high-elevation tributaries. No significant correlations were found between ranks of mainstem and tributary densities among the three species (Spearman's rs; P > 0.05). Observed spatial segregation of basin habitat by these species during summer indicated that protection provided at the level of the river basin will be necessary to assure the continued existence of all stocks.     

Effects of an extreme flash flood on the native fish assemblages across a Mediterranean catchment

Abstract  The effects of an extreme flash flood on the native fish assemblages across a Mediterranean catchment in Southwest Portugal were investigated. The fish community structure and habitat were surveyed at 10 sites pre- and post-flood. Overall species richness and rank abundances changed little after the flood, despite there being a consistent decline in the abundance of small cyprinids. Pre- and post-flood habitat correlates of abundance changed for at least some species, and variability in assemblage structure was associated with flood, depth and pH. These results indicate that extreme floods occurring early in the wet season may have little disruptive effects on the overall structure of native fish assemblages in Mediterranean streams, although may at least partially influence population dynamics for some species. Habitat quality and complexity are likely to play a role in mediating species responses to flooding.     

A comparative study of juvenile salmon density in 20 streams throughout a very large river system in northern Norway

Abstract – The objective was to compare juvenile salmon density in 20 streams throughout the very large River Tana, northern Norway, and to relate variation in density to a suite of environmental factors. Four sampling sites were electrofished in each stream (one at the mouth of the stream and three within the stream) in August and October 2000, 2001, 2002. 0+ salmon parr were absent from seven streams, present at the mouth of 11 streams, and present within only two streams, both of which were probably spawning streams. Older parr migrated upstream into most streams and their highest densities were usually found in streams flowing directly into the spawning habitat in the three largest tributaries of the Tana or the river itself. Juvenile salmon were sparse or absent in streams flowing into smaller tributaries. Most streams with high parr densities were those of dense riparian vegetation that provided terrestrial invertebrates as drift food for the salmon parr, cover for fish, cooler stream temperatures in summer, and food for benthic stream invertebrates that were also a source of food for the parr.     

Ecology of stream fish: insights gained from an individual-based approach to juvenile Atlantic salmon

Abstract – Using data from an ongoing study of juvenile Atlantic salmon growth and survival in tributaries of the Connecticut River, USA, we compare standard population-level approaches to those focusing on individuals. We highlight the potential benefits of resampling individually tagged stream fish as compared to standard approaches. Specifically we focus on growth, survival, movements and population estimation. The advantages of estimating sizes and growth rates from individual size trajectories include obtaining growth histories and the ability to perform retrospective analysis of the consequences of different life-history strategies. An example might be the patterns of growth leading to either early maturity or migration. Resampling known individuals is the only way we know to chart both short-term and long-term movements and to assign growth and mortality consequences to such movements. Finally, individual-level data permit robust estimation of survival and density/abundance using methods such as Cormack/Jolly-Seber. The results indicate that population estimates were about 10% lower using individual data than using population data, that survival from sample to sample was typically >90%, that the majority of recaptured fish did not move during the summer, that growth was rapid during spring and most fish lost mass during the summer and that growth trajectories for maturing and non-maturing fish showed substantially different patterns. An individual-based approach to stream fish ecology provides the opportunity to explore the mechanisms responsible for population-level patterns but comes at the cost of significant field effort. Tradeoffs between increased data resolution and the effort required to obtain the data must be considered before undertaking individual-based field studies of stream fishes. ^NOTE     

Fish populations in tropical floodplain pools: a re-evalution of Holden's data on the River Sokoto

Abstract– In this study we asked whether the fish populations of residual pools in a seasonally fluctuating African river varied between years. We used a series of data on the fish of the permanent floodplain pools of the River Sokoto, Nigeria compiled by M. J. Holden (1963) to address this objective. Holden provided estimates for the size and biomass of fish populations in 12 permanent dry season pools over a period of 2 to 3 years. On average, only 22% of the species present in a pool were absent from that pool in the following sampling period. Despite low interannual variability in the species composition of the pools, rank correlation analysis indlcated significant variation in the relative numbers and biomass of the 10 most numerically abundant species in most pools. Altering the spatial scale of analysis to include all possible combinations of 2 and 6 pools did not affect the results. Indices of similarity also indicated relatively high annual variability in the relative abundance of species in the pool communities. We suggest that habitat selection may contribute to the continued occurrence of fish species in pools from year to year, and such factors as changes in the overall abundance of fish species in the system and haphazard trapping during flood decline may contribute to annual variation in their relative abundance.     

Patterns in young‐of‐year smallmouth bass microhabitat use in multiple stream segments with contrasting land uses

Abstract Young‐of‐the‐year (YOY) smallmouth bass, Micropterus dolomieu Lacepéde, were evaluated in streams from eight catchments with two contrasting land uses to determine their use of microhabitats under a variety of stream conditions. Step‐wise discriminant function analyses revealed patterns of habitat use by discriminating used from available microhabitat conditions. Velocity was significant in 88% of streams sampled, whereas depth was significant in only the smallest stream in the forest‐dominated catchments and 75% of stream segments located in pasture‐dominated catchments. Mean velocities used by YOY bass were lower than available velocities, and mean depths used were greater than mean availability in all cases. Substrata varied significantly with availability in different stream segments. Error rates associated with classification ranged from 5 to 39%. Results indicate that YOY smallmouth bass are somewhat opportunistic, but use low‐velocity habitats in most cases and deeper water when streams are impacted by pasture land use and associated physical changes.     

Riparian coverage affects diets of characids in neotropical streams

Abstract – Aquatic ecosystems are influenced by the surrounding terrestrial environment. This work studied the influence of vegetation of riparian zones on the feeding patterns of two nektonic characids, Astyanax paranae and Bryconamericus iheringii, in a basin surrounded by an agricultural area. Nine streams within the Corumbataí River basin (São Paulo State, Brazil) with varying proportions of adjacent riparian forest (RF) and pastures were set apart in three arbitrary categories: Riparian Forest (>90% RF), Mixed Coverage (banks covered by 30–60% RF; MC) and Pasture (<29% RF, PA); resident characids were sampled in the dry and rainy seasons and evaluated in regard to composition of diets. Astyanax paranae fed on allochthonous food sources in RF and MC, and on autochthonous food sources on PA streams; B. iheringii fed on autochthonous food sources in RF streams and in mixed resources (detritus and sediment) in PA streams. Selection of food source was related to, and altered by, stream channel structure and composition of substratum. Preservation and restoration of native riparian vegetation is key to preservation of resident characids in small streams of this river basin.     

Influences of local habitat and stream spatial position on fish assemblages in a dammed watershed,the Qingyi Stream,China

Abstract – Identifying the underlying mechanisms that explain the spatial variation in stream fish assemblages is crucial for the protection of species diversity. The influences of local habitat and stream spatial position on fish assemblages were examined from first‐order through third‐order streams within a dammed watershed, the Qingyi Stream, China. Based on linear regression models, the most important environmental variables influencing fish species richness were water temperature and wetted width, but stream spatial position variables were less important. Using canonical correspondence analysis, five environmental variables were identified to significantly influence fish assemblages, including three habitats (elevation, substrate and water depth) and two spatial variables (C‐link and Link). Our results suggest that, in a heavily dammed watershed, by blocking the migration routes of fishes, dams weaken the influence of stream spatial position on fish species richness. However, fish species compositions are significantly influenced by both local habitat environment and stream spatial position, which is perhaps owing to the distribution of fish species according to ecological requirements not related to spatial processes.     

Biology and habitat use of three-spined stickleback (Gasterosteus aculeatus) in intermittent Mediterranean streams

Abstract –  We present the first data on three-spined stickleback ( Gasterosteus aculeatus ) life history and habitat use in seasonal Mediterranean streams, analysing populations from NE Iberian Peninsula. Stickleback populations were strictly annual, with reproduction events involving exclusively 1+ fish. Somatic growth was concentrated in two periods, one in spring and early summer, and another in autumn and winter. During summer there was a clear stop in the somatic growth, coupled with low values of somatic condition. This growth pattern contrasts both with that of other Mediterranean stream fish species and that of stickleback in other European locations. Stickleback populations occupied mainly intermediate locations along fluvial gradients. The presence of abundant aquatic vegetation was identified as one of the main factors related with both stickleback presence and the abundance of its populations, while the latter was also negatively related with that of invasive fish and crayfish species. Stickleback tended to occur in native-dominated fish communities, being almost absent from lower stream reaches, which bear high abundances of invasive fish species.     

Modelling stream fish species distribution in a river network: the relative effects of temperature versus physical factors

Abstract – The relative influence of temperature versus local physical factors on the spatial distribution of riverine fish species was investigated in a large watershed of south-western France. Using generalised additive models and hierarchical partitioning, we modelled the ecological responses of 28 fish species to a set of five environmental predictors, and we quantified the independent effect of each predictor. The spatial distribution of fish species was primarily determined by both mean temperature and position along the upstream–downstream gradient. However, responses to these environmental factors varied according to the species considered. Fish species with strong thermal requirements (e.g., common carp, black bullhead, Atlantic salmon) were mainly sensitive to temperature whereas longitudinal gradient was of primary importance for downstream species (e.g., common bream, largemouth bass, pike perch). Both the statistical methods used gave concordant results and appeared complementary. This dual-approach, quantifying the relative contribution of each environmental factor, appears particularly useful to understand the spatial distribution of stream fish species. Separating the effects of temperature versus habitat factors is crucial to accurately predict species distribution modifications in the current context of global change.