Ecology of Freshwater Fish最新文献

The kelt phase of anadromous iteroparous salmonid life history remains mysterious, particularly aspects of their habitat use and factors influencing survival. Atlantic salmon and sea-run brown trout were captured in the estuary during their return migration to the Vosso River, Norway, tagged with acoustic transmitters, and tracked in the watershed and estuary in three different years (2020–2023). We found a relatively narrow window of river exit timing among trout that survived overwinter, whereas salmon tended to leave during a more protracted period. Trout preferred overwintering in lakes within the river system, which provided for lower locomotor activity than fish that overwintered in pools in the river according to data from tri-axial accelerometer transmitters. In contrast, Atlantic salmon tended to spend surprisingly little time in lakes even though the energy expenditure in this habitat is was seemingly lower for salmon that did overwinter in the lake. Our results demonstrate different use of habitat during overwintering and could suggest that measures to protect iteroparous life history strategies of salmonids will differently impact these two iteroparous salmonids.

Dams and other in-stream obstacles disrupt longitudinal connectivity and hinder fish from moving between habitats. Fishways and other fish passage solutions are used to pass fish over these artificial migration barriers. Fish passage functionality, however, varies greatly with fish passage design and environmental conditions and depends on fish species and characteristics. In particular, swimming performance and fish behaviour are considered key characteristics to predict fish passage performance. It is also well known, but not well quantified, that the presence of conspecifics affects fish passage behaviour. In this study, we quantified individual passage rates of PIT-tagged gudgeons (Gobio gobio) over a scaled deep side notch weir in an hydraulic flume. We then quantified individual swimming capability (time to fatigue) and activity level (distance moved in an open field test) for the same individual fish and tested for potential effects on fish passage rate. To check for potential group effects, we then repeated the passage experiment for fish individually or in groups of five. More active fish displayed higher passage rates compared to less active fish, and fish passed the obstacle at higher rates in groups of five compared to alone. No effect of fish swimming capability on passage rates was detected. This result highlights the need to take both individual variation as well as the presence and behaviour of conspecifics into account in fish passage studies and evaluations. Doing so has the potential to improve the understanding of fish behaviour, and in the end, the design of fish passage solutions. Future studies should explore these results on free ranging fish and in relation to in-situ fish passage solutions.

Mixing processes in lakes are important in determining sedimentation zones and in setting the so-called “wash zone”, the area of lake bottom in contact with an oscillating thermocline during wind-driven internal seiche events. The wash zone also aligns with a sharp change in sediment roughness and hardness. Taken together, these rapid changes in temperature and sediment indicate that the wash zone is a distinctive ecotone in stratified lakes. Depth stratified randomised netting was used to develop count-based habitat use models for three common benthic fish species as a function of depth or temperature covariates. Using data from two lakes with quite different wash zone depths, we show the wash zone to describe fish habitat for two of three benthic fish species by utilising the top 50% of estimated fish abundance as an indicator of habitat use. White sucker (Catostomus commersoni) habitat use was within the boundaries of the wash zone. Lake whitefish (Coregonus clupeaformis) habitat was adjacent and within the wash zone. Longnose sucker (C. catostomus) habitat use was in the deep areas of lakes dominated by sediment focusing and did not overlap white sucker. Lake whitefish habitat use overlapped both catostomids, but peak abundance of both lake whitefish and white sucker overlapped pointing to potential interactions between these species. Smaller lakes have less vigorous mixing processes and a narrower wash zone, so with a decline in lake size the likely area of the wash zone as habitat for benthic feeding fish would become smaller.

Introduced species may exhibit variations in their preferred climatic niches between their native and introduced ranges, which can have important implications for the transferability of distribution models. In the Himalayan ecoregion, little is known about the geographic distribution and climatic niche overlap between native and introduced cold-water species. Here, we used the COUE (centroid shift, overlap, unfilling, and expansion) framework to explore the invasive potential of rainbow (Oncorhynchus mykiss) and brown (Salmo trutta fario) trout and corresponding climatic niche overlap with native snow trout (Schizothorax plagiostomus and Schizothorax richardsonii) in the Indus and Ganges River basins. Although we found more stability in the climatic niche for O. mykiss (93%) than S. trutta (58%), both species do not conserve their climatic niches in this region (p > 0.05). S. trutta has expanded more toward new environmental conditions (42%) compared to O. mykiss (7%). However, there are still available environmental gaps that O. mykiss and S. trutta can potentially occupy in the future. There was a higher overlap in climatic niches between S. plagiostomus and O. mykiss and between S. richardsonii and S. trutta. Observed shifts in climatic niches of these introduced species can negatively affect the transferability of distribution models, which may underestimate the assessments of habitat suitability for introduced trout in the Himalayas. Our study demonstrates that the information on climatic niche dynamics can inform the model-building process and improve the transferability and predictive performance to better assess vulnerability of sensitive habitats to introduced species in the Himalayas and elsewhere.

Fish assemblages in freshwater ecosystems are becoming more homogenous from multiple abiotic, environmental, and physicochemical variables at different scales. Historical fish collections (1976–1977) by Billy Michael Johnson and Dr. Johnson K. Beadles were compared to contemporary fish collections (2018–2019) in tributaries of the Eleven Point River basin in Arkansas to examine patterns of fish assemblage change. Fish assemblage change variables were compared to pasture land use/land cover (LULC) at multiple scales and in-stream habitat variables to understand relationships and discover potential correlates suggesting biotic homogenization. Fish assemblages in the Eleven Point River basin of Arkansas have experienced significant spatiotemporal changes, and LULC change and habitat alterations may have influenced this process. Increased tolerant species and decreased intolerant species at sites contributed to biotic homogenization, particularly in pool habitats. Surprisingly, expansion of some intolerant fishes was also observed that tend to occupy riffles. Sites with high percentages of pasture LULC at finer spatial scales typically had more homogenised fish assemblages. We hypothesized gravel aggradation from local pasture land use has degraded pools and increased riffle habitat, resulting in homogenised fish assemblages in the Eleven Point River basin over the study period. Few studies link LULC, in-stream habitat, and biotic homogenization when examining fish assemblage change over time, and these dynamics can be particularly complex in upland streams experiencing gravel aggradation. Similar research in other upland, gravel-bed river systems would provide a broad understanding of the presented environmental associations.

The restoration of longitudinal connectivity in rivers allows fish to colonise new habitats. However, there is a lack of information regarding the behaviour of fish when they colonise the newly opened river stretch. We used manual radiotelemetry to tracked individuals belonging to four species (trout, nase, grayling and barbel) after their release upstream of two obstacles in the Amblève River. We observed a diversity of movement behaviours and habitats used among the studied species. All the species used potential spawning habitats with distances travelled upstream reaching 2.4 km for the grayling, 7.0 km for the barbel, 16.9 km for the nase and 18.0 km for the trout, which also use tributaries and sub-tributaries of the Amblève River. Post-reproduction downstream behaviours were observed in all species, but this was made difficult by the absence of downstream migration devices at dams that forced fish to seek alternative habitats. Our study suggested that allowing fish to move upstream with fishways is beneficial as the species succeeded in reaching spawning grounds, but a holistic approach combined with the installations of devices or an opening of gates to allow post-reproduction downstream migrations would allow them to completely accomplish their biological cycle.

Predation can play an important role in structuring ecological communities, and predator–prey dynamics can be altered following the introduction of new species. An unauthorized introduction of redside shiner (Richardsonius balteatus) into reservoirs in the Upper Skagit River, Washington, USA created concern that a consequent shift in predator–prey dynamics in the reservoirs could reduce recruitment and production of native salmonids in the basin. We estimated predation mortality in Ross Lake on nonnative redside shiner and juvenile native salmonids to evaluate the potential role of predation in regulating these populations and limiting survival of native species of concern. We used bioenergetics modelling and stable isotope analysis combined with directed field measurements of growth, seasonal diet and thermal experience of piscivorous salmonids to quantify their consumption demand on prey fishes to evaluate the relative magnitude of predation mortality on invasive redside shiners and native salmonids. While redside shiner are the dominant prey fish species in Ross Lake, the modest biomass of native salmonids consumed could translate into substantial mortality, the magnitude of which depended on the timing and size at which prey fishes were eaten. This information provides important context for how nonnative species may indirectly impact native species through shared predation (apparent competition) and can inform conservation decisions surrounding nonnative species control, sustainability of native salmonids and introductions of anadromous fishes.

The interaction between fish and plants is vital for the dynamics of ecosystems since it influences plant distribution and regeneration patterns. In the floodable areas of the Amazon, these interactions are mainly structured by the flood pulse, which enables seed dispersal via water (hydrochory) and fish (ichthyochory), and which contributes to the formation of complex mutualistic networks. Our study evaluated the structure (modularity, nestedness, specialisation, and robustness) of the network of dispersal of seeds by frugivorous fish in a floodplain forest in Central Amazonia. We expect the binary network to have a nested pattern, while the weighted network is expected to have a non-nested structure; that generalist frugivorous species should constitute the core of the network, while specialist frugivorous species will be peripheral; that the size of fish and seeds is related to specialisation, and that the robustness of the network weakens as generalist frugivorous fish are removed. We found 5012 intact seeds from 49 plant species in the digestive tracts of 11 species of frugivorous fish. A nested and modular pattern was found for the binary and weighted networks, albeit with a low degree of nestedness. Our network proved relatively robust when the frugivores were removed, whereby all the fish and plant species became peripheral. No relationship was found between the size of the fish and the seeds and the degree of specialisation. Considering the anthropogenic impacts that can cause modifications in seed dispersal networks, knowing the structure of mutualistic networks is fundamental in order to be able infer the vulnerability of the interactions as a result of changes in the ecosystem.

The behaviour of two benthic species, round goby (Neogobius melanostomus) and mottled sculpin (Cottus bairdii), were examined under natural relevant downwelling light during predatory attacks by Burbot (Lota lota) and Smallmouth Bass (Micropterus dolomieu). Population declines have been observed for mottled sculpin after round goby invaded the Laurentian Great Lakes, but no data exist on prey avoidance behaviours and success for either species. The activity levels of the prey species were measured in the presence and absence of predators. Predator–prey interactions were quantified for reaction, attack, capture and retention probabilities. In addition, flight initiation distance, turns per flee and a comparison between observed and optimal escape angles were used as escape metrics to examine differences in prey survival. Trials were run under downwelling irradiances calculated for Lake Superior that correlated with dark, civil twilight, and sunrise. The number of round goby movements decreased by 74% in the presence of predators while mottled sculpin movement declined by 95% compared to baselines established without predators. Round gobies were more successful at evading predation with 18.3% of mottled sculpins consumed compared to 8.5% of round gobies during a comparable number (n = 27) trials. Round gobies also fled closer to their theoretically calculated optimal angles than mottled sculpin. Greater variation in flight initiation distances at different light intensities, fleeing at optimum angles that avoid predation and a more erratic escape path led to increased escape success for round gobies. Greater success avoiding predators may be another compounding factor, combined with round goby aggression and competition, that has contributed to the success of the round goby invasion in the Laurentian Great Lakes.

To better understand stream-fish sensitivity to fine sediment, we documented assemblage-wide responses by selected traits along a sedimentation gradient. We then discuss the management implications of these ‘dose–response’ relations in the contexts of biotic assessments and conservation of sediment-sensitive species. We identified a spatial gradient in sediment deposition among streams within the upper Piedmont of the Roanoke River basin in North Carolina and Virginia. We assessed fine-sediment sensitivity of 81 species based on eight species traits stratified by four attributes: food preference, feeding location, spawning substrate and spawning behaviour. We then ranked each trait and scored each species with respect to its sediment sensitivity. Using data from electrofishing surveys during 2018–2019, we calculated proportional abundances of traits observed at 30 sites throughout the study area and grouped species by their aggregate sensitivity scores. We assessed relations between embeddedness and silt cover and occurrences of species and traits using a combination of regression and ordination approaches. All traits tested responded to embeddedness or silt cover, or both. Feeding traits exhibited the strongest responses to embeddedness, while reproductive traits exhibited the strongest responses to silt cover. Our findings indicate that negative responses of the probability of presence for high-sensitivity traits to embeddedness and silt cover were linear, with no apparent thresholds. Additionally, proportional abundances of species with multiple high-sensitivity traits were inversely related to embeddedness and silt cover. Overall, our findings regarding population-level responses to sedimentation were consistent with our findings for trait-specific responses. Our analysis of species sensitivity to fine sediment corroborated the patterns we saw in our trait-specific analyses, indicating that population responses to sedimentation can be predicted from combinations of species traits. The ‘dose–response’ relations we documented may be applicable to managing sediment impacts on fishes, especially in the contexts of biotic assessments and conservation of sediment-sensitive species.