Ecology of Freshwater Fish最新文献

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.

Water turbidity alters prey detectability and prey selection by a predator. In dimorphic mesopredators, the effect of water turbidity on foraging success may be sex specific, primarily due to sex differences in reproductive allotment, body size and vulnerability to predation. To experimentally test the effect of turbidity on prey consumption with respect to sex, we used turquoise killifish (Nothobranchius furzeri), a small fish from ephemeral savanna pools in southeast Africa that vary widely in turbidity. Large males possess conspicuous nuptial coloration while females are smaller and drab. Vision is assumed to be a fundamental sense for turquoise killifish, despite often living in very turbid water. As mesopredators, killifish regulate the invertebrate community in ephemeral pools. We tested the consumption of bloodworms (benthic and red-coloured) and glassworms (pelagic and transparent) under clear (<1NTU) and turbid (320 NTU) water conditions. We found that turquoise killifish maintained their overall foraging success irrespective of turbidity. In both the clear and turbid water, the females consumed three times more food than males relative to their body mass. This likely stems from the females' high nutritional demands due to daily reproduction. It also suggests that females are not risk-aversive in clear water despite their smaller size. Water turbidity affected the type of prey consumed by turquoise killifish and demonstrated its potential to affect the community structure of invertebrate species in ephemeral pools.

The relationships between body size and density of salmonids in natural streams have been well studied, and density-dependent growth (somatic growth) is interpreted as the principal mechanism responsible for the relationship. Moreover, the body size–density relationship is known to vary over ontogeny. However, the relationship has been studied mostly by experimental procedures (e.g. stocking fish into streams), and knowledge about the relationship in natural populations (e.g. no human-induced input of fish) is still inadequate. In this study, we compared the relationships between body size and density of young-of-the-year (YOY) masu salmon, Oncorhynchus masou, between different ontogenetic stages, that is, fry (spring) and juveniles (autumn). We used the monitoring data of YOY body sizes and densities across three study sites collected from Horokashubuto stream in Hokkaido, northern Japan, from 2014 to 2022. In the juvenile stage, YOY body size correlated negatively with increasing density. This pattern is typical of the density dependence of salmonid growth demonstrated in many previous studies. In the fry stage, however, YOY body size correlated positively with increasing density. This study suggested that the patterns of density dependence vary as functions of the ontogenetic stages of salmonids.

Dams modify river physical and chemical attributes. This disruption hampers fish migration, leading to the introduction of non-native species and losses of specialised native species. Small hydropower plants (SHPs) have been suggested for replacing large dams to minimise reservoir size and preserve natural flow regimes. We evaluated the influences of two SHPs on the ichthyofauna in a tropical river, comparing fish taxonomic and functional beta-diversity in three periods. Period-1 preceded SHP construction (Pre-2008), when the river was free-flowing. Period-2 was 1 year after completion of SHP construction (Post-2012). Period-3 was after 10 years of SHP operation (Current-2021). We calculated 10 functional ichthyofaunal attributes based on 12 quantitative morphometric measurements related to habitat use, feeding, and locomotion. The ichthyofaunal composition varied among the periods (p = .001) and seasons (p = .009), with the highest species richness in the Post period compared to the other two periods (p = .002). Abundance significantly decreased over time (p = .004). Taxonomic beta-diversity increased in the Post period remaining stable in the Current period. Functional beta-diversity did not change between the Pre and Post periods but significantly increased in the Current period. The turnover component had the greater influence on both taxonomic and functional beta-diversity, with no temporal changes observed in nestedness. The ichthyofauna appears to have undergone heterogenisation and restructuring. Changes include the emergence of more tolerant species (e.g., Hoplosternum littorale and Pimelodus maculatus), displacement of native and sensitive species (e.g., Pogonopoma parahybae and Steindachneridion parahybae), and colonisation by a non-native predator (Plagioscion squamosissimus). This indicates that small-scale projects such as SHPs harm fish populations by altering habitats and restructuring the ichthyofauna.

Assessing the status of several migratory fishes in the Mobile River Basin, Alabama, has been complicated due to a general lack of historical data on their life history, habitat requirements, and distributions. Whether distributions were restricted by natural or man-made barriers to migration is difficult to answer because few scientific collections were made before dams were built, and the earliest dams were built at the largest biogeographic barrier in the basin: the geological fall line. Therefore, we used what information was available, including anecdotal information, primarily records from archived newspapers and government reports, to describe the ranges of six migratory species prior to the construction of dams in the Mobile Basin. We describe the complicated history of Alabama Shad Alosa alabamae and show that range declines may have been masked by the stocking of American Shad Alosa sapidissima in the late 19th century. We show that Gulf Sturgeon Acipenser oxyrinchus desotoi probably migrated well above the fall line in the Coosa River, and may have been sympatric with Lake Sturgeon Acipenser fulvescens. We found no records of Alabama Sturgeon Scaphirhynchus suttkusi above the fall line. American Eel Anguilla rostrata migrated above the fall line in every Mobile Basin river before dams were built. Finally, Paddlefish Polyodon spathula may have once occurred above the fall line in at least two rivers, but they persist today in impounded reaches in the coastal plain, unlike some other species. We hope that future work will continue to consider archival sources of information to re-trace the histories of imperilled species.

Despite the benefits that can come from coordinated movement, many diadromous fishes have evolved partial migration strategies, where a portion of a population does not migrate. Co-occurring life-history variants might nonetheless gain some advantage by exhibiting congruent phenologies, with key events timed to follow the same cue. Here, we assess this possibility by examining otolith microchemistry and structure to quantify the lunar periodicity of hatching and metamorphosis according to migration strategy in a facultative amphidromous goby endemic to Hawai'i. Our analyses corroborated prior evidence that Awaous stamineus exhibits partial migration and that residential A. stamineus are often proportionately more abundant than the migratory form. Contrary to expectation, we found a significant difference in hatching time between migratory and residential A. stamineus. A higher proportion of A. stamineus migrants hatched at the full moon and metamorphosed at the new moon, whereas residents exhibited the opposite phenology. Comparisons to Sicyopterus stimpsoni intended to provide a broader context revealed that the obligately amphidromous species tends to hatch at the new moon and metamorphose at the full moon, mirroring the phenology of residential A. stamineus. Evidence of convergent lunar phenologies suggests that synchronising life-history events can confer benefits that extend beyond species boundaries. Notably, phenological discordance could be acting as a prezygotic isolating barrier between sympatric life-history variants, pointing to the presence of heretofore unrecognised evolutionary diversity within partially migratory species like A. stamineus.