Ecology of Freshwater Fish最新文献

The damming of rivers for the formation of reservoirs causes a discontinuity in the physical and biological characteristics of the aquatic ecosystem. Changes in processes related to sedimentation and nutrients create a longitudinal gradient in water characteristics and productivity. Both the zonation and the differential distribution of primary production exert a strong influence on the other communities of these ecosystems. We hypothesised that spatiotemporal dynamics of chlorophyll-a and turbidity, driven by a longitudinal gradient, influence the ichthyofauna distribution in Sobradinho Reservoir. Using field surveys and geospatial tools, we tested the presence of a longitudinal concentration gradient for these variables, and then, its association with fish abundance (total and by trophic guilds). We used field samples between April 2008 and July 2009 and the reflectance data of Landsat 5 bands 2 and 3 to perform interpolations for each variable. The gradient was tested by extracting longitudinal profiles from the interpolation products. We tested the associations between ichthyofauna abundance and chlorophyll-a and turbidity concentrations using Spearman correlation. Sobradinho exhibited a longitudinal zonation consistent with the typical pattern of large reservoirs. Furthermore, our results highlighted the seasonal instability of this zonation. In the lacustrine zone, fish abundance was associated with seasonal productivity increase, caused by floods, whereas the fluvial zone showed lower abundances in these periods. Despite that, the fluvial zone exhibited higher fish abundance, demonstrating the common pattern for large reservoirs. The presence of favourable characteristics in this zone, such as seasonal flooding and higher environmental heterogeneity, may have corroborated the results.

A series of species introductions, overexploitation, and habitat modification preceded the extirpation of Lahontan cutthroat trout (Oncorhynchus clarkii henshawi; LCT), historically the apex predator, from Lake Tahoe, California-Nevada, USA. Studies evaluating limiting factors for LCT emphasise the need to elucidate food web interactions, yet important knowledge gaps regarding trophic interactions among nonnative pelagic fishes and invertebrates remain. We quantified the abundance and consumption demand of planktivores with an emphasis on kokanee (Oncorhynchus nerka) and Mysis diluviana. We synthesised this new information with existing information for lake trout (Salvelinus namaycush). The seasonal supply of copepods satisfied the consumption demand of kokanee, but only supported low feeding and growth rates. Kokanee relied heavily on Mysis as prey, an unusual result. Mysis exhibited a high degree of herbivory initially followed by heavier consumption on copepods by larger individuals. Consumption demand for Mysis on copepods exceeded that of kokanee during all seasons. Mysis contributed to over 50% of the annual energy budget for lake trout up to 625 mm. Consumption of Mysis by lake trout and kokanee represented a significant source of mortality when compared to the production of Mysis. Predation on kokanee was sustainable, only involved lake trout >625 mm, and was focused on prespawning aggregations. Despite the presence of Mysis-fueled lake trout, kokanee have persisted; a noteworthy pattern when considering the negative responses of kokanee to nonnative lake trout and Mysis observed elsewhere. This pattern suggests that there may still be an effective niche for LCT in the invaded Lake Tahoe ecosystem.

Freshwater ecosystems are both incredibly biodiverse and highly threatened globally. Variation in environmental parameters including habitat and flow can substantially affect many ecological processes within riverine aquatic communities, but the ties between such parameters and ecology are neither well studied nor understood. In highly variable tropical dryland river systems, assessing such relationships requires data collection over inter-decadal time scales, which is not typically permitted on development schedules driven over short periods (including election and funding cycles). Here, we used seine net sampling data collected over an 18-year period in the tropical dryland Fitzroy River, Western Australia, to assess how environmental and temporal factors including habitat, seasonality, and inter-annual variation in wet season magnitude affect the community assemblage structure, recruitment, and growth of aquatic species in dryland rivers. Results demonstrated that macrohabitat (main channel vs floodplain creek) and the magnitude of wet season rains and resultant flooding both had a substantial influence on biotic communities, alongside seasonal and diel variation. The magnitude of wet season flooding (measured as river discharge volume) had the greatest impact on assemblage composition within floodplain creek habitats and was a significant driver of recruitment rates and growth of recruits and adults of several species examined. This study highlights key considerations for conserving dryland river systems and constituent biota. Specifically, these are maintaining (a) rhythmicity of flow within each year, (b) diversity of flow volume between years, and (c) a variety of habitat types including ephemeral, semi-permanent, and permanent shallow floodplain and deeper main channel pools, in order to support a diverse array of generalist and specialist diadromous and potamodromous fishes.

Although groundwater exchange processes are known to modulate atmospheric influences on stream temperature and flow, the implications for ecological stability are poorly understood. Here, we evaluated temporal change in stream fish communities across a gradient of groundwater influence defined by karst terrain (carbonate parent materials) within the Potomac River basin of eastern North America. We surveyed 12 sites in 2022 that had been sampled 29–30 years previously with similar methods. We also collected stream temperature data from each site and used the regression slope of the air-water temperature relationship to index stream thermal sensitivity and groundwater exchange processes. Sites in karst terrain exhibited strong groundwater controls on stream temperature, and fish communities were more stable over time in these locations than elsewhere. However, stream thermal sensitivity was a stronger predictor of species persistence than the spatial distribution of karst terrain in contributing areas, highlighting the ecological importance of local variation in groundwater discharge processes. The presence of calcium precipitates (marl) in stream substrates was associated with low thermal sensitivity and ecological stability over time, and we suggest such visible features may be a useful indicator of climate change refugia in stream ecosystems.

Artificial obstructions such as dams are a key limiting factor or threat to adult Pacific lamprey (Entosphenus tridentatus) attempting to access upstream spawning habitats. Nevertheless, lamprey counted during dam passage (dam counts) is useful for monitoring abundance trends of these fish. We describe the trends in lamprey dam counts during 2005–2020 at Leaburg Dam (6.7 m height) on the McKenzie River (Oregon, USA). Despite similar flow volumes at each of two fish ladders, most lampreys in most years passed Leaburg Dam via the right bank fish ladder (vertical slot design) rather than the left bank fish ladder (half Ice Harbor). Counts ranged between 32 and 176 lampreys per year (median = 71.5 individuals). Akaike Information Criterion revealed the best fit General Additive Model (GAM) that described the cumulative proportion of lamprey passage included ‘year’, ‘day of the year’ and ‘river flow’, as opposed to other GAMs that included fewer of these variables or that included ‘water temperature’. Lamprey generally began passing during consecutive days of decreasing river flows, with most passing during annual low flows during June–August each year. In addition, total annual dam counts were strongly correlated with the sum of mean daily river flows. Thus, higher annual river flows correlate with earlier and more lamprey passage, but peak passage occurs at annual low flows. Mean daily water temperature ranged between 7.8 and 14.9°C during lamprey passage.

The increase in abundance of great cormorants (Phalacrocorax carbo sinensis) over the last decades has caused concern for the sustainability of fish populations. Cormorants are opportunistic piscivorous birds that eat fish from a wide range of species and sizes, in marine, lacustrine and riverine habitats. It has been documented that juvenile salmonids are under significant predation pressure by great cormorants, although knowledge on the predation of adult salmonids by cormorants is limited. In this study, adult anadromous brown trout (Salmo trutta) were tagged over multiple years with PIT tags during their spawning migration in a Danish lowland river. Two nearby cormorant colonies were subsequently scanned for PIT tags to estimate predation rate. It was estimated that by minimum 15.4% of tagged adult sea trout were predated by cormorants. The majority of the individuals were predated in the river, and females were more likely to be predated than males. Moreover, length had a significant effect on predation probability: individuals between 35 and 43 cm had the highest likelihood to be predated, while smaller and larger individuals were less likely to be predated. Our findings challenge the assumption that cormorants do not prey on reproductively mature salmonids. Furthermore, predation of mature individuals may have implications for the recruitment and sustainability of the population.

The coporo, Prochilodus mariae, plays a fundamental role in aquatic ecosystems as a detritivorous species facilitating the flow of carbon to the rest of the ecosystem's food web. It is also one of the most exploited freshwater fish species. Fishing, pollution and environmental changes in the Orinoquia region of Colombia have considerably reduced its population size. We analysed the population dynamics of P. mariae during an annual river cycle, including extreme drought and flood scenarios, by means of a mathematical model and simulations. The model we propose is novel because it relates biological, ecological and environmental factors to the population dynamics, including reproduction, growth in size and biomass of fish, recruitment, predation, fishing mortality and river flow. The proposed mathematical model apparently gives an approximate description of the population dynamics of P. mariae for 2010 because a good fit of the model to the catch data of the species of that year was obtained. The simulations showed that the first 3 months of the year are crucial for the species because this is when it is most affected by a combination of fishing, biological factors which increase natural mortality (e.g. upstream migration and predation) and environmental factors (e.g. low river flow). Hypothetical scenarios show that local extinction could occur if fishing were to increase and river flow were to decrease.

Environmental stressors associated with a changing climate and non-native fish, individually, represent significant threats to native fish conservation. These threats can exacerbate risks to native fishes when conditions interact at the trailing edge of a population's distribution. We collected capture–mark–recapture data for Rio Grande cutthroat trout (RGCT, Oncorhynchus clarkii virginalis) at the trailing edge of all cutthroat trout distributions from eight northern New Mexico populations. We used a factorial sampling design from streams characterised as “cool” or “warm” and whether RGCT were sympatric with non-native brown trout (Salmo trutta). We tested competing hypotheses that warm temperatures, reduced flows, high densities and sympatry with brown trout would negatively impact RGCT apparent survival rates. We found the strongest evidence for a non-native trout interaction with total trout density affecting RGCT apparent survival rates. Our results are consistent with patterns observed in northern cutthroat trout populations where non-native salmonids negatively impacted apparent survival rates. We also found that a negative density effect was observed on allopatric RGCT and sympatric brown trout apparent survival, but a positive density effect was observed for sympatric RGCT. These results suggest higher density populations of RGCT may be more resilient to displacement by non-native trout than low-density populations.

To understand the drivers of variation in digestive performance and their effects on growth, we examined relationships among food consumption, digestive metabolism, food processing efficiency, and growth rate in juveniles of fast-growing piscivore versus slow-growing insectivore ecotypes of rainbow trout reared at satiation rations on the same diet (i.e., commercial food pellets). Relative to slow-growing insectivores with lower basal metabolism, and despite a much larger maximum food ration, faster-growing piscivores presented an unexpected pattern of higher digestive efficiency through a reduction in the absolute costs of postprandial metabolism coupled with shorter or similar gut residence time and higher assimilation efficiency. These results suggest that the increase in digestive metabolism following the ingestion of larger meals can be mitigated by displacing the costs of digestion from SDA to SMR. Reducing total digestion costs (SDA + SMR) while maintaining higher assimilation efficiency may be possible through potential adaptations including (1) increased intestinal absorption capacity; (2) economies of scale that shorten gut transit time with increasing ration level; or (3) a permanently larger digestive tract that increases maintenance costs but reduces the need for cyclic upregulation and associated overhead costs.

Every fish migrating upstream through vertical slot fish passes must swim through slots, where the resistance force of flowing water could affect the passage success. We measured the hydraulic force acting on the body of preserved benthic fish in a vertical slot at different water discharge rates (80 and 130 L/s) to compare the hydraulic burden individual fish species (round goby Neogobius melanostomus Pallas, 1814, gudgeon Gobio gobio L. and bullhead Cottus gobio L.) must overcome. The forces measured in three spatial axes were then compared to acoustic Doppler velocity measurements and the passage probability of 39–45 live fish per species. Passage probability reduction of 28.26% for round goby and 39.29% for bullhead was observed at the higher water discharge. Gudgeon showed increased numbers of passages and approaches when larger hydraulic forces were experienced at 130 L/s compared to the lower water discharge. Gudgeon experienced significantly lower hydraulic forces (mean 0.27 N ± 0.12 standard deviation) compared to round goby (mean 0.32 N ± 0.12 SD) and bullhead (0.35 N ± 0.14 SD). Potentially, the increased hydraulic forces at the higher water discharge contributed to the reduction in passages in round goby and bullhead. That gudgeon behaved differently from the other species illustrates how fish species deal differently with flowing water and the hydraulic forces experienced. Our approach provides a species-oriented assessment of the flow field in ecologically relevant fish passes. These findings represent an important step towards the development of purposeful fish pass designs, which is essential for ecosystem-oriented river connectivity.