Ecology of Freshwater Fish最新文献

Riverine habitat fragmentation by barriers, including impoundments, is common and their effects on obligate aquatic organisms are manifold. Organisms, such as Atlantic salmon (Salmo salar), that make extensive river migrations are particularly vulnerable to the effects of impoundments. In this study, we use acoustic telemetry to examine the migratory behaviour of Atlantic salmon, as they migrate to sea for the first time as juvenile ‘smolts’, in a river with a series of dams that form a complex hydropower scheme. We demonstrate that overall migration success in the River Dee catchment and particularly through standing waters was remarkably high. We speculate that high migration success in standing waters could be due to relative current speeds providing good quality directional cues to migrants. Migration success past the two dams in this study, was relatively high, although the number of unsuccessful passage attempts before a successful passage was also very high. The vast majority of smolts passed the dams when the turbines were operational. At one dam, smolts did not use an available fish pass but migrated through the generating turbines. These findings provide several routes through which generation could be managed to enhance the success of downstream smolt migration in rivers where there are similar patterns of hydrogeneration in place.

In May of 2023, about 100 scientists met for the sixth time over ~25 years for the ‘Advances in the Population Dynamics of Stream Salmonids’ Symposium. This symposium, created by the father of brown trout ecology, Dr. Javier Lobón-Cerviá and colleagues, grew out of intriguing conversations regarding the regulation of the population dynamics of salmonids, as long ago as the 1980s. The first symposium was in the quaint coastal town of Luarca, Spain, in 1998 and started out small with less than ~50 scientists in attendance. The second symposium, also more modest in numbers (~85 scientists), was held in 2006 in millenary Leon in the NW of Spain, a town proud of its history and its Cathedral of nearly 2000 square metres of stained glass and in-credible (free!) tapas. The third was in 2010 back in the stunning fishing town of Luarca, where our numbers grew substantially to more than 115, we moved into a fancy new conference hall, and we feasted on fresh seafood. The fourth was in 2015 and held in Girona (101 scientists), in the NE of Spain, where we all felt ethereal while giving our talks in a stunning cathedral-like hall and where we experienced the strong Catalonian culture and cuisine. This was followed by a meeting in Granada, Spain, in 2019, where we strolled the halls and gardens of the magnificent Alhambra after riveting days of science talks.

Finally, in May of 2023, we met in lovely and lively Majorca, one of Spain's Balearic Islands in the Mediterranean, and convened at the University of Balearic Islands. We ate delicious foods, as Majorca has many cultural influences, and toured a magnificent cave, where we were serenaded by live classical music. We met with old friends and new friends and shared new experiences, and our numbers of participants grew yet again. Topics covered included the roles of tributaries, influences on growth rates, recruitment, dispersal and migration, genetics, spawning, habitat, innovative conservation, restoration and management, habitat, and even beer and salmon, to name just a few. At each iteration, we have received new fresh faces and perspectives, but our alumni base has held strong, offering continuity in the advancement of the study of the population dynamics of stream salmonids.

Selected proceedings from the May 2023 Majorca symposium follow. The articles cover a wide range of topics, from eco-evolutionary dynamics to how to measure biologically relevant temperature in fish, for example. In this way, these proceedings show the importance of understanding and studying stream living salmonids at a wide range of scales.

P.B. and L.A.V. both equally conceived of and wrote this short introduction.

The authors declare no conflicts of interest.

Fishes use a variety of physical and biological resources that shift ontogenetically, seasonally and spatially. Quantifying what resources such as prey are required for persistence can improve understanding of ecological needs of fishes and riverine macrosystem functioning. Bowfin (Amia ocellicauda) and largemouth bass (Micropterus nigricans) cohabitate in their native range and potentially compete with one another. Yet, there have been no direct comparisons of their diets across spatial gradients to assess whether they partition resources or shift in prey use. We used multiple univariate and multivariate analyses to compare diet composition, diet overlap, feeding strategy, prey importance and diet partitioning between largemouth bass and bowfin across three reaches of the Upper Mississippi River. Largemouth bass ontogenetically shifted their diet from aquatic invertebrates to fishes and a more diverse assemblage of aquatic invertebrates. Bowfin and adult largemouth bass were top predators which consumed mostly crayfish and fish and overlapped in their diets. Despite overlapping diets, predators partitioned resources by consuming different lengths and abundances of prey, and largemouth bass had greater trophic plasticity. Within a predator group, few differences in diets existed spatially, underscoring the relative homogeneity in resource use potentially from similarities in the river's physical structure. Combined, prey use likely differed sufficiently to reduce potential competition between largemouth bass and bowfin, allowing long-term coexistence in this system. Our results also highlighted the importance of crayfishes to riverine food webs and underscored the use of multiple prey and habitat types that sustain these predators.

Diets of fish larvae may vary within populations and among species and are affected by larval prey availability and foraging capacity. We aimed to describe the diet of fish larvae based on empirical field observations, emphasizing the interaction and organization of the predator–prey network using Auchenipterus osteomystax as a species model. The network showed few interactions (low connectance and modularity) but a nested structure (some items that had fewer records tended to occur together with the most frequent ones), low complementary specialization (the proportions of ingested items tended to be equivalent) and a pattern of segregation (some items tended not to be consumed together) in the use of resources among individuals. Robustness was low when the removal of prey with a higher consumption frequency occurred. The correlation between morphological variables and network attributes was significant and positive for abundance and strength, while the correlation with nested rank was negative. The availability of suitable dietary resources is likely to be the key factor for success and survival in the early stages of development. With changes in morphology during larval development, A. osteomystax showed a generalist position in the network as its predation capacity increased. A new approach to trophic ecology studies of fish larvae incorporating network analysis may help explain the individual characteristics of larvae and assess the pattern of interactions in the population.

Dispersal is a ubiquitous ecological process that has been extensively studied in many plants and animals. Anadromous salmonids are an interesting system for examining dispersal, in part because of their well-known philopatric behaviour, but also because of the conservation challenges related to the dispersal of hatchery-origin fish. Building on earlier work, we provide an updated systematic review of dispersal and gene flow in anadromous salmonids. In particular, we compared studies on the dispersal of anadromous salmonids from wild and hatchery origins, including studies providing estimates of dispersal rates, observations of dispersal and results from modelling studies. We reviewed 228 studies and found these were unevenly distributed among species, with Atlantic salmon, Chinook salmon and sea trout being well-represented. Our results showcase considerable variability in estimated dispersal rates within and across studies, which is likely related to the different methodologies, dispersal propensities across species and populations, and spatial extents considered. Overall, our results confirmed a higher tendency of hatchery fish to disperse relative to wild fish, but we also found some variation across species that warrants further study. Moreover, we found that dispersal propensity tended to decline exponentially with distance and that the drivers of dispersal varied considerably among studies. Additionally, we highlight various facets of dispersal captured across this suite of studies, including variation in terminology, methods and metrics for characterising dispersal, and the spatio-temporal scales considered. Finally, our review revealed that few studies considered, and even fewer assessed, the implications of dispersal for the conservation and management of anadromous salmonids.

Riverine fish assemblages are strongly influenced by attributes of the flow regime. Tropical savannah river systems have distinct and predictable hydrologic seasonality, reflecting the wet-dry climate, but can vary substantially in terms of dry season flow permanency and wet season flow-pulse characteristics. Understanding how flow permanence and variability influence fish assemblages, and whether these factors can be used to predict responses to future hydrological change, are key knowledge gaps that impede effective management. We examined the influence of hydrological variability on the structure and diversity of freshwater fish assemblages across rivers of the wet-dry tropics of northern Australia. We found distinct fish assemblages that varied predictably across three hydrological river types: Intermittent, Perennial Stable and Perennial Flashy flow regimes. This distinction emerged despite a common species pool across the region. Species richness was greatest in rivers with Perennial Stable flow regimes, whereas beta-diversity was greatest in Intermittent rivers. However, life history strategies of constituent species were generally poor predictors of species abundances within each hydrological river type. The distinct fish assemblages evident among hydrological classes may provide some cautious ability to both predict potential fish assemblage changes with future hydrological changes (e.g. if perennial streams became more flashy or intermittent), and to predict fish assemblages expected in unsampled rivers with particular hydrological characteristics. Our findings provide further support for the importance of maintaining regional flow-habitat heterogeneity and the connectivity between hydrological river types, and their essential role for conserving tropical fish species diversity into an uncertain hydrological future.

The round goby (Neogobius melanostomus) is an example of an invasive species where the adults are unimpressive swimmers and yet via human activities, they have managed to rapidly invade the Laurentian Great Lakes, the Baltic Sea and many rivers in Western Europe. The secondary spread from human-impacted sites has been attributed to adult life stages, despite their poor swimming capacity. However, the swimming capacity of early life stages of round goby has not been considered before. We therefore quantified critical swimming performance (U_crit), sprint swimming performance (U_sprint), burst swimming speeds and swimming behaviours in early juvenile round goby that ranged between 10 and 25 mm in body length. The average U_crit, U_sprint and burst speeds of these fish were an impressive 0.22, 0.34 and 0.67 m/s respectively, with the capacity of these early juveniles ranging between 41 and 79% of what has been documented for adults. Notably, fish spent more time actively swimming as current speed increased, while station holding decreased. Taken together, our findings highlight that despite their small size, early juvenile round goby are not simply passively moved by currents but have movement capacities that approach that of the much larger adults. Our study emphasizes the need to consider the swimming capacity of all life stages as this information will better predict dispersal and range expansion and will help to design mitigation efforts to potentially prevent the spread of this and other invasive species.