Native Stream Fishes Research Articles

Factors on Fish Richness in Native Streams of Fogang Area, Qingyuan, Guangdong Province

Rapid urbanization in the rural areas of Guangdong Province poses varying degrees of threat to the survival of native stream fishes. This study conducted over three years, utilized fishing nets, fish traps, angling techniques and lure-fishing methods to perform a quantitative assessment of stream fish species across 11 representative watersheds within Fogang County, Qingyuan City, Guangdong Province, along the upper reaches of the Pajiang River. In this study, a total of 4 orders, 4 suborders, 9 families, 4 subfamilies, 14 genera and 18 species of fish were collected. The identified species include Opsariichthys evolans, Opsariichthys bidens, Girella punctata, Acrossocheilus paradoxus, Pangasianodon hypophthalmus, Varicorhinus guangdongensis, Pseudogastromyzon fangi, Betta splendens, Micronemacheilus pulcher, Rhinogobius giurinus, Rhinogobius duospilus, Gambusia affinis, Pseudorasbora parva, Rhodeus ocellatus, Pseudorasbora pumila, Carassius auratus, Channa striata and Gobiocypris rarus. The dataset comprises 15 indigenous species and three non-indigenous species, namely the Girella punctata, Gambusia affinis and Channa striata. Based on comprehensive analysis of field surveys, fishing data and feeding data, it is evident that invasive alien species, environmental changes, water oxygen content and water quality exert significant influences on stream fish richness. Furthermore, variations in channel structure, river beds and coastal environments along the banks also contribute to alterations in species composition and diversity within aquatic ecosystems. Therefore, identifying factors that constrain the abundance of native stream fishes will help to protect the ecosystem as a whole, while restoring diversity and sustainability of the local aquatic communities and improving the living conditions and habitats of local population.

Multiscale analysis predicts native species presence based on habitat and nonnative species abundance

AbstractObjectiveThe loss and degradation of aquatic habitat through fragmentation, water extraction, and climate warming contribute to declining native stream fish diversity. In response to these declines, a large‐scale repatriation program was established in Arizona and New Mexico to expand the distribution and abundance of native fishes. This program has had variable success, with imperiled fish populations establishing and persisting in some streams, while other populations failed to establish.MethodsTo identify factors contributing to the success of repatriation, we conducted a study investigating how biotic and abiotic variables affect native fish presence or absence at differing spatial scales throughout the Gila River basin. We conducted fish and habitat surveys in 29 river reaches at three spatial scales: the 1‐km, 0.1‐km, and mesohabitat scale. We used generalized linear models to identify associations among species presence, habitat characteristics, and nonnative species abundance across spatial scales. Logistic regression models were also used to test associations with heterogeneity of habitat characteristics and species presence.ResultModels indicated strong species‐ and scale‐specific responses to these variables. Nonnative abundance was less influential than other habitat variables in predicting the presence of native fish, although the majority of associations that emerged were negative. Further, we were able to identify that water velocity, depth, and substrate size were the most common variables associated with species' presence across all scales and age‐classes, with most species responding positively to elevated velocities and variable responses for depth and substrate size. Response to variation in habitat was species‐specific, with some associations positive and others negative.ConclusionCollectively, the information from this study will help identify locations with a reasonably high likelihood of supporting native fishes and broaden our understanding of species responses to habitat and nonnative species across multiple scales.

Riverscape community genomics: A comparative analytical approach to identify common drivers of spatial structure.

Genetic differentiation among local groups of individuals, that is, genetic β-diversity, is a key component of population persistence related to connectivity and isolation. However, most genetic investigations of natural populations focus on a single species, overlooking opportunities for multispecies conservation plans to benefit entire communities in an ecosystem. We present an approach to evaluate genetic β-diversity within and among many species and demonstrate how this riverscape community genomics approach can be applied to identify common drivers of genetic structure. Our study evaluated genetic β-diversity in 31 co-distributed native stream fishes sampled from 75 sites across the White River Basin (Ozarks, USA) using SNP genotyping (ddRAD). Despite variance among species in the degree of genetic divergence, general spatial patterns were identified corresponding to river network architecture. Most species (N=24) were partitioned into discrete subpopulations (K=2-7). We used partial redundancy analysis to compare species-specific genetic β-diversity across four models of genetic structure: Isolation by distance (IBD), isolation by barrier (IBB), isolation by stream hierarchy (IBH), and isolation by environment (IBE). A significant proportion of intraspecific genetic variation was explained by IBH (x̄ = 62%), with the remaining models generally redundant. We found evidence for consistent spatial modularity in that gene flow is higher within rather than between hierarchical units (i.e., catchments, watersheds, basins), supporting the generalization of the stream hierarchy model. We discuss our conclusions regarding conservation and management and identify the 8-digit hydrologic unit (HUC) as the most relevant spatial scale for managing genetic diversity across riverine networks.

A Long-Term Vision for an Ecologically Sound Platte River

The Platte River extends about 310 mi (499 km) from North Platte, Nebraska, to its terminus at the Missouri River confluence near Plattsmouth, Nebraska. The Platte River Valley is a continentally significant ecosystem that serves as a major stopover for migratory waterbirds in the Central Flyway including the endangered Whooping Crane (Grus americana) and >1 million Sandhill Cranes (Antigone canadensis) at the peak of spring migration. However, the Platte River Valley also supports a great diversity of avifauna including grassland breeding birds, native stream fish, vascular plants, herpetofauna, mammals, pollinators, and aquatic macroinvertebrates. Despite ongoing conservation efforts since the mid-1970s the ecosystem remains largely conservation dependent and an increasing number of species across taxa are being considered at risk of regional extirpation or outright extinction. However, given the attention provided to conservation in the Platte River Valley and the need to maintain ecologically functional stopover sites in the Central Flyway, there is a great opportunity to create a resilient refugium for biodiversity conservation in the central Great Plains. To that end we convened a working group of >18 individuals representing >9 organizations including representatives from non-profit conservation organizations, universities, and state and federal natural resource agencies to develop a long-term vision for an ecologically sound Platte River Valley (PRV). We met in groups of varying size for >170 hours throughout a more than 3-year period and developed conservation priorities and objectives using a landscape design process. Landscape design is an interdisciplinary conservation planning process that incorporates components of landscape ecology and social dimensions of natural resources with the explicit intention of improving conservation implementation.

Assessing Linkages Between Small Impoundments and Long-term Trajectories of Prairie Stream Fish Assemblages

Most stream fish communities have changed over time in response to common anthropogenic disturbances. Impoundments are a widespread anthropogenic stressor that can negatively impact stream fishes as they alter flow regimes, block movements, and act as fountainheads for the introduction and spread of invasive species. Recent studies, however, have reported the occurrence and reproduction of native fishes in impoundments, suggesting they might benefit some native fishes. Our primary objective was to evaluate whether impoundment construction has led to changes in fish community structure in prairie streams. To accomplish this, we compared fish occupancy in small impoundments (,5 ha) to temporal trends in stream occupancy among species to test whether species' increases in stream occupancy were related to their occupancy in impoundments. We examined stream fish communities in the Upper Cottonwood River basin, Kansas, from 1948–2018, and sampled small impoundments in 2016 and 2017. A third (32%) of fish communities in impoundments were similar to stream assemblages, whereas most impoundments (68%) were dominated by sport or bait fishes. In streams, six species showed increases in occupancy and four species showed decreases since small impoundment construction. Of the species that exhibited increased stream occupancy, five showed a positive, logistical relationship between a species' impoundment occupancy and its increase in stream occupancy. Species declining in stream occupancy experienced continued linear declines and may still be declining. Our research suggests stream fish communities have changed since impoundment construction, and are associated with locally-invasive, native species reaching a new stable state in streams accompanied by declines in other native stream fish species.

Gut content biomass of stream fishes: associations with streamflow velocity, population density, and prey abundance at two spatial scales

Although food consumption rate has been identified as an important biological variable informing growth rates and population dynamics in fisheries management, equivalent measures receive little attention for native stream fishes. This research investigates whether spatial variation in fish gut fullness can be explained by streamflow velocity, population density, or prey abundance. We tested hypotheses associated with outcomes of habitat-specific energetic demands, exploitation competition, and resource-driven habitat use. Gut content biomass (GCB) of insectivorous fish species was compared at reach and at landscape scales in the Meramec River basin (Missouri, USA). Explanatory variables were selected using ridge regression with cross-validation. GCB of widely distributed species was correlated with body size, streamflow velocity, conspecific fish density, and prey abundance. At the reach scale, GCB was positively correlated with streamflow velocity in three species, supporting a prediction of an optimal foraging model. Negative relationships between GCB and density of Luxilus zonatus may be due to exploitation competition, while positive relationships between GCB and density of Etheostoma flabellare likely result from resource-driven habitat use. We found few relationships between GCB and explanatory variables at the landscape scale, suggesting that unmeasured biological and habitat variables are more important determining gut fullness at broad spatial scales.

Invasion of the Hawaiian Islands by a parasite infecting imperiled stream fishes

Points of origin and pathways of spread are often poorly understood for introduced parasites that drive disease emergence in imperiled native species. Co‐introduction of parasites with non‐native hosts is of particular concern in remote areas like the Hawaiian Islands, where the introduced nematode Camallanus cotti has become the most prevalent parasite of at‐risk native stream fishes. In this study, we evaluated the prevailing hypothesis that C. cotti entered the Hawaiian Islands with poeciliid fishes from the Americas, and spread by translocation of poeciliid hosts across the archipelago for mosquito control. We also considered the alternative hypothesis of multiple independent co‐introductions with host fishes originating from Asia. We inferred conduits of introduction and spread of C. cotti across the archipelago from geographic patterns of mtDNA sequence variation and allelic variation across 11 newly developed microsatellite markers. The distribution of haplotypes suggests that C. cotti spread across the archipelago following an initial introduction on O'ahu. Approximate Bayesian Computation modeling and allelic variation also indicate that O'ahu is the most likely location of introduction, from which C. cotti dispersed to Maui followed by spread to the other islands in the archipelago. Evidence of significant genetic structure across islands indicates that contemporary dispersal is limited. Our findings parallel historical records of non‐native poeciliid introductions and suggest that remediating invasion hotspots could reduce the risk of infection in native stream fishes, which illustrates how inferences on parasite co‐introductions can improve conservation efforts by guiding responses to emerging infectious disease in species of concern.

Does Habitat Restoration Increase Coexistence of Native Stream Fishes with Introduced Brown Trout: A Case Study on the Middle Provo River, Utah, USA

Restoration of altered or degraded habitats is often a key component in the conservation plan of native aquatic species, but introduced species may influence the response of the native community to restoration. Recent habitat restoration of the middle section of the Provo River in central Utah, USA, provided an opportunity to evaluate the effect of habitat restoration on the native fish community in a system with an introduced, dominant predator—brown trout (Salmo trutta). To determine the change in distribution of fish species and community composition, we surveyed 200 m of each of the four study reaches both before restoration (1998) and after restoration (2007 and 2009). Juveniles and adults of six native species increased in distribution after restoration. The variation in fish community structure among reaches was lower post-restoration than pre-restoration. Overall, restoration of complex habitat in the middle Provo River led to increased pattern of coexistence between native fishes and introduced brown trout, but restoration activities did not improve the status of the river’s two rarest native fish species. Habitat restoration may only be completely successful in terms of restoring native communities when the abundance of invasive species can be kept at low levels.

Tropical insular fish assemblages are resilient to flood disturbance

Periods of stable environmental conditions, favoring development of ecological communities regulated by density‐dependent processes, are interrupted by random periods of disturbance that may restructure communities. Disturbance may affect populations via habitat alteration, mortality, or displacement. We quantified fish habitat conditions, density, and movement before and after a major flood disturbance in a Caribbean island tropical river using habitat surveys, fish sampling and population estimates, radio telemetry, and passively monitored PIT tags. Native stream fish populations showed evidence of acute mortality and downstream displacement of surviving fish. All fish species were reduced in number at most life stages after the disturbance, but populations responded with recruitment and migration into vacated upstream habitats. Changes in density were uneven among size classes for most species, indicating altered size structures. Rapid recovery processes at the population level appeared to dampen effects at the assemblage level, as fish assemblage parameters (species richness and diversity) were unchanged by the flooding. The native fish assemblage appeared resilient to flood disturbance, rapidly compensating for mortality and displacement with increased recruitment and recolonization of upstream habitats.

Parasitism of a native Hawaiian stream fish by an introduced nematode increases with declining precipitation across a natural rainfall gradient

AbstractClimate change can promote disease emergence if shifting conditions favour infection of native fauna by introduced parasites and pathogens. In Hawai'i, climate warming is predicted to reduce net precipitation and surface flow in streams, which in turn could increase parasitism of native stream fishes by non‐native parasites. In this study, we utilised a natural precipitation gradient across the Hamakua coast on the island of Hawai'i to assess the relationship between precipitation and infection of Awaous stamineus, a native amphidromous goby, by the introduced nematode Camallanus cotti. We found that the abundance, intensity and prevalence of C. cotti in A. stamineus increased with declining rainfall. Our results also show that parasitism tracks precipitation patterns across the archipelago and that parasitism increases even with moderate decreases in rainfall. As the Hamakua coast precipitation gradient represents a proxy for predicted climate‐driven reductions in precipitation, these findings suggest that infection of native Hawaiian fishes by introduced parasites will increase if climate conditions change as expected. Our findings also suggest that parasitism may be exacerbated by other factors that reduce surface flow, including water extraction for agricultural and urban uses. If so, then adaptive management of minimum flow standards in Hawai'i and elsewhere could improve the well‐being of at‐risk native fishes by alleviating parasitism under current and future climate conditions.

Conservation Status of Five Headwater Stream Specialists in South Dakota

Native stream fish zoogeography has changed substantially across North America during the last century because habitat degradation, stream fragmentation and introductions of nonnative species have led to numerous extinctions, extirpations, and altered distributions. Insufficient information regarding imperiled species often results in reactive, rather than proactive, management, and knowledge of species status and ecology is critical in identifying conservation priorities. We used fish collection records and a habitat assessment to update the status of five fishes of conservation interest in South Dakota (Northern Redbelly Dace Chrosomus eos, Finescale Dace Chrosomus neogaeus, Northern Pearl Dace Margariscus nachtriebi, Blacknose Shiner Notropis heterolepis, and Plains Topminnow Fundulus sciadicus). We compiled records from previous collections within the White, Little White, and Keya Paha River Basins in South Dakota as well as adjoining and neighboring drainage basins in Nebraska. We also sampled fish and habitat at 42 stream reaches within the White, Little White, and Keya Paha river basins during 2010–2012, focusing on tributary streams. We detected all target species except for Finescale Dace. All species preferred tributary streams over larger rivers (third order or greater). All target species except Blacknose Shiner exhibited patchy distribution and abundance patterns, normally occurring at low relative abundance where present but occasionally detected at moderate to high relative abundance. Each target species was limited to landscapes with perennial, springfed streams that are not present in neighboring drainages. This study updates the distribution of conservation listed species, identifies landscape level habitat filters, and offers guidance for conservation and research efforts.

Status of Native Stream Fishes within Selected Protected Areas of the Niobrara River in Western Nebraska

Lotic systems within the Great Plains are characterized by highly fluctuating conditions through both space and time. Fishes inhabiting these systems have adopted specific life-history strategies to survive in such environments; however, anthropogenic disturbance to prairie streams has resulted in declines and extirpation of many native stream fishes. Terrestrial protected areas (i.e., parks and reserves) are designated to support native flora and fauna and, it is assumed, to provide protection to native fishes. We assessed the presence and relative abundance of stream fish populations within protected areas along the Niobrara River in western Nebraska based on data collected during 1979, 1989, 2008, and 2011. The spatial extent of protection, landscape changes resulting in degraded physiochemical parameters, and introduced species may reduce the effectiveness of these terrestrial protected areas in protecting native fishes in Great Plains stream environments.

Fish distributions in the Rondegat River, Cape Floristic Region, South Africa, and the immediate impact of rotenone treatment in an invaded reach

Alien fishes are considered the most serious threat to native headwater stream fishes in South Africa. A 4 km reach of the Rondegat River is the first section of a South African river to be rehabilitated through the attempted removal of alien fish by using the piscicide rotenone. The objectives of the current study were to establish the distribution and relative abundance of native and alien fish prior to treatment, and to assess the immediate impact of the treatment on the fish population. Forty-three sites were sampled using backpack electrofishing, snorkel transects and underwater video analysis. In the invaded lower reaches, native Labeobarbus capensis was detected only at very low densities, while three other native fish species were not detected. Alien fish were not detected above a barrier waterfall 5 km upstream of the river's confluence with a reservoir. The fish density of 97 fish per 100 m2 in non-invaded reaches was more than an order of magnitude higher than that of 7 fish per 100 m2 in the invaded reach. A total of 470 Micropterus dolomieu and 139 L. capensis were removed from a 4 km treatment zone during the rotenone operation. No fish were detected in this area after the rotenone treatment.

Efficacy of population size structure as a bioassessment tool in freshwaters

Bioassessments are used to measure system health and assess disturbance. While fish-based freshwater bioassessments are cost-effective and perform well in speciose systems, such bioassessments remain difficult to implement in species-poor Mediterranean regions. Population size structure metrics may provide meaningful biological information where depauperate communities preclude the richness and composition measures generally used. We focus our assessments of population size structure responses to anthropogenic perturbation on one of the most widespread native stream fish (Squalius laietanus). We explore a number of population size statistics as metrics for a Mediterranean region, where current bioassessments perform poorly. Our sampling encompassed 311 sites across Catalonia (NE Spain) where we characterized anthropogenic perturbation using a summary of impacts, including local data on stream condition and landscape indicators of degradation, via a principal component analysis. Anthropogenic perturbation in streams was collinear with altitudinal gradients and highlights the importance of appropriate statistical techniques. Of the population size structure metrics explored, average length was the most sensitive to anthropogenic perturbation and generally increased along the disturbance gradient. Although we expected to find consistent changes in variance, kurtosis, and skewness, the observed relationships were weak. River basin mediated responses suggest the importance of environmental landscape factors. The unexpected increases of mean S. laietanus body size with anthropogenic perturbation, strong effects of river basin, collinearity with spatial gradients and the species-specific nature of responses preclude the direct application of size structure in freshwater bioassessments. Although its application in fish-based freshwater bioassessments appears difficult, population size structure can provide insights in species-specific applications and management.

Landscape‐Scale Evaluation of Asymmetric Interactions between Brown Trout and Brook Trout Using Two‐Species Occupancy Models

AbstractPredicting the distribution of native stream fishes is fundamental to the management and conservation of many species. Modeling species distributions often consists of quantifying relationships between species occurrence and abundance data at known locations with environmental data at those locations. However, it is well documented that native stream fish distributions can be altered as a result of asymmetric interactions between dominant exotic and subordinate native species. For example, the naturalized exotic Brown Trout Salmo trutta has been identified as a threat to native Brook Trout Salvelinus fontinalis in the eastern United States. To evaluate large‐scale patterns of co‐occurrence and to quantify the potential effects of Brown Trout presence on Brook Trout occupancy, we used data from 624 stream sites to fit two‐species occupancy models. These models assumed that asymmetric interactions occurred between the two species. In addition, we examined natural and anthropogenic landscape characteristics we hypothesized would be important predictors of occurrence of both species. Estimated occupancy for Brook Trout, from a co‐occurrence model with no landscape covariates, at sites with Brown Trout present was substantially lower than sites where Brown Trout were absent. We also observed opposing patterns for Brook and Brown Trout occurrence in relation to percentage forest, impervious surface, and agriculture within the network catchment. Our results are consistent with other studies and suggest that alterations to the landscape, and specifically the transition from a forested catchment to one that contains impervious surface or agriculture, reduces the occurrence probability of wild Brook Trout. Our results, however, also suggest that the presence of Brown Trout results in lower occurrence probability of Brook Trout over a range of anthropogenic landscape characteristics, compared with streams where Brown Trout were absent.

A laboratory study of the effects of shelter availability and invasive crayfish on the growth of native stream fish

Summary1. The alteration of stream habitats by urbanisation reduces the availability of shelter. Reduced shelter availability may increase both predation risks and metabolic costs, negatively affecting the growth performance of stream fish. Although urbanised streams often allow the establishment of invasive species, the additive or interactive effects of shelter availability and invasive species are rarely explored. The invasive red swamp crayfish (Procambarus clarkii) is a strong shelter competitor and predator in streams.2. We conducted a stream‐channel experiment to investigate how shelter availability and this invasive crayfish species affect the growth performance (measured as the loss in body mass under starved conditions) of two native benthic species, Japanese crucian carp (Carassius auratus complex) and an endangered cobitid fish (Lefua echigonia).3. We found that both the absence of shelter and the presence of crayfish increased body mass loss in the crucian carp. However, the growth performance of the crucian carp was improved by the presence of shelter except in the presence of crayfish, in which case the shelter available did not ameliorate the negative effect of the crayfish on growth performance (i.e. an interactive effect). This result suggests that crayfish may affect the growth performance of the crucian carp through chemical cues as well as through shelter occupancy.4. In contrast, shelter availability is the primary factor affecting the body mass loss of the cobitid fish. However, the growth performance of these fish was unaffected by the presence of crayfish. The change in the growth performance of the cobitid fish in response to the absence of shelter was greater than that of the crucian carp. This finding suggests that the cobitid fish may be more vulnerable than the crucian carp to a reduction in shelter availability.5. Our study demonstrates that reduced shelter availability and/or crayfish invasion can have significant, indirect negative effects on the growth performance of native fish, but whether those effects are interactive might vary depending on the species. Our findings have clear implications for stream restoration and habitat assessment.

Specific Niche Characteristics Facilitate the Invasion of an Alien Fish Invader in Boreal Streams

We studied the ecological niche relations of native stream fish and an alien invader, brook trout (Salvelinus fontinalis), to examine if brook trout had located an underused environmental niche in our boreal study system. In both study years (1994 versus 2004), we found brook trout to have the most marginal niche position of all the fish species examined. The most important environmental variable affecting the distribution of brook trout was pH, with acid headwater sites being dominated by this species. Brown trout, in contrast, had relatively nonmarginal niche, occurring in average conditions across the sampled sites. Other fish species had niche positions between the two salmonids. Our results show that fish invasions may be strongly facilitated by the presence of suboptimally occupied environmental niche space in the recipient river system.

Anthropogenic habitat alteration induces rapid morphological divergence in a native stream fish.

Anthropogenic habitat alteration creates novel environments that can alter selection pressures. Construction of reservoirs worldwide has disturbed riverine ecosystems by altering biotic and abiotic environments of impounded streams. Changes to fish communities in impoundments are well documented, but effects of those changes on native species persisting in reservoirs, which are presumably subjected to novel selective pressures, are largely unexplored. I assessed body shape variation of a native stream fish in reservoir habitats and streams from seven reservoir basins in the Central Plains of the USA. Body shape significantly and consistently diverged in reservoirs compared with stream habitats within reservoir basins; individuals from reservoir populations were deeper-bodied and had smaller heads compared with stream populations. Individuals from reservoir habitats also exhibited lower overall shape variation compared with stream individuals. I assessed the contribution of genotypic divergence and predator-induced phenotypic plasticity on body shape variation by rearing offspring from a reservoir and a stream population with or without a piscivorous fish. Significant population-level differences in body shape persisted in offspring, and both populations demonstrated similar predator-induced phenotypic plasticity. My results suggest that, although components of body shape are plastic, anthropogenic habitat modification may drive trait divergence in native fish populations in reservoir-altered habitats.

Persistence of native fishes in small streams of the urbanized San Francisco Estuary, California: acknowledging the role of urban streams in native fish conservation

ABSTRACT Urbanization is known to have pernicious consequences for native stream fishes globally. The San Francisco Estuary (SFE), California, is one of the largest, most urbanized estuaries in North America and non‐native freshwater fishes are widespread in many of its catchments. Nevertheless, a diverse native and endemic freshwater fish species assemblage remains in this region. Historical records (1854–2007) were reviewed and sampling conducted throughout SFE catchments to determine the distribution of stream fishes. Native stream fishes were classified by zoogeographic type, habitat preferences, physiological tolerances, and whether native fishes utilized reservoirs during their life cycle. From 1993–1999, stream fishes were sampled at 270 sites distributed in 23 SFE catchments to assess the overall status and distribution of native stream fishes, and illuminate drivers of persistence. In 2009, stream fishes were sampled at 65 sites within the largest estuary catchment, Alameda Creek, to further explore distributional patterns and drivers of native fish persistence. Native stream fishes persist in the urbanized SFE because of several interacting factors, including the existence of extensive undeveloped landscapes in the headwaters of many catchments, the prevalence of saltwater dispersant native stream fishes, the wide physiological tolerances of native species, the presence of saltwater barriers between catchments that presumably reduces the spread of non‐native fishes, and the existence of reservoirs that function as habitat for several native species. These results emerged from both the SFE‐wide and the Alameda Creek analyses, suggesting they are somewhat general for this region. Study results show that streams in spatially complex urban settings retain important conservation benefits to native stream fishes, despite significant perturbations and the establishment of non‐native fishes.Copyright © 2011 John Wiley & Sons, Ltd.

Hydropower-related pulsed-flow impacts on stream fishes: a brief review, conceptual model, knowledge gaps, and research needs

The societal benefits of hydropower systems (e.g., relatively clean electrical power, water supply, flood control, and recreation) come with a cost to native stream fishes. We reviewed and synthesized the literature on hydropower-related pulsed flows to guide resource managers in addressing significant impacts while avoiding unnecessary curtailment of hydropower operations. Dams may release pulsed flows in response to needs for peaking power, recreational flows, reservoir storage adjustment for flood control, or to mimic natural peaks in the hydrograph. Depending on timing, frequency, duration, and magnitude, pulsed flows can have adverse or beneficial short and long-term effects on resident or migratory stream fishes. Adverse effects include direct impacts to fish populations due to (1) stranding of fishes along the changing channel margins, (2) downstream displacement of fishes, and (3) reduced spawning and rearing success due to redd/nest dewatering and untimely or obstructed migration. Beneficial effects include: (1) maintenance of habitat for spawning and rearing, and (2) biological cues to trigger spawning, hatching, and migration. We developed a basic conceptual model to predict the effects of different types of pulsed flow, identified gaps in knowledge, and identified research activities to address these gaps. There is a clear need for a quantitative framework incorporating mathematical representations of field and laboratory results on flow, temperature, habitat structure, fish life stages by season, fish population dynamics, and multiple fish species, which can be used to predict outcomes and design mitigation strategies in other regulated streams experiencing pulsed flows.