Reservoir Fish Research Articles

Role of riparian shade on the fish assemblage of a reservoir littoral

Research into the effects of shade on reservoir fish assemblages is lacking, with most investigations focused on streams. Unlike many streams, the canopy in a reservoir shades only a narrow fringe of water adjacent to the shoreline, and may not have the influential effect on the aquatic environment reported in streams. We compared fish assemblages between shaded and unshaded sites in a shallow reservoir. Overall species richness (gamma diversity) was higher in shaded sites, and fish assemblage composition differed between shaded and unshaded sites. Average light intensity was 66 % lower in shaded sites, and differences in average temperature and dissolved oxygen were small. Unlike streams where shade can have large effects on water physicochemistry, in reservoirs shade-related differences in fish assemblages seemed to be linked principally to differences in light intensity. Diversity in light intensity in shaded and unshaded sites in reservoirs can create various mosaics of light-based habitats that enable diversity of species assemblages. Managing to promote the habitat diversity provided by shade may require coping with the artificial nature of reservoir riparian zones and water level fluctuations.

<b>Chemical composition of lipids from native and exotic fish in reservoirs of the state of Ceará, Brazil

Current study analyzes the chemical composition of lipids in fish commonly found in the dams of the state of Ceara, Brazil, namely Pterygoplichthys pardalis (bodo), Hoplias malabaricus (traira), Cichla ocellaris (tucunare), Prochilodus brevis (curimata) and Oreochomis niloticus (tilapia). The animals were collected during the summer and Folch extraction procedure was used for the extraction of lipids, whilst Iupac methodology (International Union of Pure and Applied Chemistry [Iupac], 1987) was used to methylate the fatty acids. Methyl esters were analyzed by GC/MS and the different components in fish oil were identified. Palmitic acid, C16:0 (35.71-45.02%), was the saturated fatty acid with the highest percentage, while oleic acid, C18:1Δ9 (10.62-25.29%) had the highest percentage among the unsaturated fatty acids. The chemical composition of analyzed freshwater fish lipids revealed low levels of polyunsaturated fatty acids.

The role of submerged trees in the early development of fishes in a Neotropical reservoir.

It was hypothesized that the structural heterogeneity provided by submerged trees positively favours the spatial distribution of fish abundance at early stages of development in an area under the influence of a Neotropical reservoir in the Paraná River basin. The distribution at early stages of development of the most abundant species was evaluated. To remove any possible confounding effect related to local environmental variables, changes in these were also evaluated. Sampling was carried out at sites with and without submerged trees. Among all individuals sampled, 96·1% were classified as larvae and 3·9% as juveniles. The area without submerged trees showed higher total abundance, but there were spatial differences in the distribution of early stage fishes. From the moment the larvae are able to swim actively, they search for sites with a complex structure. The results show that reaches with submerged trees play an important role in the early development of fishes in reservoirs, and, hence, the preservation of those trees is essential to maintain biodiversity in reservoirs.

Using Hierarchical Bayesian Multispecies Mixture Models to Estimate Tandem Hoop‐net‐Based Habitat Associations and Detection Probabilities of Fishes in Reservoirs

AbstractSpecies distribution models are useful tools to evaluate habitat relationships of fishes. We used hierarchical Bayesian multispecies mixture models to evaluate the relationships of both detection and abundance with habitat of reservoir fishes caught using tandem hoop nets. A total of 7,212 fish from 12 species were captured, and the majority of the catch was composed of Channel Catfish Ictalurus punctatus (46%), Bluegill Lepomis macrochirus (25%), and White Crappie Pomoxis annularis (14%). Detection estimates ranged from 8% to 69%, and modeling results suggested that fishes were primarily influenced by reservoir size and context, water clarity and temperature, and land‐use types. Species were differentially abundant within and among habitat types, and some fishes were found to be more abundant in turbid, less impacted (e.g., by urbanization and agriculture) reservoirs with longer shoreline lengths; whereas, other species were found more often in clear, nutrient‐rich impoundments that had generally shorter shoreline length and were surrounded by a higher percentage of agricultural land. Our results demonstrated that habitat and reservoir characteristics may differentially benefit species and assemblage structure. This study provides a useful framework for evaluating capture efficiency for not only hoop nets but other gear types used to sample fishes in reservoirs.Received October 14, 2014; accepted December 23, 2015 Published online April 11, 2016

Utility of Reservoir Characteristics to Determine Minimum Sampling Effort Needed to Assess Sport Fish Populations in Kansas Reservoirs

AbstractEffective reservoir fisheries management requires fish samples suitable for addressing objectives. These samples are typically attained with fish sampling gears using standardized protocols. Some standardized protocols for sampling reservoir fishes promote objective‐based sampling, and many include a minimum number of gear deployments. This minimum number is often a function of reservoir surface area. However, reservoir size may not adequately predict the number of gear deployments needed to reach sample objectives. We used multiple linear regression to determine the relationships between the biological, chemical, and physical characteristics of reservoirs and the number of gear deployments needed to reach two sample objectives: (1) collecting 100 stock‐length fish (N100), and (2) attaining relative SE of stock‐length catch per effort (CPE) ≤25% (RSE25). These analyses were conducted using data from 34 Kansas reservoirs and six fish species. We used Akaike model averaging from a confidence model set (ΔAIC ≤ 2) to develop an average model for each sample objective (N100 and RSE25) and target species. Recent CPE was identified in N100 models for six target species and in RSE25 models for five. Conversely, reservoir surface area was identified in only one model for N100 and two for RSE25. These results suggest that reservoir characteristics other than surface area, particularly recent CPE, should be considered when developing minimum sample sizes for objective‐based fish sampling protocols. This approach would allow managers to most efficiently allocate sampling effort while still collecting representative and precise fish samples.Received March 6, 2015; accepted November 30, 2015 Published online March 22, 2016

Effectiveness of pulsed direct current at reducing walleye escapement from a simulated reservoir

Fish escapement from reservoirs is problematic and makes management of these fisheries challenging. Historically, physical barriers have been used to limit fish movement but are prone to clogging and require constant maintenance. Thus, evaluations of alternative technologies are needed to limit reservoir fish escapement. Electrical barriers may offer an effective option for reducing fish escapement, but their effectiveness may be species-specific. Here, we predicted pulsed direct current with a graduated field would (1) alter walleye Sander vitreus behavior, (2) reduce escapement and (3) not induce mortality. Laboratory experiments compared walleye behavior, escapement, and mortality at four pulse (0, 0.3, 0.5, and 0.8ms) and three voltage (0, 60, and 80V) settings. The average voltage gradient 80cm in front of the outlet was 0.09V/cm (power density=1.36μW/cm3) at 60V and 0.14V/cm (power density=3.36μW/cm3) at 80V. Our results demonstrate that pulsed direct current was successful at reducing approaches and increasing deflections of walleyes, suggesting fish avoided the barrier. Altered behavior resulted in nearly an 80% reduction in escapement with smaller fish more likely to escape compared to larger individuals. However, pulse width and voltage did not influence escapement rates. Walleye mortality was 0% for control trials, ranged from 0.5–5.7% with the current activated, and was greatest at the highest barrier setting (0.8ms, 80V). Our laboratory results indicate pulsed direct current may be effective at reducing fish escapement from reservoirs. Lower pulse and voltage settings should be used due to their ability to reduce escapement while inflicting minimal mortality compared to higher settings. Additional work should evaluate the success of electric barriers in reservoir field settings under a wider range of conditions and on additional species.

System‐Specific Variability in Murray Cod and Golden Perch Maturation and Growth Influences Fisheries Management Options

AbstractThe Murray Cod Maccullochella peelii and Golden Perch Macquaria ambigua are important recreational species in Australia's Murray–Darling Basin (MDB); both species have declined substantially, but recovery is evident in some areas. Minimum length limits (MLLs)—implemented to ensure fish could spawn at least once prior to harvest eligibility—have increased three times in the past decade. We quantified variation in length at 50% maturity (LM50), age at 50% maturity (AM50), and von Bertalanffy growth parameters (k = Brody growth coefficient; L∞ = asymptotic length; t0 = theoretical age at zero length) of these species within two rivers and two reservoirs of the MDB; to investigate whether fish length is a suitable surrogate for AM50 in setting MLLs. Between 2006 and 2013, we collected 1,118 Murray Cod and 1,742 Golden Perch by electrofishing and gillnetting. Values of k and L∞ were greater for reservoir fish than for riverine fish. For both species, AM50 was generally greater in rivers than in reservoirs; for Murray Cod, LM50 was greater in reservoirs than in rivers. A yield‐per‐recruit model demonstrated that smaller Murray Cod MLLs would be required for rivers and that an MLL at or below 600 mm (the existing MLL) across all populations could lead to overfishing in some systems. The differences in growth rate and the onset of reproductive maturation between riverine and reservoir populations suggest that system‐specific regulations would be more effective at reducing the overfishing risk and meeting fishing quality objectives.Received August 18, 2014; accepted September 10, 2015

Exploring Crowded Trophic Niche Space in a Novel Reservoir Fish Assemblage: How Many is Too Many?

AbstractIn highly managed reservoir systems, species interactions within novel fish assemblages can be difficult to predict. In high‐elevation Scofield Reservoir in Utah the unintentional introduction of Utah Chub Gila atraria and subsequent population expansion prompted a shift from stocking exclusively Rainbow Trout Oncorhynchus mykiss to include tiger trout (female Brown Trout Salmo trutta × male Brook Trout Salvelinus fontinalis) and Bonneville Cutthroat Trout O. clarkii utah, which composed a novel suite of top predators and potential competitors. We examined the interspecific interactions among Scofield Reservoir piscivores using a multifaceted approach including gut analyses, stable isotopes, and gape limitation. Large Cutthroat Trout consumed 50–100% Utah Chub and tiger trout consumed 45–80%. In contrast, small and large Rainbow Trout consumed primarily invertebrate prey and exhibited significant overlap with small tiger trout, Cutthroat Trout, and Utah Chub. Large Cutthroat Trout and tiger trout occupy a top piscivore trophic niche and are more littoral, while Rainbow Trout occupy an omnivore niche space and are more pelagic. Both Cutthroat and tiger trout varied in niche space with respect to size‐class, demonstrating an ontogenetic shift to piscivory at approximately 350 mm TL. Cutthroat Trout and tiger trout are capable of consuming prey up to 50% of their own size, which is larger than predicted based on their theoretical gape limit. Because it appears food resources (Utah Chub) are not limited, and performance metrics are high, competition is unlikely between Cutthroat Trout and tiger trout. In contrast, apparent survival of Rainbow Trout has recently declined significantly, potentially due to shared food resources with Utah Chub or negative behavioral interactions with other members of the community. Collectively, this research aids in understanding biotic interactions within a top‐heavy and novel fish community and assists towards developing and implementing suitable management strategies to control nuisance species.

Fish population dynamic in the newly impounded Nam Theun 2 Reservoir (Lao PDR)

A fish population monitoring was carried out in the reservoir and tributaries of the hydropower project Nam Theun 2 (Lao PDR) at the end of the warm and dry seasons and at the end of the warm and wet seasons between 2008 and 2013. The study focused on three aquatic systems (river upstream, transition area, and reservoir) and different drowned habitats (dense/light forests and agricultural soils) associated or not with the presence of villages. The reservoir fish population was expected to follow three distinct phases, which should be respectively a rapid increase in biomass and abundance (trophic upsurge) followed by a decline and a stabilization of the population. This succession appeared to be different to the commonly observed scenario in terms of biomass, abundance and taxonomic richness compared to other temperate and tropical reservoirs. The indicator species ( H. macrolepidota and P. carinatus ) did not show changes in their size range since impoundment. The presence of structured habitats ( e.g. inundated forest) favoured the fish population in terms of biomass and abundance. The fish population in the transition area and the river upstream improved quickly after the impoundment and presented higher taxonomic richness compared to the reservoir. Finally, the transition area appeared to be the most productive area within the Nam Theun 2 Reservoir especially if it remained outside of fishing activities.

Presence of riparian vegetation increases biotic condition of fish assemblages in two Brazilian reservoirs

Abstract The riparian vegetation in lakes and reservoirs is source of course wood structures such as trunks and branches and is used as sheltering, spawning and foraging habitats for fishes. The reduction of these submerged structures can thus, affect the composition and structure of fish assemblages in reservoirs. Aim To evaluate the influence of riparian vegetation on the biotic condition of fish assemblage by adapting the Reservoir Fish Assemblage Index (RFAI) to two reservoirs in the Upper Paranapanema river basin, São Paulo State, Brazil. Methods The RFAI was adapted from metrics related to the functional characteristics and composition of fish assemblages through a protocol of metric selection and validation, and to its response to the presence of riparian vegetation. Results The final RFAI was composed by nine metrics, been lower in sites without riparian vegetation as consequence of the predominance of larger individuals and the percent of piscivorous and detritivorous fishes. Conclusions These results suggest that increasing shore habitat complexity in reservoirs by maintaining riparian vegetation increases fish biotic integrity.

Infection of Juvenile Salmonids by Salmincola californiensis (Copepoda: Lernaeopodidae) in Reservoirs and Streams of the Willamette River Basin, Oregon

AbstractWe assessed infection prevalence and intensity by the ectoparasitic copepod Salmincola californiensis among salmonid species rearing in reservoirs and streams upstream of reservoirs in the Willamette River basin, Oregon, during 2012 and 2013. Infection levels of juvenile Chinook Salmon Oncorhynchus tshawytscha, Rainbow Trout O. mykiss, and Cutthroat Trout O. clarkii were greater in reservoirs than in streams and increased with the age and size of fish. Copepods were more likely to be attached within the brachial cavity of reservoir fish (79%), whereas fins were the most common attachment site on stream fish (71%). Chinook Salmon in reservoirs were more vulnerable to infection than other species. Age‐0 Chinook Salmon in reservoirs showed increasing infection prevalence throughout the year, reaching 84% by fall (compared with 11% in streams). Infection intensity was greater for age‐0 Chinook Salmon in reservoirs than for those in streams. Infection prevalence for reservoir‐rearing Rainbow Trout was < 1% at age 0, 22% at age 1, 36% at age 2, and 38% at age 3. Intensity was low for age‐1 Rainbow Trout and increased for age‐2 and age‐3 fish. Infection prevalence for reservoir‐rearing Cutthroat Trout collected in spring (39%) was greater than for those rearing in streams (4.5%). Juvenile kokanee O. nerka were only present in reservoirs and were rarely infected with copepods. The lack of water current in reservoirs may increase the likelihood of infection in the brachial cavity. Greater infection levels observed for juvenile Chinook Salmon compared with the other species in reservoirs may be a function of behavioral, physiological, and habitat differences. We concluded that copepod infection in reservoirs reached levels that could decrease the fitness and survival of Chinook Salmon smolts, potentially hampering conservation and recovery efforts.

Chromosomal Aberration of Snakehead Fish (Channa striata) in Affected Reservoir by Leachate with Lead and Mercury Contamination

The objectives of this study are to investigate chromosomal aberrations of snakehead fish in a leachate-affected reservoir located 100 meters from a municipal landfill which compared to non-affected reservoir. Three snakehead fish were collected and chromosomal aberrations were studied using kidney tissue. Lead and mercury were measured in water, sediment and snakehead fish from the affected reservoir at three sampling sites. The results showed that the average concentrations of lead and mercury in water were 0.0012±0.0003 and 0.0053±0.0036 mg/L, respectively. The average concentrations of lead and mercury in sediment were 3.3650±2.1930 and 0.0890±0.0272 mg/kg, respectively. These values did not exceed the standard for water and soil quality except for the mercury in the water, which was higher than acceptable. Lead was not found in snakehead fish from either reservoir. The average concentrations of mercury in snakehead fish from both reservoirs were 0.1330±0.0792 and 0.1180±0.0350 mg/kg, respectively, which were higher than the standard for mercury contamination in food. This study showed that the accumulation of mercury in snakehead fish was higher than in sediment because it accumulates in organisms through the consumption hierarchy. The diploid chromosome number of snakehead fish in both reservoirs was 2n = 42 and the percentage of chromosomal breakages of snakehead fish in the affected reservoir was higher than the non-affected reservoir. There were four types of chromosomal breakages: single chromatid gap, isochromatid gap, single chromatid breaks and isochromatid breaks. The difference in percentage of chromosomal breakages in snakehead fish from both reservoirs was statistically significant (p<0.05).

Synergistic effects between omnivorous filter-feeding fish and nutrient enrichment on algal biomass

Aim: The Nile tilapia - Oreochromis niloticus(Linnaeus 1758) - is an exotic omnivorous filter-feeding fish that has been stocked for three decades in man-made lakes of Northeastern Brazil. Most experiments manipulating omnivorous filter-feeding fish in eutrophic lakes and reservoirs shows that their presence tends to increase phytoplankton biomass and primary production. In this study, we tested the hypothesis that tilapia interact synergistically with nutrient enrichment so that the effects of omnivorous fish on phytoplankton biomass becomes more intense with increasing nutrient concentration.MethodsA field experiment with a 2×3 factorial design was performed during four weeks in twenty-four mesocosms (0.25 m3) to which six treatments were randomly allocated: fingerling addition (F), juvenile tilapia addition (J), nutrient addition (NP), nutrient and fingerling addition (NPF), nutrient and juvenile tilapia addition (NPJ) and a control treatment with no tilapia or nutrients addition (C). A two-way repeated measures ANOVA was done to test for time (t), tilapia and nutrients effects and their interaction on total phosphorus, total nitrogen and chlorophyll-a concentrations.ResultsThe results showed a positive effect of nutrient addition on total phosphorus, total nitrogen and chlorophyll-a concentrations and a positive effect of tilapia on the concentration of chlorophyll-a. As expected, we found a synergistic interaction between the positive effect of Nile tilapia and nutrient enrichment on phytoplankton biomass.ConclusionsThe above results suggest that controlling tilapia abundance through fisheries management is a potential tool to improve water quality and mitigate the effects of lake and reservoir eutrophication.

Agonistic Behavior among Three Stocked Trout Species

AbstractThe popularity of reservoirs to support sport fisheries has led to the stocking of species that did not co‐evolve, creating novel reservoir fish communities. In Utah, the Bear Lake strain of Bonneville Cutthroat Trout Oncorhynchus clarkii utah and tiger trout (female Brown Trout Salmo trutta × male Brook Trout Salvelinus fontinalis) are being more frequently added to a traditional stocking regimen consisting primarily of Rainbow Trout O. mykiss. Interactions between these three predatory species are not well understood, and studies evaluating community interactions have raised concern for an overall decrease of trout condition. To evaluate the potential for negative interactions among these species, we tested aggression in laboratory aquaria using three‐species and pairwise combinations at three densities. Treatments were replicated before and after feeding. During the three‐species trials Rainbow Trout initiated 24.8 times more aggressive interactions than Cutthroat Trout and 10.2 times more aggressive interactions than tiger trout, and tiger trout exhibited slightly (1.9 times) more aggressive initiations than Cutthroat Trout. There was no significant difference in behavior before versus after feeding for any species, and no indication of increased aggression at higher densities. Although Rainbow Trout in aquaria may benefit from their bold, aggressive behavior, given observations of decreased relative survival in the field, these benefits may be outweighed in reservoirs, possibly through unnecessary energy expenditure and exposure to predators.Received October 1, 2014; accepted January 27, 2015

A classification system for large reservoirs of the contiguous United States.

Degradation of reservoir fish habitat has become a serious concern. Habitat issues-such as sedimentation, excessive nutrient loadings, and lack of submerged structure-may emerge and worsen over time and are accompanied by undesirable shifts in the fish community and fisheries. To prioritize habitat rehabilitation efforts in reservoirs, we developed a classification system for large reservoirs in the contiguous U.S. We used a four-step classification approach based on over 50 variables descriptive of habitat impairment in a sample of almost 1300 reservoirs. To account for the broad geographic heterogeneity in climate and landscape, reservoirs were assigned to a spatial framework relevant to aquatic resources, selected based on how well it recognized regional differences in fish habitat. To account for differences among reservoirs within geographical regions, we used cluster analysis to identify classes of reservoirs with similar characteristics. Classes were compared regarding habitat impairment, the fish community, the recreational fishery, and other variables from an external dataset to seek support for the classification system. A method for classifying new reservoirs not included in the original sample was also developed. The resulting classification system identified nine geographical regions distributed throughout the contiguous U.S. and 24 reservoir classes within the nine regions. The system can serve as the framework for a reservoir assessment mechanism. Our approach may be applicable elsewhere a broad-scale dataset is not available and needs to be obtained quickly and inexpensively, whether in regards to fish habitat or other environmental information needs.

Moderate biomanipulation for eutrophication control in reservoirs using fish captured in angling competitions

Angling competitions are a popular leisure activity in reservoirs of Southern Portugal. These competitions can gather more than 100 anglers aiming to catch the maximum fish weight. Groundbaiting and catch-and-release angling are two common practices for anglers in competition. In this study, the loads of nutrients from commercial groundbait powders used in angling competitions in the Maranhao reservoir and the possible balance out of those nutrients through a moderate biomanipulation of the fish biomass caught in competitions were analysed. In order to achieve this aim, chemical analyses to groundbait powders most purchased by Portuguese anglers and to fish species most captured in competitions were made. Mass balances on inputs and outputs of nutrients considering some biomanipulation scenarios were evaluated. Results demonstrated that an effective management on angling competitions implementing a moderate biomanipulation of fish in reservoirs could promote the control of fish fauna and eutrophication, balancing out nutrients from angling.

Evaluation of the temporal development of three introduced populations of brook trout, Salvelinus fontinalis, in Jizerské mountains, Czech Republic

Three populations of brook trout, Salvelinus fontinalis, established in streams and reservoirs in the Jizersk? Mountains, Czech Republic, were studied between 1995 and 2006. The maximum age was usually 3+ to 4+, but the age 7+ was also recorded. The inflows of all reservoirs are populated mostly by 0+ to 2+ brook trout, while older specimens live in a lentic environment, migrating to lotic habitats only to spawn. The density of brook trout in streams ranged from 8 to 95 individuals per 100 m2 during spring and summer, while that for reservoirs ranged between 31 and 290 individuals per ha. A strong negative correlation between the size of adult fish and population density in reservoirs was observed. The type of management influenced both density and growth of brook trout. Further introduction of this species in the central European area should be restricted to habitats where native salmonids cannot survive, such as acidified waters.

Land use structures fish assemblages in reservoirs of the Tennessee River

Inputs of nutrients, sediments and detritus from catchments can promote selected components of reservoir fish assemblages, while hindering others. However, investigations linking these catchment subsidies to fish assemblages have generally focussed on one or a handful of species. Considering this paucity of community-level awareness, we sought to explore the association between land use and fish assemblage composition in reservoirs. To this end, we compared fish assemblages in reservoirs of two sub-basins of the Tennessee River representing differing intensities of agricultural development, and hypothesised that fish assemblage structure indicated by species percentage composition would differ among reservoirs in the two sub-basins. Using multivariate statistical analysis, we documented inter-basin differences in land use, reservoir productivity and fish assemblages, but no differences in reservoir morphometry or water regime. Basins were separated along a gradient of forested and non-forested catchment land cover, which was directly related to total nitrogen, total phosphorous and chlorophyll-a concentrations. Considering the extensive body of knowledge linking land use to aquatic systems, it is reasonable to postulate a hierarchical model in which productivity has direct links to terrestrial inputs, and fish assemblages have direct links to both land use and productivity. We observed a shift from an invertivore-based fish assemblage in forested catchments to a detritivore-based fish assemblage in agricultural catchments that may be a widespread pattern among reservoirs and other aquatic ecosystems.

Spatial structuring within a reservoir fish population: implications for management

Spatial structuring in reservoir fish populations can exist because of environmental gradients, species-specific behaviour, or even localised fishing effort. The present study investigated whether white crappie exhibited evidence of improved population structure where the northern more productive half of a lake is closed to fishing to provide waterfowl hunting opportunities. Population response to angling was modelled for each substock of white crappie (north (protected) and south (unprotected) areas), the entire lake (single-stock model) and by combining simulations of the two independent substock models (additive model). White crappie in the protected area were more abundant, consisting of larger, older individuals, and exhibited a lower total annual mortality rate than in the unprotected area. Population modelling found that fishing mortality rates between 0.1 and 0.3 resulted in sustainable populations (spawning potential ratios (SPR) &gt;0.30). The population in the unprotected area appeared to be more resilient (SPR&gt;0.30) at the higher fishing intensities (0.35–0.55). Considered additively, the whole-lake fishery appeared more resilient than when modelled as a single-panmictic stock. These results provided evidence of spatial structuring in reservoir fish populations, and we recommend model assessments used to guide management decisions should consider those spatial differences in other populations where they exist.

Laboratory Evaluation of a Bioacoustic Bubble Strobe Light Barrier for Reducing Walleye Escapement

AbstractFish escapement is a largely overlooked challenge to managing reservoir fisheries. Physical barriers may help retain fish in reservoirs but are often not practical due to high reservoir debris loads and maintenance requirements of these structures. As an alternative, nonphysical barriers may also be successful at increasing fish retention in reservoirs through the use of negative stimuli that divert fish away from targeted locations. However, the effectiveness of nonphysical barriers can vary considerably among barrier stimuli and fish species because the barrier's success is dependent upon on a behavioral response from fish. We conducted a laboratory experiment to evaluate the effectiveness of a bioacoustic bubble–strobe light barrier at reducing Walleye Sander vitreus escapement rates. We hypothesized that increasing the number and frequency of barrier stimuli would result in Walleyes approaching the barrier less frequently, reduced escapement, and increased amount of time before escapement occurred. Walleyes approached the barrier and were successfully deterred most often when lights were off and sound was on. Walleye escapement rates declined from 89.3% with the barrier off to 44.1% with low and medium sound, whereas up to 100% of the fish escaped with the addition of light. Mean time before escapement and time to 50% escapement increased with the use of sound, whereas fish escaped in less time when light was used as a deterrent. Most Walleyes escaped around sunset indicating that fish were most active during the crepuscular period. Despite reductions in escapement associated with sound–bubble barriers, we recommend that alternative nonphysical barriers be evaluated for their potential to further increase retention of Walleyes before installation of sound barrier deterrent systems in reservoirs.Received December 23, 2013; accepted June 27, 2014