The energetic impact of overwinter prey assemblages on age-0 largemouth bass, <Emphasis Type="Italic">Micropterus salmoides</Emphasis>

Synopsis We compared survival, growth, and swimming performance of two size classes of age-0 largemouth bass, Micropterus salmoides, in the spring after being fed diets of bluegill, Lepomis macrochirus, fathead minnows, Pimephales promelas, or invertebrate prey during the winter. Regardless of prey assemblage, survival was uniformly high and independent of size. Length, wet- and dry-mass, and condition was also similar among treatments for both size classes. However, variation in individual performance differed, with the lowest variability in growth occurring among small age-0 largemouth bass in the invertebrate only treatment. Absolute and length corrected swimming speeds of largemouth bass were highest for invertebrate prey assemblages, intermediate for fathead minnow prey, and lowest for bluegill prey. The patterns in growth and spring swimming performance likely reflect the varied nutritive quality of different prey, the ability of largemouth bass to capture different prey, and competition with the piscine prey.     

Does prey community composition affect the way different behavioral types interact with their environment?

We examined how different exploratory behavioral types of largemouth bass responded to differing prey communities by determining effects on growth, survival and diet in experimental ponds. We found evidence that non-explorer largemouth bass target young-of-year bluegill early on in life, but bluegill were not an important diet item by late summer. The presence of young-of-year bluegill as prey does appear to affect the foraging strategy of the two exploring types differently. In the absence of small bluegill, both behavioral types feed primarily on benthic invertebrates and zooplankton. When small bluegill were present, we saw a shift away from zooplankton as prey for largemouth bass. However, that shift was toward more benthic invertebrates for non-exploring behavioral types and toward terrestrial insects for exploring behavioral types. Thus, it appears that prey community composition can have important effects on the way in which different behavioral types interact with their environment.     

Influence of intra‐ and interspecific variation in predator–prey body size ratios on trophic interaction strengths

1. Predation is a pervasive force that structures food webs and directly influences ecosystem functioning. The relative body sizes of predators and prey may be an important determinant of interaction strengths. However, studies quantifying the combined influence of intra‐ and interspecific variation in predator–prey body size ratios are lacking.
2. We use a comparative functional response approach to examine interaction strengths between three size classes of invasive bluegill and largemouth bass toward three scaled size classes of their tilapia prey. We then quantify the influence of intra‐ and interspecific predator–prey body mass ratios on the scaling of attack rates and handling times.
3. Type II functional responses were displayed by both predators across all predator and prey size classes. Largemouth bass consumed more than bluegill at small and intermediate predator size classes, while large predators of both species were more similar. Small prey were most vulnerable overall; however, differential attack rates among prey were emergent across predator sizes. For both bluegill and largemouth bass, small predators exhibited higher attack rates toward small and intermediate prey sizes, while larger predators exhibited greater attack rates toward large prey. Conversely, handling times increased with prey size, with small bluegill exhibiting particularly low feeding rates toward medium–large prey types. Attack rates for both predators peaked unimodally at intermediate predator–prey body mass ratios, while handling times generally shortened across increasing body mass ratios.
4. We thus demonstrate effects of body size ratios on predator–prey interaction strengths between key fish species, with attack rates and handling times dependent on the relative sizes of predator–prey participants.
5. Considerations for intra‐ and interspecific body size ratio effects are critical for predicting the strengths of interactions within ecosystems and may drive differential ecological impacts among invasive species as size ratios shift.

     

Performance as a fish predator of largemouth bass [<Emphasis Type="Italic">Micropterus salmoides</Emphasis> (Lacepède)] invading Japanese freshwaters: a review

This review focuses on how predator performance of the invasive largemouth bass [Micropterus salmoides (Lacepède)] has been, or will be, formed in Japanese freshwaters. Predation impacts of largemouth bass on fish communities appear pervasive in both Japanese as well as North American freshwaters. Factors affecting performance as a piscivorous predator are (1) light intensity and water clarity, (2) oxygen depletion, (3) prey size and gape size, (4) behavioral refuge of prey, (5) weed beds as refuge for prey fish, (6) interaction with bluegill. Size and behavioral refuges requirements are so rigorous that they may have evolved only in some North American prey fish species like bluegill; therefore, most Japanese native fish species are unlikely to be equipped with such refuges. However, refuge habitats like aquatic weed beds could develop in Japanese freshwaters, allowing prey fish species to survive under predation pressure. The density, architecture, and species composition of aquatic plants may affect their suitability as refuges. Studies in Japanese waters have suggested that the presence of rich aquatic vegetation or invasive bluegill in bass-introduced waters have suppressed the predation impact of largemouth bass on fish communities. In addition to these environmental factors, original genotypic and phenotypic traits of the introduced largemouth bass, and hybridization between different lineages of largemouth bass or with Florida bass [Micropterus floridanus (Lesueur)] may be involved in further adaptation of invasive largemouth bass to Japanese freshwaters.     

Invasive carp and prey community composition disrupt trophic cascades in eutrophic ponds

The role of trophic cascades in structuring freshwater communities has been extensively studied. Most of this work, however, has been conducted in oligotrophic northern lakes that contain highly vulnerable cyprinid prey: aquatic communities where trophic interactions are likely to be stronger than in many other systems. Fewer studies have been conducted in eutrophic systems or have examined the bottom-up effects of benthivorous fishes, and none have directly compared these effects to those of piscivores on ecosystem structure and function. We conducted enclosure experiments in eutrophic ponds to examine trophic effects of invasive benthivores (common carp—Cyprinus carpio L.), native piscivores (largemouth bass—Micropterus salmoides [Lacepède]), and their interactions with common centrarchid prey with well-developed anti-predatory behaviors (age-1 bluegill—Lepomis macrochirus Rafinesque and young-of-year largemouth bass). At the end of the 60-day experiment, common carp had strong bottom-up effects that increased total phosphorus and turbidity while decreasing chlorophyll a biomass and macrophyte cover that resulted in decreased macroinvertebrate biomass and also decreased growth in both juvenile largemouth bass and bluegill. Piscivorous largemouth bass, however, did not affect the survival of either planktivorous juvenile largemouth bass or bluegill. Growth of juvenile largemouth bass was also not affected, but juvenile bluegill growth was significantly diminished, possibly due to nonconsumptive effects of predation. Our results suggest that, in a centrarchid-dominated eutrophic system, top-down effects of predators are overwhelmed by common carp-mediated bottom-up effects. These bottom-up effects strongly affected multiple trophic levels, thus altering aquatic community structure and function.     

Gape Limitation, Prey Size Refuges and the Top–down Impacts of Piscivorous Largemouth Bass in Shallow Pond Ecosystems

Top–down control of phytoplankton biomass through piscivorous fish manipulation has been explored in numerous ecological and biomanipulation experiments. Piscivores are gape-limited predators and it is hypothesized that the distribution of gape sizes relative to distribution of body depths of prey fish may restrict piscivore effects cascading to plankton. We examined the top–down effects of piscivorous largemouth bass on nutrients, turbidity, phytoplankton, zooplankton and fish in ponds containing fish assemblages with species representing a range of body sizes and feeding habits (western mosquitofish, bluegill, channel catfish, gizzard shad and common carp). The experimental design consisted of three replicated treatments: fishless ponds (NF), fish community without largemouth bass (FC), and fish community with largemouth bass (FCB). Turbidity, chlorophyll a, cyclopoid copepodid and copepod nauplii densities were significantly greater in FC and FCB ponds than in NF ponds. However, these response variables were not significantly different in FC and FCB ponds. The biomass and density of shallow-bodied western mosquitofish were reduced and bluegill body depths shifted toward larger size classes in the presence of largemouth bass, but the biomass and density of all other fish species and of the total fish community were unaffected by the presence of largemouth bass. Our results show that top–down impacts of largemouth bass in ecosystems containing small- and deep-bodied fish species may be most intense at the top of the food web and alter the size distribution and species composition of the fish community. However, these top–down effects may not cascade to the level of the plankton when large-bodied benthivorous fish species are abundant.     

Size-specific growth of bluegill, largemouth bass and channel catfish in relation to prey availability and limnological variables

Growth of sympatric populations of three important sport fish species: bluegill Lepomis macrochirus , largemouth bass Micropterus salmoides and channel catfish Ictalurus punctatus , in 14 Illinois reservoirs was assessed in an attempt to relate size-specific growth to environmental conditions. Multiple regression relationships for most species and size classes explained a large percentage of the variation in growth. Growth of small bluegill (50 mm total length, L _T) showed a strong negative relationship with bluegill catch per unit effort (cpue), per cent littoral area and pH. Large bluegill (150 mm L _T) growth was negatively related to Daphnia spp. and benthic macroinvertebrate abundance and lake volume, and positively related to bluegill cpue. Growth of small (100 mm L _T) and large (250 mm L _T) largemouth bass was not well explained by any of the measured variables. Growth of both small (300 mm L _T) and large (450 mm L _T) channel catfish was strongly positively related to forage fishes and ichthyoplankton abundance, and per cent littoral area while negatively related to benthic macroinvertebrates. By identifying environmental conditions associated with increased growth rates, these models provide direction for managing fish populations and suggest testable hypotheses for future study of the complex interactions between environmental conditions and growth.     

Predator-prey interactions in size-structured fish communities: implications of prey growth

Predator-prey interactions among size-structured populations may be strongly influenced by factors which affect growth rates of prey. I examined the importance of prey growth in the interaction between large-mouth bass (Micropterus salmoides) and their prey, bluegill (Lepomis macrochirus), by analyzing diets and growth rates of bass in a set of seven lakes in south-central Wisconsin. Sizes of bluegill consumed by bass changed dramatically across a gradient of bluegill growth, which resulted in differing patterns of bass growth. In lakes with slow bluegill growth, small bass fed on the youngest bluegill cohort, but large bass were capable of feeding on several age classes. Consequently, bass growth rates were strongly size-dependent; small bass ate small prey and had low growth, but growth rates increased substantially with size as bass ate progressively larger prey. When bluegill had high growth rates, they quickly reached a size refuge from predation and bass of all sizes were restricted to feeding on the youngest/smallest prey. In these lakes, bass growth rates were more uniform across bass sizes. Because growth rates influence population size-distributions, variation in bluegill growth can have strong effects on the structure of bass populations. These effects could potentially feed back to further influence the interaction between predator and prey.     

Examination of the effects of largemouth bass (Micropterus salmoides) and bluegill (Lepomis macrochirus) on the ecosystem attributes of lake Kawahara-oike,Nagasaki, Japan

The introduction of largemouth bass (Micropterus salmoides) and bluegill sunfish (Lepomis macrochirus) into the freshwater ecosystems of Japan has resulted in the suppression and/or replacement of native species, generating considerable concerns among resource managers. The impacts of largemouth bass and bluegill on native fauna have been examined in aquaria and isolated farm ponds, but there is limited work examining the likelihood to fundamentally modifying Japan's lakes. The objective of the present study is to examine the direct and synergistic ecological effects of largemouth bass and bluegill on the biotic communities of Lake Kawahara-oike, Nagasaki, Japan, using an ecosystem (Ecopath) modeling approach. Specifically, we examine whether the two fish species have played a critical role in shaping the trophodynamics of the lake. We attempt to shed light on the trophic interactions between largemouth bass and bluegill and subsequently evaluate to what extent these interactions facilitate their establishment at the expense of native species. We also examine how these changes propagate through the Lake Kawahara-oike food web. Our study suggests that the introduction of bluegill has induced a range of changes at multiple trophic levels. The present analysis also provides evidence that largemouth bass was unable to exert significant top-down control on the growth rates of the bluegill population. Largemouth bass and bluegill appear to prevail over the native fish species populations and can apparently coexist in large numbers in invaded lakes. Future management strategies controlling invasive species are urgently required, if the integrity of native Japanese fish communities is to be protected.     

Hunting behavior of Florida largemouth bass, Micropterus salmoides floridanus, in a channelized river

The distribution and behavior of Florida largemouth bass, Micropterus salmoides floridanus, and their main prey (sunfish, genus Lepomis, and the cichlid Tilapia mariae) were studied in southern Florida to determine how fish behave in the simplified habitats found in channelized rivers. Time budgets were constructed from focal animal observations on 69 bass. Patterns of behavior associated with hunting were performed during a significantly higher proportion of the time when bass were in vegetated habitats. Scan samples of the behavior of 236 observed bass revealed that hunting was more common in areas of high structural complexity. Only 38% of observed bass were solitary, with the majority occurring in groups with either conspecifics or in mixed-species groups with similar sized bluegill sunfish, Lepomis macrochirus. Largemouth bass (n=1014) and sunfish (n=1372) were significantly more abundant in areas with vegetation and were almost entirely absent from the water column in the center of the canal. All species of fish avoided the water column, where currents were swift and no cover was available. The structure of the habitat appears to be important in the way largemouth bass organize their activity patterns. This suggests that habitat availability in channelized rivers significantly influences important behaviors such as hunting, thus potentially altering energy budgets and population dynamics of both predator and prey.     

Survival of largemouth bass, bluegill and channel catfish embryos after electroshocking

Survival to hatching was determined after electroshocking embryos of largemouth bass Micropterus salmoides , bluegill Lepomis macrochirus and channel catfish Ictalurus punctatus . Embryos at different developmental stages were exposed for 20 s to homogeneous electric fields (4–16 V cm⁻¹) of direct current (DC) or 60 or 120 Hz pulsed direct current (PDC) in water of 100 μS cm⁻¹ ambient conductivity. For all species, DC reduced survival of embryos at developmental stages before, during, or soon after epiboly; but survival did not differ from controls during later developmental stages. Survival of largemouth bass and bluegill was not reduced by 60 or 120 Hz PDC except for bluegill exposed at 12 h post‐fertilization. Channel catfish embryo survival was <5% when exposed to 60 or 120 Hz PDC at 8 h post‐fertilization, survival improved for embryos exposed at 67 h to 60 Hz but not to 120 Hz, and all embryos survived exposure to PDC at 150 h post‐fertilization. Exposure durations as short as 5 s resulted in <10% survival of largemouth bass during sensitive stages. All bluegill embryos aged 22 h post‐fertilization hatched prematurely after exposure to 16 V cm⁻¹ DC, but survival was not affected. The use of PDC for electroshocking near largemouth bass and bluegill nests could reduce the negative effects on survival of these species; however, PDC can reduce survival of channel catfish embryos.     

Foraging in Non-Native Environments: Comparison of Nile Tilapia and Three Co-Occurring Native Centrarchids in Invaded Coastal Mississippi Watersheds

We examined the diet of the alien Nile tilapia and bluegill, redear sunfish, and largemouth bass over a two-year period in coastal Mississippi. Nile tilapia diet was visually separated from the three natives based on group-average linkage cluster analysis. Sequential two-way nested analysis of similarities indicted there was no season effect (Global R = 0.026, P = 24.3%), but there was a moderate size class effect (Global R = 0.457, P = 0.1%) and a strong species effect (Global R = 0.876, P = 0.1%). Pairwise tests indicated species fed on different components of and locations within the environment, with bluegill, redear sunfish and largemouth bass (all R ≤ 0.683, P = 0.1%) having the most similar dietary components and Nile tilapia (all R ≥ 0.953, P = 0.1%) having the most distinct. Multivariate dispersion indicated that largemouth bass (1.425) and bluegill (1.394) had the most diverse diets compared to redear sunfish (0.906) and Nile tilapia (0.918). Similarities of percentages indicated that diets were separated based on prey: bluegill and redear sunfish consumed chironomids and insects; largemouth bass consumed fish and insects; and Nile tilapia fed most often on sediment resources such as nematodes, rotifers, bryozoans and hydrozoans. Nile tilapia had the highest frequency of mud, sand and detritus in their stomachs, suggesting they fed directly on bottom sediments. These data and the fact that Nile tilapia has a 1.3–7.6 times longer intestine on average than its body length, support our contention that this alien species feeds at the base of the food web and is well adapted to survive and proliferate in non-native environments.     

Host specificity among Ancyrocephalinae (Monogenoidea) of Nebraska sunfish

This study addressed the problem of local patterns of host specificity among Ancyrocephalinae (Monogenoidea) on bass and sunfish species, when the hosts occur in different species combinations in separate ponds. One hundred fifty-three fish of the Centrarchidae, from 4 study sites in Nebraska, were collected. Host species included bluegill (Lepomis macrochirus), green sunfish (L. cyanellus), largemouth bass (Micropterus salmoides), black crappie (Pomoxis nigromaculatus), white crappie (P. annularis), and rock bass (Ambloplites rupestris). These fish occurred in different species combinations, depending on the pond sampled. Results indicated that several centrarchid species could inhabit the same pond and yet support distinct monogene communities. Clavunculus bursatus, Onchocleidus helicis, O. principalis, and Syncleithrum fusiformis were found only on largemouth bass, regardless of what other centrarchids were present in a particular pond. Haplocleidus dispar occurred on green sunfish, bluegill, largemouth bass, and black crappie, and H. furcatus occurred on both bluegill and largemouth bass. Onchocleidus cyanellus and O. ferox were found on both bluegill and green sunfish. Rock bass were present in only 1 of the 4 ponds, but were not infected with any monogenes, even though co-occurring centrarchids were often heavily infected. Largemouth bass had the most diverse ancyrocephaline communities. The degree of parasite host specificity among these monogenes was inversely related to the diversity of host species present in a particular pond. In general, the parasites were more host specific than might be inferred from the literature; parasite species did not necessarily colonize supposedly receptive host species even when the latter were present, and host relatedness was the major factor in determining whether host species shared a common parasite species.     

The influence of littoral zone coarse woody habitat on home range size, spatial distribution, and feeding ecology of largemouth bass (Micropterus?salmoides)

Coarse woody habitat (CWH) may be a critical feature of lakes that influences fish distributions, movement patterns, and feeding habits. We used radio telemetry to examine the role of CWH in determining the movements of largemouth bass (Micropterus salmoides Lacepede) in the context of two whole-lake experiments that provided a gradient of four lake basins varying in natural and manipulated CWH. We also conducted diet studies on largemouth bass in these lakes to test for correlates among consumption rate and prey selectivity with bass behavior. Our results indicated that largemouth bass in basins with lower CWH abundances had larger home ranges, spent more time in deep water, were more selective predators, and showed lower consumption rates. Largemouth bass in basins with higher CWH abundances showed the opposite patterns. Low CWH abundances were correlated with a shift in largemouth bass foraging behavior from sit-and-wait to actively searching. This increased activity, coupled with the potential decline of prey fish species in the absence of CWH, may decrease largemouth bass growth potential regardless of the prey type consumed. Our results suggest that lakeshore residential development and associated removals of CWH from lakes may influence fish behavior, while CWH augmentation may reverse some of those changes. Handling editor: Steven Declerck     

Predation of Japanese dace, Tribolodon hakonensis, by largemouth bass, Micropterus salmoides, in experimental aquaria

 To test the size range of prey fish that largemouth bass, Micropterus salmoides, can successfully consume, live Japanese dace, Tribolodon hakonensis, were given as prey fish to individual largemouth bass in aquaria. The ratio of maximum standard length (SL) of the Japanese dace consumed by largemouth bass was 46–69% of bass SL. The maximum length of Japanese dace consumed did not differ significantly between largemouth bass and smallmouth bass (M. dolomieu) previously studied, although largemouth bass have relatively larger mouth sizes than smallmouth bass. Largemouth bass occasionally injured and killed Japanese dace larger than the limit that could be consumed.     

Low temperature cardiac response to exhaustive exercise in fish with different levels of winter quiescence

We examined the cardiac responses of different fish species to anaerobic exercise at low temperatures (3 degrees C). Three species of sympatric warmwater fish with perceived differences in winter activity were used for this comparative study: the winter-quiescent largemouth bass (Micropterus salmoides); the winter-active white bass (Morone chrysops); and the intermediately winter-active black crappie (Pomoxis nigromaculatus). Perceived differences in winter activity were reflected in cardiac responses; e.g. basal cardiac values were lowest for largemouth bass, highest for white bass, and intermediate for black crappie. In addition, cardiac recovery was most rapid for white bass, slowest for largemouth bass and intermediate for black crappie. When disturbed at low temperatures, largemouth bass and black crappie elevated cardiac output principally through increases in heart rate despite substantial decreases in stroke volume. Conversely, white bass principally used stroke volume modulation to change cardiac output. The results of this study indicate that different species respond differently to exercise at low temperatures. Management strategies should recognize that such variation exists and ensure that management decisions are based upon an understanding of the low temperature exercise physiology and winter biology of the species of interest.     

Mensurative approach to examine potential interactions between age-0 yellow perch (Perca flavescens) and bluegill (Lepomis macrochirus)

Bluegill (Lepomis macrochirus) and yellow perch (Perca flavescens) populations are often sympatric in the Great Plains region of the U.S.A. and portions of Canada; however, very little attention has been given to potential interactions between these species for available resources, especially during the early life stages. Relationships between age-0 bluegill and yellow perch growth and relative abundance were explored across multiple lakes and years within the Nebraska Sandhill region, USA. In addition, four habitat patch types (open water, Phragmites spp., Typha spp., Scirpus spp.) were sampled for age-0 bluegill and yellow perch, and food habits were examined for each species during August, September, and October of 2009 in one of these lakes. Age-0 yellow perch growth was negatively related to age-0 bluegill relative abundance across a spatiotemporal scale. Age-0 bluegill and yellow perch exhibited similar habitat use (moderate–high overlap), but generally consumed different important and dominant prey taxa (bluegill consumed both macroinvertebrates—56?% and zooplankton—44?%, while yellow perch consumed more zooplankton—66?%), which resulted in low overall diet overlap between species. Previous research indicates that age-0 yellow perch diet ontogeny often results in feeding predominately on macroinvertebrates and positively selecting them (and avoiding zooplankton prey) at sizes observed in our study. Therefore, yellow perch growth rates may be compromised by the presence of bluegill because of the need to consume less energetically profitable prey items such as zooplankton.     

Phenotypic variation and vulnerability to predation in juvenile bluegill sunfish (<Emphasis Type="Italic">Lepomis macrochirus</Emphasis>)

Bluegill sunfish (Lepomis macrochirus) are known to diversify into two forms specialized for foraging on either limnetic or littoral prey. Because juvenile bluegills seek vegetative cover in the presence of largemouth bass (Micropterus salmoides) predators, natural selection should favor the littoral body design at size ranges most vulnerable to predation. Yet within bluegill populations, both limnetic and littoral forms occur where vegetation and predators are present. While adaptive for foraging in different environments, does habitat-linked phenotypic variation also influence predator evasiveness for juvenile bluegills? We evaluate this question by quantifying susceptibility to predation for two groups of morphologically distinct bluegills; a limnetic form characteristic of bluegills inhabiting open water areas (limnetic bluegill) and a littoral form characteristic of bluegills inhabiting dense vegetation (littoral bluegill). In a series of predation trials, we found that bluegill behaviors differed in open water habitat but not in simulated vegetation. In open water habitat, limnetic bluegills formed more dense shoaling aggregations, maintained a larger distance from the predator, and required longer amounts of time to capture than littoral bluegill. When provided with simulated vegetation, largemouth bass spent longer amounts of time pursuing littoral bluegill and captured significantly fewer littoral bluegills than limnetic fish. Hence, morphological and behavioral variation in bluegills was linked to differential susceptibility to predation in open water and vegetated environments. Combined with previous studies, these findings show that morphological and behavioral adaptations enhance both foraging performance and predator evasiveness in different lake habitats.     

Growth,survival, and foraging abilities of early life history stages of blue tilapia,Oreochromis aureus,and largemouth bass,Micropterus salmoides

Synopsis I compared growth, survival, and foraging abilities of early life history stages of blue tilapia,Oreochromis (=Sarotherodon = Tilapia) aureus, and largemouth bass,Micropterus salmoides, at equivalent prey (zooplankton) densities in the laboratory. Survival and growth of blue tilapia exceeded those of largemouth bass and, at comparable ages, blue tilapia were superior to largemouth bass in ability to prey on zooplankton; the enhanced survival and growth of blue tilapia appeared to result from their larger initial (egg) size. Predatory abilities of the species at equivalent sizes were similar. The success of blue tilapia in colonizing new systems and rapidly achieving high abundances in Florida may be a consequence of large initial size.     

Effects of turbidity and an invasive waterweed on predation by introduced largemouth bass

Anthropogenic activities lead to changes in characteristics of aquatic ecosystems, including alteration of turbidity and addition of invasive species. In this study, we tested how changes in turbidity and the recent invasion of an aquatic macrophyte, Egeria densa, may have changed the predation pressure by introduced largemouth bass on juvenile striped bass and delta smelt, two species that have seen a drastic decline in recent decades in the Sacramento-San Joaquin Delta. In a series of mesocosm experiments, we showed that increases in vegetation density decreased the predation success of largemouth bass. When placed in an environment with both open water and vegetated areas, and given a choice to forage on prey associated with either of these habitats, largemouth bass preyed mainly on open water species as opposed to vegetation-associated species, such as juvenile largemouth bass, bluegill or red swamp crayfish. Finally, we showed that turbidity served as cover to open water species and increased the survival of delta smelt, an endemic species at risk. We also found that such open water prey tend not to seek refuge in the vegetation cover, even in the presence of an imminent predation threat. These results provide the beginning of a mechanistic framework to explain how decreases in turbidity and increases in vegetation cover correlate with a decline of open water species in the Sacramento-San Joaquin Delta.