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USGS2025

Understanding predator-prey-competitor dynamics between Lower Missouri River Macrhybopsis and Scaphirhynchus using a population—bioenergetics model ensemble

The pallid sturgeon Scaphirhynchus albus is a long-lived, endangered fish in the Missouri River. Individuals become piscivorous as adults, so recruitment from stocking or reproduction could reduce populations of prey, including Macrhybopsis chubs. We constructed an individual- and age-based, multi-species, predator-prey-competitor model (IAMP) to represent the benthic community (sturgeons, chubs, and chironomids) of the Lower Missouri River (LMR) to explore scenarios of potential predator-prey-competitor dynamics. Our simulations suggest that chubs alone are unlikely able to support a level of LMR pallid sturgeon similar to historical or current populations. These simulations also suggest that adult pallid sturgeon may need to shift to non-chub prey fish to achieve the greater sizes observed in the Upper Missouri River. When annual hydrologic regimes were included, we found a negative relationship between chub relative abundance and previous year 30-day minimum flows. Inclusion of temporal environmental variability made it clear that large chub populations may be necessary to support LMR pallid sturgeon. When full stochasticity was included in the IAMP, chub population sizes needed to increase further to ensure continued reproduction and recruitment of both chubs and pallid sturgeon. These results support the hypothesis that the pallid sturgeon population in the Lower Missouri River may be food-limited. However, the full extent of this limitation and the management changes needed to address this will require more research on the biology and population dynamics of this fish community, on pallid sturgeon interactions with prey species, and on how sympatric species may be affected during the pallid sturgeon recovery process.

Colorado, Kansas, Minnesota, Missouri, Montana, Ne↗

USGS2025

Using angler-submitted records to interpret the spatial seasonality of a large predator (Black bass, Micropterus spp.)

In addition to having cultural, social, and economic significance, large predatory fish affect aquatic communities from the top down and serve as markers of ecosystem health. A focus on large predators is critical for managing ecosystems, conserving species, and guaranteeing the sustainability of aquatic resources. Recreational fishing is inherently biased towards large fish, and anglers possess the strength in numbers and geographical dispersion that enable them to sample the upper tiers of size distributions rarely encountered in standard fish surveys. We sought to further understand the ecological requirements and spatial seasonality of exceptionally sized black bass ( Micropterus spp.) via angler catches. Black bass > 3.6 kg were examined across 147 reservoirs in Texas, USA, with 2817 fish recorded by anglers into an online database in 2018–2024. Most fish were caught in late-winter and early-spring in line with spawning activities that included movements in-and-out of shallow water, nest building, and nest defense. Approximately 54 % of fish were caught with bottom-oriented fishing lures and techniques, and 40 % midwater; surface catches were less common. The efficacy of angling techniques varied seasonally. Those effective in winter were midwater, while those effective in summer were bottom or surface. Conversely, a combination of bottom and midwater techniques were effective in the fall and spring, suggesting cyclic habitat transitions. Moreover, the frequency with which fish were caught over various macrohabitats varied seasonally and cyclically. Our findings have the potential to inform habitat management that supports large predators and their migratory relocations. Our findings also underscore the value of using anglers and technology as sources of difficult-to-obtain fish and environmental data that may evade regular monitoring.

Texas↗

USGS2012

Seasonal zooplankton dynamics in Lake Michigan: disentangling impacts of resource limitation, ecosystem engineering, and predation during a critical ecosystem transition

We examined seasonal dynamics of zooplankton at an offshore station in Lake Michigan from 1994 to 2003 and 2007 to 2008. This period saw variable weather, declines in planktivorous fish abundance, the introduction and expansion of dreissenid mussels, and a slow decline in total phosphorus concentrations. After the major expansion of mussels into deep water (2007–2008), chlorophyll in spring declined sharply, Secchi depth increased markedly in all seasons, and planktivorous fish biomass declined to record-low levels. Overlaying these dramatic ecosystem-level changes, the zooplankton community exhibited complex seasonal dynamics between 1994–2003 and 2007–2008. Phenology of the zooplankton maximum was affected by onset of thermal stratification, but there was no other discernable effect due to temperature. Interannual variability in zooplankton biomass during 1994 and 2003 was strongly driven by planktivorous fish abundance, particularly age-0 and age-1 alewives. In 2007–2008, there were large decreases in Diacyclops thomasi and Daphnia mendotae possibly caused by food limitation as well as increased predation and indirect negative effects from increases in Bythotrephes longimanus abundance and in foraging efficiency associated with increased light penetration. The Bythotrephes increase was likely driven in part by decreased predation from yearling and older alewife. While there was a major decrease in epilimnetic–metalimnetic herbivorous cladocerans in 2007–2008, there was an increase in large omnivorous and predacious calanoid copepods, especially those in the hypolimnion. Thus, changes to the zooplankton community are the result of cascading, synergistic interactions, including a shift from vertebrate to invertebrate planktivory and mussel ecosystem impacts on light climate and chlorophyll.

Journal of Great Lakes Research↗

USGS2016

White sucker Catostomus commersonii respond to conspecific and sea lamprey Petromyzon marinus alarm cues but not potential predator cues

Recent studies proposed the use of chemosensory alarm cues to control the distribution of invasive sea lamprey Petromyzon marinus populations in the Laurentian Great Lakes and necessitate the evaluation of sea lamprey chemosensory alarm cues on valuable sympatric species such as white sucker. In two laboratory experiments, 10 replicate groups (10 animals each) of migratory white suckers were exposed to deionized water (control), conspecific whole-body extract, heterospecific whole-body extract (sea lamprey) and two potential predator cues (2-phenylethylamine HCl (PEA HCl) and human saliva) during the day, and exposed to the first four of the above cues at night. White suckers avoided the conspecific and the sea lamprey whole-body extract both during the day and at night to the same extent. Human saliva did not induce avoidance during the day. PEA HCl did not induce avoidance at a higher concentration during the day, or at night at the minimum concentration that was previously shown to induce maximum avoidance by sea lamprey under laboratory conditions. Our findings suggest that human saliva and PEA HCl may be potential species-specific predator cues for sea lamprey.

Journal of Great Lakes Research↗

USGS2021

Expansion of intertidal mussel beds following disease-driven reduction of a keystone predator

Disease shapes community composition by removing species with strong interactions. To test whether the absence of keystone predation due to disease produced changes to the species composition of rocky intertidal communities, we leverage a natural experiment involving mass mortality of the keystone predator Pisaster ochraceus from Sea Star Wasting Syndrome. Over four years, we measured dimensions of mussel beds, sizes of Mytilus californianus, mussel recruitment, and species composition on vertical rock walls at six rocky intertidal sites on the central California coast. We also assessed the relationship between changes in mussel cover and changes in sea star density across 33 sites along the North American Pacific coast using data from long-term monitoring. After four years, the lower boundary of the central California mussel beds shifted downward toward the water 18.7 ± 15.8 cm (SD) on the rock and 11.7 ± 11.0 cm in elevation, while the upper boundary remained unchanged. In central California, downward expansion and total area of the mussel bed were positively correlated with mussel recruitment but were not correlated with pre-disease sea star density or biomass. At a multi-region scale, changes in mussel percent cover were positively correlated with pre-disease sea star densities but not change in densities. Species composition of primary substrate holders and epibionts below the mussel bed remained similar across years. Extirpation of the community below the bed did not occur. Instead, this community became limited to a smaller spatial extent while the mussel bed expanded.

California, Oregon↗

USGS1984

Predation on lake whitefish eggs by longnose suckers

In November 1981, we observed intense predation on lake whitefish ( Coregonus clupeaformis ) eggs by longnose suckers ( Catostomus catostomus ) on lake whitefish spawning grounds in northwestern Lake Huron. Since longnose suckers commonly frequent the same habitat used by spawning lake whitefish, there exists the potential for high losses of eggs due to sucker predation.

Journal of Great Lakes Research↗

USGS2023

Predation of invasive silver carp by native largemouth bass is size-selective in the Illinois River

Silver carp ( Hypophthalmichthys molitrix ) are a nonnative, planktivorous, and highly invasive species of cyprinid located throughout the Mississippi River Basin. Although they co-occur with largemouth bass ( Micropterus nigricans ), an abundant native predatory fish, their predator–prey relationship is poorly understood. This potential relationship warrants investigation as largemouth bass are large-gaped predators capable of exhibiting top-down control on planktivorous fishes. The objectives of this study were to determine if largemouth bass consume juvenile silver carp, and if there was a relationship between length of largemouth bass and length of silver carp consumed. Largemouth bass were collected from the La Grange Pool of the Illinois River using 60 Hz-pulsed DC electrofishing and their diets were analyzed (n = 389, total length = 70–578 mm). Evidence of silver carp was present in 18% of diets of largemouth bass that consumed fish. Lengths of consumed silver carp were estimated from the dimensions of their recovered chewing pads or pharyngeal teeth in the stomachs of largemouth bass. A significant relationship between length of largemouth bass and length of silver carp consumed ( p < 0.001, F = 34.63, r 2 = 0.61) was observed. Estimated total lengths of silver carp were 34–101 mm and were recovered from diets of largemouth bass that were 94–262 mm total length. These results indicate enhancement of native largemouth bass populations is unlikely to substantially reduce silver carp populations in the Illinois River or in other waterways where these species co-occur.

Illinois↗

USGS2024

Kit foxes demonstrate adaptive compromise characteristics under intraguild predation pressure by coyotes in the Great Basin desert

Coyotes ( Canis latrans ) are believed to contribute to declining kit fox ( Vulpes macrotis ) numbers in the Great Basin desert through intraguild predation. Intraguild prey have been shown to exhibit adaptive compromise, whereby an animal increases selection for risky, but food-rich areas during times of food stress (i.e. winter). We evaluated the habitat selection of kit foxes in the Great Basin desert to elucidate if they demonstrated adaptive compromise as a method of coexisting with coyotes. We created 2nd order resource selection functions to analyze kit fox habitat selection associated with coyote relative probability of use (RPU), prey abundance, and type of soil substrate. In the summer, we found that kit fox selection for areas of relatively more abundant prey was not significant, and there was a small positive selection for coyote RPU. In the winter, we found a positive relationship between kit fox selection and prey abundance as well as a stronger selection for coyote RPU. These findings do follow the pattern of adaptive compromise. We also found kit foxes selected for silty and sandy soils, which are conducive to den construction, as they use dens seasonally for breeding but also year-round for multiple uses, including refugia from predators and extreme heat. Soil substrate appeared to be an important factor impacting kit fox habitat selection.

Utah↗

USGS2013

Using diets to reveal overlap and egg predation among benthivorous fishes in Lake Michigan

Ecological stability in the Laurentian Great Lakes has been altered by nonindigenous species, such as the Round Goby Neogobius melanostomus and dreissenid mussels, and by declines in native amphipods Diporeia spp. We evaluated whether these changes could influence diet overlap between three benthivorous fishes (Slimy Sculpin Cottus cognatus, Deepwater Sculpin Myoxocephalus thompsonii, and Round Goby) and whether predation on eggs of native species was occurring. We examined diets of fish collected at depths of 69–128 m in Lake Michigan offshore of Frankfort and Muskegon, Michigan, and Two Rivers and Sturgeon Bay, Wisconsin, during January–May 2009 and 2010. Important prey (by dry weight proportion and by percent frequency of occurrence) for Slimy Sculpin were Mysis (0.34; 45%), Diporeia (0.16; 34%), and Limnocalanus macrurus (0.22; 68%); important prey for Deepwater Sculpin were Mysis (0.74; 92%) and Diporeia (0.16; 54%). Round Goby consumed mainly bivalves (i.e., dreissenids: 0.68; 95%) and Mysis (0.15; 37%). The two sculpin species consumed the eggs of Bloaters Coregonus hoyi (Slimy Sculpin: 0.04, 11%; Deepwater Sculpin: 0.02, 7%) and the eggs of Deepwater Sculpin (Slimy Sculpin: 0.03, 13%; Deepwater Sculpin: 0.05, 16%) during February–May at all sites. Round Goby also consumed eggs of these species but at lower levels (≤0.01; <1%). Diet overlap was identified between sculpin species at Frankfort and Sturgeon Bay, suggesting possible interspecific competition, but their diets did not overlap at Two Rivers; diet overlap was never observed between Round Goby and either sculpin species. Given that (1) diet overlap varied by site and (2) diet proportions varied spatially more than temporally, benthivores appear to be exhibiting localized responses to recent ecological changes. Overall, these results reveal that egg predation and interspecific competition could be important interactions to consider in future examinations of the population dynamics of these species or in ecosystem models that forecast how fisheries will respond to possible perturbations or management scenarios.

Michigan↗

USGS2013

Ups and Downs of Burbot and their predator Lake Trout in Lake Superior, 1953-2011

The fish community of Lake Superior has undergone a spectacular cycle of decline and recovery over the past 60 years. A combination of Sea Lamprey Petromyzon marinus depredation and commercial overfishing resulted in severe declines in Lake Trout Salvelinus namaycush, which served as the primary top predator of the community. Burbot Lota lota populations also declined as a result of Sea Lamprey depredation, largely owing to the loss of adult fish. After Sea Lamprey control measures were instituted in the early 1960s, Burbot populations rebounded rapidly but Lake Trout populations recovered more slowly and recovery was not fully evident until the mid-1980s. As Lake Trout populations recovered, Burbot populations began to decline, and predation on small Burbot was identified as the most likely cause. By 2000, Burbot densities had dropped below their nadir in the early 1960s and have continued to decline, with the densities of juveniles and small adults falling below that of large adults. Although Burbot populations are at record lows in Lake Superior, the density of large reproductive adults remains stable and a large reserve of adult Burbot is present in deep offshore waters. The combination of the Burbot's early maturation, long life span, and high fecundity provides the species with the resiliency to remain a viable member of the Lake Superior fish community into the foreseeable future.

Lake Superior↗

USGS2010

Increase in lake trout reproduction in Lake Huron following the collapse of alewife: Relief from thiamine deficiency or larval predation?

In the Great Lakes there is still uncertainty as to the population level effects of a thiamine deficiency on salmonines caused by high consumption of alewives Alosa pseudoharengus . A resurgence of lake trout Salvelinus namaycush reproduction in Lake Huron following the crash of alewife stocks between 2002 and 2004 provided an opportunity to evaluate the relative effects of this crash on reproduction through relief from either alewife mediated thiamine deficiency or alewife predation on larval lake trout relative to possible changes in the size of the lake trout spawning stock. Changes in mean lake trout egg thiamine concentration post crash at one spawning reef in Parry Sound, where mean thiamine concentration increased by almost two-fold, were consistent with diet switching from alewives to rainbow smelt Osmerus mordax , the next most abundant prey fish in Lake Huron. Although thiamine levels for lake trout collected at a second reef in Parry Sound did not change post-crash, levels both pre- and post-crash were consistent with a rainbow smelt diet. A reef specific fry emergence index was found to be positively related to reef specific egg thiamine concentration but negatively related to reef specific occurrence of EMS, a thiamine deficiency related mortality syndrome. We found little evidence for overlap between the timing of spring shoreward migration of alewives and lake trout emergence, suggesting that relief from alewife predation effects had relatively little effect on the observed increase in lake trout recruitment. Numbers of spawners in the north, north-central, and southern zones of the lake increased from 2000 onwards. Overall the abundance post-2003 was higher than from pre-2004, suggesting that spawner abundance may also have contributed to increased lake trout reproduction. However, predicted numbers of spawners and measured abundance of wild recruits in assessment gear were poorly correlated suggesting that the increase in reproduction was not totally spawner dependent and hence relief from thiamine deficiency was also likely involved. We conclude from this that eliminating the effects of an alewife diet mediated thiamine deficiency can have positive effects on lake trout reproduction but more research is required to understand the effect of spawner number and the role of spawning habitat availability.

Lake Huron↗

USGS2016

Improving spatio-temporal benefit transfers for pest control by generalist predators in cotton in the southwestern U.S.

Given rapid changes in agricultural practice, it is critical to understand how alterations in ecological, technological, and economic conditions over time and space impact ecosystem services in agroecosystems. Here, we present a benefit transfer approach to quantify cotton pest-control services provided by a generalist predator, the Mexican free-tailed bat ( Tadarida brasiliensis mexicana ), in the southwestern United States. We show that pest-control estimates derived using (1) a compound spatial – temporal model – which incorporates spatial and temporal variability in crop pest-control service values – are likely to exhibit less error than those derived using (2) a simple-spatial model (i.e., a model that extrapolates values derived for one area directly, without adjustment, to other areas) or (3) a simple-temporal model (i.e., a model that extrapolates data from a few points in time over longer time periods). Using our compound spatial–temporal approach, the annualized pest-control value was \$12.2 million, in contrast to an estimate of \$70.1 million (5.7 times greater), obtained from the simple-spatial approach. Using estimates from one year (simple-temporal approach) revealed large value differences (0.4 times smaller to 2 times greater). Finally, we present a detailed protocol for valuing pest-control services, which can be used to develop robust pest-control transfer functions for generalist predators in agroecosystems.

Arizona, California, Kansas, New Mexico, Oklahoma,↗

USGS2014

Latitudinal and photic effects on diel foraging and predation risk in freshwater pelagic ecosystems

1. Clark & Levy ( American Naturalist , 131 , 1988, 271–290) described an antipredation window for smaller planktivorous fish during crepuscular periods when light permits feeding on zooplankton, but limits visual detection by piscivores. Yet, how the window is influenced by the interaction between light regime, turbidity and cloud cover over a broad latitudinal gradi- ent remains unexplored. 2. We evaluated how latitudinal and seasonal shifts in diel light regimes alter the foraging- risk environment for visually feeding planktivores and piscivores across a natural range of turbidities and cloud covers. Pairing a model of aquatic visual feeding with a model of sun and moon illuminance, we estimated foraging rates of an idealized planktivore and piscivore over depth and time across factorial combinations of latitude (0 – 70 ° ), turbidity (0 1 – 5 NTU) and cloud cover (clear to overcast skies) during the summer solstice and autumnal equinox. We evaluated the foraging-risk environment based on changes in the magnitude, duration and peak timing of the antipredation window. 3. The model scenarios generated up to 10-fold shifts in magnitude, 24-fold shifts in duration and 5 5-h shifts in timing of the peak antipredation window. The size of the window increased with latitude. This pattern was strongest during the solstice. In clear water at low turbidity (0 1 – 0 5 NTU), peaks in the magnitude and duration of the window formed at 57 – 60 ° latitude, before falling to near zero as surface waters became saturated with light under a midnight sun and clear skies at latitudes near 70 ° . Overcast dampened the midnight sun enough to allow larger windows to form in clear water at high latitudes. Conversely, at turbidities ≥ 2 NTU, greater reductions in the visual range of piscivores than planktivores created a window for long periods at high latitudes. Latitudinal dependencies were essentially lost during the equinox, indicating a progressive compression of the window from early summer into autumn. 4. Model results show that diel-seasonal foraging and predation risk in freshwater pelagic ecosystems changes considerably with latitude, turbidity and cloud cover. These changes alter the structure of pelagic predator – prey interactions, and in turn, the broader role of pelagic consumers in habitat coupling in lakes.

Journal of Animal Ecology↗

USGS2020

Estimating population-specific predation effects on Chinook salmon via data integration

Recent success in the conservation of many marine mammals has resulted in new management challenges due to increasing conflict with fisheries. Increasing predation by pinnipeds on threatened salmon is of particular concern. Seemingly, pinniped conservation is now in conflict with the recovery of threatened salmon, creating a dilemma for managers. We use the Lower Columbia River as a case study for examining the relationship between seasonal California sea lion Zalophus californianus abundance and survival of threatened salmon. To quantify mortality associated with increasing sea lion abundance, we examined the effect of seasonal sea lion abundance on adult Chinook salmon Oncorhynchus tshawytscha survival during migrations through the Lower Columbia River. We integrated data on survival with data on population-specific migration timing, allowing quantification of the relationship between sea lion abundance and survival in 18 populations of spring–summer Chinook salmon listed as Threatened or Endangered under the U.S. Endangered Species Act. Of the 18 populations examined, earlier migrating populations experienced lower survival in association with increased exposure to higher sea lion abundance. We estimated that in years with high sea lion abundance, the nine earliest-migrating populations experienced an additional 21.1% (95% CI = 16.3–26.1) mortality compared to years with baseline sea lion abundance, while the nine latest migrating populations experienced an additional 10.1% (7.5–13.0). Synthesis and applications . Integrating datasets on seasonal survival and migration timing made it possible for us to estimate population-specific mortality associated with increased sea lion abundance in the Lower Columbia River. This information could not be produced from any one dataset, highlighting the utility of data integration approaches. The mortality experienced by early migrating Chinook salmon suggests the potential for demographic and evolutionary consequences. Management actions such as hazing, relocating, or removing individuals that are frequent predators on salmon have been proposed. Identifying the management actions that will allow for socially and legally acceptable trade-offs between multiple conservation and other social values will be facilitated by development of explicit multi-species management frameworks. Continued monitoring will help to reduce the substantial uncertainty about the effect of pinnipeds on salmon and the predicted outcomes of alternative management actions.

Oregon, Washington↗

USGS2024

Boom and bust: The effects of masting on seed predator range dynamics and trophic cascades

Aim Spatiotemporal variation in resource availability is a strong driver of animal distributions. In the northern hardwood and boreal forests of the northeastern United States, tree mast events provide resource pulses that drive the population dynamics of small mammals, including the American red squirrel ( Tamiasciurus hudsonicus ), a primary songbird nest predator. This study sought to determine whether mast availability ameliorates their abiotic limits, enabling red squirrel elevational distributions to temporarily expand and negatively impact high-elevation songbirds. Location Northeastern United States. Methods We used two independent datasets to evaluate our hypotheses. First, we fit a dynamic occupancy model using data from camera trap surveys to evaluate red squirrel distributional responses to pulses in the tree mast. We also assessed population responses using systematic auditory surveys analysed with an open-population binomial mixture model. Further, we used modelled red squirrel abundance in nest-survival models to evaluate whether their abundance is correlated with the daily nest survival of three songbird species. Results The tree mast provided a critical resource pulse that resulted in a two-fold increase in the annual elevational distribution of red squirrels. The elevational distribution of red squirrels ranged from a minimum of ~450 m (range: 663–1145 m asl) following two consecutive years without a masting event to a maximum of over 1000 m (range: 443–1545 m asl) after a large mast event. The daily nest survival of three songbird species tended to decline with an increase in the abundance of red squirrels. Main Conclusions Tree mast is a central biological phenomenon in many temperate and boreal forests. This study reveals how this resource pulse results in range changes in a small mammal that is both a seed and bird predator, as well as prey for many carnivores. Thus, understanding this phenomenon can inform the conservation and management of northern forests, including breeding songbirds.

Connecticut, Maine, Massachusetts, New Hampshire, ↗

USGS2014

Predation on native sculpin by exotic brown trout exceeds that by native cutthroat trout within a mountain watershed (Logan, UT, USA)

We explored potential negative effects of exotic brown trout ( Salmo trutta ) on native sculpin ( Cottus sp.) on the Logan River, Utah, USA by (i) examining factors most strongly correlated with sculpin abundance (e.g., abiotic conditions or piscivory?), (ii) contrasting the extent of brown trout predation on sculpin with that by native cutthroat trout ( Oncorhynchus clarkii utah ) and (iii) estimating the number of sculpin consumed by brown trout along an elevational gradient using bioenergetics. Abundance of sculpin across reaches showed a strong ( r ≥ 0.40) and significant ( P < 0.05) correlation with physical variables describing width (positive) and gradient (negative), but not with abundance of piscivorous brown trout or cutthroat trout. In mainstem reaches containing sculpin, we found fish in 0% of age‐1, 10% of age‐2 and 33% of age‐3 and older brown trout diets. Approximately 81% of fish consumed by brown trout were sculpin. Despite a similar length–gape relationship for native cutthroat trout, we found only two fish (one sculpin and one unknown) in the diets of native cutthroat trout similar in size to age‐3 brown trout. Based on bioenergetics, we estimate that an average large (> 260 mm) brown trout consumes as many as 34 sculpin per year. Nevertheless, results suggest that sculpin abundance in this system is controlled by abiotic factors and not brown trout predation. Additional research is needed to better understand how piscivory influences brown trout invasion success, including in‐stream experiments exploring trophic dynamics and interactions between brown trout and native prey under different environmental conditions.

Utah↗

USGS2014

Experimental evaluation of rainbow trout Oncorhynchus mykiss predation on longnose dace Rhinichthys cataractae

Laboratory and in-stream enclosure experiments were used to determine whether rainbow trout Oncorhynchus mykiss influence survival of longnose dace Rhinichthys cataractae . In the laboratory, adult rainbow trout preyed on longnose dace in 42% of trials and juvenile rainbow trout did not prey on longnose dace during the first 6 h after rainbow trout introduction. Survival of longnose dace did not differ in the presence of adult rainbow trout previously exposed to active prey and those not previously exposed to active prey ( = 0.28, P = 0.60). In field enclosures, the number of longnose dace decreased at a faster rate in the presence of rainbow trout relative to controls within the first 72 h, but did not differ between moderate and high densities of rainbow trout ( F 2,258.9 = 3.73, P = 0.03). Additionally, longnose dace were found in 7% of rainbow trout stomachs after 72 h in enclosures. Rainbow trout acclimated to the stream for longer periods had a greater initial influence on the number of longnose dace remaining in enclosures relative to those acclimated for shorter periods regardless of rainbow trout density treatment ( F 4,148.5 = 2.50, P = 0.04). More research is needed to determine how predation rates will change in natural environments, under differing amounts of habitat and food resources and in the context of whole assemblages. However, if rainbow trout are introduced into the habitat of longnose dace, some predation on longnose dace is expected, even when rainbow trout have no previous experience with active prey.

Ecology of Freshwater Fish↗

USGS2023

Pelagic food web interactions in a large invaded ecosystem: Implications for reintroducing a native top predator

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

California, Nevada↗