Piscivory and diet overlap between two non‐native fishes in southern Chilean streams

Trophic relations among introduced species may induce highly variable and complex effects in communities and ecosystems. However, studies that identify the potential impacts for invaded systems and illuminate mechanisms of coexistence with native species are scarce. Here, we examined trophic relations between two introduced fishes in streams of NW Patagonia, rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta). These species originate from different regions of the Northern Hemisphere but they now coexist as invading species over the world. We used gastric contents and stable isotopes analysis to compare the diets of two size‐classes of these two invaders in three localities of southern Chile. Both species displayed similar ontogenic diet shifts with smaller trout consuming mostly invertebrates and larger trout being more piscivorous and epibenthic feeders. However, piscivory was more prevalent in brown trout than in rainbow trout and highest at the site with the greatest density of native fishes suggesting that the availability of native fishes as trout prey may limit the occurrence of trout piscivory. We found an elevated dietary overlap between the two trout species at larger sizes while at smaller size a higher intraspecific dietary overlap occurred suggesting a potential interference competition among the two fish invaders especially at larger sizes. Our results highlight that the impacts of invading species on non‐native fishes are context specific (i.e. species and ontogenic stages) and thus, difficult to generalize.     

Diet partitioning in sympatric Atlantic salmon and brown trout in streams with contrasting riparian vegetation

Prey intake by Atlantic salmon Salmo salar and brown trout Salmo trutta was measured across different riparian vegetation types: grassland, open canopy deciduous and closed canopy deciduous, in upland streams in County Mayo, Western Ireland. Fishes were collected by electrofishing while invertebrates were sampled from the benthos using a Surber sampler and drifting invertebrates collected in drift traps. Aquatic invertebrates dominated prey numbers in the diets of 0+ year Atlantic salmon and brown trout and 1+ year Atlantic salmon, whereas terrestrial invertebrates were of greater importance for diets of 1+ and 2+ year brown trout. Terrestrial prey biomass was generally greater than aquatic prey for 1+ and 2+ year brown trout across seasons and riparian types. Prey intake was greatest in spring and summer and least in autumn apart from 2+ year brown trout that sustained feeding into autumn. Total prey numbers captured tended to be greater for all age classes in streams with deciduous riparian canopy. Atlantic salmon consumed more aquatic prey and brown trout more terrestrial prey with an ontogenetic increase in prey species richness and diversity. Atlantic salmon and brown trout diets were most similar in summer. Terrestrial invertebrates provided an important energy subsidy particularly for brown trout. In grassland streams, each fish age class was strongly associated with aquatic, mainly benthic invertebrates. In streams with deciduous riparian canopy cover, diet composition partitioned between conspecifics with older brown trout associated with surface drifting terrestrial invertebrates and older Atlantic salmon associated with aquatic invertebrates with a high drift propensity in the water column and 0+ year fish feeding on benthic aquatic invertebrates. Deciduous riparian canopy cover may therefore facilitate vertical partitioning of feeding position within the water column between sympatric Atlantic salmon and brown trout. Implications for riparian management are discussed.     

Effects of temperature and a piscivorous fish on diel winter behaviour of juvenile brown trout (Salmo trutta)

相似文献   

A Bioenergetic Analysis of Factors Limiting Brown Trout Growth in an Ozark Tailwater River

We examined prey utilization and energy consumption by brown trout, Salmo trutta, in a cold tailwater (Little Red River, Arkansas, USA; LRR) having low biodiversity and low availability of fish as prey. Stomach content analysis and age estimation were performed on thirty brown trout (10 each of three size classes for a total of 710 trout) collected monthly from an upstream and downstream site over a 1-year period. Diet diversity was low at both sites, as 80% and 70% of all prey consumed by upstream and downstream brown trout, respectively, were isopods. Piscivory (<0.5% of individuals sampled) and consumption of terrestrial invertebrates were rare. There was no relation between diet diversity and trout age, and a very small ontogenetic shift in brown trout diet. Second, we investigated brown trout growth rates relative to prey consumption and temperature. Temperatures and availability of prey were less than required for maximal trout growth. However, prey availability limited trout growth directly, but sub-optimal temperatures probably buffered the effect of this reduced energy consumption by reducing metabolic energy expenditures. Brown trout growth was 54.8–57.0% of the maximum predicted by a bioenergetics model. Instantaneous growth rates for age 1 and adult brown trout were slightly higher for those downstream (0.195) versus those upstream (0.152). Although isopods are abundant within this tailwater to serve as a forage base, the displacement of native fish fauna and subsequent lack of establishment of cold-tolerant forage fish species due to the thermal regime of hypolimnetic release from Greers Ferry Reservoir probably serves as a major barrier to brown trout growth.     

Can prey exhibit threat-sensitive generalization of predator recognition? Extending the Predator Recognition Continuum Hypothesis

Despite the importance of predator recognition in mediating predator-prey interactions, we know little about the specific characteristics that prey use to distinguish predators from non-predators. Recent experiments indicate that some prey who do not innately recognize specific predators as threats have the ability to display antipredator responses upon their first encounter with those predators if they are similar to predators that the prey has recently learned to recognize. The purpose of our present experiment is to test whether this generalization of predator recognition is dependent on the level of risk associated with the known predator. We conditioned fathead minnows to chemically recognize brown trout either as a high or low threat and then tested the minnows for their responses to brown trout, rainbow trout (closely related predator) or yellow perch (distantly related predator). When the brown trout represents a high-risk predator, minnows show an antipredator response to the odour of brown trout and rainbow trout but not to yellow perch. However, when the brown trout represents a low-risk predator, minnows display antipredator responses to brown trout, but not to the rainbow trout or yellow perch. We discuss these results in the context of the Predator Recognition Continuum Hypothesis.     

Piscivory and prey selection of four predator species in a whitefish dominated subarctic lake

According to logistic regressions derived for pike Esox lucius and burbot Lota lota , the probability of ingesting fishes in Lake Muddusjärvi, northern Finland, was 50% at 19·3 and 22·1 cm L _T, whereas Arctic charr Salvelinus alpinus and brown trout Salmo trutta shifted to piscivory at the lengths of 25·7 and 26·4 cm L _T. The specialist piscivores, pike and burbot, consumed more prey species and took a wider range of prey sizes than Arctic charr and brown trout. The prey length for all predators increased in relationship to predator length. Whitefish Coregonus lavaretus was the dominant prey species in the lake and in the diet of all the piscivorous species. The whitefish population was divided into three forms, of which the slow-growing, and the most numerous densely rakered whitefish form (DR), was selected by all predator species. This form also had the smallest average size and widest habitat range, utilizing both pelagic and epibenthic habitats. Two sparsely rakered whitefish forms (LSR and SSR) occupied only epibenthic habitats and had lower relative densities than DR. These forms, LSR and SSR, had a minor importance in the diet of predator species.     

The role of trout in stream food webs: integrating evidence from field surveys and experiments

1. We evaluated the effects of brown trout on boreal stream food webs using field surveys and enclosure/exclosure experiments. Experimental results were related to prey preference of uncaged trout in the same stream, as well as to a survey of macroinvertebrate densities in streams with vs. without trout. Finally, we assessed the generality of our findings by examining salmonid predation on three groups of macroinvertebrate prey (chironomid midges, epibenthic grazers, invertebrate predators) in a meta-analysis. 2. In a preliminary experiment, invertebrate predators showed a strong negative response to trout, whereas chironomids benefited from trout presence. In the main experiment, trout impact increased with prey size. Trout had the strongest effect on invertebrate predators and cased caddis larvae, whereas Baetis mayfly and chironomid larvae were unaffected. Trout impact on the largest prey seemed mainly consumptive, because prey emigration rates were low and independent of fish presence. Despite strong effects on macroinvertebrates, trout did not induce a trophic cascade on periphyton. Uncaged trout showed a strong preference for the largest prey items (predatory invertebrates and aerial prey), whereas Baetis mayflies and chironomids were avoided by trout. 3. Densities of invertebrate predators were significantly higher in troutless streams. Baetis mayflies also were less abundant in trout streams, whereas densities of chironomids were positively, although non-significantly, related to trout presence. Meta-analysis showed a strong negative impact of trout on invertebrate predators, a negative but variable impact on mobile grazers (mainly mayfly larvae) and a slightly positive impact on chironomid larvae. 4. Being size-selective predators, salmonid fishes have a strong impact on the largest prey types available, and this effect spans several domains of scale. Discrepancies between our experimental findings and those from the field survey and meta-analysis show, however, that for most lotic prey, small-scale experiments do not reflect fish impact reliably at stream-wide scales. 5. Our findings suggest that small-scale experiments will be useful only if the experimental results are evaluated carefully against natural history information about the experimental system and interacting species across a wide array of spatial scales.     

Diet of brown trout in relation to variation in abundance and size of pelagic fish prey

The seasonal diet of a predator, brown trout Salmo trutta [total length ( L _T) 17–69 cm] and simultaneous density and size‐structure of prey populations, vendace Coregonus albula and smelt Osmerus eperlanus (4–16 cm L _T), in a large boreal lake were analysed and compared in 2001 and 2002. The upper L _T limit for consumed prey was c . 40% of the predator L _T. All brown trout, however, preferred small (<10 cm L _T) and avoided large (≥10 cm L _T) prey. The results also suggested that equal densities of similar‐sized (4–10 cm L _T) fish of the two prey species led to random foraging on these species by brown trout, but if either one of the prey species predominated (>50%) in the lake, brown trout shifted to foraging on this species almost exclusively. Brown trout diets thus reflected the density dynamics of the two alternative prey species.     

Brown trout and food web interactions in a Minnesota stream

1. We examined indirect, community‐level interactions in a stream that contained non‐native brown trout (Salmo trutta Linnaeus), native brook trout (Salvelinus fontinalis Mitchill) and native slimy sculpin (Cottus cognatus Richardson). Our objectives were to examine benthic invertebrate composition and prey selection of fishes (measured by total invertebrate dry mass, dry mass of individual invertebrate taxa and relative proportion of invertebrate taxa in the benthos and diet) among treatments (no fish, juvenile brook trout alone, juvenile brown trout alone, sculpin with brook trout and sculpin with brown trout). 2. We assigned treatments to 1 m² enclosures/exclosures placed in riffles in Valley Creek, Minnesota, and conducted six experimental trials. We used three designs of fish densities (addition of trout to a constant number of sculpin with unequal numbers of trout and sculpin; addition of trout to a constant number of sculpin with equal numbers of trout and sculpin; and replacement of half the sculpin with an equal number of trout) to investigate the relative strength of interspecific versus intraspecific interactions. 3. Presence of fish (all three species, alone or in combined‐species treatments) was not associated with changes in total dry mass of benthic invertebrates or shifts in relative abundance of benthic invertebrate taxa, regardless of fish density design. 4. Brook trout and sculpin diets did not change when each species was alone compared with treatments of both species together. Likewise, we did not find evidence for shifts in brown trout or sculpin diets when each species was alone or together. 5. We suggest that native brook trout and non‐native brown trout fill similar niches in Valley Creek. We did not find evidence that either species had an effect on stream communities, potentially due to high invertebrate productivity in Valley Creek.     

Innate Predator Recognition and the Problem of Introduced Trout

Innate predator recognition typically only occurs when there is an evolutionary history between predator and prey. Predator introductions thus can pose a substantial threat to native fauna that rely heavily on inherent identification of predators. In permanent aquatic habitats prey often encounter a variety of predatory and non-predatory fish species, and the ability to distinguish between the two is essential to avoid wasted time and energy spent in unnecessary antipredatory efforts. Here, we present a study evaluating the ability of lab-reared larvae of an endangered fully aquatic salamander (hellbenders: Cryptobranchus alleganiensis ) to recognize chemical cues from native and introduced fish predators. We recorded responses of hellbender larvae to chemical stimuli from native and non-native predatory fishes, a non-predatory fish and a blank control. Eastern hellbender larvae ( C. a. alleganiensis ) significantly reduced activity in response to chemical stimuli from native predators ( Micropterus salmoides , Micropterus dolomieu , Ambloplites rupestris , Sander vitreus , and Cottus carolinae ), but responses to non-native rainbow ( Oncorhynchus mykiss ) and brown ( Salmo trutta ) trout were not significantly different from responses to the non-predatory control (redhorse sucker, Moxostoma spp.). Responses of larval Ozark hellbenders ( C. a. bishopi ) to brown trout were similar to that of the native fishes and different from the blank control, but responses to rainbow trout did not differ from the blank control. The generally weak responses of larval hellbenders to chemical cues from introduced predatory trout could lead to increased predation in the wild, which may have exacerbated the decline of hellbender populations.     

Responses of tadpoles to hybrid predator odours: strong maternal signatures and the potential risk/response mismatch

Previous studies have established that when a prey animal knows the identity of a particular predator, it can use this knowledge to make an ‘educated guess'' about similar novel predators. Such generalization of predator recognition may be particularly beneficial when prey are exposed to introduced and invasive species of predators or hybrids. Here, we examined generalization of predator recognition for woodfrog tadpoles exposed to novel trout predators. Tadpoles conditioned to recognize tiger trout, a hybrid derived from brown trout and brook trout, showed generalization of recognition of several unknown trout odours. Interestingly, the tadpoles showed stronger responses to odours of brown trout than brook trout. In a second experiment, we found that tadpoles trained to recognize brown trout showed stronger responses to tiger trout than those tadpoles trained to recognize brook trout. Given that tiger trout always have a brown trout mother and a brook trout father, these results suggest a strong maternal signature in trout odours. Tadpoles that were trained to recognize both brown trout and brook trout showed stronger response to novel tiger trout than those trained to recognize only brown trout or only brook trout. This is consistent with a peak shift in recognition, whereby cues that are intermediate between two known cues evoke stronger responses than either known cue. Given that our woodfrog tadpoles have no evolutionary or individual experience with trout, they have no way of knowing whether or not brook trout, brown trout or tiger trout are more dangerous. The differential intensity of responses that we observed to hybrid trout cues and each of the parental species indicates that there is a likely mismatch between risk and anti-predator response intensity. Future work needs to address the critical role of prey naivety on responses to invasive and introduced hybrid predators.     

Piscivory by brown trout Salmo trutta L. and Arctic charr Salvelinus alpinus (L.) in Norwegian lakes

Size and frequency of occurrence of prey of brown trout Salmo trutta L. and Arctic charr Salvelinus alpinus (L.) were recorded in 13 Norwegian lakes during 1973–1990. Piscivores usually comprised less than 5% of the total population. Arctic charr were less piscivorous than brown trout. Trout and charr became piscivorous at 13 and 16 cm length, respectively. These size thresholds were similar to those of other facultative piscivorous freshwater fish species. When present, three-spined sticklebacks, Gasterosteus aculeatus (L.), were preferred by all length groups of piscivorous brown trout and Arctic charr. Length of prey increased with increasing predator length, and the mean body length of prey was about 33 and 25% of predator length for trout and charr, respectively. Yearlings of charr were not recorded as prey.     

The Diet of the Brown Trout Salmo trutta (L.) during the Reproductive Period: Size‐Related and Sexual Effects

We investigated the autumnal diet of the brown trout Salmo trutta, in a Prepyrenean stream (NW Iberian Peninsula) focusing on intraspecific dietary differences related to size and sex. The diet of trout included 18 types of prey, with Plecoptera and Ephemeroptera nymphs and Diptera larvae as the most consumed taxa. Large trout ate larger prey, than did small trout, and also increased the consumption of terrestrial‐surface prey with respect to aquatic‐benthic prey. As terrestrial‐surface preys were larger than aquatic‐benthic prey, the size‐related differences in the diet of trout were related to gape‐limitations. Although male and female trout did not differ in size, we found that males foraged on a more diverse type of prey than females, probably owing to male territoriality during the reproductive period. This study provides new evidence of dietary plasticity in the brown trout and confirms the importance of local dietary studies to better understand factors which drive trophic ecology of predators. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The impact of an introduced predator on a threatened galaxiid fish is reduced by the availability of complex habitats

1. The availability of complex habitats such as macrophytes may be vital in determining the outcomes of interactions between introduced predators and native prey. Introduced brown trout (Salmo trutta) have impacted numerous small native freshwater fishes in the southern hemisphere, but the potential role of complex habitats in determining the direct outcomes of brown trout – native fish interactions has not been experimentally evaluated. 2. An in‐lake enclosure experiment was used to evaluate the importance of structurally complex habitats in affecting the direct impacts of brown trout on a threatened galaxiid fish. Five Galaxias auratus and a single brown trout were added to enclosures containing one of three different habitat types (artificial macrophytes, rocks and bare silt substrate). The experiment also had control enclosures without brown trout. Habitat‐dependence of predation risk was assessed by analysis of G. auratus losses to predation, and stomach contents of remaining fish were analysed to determine if brown trout directly affect the feeding of G. auratus and whether this is also habitat‐dependent. 3. Predation risk of G. auratus differed significantly between habitat types, with the highest mortality in enclosures with only bare silt substrate and the lowest in enclosures containing artificial macrophytes. This result highlights the importance of availability of complex habitats for trout – native fish interactions and suggests that increasing habitat degradation and loss in fresh waters may exacerbate the direct impacts of introduced predators. 4. Stomach contents analyses were restricted to fish in enclosures with artificial macrophytes and rocks, as most fish were consumed in enclosures with brown trout and only bare silt substrate. These analyses suggest that brown trout do not directly affect the feeding of G. auratus in complex habitats, but it is still unknown whether its feeding is reduced if complex habitats are unavailable.     

Effects of pulsed discharges from a hydropower station on summer diel feeding activity and diet of brown trout (Salmo trutta Linnaeus, 1758) in an Iberian stream

The influence of pulsed discharges associated with hydroelectric power generation (i.e. hydropeaking) on feeding activity and diet composition of adult brown trout (Salmo trutta) was studied during the summer by comparing two sites: upstream (control site) and downstream from a power plant (hydropeaking site). Twenty fish were captured from each study site by electrofishing at 4‐hour intervals for two consecutive days and stomach contents were collected with pulsed gastric lavage. Hydropeaking events affected brown trout feeding behaviour as well as prey availability. Feeding intensity, measured by the stomach Fullness Index, showed pronounced variations with maximum values after flow pulses, which were linked to variations in prey availability because of increased drift rates of invertebrates. In contrast, brown trout living at the control site showed smoother variations in feeding activity not linked to invertebrate drift. Overall, brown trout at the hydropeaking site had higher food consumption rates and a more generalist and heterogeneous diet than trout from the control site, indicating an opportunistic feeding behaviour during flow pulses. Therefore, the hydrological disturbance caused by hydropeaking did not appear to cause direct negative impacts on feeding of adult brown trout. However, reduced trout density and imbalanced size structure in the hydropeaking site were detected, requiring further research to clarify the spatial influence of hydropeaking on other factors that could negatively affect brown trout populations.     

Temporal variability in marine feeding of sympatric Arctic charr and sea trout

The marine feeding pattern of anadromous brown trout (sea trout) Salmo trutta and Arctic charr Salvelinus alpinus was studied during June to August in 1992–1993 and 2000–2004 in a fjord in northern Norway. In general sea trout fed proportionally more on fishes than on crustaceans and insects (81, 1 and 18% by mass, respectively) by comparison with Arctic charr (52, 25 and 22% by mass, respectively). Herring Clupea harengus dominated the total fish diet of both species, but the Arctic charr also fed significantly on gadoids and sandlance Ammodytes spp. While sea trout became virtually all piscivorous at fork lengths ( L _F) ≥250 mm, the Arctic charr was ≥400 mm L _F before shifting totally to a fish diet. Despite annual variation in diet and forage ratios, there was a clear shift in diet from 1992–1993 to 2000–2004. Sandlance and different crustaceans constituted most of the diet during the initial period with a shift towards gadoids and especially herring during the latter period. This shift seemed to be associated with a high abundance of herring larvae during the latter sampling period, indicating a preferential selection on herring when present, particularly by sea trout. Furthermore, an index indicated dietary overlap in years with intensive feeding on herring of both species, and usually differences in the trophic ecology during years feeding mostly on other prey species. In combination, it was hypothesized that the two species reflect the type of marine prey present within a fjord system over time, and therefore provide an index of variation in the production and biological diversity of their potential prey within fjords.     

Effects of biotic and abiotic factors on the distribution of trout and salmon along a longitudinal stream gradient

Synopsis We examined the influence of biotic and abiotic factors on the distribution, abundance, and condition of salmonid fishes along a stream gradient. We observed a longitudinal change in fish distribution with native cutthroat trout, Oncorhynchus clarki utah, and introduced brown trout, Salmo trutta, demonstrating a distinct pattern of allopatry. Cutthroat trout dominated high elevation reaches, while reaches at lower elevations were dominated by brown trout. A transition zone between these populations was associated with lower total trout abundance, consistent changes in temperature and discharge, and differences in dietary preference. Variation in cutthroat trout abundance was best explained by a model including the abundance of brown trout and diel temperature, whereas variation in brown trout abundance was best explained by a model including the abundance of cutthroat trout and discharge. These results suggest the potential for condition-mediated competition between the two species. The results from our study can aid biologists in prioritizing conservation activities and in developing robust management strategies for cutthroat trout.     

Effects of prey dispersal on predator–prey interactions in streams

1. We studied the effect of mesh size (6 and 3 mm) on interactions between brown trout ( Salmo trutta ) and benthic invertebrates in enclosures placed in a stream in southern Sweden. We also compared how different prey exchange rates affected interactions between trout and invertebrates.
2. Trout had strong impacts on some benthic taxa, and different mesh sizes produced different patterns. Trout affected the abundance of 10 of the 21 taxa examined, six in enclosures with 3 mm mesh and six in enclosures with 6 mm mesh. The abundance of nine of the prey taxa was lower in the presence of trout, only leptocerids were more numerous in the presence of trout.
3. Our measurements of prey immigration/emigration, together with trout diet data, suggest that direct consumption by trout, rather than avoidance behaviour by prey, explains most decreases in prey abundance. There was avoidance behaviour by only two of the twenty-one prey taxa, with trout inducing emigration of the mayflies Baetis rhodani and Paraleptophlebia sp.
4. Trout indirectly increased periphyton biomass in both 3 and 6 mm enclosures. The effect of trout on periphyton was probably due to strong effects of trout on the grazer, Baetis rhodani , Heptagenia sp. and Paralepthoplebia sp.
5. Our results suggest that mesh size, through its effects on exchange rates of prey, may affect interactions between predators and prey in running waters, but that the effects of dispersal and predation on invertebrates are taxon specific.     

Interspecific competition between stream-dwelling brown trout and Alpine bullhead

Density and composition of benthic invertebrates and the diet of brown trout Salmo trutta and Alpine bullhead Cottus poecilopus were studied at two sites in one Norwegian stream. The sites were separated by an impassable waterfall, and brown trout density was five to 10 times higher at the upper, allopatric site than downstream where it lived in sympatry with the Alpine bullhead. Benthic invertebrate communities did not differ between sites; however, the size distribution of chironomids and trichopterans were skewed towards lighter individuals at the sympatric site. Diet composition suggested that sympatric brown trout foraged more on invertebrate drift and from the surface than allopatric brown trout. Alpine bullhead diet did not differ significantly from brown trout diet, except that the Alpine bullhead fed on heavier individual prey within a few taxa and did not consume chironomid pupae or surface insects. The collected data support the hypothesis that brown trout living in sympatry with Alpine bullhead feed at locations with higher predation risk, which is a probable explanation for their lower population density.     

Forest-stream linkages: effects of terrestrial invertebrate input and light on diet and growth of brown trout (Salmo trutta) in a boreal forest stream

Subsidies of energy and material from the riparian zone have large impacts on recipient stream habitats. Human-induced changes, such as deforestation, may profoundly affect these pathways. However, the strength of individual factors on stream ecosystems is poorly understood since the factors involved often interact in complex ways. We isolated two of these factors, manipulating the flux of terrestrial input and the intensity of light in a 2×2 factorial design, where we followed the growth and diet of two size-classes of brown trout (Salmo trutta) and the development of periphyton, grazer macroinvertebrates, terrestrial invertebrate inputs, and drift in twelve 20 m long enclosed stream reaches in a five-month-long experiment in a boreal coniferous forest stream. We found that light intensity, which was artificially increased 2.5 times above ambient levels, had an effect on grazer density, but no detectable effect on chlorophyll a biomass. We also found a seasonal effect on the amount of drift and that the reduction of terrestrial prey input, accomplished by covering enclosures with transparent plastic, had a negative impact on the amount of terrestrial invertebrates in the drift. Further, trout growth was strongly seasonal and followed the same pattern as drift biomass, and the reduction of terrestrial prey input had a negative effect on trout growth. Diet analysis was consistent with growth differences, showing that trout in open enclosures consumed relatively more terrestrial prey in summer than trout living in covered enclosures. We also predicted ontogenetic differences in the diet and growth of old and young trout, where we expected old fish to be more affected by the terrestrial prey reduction, but we found little evidence of ontogenetic differences. Overall, our results showed that reduced terrestrial prey inputs, as would be expected from forest harvesting, shaped differences in the growth and diet of the top predator, brown trout.