Shifting thermal regimes influence competitive feeding and aggression dynamics of brook trout (Salvelinus fontinalis) and creek chub (Semotilus atromaculatus)

The natural distributions of freshwater fish species are limited by their thermal tolerances via physiological constraints and increased interspecific competition as temperatures shift toward the thermal optima of other syntopic species. Species may mediate stress from temperature change physiologically, behaviorally, or both; but these changes may compromise competitive advantages through effects on feeding and social behavior. In the Appalachian Mountains of North America, creek chub (Semotilus atromaculatus) are found in warm‐water and cold‐water streams and overlap in range with brook trout (Salvelinus fontinalis) across lower thermal maxima, where they compete for food and space. As stream temperatures continue to increase due to climate change, brook trout are under increasing thermal stress which may negatively affect their ability to compete with creek chub. To examine the influences of temperature on competitive interactions between these species, we observed feeding behavior, aggression, and habitat use differences at three temperatures approaching brook trout thermal maxima (18°C, 20°C, and 22°C) among dyad pairs for all combinations of species in experimental flow‐through tanks. We also examined feeding and habitat use of both species under solitary conditions. We found as temperature increased, feeding and aggression of brook trout were significantly reduced in the presence of creek chub. Creek chub pairs were more likely to occupy benthic areas and refugia while brook trout pairs used surface water more. Space use patterns significantly changed by pairing treatment. Aggression and space use shifts allowed increased exploitative and interference competition from creek chub when paired with brook trout that was not present in conspecific pairs. The decreased dominance of a top predator may lead to diverse impacts on stream community dynamics with implications for the future range restriction of brook trout and demonstrate possible mechanisms to facilitate competitive advantages of warm water generalist species under thermal stress.     

Sampling strategies for estimating brook trout effective population size

The influence of sampling strategy on estimates of effective population size (N _e ) from single-sample genetic methods has not been rigorously examined, though these methods are increasingly used. For headwater salmonids, spatially close kin association among age-0 individuals suggests that sampling strategy (number of individuals and location from which they are collected) will influence estimates of N _e through family representation effects. We collected age-0 brook trout by completely sampling three headwater habitat patches, and used microsatellite data and empirically parameterized simulations to test the effects of different combinations of sample size (S = 25, 50, 75, 100, 150, or 200) and number of equally-spaced sample starting locations (SL = 1, 2, 3, 4, or random) on estimates of mean family size and effective number of breeders (N _b ). Both S and SL had a strong influence on estimates of mean family size and [^(N)]_b , \hat{N}_{b} , however the strength of the effects varied among habitat patches that varied in family spatial distributions. The sampling strategy that resulted in an optimal balance between precise estimates of N _b and sampling effort regardless of family structure occurred with S = 75 and SL = 3. This strategy limited bias by ensuring samples contained individuals from a high proportion of available families while providing a large enough sample size for precise estimates. Because this sampling effort performed well for populations that vary in family structure, it should provide a generally applicable approach for genetic monitoring of iteroparous headwater stream fishes that have overlapping generations.     

Long-term population demographics of native brook trout following manipulative reduction of an invader

Although laboratory studies have provided evidence for negative interactions between brook trout and brown trout, it is unknown how these interactions affect larger scale demographics in a natural setting. We tested the effects of invasive brown trout on brook trout demographics by removing brown trout from a sympatric population using a before–after control-impact study design. The study was conducted across a large stream network for a period of 6 years. Abundance of brook trout increased after brown trout removal primarily as a result of increased recruitment and immigration. Size structure also shifted towards larger individuals as a result of increased growth rates and a decrease in emigration of larger trout. Size at maturity and body condition did not change after brown trout removal. Adult brook trout survival increased during the post-treatment period in both the treatment and control reach. A decrease in flood intensity during the post-treatment time period may have led to increased survival. Adult survival may not be the best metric to use when assessing interactions between trout species, especially when the subordinate species has suitable areas to emigrate.     

Watershed‐level brook trout genetic structuring: Evaluation and application of riverscape genetics models

相似文献   

Population response to habitat fragmentation in a stream-dwelling brook trout population

Fragmentation can strongly influence population persistence and expression of life-history strategies in spatially-structured populations. In this study, we directly estimated size-specific dispersal, growth, and survival of stream-dwelling brook trout in a stream network with connected and naturally-isolated tributaries. We used multiple-generation, individual-based data to develop and parameterize a size-class and location-based population projection model, allowing us to test effects of fragmentation on population dynamics at local (i.e., subpopulation) and system-wide (i.e., metapopulation) scales, and to identify demographic rates which influence the persistence of isolated and fragmented populations. In the naturally-isolated tributary, persistence was associated with higher early juvenile survival ( approximately 45% greater), shorter generation time (one-half) and strong selection against large body size compared to the open system, resulting in a stage-distribution skewed towards younger, smaller fish. Simulating barriers to upstream migration into two currently-connected tributary populations caused rapid (2-6 generations) local extinction. These local extinctions in turn increased the likelihood of system-wide extinction, as tributaries could no longer function as population sources. Extinction could be prevented in the open system if sufficient immigrants from downstream areas were available, but the influx of individuals necessary to counteract fragmentation effects was high (7-46% of the total population annually). In the absence of sufficient immigration, a demographic change (higher early survival characteristic of the isolated tributary) was also sufficient to rescue the population from fragmentation, suggesting that the observed differences in size distributions between the naturally-isolated and open system may reflect an evolutionary response to isolation. Combined with strong genetic divergence between the isolated tributary and open system, these results suggest that local adaptation can 'rescue' isolated populations, particularly in one-dimensional stream networks where both natural and anthropogenically-mediated isolation is common. However, whether rescue will occur before extinction depends critically on the race between adaptation and reduced survival in response to fragmentation.     

Seasonal influence of brook trout and mottled sculpin on lower trophic levels in an Appalachian stream

1. In some situations fish have strong top‐down effects in stream communities while in others they seem to be relatively unimportant. Differences in the impact of fish may depend on a variety of factors including the foraging mode of the fish, interactions among fish species and temporal variation in environmental conditions and species interactions. 2. We investigated the effect of brook trout (Salvelinus fontinalis) and mottled sculpin (Cottus bairdi) on lower trophic levels in Appalachian streams and whether or not interactions between these fish changed their influence. Mesocosms were placed in a headwater stream in a randomized complete block design. Within blocks, mesocosms were randomly assigned to one of the following treatments: (i) no fish; (ii) sculpin only; (iii) trout only and (iv) both sculpin and trout. Fish biomass was the same in all three fish treatments. Invertebrate density and algal biomass in mesocosms were determined after 3 weeks. We repeated the experiment in the autumn, spring and summer to test for seasonality of fish effects. 3. The effect of fish on invertebrate assemblages was seasonal and depended on prey identity. Sculpin strongly suppressed grazer abundance in spring while trout had little effect on grazers in any season. The influence of both fish on insect predators was similar and relatively constant across seasons. We found little evidence of an interaction between sculpin and trout that strongly influenced their effect on prey across seasons. 4. None of the fish treatments influenced algal biomass during any of the seasons. Algal growth was also seasonal, with a two‐ to four‐fold increase in algal biomass in spring compared to autumn and summer. 5. Our results indicate that benthic and drift feeding fish differ in their effects on some, but not all prey. Furthermore, fish effects on prey were strongly seasonal for some, but not all prey types. While the temporal context is not commonly considered, our results indicate seasonality can be an important component of predator–prey interactions in streams.     

Spatio-temporal genetic structuring of brown trout (Salmo trutta L.) populations within the River Luga, northwest Russia

The brown trout populations of the Baltic Sea region have been drastically affected by various human activities during the past century. Due to their propensity to home to their natal site to spawn and their tendency to evolve local adaptations, populations may be genetically differentiated in water systems where no physical barriers preventing interbreeding exist. Consequently, identification of management units, a prerequisite for appropriate conservation and management planning, cannot necessarily be deduced from the physical properties of the habitat. In this study, microsatellite markers were employed to assess the spatio-temporal genetic structuring of inter-connected brown trout populations from a river-system in Northwest Russia. Populations were found to be genetically differentiated from each other (global F _ST 0.06) and the genetic structuring within the river to follow an isolation by distance pattern. Indications of temporal stability were found in some populations, however others appeared to be temporally unstable suggesting differences in the demographic forces affecting the populations. Based on the observed isolation by distance pattern of genetic differentiation, preserving several breeding sites spaced evenly throughout the river-system would appear to be more appropriate than focussing conservation effort on any single stretch of the river. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The influence of prey biomass on activity and consumption rates of brook trout

The objectives of this work were (1) to assess the influence of zooplankton biomass on activity and consumption rates of young-of-the-year brook trout ( Salvelinus fontinalis ) and (2) to validate an in situ enclosure approach to quantify energy allocation patterns in fish. These objectives were attained by directly estimating fish growth, consumption and activity rates on 10 occasions characterized by different levels of zooplankton biomass (0.005 to 0.100 mg dry weight 1⁻¹). One enclosure was used to estimate growth and activity rates and five additional enclosures were used to estimate consumption rates. Among-experiment variations of activity rates (sum for five trout = 2.4 to 33.5 calories day⁻¹) were proportionally more important than variations of consumption rates (sum for five trout = 59.5 to 112.7 calories day⁻¹). The results support the existence of a significant positive relationship between fish activity rates and zooplankton biomass. No significant relationship was found between consumption rates and prey biomass. Final size of fish inside the enclosure was within 7.6% of the value estimated using experimentally derived activity and consumption rates. This situation, together with the stability of among-enclosure activity and feeding schedules, suggested that the experimental design was appropriate to estimate fish energy allocation patterns. Combination of our observations with those of a previously published work indicated that small variations of fish size or zooplankton biomass can cause a two-fold variation of fish activity costs.     

To fast or feed: an alternative life history for anadromous brook trout Salvelinus fontinalis overwintering within a harbour

The seasonal feeding pattern of sea‐run brook trout Salvelinus fontinalis was studied from November to May 2010–2012 in Antigonish Harbour, Nova Scotia, Canada (45° 38′ N; 61° 55′ W). Sixty‐three S. fontinalis (mean ± s.d . fork length = 330 ± 70 mm and mass = 536 ± 351 g) captured had fed predominantly on fishes (Fundulidae and Gasterosteidae). Percentage of empty stomachs was highest during autumn (18%) and winter (22%) and lowest in spring (7%). Stomach fullness increased from autumn to a maximum during winter, relating to near‐zero body temperatures which may have effectively stopped gastric evacuation. Although feeding occurred during winter (December to March), consumption rates were calculated as negative values, and subsequently returned to positive values in spring (April to May). The over‐winter life‐history strategy of this sea‐run S. fontinalis population appears to be a feeding marine migration in which fish continually increase body condition, representing an alternative to the more common overwintering strategy of starvation in fresh water until spring.     

The population dynamics of young trout (Salmo trutta L.) in a Danish brook

The population size, dispersal of fry, growth of fry in relation to density, mortality and production of young trout ( Salmo trutta L.) were studied in a Danish brook during 1970–1972. In the first few months after emergence downstream emigration of fry took place both in 1971 and 1972, after which the trout became stationary. Growth was inversely density dependent and mortality was density dependent in the months just after emergence. Later mortality was constant and independent of density. Trout production varied between 10 g/m² and 18.6 g/m² in the 2 years.     

Spawning and emergence phenology of bull trout Salvelinus confluentus under differing thermal regimes

Median bull trout Salvelinus confluentus breeding was 2 weeks earlier in a cool stream than in a proximate warmer stream, aligning with expectations for salmonids, followed by emergence timing calculated to be 6 weeks later in the cool stream than the warm stream. This pattern is consistent with both site-specific adaptation and thermal spawning threshold hypotheses for life-history event timing in this threatened species.     

Variation in brook and brown trout survival within and among seasons, species, and age classes

The Program MARK was used to generate and test a plausible set of survival models for brook trout Salvelinus fontinalis and brown trout Salmo trutta to determine whether survival differed by season, species or age class. Apparent survival varied with time and age, but not by species. For the older (1999) age class, survival was lowest during the autumn of their age 1+ year whereas survival was lowest for the younger (2000) age class during the early summer of their age 1+ year. Additionally, estimates of survival for the younger age class exceeded those of the older age class in all but one interval (early summer 2001) but significant differences were observed in only one of these intervals (autumn 2000). To determine whether the observed seasonal differences in survival were related to seasonal differences in movement rates, multi‐strata spatial models were used within Program MARK to determine the probability of moving for each interval. In‐site movement rates were found to be low regardless of season (average for all cohorts combined was 5%). The ability of the multi‐strata modelling approach to detect temporal variability in movement, however, was potentially limited by spatial scale of the study reach ( c . 1 km). Differences in survival between different aged fishes could lead to selection acting on age at maturity or reproductive effort at a given age.     

Context‐specific influence of water temperature on brook trout growth rates in the field

1. Modelling the effects of climate change on freshwater fishes requires robust field‐based estimates accounting for interactions among multiple factors. 2. We used data from an 8‐year individual‐based study of a wild brook trout (Salvelinus fontinalis) population to test the influence of water temperature on season‐specific growth in the context of variation in other environmental (i.e. season, stream flow) or biotic factors (local brook trout biomass density and fish age and size) in West Brook, a third‐order stream in western Massachusetts, U.S.A. 3. Changes in ambient temperature influenced individual growth rates. In general, higher temperatures were associated with higher growth rates in winter and spring and lower growth rates in summer and autumn. However, the effect of temperature on growth was strongly context‐dependent, differing in both magnitude and direction as a function of season, stream flow and fish biomass density. 4. We found that stream flow and temperature had strong and complex interactive effects on trout growth. At the coldest temperatures (in winter), high stream flows were associated with reduced trout growth rates. During spring and autumn and in typical summers (when water temperatures were close to growth optima), higher flows were associated with increased growth rates. In addition, the effect of flow at a given temperature (the flow‐temperature interaction) differed among seasons. 5. Trout density negatively affected growth rate and had strong interactions with temperature in two of four seasons (i.e. spring and summer) with greater negative effects at high temperatures. 6. Our study provided robust, integrative field‐based estimates of the effects of temperature on growth rates for a species which serves as a model organism for cold‐water adapted ectotherms facing the consequences of environmental change. Results of the study strongly suggest that failure to derive season‐specific estimates, or to explicitly consider interactions with flow regime and fish density, will seriously compromise our ability to predict the effects of climate change on stream fish growth rates. Further, the concordance we found between empirical observations and likely energetic mechanisms suggests that our general results should be relevant at broader spatial and temporal scales.     

Non‐native trout limit native brook trout access to space and thermal refugia in a restored large‐river system

We used direct observation via snorkeling surveys to quantify microhabitat use by native brook (Salvelinus fontinalis) and non‐native brown (Salmo trutta) and rainbow (Onchorynchus mykiss) trout occupying natural and restored pool habitats within a large, high‐elevation Appalachian river, United States. Permutational multivariate analysis of variance (PERMANOVA) and subsequent two‐way analysis of variance (ANOVA) indicated a significant difference in microhabitat use by brook and non‐native trout within restored pools. We also detected a significant difference in microhabitat use by brook trout occupying pools in allopatry versus those occupying pools in sympatry with non‐native trout—a pattern that appears to be modulated by size. Smaller brook trout often occupied pools in the absence of non‐native species, where they used shallower and faster focal habitats. Larger brook trout occupied pools with, and utilized similar focal habitats (i.e. deeper, slower velocity) as, non‐native trout. Non‐native trout consistently occupied more thermally suitable microhabitats closer to cover as compared to brook trout, including the use of thermal refugia (i.e. ambient–focal temperature >2°C). These results suggest that non‐native trout influence brook trout use of restored habitats by: (1) displacing smaller brook trout from restored pools, and (2) displacing small and large brook trout from optimal microhabitats (cooler, deeper, and lower velocity). Consequently, benefits of habitat restoration in large rivers may only be fully realized by brook trout in the absence of non‐native species. Future research within this and other large river systems should characterize brook trout response to stream restoration following removal of non‐native species.     

Hybridization between native white-spotted charr and nonnative brook trout in the upper Sorachi River,Hokkaido, Japan

Invasion status and impacts of nonnative brook trout (Salvelinus fontinalis) in a Hokkaido stream were investigated with field surveys and genetic analyses. Nonnative brook trout was detected in nine (41 %) of the 22 sampled reaches in three tributaries of the Sorachi River, Hokkaido, Japan. Based on the external pigmentation, twelve putative hybrids between brook trout and native white-spotted charr (Salvelinus leucomaenis) were collected in two reaches. Microsatellite and mitochondrial DNA data established that 58% of these hybrids were first-generation (F₁) progenies between male brook trout and female white-spotted charr. Our results suggest potential negative impacts of nonnative brook trout on native charr populations in Hokkaido through interspecific interactions.     

Individual behaviour and resource use of thermally stressed brook trout Salvelinus fontinalis portend the conservation potential of thermal refugia

Individual aggression and thermal refuge use were monitored in brook trout Salvelinus fontinalis in a controlled laboratory to determine how fish size and personality influence time spent in forage and thermal habitat patches during periods of thermal stress. On average, larger and more exploratory fish initiated more aggressive interactions and across all fish there was decreased aggression at warmer temperatures. Individual personality did not explain changes in aggression or habitat use with increased temperature; however, larger individuals initiated comparatively fewer aggressive interactions at warmer temperatures. Occupancy of forage patches generally declined as ambient stream temperatures approached critical maximum and fish increased thermal refuge use, with a steeper decline in forage patch occupancy observed in larger fish. These findings suggest that larger individuals may be more vulnerable to stream temperature rise. Importantly, even at thermally stressful temperatures, all fish periodically left the thermal refuge to forage. This indicates that the success of refugia at increasing population survival during periods of stream temperature rise may depend on the location of thermal refugia relative to forage locations within the larger habitat mosaic. These results provide insights into the potential for thermal refugia to improve population survival and can be used to inform predictions of population vulnerability to climate change.     

Natural replacement of invasive brown trout by brook charr in an upper Midwestern United States stream

Hydrobiologia - Competition with invasive species and a warming climate have threatened brook charr (Salvelinus fontinalis) populations throughout their native range. In particular, brown trout...