Probabilistic measures of climate change vulnerability,adaptation action benefits,and related uncertainty from maximum temperature metric selection

Predictions of the projected changes in species distributions and potential adaptation action benefits can help guide conservation actions. There is substantial uncertainty in projecting species distributions into an unknown future, however, which can undermine confidence in predictions or misdirect conservation actions if not properly considered. Recent studies have shown that the selection of alternative climate metrics describing very different climatic aspects (e.g., mean air temperature vs. mean precipitation) can be a substantial source of projection uncertainty. It is unclear, however, how much projection uncertainty might stem from selecting among highly correlated, ecologically similar climate metrics (e.g., maximum temperature in July, maximum 30‐day temperature) describing the same climatic aspect (e.g., maximum temperatures) known to limit a species’ distribution. It is also unclear how projection uncertainty might propagate into predictions of the potential benefits of adaptation actions that might lessen climate change effects. We provide probabilistic measures of climate change vulnerability, adaptation action benefits, and related uncertainty stemming from the selection of four maximum temperature metrics for brook trout (Salvelinus fontinalis), a cold‐water salmonid of conservation concern in the eastern United States. Projected losses in suitable stream length varied by as much as 20% among alternative maximum temperature metrics for mid‐century climate projections, which was similar to variation among three climate models. Similarly, the regional average predicted increase in brook trout occurrence probability under an adaptation action scenario of full riparian forest restoration varied by as much as .2 among metrics. Our use of Bayesian inference provides probabilistic measures of vulnerability and adaptation action benefits for individual stream reaches that properly address statistical uncertainty and can help guide conservation actions. Our study demonstrates that even relatively small differences in the definitions of climate metrics can result in very different projections and reveal high uncertainty in predicted climate change effects.     

Sympatric relationship between redband trout and non-native brook trout in the Southeastern Oregon Great Basin

Brook trout (Salvelinus fontinalis) and rainbow trout (Oncorhynchus mykiss) have been widely introduced outside their respective ranges within North America causing declines and displacement of native trout. Yet, successful coexistence of native and non-native trout has received little attention. Here we evaluated the effect of introduced brook trout on the size and density of native redband trout in two invaded sub-basins in southeastern Oregon. In a multi-year study, we investigated whether habitat and fish communities differed between streams and stream reaches where redband trout were allopatric versus where redband trout were sympatric with brook trout. We hypothesized that redband trout would be less dense and have smaller total length in sympatry with brook trout than in allopatry, but that total trout density would not differ. We investigated whether differences in habitat existed between sympatric and allopatric locations that would indicate differentiation in site level habitat preferences for each trout species. We found that sympatric locations had more wood but similar fish community structure. Mean length and densities of redband trout were higher at allopatric locations. However, in most years at sympatric locations total trout density was twice that of allopatric redband trout sites. Using comparable data from an eastern United States system where brook trout are native, sympatric sites had lower densities of brook trout; however, total trout density did not differ. We conclude that invading trout negatively impact native trout densities; but in southeastern Oregon system the negative impact is minimized.     

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.     

Can replacement of native by non‐native trout alter stream‐riparian food webs?

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Seasonal weather patterns drive population vital rates and persistence in a stream fish

Climate change affects seasonal weather patterns, but little is known about the relative importance of seasonal weather patterns on animal population vital rates. Even when such information exists, data are typically only available from intensive fieldwork (e.g., mark–recapture studies) at a limited spatial extent. Here, we investigated effects of seasonal air temperature and precipitation (fall, winter, and spring) on survival and recruitment of brook trout (Salvelinus fontinalis) at a broad spatial scale using a novel stage‐structured population model. The data were a 15‐year record of brook trout abundance from 72 sites distributed across a 170‐km‐long mountain range in Shenandoah National Park, Virginia, USA. Population vital rates responded differently to weather and site‐specific conditions. Specifically, young‐of‐year survival was most strongly affected by spring temperature, adult survival by elevation and per‐capita recruitment by winter precipitation. Low fall precipitation and high winter precipitation, the latter of which is predicted to increase under climate change for the study region, had the strongest negative effects on trout populations. Simulations show that trout abundance could be greatly reduced under constant high winter precipitation, consistent with the expected effects of gravel‐scouring flows on eggs and newly hatched individuals. However, high‐elevation sites would be less vulnerable to local extinction because they supported higher adult survival. Furthermore, the majority of brook trout populations are projected to persist if high winter precipitation occurs only intermittently (≤3 of 5 years) due to density‐dependent recruitment. Variable drivers of vital rates should be commonly found in animal populations characterized by ontogenetic changes in habitat, and such stage‐structured effects may increase population persistence to changing climate by not affecting all life stages simultaneously. Yet, our results also demonstrate that weather patterns during seemingly less consequential seasons (e.g., winter precipitation) can have major impacts on animal population dynamics.     

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.     

Stream channel restoration increases climate resiliency in a thermally vulnerable Appalachian river

We quantified stream temperature response to in‐stream habitat restoration designed to improve thermal suitability and resiliency of a high‐elevation Appalachian stream known to support a temperature‐limited brook trout population. Our specific objectives were to determine if: (1) construction of deep pools created channel unit‐scale thermal refugia and (2) reach scale stream channel reconfiguration reduced peak water temperatures along a longitudinal continuum known to be highly susceptible to summer‐time warming. Contrary to expectations, constructed pools did not significantly decrease channel unit‐scale summer water temperatures relative to paired control sites. This suggests that constructed pools did not successfully intercept a cool groundwater source. However, we did find a significant effect of stream channel restoration on reach‐scale thermal regimes. Both mean and maximum daily stream temperatures experienced significantly reduced warming trends in restored sections relative to control sections. Furthermore, we found that restoration efforts had the greatest effect on stream temperatures downstream of large tributaries. Restoration appears to have significantly altered thermal regimes within upper Shavers Fork, largely in response to changes in channel morphology that facilitated water movement below major cold‐water inputs. Decreased longitudinal warming will likely increase the thermal resiliency of the Shavers Fork main‐stem, sustaining the ability of these key large river habitats to continue supporting critical metapopulation processes (e.g. supplemental foraging and dispersal among tributary populations) in the face of climate change.     

Hydrological Variation and Fish Assemblage Structure in the Middle Wabash River

We assessed the effect of a severe drought in 1999 upon stream morphology and brook trout (Salvelinus fontinalis) populations in seven headwater streams in the Greenbrier and Potomac River watersheds, West Virginia. During the drought, stream discharge was 96% lower than in years of normal precipitation. As a result, habitat availability and quality over all study streams was significantly lower. Riffle area was greatly reduced (?54%) relative to available pool area (?2%). Fine sediment levels (<0.063 mm) significantly increased within spawning substrate (p=0.01). Water temperature and dissolved oxygen were adequate (mean 15.8?°C, >6.0 mg l^?1, respectively) for brook trout survival in all streams during the drought. Brook trout populations were significantly reduced (adult 60%, Young-of-the-year 67%), and individual fish had significantly lower body condition during the drought relative to the post-drought period. Reductions in brook trout density and population condition during, and in the-post drought period, were related to spatially-limited food resources and/or increased fine sediment levels, but not to degraded water quality. Fisheries managers should consider the effect of periodic drought on brook trout populations and consider short-term harvest restrictions to abet recovery after such stochastic events.     

Trout affect the density, activity and feeding of a larval plethodontid salamander

1. Ecologists have struggled to describe general patterns in the impacts of predators on stream prey, particularly at large, realistic spatial and temporal scales. Among the confounding variables in many systems is the presence of multiple predators whose interactions can be complex and unpredictable. 2. We studied the interactions between brook trout (Salvelinus fontinalis) and larval two‐lined salamanders (Eurycea bislineata), two dominant vertebrate predators in New England stream systems, by examining patterns of two‐lined salamander abundance in stream reaches above and below waterfalls that are barriers to fish dispersal, by measuring the effects of trout on salamander density and activity using a large‐scale manipulation of brook trout presence, and by conducting a small‐scale laboratory experiment to study how brook trout and larval two‐lined salamanders affect each other's prey consumption. 3. We captured more salamanders above waterfalls, in the absence of trout, than below waterfalls where trout were present. Salamander density and daytime activity decreased following trout addition to streams, and salamander activity shifted from aperiodic to more nocturnal with fish. Analysis of stomach contents from our laboratory experiment revealed that salamanders eat fewer prey with trout, but trout eat more prey in the presence of salamanders. 4. We suggest that as predators in streams, salamanders can influence invertebrate prey communities both directly and through density‐ and trait‐mediated interactions with other predators.     

The effects of population density and lake characteristics on growth and size structure of brook trout Salvelinus fontinalis (Mitchill, 1815) in boreal forest lakes in Canada

This paper examines the effect of lake characteristics on population density and how this variation affects growth, mortality and population size structure of brook trout, Salvelinus fontinalis. The study was conducted on 17 recreationally fished, reproductively isolated boreal forest lakes in Newfoundland, Canada from 1993 to 2000. A standardized sampling program, the Fyke Littoral Index Netting program (FLIN) was used to collected data that describes brook trout population parameters and life history attributes. Regression analyses showed significant relationships between fish density and biomass and characteristics of the lakes. Variation in fish density and biomass was explained by lake surface area and littoral habitat area. Significant relationships were found when growth, mortality and size structure were regressed against density. The proportional stock distribution and theoretical maximum size of brook trout were negatively related to density, and natural mortality was positively related to density. The largest maximum length and highest proportional stock densities occurred at brook trout densities of less than 30 fish/ha. In general, the higher the proportion of littoral habitat area the higher the densities of brook trout, which correspondingly had important effects on growth, natural mortality and size structure of the brook trout populations. This information is critical to the development of management strategies aimed at altering size distribution to produce specific fisheries management outcomes.     

Size‐dependent survival of brook trout Salvelinus fontinalis in summer: effects of water temperature and stream flow

A 5 year individual‐based data set was used to estimate size‐specific survival rates in a wild brook trout Salvelinus fontinalis population in a stream network encompassing a mainstem and three tributaries (1·5–6 m wetted width), western Massachusetts, U.S.A. The relationships between survival in summer and temperature and flow metrics derived from continuous monitoring data were then tested. Increased summer temperatures significantly reduced summer survival rates for S. fontinalis in almost all size classes in all four sites throughout the network. In contrast, extreme low summer flows reduced survival of large fish, but only in small tributaries, and had no significant effects on fish in smaller size classes in any location. These results provide direct evidence of a link between season‐specific survival and environmental factors likely to be affected by climate change and have important consequences for the management of both habitats and populations.     

Influences of logging history and riparian forest characteristics on macroinvertebrates and brook trout (Salvelinus fontinalis) in headwater streams (New Hampshire, U.S.A.)

1. Logging can strongly affect stream macroinvertebrate communities, but the direction and magnitude of these effects and their implications for trout abundance are frequently region‐specific and difficult to predict. 2. In first‐order streams in northern New England (U.S.A.) representing a chronosequence of logging history (<2 to >80 years since logging), we measured riparian forest conditions, stream macroinvertebrate community characteristics and brook trout (Salvelinus fontinalis) abundance. Principal component analysis was used to collapse forest data into two independent variables representing variation in logging history, riparian forest structure and canopy cover. We used these data to test whether logging history and associated forest conditions were significant predictors of macroinvertebrate abundance and functional feeding group composition, and whether brook trout abundance was related to logging‐associated variation in invertebrate communities. 3. Catchments with high PC1 scores (recently logged, high‐density stands with low mean tree diameter) and low PC2 scores (low canopy cover) had significantly higher total macroinvertebrate abundance, particularly with respect to chironomid larvae (low PC2 scores) and invertebrates in the grazer functional feeding group (high PC1 scores). In contrast, proportional representation of macroinvertebrates in the shredder functional feeding group increased with time since logging and canopy cover (high PC2 scores). Brook trout density and biomass was significantly greater in young, recently logged stands (high PC1 scores) and was positively related to overall macroinvertebrate abundance. In addition, three variables – trout density, invertebrate abundance and shredder abundance – successfully discriminated between streams that were less‐impacted versus more‐impacted by forestry. 4. These results indicate that timber harvest in northern New England headwater streams may shift shredder‐dominated macroinvertebrate communities supporting low trout abundance to a grazer/chironomid‐dominated macroinvertebrate community supporting higher trout abundance. However, while local effects on brook trout abundance may be positive, these benefits may be outweighed by negative effects of brook trout on co‐occurring species, as well as impairment of habitat quality downstream. Research testing the generality of these patterns will improve understanding of how aquatic ecosystems respond to anthropogenic and natural trajectories of forest change.     

Seasonal temperature and precipitation regulate brook trout young‐of‐the‐year abundance and population dynamics

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Growth rate differences between resident native brook trout and non-native brown trout

Between species and across season variation in growth was examined by tagging and recapturing individual brook trout Salvelinus fontinalis and brown trout Salmo trutta across seasons in a small stream (West Brook, Massachusetts, U.S.A.). Detailed information on body size and growth are presented to (1) test whether the two species differed in growth within seasons and (2) characterize the seasonal growth patterns for two age classes of each species. Growth differed between species in nearly half of the season- and age-specific comparisons. When growth differed, non-native brown trout grew faster than native brook trout in all but one comparison. Moreover, species differences were most pronounced when overall growth was high during the spring and early summer. These growth differences resulted in size asymmetries that were sustained over the duration of the study. A literature survey also indicated that non-native salmonids typically grow faster than native salmonids when the two occur in sympatry. Taken together, these results suggest that differences in growth are not uncommon for coexisting native and non-native salmonids.     

Density‐dependent and density‐independent growth in a population of juvenile sea‐trout,Salmo trutta,assessed using long‐term data from a small stream in Northwest England

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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.     

Diffusion in the littoral zone: scoping emergence times and movement to essential habitat for young‐of‐year brook trout in lakes

Factors governing the process of dispersal of lake‐spawned brook trout ( Salvelinus fontinalis ) young‐of‐year (YOY) appear drastically different from those governing dispersal in more commonly studied stream salmonids. Rather than dispersal being highly density‐dependent and the result of territoriality and aggression, in brook trout it may be density‐independent and driven by a common need for coldwater habitat for summer survival. Emerging fish travel great distances from single spawning sites on lakes to cold groundwater habitat. Movement is a gradual, one‐dimensional diffusion around lake margins and represents a very unique and simplified natal dispersal pathway allowing for dispersal rates, distances, and factors controlling these parameters to be measured. We predicted timing of the emergence period for brook trout alevins from lake spawning sites using the known relation between water temperature and emergence times for salmonids. Emergence and dispersal was then observed in the field by visually estimating YOY density in segments of the littoral zone throughout the dispersal period. Fluxes in density in these sections were used to estimate rate of YOY spread. YOY behaviour and body condition was also assessed across the wave of spatial spread. We are working towards a spatially explicit model to identify critical groundwater rearing habitat needing protection from forestry activities.     

Analysis of phenotypic change in relation to climatic drivers in a population of Soay sheep Ovis aries

Climatic change has frequently been identified as a key driver of change in biological communities. These changes can take the form of alterations to population dynamics, phenotypic characters, genetics and the life history of organisms and can have impacts on entire ecosystems. This study presents a novel investigation of how changes in a large scale climatic index, the North Atlantic Oscillation (NAO) can influence population dynamics and phenotypic characters in a population of ungulates. We use an integral projection model combined with actual climate change predictions to project future body size distributions for a population of Soay sheep Ovis aries. The climate change predictions used to direct our model projections were taken from published results of climate models, covering a range of different emissions scenarios. Our model results showed that for positive changes in the mean NAO large population declines occurred simultaneously with increases in mean body weight. The exact direction and magnitude of changes to population dynamics and character distributions were dependent on the greenhouse gas emissions scenario and model used to predict the NAO. This study has demonstrated how integral projection models can use outputs of climate models to direct projections of population dynamics and phenotypic character distributions. This approach allows the results of this study to be placed within current climate change research. The nature of integral projection models means that this methodology can be easily applied to other populations. The model can also be easily updated when new climate change predictions become available, making it a useful tool for understanding potential population level responses to climatic change. Synthesis Understanding how changes in climate affect biological communities is a key component in predicting the future form of populations. Utilising a novel approach that incorporates climatic drivers (in this instance the winter North Atlantic Oscillation) into an integral projection model framework, we predict future Soay sheep dynamics under specific climate change scenarios. Tracking quantitative trait distributions and life history metrics, our results predict declining population size and increasing body weight for an increasingly positive winter North Atlantic Oscillation index, as predicted by climate models. This has important implications for future wildlife management strategies and linking demographic responses to climate change.     

Effects of Large Woody Debris Addition on Stream Habitat and Brook Trout Populations in Appalachian Streams

Large woody debris (LWD) was added to eight streams in the central Appalachians of West Virginia to determine if stream habitat could be enhanced and brook trout (Salvelinus fontinalis) populations increased. Brook trout populations were assessed one year prior to habitat manipulation and 3 years post-habitat manipulation. LWD was added by felling approximately 15 trees per 300 m stream reach. Four of the streams had LWD added to one 300 m reach with 300 m unmanipulated reaches upstream and downstream of the manipulated reach to observe within-stream effects of LWD additions on brook trout density. The remaining four streams had LWD added to three 300 m reaches and these streams were compared to those with only a single 300 m manipulated reach to observe the effects of the extent of habitat manipulation on brook trout density. New pools were formed by the addition of LWD, but overall pool area did not increase significantly in reaches where LWD was added. The relatively high gradient and coarse substrate of these streams may have precluded the added LWD from having a significant influence on stream channel morphology and habitat complexity. No pools were formed in the highest gradient stream, while the stream with the most pools formed had the lowest gradient. Brook trout populations fluctuated following habitat manipulations, and there was no overall effect of the LWD additions on within-stream variability in brook trout density. When there were significant differences among-streams with different extents of LWD additions, those streams receiving LWD additions over a large extent had the greatest brook trout densities. The full potential of added LWD to change stream habitat and influence on brook trout populations may take more time to develop than the 3 years post-manipulation period of this study.     

Seasonal and regional infestation characteristics of three ectoparasites of whiting, Merlangim merlangus L., in the North Sea

The colonization by both resident and migrating spawner populations of brown trout and the characteristics of resident and migrating juveniles derived from the two populations have been studied in a brook and its tributary over 4 years. Resident trout spawns mainly in the upstream part of the brook and migrating trout in the downstream part. There are density and growth variations for the two age classes (0+ and 1 +) of juveniles in autumn according to the year and the environment. In the brook, the population of 0 + fish increases from downstream to upstream while the density of other age classes decreases. The migrating juvenile population of the brook changes annually and consists mainly of 1 s (one summer) individuals coming from the upper part. These individuals migrate generally in autumn and winter while young trout produced in the middle and downstream parts of the brook migrate mainly in the spring. The emigration process of the 0 + population decreases markedly from upstream to downstream and appears to be independent of the autumn length and sex ratio. In the tributary, most trout are 0+ years old, the population structure is different, and no migrating fish is observed. The results are discussed and a colonization strategy of the brown trout population in this brook is suggested.