Bull Trout Research Articles

Stream‐groundwater exchange and hydrologic turnover at the network scale

The exchange of water between streams and groundwater can influence stream water quality, hydrologic mass balances, and attenuate solute export from watersheds. We used conservative tracer injections (chloride, Cl−) across 10 stream reaches to investigate stream water gains and losses from and to groundwater at larger spatial and temporal scales than typically associated with hyporheic exchanges. We found strong relationships between reach discharge, median tracer velocity, and gross hydrologic loss across a range of stream morphologies and sizes in the 11.4 km2 Bull Trout Watershed of central ID. We implemented these empirical relationships in a numerical network model and simulated stream water gains and losses and subsequent fractional hydrologic turnover across the stream network. We found that stream gains and losses from and to groundwater can influence source water contributions and stream water compositions across stream networks. Quantifying proportional influences of source water contributions from runoff generation locations across the network on stream water composition can provide insight into the internal mechanisms that partially control the hydrologic and biogeochemical signatures observed along networks and at watershed outlets.

Use of genetic markers to aid in re-establishing migratory connectivity in a fragmented metapopulation of bull trout (Salvelinus confluentus)

Dams and other barriers fragment important migratory corridors for bull trout ( Salvelinus confluentus ) across the species range. Three dams constructed without fish passage facilities prevented migratory bull trout in the Lake Pend Oreille and Clark Fork River system in Idaho and Montana, USA, from returning to their natal spawning tributaries for nearly 100 years. We genotyped bull trout from 39 spawning tributaries to assemble a baseline data set that we used to develop a real-time genotyping and analysis protocol to assist with upstream fish transport decisions. Self-assignment tests and analysis of blind samples indicated that unknown individuals could be assigned to their region of origin with a high degree of confidence. From 2004 to 2010, genetic assignments were conducted for 259 adult bull trout collected below mainstem dams. Based on genetic assignments, 203 fish were transported upstream above one or more dams. This protocol has helped re-establish connectivity in a fragmented system, providing increased numbers of spawning adults for numerically depressed populations above the dams. We discuss the utility of genetic data for assisting with upstream passage decisions.

A riverscape perspective of Pacific salmonids and aquatic habitats prior to large‐scale dam removal in the Elwha River, Washington, USA

Abstract Dam removal has been increasingly proposed as a river restoration technique. In 2011, two large hydroelectric dams will be removed from Washington State’s Elwha River. Ten anadromous fish populations are expected to recolonise historical habitats after dam removal. A key to understanding watershed recolonisation is the collection of spatially continuous information on fish and aquatic habitats. A riverscape approach with an emphasis on biological data has rarely been applied in mid‐sized, wilderness rivers, particularly in consecutive years prior to dam removal. Concurrent snorkel and habitat surveys were conducted from the headwaters to the mouth (rkm 65–0) of the Elwha River in 2007 and 2008. This riverscape approach characterised the spatial extent, assemblage structure and patterns of relative density of Pacific salmonids. The presence of dams influenced the longitudinal patterns of fish assemblages, and species richness was the highest downstream of the dams, where anadromous salmonids still have access. The percent composition of salmonids was similar in both years for rainbow trout, Oncorhynchus mykiss (Walbaum), coastal cutthroat trout, Oncorhynchus clarkii clarkii (Richardson) (89%; 88%), Chinook salmon, Oncorhynchus tshawytscha (Walbaum) (8%; 9%), and bull trout, Salvelinus confluentus (Suckley) (3% in both years). Spatial patterns of abundance for rainbow and cutthroat trout (r = 0.76) and bull trout (r = 0.70) were also consistent between years. Multivariate and univariate methods detected differences in habitat structure along the river profile caused by natural and anthropogenic factors. The riverscape view highlighted species‐specific biological hotspots and revealed that 60–69% of federally threatened bull trout occurred near or below the dams. Spatially continuous surveys will be vital in evaluating the effectiveness of upcoming dam removal projects at restoring anadromous salmonids.

Exposure histories derived from selenium in otoliths of three cold-water fish species captured downstream from coal mining activity

Establishing exposure to contaminants within a given environment is often difficult for fish species with large home ranges. Chemical analyses of muscle or visceral tissue are useful indicators of recent exposure, but depuration, metabolic transformation, and tissue redistributions can alter temporal resolution. Otoliths are metabolically stable and thus provide complete chemical records within their calcified tissues that, when coupled to the annular structure, can provide temporal resolution for exposure to trace metals. Otoliths from bull trout, cutthroat trout, and mountain whitefish from an area rich in seleniferous soils and with active coal mining activity were analyzed for selenium to determine any history of exposure to elevated levels of selenium. Selenium concentrations in otolith primordia tended to be low, indicating that these fish emerged in low selenium areas. Later life stages showed peaks of high Se concentrations, suggesting that individuals moved into areas of increased selenium later in life. Individuals captured from the same area had a wide variety of selenium exposure profiles, indicating that these fish do not move en masse into and out of high-selenium areas. Year-to-year variability of selenium exposure patterns within an otolith suggests inconsistent utilization of high- and low-selenium areas by the individual. The inconsistent exposure profiles for these fish, in addition to their home range of tens of kilometres, indicate that soft tissue concentrations, while useful indicators of recent exposure, cannot be relied upon to provide a life history recording of exposure.

Genetic Population Structure of Olympic Peninsula Bull Trout Populations and Implications for Elwha Dam Removal

Abstract In the Elwha River, two hydroelectric dams constructed nearly a century ago fragment previously continuous habitat and isolate migratory bull trout. Removal of the dams is scheduled to begin in 2011, and represents an opportunity to help recover this threatened species. Large-scale disturbance is expected when accumulated sediments behind the dams are released downstream, which may initially negatively affect bull trout. To inform restoration planning, we investigated levels of genetic variation within and among bull trout populations from six Olympic Peninsula watersheds with an emphasis on the Elwha River. We determined genetic relationships among Elwha bull trout from four distinct river sections and performed population assignments for fish collected from the lower Elwha and Dungeness rivers. There were greater levels of variation and gene flow in coastal watersheds (Hoh, South Fork Hoh, Kalaloch) compared to populations isolated by dams (Elwha, North Fork Skokomish). Elwha bull trout represe...

Validation of Morphological Characteristics Used for Field Identification of Bull Trout × Brook Trout Hybrids

AbstractBull trout Salvelinus confluentus are of conservation concern throughout much of their range, in part because of displacement by and hybridization with nonnative brook trout S. fontinalis. Hybridization between these species can complicate efforts to control brook trout because hybrids are often difficult to distinguish from parental species. Here, we assess the reliability of five morphological characteristics that were used to identify bull trout × brook trout hybrids among 106 fish collected from Quirk Creek, Alberta. Genetic analysis of up to three microsatellite loci suggested that hybrids were correctly identified 95% of the time and that no bull trout were mistaken for hybrids. Visual inspection of photographs of hybrids suggested that dorsal fin markings were the most reliable morphological characteristic for identifying hybrids. Based on these results, we recommend that field identification of bull trout × brook trout hybrids be based solely on dorsal fin markings.Received November 20, 2010; accepted March 21, 2011

Home Range Size and Foraging Ecology of Bull Trout and Westslope Cutthroat Trout in the Upper Salmon River Basin, Idaho

AbstractWe used radiotelemetry to determine how body size, foraging ecology, and seasonal activity influence the home range size of adult bull trout Salvelinus confluentus and westslope cutthroat trout Oncorhynchus clarkii lewisi in the upper Salmon River basin of central Idaho. Stomach samples were collected to determine diet composition and compare foraging strategies between the two species. Contrary to other studies of home ranges for stream‐dwelling fishes, home range size was not significantly related to total length or body mass in either species. Although overall home range size did not differ between species, monthly movement (km) was significantly greater for bull trout than for westslope cutthroat trout during July and September. Stomach content analysis revealed that the size of prey consumed was significantly larger for bull trout than for westslope cutthroat trout but was not significantly correlated with body size in either species. Home range size for bull trout and westslope cutthroat trout in our study was much larger than home ranges documented for other stream‐dwelling salmonids; our results illustrate the importance of large‐scale connectivity and the variety of habitats necessary for the persistence of these species.

Decline in angler use despite increased catch rates: Anglers’ response to the implementation of a total catch-and-release regulation

A mandatory total catch-and-release regulation and a bait ban were implemented on Lower Kananaskis Lake, Canada, due to the drastic decline of the native bull trout ( Salvelinus confluentus) population. In the decade following harvest-regulation changes, the adult bull trout population experienced a 28-fold increase in abundance. Two roving creel surveys of winter ice-anglers, the first conducted just prior to the regulation changes (1992) and the second 10 years later (2002), were used to compare catch rates, the size structure of fish caught, and angler effort before and after the bull trout population rebuilt. Supplementary information from voluntary creel cards (1996–2003) was used to evaluate temporal trends in summer catch-related fishery attributes as the fish population recovered. Winter catch rates were three-fold and 12-fold higher in 2002 than in 1992, for all bull trout and large (>50 cm) bull trout, respectively. The proportion of large fish in the catch also increased. Voluntary creel card information suggested summer catch rates and the frequency of large fish in the catch both increased as the population rebuilt. However, despite the increase in fishing “quality”, angler numbers were three- to 10-fold lower in 2002 than 1992, indicating reduced utilization of the fishery. We speculate that harvest-oriented anglers were displaced from Lower Kananaskis Lake because of restrictive regulations. Our study shows anglers are not necessarily attracted to high-catch-rate fisheries, suggesting angler behaviour is complex and not driven by catch rates alone. Thus, to meet management objectives, understanding angler effort responses to regulatory changes is fundamentally important.

Genetic Structure, Evolutionary History, and Conservation Units of Bull Trout in the Coterminous United States

AbstractThe bull trout Salvelinus confluentus is a broadly distributed char in northwestern North America that has undergone significant population declines. This species is currently protected under the Endangered Species Act across its range in the coterminous United States. To clarify patterns of phylogenetic structure and to assist with identification of conservation units, we examined genetic variation within and among 75 representative bull trout populations sampled throughout the USA. Genealogies from a 520‐base‐pair portion of the mitochondrially encoded NADH dehydrogenase 1 gene (ND‐1) revealed reciprocal monophyly between coastal and interior lineages that differed by 1.34% in DNA sequence. The geographic distribution of the two lineages was divided by the Cascade Mountains, a pattern that likely reflects postglacial dispersal from separate glacial refugia. Analysis of microsatellite variation revealed that 76% of populations had an estimated effective population size less than 50 and indicated high divergence among populations caused by genetic drift (average genetic differentiation index FST = 0.32) and mutation (average genetic differentiation index RST = 0.58). Concordant phylogeographic and phylogenetic patterns observed with microsatellite and mitochondrial DNA analyses provided evidence for two to six bull trout lineages that largely reflect historic patterns of gene flow and isolation among populations. These lineages can be further subdivided into finer‐scale units due to the extremely low dispersal among populations and small effective population sizes. In fact, Bayesian analysis of population structure identified an optimal solution of 69 genetically different groups. Based on these results, we believe that conservation efforts should ideally be focused on the 118 bull trout core areas originally identified in the draft Endangered Species Act recovery plan, which are broadly defined as metapopulations. We provide examples of how other data, such as unique life history forms and ecological setting, can be used in combination with our genetic results to refine the U.S. Fish and Wildlife Service's hierarchical conservation strategy for bull trout.

Estimating Proportional Contributions of Migratory Bull Trout from Hierarchical Populations to Mixed‐Stock Recreational Fisheries Using Genetic and Trapping Data

AbstractGenetic assignment methods were used to assign 104 adult migrant bull trout Salvelinus confluentus from five recreational fisheries in the Oldman River drainage (Alberta, Canada) to a baseline of three coarse‐scale genetic stocks that had been previously identified with a model‐based Bayesian clustering method. Based on individual assignment and genetic stock identification, most fisheries were largely dominated by the stock with the most proximate spawning tributaries; however, assignment tests suggested variation among source stocks in the proportions of long‐range (>90 river kilometers) migrants relative to short‐range migrants (i.e., that used nearby river systems draining spawning streams). Migrants originating from a subset of the drainage were then subjected to a finer‐scale mixed‐stock analysis in which populations at near‐tributary scales were used as the baseline. These stock proportions were compared with estimates from direct observations and were found to yield similar values to stock proportions derived from 2 years of trapping in several spawning streams. These genetic assignment methods may be used to infer contributions of large and fine‐scale hierarchical populations to mixed‐stock recreational fisheries and are especially applicable for use by inland recreational fisheries managers, which have traditionally not taken advantage of spatial genetic analysis tools to the extent used by coastal commercial fisheries managers.

Trophic relationships between a native and a nonnative predator in a system of natural lakes

Abstract – Bull trout, a species of char listed as threatened under the US Endangered Species Act, have been displaced from portions of their historic range following the introduction of nonnative lake trout. It has been suggested that competitive exclusion as a result of trophic overlap between bull trout and lake trout may be the causal mechanism associated with displacement of bull trout. This study used stable isotope data to evaluate trophic relationships among native bull trout, nonnative lake trout and other fishes in seven lakes in Glacier National Park (GNP), Montana. Bull trout and lake trout had greater δ15N values relative to other fishes among lakes (δ15N ≥ 3.0‰). Lake trout had greater δ15N values relative to bull trout (δ15N = +1.0‰). Bull trout had greater δ13C values relative to lake trout in six of the seven lakes examined. Although both bull trout and lake trout had greater δ15N values relative to other fishes within lakes in GNP, differences in δ15N and δ13C between bull trout and lake trout suggest that they are consuming different prey species or similar prey species in different proportions. Therefore, displacement of bull trout as a direct result of complete overlap in food resource use is not anticipated unless diet shifts occur or food resources become limiting. Additionally, future studies should evaluate food habits to identify important prey species and sources of partial dietary overlap between bull trout and lake trout.

Injury and immediate mortality associated with recreational troll capture of bull trout ( Salvelinus confluentus) in a reservoir in the Kootenay-Rocky Mountain region of British Columbia

We evaluated hooking injury and immediate mortality arising from capture of troll-caught adult bull trout ( Salvelinus confluentus) in a reservoir in the Kootenay-Rocky Mountain region of British Columbia in the spring (water temperature 2–15 °C) where regulations enabled anglers to use both barbed and barbless hooks. We captured 126 bull trout on lures and only a single mortality occurred (0.79% immediate mortality rate). Most bull trout maintained equilibrium and those that lost equilibrium were fought for significantly more time ( p = 0.03). Overall, approximately 79% of fish were hooked in the mouth. Nearly 16% of fish were foul hooked, which was independent of the number of hooks ( p = 0.76) and troll speed ( p = 0.08). Although not statistically related to troll speed, foul hooking occurred in nearly 90% of those captured at faster speeds (i.e., ≥5.3 kph). The depth that hooks swallowed was not influenced by trolling speed or the number of hooks ( p > 0.05 in all cases). Incidences of bleeding were lowest among single barbless hooks (10%) but did not significantly differ from the other hook configurations (∼18%). To our knowledge, this is the first study that examines such hook type issues in freshwater troll fisheries and the first published estimate of hooking mortality for bull trout, a species that is considered imperilled throughout much of its range. Although immediate mortality was very low, the high incidence of bleeding and foul hooking warrant further investigation into the impacts of different recreational fishing practices on short-term and delayed mortality of bull trout, especially for imperilled populations.

ASSESSING THE IMPACTS OF RIVER REGULATION ON NATIVE BULL TROUT (SALVELINUS CONFLUENTUS) AND WESTSLOPE CUTTHROAT TROUT (ONCORHYNCHUS CLARKII LEWISI) HABITATS IN THE UPPER FLATHEAD RIVER, MONTANA, USA

ABSTRACTHungry Horse Dam on the South Fork Flathead River, Montana, USA, has modified the natural flow regimen for power generation, flood risk management and flow augmentation for anadromous fish recovery in the Columbia River. Concern over the detrimental effects of dam operations on native resident fishes prompted research to quantify the impacts of alternative flow management strategies on threatened bull trout (Salvelinus confluentus) and westslope cutthroat trout (Oncorhynchus clarkii lewisi) habitats. Seasonal and life‐stage specific habitat suitability criteria were combined with a two‐dimensional hydrodynamic habitat model to assess discharge effects on usable habitats. Telemetry data used to construct seasonal habitat suitability curves revealed that subadult (fish that emigrated from natal streams to the river system) bull trout move to shallow, low‐velocity shoreline areas at night, which are most sensitive to flow fluctuations. Habitat time series analyses comparing the natural flow regimen (predam, 1929–1952) with five postdam flow management strategies (1953–2008) show that the natural flow conditions optimize the critical bull trout habitats and that the current strategy best resembles the natural flow conditions of all postdam periods. Late summer flow augmentation for anadromous fish recovery, however, produces higher discharges than predam conditions, which reduces the availability of usable habitat during this critical growing season. Our results suggest that past flow management policies that created sporadic streamflow fluctuations were likely detrimental to resident salmonids and that natural flow management strategies will likely improve the chances of protecting key ecosystem processes and help to maintain and restore threatened bull trout and westslope cutthroat trout populations in the upper Columbia River Basin. Copyright © 2011 John Wiley & Sons, Ltd.

Bull trout (Salvelinus confluentus) movement in a transboundary river

The bull trout (Salvelinus confluentus) is listed as a threatened species and is native to the Kootenai River, Idaho and Montana, USA, and British Columbia (BC), Canada. Little is known about its life history and movements downstream of Kootenai Falls, Montana. Between 1998 and 2006, 19 bull trout were monitored in the Kootenai River with radio and sonic transmitters. Two bull trout life history patterns were found; 16 bull trout were likely fluvial, and two were adfluvial. Evidence of spawning was found for only about 33% of the bull trout tracked; of those, 50% were annual spawners and 50% alternate-year spawners. Temperature of the Kootenai River during spawning migration of six bull trout that made spawning migrations ranged from 7.1°C to 15.0°C and averaged 11.4°C. Telemetry data indicated nine bull trout concentrated below Kootenai Falls during the spawning season, but it is not known if they spawned. Two tagged bull trout were located in Kootenay Lake, BC. One fish returned to the river and moved a total of 228 km from Kootenay Lake through Idaho and to Kootenai Falls. Bull trout also used several tributary streams outside of the spawning season, possibly as a thermal refuge.

Influence of Fire on Native and Nonnative Salmonid Populations and Habitat in a Western Montana Basin

AbstractAnticipated increases in the frequency and severity of wildfire may threaten the persistence of native salmonid populations in headwater streams in western North America. This study used extensive pre‐ and postfire data to assess whether wildfire leads to hypothesized declines in native westslope cutthroat troutOncorhynchus clarkii lewisiand bull troutSalvelinus confluentuspopulations along with increases in the prevalence and abundance of nonnative brook troutS. fontinalis. Postfire cutthroat trout density was negatively correlated with the proportion of basin area that burned at moderate to high severity, but the declines in density after fires were less pronounced for bull trout and brook trout. Recovery of cutthroat trout was generally rapid in severely affected reaches. Contrary to expectation, there was no evidence of a marked increase in abundance or invasion by brook trout after wildfire. Brook trout exhibited the most severe declines in debris flow–affected reaches among all species and exhibited less recovery in severely burned reaches than did cutthroat trout. Increased stream temperature was the most significant habitat change that followed wildfire, the mean maximum water temperature during summer months increasing by 2–6°C in severely burned reaches. In contrast, burned area percentage was unrelated to large woody debris density, the percentage of surface fines, substrate diversity, or the percentage of pool habitat. The characteristically high variability in fish and habitat responses to wildfire will continue to pose a challenge for the understanding and management of fire in aquatic ecosystems.

Assessing the Feasibility of Native Fish Reintroductions: A Framework Applied to Threatened Bull Trout

AbstractTranslocations to recover native fishes have resulted in mixed success. One reason for the failure of these actions is inadequate assessments of their feasibility prior to implementation. Here, we provide a framework developed to assess the feasibility of one type of translocation—reintroduction. The framework was founded on two simple components of feasibility: the potential for recipient habitats to support a reintroduction and the potential of available donor populations to support a reintroduction. Within each component, we developed a series of key questions. The final assessment was based on a scoring system that incorporated consideration of uncertainty in available information. The result was a simple yet transparent system for assessing reintroduction feasibility that can be rapidly applied in practice. We applied this assessment framework to the potential reintroduction of threatened bull trout Salvelinus confluentus into the Clackamas River, Oregon. In this case, the assessment suggested that the degree of feasibility for reintroduction was high based on the potential of recipient habitats and available donor populations. The assessment did not provide a comprehensive treatment of all possible factors that would drive an actual decision to implement a reintroduction, but it did provide a fundamental level of feasibility assessment that is often lacking in practice.Received May 28, 2010; accepted December 22, 2010

Marine Habitat Use by Anadromous Bull Trout from the Skagit River, Washington

AbstractAcoustic telemetry was used to describe fish positions and marine habitat use by tagged bull trout Salvelinus confluentus from the Skagit River, Washington. In March and April 2006, 20 fish were captured and tagged in the lower Skagit River, while 15 fish from the Swinomish Channel were tagged during May and June. Sixteen fish tagged in 2004 and 2005 were also detected during the study. Fish entered Skagit Bay from March to May and returned to the river from May to August. The saltwater residency for the 13 fish detected during the out‐migration and return migration ranged from 36 to 133 d (mean ± SD, 75 ± 22 d). Most bull trout were detected less than 14 km (8.5 ± 4.4 km) from the Skagit River, and several bay residents used the Swinomish Channel while migrating. The bull trout detected in the bay were associated with the shoreline (distance from shore, 0.32 ± 0.27 km) and occupied shallow‐water habitats (mean water column depth, <4.0 m). The modified‐minimum convex polygons (MMCPs) used to describe the habitats used by 14 bay fish showed that most areas were less than 1,000 ha. The mean length of the shoreline bordering the MMCPs was 2.8 km (range, 0.01–5.7 km) for bay fish and 0.6 km for 2 channel residents. Coastal deposits, low banks, and sediment bluffs were common shoreline classes found within the MMCPs of bay fish, while modified shoreline classes usually included concrete bulkheads and riprap. Mixed fines, mixed coarse sediments, and sand were common substrate classes found within MMCPs; green algae and eelgrass (Zostera sp.) vegetation classes made up more than 70% of the area used by bull trout. Our results will help managers identify specific nearshore areas that may require further protection to sustain the unique anadromous life history of bull trout.Received October 25, 2010; accepted May 5, 2011

Role of climate and invasive species in structuring trout distributions in the interior Columbia River Basin, USA

Recent and projected climate warming trends have prompted interest in impacts on coldwater fishes. We examined the role of climate (temperature and flow regime) relative to geomorphology and land use in determining the observed distributions of three trout species in the interior Columbia River Basin, USA. We considered two native species, cutthroat trout ( Oncorhynchus clarkii ) and bull trout ( Salvelinus confluentus ), as well as nonnative brook trout ( Salvelinus fontinalis ). We also examined the response of the native species to the presence of brook trout. Analyses were conducted using multilevel logistic regression applied to a geographically broad database of 4165 fish surveys. The results indicated that bull trout distributions were strongly related to climatic factors, and more weakly related to the presence of brook trout and geomorphic variables. Cutthroat trout distributions were weakly related to climate but strongly related to the presence of brook trout. Brook trout distributions were related to both climate and geomorphic variables, including proximity to unconfined valley bottoms. We conclude that brook trout and bull trout are likely to be adversely affected by climate warming, whereas cutthroat trout may be less sensitive. The results illustrate the importance of considering species interactions and flow regime alongside temperature in understanding climate effects on fish.

Use of cover habitat by bull trout, Salvelinus confluentus, and lake trout, Salvelinus namaycush, in a laboratory environment

Lacustrine-adfluvial bull trout, Salvelinus confluentus, migrate from spawning and rearing streams to lacustrine environments as early as age 0. Within lacustrine environments, cover habitat provides refuge from potential predators and is a resource that is competed for if limiting. Competitive interactions between bull trout and other species could result in bull trout being displaced from cover habitat, and bull trout may lack evolutionary adaptations to compete with introduced species, such as lake trout, Salvelinus namaycush. A laboratory experiment was performed to examine habitat use and interactions for cover by juvenile (i.e., <80 mm total length) bull trout and lake trout. Differences were observed between bull trout and lake trout in the proportion of time using cover (F1,22.6 = 20.08, P < 0.001) and bottom (F1,23.7 = 37.01, P < 0.001) habitat, with bull trout using cover and bottom habitats more than lake trout. Habitat selection ratios indicated that bull trout avoided water column habitat in the presence of lake trout and that lake trout avoided bottom habitat. Intraspecific and interspecific agonistic interactions were infrequent, but approximately 10 times greater for intraspecific interactions between lake trout. Results from this study provide little evidence that juvenile bull trout and lake trout compete for cover, and that species-specific differences in habitat use and selection likely result in habitat partitioning between these species.

Controls for trout and char migratory/resident behaviour mainly in stream systems above and below waterfalls/barriers: a multidecadal and broad geographical review

Northcote TG. Controls for trout and char migratory/resident behaviour mainly in stream systems above and below waterfalls/barriers: a multidecadal and broad geographical review. Ecology of Freshwater Fish 2010: 19: 487–509. © 2010 John Wiley &amp; Sons A/SAbstract – Controls for trout and char migratory and resident behaviour in rivers and streams for above and below natural and man‐made waterfalls/barriers are covered in a multi‐decadal (1950–2000) and wide geographical review (North America, UK, Europe, Japan) that includes reference to over 380 publications. These note 53 for rainbow trout, 61 for cutthroat trout, 104 for brown trout, 47 for bull trout, 41 for brook trout, 35 for Dolly Varden and 42 for white‐spotted char, plus a few general contributions of relevance on some. For each of these species, there has been a major increase in relevant decadal publications since the early 1980s, no doubt in large part because of the upsurge in micro‐genetic methodology for DNA and related technology, coupled with a broadening of interest in stream migratory behaviour of salmonids. Main mechanisms for the control of stream migratory versus resident behaviour appear to cover an interplay among both genetic and environmental factors; in some populations and locations, genetic controls seem to be more important than environmental ones, but in others the reverse. Habitat degradation by various human activities and their introductions of non‐native fish species are becoming causes of reduction in abundance of above and below waterfall stream populations for several of these salmonid species.