Distribution Of Bull Trout Research Articles

Assessing Hybridization Risk Between ESA-Listed Native Bull Trout (Salvelinus confluentus) and Introduced Brook Trout (S. fontinalis) Using Habitat Modeling

The introduction of non-native species can negatively impact native species through reduced genetic fitness resulting from hybridization. The lack of spatiotemporal data on hybrid occurrences makes hybridization risk assessment difficult. Here, we developed a spatially-explicit Hybridization Risk Model (HRM) between native Oregon bull trout, an Endangered Species Act-listed Oregon species, and introduced brook trout by combining an intrinsic potential model (IPM) of brook trout spawning habitat and existing bull trout distribution and habitat use datasets in Oregon, United States. We created an expert-based brook trout IPM classification score (0–1) of streams based on the potential of geophysical attributes (i.e., temperature, discharge, gradient, and valley confinement) to sustain spawning habitats. The HRM included a risk matrix based on the presence/absence of both species as well as the type of habitat (spawning versus other) at 100-m stream segment resolution. We defined the hybridization risk as “extreme” when stream reaches contained bull trout spawning habitat and brook trout were present with IPM moderate or greater scores (IPM >0.5). Conversely, “low” risk reaches contained historic or non-spawning bull trout habitat, brook trout were absent, and IPM scores were low (IPM <0.25). Our HRM classified 34 km of streams with extreme risk of hybridization, 115 km with high risk, 178 km with moderate risk, and 6,023 km with low risk. Our HRM can identify a differential risk of hybridization at multiple spatial scales when either both species coexist in bull trout spawning habitat or are absent. The model can also identify stream reaches that would have higher risk of hybridization, but where brook trout are not currently present. Our modeling approach can be applied to other species, such as cutthroat trout and rainbow trout, Chinook and coho salmon, or similar species occurring elsewhere that potentially hybridize in freshwaters.

Integration of eDNA‐Based Biological Monitoring within the U.S. Geological Survey’s National Streamgage Network

AbstractThis study explores the feasibility and utility of integrating environmental DNA (eDNA) assessments of species occurrences into the United States (U.S.) Geological Survey’s national streamgage network. We used an existing network of five gages in southwest Idaho to explore the type of information that could be gained as well as the associated costs and limitations. Hydrologic technicians were trained in eDNA sampling protocols and they collected samples during routine monthly visits to streamgages over an entire water year (2016). We analyzed the eDNA in the filtered water samples to determine the presence of two fish species: bull trout and rainbow trout. We then modeled the spatiotemporal distribution of each species using discharge and temperature data. To assess the influence of the spatial distribution of the gages on the biological information obtained, we also collected eDNA samples from locations between the gages three times during the water year. We found eDNA monitoring at the five gages provided meaningful information about the distribution of both species, especially when detection probabilities accounted for variations in temperature and discharge. Sampling between the gages provided additional information about bull trout distribution — the rarer of the two species. Our study suggests the integration of eDNA sampling into a streamgage network is feasible and could provide a novel and powerful source of biological information for riverine ecosystems in the U.S.

Electrofishing, Snorkel Spearing, and Piscicide Eradicate Brook Trout From a Small, Isolated Bull Trout Population

Abstract In 1992, a sampling crew from a multiagency group discovered a population of Bull Trout Salvelinus confluentus estimated at approximately 50 individuals in Threemile Creek, Oregon threatened with competition and hybridization with nonnative Brook Trout Salvelinus fontinalis. The group implemented Brook Trout and Bull Trout × Brook Trout hybrid removal using multiple techniques to conserve this population of Bull Trout in the Klamath River basin. From 1996 to 2000, backpack electrofishing and night snorkel spearing were used upstream of a culvert barrier to eradicate Brook Trout and hybrid trout from a 3.59-km section of Threemile Creek over 101 total days of effort (274 person-days of effort). Night snorkel spearing removed a lower percentage (7%) of target fish relative to electrofishing (93%), although this technique eliminated the risk of electrofishing injury to Bull Trout. Concurrent with the reduction and subsequent removal of Brook Trout, Bull Trout observations increased over 15-fold from 19 in 1996 to 299 in 2012 and Bull Trout distribution more than doubled, from 1.48 to 3.43 km during that same time. Immediately downstream in a separate 2.3-km section, the group eradicated Brook Trout using backpack electrofishing and rotenone application upstream of two man-made barriers from 2004 to 2010 over 43 total days of effort (150 person-days of effort). By 2016, Bull Trout had expanded their distribution throughout the upper 3.59-km section of Threemile Creek. Effort expended to eradicate Brook Trout was similar to successful eradication in other streams with comparable habitat characteristics and similar treatment length (< 3.0 km). However, similar removal attempts have not been successful in streams with comparable habitat characteristics that had longer treatment length (> 7.0 km). Application of piscicide may be more cost effective than manual techniques to remove Brook Trout when there is no risk to native fish of conservation concern, where target species are allopatric, and when piscicide use is publicly accepted. Brook Trout eradication proved valuable in providing Bull Trout the opportunity for range expansion and increased abundance necessary for recovery in the Klamath River basin.

Changes in native bull trout and non‐native brook trout distributions in the upper Powder River basin after 20 years, relationships to water temperature and implications of climate change

AbstractMany bull trout populations have declined from non‐native brook trout introductions, habitat changes (e.g. water temperature) and other factors. We systematically sampled the distribution of bull trout and brook trout in the upper Powder River basin in Oregon in the 1990s and resampled it in 2013–2015, examined temperature differences in the habitats of the two species and analysed trends in temperatures in the light of possible increases associated with climate change. The species’ distributions are currently similar to those in the 1990s, except in one stream where bull trout declined. However, bull trout consisting of resident forms remain restricted to a few kilometres of habitat at the upper end of fish distribution. In streams where both species occur, the typical pattern was an intermediate zone of mixed bull trout, brook trout, and hybrids downstream of allopatric bull trout and allopatric brook trout extending farther downstream. Temperature differences between where bull trout and most brook trout occurred were small (0.5–1.0°C August mean). There were no statistical increases in water temperatures in nearby streams since the 1990s and no warming trends in air temperatures for the past 25–60 years. However, peak summer water temperatures are occurring about 3 weeks earlier than 25 years ago. Future effects of climate change, including possible increases in temperature, changes in timing and other factors (e.g. snowpack, flow and extreme events) remain a concern for the persistence of these populations. However, it is difficult to precisely predict where those changes will occur and what they will be.

Spawning and rearing behavior of bull trout in a headwater lake ecosystem

Numerous life histories have been documented for bull trout Salvelinus confluentus. Lacustrine-adfluvial bull trout populations that occupy small, headwater lake ecosystems and migrate short distances to natal tributaries to spawn are likely common; however, much of the research on potamodromous bull trout has focused on describing the spawning and rearing characteristics of bull trout populations that occupy large rivers and lakes and make long distance spawning migrations to natal headwater streams. This study describes the spawning and rearing characteristics of lacustrine-adfluvial bull trout in the Quartz Lake drainage, Glacier National Park, USA, a small headwater lake ecosystem. Many spawning and rearing characteristics of bull trout in the Quartz Lake drainage are similar to potamodromous bull trout that migrate long distances. For example, subadult bull trout distribution was positively associated with slow-water habitat unit types and maximum wetted width, and negatively associated with increased stream gradient. Bull trout spawning also occurred when water temperatures were between 5 and 9 °C, and redds were generally located in stream segments with low stream gradient and abundant gravel and cobble substrates. However, this study also elucidated characteristics of bull trout biology that are not well documented in the literature, but may be relatively widespread and have important implications regarding general characteristics of bull trout ecology, use of available habitat by bull trout, and persistence of lacustrine-adfluvial bull trout in small headwater lake ecosystems.

A Review of Bull Trout Habitat Associations and Exploratory Analyses of Patterns across the Interior Columbia River Basin

AbstractAn understanding of habitat relationships for bull trout Salvelinus confluentus remains an important component for identifying future restoration, management, and recovery efforts. We examined past efforts through a comprehensive synthesis of peer‐reviewed articles evaluating bull trout habitat relationships, and we used field data within classification tree analysis (CTA) to improve our understanding of the consistency of bull trout habitat use patterns. We performed CTA using reach‐level habitat data collected from currently occupied stream networks (i.e., those within the current distribution of bull trout) and unoccupied stream networks where hierarchical filters (i.e., area and temperature) were met and from occupied areas where temperature criteria were exceeded. Results from the literature review demonstrated consistent results at the microhabitat and channel unit scales; indicated the importance of slow‐velocity, deeper habitats; and, together with observed diel shifts, highlighted the importance of complex habitat regardless of scale or season. At the reach scale, however, our results indicated substantially less consistency in bull trout habitat relationships. Including maximum stream temperature into the CTA did not result in changes to the overall structure of the CTA; results from the CTA indicated that bull trout were found in reaches with larger substrate, deeper pools, and more cover, but the specific criteria differed along a gradient of stream depth. Our results indicated (1) important gaps in our knowledge regarding the role of substrate size in juvenile bull trout habitat use, (2) the need for elucidation of habitat use patterns in downstream reaches, which may act as critical overwintering habitat or migratory corridors, and (3) the need to incorporate sampling efficiencies in future bull trout habitat evaluations.

Distribution, Abundance, and Population Trends of Bull Trout in Idaho

AbstractBroad‐scale declines in populations of bull trout Salvelinus confluentus over the past century or more led the Idaho Department of Fish and Game to implement statewide no‐harvest regulations on bull trout in 1994 and ultimately led to a threatened listing under the U.S. Endangered Species Act in 1998. Despite this listing, quantitative evaluations of trends in abundance and estimates of population size over most of the species' historical range have not been made. We evaluated bull trout distribution, abundance, and trends in abundance using stratified sampling extrapolations of fish surveys (snorkeling and electrofishing) conducted at 2,521 survey sites (most distributed nonrandomly) across 77,447 km of stream. Bull trout were captured at 887 (35%) of the sites. Within the 262 local populations designated by the U.S. Fish and Wildlife Service within seven Idaho recovery units, the number of 70‐mm total length and larger bull trout was estimated at 1.13 million; this estimate was most likely biased low due to sampling limitations. Long‐term (>20 years) intrinsic rates of change (r) were negative for 10 of 16 bull trout populations up to 1994 (3 were significantly negative; 1 was significantly positive) and were positive for 14 of 17 populations after 1994 (1 was significantly negative; 5 were significantly positive). Over the entire period of record and all trend data sets, r averaged 0.01 ± 0.01 (mean ± 90% confidence interval), suggesting stability at a broad scale. During these same time periods, trends for other salmonids in much of the study area experienced similar declines through 1994 and increases after 1994, suggesting that environmental factors with influence over large geographical areas produced the recent positive trends. Once bull trout populations were detrended by use of linear regression residuals, there was little evidence of synchrony between populations. Our results suggest that despite declines from historical levels, bull trout in Idaho are presently widely distributed, relatively abundant, and apparently stable.

Influences of Temperature and Environmental Variables on the Distribution of Bull Trout within Streams at the Southern Margin of Its Range

The bull trout Salvelinus confluentus is believed to be among the most thermally sensitive species in coldwater habitats in western North America. We conducted a comprehensive field assessment of thermal habitat associations throughout the southern margin of the species' range. We developed models of thermal habitat associations using two data sets representing a geographically diverse range of sites and sampling methods. In both data sets, maximum temperature was strongly associated with the distribution of bull trout. In spite of the potential biases in these data sets, model predictions were similar. In both cases, the probability of the occurrence of bull trout exceeded 50% when the maximum daily temperature was less than 14-16°C, a result that is consistent with recent laboratory-based thermal tolerances. In one data set, we modeled the association between the distribution of bull trout and environmental variables, including temperature, instream cover, channel form, substrate, and the abundance of native and nonnative salmonid fishes. Only temperature was strongly associated with the distribution of bull trout. Our results and related studies of landscape habitat associations suggest that conservation efforts for bull trout would benefit from a focus on maintaining and restoring large and interconnected coldwater habitats.

Distribution, Status, and Likely Future Trends of Bull Trout within the Columbia River and Klamath River Basins

Abstract We summarized existing knowledge regarding the distribution and status of bull trout Salvelinus confluentus across 4,462 subwatersheds of the interior Columbia River basin in Oregon, Washington, Idaho, Montana, and Nevada and of the Klamath River basin in Oregon, a region that represents about 20% of the species' global range. We used classification trees and the patterns of association between known distributions and landscape characteristics to predict the likely distribution of bull trout in unsampled subwatersheds. Bull trout are more likely to occur and the populations are more likely to be strong in colder, higher-elevation, low- to mid-order watersheds with lower road densities. Our results show that bull trout remain widely distributed and occur in most of the subbasins representing the potential range. Some strong and relatively secure populations exist. In general, bull trout are better represented in the region as a whole than many other native species. Important declines in distributi...

Distribution of Juvenile Bull Trout in a Thermal Gradient of a Plunge Pool in Granite Creek, Idaho

Abstract The distribution of juvenile bull trout Salvelinus confluentus was observed on three nights (0000–0200 hours) during July 24–28, 1992, in a large plunge pool in Granite Creek, a direct tributary to Lake Pend Oreille in northern Idaho. The pool contained a strong side-to-side thermal gradient (8–15°C) created by the confluence of Granite Creek (water temperature 15°C) with Sullivan Springs, a much colder (8°C) stream of comparable discharge. Juvenile bull trout chose the coldest water available (8–9°C). Distribution of bull trout within the plunge pool could not be attributed to differences in water depth, substrate, velocity, overhanging cover, or interactions with other fish.