Bull Trout Salvelinus Confluentus Research Articles

Detecting bias in abundance estimates of spawning fish from closed‐capture models using remote and physical capture data

AbstractObjectiveMixed‐data models incorporating remote antenna detections from PIT‐tagged fish together with physical capture data (mixed data) can improve precision of mark–recapture abundance estimates, particularly for spawning fish. However, if the entire population is not available for physical capture during the mark–recapture sampling period, abundance estimates will be biased low. Our objectives were to examine bias and precision of two modeling approaches and develop a simple diagnostic to determine whether the entire population was sampled.MethodsWe use a simulation modeling approach to compare specified abundances with abundance estimates from closed‐capture models using mixed data (the mixed‐data approach) and using only marked (e.g., PIT‐tagged) individuals divided by the proportion of individuals that are marked (proportional approach). We use the difference in bias between the two models as our diagnostic of whether a population was randomly sampled. We then applied our diagnostic to two case studies: a spawning population of adfluvial June Sucker Chasmistes liorus in Utah Lake, Utah, 2008–2020, and a spawning population of Bull Trout Salvelinus confluentus in the Imnaha River, a tributary of the Snake River, Oregon, 2013–2020.ResultSimulation experiments revealed that the mixed‐data approach became increasingly negatively biased as the proportion of the population that was unavailable for physical capture increased, yet the proportional approach remained unbiased. Abundance estimates from the proportional approach averaged approximately 6× greater for June Sucker and 2× greater for Bull Trout compared to the mixed‐data approach, suggesting a proportion of the population was not available for physical capture in both case studies.ConclusionUnderstanding the magnitude of bias in abundance estimates is particularly important for the management of imperiled species that are subject to recovery plans. Comparing estimates using the unbiased proportional approach that we described here with those from a mixed‐data approach when PIT tag detection data are used to estimate abundance is a straightforward method to evaluate bias in these estimates.

Evaluating streamflow and temperature effects on Bull Trout migration and survival with linear spatial capture–recapture models

AbstractObjectiveIn the U.S. Pacific Northwest, climate change is increasing air temperatures, decreasing warm season (April–September) streamflow, and increasing cool season (October–March) streamflow. Warmer water temperatures may alter conditions for migratory coldwater fishes like the Bull Trout Salvelinus confluentus. Consequently, an understanding of Bull Trout migration and survival is critical for species conservation and restoration. In the Salmon River basin, Idaho, 1992 and 1993 transpired to be two of the most opposing extreme years among the past three decades for warm season water temperature and streamflow. These extremes provided a unique opportunity to retrospectively compare Bull Trout survival and migration under potential climate change scenarios.MethodsWe evaluated prespawning and postspawning migrations and survival of fluvial Bull Trout that were radio‐tagged and tracked from 1992 to 1994. We used a Cormack–Jolly–Seber linear spatial capture–recapture model to simultaneously model the migration and survival of radio‐tagged prespawn (n = 58) and postspawn (n = 23) Bull Trout among weeks and river reaches with streamflow, water temperature, and habitat covariates.ResultMost individual prespawning migrations were similar among tagged fish, whereas postspawn fish adopted multiple migration and overwintering strategies. Movements of prespawn Bull Trout were larger when (1) weekly average daily maximum streamflow increased and (2) weekly average daily maximum water temperature increased. The model estimated that at least 52% of spawners survived to spawning, and mean weekly prespawning apparent survival was higher in the low‐streamflow year (1992) than in the year with higher and more variable streamflow (1993). Survival of 1992–1994 fish during the 38‐week postspawning period was intermediate to that in the prespawning period. Detections of prespawn Bull Trout were generally higher at sites with more complex habitats, less large woody debris, and fewer undercut banks.ConclusionWe found that the prespawn life stage can represent a shorter time frame (14–18 weeks) with increased mortality compared to the longer postspawning period (38 weeks). Bull Trout apparent survival increased with lower streamflow variability, indicating that expected future changes in climate may adversely affect Bull Trout.

Establishment of Bull Trout in a previously fishless subalpine lake by translocation

AbstractObjectiveTranslocations have increased in recent years to aid in species recovery efforts. This includes translocations outside of species' historical distribution, where threats are less severe. One candidate species for translocation is the Bull Trout Salvelinus confluentus, but few examples of successful translocations (re‐establishment or range expansion) have been documented. Here, we describe an example in which 63 Bull Trout were translocated in 1987 to establish a population in fishless Marie Lake, Alberta.MethodsThe translocation was monitored through multiple sampling events over the course of 33 years. Sampling techniques included backpack electrofishing, angling, and water quality and habitat assessments.ResultA population estimate suggested that Bull Trout increased by at least fourfold over the first 12 years; fish reached large sizes (692 mm fork length) and old ages (13 years), and the population had multiple age‐ and length‐classes, including juveniles. Bull Trout also had become established within at least 13 km of river outside of Marie Lake by 2019.ConclusionAlthough a naturally reproducing population of this at‐risk species was established, numerous factors were not considered within this translocation initiative. Most importantly, nonadfluvial Bull Trout from a disparate source population located about 4000 river kilometers away were used for the translocation. Our case study represents a rare example of a successful Bull Trout translocation and highlights considerations that should occur prior to future translocations that are intended to aid in species recovery and preservation.

Reach‐scale associations between introduced Brook Trout and juvenile and stream‐resident Bull Trout in Idaho

AbstractObjectiveNative Bull Trout Salvelinus confluentus populations can be influenced by a variety of stressors operating at multiple spatial scales, making the relative importance of biotic versus abiotic controls difficult to discern at small scales where monitoring and management typically occur. Nonnative Brook Trout S. fontinalis were widely introduced throughout western North America and negatively affect Bull Trout occurrence. Here, we examine reach‐scale associations between nonnative Brook Trout and juvenile and stream‐resident Bull Trout (i.e., <250 mm) abundances through the lens of a constraining threshold, where nonnative fish exceeding a certain fish density may constrain native fish abundance.MethodsWe used a large spatial data set to define the abiotic conditions in which stream‐dwelling Brook Trout and Bull Trout smaller than 250 mm typically co‐occur in Idaho. Next, we queried multipass electrofishing survey data collected in reaches with abiotic conditions suitable for both species within localized areas where their distributions overlap. We then used two‐dimensional Kolmogorov–Smirnov tests to identify threshold Brook Trout densities beyond which Bull Trout less than 250 mm were consistently rare or absent.ResultBull Trout smaller than 250 mm were rare or absent where Brook Trout density exceeded 0.54 fish/100 m2 across the full range of abiotic conditions over which both species overlapped. However, Brook Trout rarely occurred in habitats associated with high Bull Trout density (e.g., where mean August water temperatures were 8.2°C).ConclusionOur results support existing hypotheses that the long‐term co‐occurrence of Bull Trout and Brook Trout in stream reaches suitable for both species may be unstable. Because low densities of Brook Trout appear to threaten Bull Trout, additional research is needed to better understand factors driving ongoing range shifts and invasion dynamics in Bull Trout habitat. We provide a simple tool to inform where Brook Trout represent a primary threat to Bull Trout, with potential applications for future monitoring, threat assessments, and conservation efforts.

Engaging Stakeholders to Develop a Decision Support Model of Conservation Risk and Management Capacity to Prioritize Investments in Bull Trout Recovery

AbstractRarely are sufficient resources available to support the full suite of management actions to promote recovery of a species across its entire distribution. Decision support models are a tool that can inform natural resource management decisions with consideration of the perspectives from a variety of stakeholders who work across large geographic and jurisdictional extents. We offer an example of a decision support model that was developed by several federal and state natural resource agencies to rank Bull Trout Salvelinus confluentus core areas for prioritizing conservation investment within Oregon, USA. We engaged state‐level decision makers to identify parameters that were believed to be influential in determining funding allocations for Bull Trout core areas. Parameters were linked in a model framework that was further refined with input from local Bull Trout experts with knowledge specific to the various core areas. The model produces a relative priority value that is a combination of the conservation risk to the species and the management capacity to address threats. A series of sensitivity analyses suggested that Bull Trout persistence and threat score were most influential in determining the relative priority of a core area, whereas life history and genetic diversity were least influential. One of the more powerful products from this work is an interactive Web‐based application (https://das.ecosphere.fws.gov/public/obts/) that anyone can use to explore how their beliefs in parameter values will affect the relative priority of Bull Trout core areas across Oregon. Our modeling effort is an example of engaging stakeholders with different roles in species recovery and across a large geographic area to create a clearer path forward in allocating limited resources for species recovery. This approach can be employed to address a number of natural resource management situations across species and habitats.

Combining expert knowledge of a threatened trout distribution with sparse occupancy data for climate‐related projection

AbstractObjectiveTo evaluate the vulnerability of Bull Trout Salvelinus confluentus to potential climate changes across its range in Oregon, we compiled disparate expert knowledge of the distribution of spawning and rearing and combined these probabilistic statements as data along with documented records of breeding and rearing in a joint occupancy model.MethodsThe joint expert knowledge–occupancy model, which was based on discrete patches of cold water (≤13°C) suitable for spawning and rearing, permitted the association of true occupancy with climate and other explanatory variables while accounting for variation in detection probability. We then applied estimated relationships of patch occupancy with explanatory variables to projected coldwater patch configurations in the years 2040 and 2080.ResultProjections of the kilometers of occupied coldwater patch in future decades suggest precipitous declines if current relationships of occupancy with environmental variables are maintained. Impacts of climate changes in future decades manifest directly through the outright loss of coldwater patches and increases in winter high flows but also indirectly by increased isolation.ConclusionCombining probabilistic statements of species distributions from knowledgeable experts with sparse occupancy data may be a robust and timely alternative when large numbers of repeated occupancy surveys are infeasible.

Individual Characteristics and Abiotic Factors Influence Out-Migration Dynamics of Juvenile Bull Trout

Fragmentation of rivers through anthropogenic modifications poses an imminent threat to the persistence of migratory fish, necessitating direct actions such as trap-and-haul programs to restore and conserve the migratory life-history component in populations of partially migratory species such as bull trout Salvelinus confluentus. We used a PIT-tag system to assess how biological and abiotic factors influence the out-migration dynamics of juvenile bull trout in Graves Creek, Montana, USA. The largest fish within a cohort were more likely to out-migrate at age 1 when compared to smaller fish within the cohort, and this was particularly evident in a high-density year-class (2018), where large bull trout out-migrated an average of 115 days earlier than bull trout in the medium size category, and 181 days earlier than bull trout in the small size category. Relative changes in abiotic factors, including discharge, water temperature, and photoperiod, appeared to act as cues to out-migration, with the direction of change varying by season. These results highlight the complex interplay between individual characteristics, population dynamics, and environmental conditions, which influence out-migration dynamics and can be used to inform management actions to conserve the migratory component in bull trout populations.

Acoustic Imaging Observes Predator–Prey Interactions between Bull Trout and Migrating Sockeye Salmon Smolts

AbstractAnnual migrations by juvenile Pacific salmon Oncorhynchus spp. smolts are predictable, presenting opportunities for predators to exploit these seasonal prey pulses. Directly observing predator–prey interactions to understand factors affecting predation may be possible via dual‐frequency identification sonar (DIDSON) acoustic imaging. Within Chilko Lake, British Columbia, prior telemetry and stomach content analyses suggested that the out‐migration of Sockeye Salmon Oncorhynchus nerka smolts influences the movements and aggregations of Bull Trout Salvelinus confluentus that feed extensively on smolts during their out‐migration. Bull Trout captured at a government‐installed counting fence exhibited high consumption of smolts, but it is only assumed that feeding occurred directly at the fence. We used DIDSON to assess fine‐scale predator–prey interactions between Sockeye Salmon smolts and Bull Trout over 10 d during the 2016 smolt out‐migration. We found that smolt–Bull Trout interactions were correlated with smolt densities at the counting fence, consistent with the prior diet studies in the system. Predator–prey interactions were also coupled with nocturnal migratory behaviors of Sockeye Salmon smolts, presumably to minimize predation risk. These results demonstrate that DIDSON technology can record interactions between predators and migrating prey at a resolution that can identify variability in space and time and provide insight on the role of anthropogenic structures (e.g., counting fences) in mediating such interactions.

Inferred Trophic Characteristics and Ecological Roles of Native and Nonnative Fishes in Odell Lake, Oregon

AbstractIntroduction and establishment of nonnative fishes can negatively affect native species and ecosystems through a variety of ecological interactions. For example, competition between species that occupy a similar trophic guild can result in extirpation or reduced abundance of native fishes. We used a combination of standard sampling methods and stable isotope analysis to evaluate relative abundance and isotopic niche overlap among native and nonnative species in Odell Lake, Oregon. Our primary focus was on interactions between native Bull Trout Salvelinus confluentus and nonnative Lake Trout Salvelinus namaycush; however, we also evaluated relative abundance and isotopic niche characteristics of other native and nonnative species. Overall, the relative abundance of nonnative fishes was greater than that of native fishes. For example, Lake Trout outnumbered Bull Trout 27:1, and the numerically most dominant species in our sample was nonnative Tui Chub Siphateles bicolor. We also observed isotopic niche overlap among a variety of native and nonnative fishes. Bull Trout and Lake Trout are both top‐level predators in Odell Lake and the probability that Bull Trout were within the isotopic niche of Lake Trout was 0.23. The probability that nonnative kokanee Oncorhynchus nerka and Tui Chub were within the isotopic niche of native Mountain Whitefish Prosopium williamsoni exceeded 0.95, and the probability that Tui Chub were within the isotopic niche of Rainbow Trout O. mykiss was 0.90. Based on data presented here and rangewide patterns for Bull Trout, we conclude that competition with Lake Trout is plausible and has the potential to influence the persistence of Bull Trout in Odell Lake. Further, we discuss ecological interactions potentially influencing the abundance of other native fishes in Odell Lake.

Temporal Variation in Capture Efficiency Underrepresents Spring Out‐Migrating Bull Trout in a Trap‐and‐Haul Program

AbstractTrap‐and‐haul programs can maintain connection among habitats for migratory salmonids in fragmented systems. To conserve diversity within and among life history strategies, downstream trap and transport of juvenile salmonids could ideally mimic the natural, underlying out‐migration dynamics of the population. A two‐way trap‐and‐haul program is implemented in the lower Clark Fork River, Montana, to conserve adfluvial Bull Trout Salvelinus confluentus. We used PIT technology to assess whether downstream trapping efforts are effectively capturing variation in the out‐migration dynamics of juvenile Bull Trout in Graves Creek, a key spawning and rearing tributary in the system. We tagged 821 juvenile Bull Trout in Graves Creek and used these tagged Bull Trout in conjunction with stationary PIT antennas to monitor out‐migration and evaluate efficiency of the downstream trapping program. Capture efficiency in Graves Creek varied substantially from autumn to spring, with 89–96% of autumn out‐migrating Bull Trout captured and 5–10% of spring out‐migrating Bull Trout captured. Overall, we found that Bull Trout transported during the autumn out‐migration periods generally reflect the natural out‐migration dynamics of the population; however, Bull Trout that out‐migrate in the spring are currently underrepresented in the downstream transport program. By understanding the underlying out‐migration dynamics of the Bull Trout population in Graves Creek, management of the downstream trapping efforts can focus on minimizing potential selection for or against out‐migrants based on timing and age at out‐migration. Minimizing selection will conserve variation within the adfluvial life history strategy and therefore maximize resilience of the adfluvial Bull Trout populations.

Developing a Standardized Single Nucleotide Polymorphism Panel for Rangewide Genetic Monitoring of Bull Trout

AbstractConservation of threatened and endangered species often involves large‐scale collaboration across jurisdictional boundaries, but such efforts are typically hampered by a lack of consistent monitoring data at local, regional, and species‐distributional scales. Contemporary methods of genetic monitoring that are grounded in sequencing‐based approaches offer a powerful means to achieve the data consistency necessary for conservation of high‐profile species. Here, we describe the collaborative, multiagency development of a genotyping‐in‐thousands by sequencing panel for genetic monitoring of threatened Bull Trout Salvelinus confluentus across its range in North America. The resulting panel consists of 266 single nucleotide polymorphisms, a subset of which differentiate Salvelinus species (Arctic Char S. alpinus, Brook Trout S. fontinalis, Bull Trout, Dolly Varden S. malma, Lake Trout S. namaycush, and Whitespotted Char S. leucomaenis), as well as one sex ID locus. We then used case studies from the Pacific Northwest and northern Rocky Mountains to demonstrate the efficacy of the panel for addressing local conservation needs (e.g., genetic variation, genetic differentiation, genetic assignment tests, and number of effective breeders) and compatibility with legacy data sets. Future genotyping with this panel will provide opportunities for improved conservation prioritization across the species range and collaboration among the numerous agencies charged with conserving this species. This effort provides framework to develop population genetic tools that will contribute to robust and efficient monitoring of biodiversity.

Population Dynamics and Temporal Trends of Bull Trout in the East Fork Salmon River, Idaho

AbstractBecause of their long‐term listing under the Endangered Species Act, much interest has been placed on estimating population vital rates for Bull Trout Salvelinus confluentus, but the biotic and abiotic factors that influence the interannual variability in those vital rates have rarely been evaluated. We used mark–recapture data to estimate fish growth, survival, and trends in abundance for fluvial adult Bull Trout in the East Fork Salmon River, Idaho. Over an 8‐year period, a total of 1,205 individual Bull Trout were collected at a weir on the East Fork Salmon River (29 km upstream of its confluence with the Salmon River) during June–September, of which 420 were recaptures from prior years. Bull Trout varied in length from 215 to 756 mm and achieved a slightly larger asymptotic length and a slightly lower rate of growth relative to other fluvial and adfluvial Bull Trout populations. Apparent survival averaged 0.42 across all years, which was similar to previous studies estimating apparent survival for Bull Trout. The number of emigrating anadromous salmonid smolts in the upper Salmon River basin positively influenced East Fork Salmon River Bull Trout growth and survival, and survival was higher in years with lower annual discharge. Assessment of population growth via linear regression analysis indicated that the Bull Trout population was increasing during the study period (λ = 1.08; 95% confidence interval = 1.03–1.14). Our findings highlight the ecological link between the abundance of wild and hatchery Chinook Salmon Oncorhynchus tshawytscha, Sockeye Salmon O. nerka, and steelhead O. mykiss smolts and growth and survival of adult Bull Trout in systems where these species occur in sympatry.

Concealment of juvenile bull trout in response to temperature, light, and substrate: Implications for detection.

Bull trout (Salvelinus confluentus) are challenging to detect as a result of the species cryptic behavior and coloration, relatively low densities in complex habitats, and affinity for cold, high clarity, low conductivity waters. Bull trout are also closely associated with the stream bed, frequently conceal in substrate, and this concealment behavior is poorly understood. Consequently, population assessments are problematic and biologists and managers often lack quantitative information to accurately describe bull trout distributions, estimate abundance, and assess status and trends; particularly for stream-dwelling populations. During controlled laboratory trials, we recorded concealment, resting, and swimming behavior of juvenile wild bull trout in response to: (1) constant and fluctuating water temperature, (2) presence or absence of light, and (3) substrate size. Light level had the strongest influence on wild fish concealment and more fish concealed as light levels increased from darkness to daylight. Wild fish were 14.5 times less likely to conceal in constant darkness and 4.1 times more likely to conceal in 12 h light x 12 h darkness compared to constant light. Wild fish were 6.2 times less likely to conceal in small (26–51 mm) substrate compared to larger (52–102 mm) substrate. As water temperature increased, fewer wild fish concealed. Knowledge of wild bull trout concealment will improve field sampling protocols and increase detection efficiencies. These data also enhance knowledge of bull trout niche requirements which illuminates ecological differences among species and informs conservation and restoration efforts.

Decision Analysis for the Reintroduction of Bull Trout into the Lower Pend Oreille River, Washington

AbstractThe decision to reintroduce a species can be difficult owing to conflicting opinions and objectives as well as uncertainty over the outcome. Structured decision making addresses these considerations by identifying realistic fundamental objectives and building achievable management alternatives within a quantitative modeling framework. The process is driven by participation of stakeholders that represent diverse objectives, policy mandates, and opinions regarding decision alternatives. We applied structured decision making to evaluate the reintroduction of Bull Trout Salvelinus confluentus into the lower Pend Oreille River in northeastern Washington State. We engaged stakeholders from tribal, municipal, county, state, and federal agencies to specify fundamental objectives, formulate feasible reintroduction decisions, and conceptualize a modeling framework that included biological information and stakeholder assumptions. Stakeholders requested iterative decision sets to determine the optimal recipient streams and release strategies. The optimal decision—based on the fundamental objective of maximizing adult abundance at year 10—was artificial propagation of 4,500 juvenile Bull Trout coupled with translocation of 25 adult migrants to be reintroduced into a tributary and lake system (Sullivan Lake/Harvey Creek) that produced at least 18% more adult fish relative to alternatives. Sensitivity analyses were robust to the identity of the recipient stream (i.e., Sullivan Lake/Harvey Creek was always the optimal recipient stream) but suggested that maximizing the number of artificially produced juveniles released could generate a similar number of adult Bull Trout as the coupled‐release strategy. Results also suggested that ensuring fish passage at Albeni Falls Dam on the main‐stem Pend Oreille River could increase the abundance of adult fish. The process followed for this case study can be adapted to similar decisions regarding reintroduction or other translocations of fish in other systems.

New Insights into the Ecology of Adfluvial Bull Trout and the Population Response to the Endangered Species Act in the North Fork Lewis River, Washington

AbstractLike many other salmonids, Bull Trout Salvelinus confluentus migratory life history expressions are becoming increasingly rare. A critical step in effectively refining management and conservation strategies is a robust assessment of the effectiveness of such strategies and key biological information used in monitoring and recovery planning. To address this need, we integrated long‐term monitoring data to evaluate how the demographics (abundance) and vital rates (survival) of a Bull Trout population shifted in response to their listing under the Endangered Species Act (1998). In addition, we employed mark–recapture data to investigate Bull Trout population dynamics and assessed the life history characteristics (aging, growth, spawning migrations, and iteroparity) to improve our understanding of Bull Trout ecology and diversity. Our abundance and survival data, which extends to the early 1990s, illustrated positive responses in survival and abundance following the protection of Bull Trout under the Endangered Species Act. Over this period, we found high interannual variability in both survival and abundance, and adult survival (average = 0.45; SE = 0.04) was surprisingly lower than that of subadult individuals (average = 0.66; SE = 0.04), suggesting limitations at this important life stage. Our mark–recapture data also suggested that the attributes driving the Bull Trout population trend (i.e., recruitment to the adult stage or adult survival) has varied through time, with declining trends in the relative contribution of recruitment. Bull Trout spawning migrations varied with body size, and a considerable portion of smaller adults (<650 mm) did not spawn each year. Additionally, most spawning individuals made only one spawning migration, while <13% made three or more spawning migrations. Our results provide important insights into the effectiveness of the Endangered Species Act listing and new information regarding the life history patterns of adfluvial Bull Trout and can serve as a template to consider factors potentially limiting this and other native salmonid populations.

Utilizing environmental DNA for fish eradication effectiveness monitoring in streams

Introductions of non-native fish have the potential to cause substantial economic and ecological losses. In the western United States, non-native brook trout (Salvelinus fontinalis) are widely established and pose a threat to the persistence of bull trout (Salvelinus confluentus), a native char listed as threatened under the US Endangered Species Act, due to competition and hybridization. With brook trout identified as a factor limiting the recovery of ESA-listed bull trout in the Malheur Watershed of eastern Oregon, managers are pursuing brook trout eradication efforts. Key to the eradication efforts is reliable monitoring to ensure success. Traditional monitoring practices have included mechanical sampling methods such as seining, netting, and electrofishing, all of which are labor intensive and limited in reliability. Environmental DNA (eDNA) is genetic material naturally shed by organisms that can be found in bulk environmental samples without isolating individual organisms. Sampling for eDNA can often be done with less time and expense than traditional methods, making it ideal for effectiveness monitoring following fish eradication efforts. This study placed a single fish in a live-car where the species was not otherwise present and used eDNA sampling to infer the likelihood of detection downstream. Results suggest that a single fish can be detected reliably up to 500 m downstream when multiple samples are taken. This eDNA sampling method provides managers with the ability to conduct eradication effectiveness monitoring reliably and rapidly and may also be used to detect new fish invasions as well as rare or cryptic species.

Rapid Recolonization and Life History Responses of Bull Trout Following Dam Removal in Washington's Elwha River

AbstractConnected river systems confer advantages upon migratory salmonids by facilitating greater life history expression and, ultimately, population persistence. In Washington's Elwha River, two impassable, century‐old hydroelectric dams were removed in the world's largest dam removal project. Dam removal restored access to 130 km of habitat and reconnected headwater, estuarine, and marine areas. We used multi‐year radiotelemetry data to characterize migratory patterns of federally threatened Bull Trout Salvelinus confluentus after dam removal. Bull Trout rapidly responded to barrier removal and were the first among the Pacific salmonids to move into the newly accessible headwaters. Spatial extent and mean distance traveled upriver increased annually, and adults reached the headwaters (64 km) within 3 years of dam removal. Telemetry data revealed that Bull Trout migrated between the river and its estuary (up to 168 km), and spawning migrations occurred in consecutive years. Relocations of Bull Trout in the tidal zone and the presence of bright, silvery colored adults were indicative of marine residence. Length at age of Bull Trout significantly increased after dam removal, and fish captured before and after dam removal were larger at similar ages in comparison with migratory populations throughout their range. We described the diet of Bull Trout captured in the river and estuary after dam removal. Bull Trout primarily consumed Pacific salmonids Oncorhynchus spp., Threespine Sticklebacks Gasterosteus aculeatus, and sculpins Cottus spp., and the prevalence of sculpins in their diet decreased from the estuary to upstream areas. As the length of Bull Trout increased, they progressively consumed larger prey items. In this historic dam removal project, Bull Trout were early and rapid recolonizers and displayed migrations throughout the reconnected river and its estuary. This study is among the first to evaluate Bull Trout responses to dam removal and establishes a baseline to assess future recovery of this threatened species in the Elwha River.

Structured Decision-Making Incorporates Stakeholder Values into Management Decisions Thereby Fulfilling Moral and Legal Obligations to Conserve Species

AbstractMore than 1,500 species of plants and animals in the United States are listed as threatened or endangered under the Endangered Species Act and habitat destruction is the leading cause of population decline. However, developing conservation plans that are consistent with a diversity of stakeholder (e.g., states, tribes, private landowners) values is difficult. Adaptive management and structured decision-making are frameworks that resource managers can use to integrate diverse and conflicting stakeholder value systems into species recovery planning. Within this framework difficult decisions are deconstructed into the three basic components: explicit, quantifiable objectives that represent stakeholder values; mathematical models used to predict the effect of management decisions on the outcome of objectives; and management alternatives or actions. We use Bull Trout Salvelinus confluentus, a species listed in 1999 as threatened pursuant to the Endangered Species Act, as an example of how structured decision-making transparently incorporates stakeholder values and biological information into conservation planning and the decision process. Three moral philosophies—consequentialism, deontology, and virtue theory—suggest that structured decision-making is a justified method that can guide natural resource decisions in the future, consistent with United States Congress' mandate, and will honor society's obligation to recover Endangered Species Act listed species and their habitats. Natural sciences offer a biological basis for predicting the outcomes of decisions. Additionally, an understanding of how to integrate humanities into scientifically defensible conservation planning is helpful in providing the foundation for lasting and effective species conservation.

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.

Comparing inferences derived from microsatellite and RADseq datasets: a case study involving threatened bull trout

Technological advancements have allowed geneticists to exploit an increasing array of molecular markers, many of which have different properties and may provide contrasting insights into the evolutionary history and structure of populations. This has important consequences for conservation managers attempting to identify units at which to conserve intraspecific diversity. In this study we compared the inferences derived from nuclear microsatellites and restriction-site associated DNA (RADseq) data for a threatened freshwater fish, the bull trout Salvelinus confluentus. For both marker types we generated data for the same suite of individuals collected from 24 populations distributed across the species range. The RADseq data were low coverage (mean site coverage < 3X), so we implemented a probabilistic genotyping approach. We performed a comparable suite of analyses for both datasets. Both datasets revealed similar broad patterns of subdivision that reflected primary evolutionary lineages (Coastal and Interior clades). However, the RADseq more clearly and consistently identified the hierarchical phylogenetic structure. Some populations had varying assignments to these lineages depending on the dataset. RADseq data also suggested admixture has shaped the genomic character of several populations. Such a signal was not apparent with the microsatellites, suggesting that the datasets are revealing different aspects of population history. Our study provides a valuable case study in how advances in molecular technology can enhance our understanding of a relatively well-studied species. It also underscores the importance of framing findings generated with high-throughput sequencing technology within the context of past research to enhance conservation decision making.