Environmental DNA sampling (eDNA) has emerged as a powerful tool for detecting aquatic animals. Previous research suggests that eDNA methods are substantially more sensitive than traditional ...sampling. However, the factors influencing eDNA detection and the resulting sampling costs are still not well understood. Here we use multiple experiments to derive independent estimates of eDNA production rates and downstream persistence from brook trout (Salvelinus fontinalis) in streams. We use these estimates to parameterize models comparing the false negative detection rates of eDNA sampling and traditional backpack electrofishing. We find that using the protocols in this study eDNA had reasonable detection probabilities at extremely low animal densities (e.g., probability of detection 0.18 at densities of one fish per stream kilometer) and very high detection probabilities at population-level densities (e.g., probability of detection >0.99 at densities of ≥3 fish per 100m). This is substantially more sensitive than traditional electrofishing for determining the presence of brook trout and may translate into important cost savings when animals are rare. Our findings are consistent with a growing body of literature showing that eDNA sampling is a powerful tool for the detection of aquatic species, particularly those that are rare and difficult to sample using traditional methods.
•We used multiple experiments and an observational field study to estimate eDNA production rates and its downstream persistence from brook trout in streams•We used our empirical data in models to estimate false negative probabilities for eDNA when animals are rare, and compare these with traditional sampling•We found that eDNA was substantially more sensitive than traditional electrofishing for detecting rare brook trout
Climate change and non-native species are considered two of the biggest threats to native salmonids in North America. We evaluated how non-native salmonids and stream temperature and discharge were ...associated with Yellowstone cutthroat trout (Oncorhynchus clarkii bouvieri) distribution, abundance, and body size to gain a more complete understanding of the existing threats to native populations. Allopatric Yellowstone cutthroat trout were distributed across a wide range of average August temperatures (3.2 to 17.7 °C), but occurrence significantly declined at colder temperatures (<10 °C) with increasing numbers of non-natives. At warmer temperatures, occurrence remained high, despite sympatry with non-natives. Yellowstone cutthroat trout relative abundance was significantly reduced with increasing abundance of non-natives, with the greatest impacts at colder temperatures. Body sizes of large Yellowstone cutthroat trout (90th percentile) significantly increased with warming temperatures and larger stream size, highlighting the importance of access to these more productive stream segments. Considering multiple population-level attributes demonstrates the complexities of how native salmonids (such as Yellowstone cutthroat trout) are likely to be affected by shifting climates.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Compensatory growth—when individuals in poor condition grow rapidly to catch up to conspecifics—may be a mechanism that allows individuals to tolerate stressful environmental conditions, both abiotic ...and biotic. This phenomenon has been documented fairly widely in laboratory and field experiments, but evidence for compensatory growth in the wild is scarce.
Cutthroat trout (Oncorhynchus clarkii subsp.) are cold‐water specialists that inhabit montane streams in western North America where seasonal conditions can be harsh and growth rates vary greatly among seasons. Understanding if individuals compensate for periods of reduced growth and body condition will improve understanding of the requirements of fish throughout their life‐cycle and across freshwater habitats.
We quantified compensatory growth of juvenile cutthroat trout using extensive mark–recapture data from 11 stream populations (1,125 individuals) and two subspecies inhabiting a wide range of ecological settings in the northern Rocky Mountains, U.S.A. Our objectives were to determine how growth was linked across seasons and whether individuals behaviourally compensated for depressed body condition via emigration.
Fish in relatively poor condition consistently demonstrated compensatory growth in mass during subsequent seasons. In contrast, fish in relatively better condition responded with positive growth in length during the summer signalling these fish may be better suited to headwater environments; no compensatory growth in length was found during the winter. Furthermore, there was no evidence that individual condition mediated migration tendencies of fish to seek more favourable habitat.
Across a wide range of environmental conditions, we found consistent empirical support for compensatory growth in mass in the wild. A critical next step is to quantify how changing abiotic and biotic conditions influence the ability of stream fishes to compensate for locally or seasonally challenging conditions, thereby affecting long‐term resiliency, viability, and adaptation in the face of changing environmental conditions.
Hybridization between invasive and native species, a significant threat to worldwide biodiversity, is predicted to increase due to climate‐induced expansions of invasive species. Long‐term research ...and monitoring are crucial for understanding the ecological and evolutionary processes that modulate the effects of invasive species. Using a large, multidecade genetics dataset (N = 582 sites, 12,878 individuals) with high‐resolution climate predictions and extensive stocking records, we evaluate the spatiotemporal dynamics of hybridization between native cutthroat trout and invasive rainbow trout, the world's most widely introduced invasive fish, across the Northern Rocky Mountains of the United States. Historical effects of stocking and contemporary patterns of climatic variation were strongly related to the spread of hybridization across space and time. The probability of occurrence, extent of, and temporal changes in hybridization increased at sites in close proximity to historical stocking locations with greater rainbow trout propagule pressure, warmer water temperatures, and lower spring precipitation. Although locations with warmer water temperatures were more prone to hybridization, cold sites were not protected from invasion; 58% of hybridized sites had cold mean summer water temperatures (<11°C). Despite cessation of stocking over 40 years ago, hybridization increased over time at half (50%) of the locations with long‐term data, the vast majority of which (74%) were initially nonhybridized, emphasizing the chronic, negative impacts of human‐mediated hybridization. These results show that effects of climate change on biodiversity must be analyzed in the context of historical human impacts that set ecological and evolutionary trajectories.
Hybridization between invasive and native species is predicted to increase due to climate‐induced expansions of invasive species. Using a large, multidecade genetics dataset with high‐resolution climate predictions and extensive stocking records, we evaluate the spatiotemporal dynamics of genetic admixture between native cutthroat and invasive rainbow trout across the Northern Rocky Mountains. Hybridization increased at half of the locations with long‐term data and was driven by lingering effects of historical stocking, warmer stream temperatures, and lower spring precipitation, yet cold sites were not protected from invasion. Our results clearly show that effects of climate change on biodiversity must be analyzed in the context of historical human impacts that set ecological and evolutionary trajectories.
Effective fishery management necessitates understanding of resource partitioning by fishes that inhabit complex systems composed of biotic and abiotic features. Evaluations of non‐native species ...introductions have continually demonstrated adverse effects associated with abundance and distribution of native fishes. Therefore, understanding resource selection and interactions between native and non‐native species is important for recovery efforts. Habitat use by two native fish species (largescale sucker Catostomus macrocheilus Girard and mountain whitefish Prosopium williamsoni Girard) and one non‐native fish species (pumpkinseed Lepomis gibbosus Linnaeus) of the Kootenai River, Idaho, were evaluated in a laboratory stream system. Trials were conducted in allopatry and in sympatry with and without the presence of wood to describe habitat selection in the context of on‐going habitat rehabilitation efforts. Interactions were evident between native largescale sucker and non‐native pumpkinseed concerning use of a woody structure and current velocity. Mountain whitefish used low‐velocity habitats and selected locations that were further from wood when in sympatry with pumpkinseed. Our research suggests that habitat use of native, large‐river fishes may be influenced by the presence of a non‐native species, and that considering such interactions is critical when designing and implementing habitat rehabilitation efforts in river ecosystems.
Managing and conserving native taxa are becoming increasingly challenging because of mounting threats and limited resources, predicating the need for frameworks to prioritize conservation actions. We ...integrated attributes of population persistence, genetic status, threats from nonnative species, and threats from climatic shifts to prioritize conservation actions for Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieri. We used the individual attributes to rank populations and provide a framework for identifying the benefits of individual conservation actions. The majority of extant populations (57%) had a high probability (>0.75) of persistence, but nearly 70% of populations were either slightly hybridized or sympatric with nonnative species, and 44% of extant populations occupied habitat with low climatic resilience. Overall, we found that 36% of populations ranked as high (>0.75) conservation priority, and these populations primarily occupied large, relatively high‐elevation habitats. The prioritization framework provides a platform for identifying and ranking actions with the greatest conservation effectiveness.
Fish and microhabitat data were collected at 542 prepositioned electrofishing sites (surface area of each site = 4 m2) in the Kootenai River, Idaho, during 2014 and 2015 to evaluate small‐scale ...habitat use by fishes, as it relates to large‐scale habitat rehabilitation efforts. Samples were collected from a 12‐km braided segment of river that had received localized habitat rehabilitation treatments since 2011. Fish and microhabitat data were collected to investigate habitat drivers related to the occurrence and relative abundance of fishes. Each sampling location was selected at random and characterized as “treated” (i.e., rehabilitated) or “untreated” based on proximity to habitat treatments. Fishes sampled from backwaters composed 71% of the overall catch and 84% of the catch from locally untreated areas of the river. Species‐specific regression models suggested that water depth and current velocity influenced the occurrence and abundance of fishes. In particular, shallow habitats with low current velocities were important for small‐bodied native fishes and likely serve as important rearing areas for juvenile fish. These habitat conditions typically characterize backwater and channel‐margin habitats that are vulnerable to anthropogenic perturbation. Prioritizing process‐based rehabilitation of these areas in large, regulated rivers would allow natural channel‐forming processes for the benefit of native fishes.
We successfully eradicated nonnative Brook Trout Salvelinus fontinalis by electrofishing from 2.4- to 3.0-km treatment reaches of four Rocky Mountain streams in Montana to conserve sympatric ...populations of native Westslope Cutthroat Trout Oncorhynchus clarkii lewisi . At least 6, and as many as 14, removal treatments of two to four electrofishing passes per treatment were required to successfully eradicate Brook Trout from these treatment reaches. We increased success by modifying our treatment efforts during this study from single annual treatments to several treatments a year to take advantage of autumn spawning and winter aggregating behavior. Eradication by electrofishing cost US$3,500 to $5,500 per kilometer where no riparian vegetation or woody debris clearing was necessary, increasing to $8,000 to $9,000 per kilometer where clearing was needed. Treatment costs without stream clearing were similar to costs of eradication using piscicides. Eradication by electrofishing may be preferable where native fish occur in sympatry with nonnative fish in smaller streams (base flow wetted widths <3.0 m) because native fish can be salvaged during removal efforts and because electrofishing may be more acceptable to the public than use of piscicides. Received December 16,2013; accepted June 9,2014
Pacific trout Oncorhynchus spp. in western North America are strongly valued in ecological, socioeconomic, and cultural views, and have been the subject of substantial research and conservation ...efforts. Despite this, the understanding of their evolutionary histories, overall diversity, and challenges to their conservation is incomplete. We review the state of knowledge on these important issues, focusing on Pacific trout in the genus Oncorhynchus. Although most research on salmonid fishes emphasizes Pacific salmon, we focus on Pacific trout because they share a common evolutionary history, and many taxa in western North America have not been formally described, particularly in the southern extent of their ranges. Research in recent decades has led to the revision of many hypotheses concerning the origin and diversification of Pacific trout throughout their range. Although there has been significant success at addressing past threats to Pacific trout, contemporary and future threats represented by nonnative species, land and water use activities, and climate change pose challenges and uncertainties. Ultimately, conservation of Pacific trout depends on how well these issues are understood and addressed, and on solutions that allow these species to coexist with a growing scope of human influences.
La trucha del Pacífico Oncorhynchus spp. en el oeste de Norteamérica tiene un alto valor desde el punto de vista ecológico, socioeconómico y cultural, y ha sido objeto de importantes esfuerzos de conservación e investigación. A pesar de ello, el conocimiento que se tiene sobre su historia evolutiva, diversidad general y retos de conservación sigue siendo incompleto. Se hace una revisión del estado del conocimiento sobre estos puntos, con énfasis en la trucha del Pacífico dentro del género Oncorhynchus. Si bien la mayor parte de los estudios hechos sobre salmónidos se enfocan al salmón del Pacífico, aquí nos enfocamos en la trucha del Pacífico ya que ambos groupos de especies comparten una historia evolutiva en común sobre todo en lo que se refiere al extremo sur de sus rangos de distribución. En investigaciones llevadas a cabo en décadas recientes, se han revisado varias hipótesis relativas al origen y diversificación de la trucha del Pacífico a lo largo de su rango de distribución. Aunque se han logrado identificar adecuadamente las amenazas pasadas que enfrentó la trucha del Pacífico, las amenazas actuales y futuras que representan especies no nativas, actividades de uso de tierra y agua y el cambio climático se consideran importantes retos e incertidumbres. Al final, la conservación de la trucha del Pacífico depende de qué tan bien se comprendan y abordan estos temas, y de las soluciones que les permitan a estas especies coexistir con una gama creciente de influencias humanas.
Les truites du Pacifique ou Oncorhynchus spp. dans l'ouest de l'Amérique du Nord sont fortement valorisées du point de vue écologique, socio‐économique et culturel, et ont attiré l'attention en matière de recherche et d'efforts de conservation importants. En dépit de cela, la compréhension de leurs histoires évolutives, de leur diversité globale, et des défis liés à leur conservation est incomplète. Nous passons en revue l'état des connaissances sur ces questions importantes, en nous concentrant sur la truite du Pacifique du genre Oncorhynchus. Bien que la plupart des recherches sur les salmonidés mettent l'accent sur le saumon du Pacifique, nous nous concentrons sur la truite du Pacifique parce qu'elle partage une histoire évolutive commune et de nombreux taxons dans l'ouest de l'Amérique du Nord n'ont pas été formellement décrits, en particulier dans leur aire de répartition méridionale. Les recherches des dernières décennies ont conduit à la révision de nombreuses hypothèses concernant l'origine et la diversification de la truite du Pacifique dans toute son aire de répartition. Bien qu'on ait enregistré un succès considérable dans la lutte contre les menaces qui pesaient sur elle, les menaces contemporaines et futures que représentent les espèces non indigènes, l'utilisation de l'eau et des terres, et les changements climatiques posent des défis et induisent des incertitudes. Enfin, la conservation de la truite du Pacifique dépend de la façon dont ces questions sont comprises et traitées, et des solutions qui permettent à ces espèces de coexister en tenant compte des influences humaines croissantes.
The Yellowstone Cutthroat Trout Oncorhynchus clarkii bouvieri is native to the Rocky Mountains and has declined in abundance and distribution as a result of habitat degradation and introduced ...salmonid species. Many of its remaining strongholds are in headwater basins with minimal human disturbances. Understanding the life histories, vital rates, and behaviors of Yellowstone Cutthroat Trout within headwater stream networks remains limited yet is critical for effective management and conservation. We estimated annual relative growth in length and weight, annual survival rates, and movement patterns of Yellowstone Cutthroat Trout from three tributaries of Spread Creek, Wyoming, and two tributaries of Shields River, Montana, from 2011 through 2013 using PIT tag antennas within a mark–recapture framework. Mean annual growth rates varied among tributaries and size‐classes, but were slow compared with populations of Yellowstone Cutthroat Trout from large, low‐elevation streams. Survival rates were relatively high compared with those of other Cutthroat Trout subspecies, but we found an inverse relationship between survival and size, a pattern contrary to what has been reported for Cutthroat Trout in large streams. Mean annual survival rates ranged from 0.32 (SE = 0.04) to 0.68 (SE = 0.05) in the Spread Creek basin and from 0.30 (SE = 0.07) to 0.69 (SE = 0.10) in the Shields River basin. Downstream movements from tributaries were substantial, with as much as 26.5% of a tagging cohort leaving over the course of the study. Integrating our growth, survival, and movement results demonstrates the importance of considering strategies to enhance headwater stream habitats and highlights the importance of connectivity with larger stream networks.
Received February 17, 2016; accepted June 18, 2016 Published online September 30, 2016
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