Article

Propagule pressure and stream characteristics influence introgression: Cutthroat and rainbow trout in British Columbia

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Abstract

Hybridization and introgression between introduced and native salmonids threaten the continued persistence of many inland cutthroat trout species. Environmental models have been developed to predict the spread of introgression, but few studies have assessed the role of propagule pressure. We used an extensive set of fish Stocking records and geographic information system (GIS) data to produce a spatially explicit index of potential propagule pressure exerted by introduced rainbow trout in the Upper Kootenay River, British Columbia, Canada. We then used logistic regression and the information-theoretic approach to test the ability of a set of environmental and spatial variables to predict the level of introgression between native westslope cutthroat trout and introduced rainbow trout. Introgression was assessed using between four and seven co-dominant, diagnostic nuclear markers at 45 sites in 31 different streams. The best model for predicting introgression included our GIS propagule pressure index and an environmental variable that accounted for the biogeoclimatic zone of the site (r2=0.62). This model was 1.4 times more likely to explain introgression than the next-best model, which consisted of only the propagule pressure index variable. We created a composite model based on the model-averaged results of the seven top models that included environmental, spatial, and propagule pressure variables. The propagule pressure index had the highest importance weight (0.995) of all variables tested and was negatively related to sites with no introgression. This study used an index of propagule pressure and demonstrated that propagule pressure had the greatest influence on the level of introgression between a native and introduced trout in a human-induced hybrid zone.

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... Perhaps the artificial and transitory habitats created in river-impoundment interfaces differentially favor non-native congeners over native species (see Buckmeier et al. 2014). Conversely, maybe natives are more abundant and better adapted to upstream fluvial habitats, thus providing non-natives less opportunity for successful invasion (see Bennett et al. 2010). In the Lake Tenkiller case study, small stream size (e.g., Caney ...
... Although the proximate ecological mechanisms behind this trend remain uninvestigated, a reasonable hypothesis is that Neosho Smallmouth Bass are better adapted to the range of environmental conditions within these smaller streams than the Tennessee lake strain, which originated from fish presumably adapted to life in the much larger Tennessee River system. Similar spatial and environmental factors, like elevation, water temperature, and migration barriers have been found to counteract propagule pressure of non-native fish invasion and hybridization in other fishes (Bennett et al. 2010). In contrast, Alabama Bass in the Lake Lanier tributaries do not appear to be experiencing the same degree of ecological pressures that inhibit upstream invasion, suggesting the specific biology and life-history requirements of non-native species influences the success and eventual extent of invasion (see Marchetti et al. 2004). ...
... Natural reproductive barriers between black bass species are weakened or altogether compromised when non-native congeners are introduced into the range of native species (Koppelman 2015), indicating the potential for extinction via hybridization exists in such scenarios. Whether the propagule pressured applied by non-native abundance in downstream impoundments will increase, remain steady, or decrease over time is an important consideration, as increased pressure could overwhelm any opposing ecological mechanisms that favor natives (Bennett et al. 2010). ...
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North America’s fluvial fish fauna are becoming increasingly imperiled, primarily by habitat degradation, non-native species invasions, and fragmentation. The present study was conducted to understand how these conservation threats have affected native, fluvial-specialist black bass (genus Micropterus) species that support popular sport fisheries and that can be used as umbrella species for the conservation of other aquatic organisms. Species distribution models illustrated that Shoal Bass (M. cataractae) were potentially distributed across up to 84% of the available stream length in their native basin, but that fragmentation by dams and large impoundments, as well as a potential asymmetric relationship with non-native congeners, has contributed to range loss. A range-wide genetic survey demonstrated that although the Shoal Bass has been described as potamodromous, appreciable population structure exists. Five distinct genetic clusters were recovered at the uppermost hierarchical level, each generally corresponding to natural isolating mechanisms (e.g., the Fall Line). Some substructure was detected within these clusters, which was likely related to recent fragmentation (i.e., impoundments) and variable recruitment. Finer-scale case studies of the conservation-genetic influences of impoundments and non-native congener fisheries revealed that impoundments generate propagule pressure that encourages invasion and introgression of non-native alleles into native black bass populations inhabiting upstream tributaries, but whether impoundments serve as barriers to gene flow for native populations was somewhat unclear. Quantifying local-scale population dynamics of Shoal Bass inhabiting three isolated tributaries of the upper Chattahoochee River basin revealed that these populations grew slower, lived longer, and experienced lower annual mortality than other studied populations, which may be adaptations to variable recruitment or lower over-winter survival of age-0 fish. The Big Creek population appears at risk of extirpation because of its isolated nature, low numbers of adults, and greater variation in recruitment. Overall, results provide novel insights into the factors influencing range loss, a framework for management units to conserve existing genetic diversity, a characterization of non-native invasion and hybridization in impoundment tributaries, and quantified population dynamics of several isolated Shoal Bass populations inhabiting the northern extent of the species’ range.
... Several studies have illustrated a strong linkage between ambient climate conditions and the prevalence of hybridization between Westslope Cutthroat Trout and Rainbow Trout within stream networks (Fausch et al. 2001;Muhlfeld et al. 2009b;Bennett et al. 2010;Rasmussen et al. 2010;Yau and Taylor 2013). However, a paucity of empirical data exists describing how climate change may influence the spread and severity of hybridization over time. ...
... We found that the spread of hybridization was strongly correlated with warming stream temperatures during the summer months and the number of high-flow events during May from 1984 to 2011. High spring flow events are known to limit young-of-year survival and recruitment of introduced Rainbow Trout (Fausch et al. 2001;Warren et al. 2009), and stream temperature is strongly associated with the distribution patterns of Cutthroat Trout and nonnative Rainbow Trout hybrids within stream networks (Muhlfeld et al. 2009b;Bennett et al. 2010;Rasmussen et al. 2010). Warming stream temperatures may also favor Rainbow Trout growth due to its broad thermal tolerances (Bear et al. 2007) and result in increased overwinter survival in the early life stages of development (Quinn and Peterson 1996). ...
... North America (Bennett et al. 2010;Kozfkay et al. 2011;Yau and Taylor 2013). Larger source populations are also likely to facilitate nonnative adaptation to local conditions (Westley et al. 2012). ...
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Quantifying the effectiveness of management actions to mitigate the effects of changing climatic conditions (i.e., climate adaptation) can be difficult, yet critical for conservation. We used population genetic data from 1984 to 2011 to assess the degree to which ambient climatic conditions and targeted suppression of sources of nonnative Rainbow Trout Oncorhynchus mykiss have influenced the spread of introgressive hybridization in native populations of Westslope Cutthroat Trout O. clarkii lewisi. We found rapid expansion in the spatial distribution and proportion of nonnative genetic admixture in hybridized populations from 1984 to 2004, but minimal change since 2004. The spread of hybridization was negatively correlated with the number of streamflow events in May that exceeded the 75th percentile of historic flows (r = −0.98) and positively correlated with August stream temperatures (r = 0.89). Concomitantly, suppression data showed a 60% decline in catch per unit effort for fish with a high proportion of Rainbow Trout admixture, rendering some uncertainty as to the relative strength of factors controlling the spread of hybridization. Our results illustrate the importance of initiating management actions to mitigate the potential effects of climate change, even where data describing the effectiveness of such actions are initially limited but the risks are severe.Received November 22, 2013; accepted March 1, 2014
... Cutthroat trout and coastal rainbow trout stocking history.-Records of fish stocking in the upper Boise River were provided by IDFG and document stocking as early as 1913. Early state records are incomplete, with little or no geographic information, and thus a description of stocking is provided here for background but was not used for statistical analyses of factors such as distance from stocking source or numbers of individuals stocked, as has been achieved by others (e.g., see Muhlfeld et al. 2009b;Bennett et al. 2010). Two subspecies of cutthroat trout were introduced into the Boise River basin historically: pre-1980s stocking used Yellowstone cutthroat trout O. clarkii bouvieri, while later stocking used westslope cutthroat trout O. clarkii lewisi (M. ...
... For redband trout in particular, accurate characterization of current conservation status has been hindered by a lack of understanding of phylogenetic relationships, historical and current distributions, and rangewide genetic purity in the context of over a century of nonnative trout introductions (Thurow et al. 2007;Blankenship et al. 2011). Our assessment of populations across a large watershed in southern Idaho uncovered a spatially variable footprint of hybridization in native redband trout, and patterns were not always predictable (Boyer et al. 2008;Bennett et al. 2010;Rasmussen et al. 2010). Evaluation of population-average levels of introgression and the distribution of different types of hybrid individuals demonstrates that these fish currently exist in states ranging from genetically intact populations, to actively invaded populations, to hybrid swarms in which the native species has been almost completely replaced by nonnative trout. ...
... Furthermore, whereas documenting the consequences of hybridization is a useful first step, going further to diagnose the causes of hybridization would be particularly informative. This would involve additional efforts to document the historical locations and numbers of nonnative cutthroat trout and hatchery rainbow trout that have been stocked (Bennett et al. 2010) as well as data collections designed specifically to evaluate hypothesized local landscape influences on movement and hybridization (e.g., Rubidge and Taylor 2005;Neville et al. 2006;Muhlfeld et al. 2009b). Such an approach could help to identify populations that are more or less at risk from hybridization as well as specific factors that may contribute to hybridization, including those that could be addressed effectively by future management to protect native redband trout. ...
Article
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Hybridization is one of the greatest threats to native fishes. Threats from hybridization are particularly important for native trout species as stocking of nonnative trout has been widespread within the ranges of native species, thus increasing the potential for hybridization. While many studies have documented hybridization between native cutthroat trout Oncorhynchus clarkii and nonnative rainbow trout O. mykiss, fewer have focused on this issue in native rainbow trout despite widespread threats from introductions of both nonnative cutthroat trout and hatchery rainbow trout. Here, we describe the current genetic (i.e., hybridization) status of native redband trout O. mykiss gairdneri populations in the upper Boise River, Idaho. Interspecific hybridization was widespread (detected at 14 of the 41 sampled locations), but high levels of hybridization between nonnative cutthroat trout and redband trout were detected in only a few streams. Intraspecific hybridization was considerably more widespread (almost 40% of sampled locations), and several local populations of native redband trout have been almost completely replaced with hatchery coastal rainbow trout O. mykiss irideus; other populations exist as hybrid swarms, some are in the process of being actively invaded, and some are maintaining genetic characteristics of native populations. The persistence of some redband trout populations with high genetic integrity provides some opportunity to conserve native genomes, but our findings also highlight the complex decisions facing managers today. Effective management strategies in this system may include analysis of the specific attributes of each site and population to evaluate the relative risks posed by isolation versus maintaining connectivity, identifying potential sites for control or eradication of nonnative trout, and long-term monitoring of the genetic integrity of remaining redband trout populations to track changes in their status.
... A few authors permitted slight deviations from this standard to allow for local homoplasies (Wiens and Servedio 2000) or ancient hybridization (Brown et al. 2004) or defined genotypes probabilistically (e.g., >95% probability of being a nonadmixed individual based on results from assignment tests). We acknowledge that, particularly in studies relying on relatively few diagnostic markers, the number of hybridized fish will be underestimated because some slightly hybridized fish will be overlooked (Boecklen and Howard 1997;Bennett et al. 2010). ...
... Kanda et al. 2002). Collectively, this suggests that introgression between rainbow trout and cutthroat trout is influenced by propagule pressure (from either wild populations or stocking), environmental variables (Al-Chokhachy et al. 2014; Muhlfeld et al. 2014), or both (Weigel et al. 2003;Heath et al. 2010;Bennett et al. 2010;Rasmussen et al. 2010;Loxterman et al. 2014;Yau and Taylor 2013). Among stream fishes (and many other taxa), environmental mediation of hybrid zones may be the norm (Jiggins and Mallet 2000;Keller and Seehausen 2012;Culumber et al. 2014). ...
... Overall, these observations challenge the notion that hybridization between westslope cutthroat trout and rainbow trout inexorably leads to the formation of a hybrid swarm. Given that introgression has had over 100 years to spread in locations where rainbow trout have been introduced (including headwater lakes; Bennett et al. 2010) and thousands of years where they naturally co-occur with cutthroat trout, and that even nonanadromous rainbow trout can move tens to hundreds of kilometers in a single year (Bjornn and Mallet 1964), there has been sufficient time for individuals of this species or their hybrid offspring to have reached all portions of nearly every accessible watershed in this region. Yet we found, as have many others, that parental fish were common and allele distributions often nonrandom in hybrid zones, and consequently that hybrid swarms were rare. ...
Article
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Introgressive hybridization between native and introduced species is a growing conservation concern. For native cutthroat trout and introduced rainbow trout in western North America, this process is thought to lead to the formation of hybrid swarms and the loss of monophyletic evolutionary lineages. Previous studies of this phenomenon, however, indicated that hybrid swarms were rare except when native and introduced forms of cutthroat trout co-occurred. We used a panel of 86 diagnostic, single nucleotide polymorphisms to evaluate the genetic composition of 3865 fish captured in 188 locations on 129 streams distributed across western Montana and northern Idaho. Although introgression was common and only 37% of the sites were occupied solely by parental westslope cutthroat trout, levels of hybridization were generally low. Of the 188 sites sampled, 73% contained ≤5% rainbow trout alleles and 58% had ≤1% rainbow trout alleles. Overall, 72% of specimens were nonadmixed westslope cutthroat trout, and an additional 3.5% were nonadmixed rainbow trout. Samples from seven sites met our criteria for hybrid swarms, that is, an absence of nonadmixed individuals and a random distribution of alleles within the sample; most (6/7) were associated with introgression by Yellowstone cutthroat trout. In streams with multiple sites, upstream locations exhibited less introgression than downstream locations. We conclude that although the widespread introduction of nonnative trout within the historical range of westslope cutthroat trout has increased the incidence of introgression, sites containing nonadmixed populations of this taxon are common and broadly distributed.
... Despite strong selection against rainbow trout and their hybrids (Kovach et al., 2015;Kovach, Hand, et al., 2016;Muhlfeld, Kalinowski, et al., 2009), hybridization between these species is widespread in populations inhabiting a range of environmental conditions (Muhlfeld, McMahon, Boyer, & Gresswell, 2009;Rubidge & Taylor, 2005;Yau & Taylor, 2013). There is growing evidence that continuous immigration of dispersing hybrids from historical stocking locations is the primary vector for the spread of introgression (Bennett, Olson, Kershner, & Corbett, 2010;Boyer, Muhlfeld, & Allendorf, 2008;Kovach et al., 2015;Muhlfeld, McMahon, Belcer, & Kershner, 2009). Moreover, climate change could be promoting expansion of invasive hybridization in native trout through alterations in temperature and streamflow regimes in ways that are conducive to rainbow trout and hybrid dispersal, leading to increased sympatry with cutthroat trout . ...
... Predictor variables for each sample location included mean August stream temperature (Isaak, Young, Nagel, Horan, & Groce, 2015), spring precipitation , road density (Hitt et al., 2003), propagule pressure (Bennett et al., 2010), center timing of flow (Wenger, Luce, Hamlet, Isaak, & Neville, 2010), slope (Carim, Eby, & Pierce, 2015), basin area (Muhlfeld, McMahon, Boyer, et al., 2009), and presence of potential intermittent barriers to fish move- included "year" as a covariate to account for the fact that data were collected over several decades, during which time power to detect admixture increased (more molecular markers were used), monitoring strategies shifted to focus on locations where pure cutthroat trout may be present (see above), and dynamics of hybridization may have changed (Hitt et al., 2003;Muhlfeld et al., 2014). ...
... Together, these findings corroborate extensive literature showing that propagule pressure and introduction history play a critical role in the establishment and spread of invasive species, a central tenant in invasion biology (Blackburn & Duncan, 2001;Lockwood, Cassey, & Blackburn, 2005), including hybridization between salmonid species (Bennett et al., 2010). Until now, however, our ability to disentangle the evolutionary impacts of co-occurring climatic variation and biological invasions has been hampered by the low spatiotemporal resolution of data on climate, biological response (e.g., quantitative estimates of non-native genetic admixture), and human releases of non-native organisms (Staudt et al., 2013;Suarez & Tsutsui, 2008). ...
Article
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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.
... Wishard et al. (1984) detected no effects of hybridization from planting hatchery rainbow trout within eight tributaries of the Owyhee River drainage and suggested that hatchery rainbow trout may not be able to survive as well in those locations. The establishment of introduced fish and breakdown of reproductive barriers that causes hybridization is currently not well understood (Hindar et al. 1991; Williams et al. 1997; Weber and Fausch 2003; Susnik et al. 2004; Small et al. 2007) but is probably multifactorial and related to different stocking histories (e.g., number of years stocked, amount of fish and the strain stocked, size of released fish, fish health, date of last stocking, wild trout densities), naturalization rates of hatchery rainbow trout, and stray rates of hybrids and hatchery rainbow trout (Bennett et al. 2010), as well as environmental variables (Fausch et al. 2001; Bennett et al. 2010). The prevalence of hybrids in certain drainages in this study is most probably due to the higher stocking densities that coincided with easier road access and higher levels of angler use. ...
... Wishard et al. (1984) detected no effects of hybridization from planting hatchery rainbow trout within eight tributaries of the Owyhee River drainage and suggested that hatchery rainbow trout may not be able to survive as well in those locations. The establishment of introduced fish and breakdown of reproductive barriers that causes hybridization is currently not well understood (Hindar et al. 1991; Williams et al. 1997; Weber and Fausch 2003; Susnik et al. 2004; Small et al. 2007) but is probably multifactorial and related to different stocking histories (e.g., number of years stocked, amount of fish and the strain stocked, size of released fish, fish health, date of last stocking, wild trout densities), naturalization rates of hatchery rainbow trout, and stray rates of hybrids and hatchery rainbow trout (Bennett et al. 2010), as well as environmental variables (Fausch et al. 2001; Bennett et al. 2010). The prevalence of hybrids in certain drainages in this study is most probably due to the higher stocking densities that coincided with easier road access and higher levels of angler use. ...
Article
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The genetic structure of redband trout Oncorhynchus mykiss gairdnerii in the upper Snake River basin was investigated at various scales using 13 microsatellite loci. The majority of the genetic variation was partitioned between streams, although differentiation among watersheds was significant. This diversity was probably historically partitioned at the watershed scale when steelhead O. mykiss (anadromous rainbow trout) were present, with the exception of small, isolated, headwater streams where there may have been only resident trout. Genetic structure appears to have been altered by a combination of factors, including habitat fragmentation and hybridization with hatchery trout. Redband trout populations in the desert and montane environments both experienced reduced gene flow, but the desert populations displayed higher degrees of genetic differentiation. There was also a significant inverse relationship between the degree of genetic differentiation and the level of allelic diversity. Interspecific hybrids with cutthroat trout O. clarkii were detected within 9% of the sampled sites, but they made up only 2% of fish and were mostly confined to one sample location. In contrast, intraspecific hybrids with coastal rainbow trout O. m. irideus were detected within 31% of the samples sites and were more than twice as likely to be found where historical records indicated that stocking of hatchery rainbow trout occurred. The inclusion of intraspecific hybridized populations altered genetic structure by creating an artificial shared ancestry among populations from different drainages and led to higher levels of genetic variation in each of the populations. The threats of fragmentation and hybridization will need to be considered in developing conservation and management policies for redband trout in Idaho.Received April 6, 2010; accepted December 6, 2010
... In most cases there was no information about the hatchery used (i.e., original hatchery or subsequent Idaho hatchery source or sources). Along with the generally unresolved nature of the overall stocking history, this presented a major confounding factor for any investigation relating stocking information with observed genetic characteristics as has been done in other studies (e.g., Bennett et al. 2010). We therefore did not pursue any statistical analyses along these lines but present this information to provide the most comprehensive picture possible of the history of Brook Trout introductions in Idaho. ...
... Propagule pressure has received increasing attention as an important factor facilitating establishment and subsequent invasions in many taxa including salmonids (Colautti 2005;Simberloff 2009;Bennett et al. 2010;Consuegra et al. 2011), emphasizing the role that high genetic diversity may play in these processes (Lockwood et al. 2005;Roman and Darling 2007). Although we were not able to evaluate the relationship between genetic diversity and propagule size directly given the poor resolution of historic records and confounding factors, we suspected our samples would have relatively high genetic diversity because multiple introductions were documented at many of our sites. ...
Article
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Fish have been translocated throughout the world, and introductions often have been executed repeatedly and have used mixtures of different strains from the native range. This history might have contributed to their invasive potential by allowing introduced and invading populations to circumvent expected reductions in genetic diversity from founder effects in a scenario termed the “genetic paradox” of invasions. We characterize patterns of genetic diversity in nonnative Brook Trout Salvelinus fontinalis, which have been introduced across the western United States for over a century but have also invaded broadly and pose a primary threat to native trout. We analyzed 155 coding gene single nucleotide polymorphisms (SNPs) in 34 nonnative Brook Trout populations sampled across eight large river systems as well as samples from the only four hatchery strains with documented use in Idaho. We uncovered similar within-population genetic diversity and large effective population sizes in naturalized populations compared with hatchery samples. Naturalized populations also showed substantial genetic structuring (maximum pairwise F ST = 0.23) across and even within watersheds and indicated suggestions of admixture in certain regions. Assignment probabilities confirmed two main hatcheries as the origin of most fish collected in the field; however, the four hatcheries were excluded as being the origin for 8% of individuals, mirroring results from clustering analyses and suggesting the influence of an additional unsampled hatchery source or sources. Simulated admixtures of hatchery samples produced genetic patterns similar to those observed in field samples, further supporting an influence of multiple historic hatchery stocks on the contemporary genetic structure of Brook Trout in Idaho. Our study highlights the potential contribution of historic hatchery and introduction practices in creating genetically variable and structured naturalized Brook Trout populations across Idaho, which may have allowed these fish to defy the “genetic paradox” early on in their nonnative history and set the stage for successful establishment and subsequent invasion.Received September 4, 2012; accepted March 31, 2013
... The primary objective of our study was to assess the introgressive status of Guadalupe Bass across its range and to evaluate temporal changes in introgression using a suite of microsatellite loci. Because propagule pressure can impact the directionality and ultimate outcome of introgression in populations (Bennett et al. 2010), samples from rivers that received the greatest intensity stocking of Smallmouth Bass should exhibit the highest rates of introgression. Given that the stocking of hatchery-reared individuals and the creation of refuge populations can lead to reduced genetic diversity within populations (Osborne et al. 2006), we also evaluate the effects of conservation and restoration efforts on genetic diversity. ...
... These two systems received the greatest intensity of Smallmouth Bass stocking of the subbasins in this study. Similarly, Bennett et al. (2010) found that propagule pressure affected rates of introgression between Westslope Cutthroat Trout Oncorhynchus clarkii lewisi and introduced Rainbow Trout O. mykiss, and Marie et al. (2012) found a linear relationship between number of stocking events and rates of hybridization between domestic and wild Brook Trout Salvelinus fontinalis. Hybrid individuals in the Guadalupe subbasin also had the greatest admixture proportions attributed to Smallmouth Bass (mean admixture proportion = 0.389). ...
Article
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The stocking of fishes outside of their native range for the purpose of sport fisheries can lead to secondary contact and introgression between species that were historically allopatrically distributed. Smallmouth Bass Micropterus dolomieu were introduced within the range of Guadalupe Bass M. treculii in central Texas and introgressive hybridization subsequently occurred. One recent survey of temporal changes in introgression in the Blanco River found that introgression had increased and that Guadalupe Bass had been extirpated. Thus, a survey of changes in introgression across the range of the Guadalupe Bass was conducted in 12 subbasins in the Brazos, Colorado, Guadalupe–San Antonio, and Nueces drainages in Texas using 15 microsatellite loci. The results indicate that introgression is now occurring in four subbasins but no longer occurring in the Lampasas and San Gabriel rivers, where rates were previously 6% and 46%, respectively. Additionally, we found no evidence that stocking of hatchery-reared individuals in the Guadalupe and Nueces rivers has led to severely depressed genetic variation. The variable success of restoration efforts to prevent extirpation of the Guadalupe Bass suggests that protection of the remaining nonintrogressed populations should be a priority for the conservation of this species.Received April 24, 2012; accepted December 9, 2012
... Although many studies have recognized spatial patterns in hybridization between rainbow trout and cutthroat trout [34][35][36], these have been limited in geographic extent or have used imprecise proxies for instream conditions (e.g., elevation or precipitation to represent stream temperature or flow) because of the absence of more accurate or direct measures. Recent development of massive geospatial stream databases provides a means to represent important environmental variables accurately and consistently across broad geographic areas [37,38]. ...
... Occurrence of rainbow trout peaked at this temperature in this region. [6,7,8,11,29,35,36,95,[115][116][117] DF3: Distance (m) to mean annual flow > 2.83 m 3 /s Larger streams may favor rainbow trout. This threshold exceeds those habitats generally suitable for cutthroat trout spawning. ...
Article
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Among the many threats posed by invasions of nonnative species is introgressive hybrid-ization, which can lead to the genomic extinction of native taxa. This phenomenon is regarded as common and perhaps inevitable among native cutthroat trout and introduced rainbow trout in western North America, despite that these taxa naturally co-occur in some locations. We conducted a synthetic analysis of 13,315 genotyped fish from 558 sites by building logistic regression models using data from geospatial stream databases and from 12 published studies of hybridization to assess whether environmental covariates could explain levels of introgression between westslope cutthroat trout and rainbow trout in the U. S. northern Rocky Mountains. A consensus model performed well (AUC, 0.78±0.86; classification success, 72±82%; 10-fold cross validation, 70±82%) and predicted that rainbow trout introgression was significantly associated with warmer water temperatures, larger streams, proximity to warmer habitats and to recent sources of rainbow trout propagules, presence within the historical range of rainbow trout, and locations further east. Assuming that water temperatures will continue to rise in response to climate change and that levels of introgression outside the historical range of rainbow trout will equilibrate with those inside that range, we applied six scenarios across a 55,234-km stream network that forecast 9.5± 74.7% declines in the amount of habitat occupied by westslope cutthroat trout populations of conservation value, but not the wholesale loss of such populations. We conclude that introgression between these taxa is predictably related to environmental conditions, many of which can be manipulated to foster largely genetically intact populations of westslope cutthroat trout and help managers prioritize conservation activities.
... Hybridization risk was assessed in terms of cooccurrence between Westslope Cutthroat Trout and Rainbow Trout or Yellowstone Cutthroat Trout. Multiple studies have shown that nonnative genetic admixture declines with upstream distance from sites containing high amounts of nonnative admixture (e.g., Rubidge and Taylor 2005;Boyer et al. 2008;Bennett et al. 2010;Yau and Taylor 2013). Hybridization risk was measured based on (1) the distance between the location of interest and the closest stream or lake habitat where Rainbow Trout or Yellowstone Cutthroat Trout introgression was detected at admixture levels greater than 10% within Glacier National Park or surrounding waters (Boyer et al. 2008;Muhlfeld et al. 2014) and (2) the existence of barriers that would preclude contact with the conservation population (Table 3; Table S.1). ...
... Our assessment indicates that extensive translocations of and invasions by nonnative salmonids have led to introgressive hybridization with Westslope Cutthroat Trout populations in many watersheds within Glacier National Park and pose an imminent threat to many extant populations of high conservation value. Introgressive hybridization between introduced Rainbow Trout and native Westslope Cutthroat Trout tends to spread quickly (Hitt et al. 2003;Weigel et al. 2003;Rubidge and Taylor 2004;Bennett et al. 2010;Yau and Taylor 2013;Muhlfeld et al. 2014;Lowe et al. 2015) and can reduce fitness (Muhlfeld et al. 2009a;Kovach et al. 2015), genomic integrity (Allendorf and Leary 1988), and, ultimately, native species diversity (Allendorf et al. 2001). Furthermore, hybridization is exacerbated by habitat modification (Allendorf et al. 2001) and climate change , so this problem will probably become more serious with increasing land use and global climate change. ...
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Invasive hybridization is one of the greatest threats to the persistence of Westslope Cutthroat Trout Oncorhynchus clarkii lewisi. Large protected areas, where nonhybridized populations are interconnected and express historical life history and genetic diversity, provide some of the last ecological and evolutionary strongholds for conserving this species. Here, we describe the genetic status and distribution of Westslope Cutthroat Trout throughout Glacier National Park, Montana. Admixture between Westslope Cutthroat Trout and introduced Rainbow Trout O. mykiss and Yellowstone Cutthroat Trout O. clarkii bouvieri was estimated by genotyping 1,622 fish collected at 115 sites distributed throughout the Columbia, Missouri, and South Saskatchewan River drainages. Currently, Westslope Cutthroat Trout occupy an estimated 1,465 km of stream habitat and 45 lakes (9,218 ha) in Glacier National Park. There was no evidence of introgression in samples from 32 sites along 587 km of stream length (40% of the stream kilometers currently occupied) and 17 lakes (2,555 ha; 46% of the lake area currently occupied). However, nearly all (97%) of the streams and lakes that were occupied by nonhybridized populations occurred in the Columbia River basin. Based on genetic status (nonnative genetic admixture ≤ 10%), 36 Westslope Cutthroat Trout populations occupying 821 km of stream and 5,482 ha of lakes were identified as “conservation populations.” Most of the conservation populations (N = 27; 736 km of stream habitat) occurred in the Columbia River basin, whereas only a few geographically restricted populations were found in the South Saskatchewan River (N = 7; 55 km) and Missouri River (N = 2; 30 km) basins. Westslope Cutthroat Trout appear to be at imminent risk of genomic extinction in the South Saskatchewan and Missouri River basins, whereas populations in the Columbia River basin are widely distributed and conservation efforts are actively addressing threats from hybridization and other stressors. A diverse set of pro-active management approaches will be required to conserve, protect, and restore Westslope Cutthroat Trout populations in Glacier National Park throughout the 21st century. Received September 10, 2015; accepted March 30, 2016 Published online August 12, 2016
... Propagule pressure overcomes several limitations in the establishment process. For example, propagule pressure may increase the probability that individuals arrive during a 'window of opportunity' when environmental conditions are temporarily favourable for establishment [8]. It also overcomes the Allee effect (a positive relationship between the fitness of an individual and population density [9]) by ensuring that a sufficiently high density of individuals is present in an area [10]. ...
... The arrival time of new individuals has been shown to be important in determining establishment success [24]. This can be due to temporal fluctuations in the availability of a resource [24], environmental suitability [8] and age structure of a population [25]. Theoretical studies suggest that more frequent introduction events [26], and decreasing the time duration between such events [27], can increase the probability of establishment success. ...
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Propagule pressure is a leading determinant of population establishment. Yet, an experimental understanding of how propagule size and number (two principal parts of propagule pressure) determine establishment success remains incomplete. Theoretical studies suggest that the timing between introduction events, a component of propagule number, can influence establishment success. However, this dynamic has rarely been explored experimentally. Using Escherichia coli engineered with an Allee effect, we investigated how the timing of two introduction events influences establishment. For populations introduced below the Allee threshold, establishment occurred if the time between two introduction events was sufficiently short, with the length of time between events further reduced by reducing growth rate. Interestingly, we observed that as the density of bacteria introduced in one introduction event increased, the time between introduction events that allowed for establishment increased. Using a mathematical model, we provide support that the mechanism behind these trends is the ability of the first population to modify the environment, which can pave the way for establishment of the second population. Our results provide experimental evidence that the temporal distribution of introduction events regulates establishment, furthering our understanding of propagule pressure and may have implications in invasion biology and infectious disease.
... These species produce fertile offspring, and genetic introgression often continues until the native Cutthroat Trout genomes are replaced by hybrids (Allendorf and Leary 1988;Muhlfeld et al. 2017). Propagule pressure (a measure of the number of fish introduced to a region; Bennett et al. 2010) and ecological conditions (stream flow and water temperature) appear to mediate hybridization between these taxa (Boyer et al. 2008;Muhlfeld et al. 2009, Bennett et al. 2010Muhlfeld et al. 2014;Kovach et al. 2015;Young et al. 2016;Muhlfeld et al. 2017). Brook Trout also hybridize with other salmonids when introduced outside their native range. ...
... These species produce fertile offspring, and genetic introgression often continues until the native Cutthroat Trout genomes are replaced by hybrids (Allendorf and Leary 1988;Muhlfeld et al. 2017). Propagule pressure (a measure of the number of fish introduced to a region; Bennett et al. 2010) and ecological conditions (stream flow and water temperature) appear to mediate hybridization between these taxa (Boyer et al. 2008;Muhlfeld et al. 2009, Bennett et al. 2010Muhlfeld et al. 2014;Kovach et al. 2015;Young et al. 2016;Muhlfeld et al. 2017). Brook Trout also hybridize with other salmonids when introduced outside their native range. ...
... as an important component of the soil's hydrolyzed nitrogen, can generally occupy 30 % to 50 % of the total N in the soil generally(Hao et al., 2010;Zhang et al., 2012). There are many sources of AAN: 1, hydrolysis of proteins and amino acids in the soil by microorganisms and extracellular fermentation; 2, decomposition of fresh animal and plant residues; 3, decline and destruction of microorganisms; and 4, intermediate products produced during the process of applying organic fertilizer into the soil(Bennett et al., 2010).Fig. 7shows that the contents of AAN in studied sediments increases as TN increases, as shown by the regression equation and correlation coefficient is of y=11.7408+0.2387x, ...
Article
The contents of different organic nitrogen (N) fractions, their contributions to total N (TN) and the relationship between their mineralizable N (MN) and different organic N fractions in sediments of the water level fluctuation (WLF) zone were investigated. The contents of TN, acid hydrolyzable N (AHN), and nonhydrolyzable N (NHN) decreased in sediments from the lower altitudes of the WLF zone. The AHN and NHN accounted for 70.56 to 82.89 % and 17.11 to 29.44 % of TN, respectively. The AHN was the main organic N fraction, indicating that these sediments might promote greater water eutrophication in the Three Gorges tributaries. The distribution of amino-acid N (AAN), ammonium N (AN), amino-sugar N (ASN) and hydrolyzable unidentified N (HUN) in the WLF zone was found to be 170 m > 160 m > 150 m. AAN, AN, ASN, and HUN accounted for 34.70, 20.25, 15.52 and 29.24 % of AHN, respectively. HUN and ASN were the main contributors of MN to N release.
... Importantly, many trout were stocked into historically fishless waters above barriers. Following the founding stocking events, those same barriers have protected these populations from non-native salmonids such as brook, brown (Salmo trutta) and rainbow trout that tend to replace or hybridize with native cutthroat trout (McGrath & Lewis 2007;Metcalf et al. 2008;Peterson et al. 2008;Bennett et al. 2010;Benjamin et al. 2011). The end result is a patchwork of cutthroat trout lineages that persist in small, high elevation populations across the state of Colorado. ...
Article
Many species are threatened with extinction and efforts are underway worldwide to restore imperilled species to their native ranges. Restoration requires knowledge of species' historical diversity and distribution. For some species, many populations were extirpated or individuals moved beyond their native range before native diversity and distribution were documented, resulting in a lack of accurate information for establishing restoration goals. Moreover, traditional taxonomic assessments often failed to accurately capture phylogenetic diversity. We illustrate a general approach for estimating regional native diversity and distribution for cutthroat trout in the Southern Rocky Mountains. We assembled a large archive of historical records documenting human-mediated change in the distribution of cutthroat trout (Oncorhynchus clarkii) and combined these data with phylogenetic analysis of 19th century samples from museums collected prior to trout stocking activities and contemporary DNA samples. Our study of the trout in the Southern Rocky Mountains uncovered six divergent lineages, two of which went extinct, probably in the early 20th century. A third lineage, previously declared extinct, was discovered surviving in a single stream outside of its native range. Comparison of the historical and modern distributions with stocking records revealed that the current distribution of trout largely reflects intensive stocking early in the late 19th and early 20th century from two phylogenetically and geographically distinct sources. Our documentation of recent extinctions, undescribed lineages, errors in taxonomy and dramatic range changes induced by human movement of fish underscores the importance of the historical record when developing and implementing conservation plans for threatened and endangered species.
... Unfortunately, visual identification of Redband Trout × Rainbow Trout hybrids is not possible, and genetic analyses are too costly to perform in all streams. However, if detailed stocking history is known and stocking metrics (e.g., the total number of fish stocked) are well correlated with current levels of introgression, then simple models can be used to characterize introgression at stream locations for which genetic information is lacking (e.g., Bennett et al. 2010). ...
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Redband Trout Oncorhynchus mykiss gairdneri are likely the most abundant and most widely distributed native salmonid in the Columbia River basin, yet their current distribution and abundance across the landscape have not been well documented. We sampled 1,032 randomly distributed stream sites (usually 100 m in length) across more than 60,000 km of stream network to assess Redband Trout occupancy, abundance, and genetic purity in the upper Snake River basin of Idaho. Study locations were more often in dry desert subbasins (49% of sites) than in montane subbasins (20%), and 25% of the dry “stream sites” had no discernible stream channel whatsoever, indicating a lack of flowing water for perhaps millennia. Redband Trout were estimated to occupy 13,485 km of stream (22% of the total) and were captured more often (389 sites) than Brook Trout Salvelinus fontinalis (128 sites), Bull Trout Salvelinus confluentus (37 sites), or Brown Trout Salmo trutta (16 sites). Redband Trout were also the most abundant species of trout, with an approximate abundance of 3,449,000 ± 402,000 (90% confidence interval) of all sizes, followed by Brook Trout (1,501,000 ± 330,000), Bull Trout (159,000 ± 118,000), and Brown Trout (43,000 ± 25,000). Approximately 848,000 ± 128,000 Redband Trout were adults. From 1913 (the earliest year of record) to 2001, roughly 43 million hatchery Rainbow Trout were stocked in streams in the study area, 17.5 million of which were of catchable size (i.e., ≥200 mm total length); since 2001, all catchable trout have been sterilized prior to stocking. Genetic results from 61 study sites suggest that hybridization with hatchery Rainbow Trout is more likely to occur in streams that were directly stocked with catchable trout from 1913 to 2001. Applying these results across the landscape, we estimated that Redband Trout likely remain pure in about 68% of the streams occupied in the upper Snake River basin.Received November 13, 2012; accepted January 9, 2014
... Rainbow trout (O. mykiss) were artificially propagated and introduced into watersheds across the Continental United States for recreational purposes between 1870 and 1971 (Pister 2001;Bennett et al., 2010). Since their introduction into the Flathead River in 1880 (Hitt et al., 2003), RBT have been hybridizing with native WCT (Hitt et al., 2003;Allendorf et al., 2004;Boyer et al., 2008;Muhlfeld et al., 2017). ...
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Biological invasions are accelerating worldwide, causing major ecological and economic impacts in aquatic ecosystems. The urgent decision-making needs of invasive species managers can be better met by the integration of biodiversity big data with large-domain models and data-driven products. Remotely sensed data products can be combined with existing invasive species occurrence data via machine learning models to provide the proactive spatial risk analysis necessary for implementing coordinated and agile management paradigms across large scales. We present a workflow that generates rapid spatial risk assessments on aquatic invasive species using occurrence data, spatially explicit environmental data, and an ensemble approach to species distribution modeling using five machine learning algorithms. For proof of concept and validation, we tested this workflow using extensive spatial and temporal hybridization and occurrence data from a well-studied, ongoing, and climate-driven species invasion in the upper Flathead River system in northwestern Montana, USA. Rainbow Trout (RBT; Oncorhynchus mykiss), an introduced species in the Flathead River basin, compete and readily hybridize with native Westslope Cutthroat Trout (WCT; O. clarkii lewisii), and the spread of RBT individuals and their alleles has been tracked for decades. We used remotely sensed and other geospatial data as key environmental predictors for projecting resultant habitat suitability to geographic space. The ensemble modeling technique yielded high accuracy predictions relative to 30-fold cross-validated datasets (87% 30-fold cross-validated accuracy score). Both top predictors and model performance relative to these predictors matched current understanding of the drivers of RBT invasion and habitat suitability, indicating that temperature is a major factor influencing the spread of invasive RBT and hybridization with native WCT. The congruence between more time-consuming modeling approaches and our rapid machine-learning approach suggest that this workflow could be applied more broadly to provide data-driven management information for early detection of potential invaders.
... Remotely sensed data are becoming increasingly more available, and several recent studies show the diversity of questions that involve remotely sensed data. These include the assessment of gene flow and genetic differentiation (Weigel, Peterson & Spruell 2003;Alberto et al. 2010), determining the influence of stream characteristics on introgression in trout (Bennett et al. 2010), evaluating the efficacy of marine protected areas (Friedlander, Brown & Monaco 2007), predicting species distributions (Raxworthy et al. 2003;Spens, Englund & Lundqvist 2007) and mapping species' habitat (Rotenberry, Preston & Knick 2006). This suggests that there is available geographic information across a diverse set of landscapes, and therefore, we do not see the requirement of available covariate information throughout the study area as restricting the utility of our approach. ...
Article
1. Occupancy estimation is a commonly used tool in ecological studies owing to the ease at which data can be collected and the large spatial extent that can be covered. One major obstacle to using an occupancy-based approach is the complications associated with designing and implementing an efficient survey. These logistical challenges become magnified when working with rare species when effort can be wasted in areas with none or very few individuals. 2. Here, we develop a two-phase sampling approach that mitigates these problems by using a design that places more effort in areas with higher predicted probability of occurrence. We compare our new sampling design to traditional single-season occupancy estimation under a range of conditions and population characteristics. We develop an intuitive measure of predictive error to compare the two approaches and use simulations to assess the relative accuracy of each approach. 3. Our two-phase approach exhibited lower predictive error rates compared to the traditional single-season approach in highly spatially correlated environments. The difference was greatest when detection probability was high (0·75) regardless of the habitat or sample size. When the true occupancy rate was below 0·4 (0·05–0·4), we found that allocating 25% of the sample to the first phase resulted in the lowest error rates. 4. In the majority of scenarios, the two-phase approach showed lower error rates compared to the traditional single-season approach suggesting our new approach is fairly robust to a broad range of conditions and design factors and merits use under a wide variety of settings. 5. Synthesis and applications. Conservation and management of rare species are a challenging task facing natural resource managers. It is critical for studies involving rare species to efficiently allocate effort and resources as they are usually of a finite nature. We believe our approach provides a framework for optimal allocation of effort while maximizing the information content of the data in an attempt to provide the highest conservation value per unit of effort.
... The introduced organisms are most likely to interact with the native organisms through competition. One of the other probable interactions is intraspecific hybridization in which the introduced organisms hybridize with the native organisms and degrade their genetic identity (Allendorf et al. 2001;Bennett et al. 2010). ...
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Geographically isolated populations of freshwater fish have been introduced into conspecific native populations. One of the most representative cases is the pale chub Zacco platypus. The pale chub of Lake Biwa in western Japan has been inadvertently introduced to other waters with the release of game fish. Because they are not clearly discriminated from other populations by their morphological characteristics, the morphological detection of the colonization is not possible. Hence, a genetic analysis of fish collected from rivers of the Kanto Plain in eastern Japan, where the introduction was made, was conducted. The haplotype variety of the mitochondrial gene cytochrome b of the fish revealed the presence of two major groups of haplotypes. We concluded that one of the groups was introduced from western Japan, especially Lake Biwa, and the other was native to the Kanto Plain. The haplotypes from western Japan were established in all of the rivers studied and occurred together with the native haplotypes in the rivers within the original distribution range of the species. The allelic composition of microsatellite loci indicated that fish from the two different sources were well admixed through hybridization in the populations of the rivers of the Kanto Plain.
... An initial and warranted action is the cessation of stocking in watersheds occupied by genetically pure Cutthroat Trout. Unfortunately, terminating Rainbow Trout stocking does not address existing hybridization stemming from historical stocking practices (Bennett et al. 2010) and the fact that hybridization appears to proceed from legacy stocking sources (Muhlfeld et al. 2017). Indeed, temporal genetic data from hybrid zones between Westslope Cutthroat Trout O. clarkii lewisi and Rainbow Trout suggest that Rainbow Trout admixture can increase rapidly in river basins where stocking has not occurred for several decades (Hitt et al. 2003;Muhlfeld et al. 2014Muhlfeld et al. , 2017. ...
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Preserving remaining non‐hybridized Cutthroat Trout populations is a conservation priority often requiring management action. Although proactive Rainbow Trout and hybrid suppression programs offer a flexible tool, particularly in large interconnected river basins, this management approach is used less frequently than alternatives (barriers and piscicides). We describe the results of a targeted Rainbow Trout hybrid suppression program spanning 15 years in the upper Snake River, Wyoming, a core stronghold for Yellowstone Cutthroat Trout. Initially, Rainbow Trout hybrids were relatively common in the Gros Ventre River, a major tributary to the Snake River. Between 2002 and 2016, 926 individuals of Rainbow Trout ancestry were removed from the Gros Ventre River. Relative abundance of Rainbow Trout hybrids decreased over this time, while the Yellowstone Cutthroat Trout population increased. Temporal genetic data collected in 2007/2008 and again in 2014 demonstrate that the overall proportion Rainbow Trout admixture and the proportion of hybrids in a sample both significantly decreased in the Gros Ventre River, and did not increase elsewhere in the Snake River basin. In conclusion, proactive Rainbow Trout suppression appears to have reduced the threat of Rainbow Trout hybridization in this river basin, and helped protect an interconnected metapopulation with highly diverse life history and genetic variation important for long‐term persistence. This article is protected by copyright. All rights reserved.
... They reported that although in most streams hybridization was low, it had increased in some streams while decreasing in others, even in the absence of stocking. They reasoned that while the influence of propagule pressure was variable (sensu Bennett et al. 2010), hybridization may be influenced by the suitability of habitat and persistence of Smallmouth Bass. They found that hybridization was lower in areas where Smallmouth Bass were not found than in areas where they occurred. ...
Chapter
Interspecific hybridization among micropterids was once thought to be rare but has been documented in several cases of North American endemics. Introduction of the nonnative Smallmouth Bass Micropterus dolomieu across Texas has threatened to eliminate the Guadalupe Bass M. treculii genome throughout its native range via introgression between the species. In 1992, the Texas Parks and Wildlife Department began a stocking program in the Guadalupe River watershed to restore the genetic integrity of the local population. More than 600,000 hatchery-reared Guadalupe Bass fingerlings (~30 mm total length) were stocked in Johnson Creek over a 19-year period, and 360,000 fish were released in the North Fork, South Fork, and main-stem Guadalupe River over a 5-year period. Annual genetic monitoring indicated that hybridization significantly declined in all stream segments (P < 0.001) during the period of time when stocking occurred. Initially high hybridization rates (range, 20–100%; mean = 43.4%) were reduced to 0–24.2% (mean = 11.4%) at the termination of stocking. Linear regression indicated that hybridization in the North Fork and main-stem stream segments declined faster (9.0% per year) than all other test stream segments, whereas the South Fork Guadalupe River and upper Johnson Creek declined at 0.9% per year and lower Johnson Creek declined at 1.9% per year. Our data show that supplemental stocking is an effective approach to genetic restoration of compromised populations and should be considered as a viable management and conservation tool.
... Because stocking records in many systems may be incomplete or nonexistent, we tested whether stocking activity was predicted by geography. Given the role of humans in transporting trout across the landscape (Drake and Mandrak 2010), the distribution of non-native lineages may be predicted by the spatial configuration of human transportation networks (Bennett et al. 2010;Mehner et al. 2009;Foxcroft et al. 2004;Scott 2006). We evaluated the dependence of each of six stocking variables (times stocked, earliest stocking date, maximum number stocked in a single event, total number of individuals stocked, mean stocking over time, and minimum number of unique sources or clades) on four geographic variables (elevation, distance to roads, distance to trails, and connectivity) using multiple linear regression and step- (Young et al. 2002). ...
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Human introductions can obscure the diversity and distribution of native biota; hybridization with and replacement by introduced congeners is a primary conservation threat, particularly in salmonids. Cutthroat trout (Oncorhynchus clarkii) are an important component of biodiversity in the American West, and all recognized subspecies are targets for state and federal conservation efforts. Rocky Mountain National Park (RMNP) in northern Colorado is a microcosm of trout introductions that happened worldwide. We used a combination of extensive stocking records and molecular genetic data to ask whether native trout populations persist despite stocking and whether patterns in the distribution of cutthroat trout clades could be explained by source and intensity of stocking. Nearly 15 million cutthroat trout were stocked into RMNP from a mosaic of sources in the 20th century. A single lineage of cutthroat trout was historically native to each side of the Continental Divide in RMNP, but we detected at least five divergent clades of cutthroat trout in 34 localities on both sides of the Divide. The distribution of lineages was predicted by stocking pressure and source but not by which lineage was historically native. The future of mixed and non-native cutthroat trout populations in RMNP poses a substantial conservation challenge. ©, 2015, National Research Council of Canada. All Rights Reserved.
... Migration and moving over land. When colonising new freshwater habitats, migration capacity is an important determinant of spread 39 . However, migration capacity did not determine any division between successful and unsuccessful invaders in the TWINSPAN analysis. ...
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Biological invasions by nonindigenous species can have negative effects on economies and ecosystems. To limit this impact, current research on biological invasions uses functional traits to facilitate a mechanistic understanding of theoretical and applied questions. Here we aimed to assess the role of functional traits in the progression of crayfish species through different stages of invasion and determine the traits associated with invasive success. A dataset of thirteen functional traits of 15 species currently occurring or available for sale in the Netherlands was evaluated. Six of these crayfish appeared invasive. Important traits distinguishing successful from unsuccessful invaders were a temperate climate in the native range, a medium to high egg count and producing more than one egg clutch per year. The most successful invaders had different functional trait combinations: Procambarus clarkii has a higher reproductive output, can migrate over longer distances and possesses a higher aggression level; Faxonius limosus is adapted to a colder climate, can reproduce parthenogetically and has broader environmental tolerances. Using a suit of functional traits to analyse invasive potential can help risk management and prevention. For example, based on our data Procambarus virginalis is predicted to become the next successful invasive crayfish in the Netherlands.
... Extensive fish stocking records ; Montana Fish, Wildlife & Parks MFISH database) were used to estimate a spatially explicit index of stocking intensity for all invasive species. Specifically, stocking intensity was derived for each stream segment using the following equation where # Locations is the number of locations within a connected watershed where stocking has occurred, # Stocked is the total number of fish stocked at a location across all years, 0.05 is the constant decay rate for straying fish, and Distance is the distance to each stocking site in kilometers (40,57). Stream distances were calculated using the National Hydrography Dataset. ...
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Climate change and invasive species are major threats to native biodiversity, but few empirical studies have examined their combined effects at large spatial and temporal scales. Using 21,917 surveys collected over 30 years, we quantified the impacts of climate change on the past and future distributions of five interacting native and invasive trout species throughout the northern Rocky Mountains, USA. We found that the occupancy of native bull trout and cutthroat trout declined by 18 and 6%, respectively (1993–2018), and was predicted to decrease by an additional 39 and 16% by 2080. However, reasons for these occupancy reductions markedly differed among species: Climate-driven increases in water temperature and decreases in summer flow likely caused declines of bull trout, while climate-induced expansion of invasive species largely drove declines of cutthroat trout. Our results demonstrate that climate change can affect ecologically similar, co-occurring native species through distinct pathways, necessitating species-specific management actions.
... This time difference encompasses approximately five additional generations and numerous reproductive seasons during which kamloops stocking continued. Changes in environmental conditions or ratios of kamloops to steelhead on spawning grounds as well as increased propagule pressure (Bennett et al., 2010) likely led to kamloops introgression that was possibly rare in the early 1990 s. ...
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Fisheries managers and anglers in Minnesota have long been concerned that reproduction in the wild by a hatchery strain of rainbow trout (Oncorhynchus mykiss), called kamloops, could reduce the fitness of naturalized steelhead (migratory rainbow trout) populations in Lake Superior. A previous study found no evidence of kamloops introgression, but a new evaluation is warranted in light of continued stocking and genetic advancements over the past 25 years. We used genotypes from 10 microsatellite DNA loci to assess kamloops ancestry in adult and age-0 rainbow trout samples from 40 streams in Minnesota, one stream in Wisconsin, and two adult broodstocks. We also evaluated genetic population structure for impacts of kamlooops introgression. Overall, the average estimated kamloops ancestry was 8% (range 2–44%) in age-0 juveniles and 4% (1–19%) in adults. The average percentages of kamloops descendants in age-0 and adults were 8% (0–54%) and 5% (0–40%), respectively. Kamloops descendants were found in many Minnesota streams and in Wisconsin’s Bois Brule River, but were most prevalent in streams near the source hatchery, near recent stocking locations, and in lower reaches of longitudinally sampled streams. Feral steelhead broodstock had 9% and 6% kamloops descendants in two years while captive broodstock had no kamloops descendants. Minnesota’s populations showed little spatial genetic structure but were distinct from the Bois Brule population and from kamloops, which indicated that kamloops introgression had not substantially altered structure. Kamloops introgression into Minnesota steelhead populations and impacts on other jurisdictions contributed to the decision to discontinue the kamloops stocking program.
... & Benjamin N. Sacks bnsacks@ucdavis.edu as continuous sources of introduction and, consequently, increase the likelihood of extensive introgression (Bennett et al. 2010). Genetic introgression into native populations by commercially farmed animals has been documented in birds (Gering et al. 2015), ungulates (Goedbloed et al. 2013;Mager et al. 2013), fish (Bourret et al. 2011), and carnivores (Noren et al. 2005;Kidd et al. 2009;Sacks et al. 2011). ...
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Fur-animal farms can affect the genetic constitution of wild conspecifics through escape and subsequent interbreeding. We studied this problem in red foxes (Vulpes vulpes) on the Canadian island of Newfoundland, where a large commercial fox farm (the only large farm on the island) has operated adjacent to the native wild red fox population for >30 years. To test for gene flow from these fur-farm foxes into the wild population, we compared mitochondrial DNA (mtDNA) sequences and nuclear microsatellite genotypes (21 loci) of 93 individuals from the fox farm to those of 79 modern wild foxes sampled from across the island. For reference, we also included 12 historical museum specimens of wild eastern Canadian red fox, all of which were sampled before the introduction of fur farming in the region. Many mtDNA haplotypes were shared among contemporary farmed and wild foxes and the historical eastern Canadian samples, as expected based on the eastern Canadian origin of fur-farming. However, only the fur farm additionally contained haplotypes originating from other parts of North America. More significantly, microsatellite markers, which reflect contemporary gene flow, indicated strong differentiation (FST ≥ 0.14, P < 0.001) between fur-farm and wild foxes (including the historical samples) and little to no gene flow between them. Admixture and principle components analyses similarly supported clear separation of fur-farm and wild red foxes. Together, these findings indicate that the presence of a large red fox fur farm had little, if any, effect on the genetic constitution of the native wild population in Newfoundland. Tight biosecurity (lack of escapees) or failure of captive-reared foxes to establish in the presence of native wild foxes could explain these findings.
... This pattern may simply indicate that selection acting against rainbow trout is not as severe or consistent in these environments, or that human releases of rainbow trout in certain areas overwhelmed selective regimes. Rainbow trout were stocked routinely and abundantly throughout the early part of the twentieth century, and these stocking events occurred predominantly in lower elevation rivers and lakes that often are warmer than those at higher elevation [37,55,56], suggesting that spatial patterns in rainbow trout admixture probably reflect stocking and subsequent dispersal, more than selection favouring rainbow trout in certain environments [39,57]. ...
Article
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Evolutionary and ecological consequences of hybridization between native and invasive species are notoriously complicated because patterns of selection acting on non-native alleles can vary throughout the genome and across environments. Rapid advances in genomics now make it feasible to assess locus-specific and genome-wide patterns of natural selection acting on invasive introgression within and among natural populations occupying diverse environments. We quantified genome-wide patterns of admixture across multiple independent hybrid zones of native westslope cutthroat trout and invasive rainbow trout, the world's most widely introduced fish, by genotyping 339 individuals from 21 populations using 9380 species-diagnostic loci. A significantly greater proportion of the genome appeared to be under selection favouring native cutthroat trout (rather than rainbow trout), and this pattern was pervasive across the genome (detected on most chromosomes). Furthermore, selection against invasive alleles was consistent across populations and environments, even in those where rainbow trout were predicted to have a selective advantage (warm environments). These data corroborate field studies showing that hybrids between these species have lower fitness than the native taxa, and show that these fitness differences are due to selection favouring many native genes distributed widely throughout the genome.
... Our observation of a significant association between propagule pressure and the amount of introgression between farmed and wild salmon present supports the use of propagule pressure as a predictor of genetic impacts in wild populations. Similar links between propagule pressure and genetic introgression have been detected elsewhere (Bennett et al. 2010;Consuegra et al. 2011;Lamaze et al. 2012;Marie et al. 2012), supporting the use of propagule pressure as a management tool (Pritchard et al. 2007). Moreover, associations between the incidence of escaped farmed salmon in rivers and river-specific estimates of temporal genetic change ) and admixture Heino et al. 2015;Karlsson et al. 2016) have been reported. ...
Article
The escape of Atlantic salmon (Salmo salar) from aquaculture facilities can result in both negative genetic and ecological interactions with wild populations, yet the ability to predict the associated risk to wild populations has remained elusive. Here we assess the potential of a spatiotemporal database of aquaculture facility locations, production estimates, and escape events to predict the distribution of escaped farmed salmon and genetic impacts on wild populations in the Northwest Atlantic. Industry production data, reported escape events, and in-river detections of escaped farmed salmon were collected from across the Northwest Atlantic. Genetic estimates of impact were obtained using single nucleotide polymorphisms (95 loci) representing aquaculture and wild salmon throughout the region (30 populations, 3048 individuals). Both the number of escaped farmed salmon detected at counting facilities and the magnitude of genetic impacts were positively correlated with a cumulative spatial measure of aquaculture production. Our results suggest that the risk of escapees and genetic introgression from wild–farmed salmon interactions can be assessed using information on farm production characteristics. This represents a first step in predicting the impact of existing cage-based farms on wild Atlantic salmon.
... Spatial patterns of hybridization in cutthroat trout can be complex. In many systems, distance to a source of rainbow trout is a primary predictive variable of the extent of hybridization (Rubidge and Taylor 2005;Boyer et al. 2008;Gunnell et al. 2008;Muhlfeld et al. 2009c;Bennett et al. 2010;Rasmussen et al. 2010). However, various local environmental conditions (such as water temperature, stream width, and elevation) may also correlate with variation in spatial patterns (Weigel et al. 2003;Gunnell et al. 2008;Muhlfeld et al. 2009c;Rasmussen et al. 2010). ...
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Human-induced hybridization between fish populations and species is a major threat to aquatic biodiversity worldwide and is particularly relevant to management of the subspecies of cutthroat trout Oncorhynchus clarkii. The upper Snake River basin in Wyoming contains one of the largest remaining populations of Yellowstone cutthroat trout O. clarkii bouvieri, a subspecies of special concern throughout its range; however, little is known about levels of hybridization between Yellowstone cutthroat trout and exotic rainbow trout O. mykiss or about the overall genetic population structure for this river basin. There is concern that the Gros Ventre River is a source of hybridization for the Snake River basin. We sampled across the upper Snake River basin to estimate levels of hybridization and population structure and to describe hybrid zone structure and spatial patterns of hybridization throughout the basin. We used this information to help resolve whether the Gros Ventre River was acting as a potential source of hybridization for the upper Snake River basin. We found that Yellowstone cutthroat trout genotypes dominated the river system, but hybridization was detected at low levels in all populations. The Gros Ventre River contained the highest levels of hybridization (population and individual) and displayed evidence of ongoing hybridization between parental genotypes. Levels of hybridization decreased as a function of distance from the Gros Ventre River, suggesting that this population is acting as a source of rainbow trout genes. These patterns were evident despite the fact that levels of genetic connectivity appeared to be higher than those observed in other cutthroat trout populations (global genetic differentiation index F ST = 0.04), and we did not find evidence for genetic isolation by distance. Management actions aimed at reducing the presence of highly hybridized cutthroat trout or rainbow trout individuals in the Gros Ventre River will help to maintain the upper Snake River basin as an important conservation area.Received August 30, 2010; accepted August 9, 2011
Article
Introgressive hybridization with introduced species is threatening the genetic integrity of many native fish populations worldwide. To date, several studies have indicated a direct relationship between rates of hybridization (H) within a sub-population of native fish and the stream distance (D) separating that sub-population from the closest source of introduced non-native genes. However, the relationship between D and H is rarely quantified, and the effect of the spatial arrangement of stream bifurcations and sub-populations (i.e., the network topology) is typically ignored. For this study, we developed and applied a novel individual-based simulation model to compare the spread of non-native genes across three stream networks with differing network topologies: linear, trellis, and dendritic. The model we used simulates mating, survival, and the movements of each fish in the network, where the likelihood of a fish to move between two sub-populations is a function of both D and the number of bifurcations between the two sub-populations. To monitor the spatiotemporal spread of hybridization, the model keeps track of the genetic composition and the breeding location of each fish present in the network over time. Simulation results agree with past field studies that suggest that D is a strong predictor of H. However, our simulations further suggest that the nature and the strength of the H vs. D relationship are likely to be a function of the stream network topology. Specifically, in our simulations, network bifurcations act as permeable barriers to the spread of non-native genes across a network while the strength of the H vs. D relationship is inversely proportional to the complexity of the spatial arrangement of bifurcations and sub-populations. Our study shows that considering network topology could yield a better understanding of observed patterns of hybridization across stream systems, and thus may help inform effective strategies for the management of native fish populations threatened by introgression.
Article
The threatened Paiute cutthroat trout (Oncorhynchus clarkii seleniris, PCT) is endemic to Silver King Creek, California, USA, which was stocked with non-native trout beginning in 1930. Single nucleotide polymorphism (SNP) and microsatellite data reveal that the trout population in Silver King Creek is weakly structured and composed of introgressed California golden trout (Oncorhynchus mykiss aguabonita, CAGT), hatchery rainbow trout (Oncorhynchus mykiss, RT), and some native PCT. Two SNP groups were analyzed: (i) one mitochondrial and five autosomal SNPs, diagnostic between Lahontan cutthroat trout (Oncorhynchus clarkii henshawi) or PCT and CAGT or RT and (ii) one mitochondrial and five autosomal SNPs nearly diagnostic between CAGT and RT. The five autosomal cutthroat–rainbow SNPs were used to jointly estimate the cutthroat trout mixing proportion in Silver King Creek and effective population size (Ne) of the admixed population, using a coalescent-based maximum likelihood method. Given the stocking history of Silver King Creek, there are two different scenarios that bound the range of expected point estimates for Ne. We obtain point estimates of Ne = 150 and Ne = 750 for Silver King Creek under these two scenarios. This method will be useful in cases with differentiated taxa and in prioritizing conservation and restoration programs where the populations of concern are introgressed.
Article
The spread of nonnative species over the last century has profoundly altered freshwater ecosystems, resulting in novel species assemblages. Interactions between nonnative species may alter their impacts on native species, yet few studies have addressed multispecies interactions. The spread of whirling disease, caused by the nonnative parasite Myxobolus cerebralis, has generated declines in wild trout populations across western North America. Westslope Cutthroat Trout Oncorhynchus clarkii lewisi in the northern Rocky Mountains are threatened by hybridization with introduced Rainbow Trout O. mykiss. Rainbow Trout are more susceptible to whirling disease than Cutthroat Trout and may be more vulnerable due to differences in spawning location. We hypothesized that the presence of whirling disease in a stream would (1) reduce levels of introgressive hybridization at the site scale and (2) limit the size of the hybrid zone at the whole-stream scale. We measured levels of introgression and the spatial extent of hybridization between Rainbow Trout and Westslope Cutthroat Trout in four disease-positive streams and six disease-negative streams within the Blackfoot River basin of Montana. In addition to disease status, we considered habitat quality, stream slope, distance from the confluence, temperature, and elevation. Whirling disease presence was not associated with either the level of introgression at a site or the size of the hybrid zone. Temperature, elevation, and stream slope were all influential in determining levels of introgression at the site scale. Stream slope was the most influential factor determining the size of the hybrid zone, as longer, steeper streams contained smaller hybrid zones. Stream slope is a driver of many habitat characteristics that may provide refuge from invasive species in the coming decades. Although the multispecies interactions examined in this study did not alter the impacts of invasion on native species, community assemblages will continue to change with the spread of nonnative species, requiring continued assessment to determine their impacts on native species.
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Invasive hybridization—when invasive species interbreed with native species—is a pervasive conservation issue. Hybridization presents difficult management decisions and poses complex problems at the intersection of contemporary evolution, invasion biology, physiology, and landscape ecology. I examined the invasion scenario playing out in the Lamar River watershed of Yellowstone National Park where native Yellowstone cutthroat trout (YCT) are undergoing hybridization with introduced rainbow trout (RT). I first test the hypothesis that a breeding timing mismatch of an invasive species (i.e., RT often spawn far earlier than YCT, and eggs are scoured by snowmelt runoff) can be overcome by hybridization with a locally adapted native species, that spawn later (Chapter 2). I found support for this hypothesis. Spawning timing was strongly related to the degree of non-native admixture at the individual level, indicating that hybridization alters breeding timing in ways that could benefit hybrids. At the population level, hybrid spawning timing closely matched that of native taxa and was strongly correlated to stream flow conditions. Overall, these data suggest poorly matched spawning timing is unlikely to serve as a strong mechanism limiting invasive hybridization of YCT. Next, I mapped the spatial distribution of hybridization in the Lamar River watershed (Chapter 3). Many non-hybridized populations persist in the upper watershed, whereas a prominent source of RT in the lower watershed has likely contributed inordinately to the spread of introgression. Because hybridized populations occurred across a full range of environmental conditions, I do not predict that abiotic conditions (i.e., cold water, late-stream flow, high elevations, or small stream size) will prevent the spread of hybridization in the long-term. As such, management interventions are recommended in chapter 4 and 5. I developed a simple taxonomic key to identify hybrids and guide selective removal efforts (Chapter 4). Additionally, I used volunteer angler surveys to estimate that recreational anglers visiting the watershed (~10,000 per year) could likely harvest a substantial number of non-native trout that would contribute to genetic management goals. I conclude by providing recommendations for management and monitoring (Chapter 5).
Article
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Understanding factors mediating hybridization between native and invasive species is crucial for conservation. We assessed the spatial distribution of hybridization between invasive rainbow trout (Oncorhynchus mykiss) and native Yellowstone cutthroat trout (O. clarkii bouveri) in the Lamar River of Yellowstone National Park using a paired telemetry and genetic dataset. Spawning populations containing hybrids (15/30) occupied the full spectrum of abiotic conditions in the watershed (stream temperature, stream size, runoff timing), including an intermittent stream that dried completely in late-June, and mainstem spawning locations. Hybrids and rainbow trout occupied an entire high-elevation (~ 2,500 – 1,900 m) tributary where rainbow trout ancestry was highest in headwaters and decreased downstream. Fluvial distance to this ostensible source population was the only covariate included in top hybridization models; effects of abiotic covariates and stocking intensity were relatively weak. In this watershed, abiotic conditions are unlikely to mediate continued hybridization. We conclude that management intervention is important for the persistence of non-hybridized Yellowstone cutthroat trout, and highlight the value of pairing telemetry with genetic analysis to identify and characterize populations for hybridization assessments.
Article
In this study we examine how the stocking of rainbow trout (Oncorhynchus mykiss), as well as the presence of fish movement barriers, influences the probability of introgression with westslope cutthroat trout (Oncorhynchus clarkii lewisi). We measured the level of introgression in cutthroat trout sampled from 32 locations that occurred either above or below fish movement barriers along with the frequency and number of rainbow trout stocked in the watershed over a 43-year period. The occurrence and level of hybridization in cutthroat trout were not related to whether the site was above a movement barrier or not. In contrast, the level of introgression was related to the distance to the nearest stocking location, the number of stocking events within the nearest watershed, and the total number of rainbow trout stocked in that watershed. Our data indicate that westslope cutthroat trout located further from stocking have a lower risk of introgression with rainbow trout, but those isolated above movement barriers should not be considered free from introgression until a thorough genetic assessment of the location has been made.
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Plant can directly take up the intact amino acids, thus bypass the microbial mineralization of organic nitrogen. As an excellent carbon and nitrogen source, there exists competition for amino acid absorption between plant roots.and soil microorganisms. And the total flux of amino acids in soil may be enormous due to the extensive sources and short half-life. Studies on amino acid nitrogen nutritional contribution for plant by the technique of nitrogen isotopic tracer, has become a research topic in recent years ,which will help us better understand the principle of soil fertility. This paper summarized the recent researches on amino acid morphological characteristics in soil and its metabolic mechanism and nitrogen nutritional contribution for plant in different ecosystems, and discussed the present status and development trend of the amino acid circulation mechanism in the plant-soil-microorganism ecosystem and its bioavailability for plant. Finally, the topics of environmental regulating mechanism of amino acid bioavailability, amino acid carbon-nitrogen metabolism, and how to improve the field organic nitrogen management were all the core issues to be resolved.
Article
Hybridization can profoundly affect the genomic composition and phenotypes of closely related species, and provides an opportunity to identify mechanisms that maintain reproductive isolation between species. Recent evidence suggests that hybridization outcomes within a species pair can vary across locations. However, we still don't know how variable outcomes of hybridization are across geographic replicates, and what mechanisms drive that variation. In this study, we described hybridization outcomes across 27 locations in the North Fork Shoshone River basin (Wyoming, USA) where native Yellowstone cutthroat trout and introduced rainbow trout co‐occur. We used genomic data and hierarchical Bayesian models to precisely identify ancestry of hybrid individuals. Hybridization outcomes varied across locations. In some locations, only rainbow trout and advanced backcrossed hybrids towards rainbow trout were present, while trout in other locations had a broader range of ancestry, including both parental species and first‐generation hybrids. Later‐generation intermediate hybrids were rare relative to backcrossed hybrids and rainbow trout individuals. Using an individual‐based simulation, we found that outcomes of hybridization in the North Fork Shoshone River basin deviate substantially from what we would expect under null expectations of random mating and no selection against hybrids. Since this deviation implies that some mechanisms of reproductive isolation function to maintain parental taxa and a diversity of hybrid types, we then modeled hybridization outcomes as a function of environmental variables and stocking history that are likely to affect prezygotic barriers to hybridization. Variables associated with history of fish stocking were the strongest predictors of hybridization outcomes, followed by environmental variables that might affect overlap in spawning time and location. This article is protected by copyright. All rights reserved.
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In the neotropics, potamodromous fish species are among the most severely impacted by dams, which can lead to blocking of the migratory routes, elimination of the breeding areas, and population isolation in this group. However, growing evidence has indicated that free-flowing tributaries along fragmented watersheds provide important contributions to the reproductive migration and recruitment of migratory fish. If this is really occurring, we could expect low or undetectable population differences in different reservoirs and respective unimpeded tributaries along watersheds fragmented by dams. Aiming to test this hypothesis, we assessed the genetic diversity and population structure of Pimelodus maculatus, a migratory catfish species, in seven reservoirs and nine tributaries along the Paranapanema River basin, Paraguay-Paraná-Plata system, South America. As predicted in our initial hypothesis, after analyzing nine microsatellite loci and a 406-bp mitochondrial DNA sequence (D-Loop) in 640 individuals, we found high nuclear genetic diversity and non-significant genetic substructuring among each reservoir and its tributaries, contrasting with the results between samples separated by dams. Our findings reinforce the idea that free‐flowing tributary rivers are contributing to maintenance of wider population distributions, larger effective population sizes, and satisfactory genetic diversity levels.
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The distribution and genetic integrity of all inland cutthroat trout (Oncorhynchus clarki ssp.) have been negatively affected by the introduction of non-native salmonid species throughout their range. Westslope cutthroat trout (WCT, O. c. lewisi) have the largest historic distribution of all the inland cutthroat trout. In the USA the range of WCT has contracted and many remaining populations have hybridized with introduced salmonids, especially rainbow trout (RBT, O. mykiss). In this study I evaluate the genetic integrity of WCT in the Upper Kootenay River, British Columbia. We used diagnostic genetic markers and the program NEWHYBRIDS to determine the genotypes of 2,670 fish at 45 sites between 1999 and 2006. A broad hybrid zone stretching over 200 km was observed with WCT backcross individuals as the dominant hybrid type present (6%). Population genetic analysis revealed that much of the hybridization is relatively recent (2-3 generations) and likely results from stocking RBT in Koocanusa Reservoir. I assessed the ability of a variety of environmental and propagule pressure related variables to predict the levels of introgression using GIS and logistic regression analysis and found that a relative measure of propagule pressure was the best predictor of introgression. Long-term monitoring revealed that most low elevation sites were close to becoming complete hybrid swarms, and introgression at mid elevations < 80 km from the Koocanusa Reservoir was increasing as a result of hybrids straying from the low elevation sites. We recommend that the sources of RBT be more thoroughly identified, remaining pure WCT populations be confirmed, more inventory work be conducted to determine which streams are non-fish bearing, a ban on all fertile RBT stocking be implemented, and more studies be undertaken to evaluate the life history characteristics of the native WCT.
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We examined spatial and temporal patterns of hybridization between native westslope cutthroat trout, Oncorhynchus clarki lewisi, and normative rainbow trout, O. mykiss, in streams of the Flathead River system in Montana, U.S.A. We detected hybridization in 24 of 42 sites sampled from 1998 to 2001. We found new Oncorhynchus mykiss introgression in seven of 11 sample populations that were determined to be nonhybridized in 1984. Patterns of spatial autocorrelation and linkage disequilibrium indicated that hybridization is spreading among sites and is advancing primarily via post-F-1 hybrids. Although hybridized populations were distributed widely throughout the study area, the genetic contribution from O. mykiss decreased with increasing upstream distance from the Flathead River mainstem, suggesting that O. mykiss introgression is spreading in an upstream direction. The spread of hybridization may be constrained more by demographic than by environmental factors, given that (i) hybridized populations generally encompassed the range of environmental variability in nonhybridized populations, and (ii) hybridization status was more strongly associated with neighborhood statistics than measured environmental gradients.
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Water temperature appears to play a key role in determining population persistence of westslope cutthroat trout Oncorhynchus clarkii lewisi, but specific thermal performance and survival criteria have not been defined. We used the acclimated chronic exposure laboratory method to determine upper thermal tolerances and growth optima of westslope cutthroat trout and rainbow trout O. mykiss, a potential nonnative competitor that occupies much of the former range of westslope cutthroat trout. Rainbow trout had a distinct survival advantage over westslope cutthroat trout at water temperatures above 20°C. The ultimate upper incipient lethal temperature of rainbow trout (24.3°C; 95% confidence interval [CI] = 24.0–24.7°C) was 4.7°C higher than that of westslope cutthroat trout (19.6°C; 95% CI = 19.1–19.9°C). In contrast, both species had similar growth rates and optimum growth temperatures (westslope cutthroat trout: 13.6°C; rainbow trout: 13.1°C) over the temperature range of 8–20°C, although rainbow trout grew over a wider range and at higher temperatures than did westslope cutthroat trout. The rainbow trout's higher upper temperature tolerance and greater growth capacity at warmer temperatures may account for the species' displacement of westslope cutthroat trout at lower elevations. Our results indicate that maximum daily temperatures near the optimum growth temperature of 13–15°C would ensure suitable thermal habitat for westslope cutthroat trout populations. The low upper temperature tolerance and optimum growth temperature of westslope cutthroat trout relative to those of other salmonids suggest that this subspecies may be particularly susceptible to stream temperature increases associated with global warming and anthropogenic habitat disturbance.
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Many recent studies of nonindigenous species (NIS) have used life history and morphological characteristics of invaders to either (i) build statistical models that predict new invaders or (ii) test ecological and evolutionary hypotheses. However, species characteristics may be confounded if NIS are transported or introduced nonrandomly with respect to the chosen contrast group, which typically consists of native or globally available species. For example, deliberately introduced NIS are often chosen according to economic rather than ecological factors. Here, I use stocking records of salmonid species introduced into Nevada, USA, to test for propagule biases within this system. I find that established salmonids are introduced significantly more times, and in greater numbers, than are those that fail and that species chosen for introduction are a nonrandom sample of the global salmonid species pool. Statistical differences among characteristics of salmonid species that established, those that were introduced, and those from the global source pool suggest that maximum reported size and weight as well as latitudinal range and midlatitude all represent propagule-biased characteristics of salmonids introduced into Nevada. These results highlight the need for caution when using characteristics of invaders to develop statistical models or to test hypotheses relevant to ecology and evolution.
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Artificial barriers are important management tools for protecting populations of native fishes from encroaching nonnative species. We evaluated the effectiveness of gabion and culvert barriers in preventing upstream movement of brook trout Salvelinus fontinalis in four small Rocky Mountain streams that contained native populations of Colorado River cutthroat trout Oncorhynchus clarki pleuriticus. A rock-filled gabion in one stream and a road culvert in a second stream appeared to block upstream movement of brook trout; no fish marked and released downstream of the barriers were subsequently found upstream of the barriers. However, in a third stream, 18 of 86 brook trout marked and placed downstream of a rock-filled gabion barrier were later found upstream of the barrier during 3 years of evaluation. These fish ranged in length from 81 to 224 mm total length, so all size-classes were able to navigate past the structure. One brook trout moved upstream past the gabion twice, the second time during low flows when all water was percolating through the structure. We concluded that brook trout were able to move upstream through the rocks in this gabion barrier because fine sediments had not filled in all the interstitial spaces. Attention should be given to preventing movement of fish through gabion-type barriers, not just over or around them. In the fourth stream, 1 of 48 marked brook trout was found upstream from a road culvert barrier. Because this barrier appeared to be functioning properly during our study, we suspect this fish was moved upstream by an angler.
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We describe the historical and current distributions and genetic status of westslope cutthroat trout Oncorhynchus clarkii lewisii (WCT) throughout its range in the western United States using data and expert opinion provided by fish managers. Westslope cutthroat trout historically occupied 90,800 km and currently occupy 54,600 km; however, these are probably underestimates due to the large-scale (1:100,000) mapping we used. Genetic analyses found no evidence of genetic introgression in 768 samples (58% of samples tested), but the numbers of individuals tested per sample were variable and sample sites were not randomly selected. Approximately 42% of the stream length occupied by WCT is protected by stringent land use restrictions in national parks (2%), wilderness areas (19%), and roadless areas (21%). A total of 563 WCT populations (39,355 km) are being managed as “conservation populations,” and while most (457, or 81%) conservation populations were relatively small, isolated populations, large and interconnected metapopulations occupied much more stream length (34,820 km, or 88%). While conservation populations were distributed throughout the historical range (occupying 67 of 70 historically occupied basins), they were much denser at the core than at the fringes. From the information provided we determined that conserving isolated populations (for their genetic integrity and isolation from nonnative competitors and disease) and metapopulations (for their diverse life histories and resistance to demographic extinction) is reasonable. We conclude that while the distribution of WCT has declined dramatically from historical levels, as a subspecies WCT are not currently at imminent risk of extinction because (1) they are still widely distributed, especially in areas protected by stringent land use restrictions; (2) many populations are isolated by physical barriers from invasion by nonnative fish and disease; and (3) the active conservation of many populations is occurring.
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Native subspecies of cutthroat trout Oncorhynchus clarki have declined drastically because of the introduction of nonnative salmonids, overharvesting, and habitat degradation. Con- servation of most declining subspecies will include establishing new populations through trans- location of genetically pure fish. Recovery of greenback cutthroat trout O. clarki stomias has been ongoing for 25 years, so the attempted translocations of this subspecies provide unique empirical information to guide recovery of other nonanadromous salmonids. We compared 14 translocations that successfully established populations of greenback cutthroat trout to 23 that failed to determine the factors that influenced translocation success. Of the translocations that failed, 48% were re- invaded by nonnative salmonids, 43% apparently had unsuitable habitat, and 9% experienced suppression by other factors. Reinvasion occurred most often because of failed artificial barriers or incomplete removal of nonnative salmonids in complex habitats. Of those areas that were not reinvaded, success was highest in receiving waters with at least 2 ha of habitat that had previously
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A major cause of population declines among interior cutthroat trout subspecies Oncorhynchus clarki ssp.is hybridization with introduced rainbow trout O. mykiss ssp. Coastal cutthroat trout O. c. clarki have also experienced population declines in recent decades and are known to hybridize with coastal rainbow trout/steelhead O. m. irideus. However, unlike interior cutthroat trout, coastal cutthroat trout are naturally sympatric with coastal rainbow trout/steelhead, and the role of hybridization in their population declines remains unclear. Further, little is known about the spatial and temporal distributions of hybridization in these coastal subspecies. As a step toward better characterization of this hybridization, we developed a suite of species-specific DNA markers for coastal cutthroat trout and coastal rainbow trout/steelhead. Of 11 loci presented here, 8 exhibit fixed differences between coastal cutthroat trout and coastal rainbow trout/steelhead. The other three loci revealed frequency differences great enough to make them useful as species markers. To demonstrate their utility, five of the markers developed here were used to assay a coastal cutthroat trout hatchery broodstock for the presence of hybrids. DNA-based markers can be assayed using nonlethal fin clips or archived samples and hence offer advantages for the study of historical and threatened contemporary populations.
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It is often claimed that we do not understand the forces driving the global diversity gradient. However, an extensive literature suggests that contemporary climate constrains terrestrial taxonomic richness over broad geographic extents. Here, we review the empirical literature to examine the nature and form of the relationship between climate and richness. Our goals were to document the support for the climatically based energy hypothesis, and within the constraints imposed by correlative analyses, to evaluate two versions of the hypothesis: the productivity and ambient energy hypotheses. Focusing on studies extending over 800 km, we found that measures of energy, water, or water-energy balance explain spatial variation in richness better than other climatic and non-climatic variables in 82 of 85 cases. Even when considered individually and in isolation, water/ energy variables explain on average over 60% of the variation in the richness of a wide range of plant and animal groups. Further, water variables usually represent the strongest predictors in the tropics, subtropics, and warm temperate zones, whereas energy variables (for animals) or water-energy variables (for plants) dominate in high latitudes. We conclude that the interaction between water and energy, either directly or indirectly (via plant pro- ductivity), provides a strong explanation for globally extensive plant and animal diversity gradients, but for animals there also is a latitudinal shift in the relative importance of ambient energy vs. water moving from the poles to the equator. Although contemporary climate is not the only factor influencing species richness and may not explain the diversity pattern for all taxonomic groups, it is clear that understanding water-energy dynamics is critical to future biodiversity research. Analyses that do not include water-energy variables are missing a key component for explaining broad-scale patterns of diversity.
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The "restricted-movement paradigm" (RMP) states that adult fish in streams are sedentary and spend most of their lives in short (20-50 m) reaches of stream. In mark-recapture studies, however, many fish initially marked are often never recaptured. As well, turnover rates of individuals in the home section (where fish were originally marked) can be high when marked fish moving out are rapidly replaced by unmarked ones. Recent challenges to the RMP have been based on the inference that high turnover indicates high mobility. However, when the home section is small many individuals may leave (high turnover) but not move far away (low displacement). I present two models for the frequency distribution of displacement distances: one represents populations as homogeneous ensembles with a single mobility parameter; the second represents populations as a mixture of stationary and mobile individuals. Both readily distinguish the turnover and displacement components of movement and show that high turnover rate is compatible with low displacement. The models were then fit to dispersal curves for six species of stream salmonids in 27 populations. Empirical estimates of turnover rate were high (median: 0.53), variable among populations (range: 0.15-0.78), but unrelated to displacement distance. Median displacement was
Article
A popular trout fishery in the Clinch River below Norris Dam, Tennessee, is maintained by an extensive stocking program. However, survival and return rates of rainbow trout Oncorhynchus mykiss stocked as catchables are low. Twenty rainbow trout (mean total length (TL) = 307 mm) that had resided in the tailwater at least 5 months were collected from the river and implanted with radio transmitters in June 1998. Similarly sized rainbow trout were implanted with radio transmitters at a hatchery and stocked into the Clinch River on 8 July 1998 (N = 19; mean TL = 304 mm) and 16 September 1998 (N = 11; mean TL = 311 mm). The stocked rainbow trout dispersed rapidly and nearly all (93%) of those fish died quickly or emigrated from the tailrace. Resident fish were significantly less active than stocked fish, and they persisted significantly longer (Kruskal–Wallis tests, P = 0.0001). Poor return rates and survival of rainbow trout stocked as catchables were attributed to their rapid, long-range movements and high levels of activity. Such behaviors are energetically inefficient and probably rendered them more vulnerable to predation.
Article
Despite their protected status, aquatic ecosystems of Banff National Park have been subjected to a number of human stresses. Largely as the result of stocking programs earlier in the century, 10 species of nonnative fishes now occur in the Park, while one endemic subspecies of fish has been extirpated, and 2 other species are threatened. A number of rare invertebrates occur in hot springs and caves, including one mollusk that is endangered. Key invertebrates were extirpated from a number of fishless lakes by stocked fish, and in some cases have not returned, even though fishes did not survive. Restoration efforts in 2 small alpine lakes are described. Addition of nutrients and road salt have changed the chemical nature of the Bow River and its tributaries, and caused incidence of benthic algal mats to form in some sections. Impoundment and diversions affect over 40% of the Bow River catchment within the Park. Airborne organic contaminants concentrate in glaciers and high elevation snowpacks, yielding amounts high enough to contaminate fisheries to levels that in some cases approach guidelines for human consumption.
Book
1. Introduction 2. Estimation 3. Hypothesis testing 4. Graphical exploration of data 5. Correlation and regression 6. Multiple regression and correlation 7. Design and power analysis 8. Comparing groups or treatments - analysis of variance 9. Multifactor analysis of variance 10. Randomized blocks and simple repeated measures: unreplicated two-factor designs 11. Split plot and repeated measures designs: partly nested anovas 12. Analysis of covariance 13. Generalized linear models and logistic regression 14. Analyzing frequencies 15. Introduction to multivariate analyses 16. Multivariate analysis of variance and discriminant analysis 17. Principal components and correspondence analysis 18. Multidimensional scaling and cluster analysis 19. Presentation of results.
Article
Our goal was to assess the likelihood of hybridization between introduced rainbow trout Oncorhynchus mykissand native Yellowstone (YS) cutthroat trout O. clarki bouvieri, based upon habitat use and temporal overlap during spawning. We used radio transmitters in 1996 and 1997 to describe the spawning behavior of rainbow trout, hybrids of rainbow trout and YS cutthroat trout, and YS cutthroat trout (1997 only). Fish displayed two distinct spawning strategies, either spawning in side channels of the main stem (9 rainbow trout, 14 hybrids, and 10 YS cutthroat trout) or in tributaries (5 rainbow trout, 3 hybrids, and 7 YS cutthroat trout). Within the main stem, the majority of rainbow trout and YS cutthroat trout migrated to the same 8-km section to spawn, whereas hybrid trout spawned throughout the study site. The median spawning date for main-stem-spawning YS cutthroat trout (June 9) was significantly later than for rainbow trout (May 19) and hybrids (May 18). However, long spawning periods for rainbow trout (94 d), hybrids (113 d), and YS cutthroat trout (71 d) allowed for considerable overlap. The amount of spawning overlap varied among the four tributaries. In one tributary, complete spatial and some temporal overlap occurred (three rainbow trout, two hybrids, and two YS cutthroat trout); in another tributary no spatial or temporal overlap occurred (four rainbow trout and three YS cutthroat trout); and only YS cutthroat trout used the remaining two tributaries (one YS cutthroat trout in each). Molecular analyses verified that females of both rainbow trout and YS cutthroat trout were hy- bridizing and showed that the genetic composition of hybrid trout was more similar to rainbow trout than to YS cutthroat trout (mean 5 64% rainbow trout markers). These results suggest that the majority of YS cutthroat trout (12 of 17) experience spatial and temporal overlap with rainbow trout and hybrids, but three tributaries may still provide some reproductive isolation for native fish.
Article
Hybridization between native bull trout Salvelinus confluentus and introduced brook trout S. fontinalis occurs over a wide geographic area in the western United States. We described the extent to which introgressive hybridization has occurred between these species using biochemical and molecular genetic techniques in samples collected from five streams in western Montana. We found that about three-quarters of the hybrids detected were male, first-generation (F1) hybrids. Most of the rest were backcrosses to the parental species, indicating that F1 hybrids can reproduce. We found no evidence of hybrid swarms in which all individuals were of hybrid origin. Our results suggest that both the reduced fertility of F1 hybrids and the reduced survival of their progeny prevents these species from forming such hybrid swarms. We also found that hybridization between bull and brook trout tends to occur predominantly between female bull trout and male brook trout, indicating that hybridization represents greater wasted reproductive effort for bull trout than for brook trout.
Article
We surveyed 53 stream reaches from the eastern slopes of the Canadian Rocky Mountains and examined the distribution of native and nonnative salmonids as related to habitat variables measured at the reach scale (100 m). The most common fishes encountered in these surveys were cutthroat trout Oncorhynchus clarki, bull trout Salvelinus confluentus, brook trout S. fontinalis, and rainbow trout O. mykiss. Of these salmonids, only cutthroat and bull trout are native to Kananaskis Country; however, cutthroat trout have also been extensively stocked throughout the region. Reach elevation, which strongly influenced mean summer stream temperatures, was the only habitat variable that was significantly related to the presence of all four salmonids. Both cutthroat and bull trout were more likely to occur in the higher elevations, whereas brook and rainbow trout were more likely to occur in the lower elevations. Because the distribution of stocked fishes is not independent of their original stocking locations, we tested the hypothesis that their distribution was simply an artifact of past stocking. Based on the historical stocking record for the surveyed region, brook and rainbow trout would be more prevalent in higher elevations if stocking location only dictated their presence. This expectation directly contradicts our observed results, suggesting there has been a preferential downstream movement of brook and rainbow trout to colonize streams at lower elevations. In contrast, the distribution of cutthroat trout predicted from the stocking record and observed from the stream surveys did not differ, suggesting their current distribution may reflect past stocking.
Article
We used polymerase chain reaction (PCR) primers that are complementary to interspersed nuclear DNA elements to identify genetic markers capable of detecting hybridization between native Colorado River cutthroat trout Oncorhynchus clarki pleuriticus (CRCT) or greenback cutthroat trout O. c. stomias (GCT) and introduced Yellowstone cutthroat trout O. c. bouvieri (YCT) or rainbow trout O. mykiss (RT). Using four different pair combinations of five PCR primers, we detected 6 genetic markers that distinguish CRCT from YCT (3 that are characteristic of CRCT and 3 that are characteristic of YCT) and 14 markers that distinguish CRCT from RT (9 characteristic of CRCT and 5 of RT). Likewise, we detected 5 genetic markers that distinguish GCT from YCT (2 characteristic of GCT and 3 of YCT) and 14 that distinguish GCT from RT (8 characteristic of GCT and 6 of RT). We did not, however, find markers that distinguish CRCT from GCT. This molecular genetic technique will thus be effective as a nonlethal means of detecting hybridization between CRCT or GCT and YCT or RT. Although no marker was identified that differentiates CRCT and GCT, additional combinations of PCR primers might uncover such markers.
Article
Introgressive hybridization threatens the persistence of several species of native salmonids in the western United States, but little is known about the factors influencing the establishment and maintenance of introgressed populations. We examined the occurrence of introgressive hybridization in westslope cutthroat (Oncorhynchus clarki lewisi) and rainbow trout (O. mykiss) populations in relation to physical characteristics of streams, trout density estimates, and the distance from stocking source. Trout were sampled from 80 stream sites in the Clearwater River Basin, Idaho, USA, and tissues from individual trout were analyzed to detect hybridization using noncoding sequences of nuclear DNA. We found a broad zone of hybridization detected at 64% of the sampled sites. The presence and degree of introgression was negatively related to elevation and positively related to stream width in our logistic regression model. Stream elevation and size likely influence hydrologic and thermal regimes. An interaction between the life history characteristics of the native and nonnative trout with these hydrologic and thermal stream gradients could explain the invasion success of rainbow trout and hence, the extent of the hybrid zone. Alternatively, the influence of elevation and stream width could be the result of habitat selection by the parental species, thereby reducing the opportunity for hybridization. Understanding the relationship between abiotic factors and introgressive hybridization will assist fisheries managers when evaluating the potential threat of introgression in different stream habitats and applying the necessary management actions to conserve the native cutthroat trout genotypes across broad landscapes.
Article
The use of molecular genetic techniques is becoming increasingly widespread in analyses of hybrid zones. Yet, exactly how many molecular markers are required to provide a given degree of resolution remains an open question. We present statistical models that relate the number of markers examined to their power to discriminate between pure species, Fl's, and backcross individuals. Our models indicate that only about four or five markers are required to provide a coarse classification of individuals in hybrid zones, whereas upwards of 70 markers are required to discriminate between pure species and advanced backcrosses. The models provide hybrid zone researchers a basis upon which to balance the time and expense of examining large numbers of markers against the magnitude of classification errors when smaller numbers of markers are examined.
Article
Historic introductions of nonnative rainbow trout Oncorhynchus mykiss into the native habitats of cutthroat trout O. clarkii have impacted cutthroat trout populations through introgressive hybridization, creating challenges and concerns for cutthroat trout conservation. We examined the effects of rainbow trout introductions on the native westslope cutthroat trout O. c. lewisii within the Stehekin River drainage, North Cascades National Park, Washington, by analyzing 1,763 salmonid DNA samples from 18 locations with nine diagnostic nuclear DNA markers and one diagnostic mitochondrial DNA (mtDNA) marker. Pure westslope cutthroat trout populations only occurred above upstream migration barriers in the Stehekin River and Park Creek. Two categories of rainbow trout admixture were observed: (1) less than 10% within the Stehekin River drainage above the Bridge Creek confluence and the middle and upper Bridge Creek drainage and (2) greater than 30% within the Stehekin River below the Bridge Creek confluence and in lower Bridge Creek. Hybrid indices and multilocus genotypes revealed an absence of rainbow trout and reduced hybrid diversity within the Stehekin River above the Bridge Creek confluence relative to hybrid diversity in the Stehekin River below the confluence and within lower Bridge Creek. Cytonuclear disequilibrium statistics revealed assortative mating between westslope cutthroat and rainbow trout but not among hybrids within the same locations. This suggests that a randomly mating hybrid swarm does not currently exist. However, continual migration of parental genotypes into the study location could also create significant cytonuclear disequilibria. The Stehekin River represents a novel and unique example of a dynamic hybridization zone where the invasion of rainbow trout alleles into the Stehekin River westslope cutthroat trout population above the Bridge Creek confluence appears to be impeded, suggesting that divergent ecological or evolutionary mechanisms promote the population structure within the Stehekin River drainage, depending upon location.
Article
Influences of large-scale abiotic, geomorphic characteristics on distributions of Yellowstone cutthroat trout Oncorhynchus clarki bouvieri are poorly understood. We sampled 151 sites on 56 perennial streams in the Greybull–Wood river drainage in northwestern Wyoming to determine the effects of geomorphic variables on Yellowstone cutthroat trout distributions. Channel slope, elevation, stream size, and barriers to upstream movement significantly influenced the presence and absence of Yellowstone cutthroat trout. Wild populations of Yellowstone cutthroat trout were not found upstream of barriers to fish migration, at sites with channel slopes of 10% or greater, or at elevations above 3,182 m. Based on channel slope alone, logistic regression models correctly classified presence or absence of Yellowstone cutthroat trout in 83% of study sites. The addition of elevation and stream size in the models increased classification to 87%. Logistic models tested on an independent data set had agreement rates as high as 91 % between actual and predicted fish presence. Large-scale geomorphic variables influence Yellowstone cutthroat trout distributions, and logistic functions can predict these distributions with a high degree of accuracy.
Article
At least 39 species and subspecies of fishes have been introduced into the waters of Nevada since 1873. Of these, 24 kinds are now known to occur in the state. A thorough survey of the exotic fishes has not been made, but specimens or records of introduced species have been kept in the course of rather extensive collecting of the native fish fauna from 1934 to 1943. Consequently it is believed that the number of introduced species herein enumerated approaches a complete tabulation. Some additions among the sunfishes and catfishes may be expected.The annotated list is divided into two parts: species now present in the state, and species introduced but never established. The established kinds constitute about two-thirds of the total number of known native species, but are far outnumbered by the indigenous fishes when all the local subspecies (Hubbs and Miller, in press) are included.The stocking of cutthroat trout and rainbow trout in the same creek should be discouraged since these two species hybridize extensively and the cutthroat trout are speedily eliminated. Brook trout and cutthroat trout, however, do not hybridize. A suggested practice would be to select separate streams when planting rainbow and cutthroat species, a procedure greatly simplified by the presence of many isolated creeks throughout the state.The further distribution of the green sunfish, Lepomis cyanellus, is not recommended as this species is a serious competitor and does not reach a size suitable for game fishing.
Article
As stream order (1–5) increased, width and depth and percent of channel containing rubble increased. With increasing order, channel gradient, channel elevation, and percent of channel composed of gravel decreased. As stream order increased, the number of fish species, summer water space (depth times surface area) for fish, and the total numbers of fish increased. With increasing order, the numbers of chinook salmon, rainbow trout, and sculpin increased, but the numbers of cutthroat trout and Dolly Varden decreased. The analysis demonstrated the value of headwater streams to Dolly Varden and to cutthroat and rainbow trout and resulted in management's emphasizing protection of such waters. Stream order can be used to determine approximate stream size by providing estimate of width and depth.
Article
High-mountain lakes provide important fisheries in the Rocky Mountains; therefore we sought to gain an understanding of the relationships among environmental factors, accessibility to anglers, stocking rates, and features of stocks of cutthroat trout Oncorhynchus clarki in high-mountain lakes of the Bighorn Mountains, Wyoming. We sampled fish with experimental gill nets, measured lake habitat features, and calculated factors affecting angler access among 19 lakes that lacked sufficient natural reproduction to support salmonid fisheries and that were stocked at 1-, 2-, or 4-year intervals with fingerling cutthroat trout. We found that angler accessibility was probably the primary factor affecting stock structure, whereas stocking rates affected the densities of cutthroat trout among lakes. The maximum number of years survived after stocking appeared to have the greatest affect on biomass and population structure. Our findings suggest that control of harvest and manipulation of stocking densities can affect the density, biomass, and structure of cutthroat trout stocks in high-elevation lakes.
Article
We evaluated the effectiveness of isolation management and stocking to meet protection and enhancement goals for native Colorado River cutthroat trout ( Oncorhynchus clarki pleuriticus ) in Wyoming ( U.S.A. ). As a management strategy of the Wyoming Game and Fish Department, cutthroat trout were isolated upstream of artificial barriers in small headwater streams. Non-native trout that might have hybridized, competed with, or preyed upon cutthroat trout were removed from the isolated reaches, and then cutthroat trout of hatchery origin were stocked to augment populations. We monitored the abundance and body condition of cutthroat trout for 4–7 years following isolation in four streams with barriers and in two reference streams without barriers. Barriers limited new invasions by non-native trout, and removals of non-native trout greatly reduced their abundance but did not eliminate them ( mainly brook trout [ Salvelinus fontinalis] ). Wild cutthroat trout persisted in low numbers upstream of barriers, but there was no evidence of enhancement of populations. Stocked cutthroat trout did not persist upstream of barriers, and many moved downstream over barriers. The body condition of wild cutthroat trout was comparable among populations upstream and downstream of barriers and in reference streams. Isolation management provided only short-term benefits by minimizing the risks of hybridization and allowed populations to persist during the study. Removal of non-native trout and stocking did not enhance wild cutthroat trout populations, however, likely because the isolated reaches lacked critical habitat such as the deep pools necessary to sustain large fish. Also, barriers disrupt migratory patterns and prevent seasonal use of headwater reaches by adult cutthroat trout. Longer-term consequences of isolation include vulnerability to stochastic processes and loss of genetic diversity. Where non-native species pose an immediate threat to the survival of native fishes, isolation in headwater streams may be the only conservation alternative. In such situations, isolated reaches should be as large and diverse as possible, and improvements should be implemented to ensure that habitat requirements are met. Resumen: Evaluamos la efectividad del aislamiento y de la repoblación para alcanzar las metas de protección y mejoramiento de la trucha nativa del río Colorado, Oncorhynchus clarki pleuriticus, en Wyoming ( EE.UU. ). Como una estrategia de manejo del Departamento de Caza y Pesca de Wyoming, se aislaron las truchas nativas aguas arriba de barreras artificiales, en arroyos de cabecera. Se removieron de estas zonas aisladas las truchas no nativas que pueden hibridizar, competir o depredar a la trucha nativa y se sembraron estas zonas con truchas de criadero para aumentar las poblaciones. Hicimos un seguimiento de la abundancia y la condición corporal de las truchas por 4 a 7 años después del aislamiento en cuatro arroyos con barreras y en dos arroyos sin barreras como referencia. Las barreras limitaron nuevas invasiones de truchas no nativas, y las remociones de truchas no nativas redujeron su abundancia pero no las eliminaron ( principalmente Salvelinus fontinalis ). Las truchas nativas silvestres persistieron en pequeño número aguas arriba de las barreras; sin embargo, no hubo evidencia de incrementos de sus poblaciones. Las truchas sembradas no persistieron aguas arriba de las barreras y muchas se desplazaron aguas abajo cruzando las barreras. La condición corporal de las truchas nativas era similar entre las poblaciones aguas arriba y aguas abajo de las barreras y en los arroyos sin barreras. El aislamiento como herramienta de manejo solo proporcionó un beneficio a corto plazo al minimizar los riesgos de la hibridación y permitió que las poblaciones persistieran durante el estudio. Sin embargo, la remoción de truchas no nativas y la siembra no mejoró las poblaciones de truchas nativas silvestres, debido probablemente a que las áreas aisladas carecían del hábitat crucial tal como pozos profundos necesarios para proveer sustento a los peces de mayor tamaño. Además, las barreras desestabilizan los patrones migratorios e impiden que las truchas adultas hagan un uso estacional de los arroyos de cabecera. Las consecuencias a largo plazo del aislamiento incluyen la vulnerabilidad a procesos estocásticos y la pérdida de diversidad genética. El aislamiento de arroyos de cabecera puede ser la única alternativa de conservación en la que las especies no nativas son una amenaza inmediata para la supervivencia de peces nativos. En tales situaciones, las áreas aisladas deben ser tan extensas y diversas como sea posible, y se deben implementar mejoras para asegurar que se cumplan los requerimientos de hábitat.
Article
The cutthroat trout (Salmo clarki) presents a series of unusual and difficult problems in conservation biology. As many as 16 subspecies have been recognized in the recent literature. The genetic distance between subspecies based upon 46 enzyme loci ranges from that usually seen between congeneric species to virtual genetic identity. Subspecies from the western portion of the range of the cutthroat trout are genetically more similar to rainbow trout (Salmo gairdneri) than they are to the other subspecies of cutthroat trout. In addition, much of the genetic variation within the west‐slope cutthroat trout (S. c. lewisi) results from alleles found in only one or two local populations, but they often occur at high frequencies in those populations. Thus, preserving the genetic variation in westslope cutthroat trout entails preserving as many local populations as possible. Captive populations of cutthroat trout present a series of opportunities and genetic problems. A number of management agencies are using captive populations to supplement and reestablish natural populations. Basic genetic principles must be understood and followed in establishing and maintaining captive populations. We describe examples of unsuccessful and successful efforts by management agencies to develop captive populations. The greatest danger to the conservation of the cutthroat trout is introgressive hybridization among subspecies and with rainbow trout. Several factors make salmonid fishes especially susceptible to problems associated with introgressive hybridization. We conclude that biochemical analysis provides a more reliable and informative means of detecting interbreeding than morphological characters. Interbreeding between westslope and Yellowstone cutthroat trout and nonnative Salmo appears to be common and widespread throughout the natural range of these subspecies.
Article
Provides an overview of the status of fish populations and management of high mountain lakes in the western US based on interviews of state fishery managers in each of 43 regions in 11 states. Most regions manage mountain lakes fisheries with little survey or research data on which to base stocking programs. Few managers consider the health of indigenous trout populations, other aquatic species, lake ecosystems or the concerns of affected recreational users when conducting stocking programs. Intensive, on-going and largely indiscriminate stocking of lakes in most mountanous regions in the western US may be causing large-scale degradation to aquatic ecosystems, indigenous fish, invertebrates, amphibian fauna and potential quality fisheries. Some management regions have expanded lake surveys and reduced stocking efforts to protect native and wild trout populations, quality fisheries, and pristine fishless lakes. -from Author
Article
Much as Rachel Carson's "Silent Spring" was a call to action against the pesticides that were devastating bird populations, Charles S. Elton's classic "The Ecology of Invasions by Animals and Plants" sounded an early warning about an environmental catastrophe that has become all too familiar today-the invasion of nonnative species. From kudzu to zebra mussels to Asian long-horned beetles, nonnative species are colonizing new habitats around the world at an alarming rate thanks to accidental and intentional human intervention. One of the leading causes of extinctions of native animals and plants, invasive species also wreak severe economic havoc, causing $79 billion worth of damage in the United States alone. Elton explains the devastating effects that invasive species can have on local ecosystems in clear, concise language and with numerous examples. The first book on invasion biology, and still the most cited, Elton's masterpiece provides an accessible, engaging introduction to one of the most important environmental crises of our time. Charles S. Elton was one of the founders of ecology, who also established and led Oxford University's Bureau of Animal Population. His work has influenced generations of ecologists and zoologists, and his publications remain central to the literature in modern biology. "History has caught up with Charles Elton's foresight, and "The Ecology of Invasions" can now be seen as one of the central scientific books of our century."-David Quammen, from the Foreword to "Killer Algae: The True Tale of a Biological Invasion"
Article
During 1959-61, 10,000 catchable-sized, hatchery-reared, rainbow trout were jaw-tagged and released in the upper Salmon River, Idaho, and 2,247, 619, and 539 wild cutthroat trout, Dolly Varden, and rainbow trout, respectively, were caught on hook and line, tagged, and released in the Middle Fork of the Salmon River. More than 1,500 of the tagged, hatchery-reared, rainbow trout were recovered after being in the stream up to 1 year. Of those recovered the same season as released, more than 90 percent were taken within 2 miles of the release site. Ninety percent of those recovered after having been in the river over winter were taken within 5 miles of the release site. Of 253 tagged wild cutthroat trout recovered, 64 were recovered in release areas, and 189 were recaptured one or more miles from their release sites (average for the latter, about 19 miles). Of 95 tagged wild Dolly Varden recovered, 27 were recovered in the release areas, and 68 were recovered one or more miles from release sites (average for the latter, 22.2 miles). Twenty-seven tagged wild rainbow or steelhead trout were recovered; 14 in release areas, and 13 downstream from the release sites. Only 25.3 percent of the cutthroat trout and 28.4 percent of the Dolly Varden were recovered within 1 mile of release sites.
Article
We construct a prediction rule on the basis of some data, and then wish to estimate the error rate of this rule in classifying future observations. Cross-validation provides a nearly unbiased estimate, using only the original data. Cross-validation turns out to be related closely to the bootstrap estimate of the error rate. This article has two purposes: to understand better the theoretical basis of the prediction problem, and to investigate some related estimators, which seem to offer considerably improved estimation in small samples.
Article
This study was conducted by Montana Department of Fish, Wildlife and Parks in contractual agreement with Bonneville Power Administration and addresses measure 804(a)(9) of the Northwest Power Planning Council's Columbia River Basin Fish and Wildlife Program. Objectives were to determine instream flow needs in Kootenai River tributaries to maintain successful fish migration, spawning and rearing habitat of game fish, evaluate existing resident and rearing fish populations, and compile hydrologic and fishery information required to secure legal reservation of water for the fishery resource.
Article
Quantitative data on how high brook trout Salvelinus fontinalis can jump are crucial for efforts by fisheries managers to exclude brook trout from streams containing native cutthroat trout Oncorhynchus clarkii subspp. and to build effective fishways for brook trout migration. We identified factors that could influence brook trout jumping ability and demonstrated how this knowledge could be applied to improve the design of barriers to brook trout migration or fishways to facilitate their migration. Our objective was to measure brook trout jumping performance under laboratory conditions to identify design features for constructing waterfall-type barriers or pool-and-weir-type fishways. We used flashboard-type and flume-type adjustable waterfall devices to measure brook trout jumping performance at various combinations of vertical or waterfall height (13.5–93.5 cm in 10-cm increments) and plunge pool depth (10–60 cm in 10-cm increments) over a 24-h interval. We tested three size-classes of brook trout: 10–15 cm total length (TL) (mean ± SD: 13.09 ± 1.67 cm), 15–20 cm (19.30 ± 1.19 cm), and 20 cm or more (26.52 ± 2.13 cm). The 10–15-cm brook trout could jump a 63.5-cm-high waterfall, equivalent to 4.7 times their body length, from a 50-cm-deep plunge pool, which was 3.7 times their body length. Larger size-classes were capable of jumping 73.5-cm waterfalls, or 2.9–4.0 times their body length, provided the plunge pools were at least 40 cm deep (>1.6 times their body lengths). Shallow plunge pools (10 cm) prevented brook trout from all size-classes from jumping waterfalls 43.5 cm or more in height. Small fish were capable of jumping a greater number of body lengths over vertical obstacles than large fish. The data analyses identified vertical height, plunge pool depth, fish total length, and fish condition as factors important in predicting brook trout jumping performance.
Article
Biological invasions are a major and increasing agent of global biodiversity change. Theory and practice indicate that invasion risk can be diminished by reducing propagule pressure, or the quantity, quality, and frequency of introduced individuals. For aquatic invasions, the primary global invasion pathway is ballast-water transport, and the primary risk reduction strategy is currently open-ocean exchange. Exchange was developed with shipping between freshwater ports in mind, but the majority of shipping connects brackish and marine ports. A worldwide convention, adopted in 2004 by the International Maritime Organization, now mandates ballast-water exchange (or equivalent management) for its 164 member states. Will exchange be as effective in reducing invasion risk for euryhaline species (those capable of tolerating a wide range of salinity levels) in saltwater ports? Here we develop a simple mathematical framework for optimizing ballast-water exchange in terms of exchange level, timing, and species salinity tolerance. Our model shows that when species survival is worse in the post-exchange than in the pre-exchange water, exchange is always effective. However, when survival is equal or better following exchange, a critical level and timing are required for effective exchange. We illustrate the model's applications with a variety of introduced marine and estuarine organisms.
Article
Salmonids have been introduced worldwide to regions where they were not indigenous. This has led to many combinations of species in unnatural sympatry, some of which are suspected to interact strongly, but we currently have inadequate knowledge to allow us to predict the outcome of most such introductions. For example, despite current controversy about the potential effects of Pacific salmonids now stocked in Atlantic waters, we have only empirical evidence with which to judge whether they will be detrimental to Atlantic salmon Salmo salar. Most experimental tests of interspecific competition between other pairs of stream salmonids have not been rigorous. A review of literature about the suspected competition between brook trout Salvelinus fontinalis and rainbow trout Salmo gairdneri in streams reveals that despite empirical evidence that water temperature and velocity play a critical interacting role in determining the outcome, most experiments have failed to elucidate the important mechanisms involved. -from Author