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Schematic representation of a metapopulation. Size of the circle represents the relative size of a population and the potential for emigration of individuals. Arrows represent the pathways of exchange among populations. The broken circle represents a population that has a high probability of local extinction, and is likely to persist only through support from other populations.
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Under the National Forest Management Act of 1979, the USDA Forest Service is charged with maintaining viable populations of all existing native vertebrate species on lands they administer. Accomplishment of this responsibility requires complete assess- ment of all federally authorized, funded, or implemented projects that may jeopardize the continu...
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... component populations in complex habitats spread the risk of synchronous extinctions (Morrison and Barbosa 1987;Quinn and Hastings 1987). Stronger populations provide sources for recolonization (Brown and Kodric-Brown 1977;Sjogren 1991), or support of other weaker populations through dispersal of surplus animals (Hanski 1985;Pulliam 1988) (Figure 2). ...
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While Pacific salmon are economically and culturally important worldwide, Alaska, USA is one of the few remaining places on earth where sustainable management of salmon is possible, even in the face of wide-ranging threats, including overharvesting and the impacts of climate change. A continuing challenge that we face is to understand the ecologica...
Citations
... The impacts of hydrologic alterations and climate change can have consequences, reducing population sizes and functional connectivity (e.g., Almodóvar et al. 2012). In addition, because of their higher vulnerability to stochastic demographic and environmental events, the risk of local extinction is expected to increase (Rieman et al. 1993). Understanding the impacts of barriers and the loss of structural connectivity on brown trout genetic patterns at a river network scale is essential to advance our understanding of how populations are genetically structured and to implement appropriate and efficient management and conservation strategies. ...
The alteration of structural connectivity in fluvial networks is important for the genetic dynamics of aquatic species. Exploring the effects of network fragmentation through genetic analysis is crucial to assess the conservation status of riverine species. In this study, we investigated the genetic consequences of the altered connectivity of brown trout in the Deva–Cares catchment (northern Spain). We investigated (1) genetic diversity, (2) genetic differentiation and genetic structure, (3) migration rates and effective population size and (4) genetic differentiation and riverscape characteristics. Analysis of the genetic variation among 197 individuals from the 13 study sites revealed a high degree of genetic differentiation ( F ST = 0.181). Below-barrier study sites had higher genetic diversity and lower F ST values, while headwater and above-barrier study sites had lower genetic diversity and higher F ST values. Most of the genetic groups identified were separated by one or more impermeable barriers. We reported an abrupt decrease in genetic diversity and effective population size in upper course tributaries and isolated reaches. Likewise, a downstream-biased gene flow was found, and it was most likely related to the fragmentation caused by barriers, since the results from migration indicated that gene flow between groups without impermeable barriers was higher bidirectionally. Isolation by impermeable barriers played a more important role than hydrological distance in determining the genetic structure. Most of the genetic groups showed small effective population sizes. Genetic analysis at the river network scale provides evidence for the role of barriers in determining genetic diversity patterns, highlighting the importance of maintaining and restoring river longitudinal connectivity.
... If presented with the opportunity, brook, brown, and rainbow trout will move great distances to fulfill these requirements (Riley et al., 1992; Gowan et al., 1994; Meyers et al., 1992; Clapp et al., 1990; Gowan and Fausch, 1996 ). Dams and other water restrictions impede these migrations and generally create a situation where populations become isolated (Rieman et al., 1993; Young, 1995b). Such isolation has the potential for creating genetic bottlenecks, genetic drift, and ultimately sub-population loss through reduction of individuals below a minimum viability threshold (Morita et al., 2009; Wofford et al., 2005). ...
... Although barriers provide protection from invasion by nonnative species, isolation has its own risks (Peterson et al. 2008; Fausch et al. 2009). When immigration is blocked by barriers, isolated populations may be vulnerable to extinction because of stochastic demographic or environmental events (Rieman et al. 1991; Hilderbrand 2003). Isolation also results in reduced gene flow and genetic variation, increasing the risk of inbreeding depression and reducing evolutionary potential (Allendorf and Ryman 2002). ...
... Once a population is small enough that declines cause genetic bottlenecking, reduced fitness due to genetic factors can lead to further declines. The combined effects of low genetic variation, environmental stressors, and catastrophic events are hypothesized to lead to negative population growth rates, a phenomenon that has been described as an ''extinction vortex'' (Gilpin and Soulé 1986; Rieman et al. 1991). For isolated cutthroat trout populations, demographic support from nearby populations is not available and negative population growth is a sign that a population may not persist (Peterson et al. 2008). ...
For populations of cutthroat trout Oncorhynchus clarkii, isolation in headwater streams may provide protection from invasion by nonnative species but also may enhance a population's vulnerability to extirpation. We assessed the risk of extirpation for eight Colorado River cutthroat trout O. clarkii pleuriticus populations isolated above water diversion structures in the North Fork Little Snake River drainage, Wyoming. The populations had been isolated for 25–44 years, occupied headwater streams that ranged from 850 to 6,100 m in length, and had adult populations that were estimated to range from 12 to 506 fish. Adult population sizes were compared with published occurrence models to identify populations that may be at risk of extirpation. One population had experienced an 11% annual rate of decline in abundance over the past 29 years, but there was no evidence of declines among the other populations. There was evidence of recruitment failure for age-1 fish in two of the smaller populations. Abundance estimates and published logistic regression models consistently identified the largest tributary in the drainage as being the most likely to support a Colorado River cutthroat trout population in the future and the smallest tributary as being the least likely to support a population in the future. The analyses indicated that isolated populations may persist for decades, but small effective population sizes can make populations vulnerable to eventual loss of genetic variability and to extirpation.
... Upper bounds on estimates of effective population sizes in the Salt and Blackfoot watersheds are 41,289 and 2,415, respectively (Meyer et al. 2006). Because of their large size and primarily migratory life history, these watershed-scale metapopulations are not likely to go extinct unless selenium concentrations across the watershed exceed means of 17 to 20 µg/g, enough to reduce the effective population sizes, N e , to 500, below which populations can not generally maintain the genetic diversity necessary for long-term adaptation (Rieman et al. 1993). On the other hand, the migratory nature of these populations means that the majority of spawning and juvenile residence is occurring in headwater areas where mining, and hence the potential for selenium contamination, occurs. ...
... Chinook salmon populations of more than 100 cannot be confirmed in any year and returns are likely inflated by hatchery fish. Rieman et al. (1993) characterize a salmonid population as at moderate risk of extinction when: ...
... However, even hatchery based recovery necessitates having healthy donor stocks with sufficient numbers of individuals so that eggs taken would not jeopardize the population of origin. Rieman et al. (1993) noted that adjacent populations historically strayed to avoid habitat degradation and also re-colonized habitat after it recovered. This synergy between local populations is known as metapopulation function. ...
... This synergy between local populations is known as metapopulation function. Rieman et al. (1993) stated that: "Maintaining strong populations in the best possible habitats throughout the landscape and preserving the ecological processes characteristic of metapopulations are the best hedges against extinction." Figure 51. This map shows the location of the last coho salmon populations that consistently numbered in the hundreds according to Brown et al. (1994). ...
New Jersey supports reproducing populations of three lotic salmonids. Only Brook Trout (Salvelinus fontinalis) are native and until approximately 100 years ago, were found in abundance throughout the northern part of the state. Presently, native populations have been documented in 115 streams or stream sections and declines are
thought to be in response to anthropogenically originated environmental stressors. To evaluate the deterioration extent and assess numbers of breeding non-native Brown Trout (Salmo trutta) and Rainbow Trout (Oncorhynchus mykiss), comparisons are made between sets of historical (1968-1977) and modern (2001-2010) young-of-the-year presence/absence and abundance data and several geologic and land use/land cover
characteristics hypothesized to influence species’ occurrence. The range of reproducing Brown Trout populations have expanded, while groups of Rainbow and Brook Trout, as well as the overall amount of non-trout water have all decreased slightly. Results show that land use and land cover catchment value thresholds exist at < 12% agriculture, <22% barren and urban, > 64% wetland and forest, and < 4-6% impervious cover to allow for natural Brook Trout reproduction. Values for Brown Trout reproduction include <14% agriculture, < 27% barren and urban, > 58% wetland and forest, and < 5-7% impervious cover. Additionally, a previously undocumented Brook Trout metapopulation has been discovered with abundance estimates suggesting that a flourishing, reproductive and viable population is being maintained. Also, observed movement between connected waters allows for gene flow and overall isolation may permit the existence of one of New Jersey’s remaining relict Brook Trout groups. Conservation of the once endemic native species has become a regional priority and a review of current lotic salmonid management strategies has identified some practices that
may undermine protection efforts. Suggestions to reverse declines and bolster unique populations include: 1) establishing a ‘Wild Native’ angling regulation, 2) creating stricter land use directives to support more natural flows, 3) curtailing or cessation of domestic salmonid stocking at larger catchment levels, 4) developing hatchery operation expansion to include indigenous origin fish, 5) removal of non-native fish from favorable
standing within the State’s Wildlife Action Plan, and 6) obtaining new or reallocating current funds to support more research.
To ascertain the structure and movement of an eastern brook trout population(s) we conducted surveys and marked fish in the South Branch of the Raritan River headwaters in New Jersey. In 2010, 425 trout were tagged and recapture efforts occurred in early 2011. Based upon the recapture success, we approximate that the surveyed subwatershed sections hold approximately 3,008 trout, with most supplied from three tributaries. Fish size ranged from 50–254 mm (total length) and five individuals traveled to locations other than where they were initially marked. Our work suggests that trout movement occurs among the tributaries of this locale and the potential for gene flow exists within this watershed. Perhaps most importantly, this population may represent one of the remaining relict brook trout populations in New Jersey.
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.
Extensive hydroelectric development in the Columbia River system has eliminated most mainstem riverine habitat available for spawning by fall chinook salmon (Oncorhynchus tshawytscha). The two remaining populations, Hanford Reach, Columbia River and Hells Canyon Reach, Snake River, are separated geographically and their status is markedly different. Annual escapements to Hanford Reach have averaged approximately 80 000 adults, while the Snake River run size has declined to <1500 adults over the past 10 years. We compared their spawning habitat characteristics over a range of measurement scales, as a means to identify strategies for rebuilding the weak Snake River population. Physical habitat characteristics of redds were similar for both study areas. Redd locations were correlated with channel characteristics, such as braiding and sinuosity. Several differences between the two spawning areas were identified at the watershed scale: the Hells Canyon Reach had a much steeper longitudinal gradient, was largely confined by bedrock, and had a more variable flow regime. These features are controlling variables that operate at the reach-scale to limit the availability and size of substrate and other conditions that influence egg deposition and incubation survival. Geomorphological characteristics of the two study sites are sufficiently different to indicate that the production potential of the Hells Canyon Reach population is markedly lower than that of the Hanford Reach population. Copyright © 2000 John Wiley & Sons, Ltd.
Public agencies are being asked to quantitatively assess the impact of land manage- ment activities on sensitive populations of salmonids. To aid in these assessments, we developed a Bayesian viability assessment procedure (BayVAM) to help characterize land use risks to salmo- nids in the Pacific Northwest. This procedure incorporates a hybrid approach to viability analysis that blends qualitative, professional judgment with a quantitative model to provide a generalized assessment of risk and uncertainty. The BayVAM procedure relies on three main components: (1) an assessment survey in which users judge the relative condition of the habitat and estimate survival and reproductive rates for the population in question; (2) a stochastic simulation model that provides a mathematical representation of important demographic and environmental processes; and (3) a probabilistic network that uses the results of the survey to define likely parameter ranges, mimics the stochastic behavior of the simulation model, and produces probability histograms for average population size, minimum population size, and time to extinction. The structure of the probabilistic networks allows partitioning of uncertainty due to ignorance of population parameters from that due to unavoidable environmental variation. Although based on frequency distributions of a formal stochastic model, the probability histograms also can be interpreted as Bayesian probabilities (i.e., the degree of belief about a future event). We argue that the Bayesian interpretation provides a rational framework for approaching viability assessment from a management perspective. The BayVAM procedure offers a promising step toward tools that can be used to generate quantitative risk estimates in a consistent fashion from a mixture of information.
