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Global distribution of Rainbow Trout, Brown Trout, and Brook Trout by country within their native and introduced (nonnative) ranges.
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Trout are one of the most culturally, economically, and ecologically important taxonomic groups of freshwater fishes worldwide. Native to all continents in the Northern Hemisphere, trout belong to seven genera, which are distributed across 52 countries. Despite their broad importance as societal icons and as indicators of biodiversity, many of the...
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... introductions of invasive species have resulted in rapid and widespread declines of native trout and char populations across the globe. This includes trout species such as Rainbow Trout, Brook Trout, and Brown Trout that have been introduced globally for food, culture, and recreation ( Figure 4). The ecological impacts of invasive species are often irreversible and far-reaching, often causing reductions in the distribution, abundance, and diversity of native species, trophic cascade effects, and increases in the prevalence of disease outbreaks ( Simberloff et al. 2013). ...
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... it is the most commonly cited extinction threat to trout and char ( Figure 3C), in addition to protecting and restoring watersheds and habitat, the control or eradication of nonnatives will be paramount to trout and char conservation. This includes other trout species that have been introduced across the globe for food and recreation (Figure 4). Nonnative species pose competition, predation, and hybridization threats to native trout and char and need to be removed using physical or chemical methods, where feasible ( Buktenica et al. 2013;Al-Chokhachy et al. 2014;Fredenberg et al. 2017). ...
Citations
... Given this multitude of stressors, it is critical to investigate concurrent threats and develop a mechanistic understanding of biological responses to effectively manage species of conservation concern into the future (Wenger et al. 2011a;Craig et al. 2017;Bell et al. 2021). Salmonids are a family of fishes primarily limited to coldwater, which together with strong life history ties to hydrologic regimes, renders the group highly vulnerable in a changing climate (Penaluna et al. 2016;Muhlfeld et al. 2019). Stream temperatures have a strong influence on physiological processes such as metabolic rate and cardiac performance (Brett 1979;Farrell 2002;Bear et al. 2007; Whitney et al. 2016). ...
Warming rivers and interactions with non-native species impact salmonid species globally. Understanding how hydroclimatic conditions synergistically and independently interact with non-native species is critical for effectively managing salmonids into the future. We used a 10-year mark–recapture dataset to assess how native Yellowstone cutthroat trout (YCT) Oncorhynchus virginalis bouvieri and non-native brown trout Salmo trutta growth rates and apparent survival were affected by hydroclimatic conditions and (for YCT) the presence of brown trout in a tributary. Growth (YCT) and survival (both species across size classes) were negatively related to warming stream temperatures. Brown trout growth was positively related to increasing daily streamflow variability (a proxy for streamflow), but this variable was not included in the top YCT growth model. Density-dependent effects appeared to be non-existent (growth) or weakly positive (survival). When sympatric with brown trout, YCT displayed worse survival than allopatric YCT across environmental conditions. Broadly, we found native and non-native trout respond to different hydroclimatic conditions that shift with changing climatic conditions, and brown trout represent an additional threat to YCT survival.
... It is estimated that the overlap with a radiative forcing of 8.5 W·m −2 (business-as-usual scenario) will be approximately half that of the "peak and decline" scenario where radiative forcing is limited to 2.6 W·m −2 (Fig. 5). This is attributed to a reduction in trout distribution, consistent with global observations of trout reduction (Kovach et al. 2016;Muhlfeld et al. 2019), as well as a reduction in the distribution of native fish that are highly vulnerable to trout predation. Of the latter, a business-as-usual scenario is predicted to reduce the distributions of 7 of the 10 highly vulnerable taxa almost entirely, potentially resulting in their extinction or near-extinction. ...
Climate change is poised to reshape ecological communities globally by driving species into new environments and altering interactions between species. Conservation efforts should not only address current pressures but also plan for future pressures, such as sensitive species moving into degraded environments or arising problematic trophic interactions. This study sought to assess how climate change may affect the end-of-century distributions of New Zealand’s native and nonnative freshwater fish, including consequences for the overlap between trout (a nonnative sports fish) and native species vulnerable to trout predation. Random forest modelling was used to predict end-of-century distributions for New Zealand’s freshwater fish based on six hydrologically downscaled global climate models across four representative concentration pathways. Severe climate change impacts could drive nine native fish species to extinction or near-extinction and cause substantial declines in another eight native species. Seven nonnatives are also predicted to decline substantially, including a 30%–40% reduction in the extent of trout. To avert these potential extinctions, it is crucial to mitigate climate change severity and improve land use impacting freshwater ecosystems.
... This diversity and discreteness are often associated with complex landscape patterns that shape habitat conditions and connectivity of stream reaches, which in turn influence migratory patterns and isolate populations (Rieman and Dunhamm 2000;Quinn, 2021). Diverse life histories are exemplified among trout and charr species throughout the world, and require careful and targeted conservation measures Muir et al., 2016;Muhlfeld et al., 2019). For example, brook trout Salvelinus fontinalis are native to many coldwater streams in eastern and northern portions of North America, with distinct life histories exhibited by anadromous stocks ("salters") on the northern Atlantic coast and lake-dwelling and adfluvial "coaster" life history forms within the Laurentian Great Lakes, most notably Lake Superior (Hudy et al., 2008;Mamoozadeh et al., 2023). ...
... This species once occupied an extensive 12,000 km of rivers throughout Europe (Holčík 1990). However, due to various anthropogenic activities, the suitable habitat for Danube salmon has been drastically reduced to less than 33% of its original distributional range, resulting in a highly fragmented distribution (Freyhof and Kottelat 2008;Muhlfeld et al. 2019). Dams, obstacles, hydropower development and river regulation have played a pivotal role in hindering species migration and contributing to its ongoing decline (Holčík et al. 1988;Ihuţ et al. 2014). ...
... Dams, obstacles, hydropower development and river regulation have played a pivotal role in hindering species migration and contributing to its ongoing decline (Holčík et al. 1988;Ihuţ et al. 2014). Secondary threats, though equally significant, include global climate change, deforestation (Markovic et al. 2013), alteration of landscapes and watersheds, water abstraction, pollution (Mrakovčić et al. 2006;Dauwalter et al. 2020), genetic contamination (Geist et al. 2009), limited genetic diversity (Weiss, Marić, and Snoj 2011;Snoj et al. 2022), stocking (Weiss and Schenekar 2016), overfishing (Witkowski et al. 2013;Dauwalter et al. 2020) and the introduction of non-native species (Muhlfeld et al. 2019). The historical distribution records in Croatia indicate the presence of Danube salmon along the Sava, Drava, Kupa, Dobra and Mrežnica rivers (Witkowski et al. 2013). ...
The last populations of Danube salmon (Hucho hucho) in Croatia are found in the Kupa and Una Rivers; however, the size of the suitable area that could serve as the best spawning ground for the remnant Danube salmon population in these rivers is not known. The study aimed to leverage anglers' experiences to determine the sections of the Una and Kupa Rivers where the last populations of Danube salmon (Hucho hucho) in Croatia are most abundant, identify potential spawning sites, and assess threats that could impact the species' existence. In the Kupa and Kupica Rivers, the survey identified 25 Danube salmon spawning sites. The Kupica River emerged as a tributary of the Kupa River with a large Danube salmon population in Croatia. Experienced divers conducted three dives along a 350-meter transect in the Kupica River, estimating a total of 13 Danube salmon individuals ranging from 50 to 115 cm in total length, in pool and run mesohabitat types. The primary local threats identified for the Danube salmon population include small hydropower plants, the construction of a radioactive waste disposal site, water abstraction, the removal of riparian vegetation, overfishing, and climate change. The study strongly recommends the implementation of protective measures against these threats and the establishment of an ichthyological reserve specifically for Danube salmon in the Kupica River. This recommendation aligns with the EU Biodiversity Strategy, emphasizing the need to identify designated areas by 2030.
... Salmonid fishes are especially sensitive to climate change and altered environmental conditions because they require cold-water habitats that are increasingly fragmented by human activities, thereby forcing populations to tolerate environmental conditions in situ (Kovach et al., 2016). Consequently, many native trout and char species and lineages are endangered across the Northern Hemisphere (Muhlfeld et al., 2018;Muhlfeld et al., 2019). Arctic char (Salvelinus alpinus) is the most cold-adapted and northerly distributed freshwater fish globally that may be especially sensitive to climate change (Layton et al., 2021;. ...
Climate change is anticipated to cause species to shift their ranges upward and poleward, yet space for tracking suitable habitat conditions may be limited for range-restricted species at the highest elevations and latitudes of the globe. Consequently,
range-restricted species inhabiting Arctic freshwater ecosystems, where global warming is most pronounced, face the challenge of coping with changing abiotic and biotic conditions or risk extinction. Here, we use an extensive fish community and environmental dataset for 1762 lakes sampled across Scandinavia (mid-1990s)
to evaluate the climate vulnerability of Arctic char (Salvelinus alpinus), the world's most cold-adapted and northernly distributed freshwater fish. Machine learning models show that abiotic and biotic factors strongly predict the occurrence of Arctic char across the region with an overall accuracy of 89 percent. Arctic char is less likely to occur in lakes with warm summer temperatures, high dissolved organic carbon levels (i.e., browning), and presence of northern pike (Esox lucius). Importantly, climate warming impacts are moderated by habitat (i.e., lake area) and amplified by the presence of competitors and/or predators (i.e., northern pike). Climate warming projections under the RCP8.5 emission scenario indicate that 81% of extant populations are at high risk of extirpation by 2080. Highly vulnerable populations occur across their range, particularly near the southern range limit and at lower elevations, with potential refugia found in some mountainous and coastal regions. Our findings highlight that range shifts may give way to range contractions for this cold-water
specialist, indicating the need for pro-active conservation and mitigation efforts to avoid the loss of Arctic freshwater biodiversity.
... The brown trout is phenotypically very plastic, leading to a large number of life history types and morphologies, and broad variation in individual behavior. Consequently, controversies have arisen regarding species definitions and boundaries, evolutionary history, and ultimately, conservation and management of populations (Bernatchez 2001;Kottelat and Freyhof 2007;Jonsson and Jonsson 2011;Sanz 2018;Muhlfeld et al. 2019;Whiteley et al. 2019). ...
Brown trout Salmo trutta populations are common in small boreal streams in Scandinavia. Populations are often small and isolated. In this chapter, I summarized studies conducted for 8 years on a population of small-sized brown trout living in a small Norwegian boreal stream exposed to harsh winters (>5 months of ice cover) and low water levels during summer. Subsequently, I evaluated factors influencing local use of spawning areas and the distribution of age-0 individuals during autumn in a contiguous 1.4 km portion of the stream. Finally, I analyzed the local and temporal variation in individual length of the age-0 individuals during late fall and related distribution of age-0 brown trout to habitat qualities, including fish density and environmental factors varying at the catchment scale (i.e., discharge and temperature) or at the local scale (i.e., habitat characteristics summarized using principal component analysis and presence/absence of competitors). Spawning occurred throughout the stream, indicating that female brown trout were able to find small patches of suitable spawning habitat in most study sections. Age-0 brown trout were also found in all sections of the stream, with large variation among sections. General linear mixed effects models, with year as a random effect, indicated that variation in the second principal component was the main factor determining density of both mature and age-0 brown trout. However, the effect was in opposite direction for the two groups. Variation in length of age-0 brown trout was substantial, and associated with most of the measured parameters. There was a significant negative density effect, and this effect was exacerbated by the presence of alpine bullhead Cottus poecilopus. Both mature brown trout and age-0 juveniles utilized the full extent of the study area, leading to substantial phenotypic variation.
... Fisheries managers have stocked rainbow trout Oncorhynchus mykiss in rivers and lakes to support conservation and recreational objectives for over a century [34]. The native range of rainbow trout is restricted to western North America and eastern Russia, but rainbow trout currently inhabit much of the world and persist as self-sustaining populations outside the native range as a result of these stocking programs [8,31]. However, there is also extensive stocking within their native range. ...
Fisheries managers stock triploid (i.e., infertile, artificially produced) rainbow trout Oncorhynchus mykiss in North American lakes to support sport fisheries while minimizing the risk of genetic introgression between hatchery and wild trout. In Washington State, the Washington Department of Fish and Wildlife (WDFW) allocates approximately US $3 million annually to stock hatchery-origin rainbow trout in > 600 lakes, yet only about 10% of them are triploids. Many lakes in Washington State drain into waters that support wild anadromous steelhead O. mykiss that are listed as threatened under the U.S. Endangered Species Act. As a result, there is a strong interest in understanding the costs and benefits associated with stocking sterile, triploid rainbow trout as an alternative to traditional diploids. The objectives of this study were to compare triploid and diploid rainbow trout in terms of: (1) contribution to the sport fishery catch, (2) fine-scale movements within the study lakes, (3) rate of emigration from the lake, and (4) natural mortality. Our results demonstrated that triploid and diploid trout had similar day-night distribution patterns, but triploid trout exhibited a lower emigration rate from the lake and lower catch rates in some lakes. Overall, triploid rainbow trout represent a viable alternative to stocking of diploids, especially in lakes draining to rivers, because they are sterile, have comparable home ranges, and less often migrate.
... These species provide food for millions of people, as well as recreation and sport, and they play key roles in ecosystem functioning and health [8,9]. However, many salmonid species are in decline because of a multitude of human-induced pressures including climate warming [10][11][12][13]. For instance, brown trout (Salmo trutta L., 1759) has been in strong decline in southern Europe because of climate warming and an increased prevalence of extremely warm events [14][15][16]. ...
Here, I review thermal influences on metabolic rates and aerobic scope; growth; adult body size; and reproductive and behavioural traits, such as tendency and timing of the migration of salmonid fishes. A thermal window bounded by the upper and lower incipient lethal temperatures (UILT and LILT) determines where salmonids can survive. For most salmonids, LILT is close to 0 and UILT is between 20 and 30 °C. UILT and LILT are influenced by the acclimation temperature. Thermal tolerance is affected by fish size and ambient oxygen content, which decreases with increasing temperature. Standard metabolic rate (SMR), the energy required to maintain essential functions, increases with temperature, whereas maximum metabolic rate (MMR) increases with temperature until reaching a peak (pejus). Then, it decreases gradually to zero, i.e., the upper critical limit (TCrit). Aerobic scope (AS = MMR-SMR) reaches its maximum at the pejus temperature. Metabolic rates and aerobic scope can be modified by temperatures that the fish experiences during embryogenesis and possibly also as larvae and young fry. At maximum feeding, maximum growth increases to a point at or below the pejus temperature. The optimum temperature for growth decreases with reduced food intake and increased body size. As for metabolic rate, the growth rate is influenced by the temperature during embryonic development. In a warmer climate, adult body size is expected to decrease chiefly because of a younger age at maturity. Parental fish retained at a higher temperature during maturation produce larger eggs, and this change in egg size may also be transferred to next-generation offspring. Furthermore, embryogenesis in warmer water leads to larger gonad and egg sizes at maturity. Water temperature influences locomotion, foraging and migratory activity. In a warmer climate, juveniles migrate to the sea earlier in spring. In addition, higher embryo temperature leads to delayed return of adult salmon from the ocean. Thus, temperature affects life history traits of salmonid fishes, partly as a direct effect on metabolic rates and food consumption and partly induced as a phenotypically plastic effect. The phenotypically plastic response may preadapt offspring to perform better in the expected future thermal environment.
... In addition to being valuable study systems in ecology and evolution, fishes of the genus Salvelinus are of conservation concern throughout the Holarctic (Muhlfeld et al. 2020). There is, however, incomplete understanding of the conservation status of various species and subspecies of Salvelinus in western North America. ...
The western North American Arctic char (AC, Salvelinus alpinus), Dolly Varden (DV, Salvelinus malma), and bull trout (BT, Salvelinus confluentus) are described as a “species complex” due to their close inter-relationships, variable morphology, and tendency to hybridize. Consequently, there has been considerable historical debate about the taxonomic status of the three species, and their physical identification is often problematic. A genotyping-by-sequencing (GBS) library of AC, DV, and BT samples from across the North Pacific and Arctic Canada was exploited to find species-specific single nucleotide polymorphisms (SNPs) to design and test TaqMan™ assays for efficient species identification. A total of 10 AC/DV and 10 DV/BT TaqMan™ assays were developed and tested for efficient, cost-effective, and accurate genotyping of sympatric char species and their hybrids in samples from diverse subspecies, and phylogeographic lineages, and geographic groups. Both in silico and lab genotyping tests using these diagnostic SNPs resulted in highly concordant and accurate identification when compared to previous identifications using microsatellite, single copy nuclear DNA, GBS SNP data and information on geographic distributions. The TaqMan™ assays confirmed the utility of a relatively small number of diagnostic markers to identify these species and F1 hybrids, and samples that were moderately admixed between species. This work represents the first SNP-based diagnostic markers for these three species that can be used for a wide variety of applications in research and monitoring in the char species complex.
... freshwater resident Arctic char at high risk to climate change, as in other studies (Muhlfeld et al., 2019), although we also emphasise the risk to localised populations of salmon, trout, shad and coregonids, which urgently require more conservation measures. Our study also attempted to rank the priority of species using non-climatic stressors, which should be considered in conjunction with climate-change effects. ...
Climate change can affect fish species directly (e.g. through physiological stress) or indirectly (e.g. species interactions). Whether individual species will experience net benefits or net losses is important to understand from a fisheries management perspective. Ireland has a unique freshwater fish community that faces considerable uncertainty in relation to the impact of climate change. Vulnerability of fish species and subspecies (n = 32) in Ireland were investigated through an expert‐based questionnaire and a trait‐based assessment. Fish species were assessed based on exposure, sensitivity and adaptive capacity. The expert‐based questionnaire predicted that one species, Arctic char Salvelinus alpinus was assigned the rank of high vulnerability, seven species were assigned moderate to high vulnerability, twenty species were assigned moderate vulnerability, and four species were of low to moderate vulnerability. Life‐history characteristics of the fish species were analysed to identify traits characteristic of vulnerable fish species (e.g. Vulnerability to fishing and Trophic level). Coldwater species are highly vulnerable, with indirect effects through interactions with other species or in combination with non‐climatic stressors (e.g. water quality & barriers to migration) being a significant concern. The results provide a vulnerability ranking for Ireland's freshwater fish, that can be utilised by fisheries managers and allows for prioritising of an often‐limited conservation resource.
