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Trout and Char of Central and Southern Europe and Northern Africa

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Abstract

Here we summarize the current knowledge on the trout and char of central and southern Europe, including Germany, The Netherlands, Switzerland, Austria, Czech Republic, France, Spain, Portugal, Italy, the Mediterranean Islands, and northwestern Africa (Morocco and Algeria). We focus on the only two widely recognized native species: Brown Trout Salmo trutta, which is common and widespread throughout the region, and Alpine Char Salvelinus umbla, which occurs in high alpine lakes. We also discuss four named relatives of Brown Trout endemic to Italy, Salmo fibreni, S. carpio, S. cettii, and S. marmoratus, and a taxonomically complex group of Brown Trout relatives from North Africa. We provide information on three nonnative species from North America that have established naturalized populations in the region: Rainbow Trout Oncorhynchus mykiss, Brook Trout Salvelinus fontinalis and Lake Trout S. namaycush. For each species, we discuss the distribution, status, socioeconomic value, and management context. We organize our discussion using hydrological and political boundaries in order to accommodate the natural biogeography of the species and the disparate availability of relevant data across the region.

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... Italian freshwaters host many native trout lineages whose populations evolution was promoted by isolation in a wide variety of environmental conditions, and their taxonomy has long been debated (Lobón-Cerviá et al., 2019). According to the International Union for Conservation of Nature (IUCN), four native trout are listed in Italy: Zerunian & Gandolfi, 1990, Salmo carpio Linnaeus, 1758, Salmo marmoratus Cuvier, 1829and Salmo cettii Rafinesque, 1810(IUCN, 2017, although probably the taxonomy of these species has not yet been resolved Zanetti et al., 2014). ...
... In Central Italy the Mediterranean trout Salmo cettii is currently strongly threatened by the introgressive hybridization with the alien S. trutta (Lorenzoni et al., 2006(Lorenzoni et al., , 2018aSplendiani et al., 2016). In fact, for many years in Italy, restocking of brown trout has been carried out using hatchery-reared individuals selected from Atlantic stocks (Giuffra et al., 1994;Nonnis Marzano et al., 2003;Zaccara et al., 2015;Lobón-Cerviá et al., 2019;Rossi et al., 2019). As a result, the current range of the Mediterranean trout is greatly reduced compared to the past, and hybrids between S. cettii and S. trutta dominate most of the upper stream reaches in Central Italy (Lobón-Cerviá et al., 2019;Splendiani et al., 2016). ...
... In fact, for many years in Italy, restocking of brown trout has been carried out using hatchery-reared individuals selected from Atlantic stocks (Giuffra et al., 1994;Nonnis Marzano et al., 2003;Zaccara et al., 2015;Lobón-Cerviá et al., 2019;Rossi et al., 2019). As a result, the current range of the Mediterranean trout is greatly reduced compared to the past, and hybrids between S. cettii and S. trutta dominate most of the upper stream reaches in Central Italy (Lobón-Cerviá et al., 2019;Splendiani et al., 2016). The pure individuals belonging to the two species are distinguishable from the morphological point of view for some characteristics, mainly related to the colour pattern ( Figure 1), while hybrids show intermediate features, and their determination should be based on genetic analysis . ...
Article
In Italian freshwaters the introgressive hybridization with the alien Atlantic trout represents the principal threat to the native endangered Mediterranean trout. The aim of the research was to test the effectiveness of alien trout removal activities carried out by electrofishing in four streams in Central Italy. The four sites were chosen on the basis of the severe genetic introgression level of the trout populations. The removal activities were carried out from December 2014 to July 2017, for a total of 10 eradication campaigns in each site. During each field activity, five environmental parameters (flow rate, conductivity, average depth, average width, accessibility) were collected, since they could influence both the effectiveness of the electrofishing and the biological characteristics of the fish populations. A total of over 22,000 alien trout accounting for a biomass of over 700 kg were removed from the removal sites. For each site, a progressive drastic decrease over time in density and standing crop values was observed. Removal rates ranged from 94.22% to 100.00% for density, and from 96.57% to 100.00% for standing crop. The correlation analysis showed an inverse significant relationship between catchability and populations abundance, confirming that low density populations are more suitable to removal efforts. The progressive removal of specimens improved the catchability over time, indicating that even the largest populations could be eradicated, providing the necessary number of steps in a fishing season. The improved body condition and the greater growth rates observed during the eradication period, in low abundance conditions, seemed to confirm the key role that intraspecific competition and density‐dependent phenomena play in the Apennine trout population dynamics. The results obtained in the present research provided evidence that electrofishing removal could be an effective management tool for the Mediterranean trout conservation, especially in watercourses of modest dimensions in terms of flow rates, width and depth.
... The salmonid fish genus Salmo Linnaeus, 1758 harbours in Italy different phenotypes living in different freshwater habitats, like i) mountain streams along south-western Alps, Apennines and main islands (the Mediterranean trout, characterized by medium-small size and more or less numerous dark and/or reddish spots on flanks superimposed on vertical Parr-marks), ii) upper and lower reaches of the Po river basin (the marble trout, bigger in size and with irregular brown lines forming a marbled pattern) and iii) the lacustrine trout (the "carpione") from Garda (up to 500 mm in standard length with uniform, silver coloration and few dark spots) and Fibreno (small size, with large reddish or dark brown ocellated spots on flanks, superimposed on Parr-marks) lakes ( Figure 1). These forms are collectively attributed to the trout of the Salmo trutta Linnaeus, 1758 complex (see Caputo et al. 2009;Splendiani et al. 2019), to which a systematic review was recently devoted, with reference to Mediterranean (Europe and North Africa) river basins (Lobón-Cerviá et al. 2018). ...
... A paragraph in the work of Lobón-Cerviá et al. (2018) focused on the systematic status of the Italian brown trout, long sinceand still todaysubject of controversies among ichthyologists. In fact, the specific name and the taxonomic rank attributed to populations living along the Alpine and Apennine chains and in the major islands (Corsica, Sardinia and Sicily) changed several times in the last years (see Kottelat 1997;Kottelat & Freyhof 2007;Bianco & Delmastro 2011;Zerunian 2013;Bianco 2014) and the natural occurrence of this salmonid fish in some Italian areas was also questioned (see Gandolfi et al. 1991). ...
... Corsican and Sardinian specimens are characterized by AD, MA and ME haplotypes (Sabatini et al. 2011(Sabatini et al. , 2018Lerceteau-Köhler et al. 2013;Zaccara et al. 2015;Berrebi et al. 2019), while Sicilian ones are the only Italian trout having haplotypes belonging to the southern AT or African sub-clade (Schöffmann et al. 2007;Snoj et al. 2011;Fruciano et al. 2014;Tougard et al. 2018) (Figure 4). Thus, on the base of these consistent molecular data, the name Salmo cettii is useless for designating Tyrrhenian and insular (e.g., Kottelat & Freyhof 2007) or even all Italian Mediterranean trout (see Rondinini et al. 2013;Lobón-Cerviá et al. 2018). In fact, the species "cettii" was described on specimens from rivers of eastern Sicily (see above), phylogenetically linked to Maghreb trout populations (see also Duchi 2018). ...
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The systematic status of the Italian trout in the Salmo trutta L., 1758 complex (including marble, Mediterranean and lacustrine trout), has long been - and is still today - subject of controversies among ichthyologists. The specific name and the taxonomic rank changed several times in the last years, and the natural occurrence of this salmonid fish in some Italian areas was debated due to spread of alien strains. The main difficulty with the taxonomy of the Italian trout stems from the impossibility of disentangling it “on paper” or, even worse, trying to face this systematic issue considering only a very limited (local/national scale) part of the brown trout range. The taxonomy of the Italian trout population is inextricably linked to the necessity of clarifying first phylogeny and phylogeography in an overall Mediterranean context. The opportunity of a non “self-referential” taxonomy is even more fundamental for a vulnerable salmonid like the Italian brown trout, for which there is a very conflicting management problem related to sport fishing and, at the same time, the urgent need for effective conservation measures. It is, however, necessary to emphasize that conservation is independent from taxonomy but must start from the level of the local population. In fact, management units need stability and they cannot, therefore, coincide with entities - the Linnean species - requiring continuous taxonomic revisions. Modern molecular methods are the best tools for defining these units of management and conservation in an evolutionary perspective.
... Native Mediterranean salmonids are subject to multiple anthropogenic stressors, such as habitat modifications, water pollution, altered flow regime, climate changes, overfishing, and invasive species (Clavero et al., 2010;Lobón-Cerviá et al., 2019;Lorenzoni et al., 2019). Above all, being of high interest for sport fishing, these species are heavily affected by invasive salmonids, which have been introduced in larger numbers to increase wild fish stock in favour of freshwater recreational fisheries (Splendiani et al., 2016a). ...
... Inland recreational fisheries are managed in different ways, and often based on regulations with a goal of fish stock conservation (Shepard et al., 2019), even if they are not always based on scientific knowledge . In Italy, the regulations regarding trout fishing are issued by local and regional governments, and mainly include length and bag limits, gear restrictions, and seasonal closures during trout reproductive periods (Lobón-Cerviá et al., 2019). In recent decades, the practice of total Catch and Release (C&R) has also been increasing in many salmonid streams. ...
Article
Overexploitation and consequent depletion of the breeding stock is one of multiple stressors affecting Mediterranean trout Salmo cettii Rafinesque, 1810 in central Italy. The practice of total Catch and Release (C&R), combined with gear restrictions and seasonal closures, reduces catch-related impacts. To test for the effects of C&R management, the goals of the study were to: (i) analyse the status of trout inhabiting 8 C&R areas of the Nera River Basin, and (ii) compare the results with those from 11 exploited areas and 15 no-fishing areas. Fish data were collected by electrofishing from 1997 to 2020. Abundance, growth, age structure, and relative weight were estimated. Trout populations in the C&R sectors exhibited high abundances, well-balanced age structures, and a congruous number of age classes according to the longevity of the species. However, the abundance values never reached those of the no-fishing areas. The results provided evidence for an unbalanced population structure in fishing areas, where intensive size-selective harvest caused negative demographic effects, especially on older fish, and the legal-limit length was not adequate for maximal yield length. C&R angling appeared to maintain the fishery value of trout stocks favouring the conservation of native trout, although a certain impact on fish population status remains and thus, it cannot completely replace the adoption of more restrictive criteria.
... The pronounced distinctiveness of S. marmoratus is concordant with previous studies (Delling, 2002;Giuffra et al., 1994;Gratton et al., 2014;Lecaudey et al., 2018;Pustovrh et al., 2014;Sušnik et al., 2007a). Lobón-Cerviá et al. (2018) considered all brown trout populations found in insular and peninsular Italy to be Salmo cettii, whereas our results showed that S. cettii from the type locality (Sicily) is genetically very distinct from the Sardinian brown trout. In addition, Schöffmann et al. (2007), Snoj et al. (2011), Fruciano et al. (2014, and Tougard et al. (2018) reported a similarity between the Sicilian and the North African brown trout based on mtDNA phylogeny. ...
... Salmo carpio is considered as one of the accepted endemic brown trout species of Italy (Bianco, 2014;Giuffra et al., 1994;Gratton et al. 2014;Lobón-Cerviá et al., 2018). Splendiani et al. (2017Splendiani et al. ( , 2019 refered to S. carpio only as an "ecotype" of Adriatic brown trout in Lake Garda, Italy. ...
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There are particular challenges in defining the taxonomic status of recently radiated groups due to the low level of phylogenetic signal. Members of the Salmo trutta species-complex, which mostly evolved during and following the Pleistocene, show high morphological and ecological diversity that, along with their very wide geographic distribution, have led to morphological description of 47 extant nominal species. However, many of these species have not been supported by previous phylogenetic studies, which could be partly due to lack of significant genetic differences among them, the limited resolution offered by molecular methods previously used, as well as the often local scale of these studies. The development of next-generation sequencing (NGS) and related analytical tools have enhanced our ability to address such challenging questions. In this study, Genotyping-by-Sequencing (GBS) of 15,169 filtered SNPs and mitochondrial DNA (mtDNA) D-loop sequences were combined to assess the phylogenetic relationships among 166 brown trouts representing 21 described species and three undescribed groups collected from 84 localities throughout their natural distribution in Europe, west Asia, and North Africa. The data were analysed using different clustering algorithms (admixture and discriminant analysis of principal components -DAPC), a Bayes Factor Delimitation (BFD) test, species tree reconstruction, gene flow tests (three- and four-population tests), and Rogue taxa identification tests. Genomic contributions of the Atlantic lineage brown trout were found in all major sea basins excluding the North African and Aral Sea basins, suggesting introgressive hybridization of native brown trouts driven by stocking using strains of the Atlantic lineage. After removing the phylogenetic noise caused by the Atlantic brown trout, admixture clusters and DAPC clustering based on GBS data, respectively, resolved 11 and 13 clusters among the previously described brown trout species, which were also supported by BFD test results. Our results suggest that natural hybridization between different brown trout lineages has probably played an important role in the origin of several of the putative species, including S. marmoratus, S. carpio, S. farioides, S. pellegrini, S. caspius (in the Kura River drainage) and Salmo sp. in the Danube River basin. Overall, our results support a multi-species taxonomy for brown trouts. They also resolve some species in the Adriatic-Mediterranean and Black Sea drainages as members of very closely related genomic clusters that may need taxonomic revision. However, any final conclusions pertaining to the taxonomy of the brown trout complex should be based on an integrative approach combining genomic, morphological, and ecological data. To avoid challenges in taxonomy and conservation of species complexes like brown trouts, it is suggested to describe species based on genomic clusters of populations instead of describing species based only on morphologically differentiated single type populations.
... Similarly, new trout species were recently described in the territory of Turkey in the Mediterranean Sea, Black Sea and Persian Gulf river drainages [6][7][8][9][10][11], presently encompassing 12 species. However, several authors have already recognized the taxonomic diversity of this region's brown trout ( [9,12,13] and references therein). Among these for Invitrogen FITC-Streptavidin) and superimposed using Adobe Photoshop software, version CS5. ...
... Recently, FishBase [93] lists 50 formally described Salmo species. However, many molecular phylogeneticists and phylogeographers question this biological species concept of taxonomic diversity of the genus Salmo by pointing to negligible and/or weak genetic differentiation among some of those populations/taxa (to cite from numerous ones e.g., [13,89,[94][95][96][97][98][99]). Yet, other colleagues detected significantly larger genetic differences (e.g., [100][101][102][103][104]). ...
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Salmonids are extremely important economically and scientifically; therefore, dynamic developments in their research have occurred and will continue occurring in the future. At the same time, their complex phylogeny and taxonomy are challenging for traditional approaches in research. Here, we first provide discoveries regarding the hitherto completely unknown cytogenetic characteristics of the Anatolian endemic flathead trout, Salmo platycephalus, and summarize the presently known, albeit highly complicated, situation in the genus Salmo. Secondly, by outlining future directions of salmonid cytogenomics, we have produced a prototypical virtual karyotype of Salmo trutta, the closest relative of S. platycephalus. This production is now possible thanks to the high-quality genome assembled to the chromosome level in S. trutta via soft-masking, including a direct labelling of repetitive sequences along the chromosome sequence. Repetitive sequences were crucial for traditional fish cytogenetics and hence should also be utilized in fish cytogenomics. As such virtual karyotypes become increasingly available in the very near future, it is necessary to integrate both present and future approaches to maximize their respective benefits. Finally, we show how the presumably repetitive sequences in salmonids can change the understanding of the overall relationship between genome size and G+C content, creating another outstanding question in salmonid cytogenomics waiting to be resolved.
... Trout of the genus Salmo are native to Europe, central and western Asia, and northwest Africa, although many natural populations are now extinct Lobón-Cerviá et al., 2019;Rasmussen et al., 2019;Schöffmann et al., 2019). Considerable variation in morphology, life history, genetics, physiology and other characteristics has led to Salmo trout being regarded as among the most variable of the vertebrates (Ferguson, 1989;Klemetsen, 2013). ...
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Salmonid (Salmonidae) sympatric diversity is the co-occurrence, in a lake or river, of two or more reproductively isolated populations/subpopulations, or phenotypes resulting from phenotypic plasticity. Sympatric populations can arise through allopatric and/ or sympatric evolution. Subsequently, allopatric lineages can occur in sympatry due to independent colonisation and/or through anthropogenic introduction. Sympatric divergence is often driven by feeding opportunities, with populations segregating as planktivorous, benthivorous and piscivorous ecotypes ("trophic polymorphism"), and further segregation occurring by feeding depth and body size. Subpopulations evolve by natal homing where a water has two or more discrete spawning areas, often resulting in phenotypically and ecologically cryptic sympatry. Most known sympatric populations/phenotypes in trout of the genus Salmo (Eurasian trout aka brown trout) involve sympatric piscivorous (ferox) and lifetime invertivorous trout. Segregation on the benthic-limnetic axis has been poorly studied in Eurasian trout compared with other salmonids but is likely commoner than currently described. While three sympa-tric populations/species of Eurasian trout are recognised from Lake Ohrid (Albania/ North Macedonia), limited ecological information is available and there are only two lakes with three or four sympatric populations with described benthic, limnetic and piscivorous trophic segregation: Lough Melvin (Ireland) and Loch Laidon (Scotland), the latter having the only identified case of a sympatric profundal benthic feeding populations, possibly due to the absence of Arctic charr (Salvelinus alpinus) in the lake. Many thousands of waters are yet to be examined. Some sympatric populations are extinct, and others are vulnerable with conservation action being urgently required. This should ideally be based on populations/conservation units, but the lack of recognition of intraspecific units in most legislations in the native Eurasian trout range necessitates a pragmatic approach, with species classification, where appropriate, based on integrative taxonomy. Some sympatric populations clearly merit species status and should be formally classified as such if a valid previous name is not available. K E Y W O R D S conservation units, ecotype, ferox, genetic markers, integrative taxonomy, Salmonidae This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
... Kohout et al. (2013) further split the Danubian (sensu lato) lineage into two subgroups: the Danubian (sensu stricto) (DaDA sub-lineage; haplotypes of most of the Danube drainage, together with the Caspian and Aral Sea basins) and the Black Sea (DaBS sublineage; haplotypes mostly distributed in the lower Danube drainage and southern Black Sea basin). Extensive genetic differentiation also exists between populations within each of these lineages, and a number of species is recognised within most of them (Kottelat and Freyhof 2007;Lobón-Cerviá et al. 2019;Schöffmann et al. 2019). To preserve genetic integrity and diversity of the species, conservation measures and management should focus on protecting locally adapted populations where possible (e.g. ...
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In brown trout, instances of genetic homogenization after introducing hatchery-reared allochthonous Atlantic strains are well documented. Therefore, mitigation-driven translocation with autochthonous lineages is gaining support. However, when the origin of local donor populations is not clear they should be genetically characterized prior to translocation. Here we present a case study from the Vlasina Plateau in Southeast Serbia, where two drainages, Danube and Aegean, are adjoining. The status of Danubian and Aegean brown trout populations was investigated with respect to inter-relationship and genetic admixture using mtDNA and microsatellite loci. Results revealed a complex genetic structure and demonstrated different levels of introgressive hybridization from the Aegean populations (which belong to the Adriatic evolutionary lineage) into the Danubian populations as a direct consequence of human mediated translocations. While most introgressed Danubian locations showed low to intermediate proportions of allochtonous genes this was not the case with the upper Jerma location, where all individuals were characterized as pure Adriatic lineage of brown trout. Contrarily, Aegean locations from the Plateau are inhabited by pure Adriatic brown trout. Finally, our analysis clearly demonstrates that the biological invasion followed a stepping-stone scenario via the upper Jerma, which served as a local donor population for supplementing other Danubian populations, and excludes the possibility of brown trout invading through physical connections between the two drainages that were established because of Vlasina hydroelectric power plants. Furthermore, evidence of increased stocking in the wider region is additionally supported by the detection of low level introgression with the domesticated Atlantic brown trout.
... Here, we investigate the genetics of introduction, subsequent patterns of dispersal and colonisation routes of brown trout Salmo trutta on the island of Newfoundland, eastern Canada, as a model of species range expansion. Salmo trutta is an excellent species for such an investigation since it has been successfully introduced worldwide from its native western Palaearctic distribution, chiefly for sports angling, and usually with good written records (Jonsson and Jonsson 2011;Ferguson et al. 2019b;Lobón-Cerviá et al. 2019). The species has also been extensively studied genetically, both within and outside its native range (see Lobón-Cerviá and Sanz 2018 for a recent review). ...
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Although historical records of introductions that trigger successful biological invasions are common, subsequent patterns of dispersal and colonisation routes are unclear. We use microsatellites to examine genetic population structuring of established invasive brown trout (Salmo trutta) populations in Newfoundland, Canada, for evidence of “natural” dispersal, human-mediated introductions, and colonisation routes. We also explored ancestry of contemporary populations relative to presumed progenitors. Results analysed using STRUCTURE, DAPC, a NJ tree and F ST comparisons support records of historical introductions; current Newfoundland populations are largely descended from Scottish stock, with St. John’s the primary introduction site. Subsequent dispersal of these trout was facilitated principally by anadromy, largely consistent with a classic stepping-stone model, with significant isolation-by-distance. With one exception, dispersal along the north and south coasts of the Avalon peninsula appears to be natural and independent, involving stochastic processes resulting in unique outcomes for population composition. This study is a good example of dispersal patterns during a contemporary invasion underscoring the potential for non-anadromous founders to re-express anadromy, facilitating colonization of distant sites.
... The singularity of the trout inhabiting the headwaters of the Dades river and its tributary M'Goun in the High Atlas Mountains of North-West Africa was unknown until recently (Lobón-Cerviá et al. 2019). Snoj et al. (2011) originally described this fish naming it Dades trout and placing it in its own monotypic brown trout (Salmo trutta) lineage. ...
... However, the unique native populations in Corsica and Sardinia are threatened by restocking operations leading to introgression with non-native Atlantic and Mediterranean trout lineages, habitat fragmentation by hydroelectric dams, poaching and competition with non-native rainbow trout Oncorhynchus mykiss (Walbaum, 1792) and brook trout Salvelinus fontinalis (Mitchill, 1814) (e.g., Massidda, 1995;Berrebi, 2015;Lobón-Cerviá et al., 2019). Ancestral (or native) Corsican populations are currently the most conserved and exhibit low intra-population genetic diversity as well as a high level of inter-population differentiation. ...
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The introduction of the use of molecular data has caused debates on the taxonomy of Corsican and Sardinian trouts, also referred to as Tyrrhenian trouts (i.e. Salmo trutta, Salmo macrostigma, Salmo cettii). A recent study by Delling et al. (2020) (Morphologic and genetic characterization of Corsican and Sardinian trout with comments on Salmo taxonomy. Knowl Manage Aquat Ecosyst 421: 21) introduces important evidence regarding the taxonomy of these populations. However, their subsequent denomination as Salmo sp., that is, an undefined taxon, could have serious consequences on their future conservation management plans. Considering their threatened status, the Tyrrhenian trouts should be referred to as Salmo trutta until the ongoing taxonomic uncertainty can be unambiguously resolved. These populations must then be treated as an Evolutionary Significant Unit (ESU) or as an Operational Conservation Unit (OCU) for further conservation managements plans, as already done for other Mediterranean trout lineages.
... Because of their notable recreational and economic value, particular attention is paid to the conservation and management of fish in the genus Salmo (Filipe et al., 2013). In Italy, several trout genetic lineages belong to the genus Salmo (Lobón-Cerviá et al., 2019). The native species derived from colonization processes which occurred in the past geological eras, mostly influenced by Pleistocene glaciations, while non-native species are represented by domestic trout of Atlantic origin, introduced by restocking activities (Caputo, Giovannotti, Nisi Cerioni, Caniglia, & Splendiani, 2004;Meraner & Gandolfi, 2018;Splendiani et al., 2019). ...
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Salmonids inhabiting Mediterranean rivers are of particular concern for biodiversity conservation, as they are threatened by various stressors, including habitat alterations, overfishing, climate change, and introgressive hybridization with alien species. In the Tiber River basin (Central Italy), genetic introgression phenomena of the native Salmo cettii with the non‐native Salmo trutta hinder the separate analysis of the two species, which are both included in the S. trutta complex. Little is known about the factors currently limiting the trout populations in this area, particularly with respect to climate change. With the intention of filling this gap, the aims of the current study were to (a) quantify changes in the climate and (b) analyze the distribution, status, and ecology of trout populations, in the context of changing abiotic conditions over the last decades. Fish stock assessments were carried out by electrofishing during three census periods (1998–2004, 2005–2011, and 2012–2018) at 129 sites. The trend over time of meteorological parameters provided evidence for increased air temperature and decreased rainfall. Multivariate analysis of trout densities and environmental data highlighted the close direct correlation of trout abundance with water quality, altitude, and current speed. Climate‐induced effects observed over time in the sites where trout were sampled have not yet led to local extinctions or distribution shifts, indicating a marked resilience of trout, probably due to the buffering effect of intrinsic population dynamics. Decreasing body conditions over time and unbalanced age structures support the hypothesis that variations in hydraulic regime and water temperature could overcome these compensatory effects, which may lead to a severe decline in trout populations in the near future. In a climate change context, habitat availability plays a key role in the distribution of cold‐water species, which often do not have the possibility to move upstream to reach their thermal optimum because of water scarcity in the upper river stretches.
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This paper reviews the research on the Tellesimo Stream trout population, which was first described and recognized as scientifically important 30 years ago, when its main threats were identified for the first time. Protection against introgression, and possibly even the current existence of this population, appears to be the result of protection and conservation measures that were implemented soon after this research. The possible distinction between Sicilian and other Italian trout was first suggested by a genetic study carried out about 20 years ago, which found that the trout population of Tellesimo clustered separately from all other salmonids analysed. Existant parce que important ou important car existant ? Sur l’importance scientifique et la conservation d’une population sicilienne génétiquement pure de l’espèce menacée Salmo cettii Rafinesque, 1810. Cet article passe en revue les recherches sur la population de truites du ruisseau Tellesimo en Sicile et montre que celle-ci avait été décrite et reconnue comme étant scientifiquement importante il y a 30 ans déjà, lorsque ses principales menaces ont été identifiées. La protection contre l’introgression, et peut-être même l’existence actuelle de cette population, est le résultat de mesures de protection et de conservation mises en place après ces recherches. Le rôle actif des pêcheurs est mis en évidence. La distinction possible entre la truite sicilienne et les autres truites italiennes a été suggérée pour la première fois par une étude génétique réalisée il y a environ 20 ans, qui a révélé que la population de truites de Tellesimo était regroupée séparément de toutes les autres populations de salmonidés italiens analysées.
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Introduction to the book, Trout and Char of the World
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This is the first comprehensive look at the taxonomy, life history, and conservation status of the world’s trout and char. These are fascinating and beautiful fish that rate high for the angler as well as for tourist and recreational economies. Trout and char also play key roles in the ecology of many lake and river systems around the world. Trout and char are abundant in many regions, but most native species are on the decline. Some are classified as vulnerable, threatened, or endangered. Because of their widespread stocking in regions where they are not native, some trout and char also are the cause for threats to other native species. Loss of habitat, an expanding human population, and rapid climate change are challenging their future as streams warm and waters become more variable in their flows. This book examines trout and char from all these perspectives. Early chapters explore the unique diversity and life history aspects of trout and char and provide information on the taxonomy and systematics while also detailing some of unique life histories. New information is presented about species diversity and distributions by country. Summary chapters explore significant conservation and management challenges of broad interest to scientists, resource managers, anglers, and interested public. The book end s with a series of essays exploring the future of trout and char over the next 50 years. This book will be a primary resource for trout and char biologists, conservationists, and anglers in the many countries where trout and char are native or have been introduced, and a resource for anyone interested in learning more about the diversity and distribution of trout and char worldwide.
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Upper Lake Constance (ULC) is a large pre-alpine lake situated between Austria, Germany and Switzerland (9°18'E, 47°39'N). Along with the smaller, conjoined expanse of Lower Lake Constance, it forms the third largest lake in Europe. Its waters underwent pronounced eutrophication during the 20th century. Commercial fisheries benefitted strongly from the increased productivity during an initial mesotrophic phase, but these advantages were effectively neutralized when eutrophication became severe. By the turn of the 21 st century, internationally coordinated measures to reduce nutrient input to the lake had returned ULC to its historic reference state as an oligotrophic ecosystem. However, the remarkable success of the nutrient management program has been to the detriment of commercial fishers. Yields of most commercially important fish species have decreased, along with lake productivity. As a consequence, the high market demand for local fish products is nowadays met mainly by imports, the ecological footprint of which offsets the local benefits of environmental restoration. Responsibility for fisheries and environmental aspects of ULC managing is shared by the national and federal state administrations and in all cases, tourism, drinking water and environmental interests now take priority over fisheries. As a result, the number of fishers operating viably on Germany's largest inland water body continues to decline and the long-term viability of commercial capture operations is in doubt. Aquaculture of locally desired fish species may become an important factor in the future of the Lake Constance fisheries.
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Environmental, climate and historical factors are important to explain patterns of freshwater biodiversity and population dynamics in the Mediterranean area. This region is one of the most important areas for the maintenance of native lineages for brown trout. The aim of this study was the identification of the main drivers for the spread and the distribution of genetic introgression between alien brown trout and two native Mediterranean salmonids (brown and marble trout). Estimates of mitochondrial and nuclear introgression were from both the literature and original data and were used as dependent variables in a multivariate framework, correlating them to a suite of environmental and climate parameters. The last glacial maximum appeared as an important factor explaining the geographic pattern of alien brown trout genes throughout the Alps. Here, native populations of Mediterranean salmonids persisted in former refugia. Throughout the Italian Peninsula and major islands, geological setting of catchment and current climate conditions are key factors for securing the persistence of native trout populations. The reevaluation of genetic data regarding the spread of alien brown trout lineage into Mediterranean salmonids populations with a landscape approach allowed us to reveal the role of important factors implicated with the current pattern of distribution of remnant native populations of salmonids. This information provides new insights for improving conservation strategies and management of taxa threatened by the incipient global climate changes.
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The winter diet of the great cormorant (Phalacrocorax carbo) was studied by means of examining regurgitated pellets, individual fish bones and fish remains collected from below the roosting trees in two sites on the River Vltava in Vyšší Brod and at Slapy Reservoir, Czech Republic, and by analysis of stomach contents of birds shot on the River Vltava in Prague. Using diagnostic bones (os pharyngeum, dentale, maxillare, praeoperculare) and own linear regression equations between measured dimension of the diagnostic bone and fish total length (L T), a total of 1152 fish of 22 species and 6 families were identified in the diet of great cormorants and their sizes were reconstructed. At all three localities on the main stream of the River Vltava, roach (Rutilus rutilus), bream (Abramis brama), bleak (Alburnus alburnus), European chub (Squalius cephalus), European perch (Perca fluviatilis) and ruffe (Gymnocephalus cernuus) made up at least 74.2 % of the cormorants' diet. A great potential for fish stock losses was identified for the River Vltava at Vyšší Brod and in Prague where the loss of fish due to overwintering great cormorants was estimated to be 22 kg ha –1 and up to 79 kg ha –1 respectively, i.e. belonging among the highest ever published figures for fish withdrawal caused by great cormorants from any inland waters (carp fishponds excluded). Most probably, both great cormorants and anglers are responsible for the decrease in catches of brown trout (Salmo trutta m. fario) and grayling (Thymallus thymallus) from the River Vltava in Vyšší Brod.
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Four native Salmo species are reported from Morocco and Algeria. Salmo pallaryi from Aguelman (lake) Sidi Ali is diagnosed by 12-13 (14) anal fi n pterygiophores, vs. 9-11, rarely 12 in other Salmo species. Salmo pallaryi has a unique morphology of the dermethmoid bone and resembles S. ohridanus in circumorbital bones. It is regarded as extinct since 1938. Ordination of head measurements by means of principal component analyses groups S. pallaryi with the 'archaic trouts', S. ohridanus, S. obtusirostris and S. platycephalus, with which it shares short jaws. Salmo akairos, new species, the endemic 'dwarf trout' from Lake Ifni, is diagnosed by the combination of long jaws and long fi ns, contrasting black and white leading edges on anal and dorsal fi ns, high gill raker and dorsal fi n pterygiophore counts. Distinctiveness of S. macrostigma and S. pellegrini is discussed but no fi nal conclusion is reached. Salmo pellegrini and trout from watercourses emptying to the Atlantic Ocean are characterised by com-paratively high gill raker and low vertebral counts compared to S. macrostigma and trout from watercourses emptying to the Mediterranean Sea.
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There is growing awareness that predicting biological invasions will require the development of conceptual models for specific taxa at appropriate scales. Salmonids are ideal taxa for testing factors that influence invasions, because large numbers have been introduced worldwide for long periods and their ecology is well known. We evaluated the hypothesis that, among regions with suitable water temperatures, environmental resistance from flood disturbances that wash away trout fry strongly influence invasion success of rainbow trout (Oncorhynchus mykiss), the most widely introduced fish species. We predicted that flow regimes in regions where rainbow trout invasions are successful would match those in their native range and would differ from those in regions where invasions are moderately successful or failed. We tested six specific predictions about how timing, pre-dictability, frequency, duration, and annual variability of floods, as well as timing of low flows, will differ relative to timing of rainbow trout fry emergence among five Holarctic regions. Analysis of hydrologic regimes for eight rivers each in the native range (Pacific Coast) and four regions where rainbow trout invasions varied from highly successful (South-ern Appalachians) to moderate (Colorado, USA, and Hokkaido Island, Japan) or failed (Honshu Island) showed that winter flooding and summer low flows in Pacific Coast rivers that favor spring emergence of rainbow trout were closely matched by Southern Appalachian flow regimes. In contrast, the other three regions had spring or summer flooding that hampered rainbow trout recruitment to different degrees, and winter low flows. Rainbow trout invasion success was best explained by a match between timing of fry emergence and months of low flood probability. Alternatively, cold water temperatures, which hamper reproduction, and biotic interactions with brown trout (Salmo trutta) and whirling disease parasites may account for low invasion success in European regions. However, differences in genetic makeup of donor stocks and propagule pressure are unlikely mechanisms to explain invasions. Understanding how abiotic disturbances interact with timing of critical life history events to limit nonnative species will help ecologists develop more robust theories to predict invasion success.
Book
A comprehensive guide to the most current research, history, genetics and ecology of the brown trout including challenging environmental problems. The brown trout is an iconic species across its natural European distribution and has been introduced throughout the World. Brown Trout offers a comprehensive review of the scientific information and current research on this major fish species. While the brown trout is the most sought species by anglers, its introduction to various waters around the world is causing serious environmental problems. At the same time, introduction of exogenous brown trout lineages threats conservation of native gene pools of populations in many regions. The authors summarize the important aspects of the brown trout's life history and ecology and focus on the impact caused by the species. The text explores potential management strategies in order to maintain numerous damaged populations within its natural distributional range and to ameliorate its impacts in exotic environments. The authors include information on a wide-range of topics such as recent updates in population genetics, evolutionary history, reproductive traits and early ontogeny, life history plasticity in anadromous brown trout and life history of the adfluvial brown trout and much more. This vital resource: Contains the latest research on the biology and ecology of brown trout. Includes information on phylogeography, genetics, population dynamics and stock management. Spotlights the brown trout's introduction to regions around the world and the serious environmental impacts. Offers a comprehensive review of conservation and management techniques. Written for salmonid scientists and researchers, fishery and environmental managers, and students of population genetics, ecology and population dynamics, Brown Trout explores the most recent findings on the history, ecology and sustainability of this much-researched species.
Chapter
The survival of populations in several glacial refuges allowed the accumulation of genetic differences, the apparition of ancestral divergent lineages and ultimately promoted speciation. As a consequence, high genetic richness is common in extant brown trout populations from southern Europe. In the Iberian Peninsula, as many as four ancient mitochondrial DNA lineages of brown trout are distributed among the rivers, with several of the lineages coexisting within populations. Population structure studies using nuclear markers also have indicated a complex and high level of genetic diversity within and among Iberian brown trout populations. At a macro-geographic scale, the distribution of native genetic diversity is associated with the major drainage systems in the Atlantic Basin, whereas a mosaic pattern of genetic diversity is observed in the Mediterranean brown trout. In both cases, the replacement of native gene pools by exogenous (specifically, northcentral European) hatchery fish is evident.
Article
Montane biota is vulnerable to climate change, especially in the case of relict species in environmentally extreme areas. The Dades trout Salmo multipunctata is a relict species from the Draa basin, on the southern slopes of the High Atlas Mountains, Morocco. Apart from its genetic and morphological singularity almost nothing is known about this species. We surveyed the whole potential distribution range of the Dades trout and found that only two isolated populations exist (in the Dades and M'Goun catchments), occupying an extremely small range
Article
The colonization by both resident and migrating spawner populations of brown trout and the characteristics of resident and migrating juveniles derived from the two populations have been studied in a brook and its tributary over 4 years. Resident trout spawns mainly in the upstream part of the brook and migrating trout in the downstream part. There are density and growth variations for the two age classes (0+ and 1 +) of juveniles in autumn according to the year and the environment. In the brook, the population of 0 + fish increases from downstream to upstream while the density of other age classes decreases. The migrating juvenile population of the brook changes annually and consists mainly of 1 s (one summer) individuals coming from the upper part. These individuals migrate generally in autumn and winter while young trout produced in the middle and downstream parts of the brook migrate mainly in the spring. The emigration process of the 0 + population decreases markedly from upstream to downstream and appears to be independent of the autumn length and sex ratio. In the tributary, most trout are 0+ years old, the population structure is different, and no migrating fish is observed. The results are discussed and a colonization strategy of the brown trout population in this brook is suggested.
Article
Background Classification of species within the genus Salmo is still a matter of discussion due to their high level of diversity and to the low power of resolution of mitochondrial (mt)DNA-based phylogeny analyses that have been traditionally used in evolutionary studies of the genus. We apply a new marker system based on nuclear (n)DNA loci to present a novel view of the phylogeny of Salmo representatives and we compare it with the mtDNA-based phylogeny.Methods Twenty-two nDNA loci were sequenced for 76 individuals of the brown trout complex: Salmo trutta (Danubian, Atlantic, Adriatic, Mediterranean and Duero mtDNA lineages), Salmo marmoratus (marble trout), Salmo obtusirostris (softmouth trout), and Salmo ohridanus (Ohrid belvica or belushka). Sequences were phylogenetically analyzed using maximum-likelihood and Bayesian Inference methods. The divergence time of the major clades was estimated using the program BEAST.ResultsThe existence of five genetic units i.e. S. salar, S. ohridanus, S. obtusirostris, S. marmoratus and the S. trutta complex, including its major phylogenetic lineages was confirmed. Contrary to previous observations, S. obtusirostris was found to be sister to the S. trutta complex and the S. marmoratus clade rather than to the S. ohridanus clade. Reticulate evolution of S. obtusirostris was confirmed and a time for its pre-glacial origin suggested. S. marmoratus was found to be a separate species as S. trutta and S. obtusirostris. Relationships among lineages within the S. trutta complex were weakly supported and remain largely unresolved.Conclusions Nuclear DNA-based results showed a fairly good match with the phylogeny of Salmo inferred from mtDNA analyses. The comparison of nDNA and mtDNA data revealed at least four cases of mitochondrial–nuclear DNA discordance observed that were all confined to the Adriatic basin of the Western Balkans. Together with the well-known extensive morphological and genetic variability of Balkan trouts, this observation highlights an interesting and variegated evolutionary history of Salmo in this area.
Chapter
Within its overall area of distribution, the brown trout (Salmo trutta L.) is not always present, nor is it evenly distributed in the water courses. Among the factors regulating natural populations of trout, environmental conditions are of great importance and allow the definition of the habitat of this species.
Article
The brown trout Salmo trutta is represented by three lineages in Corsica: (1) an ancestral Corsican lineage, (2) a Mediterranean lineage and (3) a recently stocked domestic Atlantic S. trutta lineage (all are interfertile); the main focus of this study was the ancestral Corsican S. trutta, but the other lineages were also considered. A total of 38 samples captured between 1993 and 1998 were analysed, with nearly 1000 individuals considered overall. The Corsican ancestral lineage (Adriatic lineage according to the mitochondrial DNA control region nomenclature, AD) mostly inhabits streams in the southern half of the island; the Mediterranean lineage (ME) is present more in the north, especially in Golu River, but most populations are an admixture of these lineages and the domestic Atlantic S. trutta (AT). Locations where the Corsican ancestral S. trutta is dominant are now protected against stocking and sometimes fishing is also forbidden. The presence of the Corsican S. trutta is unique in France.
Article
Abstract Stocking has had a considerable effect on wild brown trout, Salmo trutta L., populations throughout Europe. To elucidate this impact and to outline further management strategies, the genetic structure of 25 wild populations and five hatchery stocks from Czech Republic and Slovakia were analysed using mitochondrial (control region) and nuclear DNA (microsatellites, LDH‐C1*) markers. Stocking practices have caused massive hybridisation between the Atlantic and Danube brown trout strains in the central Danube basin and have lead to a loss of among‐population divergence in Slovakia and the eastern part of Czech Republic. Comparison with studies from neighbouring countries revealed substantial differences in haplotype, allele frequencies and genetic diversity across Central Europe. Differences in stocking management and origin of breeding stocks appear to be crucial factors for the spatial variability of the genetic structure of brown trout.
Article
Genetic introgression of aquaculture stocks in local forms is well documented in many fish species but their evolutionary consequences for the local populations have not been thoroughly explored. Due to its wide geographical range, the existence of many locally adapted forms and the frequent occurrence of introgression of aquaculture stocks in local forms, brown trout represents the ideal system to study the effects of such introgressions. Here, we focus on a group of rivers and streams in Sicily (Italy), and, by using molecular tools, we show that autochthonous populations are probably derived from the Southern Atlantic clade, which is present in the Iberian peninsula and North Africa. Three out of the four studied rivers reveal signs of genetic introgression of domestic stocks. Finally, by using advanced geometric morphometric analyses, we show that genetic introgression produces a higher degree of morphological variability relative to that observed in non-introgressed populations. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, ●●, ●●–●●.
Article
Two major mtDNA lineages of brown trout come into contact in the upper Danube basin of Central Europe. The region is additionally confronted with stock management programs that often use domesticated foreign strains creating confusion as to what constitutes native and non-native populations as well as how to define major management units. In a unique system in north eastern Austria we provide additional support that the so-called Atlantic lineage of brown trout is native to the upper Danube and provide a high resolution microsatellite screening protocol that clearly distinguishes between natural and anthropogenic introgression, with the latter being minimal. Sequencing of 6,000 bp of mtDNA also shows that domesticated stocks primarily stem from a distinct albeit genetically diverse sub-clade of the Atlantic lineage, approximately 50,000–100,000 years divergent from the native Atlantic stocks, thought to have expanded into the region during the Holocene. The futility in defining large-scale management units based on mtDNA lineages for such broadly distributed and highly fragmented species is discussed.
Article
Understanding the factors that determine successful salmonid embryo incubation in the many structurally modified river systems of the Northern Hemisphere is crucial for maintaining healthy salmonid populations. In this context, the joint impact of fine sediment accumulation together with anthropogenic river modifications on salmonid embryo survival has been rarely investigated.We investigated brown trout embryo survival to hatch (STH) together with ten physicochemical, hydraulic and morphological parameters in artificial brown trout redds in a heavily modified stream (i.e. channelized, artificial log steps) in central Switzerland. We were interested to understand whether (i) STH is more sensitive to the timing and duration of low oxygen rather than a mean oxygen concentration, (ii) STH was negatively affected by increased fine sediment deposition decreasing redd gravel permeability, (iii) higher water levels, causing fine sediment resuspension, benefit STH, (iv) STH was negatively affected by organic content in the redds and especially (v) hydraulic gradients related to redd scale bed-form and/or the artificial step structure benefit embryo STH, and hence could mitigate the negative impact of fine sediment and/or organic content.Up to 50%, brown trout embryos survived with interstitial oxygen exceeding 3 mg L−1. Embryos endured up to 6 days ≤ 1 mg L−1 but were more sensitive to oxygen depletion close to hatch. Therefore, timing and duration of low oxygen were important for embryo STH, and hence, oxygen dynamics need to be considered when assessing in redd conditions for salmonid STH.Partial least squares regression identified the horizontal hydraulic gradient, Fredle index, distance to artificial log steps upstream and amount of accumulated fine sediment as influential predictors for embryo STH. The water level above the redd and total organic carbon content in the redd were not influential. Among the identified influential predictors, 70.9% of the variation in STH could be explained by a logistic regression model containing redd distance to the next upstream step (26.4%, P = 0.004), Fredle index (27.2%, P = 0.003) and horizontal hydraulic gradient (10.1%, P = 0.04). In the logistic regression, the amount of accumulated fine sediment (P = 0.75), field seasons (P = 0.93) and field sites (P = 0.66) was non-significant.In summary, brown trout STH was sensitive to redd gravel permeability, which was measured as Fredle index and affected by fine sediment deposition. At the same time, hydraulic gradients related to artificial log steps, which enhanced hyporheic exchange, benefited embryo STH, and hence mitigated fine sediment impact. This result can be probably transferred to other surface water-dominated river systems with good hyporheic water quality. To what extent it can be transferred to river systems with other hydraulic boundary conditions remains to be evaluated. Altogether, our results clearly indicate that the impact of fine sediment on salmonid incubation success needs to be understood in the hydrological and morphological context of the particular river system.
Article
In Italy, as in several other circum-Mediterranean countries, there is a unique assemblage of endemic freshwater fishes. Speciation processes, especially of endemic primary or near-primary freshwater fish, most probably occurred during the Lago Mare era of the Mediterranean (about 5 million years bp). However, the present-day distribution patterns are surely the result of events that occurred more recently, from the Pleistocene until historical times. However, natural events are now being superseded by anthropogenic interference with fish faunas. Among the various negative human factors the most harmful is the introduction of non-native species, which in Italy are responsible for the present catastrophic situation. Of the 71 species currently with natural self-sustaining populations in Italian waters, only 45 are natives. Of the latter, only 16 (or fewer) have not been subjected to deliberate human transfers. In Italy there about 28 endemic Mediterranean taxa, but most have either been deliberately or accidentally introduced to areas outside their natural range. The result of this persistent practice on a little known and unique fish fauna is zoogeographic pollution, massive cases of hybridization and loss of genetic identity by local native populations. The problem of freshwater fish conservation is not a matter of public concern in Italy. Sport fishing has a political and economic value and introductions are legally carried out and ‘welcomed’ by most fishermen; most biologists and conservationists are either unaware or unconcerned.
Article
Species inhabiting fresh waters are severely affected by climate change and other anthropogenic stressors. Effective management and conservation plans require advances in the accuracy and reliability of species distribution forecasts. Here, we forecast distribution shifts of Salmo trutta based on environmental predictors and examine the effect of using different statistical techniques and varying geographical extents on the performance and extrapolation of the models obtained. Watercourses of Ebro, Elbe and Danube river basins (c. 1,041,000 km2; Mediterranean and temperate climates, Europe). The occurrence of S. trutta and variables of climate, land cover and stream topography were assigned to stream reaches. Data obtained were used to build correlative species distribution models (SDMs) and forecasts for future decades (2020s, 2050s and 2080s) under the A1b emissions scenario, using four statistical techniques (generalised linear models, generalised additive models, random forest, and multivariate adaptive regression). The SDMs showed an excellent performance. Climate was a better predictor than stream topography, while land cover characteristics were not necessary to improve performance. Forecasts predict the distribution of S. trutta to become increasingly restricted over time. The geographical extent of data had a weak impact on model performance and gain/loss values, but better species response curves were generated using data from all three basins collectively. By 2080, 64% of the stream reaches sampled will be unsuitable habitats for S. trutta, with Elbe basin being the most affected, and virtually no new habitats will be gained in any basin. More reliable predictions are obtained when the geographical data used for modelling approximate the environmental range where the species is present. Future research incorporating both correlative and mechanistic approaches may increase robustness and accuracy of predictions.
Article
La forme autochtone d'Omble chevalier du lac de Neuchâtel a disparu vers 1970. Sa réintroduction en 1979 à partir de 30 000 estivaux provenant du Léman a permis la recapture de 23 % des effectifs jusqu'en 1982. Le fait que la majorité des individus se capturent jusqu'à la classe d'âge 2+ pose des problèmes de gestion à long terme.
Article
Potamodromy is examined for river-dwelling populations of 13 coregonine species, 2 thymalline species, and 19 salmonine species to uncover common and contrasting migratory patterns in flowing waters. Members of these subfamilies probably have recolonized rivers and streams repeatedly over the past million years or more in the face of several glaciations, ice recessions, and interglacial periods. To do so they may have evolved migratory behavioral patterns adapted to life in fast-running, cold, highly turbid, changeable, and unpredictable lotic systems. Their migratory behavior coalesces into three cyclic patterns of movement (trophic, refuge, and reproductive) to gain access at appropriate times in their life histories or seasonal periods to three patchily distributed but critical types of habitat (feeding, survival, and spawning). Trophic and refuge movements to respective feeding and survival habitats show considerable site fidelity and, though changing over individual life spans of some species considered, remain similar between successive generations. Reproductive movements to spawning habitats show high levels of site fidelity (homing) from parent to offspring and for repeat-spawning individuals. Specialized features of potamodromy are briefly discussed in relation to long-term occupation of riverine systems. Comments are made on the complexity of salmonid potamodromy in relation to fisheries management practices.
Article
Peri-alpine lakes in Switzerland and France exhibit a spectrum of intensities of eutrophication and re-oligotrophication over the past 30 years. Phosphorus inputs have been decreasing since the 1970s. TP has altered from 135 to 50 μg l−1 in the more eutrophicated lakes, and 25–2 μg l−1 in the others. Fish communities were dominated by cyprinids and perch in eutrophic lakes. During re-oligotrophication, the total yield remains nearly the same while coregonids become dominant. In oligotrophic lakes, when the TP was below 5 μg l−1, the total yield decreased rapidly, and fish production was low.
Article
The phylogeography of Atlantic brown trout (Salmo trutta) was analysed using mitochondrial DNA control region complete sequences of 774 individuals from 57 locations. Additionally, the available haplotype information from 100 published populations was incorporated in the analysis. Combined information from nested clade analysis, haplotype trees, mismatch distributions, and coalescent simulations was used to characterize population groups in the Atlantic basin. A major clade involved haplotypes assigned to the Atlantic (AT) lineage, but another major clade should be considered as a distinct endemic lineage restricted to the Iberian Peninsula. The phylogeography of the Atlantic populations showed the mixed distribution of several Atlantic clades in glaciated areas of Northern Europe, whereas diverged haplotypes dominated the coastal Iberian rivers. Populations inhabiting the Atlantic rivers of southern France apparently contributed to postglacial colonization of northern basins, but also comprised the source of southern expansions during the Pleistocene. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 97, 904–917.
Article
The mitochondrial cytochrome b gene was sequenced from Acantholingua ohridana from Lake Ohrid, Macedonia, and Salmo salar; and these sequences were compared to those previously obtained from S. trutta and five other salmonid species. In addition, a nuclear sequence, the first internal transcribed spacer (ITS1) of the ribosomal DNA, was obtained from A. ohridana, S. salar, and S. trutta and compared with sequences obtained from the same five salmonid species. Combination of these data with nuclear GH2C intron sequences for the same taxa yielded a combined dataset of approximately 2100 aligned bp for eight species. Phylogenetic analysis of all datasets supported the inclusion of A. ohridana in Salmo and a sister relationship between A. oridana and S. trutta.
Article
The potential for genetic interactions between hatchery and wild populations of salmonids in northwestern North America has increased considerably in recent decades. Efforts to mitigate severe losses to many wild stocks caused by overfishing, destruction of habitat, and blockage of migratory routes have focussed on boosting artificial production in public hatcheries. Opportunities for genetic interactions between hatchery and wild fish will increase if efforts to supplement wild production with hatchery-reared fish continue. Concerns center on three issues: (1) direct genetic effects (caused by hybridization and introgression); (2) indirect genetic effects (principally due to altered selection regimes or reductions in population size caused by competition, predation, disease, or other factors); and (3) genetic changes to hatchery stocks (through selection, drift, or stock transfers), which magnify the consequences of hybridization with wild fish. Strategies for minimizing these genetic risks and monitoring the consequences of various management options are discussed, and some important areas for future research are identified.
Article
Analysis of both uni-(two mtDNA gene sequences) and bi-parentally (seven microsatellite loci) inherited genetic markers, together with analysis of 40 morphological characters, described Salmo ohridanus as a highly divergent member of the genus Salmo. Based on comparative substitution rate differences at the cytochrome b gene, and a rough estimated age of the Salmo trutta complex (i.e. at least 2 million years), the S. ohridanus and Salmo obtusirostris clade probably split from a common ancestor of brown trout Salmo trutta > 4 million years ago, overlapping with minimum age estimates of the formation of Europe's oldest freshwater habitat, Lake Ohrid. Comparative analysis with Lake Ohrid brown trout (known regionally as Salmo letnica), supported the notion that these fish have more recently colonized the lake and phylogenetically belong to the Adriatic lineage of brown trout. It is further suggested that species-specific saturation in the mtDNA control region underestimated the divergence between S. ohridanus and S. trutta. Evidence of rare hybridization between S. ohridanus and Lake Ohrid brown trout was seen at both mtDNA and microsatellite markers, but there was no support for extensive introgression. (c) 2006 The Fisheries Society of the British Isles.
Article
Both anglers and researchers have documented a dramatic decline in fish in Swiss streams and rivers. Patricia Burkhardt-Holm of the University of Basel; Walter Giger, Herbert Güttinger, Armin Peter, Karin Scheurer, and Marc J.-F. Suter with the Swiss Federal Institute of Aquatic Science and Technology (Eawag); Ueli Ochsenbein from Switzerland's Cantonal Laboratory for Soil and Water Protection; Helmut Segner at the University of Bern; and Erich Staub in the Swiss Agency for the Environment, Forests, and Landscape outline how they sorted through a number of theories and mounds of data to find the sources of the decline.
Book
Previous protein studies found diagnostic alleles for Atlantic and Mediterranean brown trout populations. Lake Geneva and the upper Rhône belong to the Mediterranean drainage system. Therefore, we would expect that autochthonous brown trout populations from this area show the Mediterranean alleles. In most cases, however, we found Atlantic alleles in high frequencies (f > 0.8). Intense stocking has occurred in this area with hatchery strains originating from the Atlantic drainage system. Thus, the obvious interpretation of our data is that the, presence of Atlantic alleles results from stocking. However, if we take into account information other than present geography we may propose alternative hypotheses that would explain the Atlantic alleles, e.g., an immigration of Atlantic trout from the Rhine system after the last Ice Age. Several post-glacial colonization scenarios for Lake Geneva and its tributaries are discussed and compared to our protein data. The implications of our findings relative to conservation of the genetic diversity of brown trout in this region are also discussed.
Article
Complete sequencing of the mitochondrial control region was undertaken among brown trout Salmo trutta from North Atlantic areas where previous studies, based on smaller mtDNA fragments, failed to detect any phylogeographic signal. Comparison of sequences suggests that brown trout in the Iberian Peninsula and Scandinavia belong to largely divergent evolutionary units.
Article
Comparative analysis of protein loci, microsatellite and mtDNA markers revealed generally comparable estimates for introgression and apparent admixture rates in stocked brown trout populations at two sites in the River Doubs (Rhône dainage, Switzerland), which are 10 km apart and which belong to the same management unit. At one site, a significant deviation between mtDNA and nuclear markers could be explained by stocking of F1 hybrids originating from crosses between hatchery females and males from the local population. Substantial differences between diagnostic protein loci and protein loci having non-fixed private alleles indicated that caution must be exercised when using genetic markers not strictly diagnostic for the distinction of the populations under investigation. Congruent estimates of introgression and apparent admixture rates between diagnostic protein loci and presumed diagnostic microsatellite loci suggest that the latter can be regarded as reliable genetic markers for the estimation of introgression in Mediterranean brown trout populations stocked with trout of Atlantic origin. Significant differences in introgression and apparent admixture rates between the two sites and between age-classes of one study site were observed. Introgression is suggested to depend on environmental factors. Significantly lower introgression rates in age-class 2+ years as compared to juvenile trout might further indicate that introduced Atlantic brown trout and hybrids decrease in proportion between age-classes 1+ and 2+ years.
Article
Analysis of trout from 13 stations on the Mediterranean slopes of the French Pyrenees by 31 presumptive enzyme loci demonstrated the major impact of restocking programmes. Although the annual introgression resulting from these introductions was small, the accumulation of genes of Atlantic origin has resulted in a change in allele frequencies. Genetic disequilibria within and between loci exist. Introgression by genes of domestic (hatchery) origin varied from 0 to 77% among stations. Natural Mediterranean populations show no detectable geographical structure. There was a direct relation between the degree of introgression and heterozygosity. However, restocking could not explain all of the observed genetic disequilibria.
Article
In the Doubs River (Rhone drainage) two distinct brown trout (S. trutta) phenotypes are observed. One phenotype is locally called Doubs trout and is characterized by four black stripes on the sides, similar to perch (Perca fluviatilis L.) and the other is the common phenotype of the fluviatile ecotype of brown trout, Salmo trutta f. fario. Protein data for three samples from the Doubs show that the Doubs trout belongs to the Mediterranean population group of brown trout, whereas the fario phenotype originates from stocking with hatchery strains of Atlantic basin origin. The two forms, however, do not hybridize freely. This is indicated by considerable gametic phase disequilibrium between alleles of hatchery and Doubs trout at one sampling site, and by lack of intermediate genotypes and phenotypes at another sampling site. The introgression patterns observed at the two sites suggest that differences in local habitat conditions can affect the degree of hybridization and introgression.
Article
An attempt was made to extend the area of distribution of a native population of brown trout Salmo trutta belonging to a Mediterranean lineage (ML), which has maintained itself in the Dranse d’Abondance, a fast-flowing alpine stream (Haute-Savoie, France), despite several decades of intensive restocking with brown trout derived from the Atlantic lineage (AL). This was done by releasing an ML component into the predominantly AL population still present on the Ugine, the main tributary of the Dranse d’Abondance. This strategy of rehabilitation restocking was tested using fluoro-marked juveniles produced from a captive breeding stock derived from the wild Dranse d’Abondance ML stock. Samples of 0+ year fish were collected over the period 1995–2003 in order to assess the impact of the restocking. Percentages of fluoro-marked otoliths revealed significant contributions of ML restocking in the 0+ year autumnal standing population, with levels ranging from 34·3 to 61·4%. The change in the genetic characteristics of the 0+ year population produced by natural recruitment was monitored by analysing the unmarked subjects. Frequencies observed at two microsatellite loci revealed a considerable rise (from 0 to 60%) in the level of Mediterranean alleles in the natural 0+ year population since the introduction of restocking using ML individuals.
Article
Abstract  Recaptures of adult, hatchery-reared, brown trout, Salmo trutta L., and fishing time from anglers were used to evaluate the benefits of stocking programmes with repeated releases of adult brown trout. The recapture rate varied between 17% and 29%. The time between stocking and capture (referred to as residence time) varied between 1 and 160 days (median 3–49 days). Between 67% and 84% of trout caught in the river were recently released fish. Fishing effort increased after stocking, thereby increasing the impact of angling on wild stocks. Stocking with adult brown trout decreases the impact of angling on wild trout only if the time spent fishing by all anglers is kept stable. Furthermore, because of the short residence time of stocked trout, long-term impacts through competition for space and food, or genetic impact through introgression, are limited.
Article
Twenty-five years of extensive water temperature data show regionally coherent warming to have occurred in Alpine rivers and streams at all altitudes, reflecting changes in regional air temperature. Much of this warming occurred abruptly in 1987/1988. For brown trout populations, the warming resulted in an upward shift in thermal habitat that was accelerated by an increase in the incidence of temperature-dependent Proliferative Kidney Disease at the habitat's lower boundary. Because physical barriers restrict longitudinal migration in mountain regions, an upward habitat shift in effect implies habitat reduction, suggesting the likelihood of an overall population decrease. Extensive brown trout catch data documenting an altitudinally dependent decline indicate that such a climate-related population decrease has in fact occurred. Our analysis employs a quantitatively defined reference optimum temperature range for brown trout, based on the sinusoidal regression of seasonally varying field data.