Trout and Char of Central and Southern Europe and Northern Africa

Home , Arctic char, Brook trout, Brown trout, Cutthroat trout, Gillaroo, Lake trout

12 Trout and Char of Central and Southern Europe and Northern Africa

Javier Lobón-Cerviá, Manu Esteve, Patrick Berrebi, Antonino Duchi, Massimo Lorenzoni, Kyle A. Young

Introduction

!e area of central and southern Europe, the Mediterranean, and North Africa spans a wide range of climates from dry deserts to wet forests and temperate maritime to high alpine. !e geologic diversity, glacial history, and long human history of the region have interacted with broad climatic gradients to shape the historical and current phylogeography of the region’s native trout and char. !e current distributions and abundances of native species are determined in large part by their fundamental niches (i.e., clean, cold water with high dissolved oxygen). Brown Trout Salmo trutta are relatively common and widespread in the northern and mountainous areas of the region but occur in isolated headwater populations in the warmer southern areas of the region. !ese southern areas provided glacial refugia for salmonids and today harbor much of the region’s phylogenetic diversity. Despite relatively narrow ecological requirements in terms of water quality, native and invasive trout and char occur throughout the region’s rivers, lakes, estuaries, and coastal waters. Despite having only a single widely recognized native trout species, the region’s range of environments has produced a remarkable diversity of life histories ranging from dwarf, stunted, short and long-lived, small- and large-sized, stream-resident, lake-resident, fluvial potamodromous, adfluvial potamodromous, and anadromous (see Chapter 7). Only one trout and one char are native to the region, Brown Trout and Alpine Char Salvelinus umbla. !ere are four currently recognized Brown Trout relatives from the Italian peninsula and Mediterranean islands—Salmo fibreni, S. carpio, S. cettii, and S. marmoratus—and a taxonomically complex and poorly studied group of Brown Trout relatives in Morocco and Algeria. !ree nonnative species from North America (sensu International Union for Conservation of Nature [IUCN]) have been introduced and established naturalized populations: Rainbow Trout On- corhynchus mykiss, Brook Trout Salvelinus fontinalis, and Lake Trout S. namaycush. !is chapter summarizes the information available on the distribution, status, and management of these trout and char. 1 2  12 Native Trout and Char Brown Trout

Brown Trout is native throughout the region and is the most important species in terms of distribution, abundance, genetic and phenotypic diversity, and scientific, public, and economic interest. Brown Trout is one of the world’s most studied species and is used as a model system by population, behavioral, and evolutionary ecolo- gists and geneticists. Beyond the thousands of peer-reviewed journal articles, the vast literature on Brown Trout includes dozens of books, monographs, and symposia volumes. Newton (2013) and Lobón-Cerviá and Sanz (2017) provide contemporary summaries of Brown Trout biology and management. Phylogeography.—A dizzy array of colors and morphology typifies Brown Trout across its native range (see www.cartapiscicola.es or www.sibic.org/en/spanish-fish- chart/). Such variability in morphology, color, and life history has led to the nam- ing of more than 40 species! However, contemporary genetic data suggest that the single species Salmo trutta was modified by glaciation processes and colonization histories into multiple genetic lineages. Several lineages and sublineages in Italy, the Mediterranean islands, and North Africa have been elevated to species level. Fur- thermore, species designations are likely warranted for other sublineages in northern Europe (see Chapter 10), the Balkans, the Turkish peninsula, and northeastern Asia. Bernatchez et al. (1992) recognized five main genetic lineages for European Brown Trout: Atlantic trout (AT), Danubian trout (DA), Marble Trout of north Adriatic rivers (MA), Adriatic trout (AD), and Mediterranean trout (ME). Subse- quent studies (Bernatchez 2001; Cortey and García-Marín 2002) highlighted several genetically distinct sublineages with some of these main lineages. !ese include the Duero lineage (DU) from the Iberian Peninsula (Suarez et al. 2001), the Dades lineage (DAD) in North Africa (Snoj et al. 2011), and the Tigris sublineage (TI; Bardakci et al. 2006) from the Euphrates River (Turkey). Two sublineages, Salmo obtusirostris and S. ohridanus, have been recently reclassified into the genus Salmo as distinct species (Phillips et al. 2000; Sušnik et al. 2006; Snoj et al. 2009). Six of these lineages occur in the region covered by this chapter: 1. !e AT lineage occurs in rivers from Norway to the Iberian Peninsula and Sicily (Schöffmann et al. 2007; Cortey et al. 2009; Fruciano et al. 2014). Several morphological species have been described within the AT lineage (gillaroo Salmo sto- machicus Günther 1866; sonaghen S. nigripinnis Günther 1866, and S. ferox Jar- dine 1835). Sicilian trout were described as S. cettii Rafinesque 1810 but later on assigned to the AT lineage (Schöffmann et al. 2007; Fruciano et al. 2014). !e AT lineage has been widely stocked outside its native range but is considered native to the upper Danube (Schenekar et al. 2014) and is probably native in some north Italian rivers draining to the Mediterranean (Meraner et al. 2007).     /     3 2. !e DU lineage is native to the Duero and Miño rivers in the Iberian Peninsula (Vera et al. 2010). 3. !e ME lineage has a native range in the Mediterranean rivers of the Iberian Peninsula (Cortey et al. 2004), southern France and Corsica (Berrebi et al. 2000; Berrebi 2015), and Italy and Greece (Giuffra et al. 1994; Bernatchez 2001). 4. !e MA lineage is native to rivers of the northern Adriatic basin (Bernatchez et al. 1992; Giuffra et al. 1994; Snoj et al. 2000). !e recent revision by Pustovrh et al. (2014) assigns the species to this MA lineage. 5. !e AD lineage is distributed along the Mediterranean rivers from the southern Iberian Peninsula to Turkey, including Corsica (Cortey et al. 2004; Snoj et al. 2011; Berrebi 2015). Several morphological species endemic to the Italian peninsula (Salmo carpio Linnaeus 1758; S. cenerinus Kottelat 1997, S. cetti Rafinesque 1810, and S. fibreni Zerunian & Gandolfi 1989 [Gratton et al. 2014]) and the Balkans and Turkish Peninsula (S. dentex Heckel 1851, Flathead Trout S. platycephalus Behnke 1969, S. macrostigma Duméril 1858, S. lourocensis Delling 2011, Ohrid Trout S. letnica Karaman 1924, S. peristericus Karaman 1938, and S. pela- gonicus Karaman 1938) are members of the AD lineage (Sušnik et al. 2004, 2007; Lo Brutto et al. 2010; Snoj et al. 2011). 6. !e DA lineage is native to the Danube basin and Vistula River flowing to the At- lantic (Kohout et al. 2012). Several morphological species (Sevan Trout Salmo ischchan Kessler 1877, Tigris Trout S. tigridis Turan et al. 2011, Black Sea Salmon S. labrax Pallas 1814, Caspian Salmon S. trutta caspius Kessler 1887, and Amu- Darya Trout S. t. oxianus Kessler 1874) are members of the DA lineage. Within and among these lineages, Brown Trout exhibit several life-history forms. !ese forms, generally known as resident, anadromous, and lacustrine-adfluvial, have recently being reviewed according to Varley and Gresswell (1988) and Northcote (1997) as follows. Fluvial populations are where reproductive, feeding, and refuge mi- grations occur in the rivers and streams of the home range. Fluvial-adfluvial populations migrate from main stems into tributaries to spawn, but progeny may move downstream for growth and refuge. Lake-dwelling populations may spawn in inlets (lacustrine-adfluvial migration pattern), outlets (allacustrine migration pattern), and the lake itself (nonmigratory lacustrine spawners). Nevertheless, life-history expressions is a complex topic of much ongoing investigation because it is a heritable but plastic trait and many fish express alternative life histories in partial sympatry and interbreed. For example, within a river draining into the Atlantic Ocean, the ratio of anadromous to resident trout typically decreases with distance from the sea and anadromy is more common among females assumedly because fitness of females depends more on body size than males. Similarly, in a single river, resident forms may predominate in headwaters and adfluvials in the main-stem rivers draining into lower elevation lakes. We recognize this life-history diversity and distinguish among forms throughout the text. 4  12 Distribution.—!e naturally complex distribution of Brown Trout lineages and life-history forms in central and southern Europe has been modified through habitat fragmentation and stocking of nonnative lineages. For example, in the Czech Repub- lic, more than 500 km from the nearest estuary, anadromous forms occurred until the damming of the Elbe and Oder rivers in the early 20th century, but now only resident trout occur in the headwaters of the Elbe, Danube, and Oder (Kohout et al. 2012). Although there is evidence that the distributions of lineages naturally overlap in some basins (Bernatchez 2001; Lerceteau-Köhler et al. 2013), the range of the AT lineage, in particular, has expanded dramatically through stocking. In Germany, resident trout are common in high altitude streams, adfluvial individuals occur in subalpine lakes and large reservoirs, and anadromous forms predominate in the North Sea drainages of Schleswig-Holstein, Lower Saxony, Saxony-Anhalt and North Rhine-Westphalia. Historically, anadromous forms were present up to the Bohemian tributaries of the Elbe and Upper Rhine. Six rivers currently have sea trout: the Eider, Elbe, Weser, Ems, Meuse, and Rhine. !e Kiel Canal, built in 1890, allowed historically isolated anadromous populations from the Baltic and North Sea basins to hybridize (Petereit et al. 2015). In neighboring Netherlands, anadromous trout were likely present historically, but now, only resident forms remain in coldwater refugia of severely degraded and fragmented channel networks. In Switzerland, the presence of five genetic lineages, complex topography, and long history of stocking exemplify how natural and anthropogenic factors interact to affect the distribution of Brown Trout lineages and life-history forms. Brown Trout are widespread in each of the five major river basins (Rhine, Rhône, Po, Danube, and Adige) and occur naturally in 91% of rivers and 57% of lakes below 2,800 m. Adfluvial individuals occur in major lakes of each basin: the Plateau and Préalpes regions (Lakes Geneva, Brienz, !un, Constance, and Lucerne), the foothills of Jura (Lakes Neuchatel and Bienne), and Tessino (Lakes Maggiore and Lugano). Adfluvials have been introduced into lakes up to 2,600 m and are found in 4% of rivers and 12% of lakes. Anadromous individuals are limited to the Rhine and migrate to the North Sea. !e AT lineage occurred originally in the Rhine but has been widely stocked throughout the area. Signs of AT introgres- sions are evident in each of the other four major river basins (Largiadèr and Scholl 1995; Largiadèr and Hefti 2002; Keller et al. 2011). !e DA lineage occurs in the Inn River flowing to the Danube. Southern rivers flowing to the Adige and Po host AD and MA lineages. In Ticino River, the DA and MA lineages have been completely replaced by nonnative AT lineage (Dagani 2010). A recent analysis of 14 populations in Danube and Adriatic tributaries found that 59% and 85% of haplotypes, respectively, are nonnative, with an overwhelming predominance of AT haplotypes (Vonlanthen and Hefti 2016). In France, Brown Trout are widespread in rivers from sea level up to 2,000 m. Riv- er residents predominate in the northwest (Brittany) and southwest (Pyrenees). Anad- romous Brown Trout are common in rivers draining into the Atlantic (Baglinière et al. 1989; Haury et al. 1999; Klemetsen et al. 2003). Adfluvial Brown Trout occur in     /     5 Lake Geneva and other subalpine lakes (Lakes Annecy, Bourget, and Aiguebelette). Stocked populations with migratory behavior also occur in Lakes Serre-Ponçon (Du- rance River), Sainte-Croix (Verdon River), and Leman. !ree genetic linages are native to France. !e AT lineage occurs in two sublineages: Garonne to Rhine basins in the north and the Adour basin in the south (Ber- rebi and Schikorski 2016). !e ME lineage is native to the Rhône River and coastal rivers between the Spanish and Italian borders. !e AD lineage occurs in Corsican headwater streams as pure ancestral Corsican trout and also has a scattered distribution in the Alps and Pyrenees where it occurs with the ME lineage. On the Iberian Peninsula, resident trout occur in mountain streams as far south as northern Portugal in the west and south to the Tajo River in Spain. Trout are also native in southern rivers flowing to the Atlantic (Guadalquivir) and Mediterranean (Ebro, Segura, and smaller Valencian and Catalonian rivers). Recent reviews (Sanz 2017; García-Marchín et al. 2018) have identified four genetic lineages: Adriatic (AD), Mediterranean (ME), Atlantic (AT), and Duero (DU). !e AD and ME lineages occur in Mediterranean basins from the Pyreneans to Gibraltar, and in the upper tributaries of Guadalquivir (flowing to the Atlantic). !e AT lineages inhabits all rivers flowing north and northwest from France to northern Portugal with a southern limit at the Tajo River. !e DU sublineage is endemic to the Duero and Miño rivers flowing into the Atlantic Ocean in northern Portugal. Historically, anadromous trout were common in Atlantic coastal rivers as far south as the Mondego River in Portugal. !e frequency of anadromy has declined at the southern end of this range due to river regulation, and sea trout are now common only as far south as the Minho and Lima rivers. However, anadromous individuals are present in the fisheries off the coast of Portugal during the summer. In Italy, the AT lineage may be native to a few northern rivers but has been widely introduced through stocking. At least three rivers in the northeast, the Slizza River (near Tarvisio), Drava River, and Spol River host native trout of the DA lineage. (Meraner et al. 2007). Brown Trout have been stocked in Italy since at least 1860, and the species (mostly the AT lineage) is now broadly distributed in coldwater streams across country (Splendiani et al. 2016). Status.—!e status of Brown Trout varies widely across the region. In some areas, healthy populations support sustainable fisheries, but in others, the populations are subject to suites of anthropogenic stressors. Although the broad geographic range, dispersal ability, and life-history flexibility of Brown Trout render extinction improb- able, many populations have been extirpated or suffered declines in abundance and range contraction. Even where habitat supports healthy populations, translocations have eroded the natural phylogenetic integrity of the species and stocking has led to the persistent immigration of domesticated phenotypes into wild populations. In the Czech Republic, data from the Anglers Union reveal that catches declined fivefold between 1990 and 2015. !is figure contrasts with a threefold increase in Czechoslovakia between 1950 and 1990 (Kohout et al. 2012). !e persistence of many 6  12 populations depends on stocking programs that have mixed Atlantic and Danube lineages. Moreover, preferential stocking with the fast-growing Kolowrat strain has further eroded genetic diversity. River Elbe populations seem less affected by stocking than Danube populations (Závorka et al. 2015). In many streams, anthropogenic migration barriers limit the movement of trout throughout channel networks (Slavík et al. 2012). Increasing water temperatures, water diversion, and eutrophication have reduced habitat quality and increased competition with warmwater cyprinids (European Chub Squalius cephalus and Leuciscus aspius). !ere is also concern that increased pre- dation by piscivorous birds (great cormorant Phalacrocorax carbo) may threaten some populations (Čech and Vejrik 2011). In neighboring Germany, resident trout in the south are considered near threatened, but in other German states, their status ranges from not endangered to critically endangered. Adfluvial trout are considered endangered in Lake Constance and other large lakes (Baer et al. 2014). Anadromous trout are endangered or critically endangered (Neumann 2002) due to impassable barriers, pollution, eutrophication, loss of spawning habitat, and overharvest. In Austria, healthy resident populations of native lineages occur principally in headwater streams. Water diversion for hydropower and habitat fragmentation pose the principal threats to these formerly connected populations. In the lower reaches of river catchments, anthropogenic stressors increase with human population density. In many lowland rivers, overharvest has compounded these problems, and Brown Trout have declined dramatically or even disappeared. Stocking poses an additional threat through hybridization between lineages. Recently, the restriction of populations to higher altitudes because of increased water temperatures has been documented (Filipe et al. 2013). Although the relationships among parasites, hosts, and water temperature are poorly understood, there is growing evidence that proliferative kidney disease (PKD) is also contributing to population declines (Unfer et al. 2015). !e reintroduction of native predators such as the Eurasian otter Lutra lutra and goosander Mergus merganser may pose additional threats (Pinter et al. 2016). In Switzerland, recreational and commercial trout catches have declined by 60% in recent decades. Harvest of stream-resident trout reached a maximum of 1.55 million individuals in 1974, falling to 0.3 million by 2012 (Escher and Vonlanthen 2016). In Lake Constance, commercial harvest of adfluvial trout declined from 12,000 to 3,000 kg between 1950 and 1980 (Ruhlé 1996). More recently, the total catch of adfluvial trout from 15 major lakes during 1997–2014 averaged 14.5 metric tons (mt) with no obvious temporal trend (OFS 2017). Habitat degradation, poor water quality, and PKD (Burkhardt-Holm et al. 2005) appear responsible for population declines (Hari et al. 2006; Burkhardt-Holm 2008). Although wastewater treatment has improved during the past 30 years, the quality of their waters is compromised by the occurrence of heavy metals, pesticides, and estrogen disrupters (Aerni et al. 2004; Vermeirssen et al. 2005; Michel et al. 2014). More than a century of intensive stocking with the AT lineage into >85% of Swiss rivers (Pedroli et al. 1991) has compromised the phylogeo-     /     7 graphic integrity of Brown Trout in the country. Most populations from the Rhône, Danube, Pô, and Adige show introgression by the AT lineage (Largiadèr et al. 1996; Mezzera and Largiadèr 2001). In France, the range, abundance, and integrity of native lineages are threatened by habitat degradation (Poulet et al. 2011) and introgression by the AT lineage. !e threat from AT introgression is particularly acute for the few populations of ME lineage (Caudron et al. 2006). !e effects of global warming, PKD, and overfishing contribute additional stressors. To mitigate these pressures, angler harvest targets stocked trout rather than native, wild individuals (Mezzera and Largiadèr 2001). On the Iberian Peninsula, resident Brown Trout are vulnerable and of least concern in Portugal, whereas anadromous fish are vulnerable in Spain and critically endangered in Portugal. Most populations inhabiting northern Iberian streams are demographically stable despite introgression by nonnative lineages (Sanz et al. 2000, 2002). In Portugal, fisheries legislations are implemented by regional administrations and local municipalities. !erefore, it is difficult to design spatially coherent management strat- egies. In both countries, a shortage of government fishery biologists and inadequate monitoring compromise population status assessments. Currently, too few data are available to meaningfully evaluate long-term population trends. Value.—In central and southern Europe, Brown Trout has unequalled cultural, historical, and economic status. It is the most popular fish for recreational angling and supports locally important commercial fisheries. Given its cultural importance and association with clean and cold water, Brown Trout is widely appreciated by the public as an indicator of aquatic ecosystem health. !e ecological importance of Brown Trout is well exemplified by its role in regu- lating the abundance and community structure of aquatic invertebrates (Závorka et al. 2015). Brown Trout are also important prey for recovering predators such as the otter and serve as host for the larvae of freshwater pearl mussel (also known as eastern pearlshell) Margaritifera margaritifera. In the Czech Republic, pearl mussels of the Malše, Blanice, and Vltava rivers are threatened by an increased abundance of cyprinids out-competing Brown Trout. Many trout populations are exploited by recreational anglers, and some, mostly adfluvial populations, support locally important commercial fisheries. For example, in Switzerland, 150,000 anglers harvested 65 mt of resident trout in 2015, and commercial harvest of adfluvial trout averaged 13 mt annually (OFS 2017), with Lakes Geneva and Neuchatel yielding annual harvests of more than 3 mt. Adfluvial trout are also highly prized by anglers whose average harvest of more than 10 mt is comparable to that of commercial fisheries. In Lake Constance, German anglers and commercial fishermen harvest some 5 mt of adfluvial trout annually (Baer et al. 2016). Few data are available for sport or commercial harvests from other countries in the region. !e socioeconomic importance of Brown Trout is demonstrated by documented efforts from the Middle Ages to increase the productivity of trout fisheries (Kohout et 8  12 al. 2012). Today, hundreds, if not thousands, of trout farms in the region produce trout from the egg to adult stages to support stocking programs, private fisheries, and food markets. In some cases, these farms are government-owned and funded by the public through taxes. In other areas, like Austria, private farms predominate, which poses a challenge for agencies hoping to regulate the introduction and distribution of native and nonnative lineages (Pinter et al. 2017). Management.—Brown Trout have been harvested in the region for centuries. Un- til very recently, most waters hosting Brown Trout were open to harvest. With a few exceptions, fishing focuses on rod and line. Most waters and trout populations in the region are managed as public resources by governmental administrations. An exception is Austria where fishing rights are privately owned. Trout fishery regulations are mostly developed by local administrations and differ within and among countries. Recreational angling regulations do share some common features throughout the region: a license fee, an open (spring and summer) and closed (before and during spawning) season, a minimum size for harvest, and daily quotas. Although in most countries a sportfishing license can be acquired by simply paying a fee, Germany, Switzerland, and Austria require anglers to pass an exam. Commercial fisheries targeting adfluvial trout are regulated by lake-specific administrations. !e regulatory specifics for minimum size for harvest, fishing seasons, and quotas vary within and among countries and regions. For example, in Germany, the minimum capture size is 30 cm for residents and 50 cm for adfluvial individuals. In the coastal waters of Schleswig-Holstein where sea trout are common, the minimum size is the same, but fish in spawning coloration must be released from October 1 through De- cember 31. In contrast, in Spain and Portugal, where angling is popular but there are no commercial fisheries, the open season runs from March to August–September with a minimum harvest size ranging from 18 to 25 cm. In Spain, some administrations establish cotos (preserves) for specific stream reaches with expectedly exceptional angling. An additional fee is required to fish in these cotos, which often have reduced daily quotas and mandatory catch and release to protect fishery quality. Similar approaches to managing high-value fisheries exist throughout this region. However, most fishing regulations are based on managers’ intuition and anglers’ advice rather than on robust monitoring and formal adaptive management. Stocking of hatchery-reared Brown Trout remains popular. Manage- ment agencies increasingly monitor stocking programs and/or permit stocking only with offspring of Brown Trout from the local populations. However, elsewhere, stocking into wild populations occurs without restrictions or management oversight. Most hatcheries are operated by local fishery administrations, although some are owned by angling associations or even by restaurants (e.g., in Portugal). Regardless of regulatory differences, stocking remains a popular management response to anglers’ demands for more catchable trout; however, this is changing because the overwhelming body of scientific evidence suggests that stocking poses a     /     9 threat to wild trout populations. Increasingly, government and private fishery managers are improving trout fisheries through habitat restoration, local fishery closures, and catch-and-release regulations. !is transition is motivated in part by the EU Water Framework Directive (2000), which makes stream and watershed restoration a legally mandated priority for all national governments. Despite a growing awareness of the risks of stocking and the value of habitat restoration for the conservation of native trout populations, important challenges remain. In several countries and regions, nonnative Brook Trout and Rainbow Trout are considered naturalized and fishery regulations do not distinguish between native Brown Trout and nonnative salmonids. !us, there are no species-specific restrictions to stocking Brook Trout or Rainbow Trout, or harvest regulations that target nonnatives to the benefit of native Brown Trout. In some areas, differences among Brown Trout life-history forms are not recognized, and resident, fluvial, and adfluvial populations are stocked and managed without distinction. Remarkably, many areas still allow the stocking of Brown Trout from different evolutionary lineages into wild populations. !is exacerbates historical management indiscretions and likely contributes to the persistent presence of the AT lineage outside its native range (Largiadèr and Scholl 1995). Fortunately, there is a growing appreciation for the evolutionary importance of trout lineages, and protecting within-species genetic and phenotypic diversity is becoming a management priority. !e organizational structure of trout management and the role of scientific evidence likely affect the efficacy of emerging stocking policies. For example, in France, the national Ecology Ministry consults with researchers and scientific organizations to develop national policy. In turn, more than 100 private and independent depart- mental federations work directly with river managers. !rough this system, stocking is framed around three objectives: recover extinct or endangered populations, maintain wild populations, and support sport and leisure. To meet these objectives, three types of Brown Trout are used: local strains from wild-broodstock schemes, domesticated hatchery trout of the AT lineage, and sterile triploids to reduce the risk of interbreed- ing with wild populations. All Brown Trout for stocking are grown by angler’s associations and/or by administrative hatcheries. It is too early to determine whether this approach will meet the complex challenge of restoring wild populations, protecting intraspecific Brown Trout biodiversity, and meeting the demands of anglers for a har- vestable surplus of Brown Trout. In Germany, Brown Trout are managed by anglers’ associations, and limiting introgression between lineages and between wild and hatchery fish remains an ongoing challenge. In an attempt to inform disparate stocking programs, Schmidt et al. (2015) genetically analyzed 35 native populations from the Elbe (n = 13), Weser (n = 6), Rhine (n = 8), Danube (n = 6), and Odra (n = 2) rivers. Populations from all catchments except the Elbe contained haplotypes of the AT lineage. !e Danube populations harbored a distinctly high number of differentiated haplotypes. !ese results 10  12 support the recommendation that stocking should involve only offspring from the same fish populations (Baer et al. 2007). Italian Trout

!e 1,000-km-long3 peninsula of Italy and its principal islands of Sardinia and Sic- ily contain a broad range of freshwaters environments. From cold alpine streams and lakes to the mild freshwaters of Sardinia and Sicily, this diversity of habitats host several Brown Trout lineages whose populations have evolved in isolation in a broad range of hydrologic, thermal, and chemical environments. Debate on the taxonomy of the Italian Salmo spp. has a long history. Other than the three Brown Trout populations inhabiting streams flowing to Danube River in the northeast corner of the country, the challenge of trout taxonomy has been met through iterative debates. Bianco (1995) recognized three species, S. trutta, S. marmoratus, and S. carpio, whereas two species, S. fibreni and S. carpio, and a superspecies composed of three semi-species: S. (trutta) trutta, S. (trutta) macrostigma, and S. (trutta) marmoratus were reported. Later, Bianco (2014) recognized six species: S. carpio, S. fibreni, S. cenerinus, S. cettii, S. marmoratus, and S. rhodanensis, the latter endemic to the Roja river at the Ital- ian–French border. Most recently, the Italian Association of Freshwater Ichthyologists (AIIAD) proposed an updated list (Zanetti et al. 2014) with five native species: S. fibreni, S. carpio, S. marmoratus, S. cettii, and S. ghigii and one nonnative invader, S. trutta. !is is the list used here with the exception of S. ghigii (S. cenerinus) because there is currently insufficient evidence to warrant species designation (Gratton et al. 2014). !e four native trout of Italy, S. fibreni, S. carpio; S. cettii, and S. marmoratus, belong to one of five main mitochondrial DNA lineages (and so probably belong to S. trutta): MA, ME, AD, native AT, and nonnative AT. Moreover, we note that recent molecular analysis of Sicilian Brown Trout (Fruciano et al. 2014) revealed that these populations might be native derivatives of a South Atlantic lineage, similar to trout of Morocco (Snoj et al. 2011). !e hypothesis is based on the notion that they could have reached Sicily through North Africa during the Pleistocene, and thus, the Atlantic lineage should be also considered native of Italy (Schöffmann et al. 2007; Snoj et al. 2011). !is hypothesis has recently received phenotypic support (Duchi 2018). !erefore, the Sicilian populations would be unique since they are the only Italian Brown Trout of South Atlantic origin. Distribution

!e four Italian trout show substantial morphological and life-history diﬀerences (Figure 1). For the most they are allopatric, but they may overlap in some streams. Salmo marmoratus and S. cetti are stream residents with broad distributions. Salmo marmoratus (the MA lineage) inhabits Po River tributaries draining the European Alps. Salmo cettii inhabits Mediterranean rivers of the Apennines, Sardinia, and Sic- ily. !ere are several isolated populations in the western Alps (Splendiani et al. 2016), but its presence in the Po River system is controversial. Salmo ﬁbreni and S. carpio are original     /     11

Figure 1. Distribution of the four native Italian Brown Trout relatives. 12  12 endemic lake-dwelling species. Salmo ﬁbreni occurs in the small Posta Fibrenio Lake of central Italy, which is part of a karst system with a constant water temperature of 10°C year-round. Salmo carpio inhabits the relatively large and warm Lake Garda of the northern Po Valley and is found mainly at depths between 100 and 200 m. Status

All native trout of Italy are included in national or international red lists, with slight differences related to different geographical regions, period of evaluation, or basic criteria (Table 1). Salmo carpio and S. fibreni are considered of critical status due to illegal fishing, nonnative species introductions (Coregonus sp. in Garda Lake), pollution, and habitat degradation. For S. cettii and S. marmoratus, the principal threat is interbreed- ing with nonnative Brown Trout (Schöffmann et al. 2007; Querci et al. 2103; Fruciano et al. 2014; Gratton et al. 2014; Splendiani et al. 2016). Nonintrogressed S. cettii are absent from the central and eastern Alps, but they are distributed as 20.0% in the western Alps, 2.8% in the Apennines, 50.0% in Sardinia, and 33.3% in Sicily (Splen- diani et al. 2016). Streams with nonnative invasive Brown Trout or introgressed native trout populations are common in the eastern (94.3%), central (100%), and western Alps (60.0%) and less common in the Apennines (59.2%) and Sardinia (50.0%), but Sicily remains relatively unaffected by nonnative lineages. For S. marmoratus, all central Alps populations are introgressed, but original populations remain in the western (75%) and eastern (100%) Alps (Splendiani et al. 2016). Although the mechanisms underlying variation in the rate of nonnative introgression remain poorly documented, geological and climate conditions appear important for Salmo cettii (Splendiani et al. 2016). Native trout tend to be absent or rare in rivers with modified flow regimes. Such rivers have been target of stocking with Brown Trout and if so, the ratio of nonnative to native trout would make introgression more likely. Other threats to S. marmoratus and S. cettii include poaching, habitat fragmentation, pollution, water diversion, and competition with nonnative invasive species. Value

Brown Trout are abundant in the headwater stream reaches where they are important components of aquatic and terrestrial food webs. !eir recognized ecological impor-

Table 1. Conservation status of Italian native trout. Abbreviations: CR = critically endangered, EN = endangered, VU = vulnerable, NT = near threatened, and LC = of least concern.

IUCN Red List Italian Red List Italian Red List Species of !reatened Species of Fish of Vertebrates Salmo carpio CR CR EN S. cettii NT CR CR S. fibreni VU CR CR S. marmoratus LC EN CR     /     13 tance led to their inclusion in the Italian biological indices of water pollution with special reference to fish populations following the EU Water Framework Directive (2000). Recreational angling for stream-dwelling Brown Trout is economically important nationally. Salmo marmoratus and S. cettii fisheries are particularly popular for anglers in the Alps and Apennines, respectively. Salmo carpio supports an important, but declining, commercial fishery in Lake Garda. Harvests declined dramatically from the 1960s (16–40 mt/year) to 1970s (<1 mt/year). Harvest declined further through the 1990s, resulting in the closure of the fishery and initiation of a stocking program. Since ancient times, S. fibreni has been harvested, but declining catches and conservation concerns led to the fishery being closed in 1995. Management

Angling throughout Italy is managed by local and regional administrations, except in Sicily where angling is regulated in only four of the nine provinces. As elsewhere in Europe, exploited populations are mainly managed principally through daily quotas and minimum harvest sizes. Importantly, anglers record all captures in official notebooks. Most trout populations are stocked with hatchery fish bred from nonnativenative parents from specific drainages. Ongoing initiatives aimed at protecting genetically remnant and native populations are being implemented in several regions. !ese initiatives rely heavily on small hatcheries that use native broodstock to produce fish for stocking (Querci et al. 2103). Efforts to eradicate nonnative Brook Trout and Brown Trout are ongoing, as are programs to restore stream habitat, improve connec- tivity, and protect and restore ecological flows. Interestingly, Salmo carpio is included in the Ark of Taste (www.fondazioneslowfood.com/en/what-we-do/the-ark-of-taste/), a catalog of endangered heritage recipes by Slow Food, an international organization aimed at preserving local traditional food and cuisine together with their farming and/ or fishing. Trout of Northwest Africa

!e phylogeography and natural history of Brown Trout (Salmo spp.) in northwest Africa have received sporadic attention by scientists. Our understanding of how Brown Trout relatives colonized and spread throughout northwest Africa has been obscured by introductions of nonnative trout from Europe and North America during the 19th and 20th centuries (Mouslih 1987; Azeroual et al. 2000). !e Morocco Environmental Division continues stocking hatchery fish of different origins in rivers with native trout, making it increasingly difficult to identify the genetic origin of native populations (A. Snoj, University of Ljubljana, personal communication). !e situation is still worse in Algeria. Native trout were confined to two to three coastal rivers, and stocking of hatchery fish of unknown origin may have rendered these populations functionally extirpated ( J. Schöffmann, St. Veit/Glan, Austria, personal communication). Nevertheless, in certain remote rivers of the High Atlas 14  12 Mountains, there remain a few isolated populations of “truly African” trout whose taxonomic status is under current investigation. Here we review the current knowl- edge of trout distribution in northwest Africa, including nonnatives, and provide unpublished material and preliminary results from a recent expedition to the Mo- roccan High Atlas. Distribution

African trout likely originate from Brown Trout belonging to the southern clade of Atlantic lineage (Bernatchez 2001). It appears that trout colonized Africa during three migration events: 1.2, 0.4, and 0.2–0.1 million years ago (Snoj et al. 2011). !e range of trout in Africa varied during the glacial cycles of the mid- and late Pleisto- cene. Evidence suggests that trout have extended as far east as Algeria and as far south as the Draa River in southern Morocco (Schöffmann et al. 2007). Based on morphological criteria, four species have been described in northwest Af- rica: Salmo macrostigma (Duméril 1858), S. pallaryi (Pellegrin 1924), S. pellegrini (Wer- ner 1931), and S. akairos (Delling and Doadrio 2005). Salmo macrostigma was the only species present in Algeria, where it was also named S. lapasseti (Zill 1858). Moreover, S. pallaryi was described from Sidi Ali Lake, in the Middle Atlas Mountains, but it is now extinct due to changes in trophic conditions following the introduction of Common Carp Cyprinus carpio (Schöffmann 2013). Two native populations are currently being as- sessed as potential species: the “green trouts” of Lake Isli, S. viridis (Vivier 1948; Doadrio et al. 2015), and trout of the Dades and M´Goun headwaters (Snoj et al. 2011; Doadrio et al. 2015; Clavero et al. 2018). !is four-species perspective has been challenged by recent comparative (mainly molecular) studies, and there remains no consensus for how to assign taxonomic status to what are usually small, isolated populations (Table 2). Snoj et al. (2011) and Schöffmann (2013) have recently reviewed the trout distribution in northwest Africa (Figures 2 and 3). We use this framework to synthesize current information on African trout (Table 3). Overall, native populations can be divided into the Mediterranean and the Atlantic drainages (Schöffmann 2013). Trout have also been found in headwater tributary of the River Ziz, which originates in southern High Atlas and drains into the Sahara Desert (Snoj et al. 2011). !e traditional view that Salmo pellegrini occupies rivers draining into the Atlantic and S. macrostigma those draining into the Mediterranean (i.e., Atlantic and Mediter- ranean trout; Delling and Doadrio 2005) may be inappropriate. It is confusing because all native African trout share a common ancestor of the southern clade of the Atlantic lineage; all Moroccan and Algerian trout are Atlantic trout (but see the Dades trout case below). Furthermore, the distribution of species are not strictly defined by where rivers enter the ocean. For instance, there are Atlantic type populations in rivers draining into the Mediterranean and vice versa (Table 3). !e extent to which lineages and distributions have mixed due to natural geological processes in headwater catchment boundaries or historic and contemporary stocking remains unclear.     /     15 Table 2. Five comparative studies of native trout in northwest Africa (Morocco and Algeria).

Species or subpecies studied Methodology Remarks Delling and Salmo pallaryi, Morphology Head morphology groups S. pallaryi with Doadrio Lake Ifni the archaic trouts: S. ohridanus, 2005 trout, S. obtusirostric, and S. platycephalus. S. pellegrini, Description of a new species from S. macrostigma Lake Ifni: S. akairos. Salmo pellegrini and S. macrostigma present morphological differences but no conclusion about whether they are different species was reached. Salmo trutta Allozyme All the native trout from Morocco macrostigma, markers belong to a single subspecies, S. trutta S. akairos, macrostigma. Morphological differences S. pallaryi contrast strongly with a high genetic homogeneity. Snoj et al Salmo akairos, Mitochondrial All the trout in Morocco are S. trutta 2011 S. pellegrini, and belonging to the Atlantic lineage Lake Isli microsatellite (especially the southern Atlantic clade). trout, Dades DNA Salmo akairos, S. Pellegrini, and Lake River trout Isli Trout are just three forms of Brown Trout. Dades trout has a specific genetic make-up that reflects a basal position respect to rest of the native trout in Africa. Its status as a species should be evaluated. Doadrio et Dades trout, Morphology, Dades trout was described as a new al. 2015 Lake Isli mitochondrial species: S. multipunctata. Lake Isli trout DNA trout was described as a new species: S. viridis. Dades River trout was found to be basal to all the other trout in Africa.

Nonnative trout

Trout aquaculture in Africa began in Morocco in 1924 when a hatchery was built to promote angling through stocking into Middle Atlas lakes and rivers (FAO 2005– 2017). Stocking of Rainbow Trout in Morocco began in 1925 (Welcomme 1988; Az- eroual et al. 2000), and the species was introduced to Algeria in 1937 (FAO 2006– 2017). !ere are now naturalized Rainbow Trout populations in various rivers of the Middle Atlas, and stocking continues. Brown Trout from France were introduced in 16  12

Figure 2. Map showing different trout populations in Morocco (from Snoj et al. 2011).

Figure 3. Map showing different trout locations across the High Atlas Mountains in Morocco. From southeast to northwest: Ifni Lake, Ourika River, Tamda Lake, Ait Bouguemmez stream, Tassaoute River, M´Goun headwaters, Ahansai stream, Dades headwaters, Assif Melloul, Isli Lake, and Zaouia Sidi Hamsa.     /     17 Table 3. Reported native trout distribution in northwest Africa.

Catchment/ Drainage mountain Rivers, streams, Altitude; coordinates range lakes (speciesa) Mediterranean Sea basin El Abaich (Algeria) (1) Sea basin Zhour (Algeria) (1) Sea basin Amizour (Algeria) (1) Sea basin/Rif El Kanar (1) Laou (1) Sea basin/Rif Adelma (1) Mouluya/ Middle Berrem (3) (1) Atlas Ikiss 1,719 m; 32.58228, –4.76718 (3) Ansegmir (1) Melloulou (1) Atlantic Sebou/Middle Sidi Ali Lake 2,077 m; 33.075119, –4.993889 (2) Atlas Tigrigra (1) Tensift/High Ourika (3) Atlas Aït Mizane (3) Nﬁss (3) Imlil 1,921 m; 31.125006, –7.919222 (3) Tamda Lake 2,663 m; 31.315590, –7.000000 (3) Oum-er-Rbia/ Miaami Lagoon 1,480 m; 32.8985, –5.375966 (3) Middle Melloul 2,323 m; 32.033595, –5.4694132 (3) Atlas and Isli Lake 2,272 m; 32.217526, –5.548031 (4) High Atlas Lakhdar 1,655 m; 31.604651, –6.597173 (3) Tessaout 2,426 m; 31.475667, –6.586517 (3) Draa/High M’Goun 2,190 m; 31.6004, –6.2794 (5) Atlas Dades 2,180 m; 31.871776, –5.738205 (5) Souss/High Ifni Lake 2,323 m; 31.030532, –7.884218 (6) Atlas Ziz/High Sidi-Hamza 1,645 m; 32.433030, –4.715145 (3) Atlas a (1): Mediterranean type, (2): Salmo pallaryi, (3): Atlantic type, (4): S. viridis, (5): S. multipunctatus, and (6): S. akairos. the 1950s (Mouslih 1987). At least three char, Lake Trout Salvelinus namaycush, Brook Trout, and Arctic Char S. alpinus, were introduced to Morocco from 1941 to 1953 (Mouslih 1987), but only Brown Trout and Rainbow Trout have established naturalized populations (Mouslih 1987). Status

!ere are no formal data on the conservation status of trout in Morocco. According to Dr. I. Doadrio, Spanish National Research Council (personal communication), 18  12 trout are abundant in the Tamda, Ifni, and Isli lakes. In the High Atlas, Brown Trout are abundant in isolated headwater streams but are likely vulnerable to natural and anthropogenic environmental stressors. Brown Trout are rare in the Rift rivers draining to the Mediterranean. Apparently, the Melloul, Lakdar, Oum er Rbia, and Sidi Hamza rivers harbor stable Brown Trout populations, which are demographically supported by stocking (Doadrio, personal communication) !ere is no information on the native trout in Algeria. J. Schöffmann conducted an expedition to Algeria in 1987 and was unable to find a single native trout. Although he did not explore every possible location, he en- countered only Rainbow Trout (Schöffmann, personal communication). Management

Beyond the lack of monitoring data, African trout management poses a number of challenges. Small, isolated populations may suﬀer from genetic drift and inbreed- ing depression and are vulnerable to environmental and demographic stochasticity (Doadrio, personal communication). Habitat degradation, water diversion, pollution, and climate change compound these natural threats. !e negative eﬀects of hatcheries on native Brown Trout have been known for decades (Waples 1991; Araki et al. 2007); however, management policies in Morocco continue to prioritize stocking, and hatchery practices regularly mix lineages between populations (Doadrio, personal communication). In Algeria, stocking of Rainbow Trout has probably contributed to what appears to be the loss of native Brown Trout. Special Features

!e Dades trout.—Snoj et al. (2011) found Dades trout (present also in the M’Goun River) to be phylogenetically basal to all trout of Africa. !ese trout may have colonized Africa 1.5 million years ago and are thus older than the Brown Trout genetic lineages. Doadrio et al. (2015) supported these ﬁndings and provided morphological and molecular evidence for considering Dades trout as a new species. A recent survey by Clavero et al. (2018) concludes that the status of Dades trout in the Dades and M’Goun is critical since the populations are conﬁned to isolated headwaters reaches totaling less than 22 km. !e Isli trout.—!e commonly named “green trout” is endemic to Lake Isli (Figure 4), near Imilchil, Er Rachidia Province (Prosek 2013). Like the Dades trout, this is an endemic African trout whose ecological traits and status remain undocumented. Sev- eral authors suggested that the Isli trout could belong to the now extinct Salmo pallaryi from Sidi Ali Lake (Delling 2003). Recently, Doadrio et al. (2015) suggested that molecular and morphological data warrant species designation. Observations and data from 29 individuals captured during a 2011 expedition (M. Esteve and colleagues, unpublished) provide the following preliminary observations to guide further research (Figures 5–7): Isli trout display polymorphic coloration (green and white) not related to sex (Figure 5). Spawning occurs on shallow beaches during November and probably during the night (Esteve et al. 2008).     /     19

Figure 4. Isli Lake in the Atlas Mountains of Morocco.

African trout conservation—!ere is a real chance that African trout biodiversity will be lost before it is documented or understood. A number of urgent management actions are required to avoid this tragedy. Habitat protection and restoration should be prioritized for areas where native trout remain. Restrictions on harvest and stocking should be based on contemporary science and the precautionary principle. !e taxonomy of African trout should be revised using a total evidence tree that combines behavioral, life history, ecological, morphological, and molecular data (Brooks and

Figure 5. Isli Lake trout. 20  12

Figure 6. Assif Melloul (near Agoudal village) trout.

Figure 7. Lake Ifni trout (Morocco).     /     21 McLennan 2002). African trout are similar morphologically to other archaic trout: Salmo ohridanus, S. obtusirostris, and S. platycephalus (formerly placed in genera Ac- antholingua, Salmothymus, and Platycephalus, respectively). Improving African trout taxonomy may also help elucidate the evolutionary history of these salmonids (Esteve et al. 2014). Alpine Char Distribution

Alpine Char inhabit lakes and their tributaries. In France, they are native to Lakes Geneva and Bouget and have been introduced to more than 130 lakes in the Alps, Massif Central, and Pyrenees (Gerdeaux 2011). In Italy, Alpine Char occur naturally in lakes of the Trentino Alto Adige region and have been introduced elsewhere. In Germany, the species is native in all subalpine lakes and has been intensively stocked in high-elevation lakes. !e taxonomy of German char remains controversial. !e char of Lake Ammer- see (Bavaria) was described as an endemic Salvelinus evasus while the dwarf char of Lake Constance was named S. profundus. Until the 1970s, S. profundus was captured by commercial ﬁsheries but declined due to severe eutrophication (Baer et al. 2016). It was declared extinct by the IUCN in 2008, but a small population has recently been discovered. In Austria, Alpine Char occur in numerous alpine lakes but their natural distribution remains unknown because of extensive and poorly documented stocking. In Switzerland, Alpine Char is native to the major lakes of the four main basins (Rhône, Rhine, Po, and Danube) and has established naturalized populations following stocking in lakes up to 2,790 m. Overall, the species is present in 14% of Swiss ﬁsh-bearing lakes and in <1% of the rivers (Zaugg et al. 2003). Unlike northern populations, Al- pine Char tend to not migrate into adjacent rivers. Status

Although intensively stocked, Alpine Char have rarely established naturalized populations outside of their native range. A notable exception is a naturalized population of a high-altitude fishless lake, Obago, in the Spanish Pyrenees. Alpine Char populations are variably threatened by eutrophication, climate change, and nonnative species. In many lakes in Germany (and elsewhere), populations declined dramatically following severe eutrophication in the 1970s. However, due to recent human-induced reoligotrophication, populations are recovering. According to the IUCN Red List of !reatened Species (www.iucnredlist.org), Alpine Char remain endangered in Lake Constance and near threatened in Bavarian lakes. Climate change poses an additional threat to Alpine Char in low-elevation lakes. For example, in Austria’s Lake Lunz (600 m above sea level), Alpine Char appear to have been extirpated as warming facilitated the broad establishment of predatory North- 22  12 ern Pike Esox lucius. Habitat degradation and hybridization with nonnative Brook Trout pose additional threats. Apparently, populations in high-elevation lakes are less threatened by eutrophication, climate change, and nonnative species. As elsewhere, the native populations of Lakes Geneva and Bourget are supported by stocking with local offspring (Gerdeaux 2011), but the evolutionary consequences of such schemes remain poorly understood. In many Swiss lakes, eutrophication during the 1950s and 1970s led to declines of Alpine Char populations, and in Lake Neuchâtel, the species was extirpated (Ruhlé 1977; Rösch 2014). Alpine Char were reintroduced to Lake Neuchâtel in 1979 using offspring from Lake Geneva (Pedroli 1983). Alpine Char are now recovering throughout the country thanks to improved land management and human-induced reoligotrophication (Gerdeaux et al. 2006). Swiss populations (Gerdeaux 2011) provide valuable insights into how climate change threatens char through the direct effects on thermal stress and reproduction success and indirect effects such as increased suscepti- bility to PKD and modified interspecific interactions (with, for example, Brown Trout and Northern Pike). Value

In Switzerland, Alpine Char supports important recreational and commercial fisheries and it is a popular food in homes and restaurants. Commercial fisheries harvest nearly 20 mt of char annually from the major lakes (OFS 2017). In Lake Geneva, which supports the largest fishery by far, catches have declined recently, most likely due to climate change and despite intensive stocking programs (Gerdeaux 2011). Rec- reational anglers in Switzerland harvested more than 10 mt of char annually between 2004 and 2015. In addition to these fishery harvests, fish farms produce more than 5 mt of Alpine Char annually. Outside of Switzerland, char are economically and cul- turally important in mountainous areas of France due to extensive introductions, but recreational fisheries are relatively minor elsewhere. Management

In Germany, intensive historically stocking was applied to support local populations and establish new populations (Hartmann 1984). About 20 years ago, the interchange of eggs or fry among lakes was banned, and most recently stocking is only permitted with offspring from the same populations. In Switzerland, many Alpine Char fisheries are sustained by stocking. Between 1994 and 2013, almost 3 million individuals (all life stages pooled) were released annually in Swiss lakes. !e contributions of stocking to fisheries are lake-specific and likely depend on environmental conditions and the size of the recipient population. In Lake Geneva, stocked fish accounted for 65–92% of harvest during the 1980s, with a yield of 0.04–0.06 mt per 1,000 summerlings released. Since 2000, stocking effort and harvest are uncorrelated, and the yield from stocked fish has declined to 0.01 mt per 1,000 summerlings released (Champigneulle and Caudron 2012).     /     23 Nonnative Trout and Char Rainbow Trout

Distribution.—Native to the Pacific Rim, from northern Mexico to Russia, and cherished by anglers everywhere, Rainbow Trout is one of the world’s most widely distributed fish species. Introduced to Europe during the late 19th century, Rainbow Trout from the McCloud River (California, USA) first established naturalized populations in France. Rainbow Trout were soon introduced to Germany (Baer et al. 2007) and Switzerland, have been stocked throughout central and southern Europe for more than a century, and have established naturalized populations across the region. Management.—In Europe, Rainbow Trout are not perceived as a major threat to native Brown Trout because many stocked fish are sterile triploids, Rainbow Trout are less aggressive than Brown Trout, and Rainbow Trout are more susceptible to angling. Given the history of extensive stocking, Rainbow Trout have established relatively few populations in Europe, although the species is widely naturalized in Austrian rivers. Rainbow Trout continue to be stocked because of popularity with anglers. In some areas, angling regulations are species-blind, but in others, they are used to encour- age anglers to harvest Rainbow Trout. For example, in Vorarlberg (Austria), Rainbow Trout and Brown Trout have the same open seasons and harvest size limits, whereas in Salzburg, Rainbow Trout harvest is not limited by daily quotas or size limits. Despite not being listed as an invasive species of concern in recent EU regulations on invasive species, Rainbow Trout are increasingly managed as such. In Spain, recent legisla- tion forbids stocking Rainbow Trout, and the few naturalized populations are being targeted for eradication. Stocking Rainbow Trout is also forbidden in several German regions. In Switzerland, Rainbow trout have not been stocked into open waters since 1991 but can be stocked into closed waters to support sport fisheries. Status.—Despite a long history of stocking, naturalized populations of Rainbow T Rrout are rare in central and southern Europe, but naturalized populations are well documented in the Italian islands, the Austrian Alps, the French Pyrenees, and the Iberian Peninsula. Although there are no clear environmental correlates, naturalization success likely depends on interactions between hydroclimatic conditions (Fausch et al. 2001), propagule pressure through stocking, Rainbow Trout stock origin, and ecological interactions with native Brown Trout. Interestingly, there is a naturalized lacustrine-adfluvial population in Lake Constance where Rainbow Trout displays life- history traits similar to native steelhead (anadromous Rainbow Trout) from western North America. Value.—Rainbow Trout support valuable recreational fisheries and are used widely in commercial aquaculture. Although the economic value of Rainbow Trout to these sectors has not been formally quantified, the few data available suggest that it is substantial. For example, in Germany, farmed Rainbow Trout production reached 8,500 mt in 2015, and farms in Switzerland produced more than 1,000 mt in 2003–2004. In the late 20th century, there were more than 300 and 400 Rainbow Trout farms in Spain and Italy, respectively. 24  12 Brook Trout

Distribution.—Brook Trout from eastern North America were widely introduced to Europe during the late 19th century. In France, Brook Trout were first introduced in 1878 in Marne River. During the 1950s, Brook Trout were stocked into lakes and rivers of the Pyrenees, the Alps, the Vosges, the Jura, and Massif Central. Naturalized populations are now widespread but relatively rare in alpine lakes. Stocking of eight lakes in Corsica has resulted in at least two naturalized populations (Lakes Melo and Bastani). In Germany, Brook Trout stocking began around 1880, but its contribution to fisheries was considered disappointing and stocking effort was soon reduced. Natu- ralized populations are well documented in headwater streams of Alps but appear rare elsewhere. In Italy, there are a few naturalized populations in the small lakes and streams of the Alps and north Apennines. In Switzerland, Brook Trout have colonized all four main basins (Rhin, Rhône, Po, and Adige) and occur in 3% of streams and 10% of lakes. Brook Trout have been particularly successful in colonizing previously fishless high-elevation lakes in Switzerland and Austria. Status, management, and value.—Scattered naturalized populations support small and largely unregulated sport fisheries. In recent decades, stocking and aquaculture production have declined. In several German states, stocking Brook Trout is forbidden (e.g., Lake Constance). In Corsica, there is evidence that Brook Trout affect the foraging behavior of native Brown Trout. Lake Trout

Distribution.—Lake Trout native to northern coldwater North American lakes (pri- marily Canada and Alaska and northeast USA) were first introduced to Austrian and French Pyrenean lakes during the mid-20th century. Later on, this species was introduced into lakes of the central Alps and Jura Mountains. In Switzerland, Lake Trout are now naturalized in all five major river basins (Rhine, Rhône, Pô, Adige, and Danube), are common in high altitude lakes, and are present in 21% of the fish-bearing lakes.

Status, value, and management.—Naturalized populations have been documented in France and Switzerland since the 1970s. !e fishery value is limited, and there is no specific management. Although no study has evaluated the effects of Lake Trout on native fish fauna, Lake Trout stocking is associated with declines of toads in the Alps and of salamanders Euproctis sp. in the Pyrenees. Acknowledgments

We acknowledge the important contributions of several experts who contributed local, region, and national information: Christoph Petereit, Jan Baer, Klaus Wysujack, Ar- min Nemitz, Kurt Christoph Petereit, Jan Baer, Klaus Wysujack, Armin Nemitz, and Jens Salva (Germany); Kurt Pinter, Florian Pletterbauer, and Günther Unfer (Aus- tria); Franck Cattáneo (Switzerland); Libor Zaborka (Czech Republic); Gerard de     /     25 Laak (!e Netherlands); Teresa Ferreira and Filip Ribeiro (Portugal); and Nuria Sanz (Spain). References

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