Salvelinus spp

Alexander, Timothy & Seehausen, Ole, 2021, Diversity, distribution and community composition of fish in perialpine lakes – “ Projet Lac ” synthesis report, Eawag: Swiss Federal Institute of Aquatic Science and Technology : 137-139

Salvelinus spp (lake char)

The perialpine lakes of Switzerland form the southern geographic range limit of the genus Salvelinus (lake char). Officially, one species of Salvelinus is currently native to Switzerland according to federal law (VBGF): Salvelinus umbla . This species naturally occurs in all deep perialpine lakes north of the Alps, and was introduced into many alpine and southern perialpine lakes, beginning in medieval times and extensively in the 19 th – 20 th century. Two additional endemic species of Salvelinus once occurred in Switzerland: a deep-water adapted (profundal) species in each of lakes Constance ( Salvelinus profundus ) and Neuchatel ( Salvelinus neocomensis ). These species were considered to have been driven extinct by the negative effects of lake eutrophication.

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The genus Salvelinus is renowned for its diversity of ecologically distinct forms in northern latitude lakes, for example Iceland, Scandinavia and Siberia, often with multiple forms occurring within the same lake. In several cases, these forms have been shown to be genetically distinct sympatric species. A considerable diversity of forms also occurs in some deep perialpine lakes in Switzerland.The Swiss naturalist Konrad Gessner already described three forms of Salvelinus in 1575 ( Figure 48 ). Gessner mostly focused on the strong size differences between the forms, and named them accordingly:Umbla minor, Umbla major, and Umbla maxima . However, with the exception of the two profundal species of lakes Constance and Neuchatel, the diversity of Salvelinus has not been studied since the birth of modern taxonomy.

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A large variety of forms can still be found among Salvelinus in some Swiss lakes ( Figure 49 ). A widespread “generalist” form lives in many smaller lakes, as well as in some larger lakes as the single known surviving form (such as Geneva, Zug and Zurich; Figure 50 ), and often has a bright red belly. Four other ecologically specialized forms 5 can be distinguished in several lakes: limnetic (living in open water), benthic (near the lake floor), profundal (deepwater) and piscivorous giant (fish feeding). Limnetic forms are characterized by a slender body and a rather small head, and often exhibit an orange belly during the spawning period. Benthic forms of Salvelinus have a bulkier body shape with a long, wide head. Profundal forms are adapted to live in the deep zones of the lake, with especially large eyes, pale body coloration, and often have inflated bellies when brought to the surface. Piscivorous giant forms are mainly characterized by their large body size and often by large jaws. All four specialized forms can co-occur in the one lake, as is the case in Lake Thun 6 ( Figure 49 ). Lake Thun has several additional forms that are currently being investigated using morphological and genetic methods (Doenz, Seehausen et al, in prep [25]).

It is currently unclear whether and which of the Salvelinus forms are different species. It is also unknown how many different species there used to be in Switzerland. In lakes where Salvelinus has been extensively studied and where many individuals of each of the different forms are available, genetic differentiation has been shown between coexisting forms. For example, such studies show that S. profundus is clearly a distinct species from S. umbla , and also suggest that there are several species in Lake Thun [25].

In Projet Lac, native Salvelinus were caught in lakes Thun, Brienz, Walen, Upper Constance, Upper Zurich, Lucerne and Zug in the Rhine catchment, and Geneva and Annecy in the Rhone. Salvelinus was also recorded as a non-native species in the two alpine (Sils and Poschiavo) and several southern perialpine lakes (Iseo, Lugano, Como, Mezzola).The highest diversity of Salvelinus was observed in lakes Thun, Lucerne and Walen, each with three forms ( Figure 49 ). At least two other distinct forms are known from lakes Thun and Brienz, with at least one other disctinct form known from Lake Lucerne [25]. The rediscovery of the presumed extinct S. profundus in Upper Lake Constance was particularly remarkable. It was caught in nets set at the location where this species was last documented in 1974 [166].

Several samples of Salvelinus from Projet Lac have been used for genetic investigations (i.e. lakes Thun, Walen, Lucerne, Constance, Geneva, Sils and Poschiavo). While these analyses are not yet complete, it can already be said that the data show that several genetically differentiated forms coexist in some lakes.The results also show that biogeographical context, ecological adaptation, as well as past stocking practices must be considered in order to understand the origins of the sympatric forms, and the wider phylogenetic relationships among the Salvelinus species and forms in the region. Salvelinus introduced into lakes Sils and Poschiavo from Austrian populations ( Figure 51 ) are genetically very different from the native Salvelinus in Swiss perialpine lakes. Genetic data also indicate that each lake originally harbored its own char populations, and that individuals of different forms from the same lake were often more closely related to each other than the same forms in other lakes [25, 167]. However, analyses of the same genetic data also showed clear traces of stock transfer among lakes ( Figure 51 ). For example, the original Salvelinus populations of lakes Constance, Thun and Brienz have been strongly mixed with introduced populations from other lakes. The native population in Lake Neuchatel, seems to have been completely replaced by a population introduced from Lake Geneva ([25]; no Salvelinus were caught by Projet Lac in Neuchatel). Detailed analyses are underway to characterize what remains of the native populations in these lakes.

Figures

Figure 48: The three forms of Salvelinus in Swiss lakes described by Konrad Gessner in 1575.

Figure 49: Diversity of Salvelinus in Swiss lakes with more than one surviving form (based on current scientific knowledge). Forms that were caught during Projet Lac are indicated by *. The generalist form is treated as S. umbla in this report and the specialized forms as distinct taxa. Additional photos of the forms during the breeding season are shown where available (individuals with more orange belly). Horizontal white bar indicates 5 cm. Photos by Projet Lac, Carmela Doenz and local fishermen.

Figure 50: Generalist forms of Salvelinus umbla in lakes with only a single known surviving form.Two genetically distinct clusters of S. umbla occur in Lake Zurich.The pictured fish was caught by Projet Lac in Upper Lake Zurich and is genetically and phenotypically similar to the generalist form from Lake Walen. On the other hand, Salvelinus analyzed from Lower Lake Zurich (none caught in Projet Lac) tend to be genetically and phenotypically more similar to S. umbla from Lake Zug (Carmela Doenz, personal communication).

Figure 51: Genetic traces of stock transfer of Salvelinus spp among investigated Swiss and Austrian lakes detected using genetic methods (Doenz, Seehausen et al, in prep [25]). These traces indicate that when stocks were introduced to lakes that had native char, the introduced char populations hybridized with the native populations.