Eawag: Endangered fish diversity in streams is recorded
By systematically fishing Swiss rivers, Eawag researchers have documented more than 40 fish species in the "Progetto Fiumi" project. In addition, the Eawag team has found a diversity within the species that had previously been recorded only rudimentarily. The project thus provides a basis for the protection of this genetic and ecological diversity.
Switzerland's waters are home to a unique diversity of species. In order to record this more precisely for the first time, researchers from the Fish Ecology and Evolution department systematically fished hundreds of rivers and streams in September and October between 2013 and 2018 as part of the "Progetto Fiumi" project. "More than half of the catches were trout," says Jakob Brodersen, who coordinates the FOEN-funded project. "And we found them in almost all habitats - from small mountain streams at over 2000 meters above sea level to lowlands." In total, the researchers sampled fish at 308 sites spread across Switzerland and all river and stream types.
The fact that not all trout are the same has been known for a long time. Thus, five species have been distinguished so far, which have developed completely separately from each other in the large river systems. The brown trout (Salmo trutta) in the tributaries of the Rhine, the Doubs trout (Salmo rhodanensis), the marble and Italian brown trout (Salmo marmoratus and Salmo cenerinus) in the tributaries of the Adriatic Sea and the black sea trout (Salmo labrax) in the Inn. Swiss fish biologists also pointed out different trout forms around the Engadine lakes already in the early 20th century.
New insights into trout diversity
Brodersen's team has systematically documented the many variations between and within species - and found forms that differ in appearance, behavior and, in some cases, genetic makeup. Studies in the catchment area of Lake Lucerne, for example, showed that trout in streams with constant water flow are individually more specialized in their choice of prey than trout in torrents with strongly fluctuating water flow. In Graubünden, the researchers compared brown trout living at low elevations under more favorable environmental conditions with their relatives in the barren headwaters of wild streams. But contrary to expectations, the "high mountain trout" were not smaller when they spawned for the first time, but on the contrary significantly larger than the trout in the lowlands - an important piece of information when it comes to setting minimum catch levels. And in Vaud, authorities and fisheries supervisors drew the team's attention to a stream where trout with points lived alongside others without points. Genetic studies revealed that the spotted animals are closely related to other brown trout in the area, but not to their spotless neighbors, with whom they usually do not reproduce.
Fish diversity database
Different ecological adaptations and local forms were also found by the Eawag team in all other fish species - from the widespread bullheads to barbel, minnows and other carp species, which dominate the large, slow-flowing waters. Initial genetic analyses did not confirm some previous assumptions and suggest that surprises are to be expected in these species as well.
A collection was established for further research into the hitherto largely unknown intraspecific diversity. Today, it comprises a good 10,000 fish, 20,000 tissue samples and environmental samples providing information on the food web of the sampling sites. "The collection at Eawag in Kastanienbaum is available as a large-scale database for local studies," says Jakob Brodersen. "Conversely, it is continuously expanded and refined through reports from the public and local investigations."
For protection that works
The collection is already being used for various applied research projects. This is because fish diversity is threatened by stream obstructions, migration obstacles, hydropeaking problems downstream of power plants and other human impacts. With the new Water Protection Act, Switzerland aims to rehabilitate severely impaired habitats. Among other things, the Progetto Fiumi provides the basis for monitoring programs and applied research. It helps to ensure that investments in restoration measures are used in a way that really benefits the fish and that genetic diversity is not lost before it has even been properly recorded.
Inventory also in the lakes
Similarly to the "Progetto fiumi", Eawag investigated fish diversity in lakes near the Alps from 2010 to 2015 in the "Projet Lac". Together with the cantons, the Federal Office for the Environment, the University of Bern and the Natural History Museum of the Bernese Burgergemeinde, as well as other partners, over 70 fish species were recorded. Many species from greater water depths, especially whitefish and char, are found only in individual lakes, where they evolved in the course of evolution - mostly only since the last ice age - by adapting to the extreme habitats. However, many of the former deep-water fish species have been lost again with the over-fertilization of the lakes. www.eawag.ch/projetlac
