how the marble trout was saved
in the Soča River

photography by
Marcus Sies & Benjamin Laschet



The Marble trout and the Soča river are connected to each other through thousands of years of evolution. A spectacular hue somewhere in the spectrum between green and blue gives them both a precious and elegant appearence and is a beautiful reminder of the wonderful process of natural evolution and uniqueness of a river systems biodiversity. 

In 1993 scientists of the Fisheries Research Institute of Slovenia realized the imminent threat of extinction of the Marble Trout. After decades of hyhridization with foreign brown trout the marble trout seemed to have disappeared as a result of genetic pollution from the' Soča River. After searching numerous tributaries to the Soča river, genetically pure marble trout have been found high up in the mountains isolated from the main Soča river system through waterfalls. ​In the following years a group of scientists created the "ACTION PLAN for Marble Trout", a detailed plan outlining actions for marble trout saving in the Soča river system. To reinforce genetic diversity of the broodstock, phenotypically appropriate individuals have been sorted out from the zone of hybridization and their tissue sent for genetic analysis. Only genetically adequate individuals have been used as genitors and included in repopulation process along with individuals from genetically pure populations.

In 2022 the team around Tomo Sotensek produced over 350,000 marble trout eggs that will be breed and stocked to the Soča river. Thanks to huge efforts by the Fisheries Research Institute and the Tolmin Angling Club, natural and genetically pure marble trout are now again the dominant species in the Soča watershed. This Story is a great example of how awareness, science and action can correct mistakes of the past and creating a better future for natural habitats of endangered species.




I met Tomo Sotensek, the manager of the Tolminka Fish Farm, on a trip to Slovenia in Summer 2021, he showed me the fish farms in Tolmin and answered a lot of my questions about the Marble Trout situation in the Soca River. I quickly decided to come back during the spawning season in Winter.

In Dezember 2021 I spent 7 days in Tolmin together with photographer Benjamin Laschet to visit Tomo and his Team to document their important work with the marble trout. We shot every day, at the old fish farm with the big marble trout, at the new fish farm where they breed and control the eggs, and at the hatchery in Modrej, where they count and fertilize the eggs and prepare the fish tanks for the new hatchlings. We also went out and found mature spawning Marble trout in the Soca River. There is a high chance these fish hatched in Modrej 5-10 years ago.

Marcus Sies