Luka Dakskobler

Stories: SAVING THE MARBLE TROUT

Fishermen and scientists in the River Soča basin in Slovenia have been working hard for more than 15 years to preserve and rehabilitate populations of the endangered genetically pure Marble trout in the upper parts of Soča basin, that have disappeared over the years of hybridization with Brown trout. Marble trout is famed for being illusive, mysterious, that it can grow to enormous sizes and weigh more than 30kg. In Slovenia, the largest one, found dead, weighed 24kg and was 117cm long. But the largest one caught by sports fishing weighed 22,5kg and was 120cm long. However, in 2008, most Marble trout in Soča river basin were hybrids. Since 1906, the Adriatic basin was stocked with non-autochthonous Brown trout that resulted in hybridization and subsequent disappearance of genetically pure native Marble trout. Before the start of the international project of rehabilitation and preservation of Marble trout, only one remaining population of pure Marble trout was known. In the next years, after the project started and provided with crucial information, fishermen and scientists have found seven additional remaining populations of pure Marble trout that are now used to breed their duplicates. The project was supposed to study the existing pure populations, create new ones by breeding them in captivity, and try to raise the level of pure DNA in hybrids until one day foreign DNA would be eliminated. The new pure populations are stocked in empty streams without connection to the habitat of hybrids. Many new streams have been populated with pure Marble trout since then. All streams are monitored twice a year. Fishermen and scientists go into the mountainous inaccessible gorges to count the fish, tag them, take fin and skin samples, weigh and measure them. These headwater streams in inaccessible gorges are isolated from hybridization zones (basically all other rivers) by waterfalls or other obstacles that Brown trout cannot defeat to migrate upstream and mix with Marble trout. Today, the captive breeding program involves seven original populations and their progeny. The fish are also stocked into Soča river to raise the pure DNA level in hybrids. In 2012, they toppled the scale. The level of pure Marble trout DNA reached over 50% and was advancing exponentially. The genetically pure Marble Trout is now again prevaling in the Soča river.  

  • Thousands of fishermen flock to Soca River basin to try and catch the illusive and famous Marble trout, known to grow over 120cm and weigh over 25kg. Fishing regulation in Slovenia is strict, permits are very expensive, and size and quantity limits of a Marble trout catch are very low. All in the name of preserving the species.
  • A team of fishkeepers, scientists and fishermen walks up a riverbed through a gorge littered by debree from a devastating flood months before. Monitoring of these streams runs twice a year for two weeks in at least seven difficult gorges.
  • Fishkeepers Zoran Kocič and Robert Svetičič fish for pure Marble trout in a headwater stream in Huda grapa using a generator to stun them. It takes at least two passes of each sector of a stream to catch them all. Originally there were eight streams where pure Marble trout remained. Others are now manmade.
  • A team of scientists and fishkeepers examine pure Marble trout in Zadlaščica stream, the original stream known to contain genetically pure Marble trout. Monitoring is crucial to determine their demographics.
  • The pure Marble trout are tagged to indicate their number, where they are from and even which sector of the stream they are from to see how these fish migrate in their own streams.
  • Fishkeeper Dušan Peršič releases a Marble trout into Zadlaščica stream. To populate new stream fishermen must first empty it by an electrical generator and relocate their former {quote}residents{quote}. It takes three years for each stream to be completely emptied, before they can stock it with pure Marble trout and be certain nothing will contaminate their DNA.
  • From left, Robert Svetičič, John Zablocki, Zoran Kocič and Dušan Jesenšek extract fish eggs from an adult female Marble trout in the Tolminka fish farm. An adult female Marble trout can produce up to 4000 fish eggs, but the avarage is just over a thousand.
  • Dušan Jesenšek extracts semen from an adult male Marble trout in the Tolmin fish farm. When they later fertilize the eggs, they use semen from several males fish to ensure successful spawning.
  • Dušan Jesenšek takes twenty fish eggs, weighs them to calculate the weight of a single egg. Then he weighs all the eggs from a single fish to calculate how many fish eggs they have collected.
  • The fish eggs are fertilized, and a fixing solution is poured in to prevent eggs from closing in water that has different salinity then they and to help semen fertilize them. After the fish eggs swell up in about two hours, they are put in the hatching tanks.
  • Eyed eggs contain a fetus that has already developed eyes. It happens a good month after fertilization. In recent years, eyed eggs are stocked into streams to make their development more natural. Half a million of them are stocked annually.
  • Fishkeepers hike up a gorge to insert eyed eggs into Martinkov potok. Martinkov potok is one of the newer streams that were cleared before pure Marble trout was introduced. They sweep it with a generator in spring and autumn at least three times, before they can be sure it is empty.
  • Fishkeeper Zoran Kocič digs a nest in the middle of Soca river to insert eyed eggs. Only hybrids prevail in Soca, but they keep stocking it with pure Marble trout to study the way Marble trout mixes with Brown trout, and to try and raise the level of pure DNA in hybrids.
  • Eyed eggs are inserted into a nest, temporarily protected by a bottomless barrel to prevent river current to wash them away. The eggs will then be covered with gravel and in two months the fry will hatch. By then it will be spring and they will have plenty of food.
  • Three weeks old sac fry are still kept in the hatchery in Modrej near Tolmin. Shortly, they will lose the yolk sac, and when they grow to about 5cm in length, they will be stocked into streams. But the hatchery can only accommodate a certain amount of fry, which is another reason for the eyed eggs method used in recent years.
  • Stories
    • Slovenia wildfire 2022
    • Exhibition Affliction-Geist
    • Anti-government Protests 2020
    • The Pandemic
    • Zero Waste Ljubljana
    • The Krampusse of Duplje
    • Urban beekeeping
    • The Astronaut
    • Land Grabbing in Senegal
    • The Girl Inside
    • Safeguarding the Venetian Lagoon
    • Anti-Government Protests
    • Air Lyra
    • 15 Years After the Genocide
    • Saving the Marble Trout
    • The Sad Lake
    • The Long Nights on the Marmara Sea
    • Student Protests in Ljubljana
    • The Bora
    • Tito's Infamous Prison Islands
    • The Zice Carthusian Monastery
    • Floods in Slovenia 2010
    • Medieval Reenactments
    • No More Bella Italia
    • Ice Engulfs Slovenia
    • National Fly Fishing Championships
    • Flash floods in Zelezniki
    • The Middle East
  • Who they are
    • Mary Wilson of the Supremes
    • The Jason Cale Band
    • Martina Marenčič
    • Darko Đurič
    • Andrew Obeng
    • Linda Tellington-Jones
    • Florence Williams
    • Benka Pulko
    • In passing
    • Idols
  • On Set
    • Wake Me
    • Going Our Way 2
  • Events/News
  • Tearsheets
  • Multimedia
    • Affliction-Geist
    • The Girl Inside
    • Air Lyra
    • The Long Nights on the Marmara Sea
    • 15 Years After the Genocide
    • National Fly Fishing Championships
  • Info
    • Bio
    • Awards
  • Contact
  • Slovensko

All photos on this site are © LUKA DAKSKOBLER. Any use without permission is subject to a fine. Site design © 2010-2023 Neon Sky Creative Media