Soft Mouth Trout: Endangered Fish Species in Balkan Rivers

SOFTMOUTH TROUT:

Endangered Fish Species in Balkan Rivers

The Softmouth trout (Salmo obtusi rostris) is the most intriguing member of the genus Salmo. It is extremely rare, seriously endangered, very shy and among the most enigmatic members of the Sal monidae family. It is yet to be sufficiently described and urgently needs scientific attention.

By CORNELIA WIESER and THE EDITORIAL STAFF Photos by JOHANNES SCHÖFFMAN, RASMUS OVESEN, ARNE HODALIC, AND BENEDIKT SCHÖFFMANN

Endemic to the beautiful rivers of the Western Balkans that drain into the Adri atic Sea, five distinct populations of soft mouth trout exist: in the Jadro, Vrljika, and Krka rivers of Croatia, the Neretva Basin in Bosnia-Herzegovina, and the Zeta and Morača rivers in Montenegro. None of the five populations can deal with dams. Despite their sensitivity to dam construction and the fact that they are already endangered, plans for hydro power project exist in their habitat.

Planned dams on the Morača River would most likely eliminate the species in that system. The Neretva system con tains, by far, the largest population of this species, and is therefore the last stronghold of this species on the planet. Sev en dams foreseen on the upper Neretva River threatens to exterminate 50% - or more, of the Neretva River-populations.

Within the “Save the Blue Heart of Europe campaign”, NGOs and scientists are fighting side by side to keep the Neretva refuge intact. During a week of research in sum mer 2022, more than 50 scientists, accompanied by journalists, activ ists, chefs, and an artist from across Europe, participated in a multidisciplinary expedition to collect samples of the largely unknown local biodiversity (https://balkanrivers.net/en/news/The-NeretvaScience-Week-50-scientists). This data will be used to legally chal lenge the hydropower projects. (Find the preliminary report here: https://balkanrivers.net/en/studies/neretva-science-week-preliminary-report).

A highlight of the Neretva Science Week was the detection of softmouth trout in a deep pool on the Neretva River at Glavatičevo, caught on camera by videographer Josh D. Lim, who got close to hypothermia for the video footage, after a combined effort of the fish group from BOKU University and the University of Graz to locate it.

Fact File//

Softmouth trout are a pre-glacial species that feed on small aquatic insects such as caddis, mayfly nymphs, and – espe cially – gammarus. They like relatively swift currents and are – usually – found in fairly deep pools and runs. While their whole physiognomy underlines its preference for feeding along the bot tom, softmouth trout can sometimes be caught on dry flies. Especially in August and September, they can be found surface feeding on caddis and small may fly species. The most effective fly fishing technique for softmouth trout, however, is euro nymphing with a heavy anchor fly and one or two small Perdigon nymphs or Gammarus imitations as droppers. Fished on long, thin leaders and care fully mended these flies will be able to tempt the mainly bottom-dwelling fish.

Softmouth trout are found in the Krka River in Croatia (Salmo obtusirostris krkensis), in the Jadro River in Croatia (Salmo obtusirostris salonitana), the Vrljika River in Bosnia and Herzegovi na, the Zeta River in Montenegro (Salmo obtusirostris zetensis), and in the Ner etva watershed in Bosnia and Herzegovina (Salmo obtusirostris oxyrhynchus).

Fun fact: These fish are called softmouth because of their fleshy mouths and lips – which become more and more pronounced as they grow bigger. They look similar to both trout and grayling (and lenok trout in Mongolia). And while they are closely re lated to trout (similar DNA), interestingly, their appearance - and some of their mannerisms - are more similar to grayling. They spawn in the spring, like grayling, and also feed on the bottom of the riv erbed, like grayling. Yet, they live in completely different rivers compared to grayling.

The “Save the Blue Heart of Europe” campaign is dedicated to save the Balkan rivers from destruc tion by 3500 dam pro jects. Find out more here:

www.balkanrivers.net