Conservation genetics study of huchen in Slovenia recommends river system‐based management and indicates self‐sustainability of the middle Sava population

Abstract

The middle part of the Sava River in Slovenia provides one of the longest free‐flowing habitats for huchen, a threatened species that is also protected by the European Habitats Directive. However, there are plans for the construction of a chain of hydropower plants along this stretch of river. It has previously been assumed that huchen is no longer self‐sustainable here, but dependent upon stocking with hatchery‐reared fish. Using microsatellite and mitochondrial DNA, the genetic structure of huchen in its entire range in Slovenia was analysed with the particular aim of assessing the self‐sustainability of the species in the middle Sava. Using factorial correspondence analysis and assignment tests, a distinct genetic cluster was identified for each of the three main river systems in the country (Sava, Kolpa and Mura–Drava). In the middle Sava, a genetic admixture between stocked and local individuals, observed beyond F1, and a unique genetic substructure not corresponding to the stocking sources, were found. These results indicate the self‐sustainability of the middle Sava population and justify its protection. The estimated effective population size in the middle Sava is below the accepted minimum, and additional fragmentation arising from dam construction would cause the genetic breakdown of this huchen population. To preserve local genetic pools and possible inter‐population adaptive differentiation, we recommend that the three, historically isolated, river system‐bound populations (from the Sava, Kolpa and Mura–Drava) are managed separately. However, separate management of the small, isolated populations in the once free‐flowing Sava river system is not encouraged as it may cause their genetic impoverishment. The potential impact of this study on the conservation management of huchen more widely is discussed, with emphasis on the Balkans, where large populations still exist and their management is just beginning.

The minnowPhoxinus lumaireul(Leuciscidae) shifts the Adriatic–Black Sea basin divide in the north‐western Dinaric Karst region

“…While the difference might relate to different hydrological conditions (e.g., greater flow velocities and water volumes in rivers with fewer underground connections compared with small streams in the LRS with numerous subterranean water connections), the genetic isolation of the Krka and KORS has also been noticed in other fish (e.g., Cottus sp. in Kolpa, Bravničar et al, 2021; Hucho hucho , Snoj et al, 2022; and Thymallus thymallus [unpublished data]) and in invertebrate species (Kolpa: Trontelj et al, 2005; Klobučar et al, 2013; Ivković & Plant, 2015; and Krka: Verovnik et al, 2004). The timing analysis suggests a split between mt‐1a–c and mt‐1d–f within P. lumaireul to the middle or late Pliocene, with the start of genetic isolation coinciding with the beginning of the karstification process (Trontelj et al, 2007).…”

History, Life History, and Fate of a Salmonid Flagship Species: The Danube Salmon

“…The decline in populations is the result of numerous interventions found in large parts of the Danube River basin. Snoj et al (2022) report that Danube Salmon populations in the Slovenian Sava River have declined and are under severe threat due to hydropower expansion plans. Only isolated occurrences are left in the Carpathian Mountains (Ihut et al 2014).…”

“…Snoj et al. (2022) report that Danube Salmon populations in the Slovenian Sava River have declined and are under severe threat due to hydropower expansion plans. Only isolated occurrences are left in the Carpathian Mountains (Ihut et al.…”

“…A limited number of international publications address the protection and status of Danube Salmon stocks (cf. Holčík 1990;Geist et al 2009;Treer et al 2014;Weiss and Schenekar 2016;Bănăduc et al 2019;Snoj et al 2022;Wild et al 2023). Even fewer delve into topics closely related to the species' ecology and biology, highlighting the scarcity of sound knowledge on the ecology of Danube Salmon (cf.…”