”When we in REVIVO think about the past summer in these autumn days, first thing that comes to mind is the extensive filed work campaign that we implemented - sitting in our boat on the Mura and Sava rivers, sampling macroinvertebrates, defining sediment type or fishing from morning to late night hours.”

Our aims are: first, to adapt the sturgeon sampling methodology, presented by our Romanian colleagues during the workshop in Tulcea last year, to the specific conditions of smaller tributaries such as the fast flowing Mura and Sava rivers; second, to find the spawning, wintering, nursery and feeding areas by surveying macroinvertebrate communities in the potential sturgeon habitats (F. 1-2). Of course, one of our main aims is to confirm the presence of sterlets in the Mura river.

F.1: sampling during macroinvertebrate survey

F.2: collecting macroinvertebrates from sample

Since not much is known about starlet habitat selection in Slovenian rivers, our last aim – finding the sterlets - will not be easy. There is no sturgeon fishing tradition in Slovenia, so the rare sturgeon catch by is a coincidence, not a result of targeted fishing activity based in the knowledge of the species’ behavior. Therefore, advancing the knowledge through habitat mapping (i.e. suitable prey composition, depths, …) will help us narrow down the locations to survey fish presence in future surveys.

However, during these summer months spent on the Mura and Sava Rivers we also tested a potential fish sampling method for smaller, fast flowing tributaries of the Danube – longlines (F. 3). While we were not successful in confirming the presence of sterlets, we did catch representatives of another important migratory species - Asp (Aspius aspius; F. 4) - as well as European catfish (Silurus glanis) and Chub (Squalius cephalus; F. 5).

F.3: baiting the longlines

F.4: Asp (Aspius aspius) caught on the Mura

F.5: Chub from the Mura river

We will continue with the sampling campaign in the first months of 2020 to survey the potential wintering habitats which were identified during the 2019 summer sonar scanning trips. We will use trammel nets to try to confirm the presence of migratory fish species in these locations. In addition, in spring 2020 our filed sampling campaign will continue with the larvae sampling using D-shaped nets in a hope to detect and confirm spawning of several species of migratory fish.    

These surveys will provide the missing data about the potential spawning, nursey, feeding and wintering habitats for sturgeons and migratory fish species on the Mura and Sava River in Slovenia. The much needed methodology for sturgeon sampling and monitoring on these Danube’s tributaries will be developed during the field work which will be later described in the Migratory fish habitat mapping manual as one of the main outputs of the MEASURES project. 

It looks like our New Year’s wish will stay the same for 2020 and let’s hope it comes true this time!