On 16 December at 12:15 Einar Kärgenberg will defenf his doctoral theseis “Movement patterns of lithophilous migratory fish in free-flowing and fragmented rivers” for obtaining the degree of Doctor of Natural Sciences (in ichthyology and fisheries).
Professor Toomas Saat, University of Tartu
Research Fellow Anu Albert, University of Tartu
Professor Jaakko Erkinaro, Natural Resources Institute Finland (Finland)
Spies among fish is real science, not fiction. For the first time in Estonia, bony fishes (so-called classic fish) were tagged with individual acoustic transmitters and released into natural waterbodies. These “spy agents” continued their normal activities, giving us insight into larger schools moving with them. More precisely, salmon juveniles descended towards the sea through a hydroelectric plant on the Purtse River; vimba bream moved to their spawning grounds in the Pärnu River and to the sea thereafter; protected asp continued moving between spawning, feeding and wintering areas in a large Peipsi-Emajõgi-Võrtsjärv lake-river system. After following the fish and analysing the big database, it turned out that keeping migratory routes open is vital, but sometimes deadly also. An exceptionally high proportion of juvenile salmon - 36% - died while using the turbine channel as a migration route. Luckily, a nature-like fishway was also available for fish that caused no mortality. Thus, the overall mortality for the whole descending salmon juveniles was 9%. The use of narrower bar racks on salmon rivers was found to be essential (for now mandatory). Elsewhere, fish also behaved diversely while the movement routes were opened. Several vimba bream individuals migrated far upstream, others changed their location between nearby spawning grounds. Asp utilised different rivers and lakes during a single year but with a tendency to repeat habitat use patterns between years. Surprising for asp was the location of several key-habitats and migration timing between them. The presence of continuous rhythms during all months was also unexpected. These are only a few examples of the fascinating results found in these studies. In conclusion, it was found that fish populations and habitats need to be approached on an individual level, as fish behaviour may vary across waterbodies. In this way, the most relevant information can be gathered and the best strategy for the protection and management for fish can be chosen. The “recruitment of spies" proved to be very effective and their continued use is recommended.