LATVIA
Scientists at BIOR deploy a fish counter to study population trends
New method for salmon stock monitoring The Salaca is the main natural salmon river in Latvia - the salmon population is maintained through natural spawning, and not through fish rearing and release. This is also one of the rare rivers in Latvia where salmon and sea trout fishing is permitted.
F
ishing for salmonids is gaining popularity in Latvia and especially in the Salaca. However, the most recent studies of the south-east coast of the Baltic Sea suggest the overall salmon population is decreasing, necessitating further investigations and, perhaps, also protective actions.
Equipment customised for the purpose at hand Scientists of the Institute of Food Safety, Animal Health and Environment (BIOR) have begun counting the number of salmon and sea trout migrating to spawning areas in the Salaca river with an automatic fish counter—a data collection tool and programme developed especially for this task. The automatic fish counter with a dividing fence is a seasonal construction placed in the river at the beginning and disassembled at the end of the salmonid fish migration period, taking the hydrological conditions into account. The dividing fence is made from panels of modular PVS pipes and has no effect on smaller fish migration up- or downstream, however, migrating salmon and sea trout can only pass the fence through a tunnel. The automatic fish counter is made by an Icelandic company. It consists of a scanner and photo tunnel and is
Data on the salmon population in the Salaca river in Latvia are being collected to assess stock development and to identify if conservation measures are needed.
placed on the upstream side of the tunnel. The scanner is activated when a fish goes through the tunnel; it registers the silhouette, length, and theoretical weight of the fish, as well as the direction of migration. A video is recorded in the photo tunnel when a fish passes through it.
A variety of data collected by the counter The use of this tool provides the scientists of institute BIOR with information about salmonid fish composition, length and weight, sex, migration period (time), and intensity. The results of the study will contribute to understanding
the reasons for the decline in the salmon population in the Salaca by throwing light, for example, on whether the number of migrating fish has decreased or if the quality of spawning areas has declined and needs to be restored. The results will facilitate the long term, science-based management of fishing in the Salaca river enabling both the protection of salmon and the development of fishing. The salmon population in rivers in the Baltic Sea region is evaluated by the International Council for the Exploration of the Sea; it develops scientific guidance for the sustainable exploitation of
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salmon population taking into account the results obtained by the institute, BIOR. The data collection program is supported by the European Maritime and Fisheries Fund and carried out by the institute BIOR in collaboration with SalacgrƯva municipality and local angler association Salackrasti For more information, contact: Didzis Ustups National Institute of Food Safety, Animal Health, and Environment (BIOR) Tel.: 371 6761 2409 didzis.ustups@bior.lv www.bior.lv &VSPlTI .BHB[JOF
07/10/20 8:25 PM