Fish stocks must be known to exploit the fish sustainably

Fisheries monitoring in the Baltic Sea focuses on economically important fish species. The main objective of such monitoring is to maintain and promote the sustainable exploitation of the fish stocks. This will safeguard the conservation of marine resources and the future of the fishing industry.

The Natural Resources Institute Finland evaluates the status of fish stocks by various means

The Natural Resources Institute Finland (LUKE) assesses the abundance of herring and sprat and the structure of fish stocks annually. This assessment is carried out with the help of a sonar echo sounder on the research vessel Aranda. Herring and sprat samples are regularly collected from fishermen’s catches also.

The status of coastal fish stocks such as pike-perch, whitefish, and perch is also estimated from catch samples. Such information is updated and published annually. Complete stock assessments are only made for pike-perch in the Archipelago Sea, and sporadically for perch also. 

The status of salmon stocks is assessed by LUKE through river basin surveys. These surveys determine how many fish ascend rivers to spawn in salmon rivers that have preserved their natural status. Similarly, the numbers of salmon juveniles migrating to the sea are also investigated.

The status of sea trout populations is also monitored mainly in river basins. The density of juveniles in a river is determined by electro-fishing. The electric current stuns the fish momentarily, allowing them to be collected and counted.

Stock-related data provides the basis for fishing quotas

Other coastal states in the Baltic Sea also collect fisheries data using similar methods to those employed in Finland. This data collected by the different countries is compiled annually. Based on this information, the International Council for the Exploration of the Sea (ICES) prepares common stock assessments. They serve as a basis for negotiating fishing catch quotas for the Baltic Sea.

The research data collected in Finland is also used in domestic decision-making. This information helps to regulate salmon fishing, as well as for other species. Such regulation has, among other things, led to a marked increase in the production of wild salmon juveniles in the Tornionjoki River. Similarly, based on the research data, a new minimum catch size has been set for pike-perch.

 Herring and sprat on a conveyer belt
The stocks of both herring and sprat are assessed annually on sonar expeditions.

Important fish reproduction areas are identified through research

Reproduction is the most critical phase of fish production. A reproductive period lasting only a few weeks will dictate how many new juvenile fish are born throughout the year, as well as how much fish will be available later for fishing.

Almost all fish species in Finnish marine areas reproduce either near the coast or in the archipelago. Each species has its own typical breeding areas. These are usually located in shallow water and are often only a few metres deep.

Since 2004, fish reproduction areas have been mapped under the VELMU Programme (Underwater Marine Biodiversity Inventory Programme). In these surveys, researchers seek out the fish juveniles because they are easier to find than fish spawn. The results of the mapping inventories can be extrapolated to larger areas with the help of statistical modelling. Once the reproduction sites are known, they can be protected and, if necessary, restored.

There is also a lot of research related to fish reproduction, as well as river basin rehabilitation in those rivers which drain into the Baltic Sea. The aim is to make salmon and sea trout, in particular, reproduce naturally in rivers where hydroelectric power production has prevented fish from reproducing.

 Searching for fish fry from the shoreline vegetation
The search for fish fry among the shoreline vegetation.