Seal depradation consists of lost catch (completely devoured or damaged fish) and broken fishing gears. Grey seals in particular are detrimental to coastal fishing. On the other hand, seals are unintentionally caught as by-catch. For example, mortality due to being by-caught is the single most important risk factor for the endangered Saimaa ringed seal.
The Natural Resources Institute Finland investigates and develops methods enabling the coexistence of fishing and seals. The damage caused by seals and mortality due to by-catch has been reduced by developing the structure and materials of fyke nets. For example, in collaboration with professional fishermen, Luke has developed fyke net structures which enable the survival of seals that are caught. These methods enable seals to be caught alive and either used or released.
Traps are raided by male grey seals in particular
Data on seal behaviour lays the foundation for properly targeted population management measures. Research conducted by Luke has found that pontoon traps are mainly raided by male grey seals. Due to the grey seal’s fidelity to specific feeding areas, removing seals from the vicinity of fyke nets is one way of decreasing the damages.
However, the ringed seal does not exhibit similar fidelity to a specific limited feeding area.
Baltic herring is the principal food of Baltic seals
Seals feed on the prey that is most abundant and easiest to catch at any particular time. Easily accessible food attracts seals, causing them to enter traps. Fish species with large populations, such as the Baltic herring, make up the bulk of Baltic seals’ diet. Other important species include sprat, European whitefish, vendace and other salmonoids. The three-spined stickleback is an important fish of prey for the ringed seal. While grey seal feed exclusively on fish, the ringed seal also forages on crustaceans.
According to Section 62 of the Fishing Act, the owner or user of fishing gear must notify the National Resources Institute Finland without delay of any seal or harbour porpoise caught in the gear.
Picture on top of the page: Mervi Kunnasranta