Damage by seal in the fisheries (Sælskader i fiskeriet)

In the waters around Denmark, the populations of both grey and harbour seals have increased significantly since their protection in the 1970s. For example, the grey seal population has increased from 4,000 to more than 60,000 individuals in the Baltic Sea (Harding and Härkönen, 1999; HELCOM, 2023a). However, large seal populations often cause conflicts with fisheries (Olsen et al., 2018) and many fisheries complain that seals damage their catches, scare fish away from the areas and eat large amounts of fish (Königson et al., 2009, 2007). Seal damage to fish catches is well documented in Sweden, with particular damage found in gillnet and hook fisheries (Blomquist and Waldo, 2021; Kindt-Larsen et al., 2023; Königson et al., 2015b). The seals can either eat the whole fish or part of it, but in both cases the fisherman will lose the value of the fish. In southern Sweden, it was estimated in the cod fishery that approximately 44% of the fish catch disappeared without trace in 2009 (Königson et al., 2009). In Denmark a similar experiment was conducted where 75% of the cod catch disappeared after three days. DTU Aqua, Danish Fishermen PO and Foreningen for Skånsomt Kystfiskeri therefore want to conduct a project that sheds light on how much of the catches in gillnet fishing are destroyed by seals or disappear completely without a trace.

This project will shed light on the problem from several different angles and provide great insight into the seals' direct impact on gillnet fishing. The project consists of:
1) Interviews. The first part will focus on updating the studies that DTU Aqua conducted more than 10 years ago before the issue was described. Here, the fishery will be interviewed about problems with seals.
2) Documented seal-damaged fish. DTU Aqua has since 2010 monitored by-catches of protected species in Danish net fishing using electronic monitoring. Several of the participating vessels have also presented their seal-damaged fish. The idea is therefore to summarize all these registrations and to show which areas, seasons and target species are affected by seal damage and not least how large parts of the fishery are affected.
3) Missing fish. In 2021-2022 DTU Aqua documented that large parts of the cod catches in the gillnet fisheries disappeared around Bornholm. But it's not only around Bornholm that the fishery experience these problems. Therefore, similar experiments will be conducted in the North Sea and in the inner Danish waters to document effects on a fine scale.

Funding
The project is funded by Fiskeafgiftsfonden.

Research area: Ecosystem based Marine Management