Sælsikkert fiskeri: Udvikling og afprøvning af sælsikre redskaber

In the last 10-15 years, there has been an increasing conflict between fisheries and the growing number of seals in Danish waters. Harbour seals have increased in Danish waters from around 2,000 animals in 1976 to around 16,500 animals in 2016, and grey seals in the Baltic Sea have increased from around 2,000 animals in the late 1970’s to more than 30,500 animals in 2017.

The number of grey seals in the Danish part of the Baltic has grown similarly. At Christiansø their numbers increased from 0 in year 2000 to more than 800 observed in 2016. Both harbour and grey seals are involved in attacks on fish caught in fishing gear resulting in damaged fish as well as damaged fishing gear.

These attacks occur exclusively in fishing with passive gear like gillnets, hooks/lines and fykes/traps. In some parts of the Danish waters, the damages are so high that they threaten the survival of the small-scale coastal fisheries, in particular fisheries for cod, salmon and lumpfish. It is unrealistic to reduce the number of seals to a level where damages are insignificant, so it is necessary to find other ways of resolving the conflict, like introduction of alternative fishing gear, where the gear and the catch is protected from the seals, or modification of existing gear.

The present report describes the results of trials with two different alternative gears: the Swedish Pontoon-trap and the small-scale Danish seine, and trials of a seal scarer for use with longlines or gillnets. The Pontoon-trap was originally developed in Sweden for the salmon fishery, but has also been used for other species like herring and, to a limited extent, for cod.

The aim of our trials was to determine if the Pontoon-trap could attain catch rates of cod that were sufficiently high that the Pontoon-trap could be a viable alternative to gillnets. We conducted two fishing trials with the trap, one in Nakskov Fjord in March-May 2018 and the other at Bornholm in June 2019.

Both trials caught mostly European flounder and very little cod, but other information from the two areas suggested that the abundance of cod in the areas fished was low. We recommend that the trials are continued in areas with higher abundance of cod and includes trials with using bait to attract cod to the trap.

The aim of the trials with the small-scale Danish seine was to evaluate if it could be a viable alternative to gillnet fishery for cod. The trials were conducted around Bornholm in August-October 2018 on board a gillnet vessel, which had been modified to accept the small-scale seine system. We conducted a total of 65 hauls of which 38 could be used in the analyses of catches.

Catch rates varied considerably between 0-49 kg of cod above 35 cm with a mean catch rate across all hauls of c. 10 kg per haul. The aim of the seal scarer trials was to evaluate if seals scarers could reduce grey seal depredation on salmon caught on longlines. The trials were conducted in the Baltic salmon longline fishery in February 2018 and January-February 2019.

We tested two different types of seal scarers, the RT1 from AceAquatec and a prototype from GenusWave. Grey seals exposed directly to the RT1 signals showed very strong reactions, while reactions to the GenusWave prototype were less pronounced. However, too few data were obtained during the trials to determine if the scarers had a significant effect on the frequency of damaged salmon caught on the longlines.

Since these trials, GenusWave has developed a smaller, autonomous device, which can be deployed with the longlines while they are fishing. We recommend that trials are conducted with this new device as soon as one can be made available from the company.