What is the catch of gillnet fishers?

Background and Objective

The gill net fisheries are of great importance along the German Baltic Sea coast, both from a fishing and socio-economic point of view. In the past, little was known about the dynamics of these fisheries, except for the landings. Since several years we regularly have scientific observers onboard of vessels of this important fleet segment, for example to estimate discards.

The gill net fisheries generally are a very selective and environmentally sound catch method. However, the nets consist of very thin material that is virtually invisible for both fish and other animals. Harbor porpoises (Phocoena phocoena) or diving sea birds can entangle in the nets and drown. These bycatches are not intended by the fisher but could pose a threat to the affected populations of sea birds and marine mammals like harbor porpoises if too many specimens die as unwanted bycatch. Our scientific observers also document such bycatch events.

Approach

The sampling of the gill net fisheries is carried out by scientific observers which measure the catch on board of commercial fishing vessels. The data are mainly used to calculate discard ratios of the passive gear fisheries. In addition, documentation of the amount of unwanted bycatches may help to estimate the level of threat possibly affecting populations of sea birds and marine mammals. Both observer trips with and without bycatches are documented; this is important for extrapolations, because the vast majority of observer trips do not have unwanted bycatch.

Preliminary Results

Intensive sampling of the gillnet fishery improves our data base for stock assessment, forecasting and fisheries management. Furthermore, the documentation of incidental bycatch serves as an impact assessment of the impact of gillnet fisheries on birds and marine mammals (especially harbor porpoises and grey seals).