Background and Objective

Protecting harbour porpoises against bycatch shall be achieved by technical measures which use most recent knowledge about the behavior of these small cetaceans regarding communication and orientation. A suitable technical innovation, to be used by the German gillnet fishery, was developed and tested that reduces the conflict between economical and nature conservational targets and thus gives the German fisheries sector a sustainable competitive perspective.

Approach

The Project was organised in three steps:

1. Research in the laboratory to develop the PAL signal technically and to construct a housing that is suitable to be used in commercial fisheries;
2. Field research on harbour porpoise to optimize the avoidance strategies against gill-net dummies (without net to avoid real bycatch) that are equipped with PAL devices;
3. Trials of PAL devices in commercial gill net fisheries in the Western Baltic sea.

Data and Methods

TI-OF organised mainly the field trials of the PAL devices in the commercial gill net fisheries and analyses the results. Thus, practicability and effectiveness of PALs was tested, but also, whether these devices might potentially have an impact on amount and composition of catches of target fish species.

Results

Main result of this project: A new, innovative alarming device is able to significantly reduce the bycatch of harbour porpoise in gill net fisheries. In addition, better data about fishing effort and patterns as well as bycatch rates in the gill net fisheries were achieved by carrying out the commercial fisheries trials.

A suitable harbour porpoise communication signal, which in field experiments lead to avoidance reactions and increased the click-rate of wild harbour porpoises, was identified. The communication signal was tested in the gill net fisheries of several commercial gill net fishers in German and Danish waters until the end of 2016. The fishers set half of their nets equipped with PALs, the other half of their nets without PALs as control. The results in the Western Baltic are unequivocal: Significantly more harbour porpoises were bycaught in the nets WITHOUT PAL than in the nets with PAL. The probability of gill nets for bycatch of harbour porpoise is reduced by 80%.