How do we avoid the drowning of porpoises in fishing nets?
Center for Sound Communication, Institute of Biology, University of Odense
Vortrag am 12. Januar 1999 an der Tierärztlichen Hochschule Hannover in der „Alten Apotheke“
An estimated 5-10.000 harbour porpoises dies annually in the Danish gillnet fishery. Concern has been expressed that this by-catch may not be sustainable. An abundance of about 300.000 harbour porpoises has been estimated in the North Sea and adjacent waters. Preliminary studies on population structure suggest the existence of several sub-populations, that could well be affected very differently by the geographically concentrated fishery. However, the specific impact of the by-catch on each of these sub-populations is not known. Similarly, the reason why harbour porpoises become entangled in these gillnets is not well known either. Studies on harbour porpoises migrations and preferred habitats as well as studies on the behaviour of these animals around gillnets are therefore essential in order to understand the processes that govern susceptibility to by-catch.
To address this problem we mounted satellite-linked-time-depth-recorders on nine wild harbour porpoises to study their movements and diving behaviour. The porpoises were by-caught alive in pound nets in 1997-98 in the Danish Belt seas. The animals were followed for up to 70 days.
Further, the acoustic abilities of porpoises to detect gillnets and the possibility of scarring them away from gillnets by use of alarms have been studied on captive porpoises in Denmark.
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