Department of Physics, Chemistry and Biology (IFM)

Introduction
A pinger is a sound emitting device put on fishing gear to deter animals so that they don’t get caught as bycatch.  The subpopulation of Harbour porpoises  (Phocoena phocoena) in the Baltic is critically endangered. There is approximately 450 individuals left and their main threat is human activity where the  porpoises get stuck in fishing nets and drown.  To avoid the porpoises from getting stuck, pingers are used to make the porpoises avoid the nets. And this works. Nets with pingers catch less porpoises than nets without pingers. Unfortunately s eals have learned to use the pingers to find the fishing nets and the same individual can be responsible for many many attacks. During a visit a seal can eat a lot of the already caught fish, scare of future catches and break the fishing gear. The seal could also get stuck and drown, just like the porpoise. Beacuse of the damage caused by seals, there is a reluctance to use pingers. And when pingers are not used we are back on square one where the endangered porpoise is getting caught.

This project is the first step towards developing a seal safe pinger. A seal safe pinger is a pinger that deters porpoises while not being detected by seals. Porpoises can hear higher frequencies than seals so the sound emitted by the seals safe pinger needs to have higher frequencies than the seals can hear.  The sounds used in this study came from the Aqua mark 100 which generates eight different sounds .

Aim
The aim is to find and test a procedure for finding the hearing threshold in two grey seals and a harbor seal in human care, for the sounds from an Aquamark100 pinger, with the frequency spectrum adjusted according to the audiogram of the seals.