Did you know that we have whales in Swedish waters and even in the Baltic sea?
The whale I'm talking about is the very small harbour
porpoise. Unfortunately the population in the Baltic sea has declined
rapidly and is now estimated to only about 600 individuals, which is
very little. Many porpoises get entangled in
fishing nets and drown every year, because they do not discover the fishing nets in
time. To help porpoises avoid entanglement, acoustic alarms, also
called pingers, have been developed. Pingers emit high frequency displacement sounds that make
porpoises avoid the area around nets. They have reduced by-catch in several fishery trials and are
now mandatory in several countries. There are however some potential
negative side effects to these conventional pingers, since they emit
sounds continuously. In the NIPPER project, which my thesis is a part
of, we tested an alternative - the "interactive"
pinger. It only emits displacement sounds when a porpoise has
triggered it with its sonar, hence only when a porpoise is in the area! On this homepage you can read more
about the results of the study, and also find out more about the