Do seal-safe pingers increase depredation in seals?
Our results show that these pingers don’t increase depredation, but we cannot say this with confidence. More studies will be necessary on these two models of pingers to confirm whether they increase depredation or not.
There are a few things that might have affected this experiment such as the time of the year and the other experiments happening simultaneously. Regardless, low engagement rate seems to be common in this type of experiment so in the future a larger data collection period will be very important.
Do seal-safe pingers reduce porpoise bycatch?
Yes! This matches what we know about pingers and the two models tested in this project were no exception. The importance of this thesis is that pingers are rarely tested in real-life situations. Most of the time the experiment is designed and carried out fully by trained scientists. In this case, the volunteer fishermen used the pingers during their normal fishing activities, so this provides a more realistic image of how effective pingers are.
Fishing area is also a very interesting factor to be significant. While the explanation for why one of the fishing areas had more bycatch than the others isn’t clear, it would be a very interesting topic for a future study. Perhaps conservation efforts should be focused on this area, as it might be an important spot for harbour porpoises.
Soak time and net length are two factors that intuitively affect bycatch, as the larger a net is and the longer it spends in the water, the more likely a porpoise is to get caught in it.
Finally, the overall low number of bycaught porpoises over the course of several years could be an indicator of a larger issue. Information regarding the current population size of the harbour porpoise in the Baltic Sea is scarce. There is a possibility that this population is very dimished and hence not being often bycaught, or noise pollution drives individuals away from common fishing areas. Either way, a focus on understanding why so few porpoises were bycaught in the nets of this study would be a good start for future studies.