Pingers: avoiding seals for a porpoise
2022
Fonseca Pilzecker, Rebecca
Bycatch in fishing gear is a global issue that affects numerous species worldwide, including the critically endangered Baltic Sea population of harbour porpoises. Acoustic deterrent devices or pingers have been shown to be very effective at reducing bycatch of harbour porpoises, and are currently widely used, but may have a serious negative side effect in aggravating seal depredation caused by the so-called “dinner bell” effect. This project consisted of two parts, the first one looked at the possible presence of a “dinner bell” effect in seals in three different pingers (Banana pinger from Fishtek, Netguard dolphin pinger from Future Oceans and a custom-configured PAL pinger from F3 Maritime Technology) all claimed to be seal-safe. This was tested by deploying baited stations, with and without pingers, at random locations near a seal haul-out site in the Blekinge County archipelago, Sweden. No evidence of a “dinner bell” effect was found, but the low seal engagement rate did not allow for high certainty in these results. The second part of this project looked at the effectiveness of these pingers (except the custom-configured PAL) at reducing porpoise bycatch in small-scale commercial fisheries on the Swedish West coast. For this, volunteer fishermen set their gillnets both with and without pingers and entered bycatch information in logbooks. An onboard, semi-autonomous two-camera monitoring system was also installed on their boats. The film and logbook data were compared, and the possible effect of the pingers on bycatch was investigated. The FO pinger was found to be effective at reducing porpoise bycatch, while the banana pingers in one area reduced bycatch, but in another had more bycatch than the control nets without pingers.
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