In late spring 2025, the CIBBRiNA “Gillnet North” team collaborated with local fishers in Iceland to run harbour porpoise bycatch mitigation trials off the north coast of Iceland. Our goal: to see whether PearlNets – gillnets with small, evenly spaced acrylic spheres attached to the netting to make them more visible underwater – could help reduce porpoise bycatch without affecting fishing efficiency. At the same time, we also tested pingers, devices which emit sound designed to deter porpoises and other small cetaceans from approaching the nets.
Working together at sea
The trials took place in two different fishing grounds within the same fjord system: a sheltered, shallow innermost part of the fjord and a more exposed offshore area of deeper water in the outer part of the fjord. Even though the start of the trial did not go entirely as planned (for example, fewer PearlNet panels were available than expected), we were able to deploy nets on 13 occasions – eight without pingers and five with pingers – and recorded detailed information on catch, bycatch, net handling, and acoustic activity. This included:
- Counting catches and analysing the contents of cod stomachs to see whether potential porpoise prey species were present in the area
- Dissecting deceased porpoises to better understand how healthy they were at the time of their accidental capture.
- Tracking porpoise clicks and movements with the use of acoustic recorders (F-PODs and SoundTraps), to gain insights into how the animals approached – or avoided – the gear.
The focus of the study: the PearlNet, a gillnet equipped with acrylic beads to make it more visible to harbour porpoises and other toothed whales which use sonar.
Early results – and a few surprises
In total, we recorded 32 harbour porpoise bycatches – 29 in standard nets, and just 3 in PearlNets. While we fished more standard gillnets than PearlNets, this difference is promising, although detailed analyses are still pending. Crew feedback suggested that handling times were similar between the two net types, though some extra tangles were reported for the PearlNets. This may have been due more to the poor condition and rigging of the trial nets than to the design itself, as some nets hadn’t been stored properly before the work began.When looking at the effect of pingers, a pattern emerged: in nets equipped with pingers, no harbour porpoises were caught. While the sample size is still small, the result suggests that the pingers are effective, consistent with other studies.
Collaboration in practice
Both at sea and on shore, the trials were a real team effort. Fishers shared their experiences and adapted to the experimental setup, scientists worked long hours collecting and processing data, and everyone pitched in to troubleshoot gear and logistics. In a local press article, the skipper summed up the attitude well: “We don’t want to kill porpoises unnecessarily – if there’s a way to avoid it, we’ll try it.”
There was even a lighter moment when a porpoise surfaced and swam free of the nets. Someone on deck grinned and shouted: “Another one saved from the grill!”. A reminder that every avoided bycatch is a small win.
What’s next?
The full dataset – including acoustic recordings, catch composition, and environmental monitoring – will now be analysed in full, looking at the combined and separate effects of PearlNets and pingers. For the CIBBRiNA team, the trials served as a reminder that progress comes from working side-by-side – across countries, languages, and professions – towards a shared goal: fishing smarter, and fishing with care.
Additional resources on the gears discussed can be found below: