Underwater Recorders Capture a Porpoise Struggling in a Fishing Net

Researchers monitoring a fishing net off Cornwall unexpectedly recorded a harbor porpoise becoming trapped, along with the animal’s attempts to escape and acoustic exchanges with another porpoise nearby. The incident was documented by passive acoustic monitoring equipment operated by researchers at the University of St Andrews. The devices, deployed on a static gill net, recorded sounds and underwater movement as two harbor porpoises foraged near the gear. According to the university research reported by Phys.org, the animals appeared to recognize and avoid the net for several minutes before one became entangled. The trapped porpoise generated enough force to lift the net but not enough to break free. Movement data showed the animal attempting to swim toward the surface while the recordings captured echolocation clicks, which porpoises use to sense their surroundings. The devices also detected rapid sequences of clicks from the animals. Researchers described the call patterns as distinct and said they may have been distress signals. The recordings were modified so that humans could hear the porpoise clicks, which are normally beyond the human hearing range. Researchers believe the event may be the first time a bycatch incident involving these animals has been recorded in such detail, although the source describes that assessment as a possibility rather than a confirmed first. The study’s authors said the observations could inform efforts to reduce accidental entanglements. Potential approaches include making nets more acoustically reflective so they are easier for animals to detect, developing net designs that allow larger or stronger animals to escape, and using acoustic deterrents modeled on natural warning sounds. The researchers did not present these ideas as tested solutions in this recording. Bycatch is described as the leading direct human-caused source of death for dolphins and porpoises worldwide. In the United Kingdom, an estimated 1,000 porpoises are lost each year after becoming trapped in static nets. The St Andrews team conducts monitoring through the UK Bycatch Monitoring Program and works with fishing communities, emphasizing that the goal is to develop practical ways to reduce deaths rather than simply call for an end to static-net fishing.