Porpoise Net Recording | How New Data Could Reduce Bycatch

Acoustic Evidence of Marine Entanglement

Researchers at the University of St Andrews recently captured rare, high-definition acoustic data detailing the death of a harbour porpoise off the coast of Cornwall. The team operated a passive monitoring system attached to a static gill net when the sensors picked up the movements and vocalizations of two porpoises foraging in the immediate vicinity. The recordings suggest that both animals initially identified the presence of the net. Still, one became distracted during the hunt and eventually tangled its body in the mesh.

This documentation marks a milestone in marine biology. It provides the first clear record of how these mammals behave moments before an accidental catch. Dr. Jamie Macaulay, the lead author of the study published in Royal Society Open Science, noted that the data reveals the animals possess enough awareness to avoid gear under normal conditions. The fatal encounter occurred only after the porpoise lost focus, indicating that current deterrents may be insufficient when animals are actively pursuing prey.

The Scope of the Bycatch Crisis

Bycatch stands as the primary human-driven cause of death for dolphins and porpoises globally. The sheer scale of the issue is difficult to quantify without such precision data, but estimates from organizations like Wildlife and Countryside Link indicate that over 1,000 cetaceans perish annually in UK waters alone. These animals often drift into shallow, coastal zones to find food, bringing them into direct contact with active fishing zones. The Cornwall Wildlife Trust reported that 27 carcasses washed ashore in January, a statistic that underscores the frequency of these incidents.

Static net fishing remains a vital component of the commercial industry. Dr. Macaulay emphasized that the research team does not intend to end this practice. Instead, the focus is on developing modifications for the equipment. By better understanding the acoustic environment of these nets, scientists hope to produce gear that is more visible to marine life or that allows larger animals to break free if they do become ensnared. The goal is to move beyond temporary warning signals and toward long-term design changes that mitigate risk without compromising the livelihoods of fishers.

Broader Threats and Future Mitigation

Harbour porpoises face multiple environmental pressures beyond entanglement. Marine charity ORCA points to a downward population trend over the last 40 years driven by chemical pollution, heavy vessel traffic, and the depletion of primary food sources through overfishing. Because these mammals prefer shallow, coastal habitats, they are uniquely exposed to the cumulative effects of human maritime activity. Underwater noise pollution further complicates their ability to navigate and locate prey, leaving them more vulnerable to industrial gear.

Future work will center on integrating these findings into existing conservation strategies. The audio captured by the St Andrews team includes what researchers suspect are distress signals, providing a key marker for future acoustic sensors. If scientists can identify the frequency of these specific calls, they may be able to create automated alerts for vessels in the area. The findings establish a baseline for evidence-based solutions that balance commercial necessity with environmental stewardship. As the industry looks for ways to lower the rate of bycatch, this recording will serve as the foundation for the next generation of non-lethal marine protection.