The discovery emerged from a passive acoustic monitoring system deployed on a static gill net off the coast of Cornwall. Passive acoustic monitoring, commonly known as PAM, uses underwater instruments to listen to sounds produced by marine animals without actively transmitting signals into the water. Harbour porpoises rely heavily on sound because their underwater environment is often dark, murky and visually limited. They produce extremely high-frequency echolocation clicks, typically far above the range of human hearing, and interpret returning echoes to detect prey, obstacles and other features of their surroundings. The monitoring equipment was designed to study porpoise activity near the fishing gear, but it unintentionally recorded a bycatch event in exceptional detail. The resulting data allowed researchers to compare the animals’ acoustic behaviour with their movements around the net and during the entanglement.

At first, the recordings showed two harbour porpoises foraging close to the fishing gear. Their repeated movements and echolocation activity suggested that the animals were searching for prey in the area while navigating around the net. The porpoises appeared capable of detecting and avoiding the structure for several minutes, a finding that complicates the simple assumption that animals fail to sense fishing nets. Gill nets are made from thin, nearly transparent monofilament or multifilament lines that can be difficult for marine mammals to perceive, particularly when water conditions, light levels or background noise reduce the clarity of the returning echoes. The animals may have recognized the net as a potential hazard, but the researchers believe that a brief loss of attention—possibly during a rapid pursuit of prey—may have brought one porpoise into contact with it. In a moment, an animal that had been successfully navigating around the gear became caught.

Once entangled, the porpoise began a sustained effort to free itself. Movement data indicated that it was able to generate enough force to lift the net, but not enough to tear through or break the material. This distinction is important because the physical properties of fishing gear strongly influence whether an animal survives an encounter. A net that is flexible but exceptionally strong may hold an animal in place while allowing it to drag or raise a section of the gear, increasing energetic demands and restricting access to the surface. Harbour porpoises must breathe air, so every dive is constrained by the need to return to the surface. An entangled animal can become trapped below the water, lose efficient swimming ability, exhaust its oxygen reserves and drown. Even when it can reach the surface, the additional drag and stress may prevent normal breathing, escape or feeding.

The acoustic recordings provided evidence that the second porpoise remained nearby during the crisis. Both animals continued to produce echolocation clicks, which would have helped them sense the net, the surrounding seabed and one another. However, the researchers also detected rapid sequences of clicks that sounded like a buzzing signal after the recordings had been shifted into a frequency range audible to humans. Porpoise clicks are normally ultrasonic and cannot be heard directly by people. The rapid click trains identified in the recording are thought to represent communication signals, potentially associated with distress, agitation or attempts to maintain contact. Although scientists cannot determine the precise meaning of the signals from a single event, the contrast between ordinary echolocation and unusually rapid acoustic activity offers a rare glimpse into how porpoises may respond socially to danger.

The event lasted several minutes, long enough for the instruments to capture changes in movement, sound production and interaction between the two animals. Such data are extraordinarily difficult to obtain because researchers cannot safely or ethically recreate an entanglement, and direct observation in the open ocean is nearly impossible. Monitoring only a fraction of the thousands of kilometres of fishing nets deployed in UK waters, researchers say the probability of recording a bycatch event at the exact moment it occurs is extremely small. The observation therefore acts like an underwater black box, preserving a sequence that would normally vanish without a trace. It shows the animal approaching and working around the net, becoming trapped, attempting to escape and remaining acoustically connected with its companion. For conservation scientists, that sequence is more informative than a simple record that an animal was found dead or missing.

The findings could influence the design of fishing gear and acoustic deterrence technologies. One possibility is to make nets more acoustically reflective, increasing the strength or clarity of the echoes returned to a porpoise and making the net easier to detect. Researchers are also investigating modified net materials and construction methods that could allow larger or stronger animals to break free rather than remain trapped. These approaches must be tested carefully because a change intended to protect porpoises could alter the net’s performance, reduce target catches or create new hazards for other species. Another potential strategy involves biomimicry: developing warning signals inspired by naturally meaningful sounds or by the acoustic cues marine mammals already use to assess danger. The challenge is to discourage porpoises from entering a hazardous area without causing harmful stress, disrupting essential behaviour or driving animals away from important feeding grounds.

The study also highlights why practical solutions must be developed with fishing communities rather than imposed without considering the realities of working at sea. Static net fishing supports coastal livelihoods and is an important part of the fishing industry, meaning that eliminating all such gear is neither a simple nor necessarily realistic conservation strategy. The more immediate goal is to understand precisely how and why entanglements happen, then reduce the risk through evidence-based changes that fishers can use. Researchers at St Andrews work with fishing communities through the UK Bycatch Monitoring Programme, funded by the Department for Environment, Food and Rural Affairs, and through CIBBRiNA, a European Union-funded initiative focused on reducing bycatch of endangered, threatened and protected species. Collaboration can help determine which modifications are affordable, effective and compatible with real fishing conditions.

The scale of the problem makes those improvements urgent. In the United Kingdom alone, approximately 1,000 harbour porpoises are estimated to die each year after becoming trapped in static fishing nets, while global losses affect numerous species of dolphins, porpoises and whales. Harbour porpoises are small, fast-moving cetaceans with high metabolic demands, so an entanglement can become fatal quickly. Their dependence on high-frequency echolocation also means that the acoustic properties of fishing gear may be central to both the problem and the solution. The new recording does not provide a complete explanation for every bycatch event, and the meaning of the porpoises’ communication signals remains uncertain. It does, however, transform an invisible conservation threat into a documented behavioural sequence. By listening to the final minutes of an entangled animal’s struggle and the possible distress calls of its companion, scientists may be closer to designing fishing nets that marine mammals can detect, avoid or escape—turning a tragic accidental recording into a potential blueprint for saving thousands of animals.

Subject of Research: Animals, specifically harbour porpoises

Article Title: First detailed insights into harbour porpoise behaviour during a bycatch event

News Publication Date: 26 August 2026

Web References: https://doi.org/10.1098/rsos.260565

References: Royal Society Open Science, “First detailed insights into harbour porpoise behaviour during a bycatch event,” DOI: 10.1098/rsos.260565

Image Credits: Sea Mammal Research Institute/University of St Andrews

Keywords: harbour porpoise, bycatch, fishing nets, passive acoustic monitoring, marine mammals, echolocation, distress calls, marine conservation, gill nets, cetacean behaviour

Historically, tracking North Atlantic right whales has relied heavily on expensive and often dangerous aerial surveys. These methods, while effective, pose significant risks to both the survey teams and the whales themselves. In contrast, the new methodology developed by the Cornell team allows for non-intrusive and cost-effective monitoring, leveraging sound recordings to ascertain both the presence and approximate population numbers of these majestic creatures in their natural habitat, particularly in Cape Cod Bay, a crucial feeding ground where the whales congregate each spring.

Lead author Marissa Garcia of the Cornell Lab’s K. Lisa Yang Center for Conservation Bioacoustics emphasized the transformative nature of their study. While monitoring whale populations via sound recordings is not a novel concept, this research advances the standard by moving beyond simple presence detection to provide quantitative estimates of whale numbers. This is a crucial advancement, as understanding population density is vital for effective conservation strategies and management decisions.

The study used an array of marine autonomous recording units (MARUs) strategically placed throughout Cape Cod Bay to capture the unique vocalizations of right whales. These passive acoustic monitoring devices are capable of operating without human intervention, capturing sound data continuously, day and night, thus overcoming the limitations of aerial surveys that can only be conducted in daylight and under good weather conditions.

Once the MARUs were deployed, the team utilized a deep-learning model that was meticulously trained and validated to automatically detect right whale sounds with an impressive accuracy rate of 86%. By analyzing the distinctive upcall vocalizations characteristic of right whales, the research team could maintain continuous monitoring of their presence. This round-the-clock oversight provided a wealth of data that could significantly enhance the understanding of right whale behavior and distribution patterns.

Garcia noted that while the study yielded promising results, there remains a degree of uncertainty in the population counts generated. The research team is committed to addressing these uncertainties in future studies, driven by optimism that the vocalization monitoring techniques hold considerable potential for estimating right whale numbers. This technique could also be integrated into broader conservation efforts aimed at safeguarding the species as they face multiple threats.

The population of North Atlantic right whales has alarmingly dwindled to fewer than 370 individuals, primarily due to human-induced dangers such as ship strikes and fishing gear entanglement, coupled with changing ocean conditions affecting their food sources. This significant decline makes every insight gained through advanced monitoring techniques critical in efforts to avert further losses and to promote recovery.

The implications of this research extend beyond Cape Cod Bay. As Garcia pointed out, the use of passive acoustic monitoring paired with machine learning tools allows for more expansive monitoring of the species across broader geographic areas. Moreover, this advancement in methodology could lead to more comprehensive assessments of population dynamics and trends across the entire range of the species, from New England down the Eastern Seaboard.

Furthermore, leveraging machine learning for acoustic data analysis represents a pivotal step forward in the application of technology in wildlife conservation. This integration signifies not just an evolution in monitoring techniques but also a promise for resource-efficient strategies in tracking and studying other endangered species facing similar threats.

As conservation efforts for the North Atlantic right whale evolve, the findings from this study present a template that could be emulated in other marine contexts where traditional monitoring methods encounter limitations. The ability to quickly process vast amounts of acoustic data and generate actionable insights reflects a substantial shift in how researchers can engage with marine life on a profound level.

Overall, the collaboration between acoustic monitoring technology and machine learning recognizes an urgent need: to create innovative solutions for dynamic and pressing conservation challenges. As humanity confronts the realities of biodiversity loss and environmental change, studies like those conducted by the Cornell team offer not just hope but a pathway forward, illuminating ways to protect our planet’s most vulnerable inhabitants.

In conclusion, Cornell University’s pioneering research into the monitoring of North Atlantic right whales embodies a perfect fusion of tradition and technology. By harnessing sophisticated methods designed to crack the code of underwater communicative patterns, the team sets a precedent that pushes the boundaries of marine research while inspiring broader conservation initiatives that could make a critical difference in the survival of endangered species worldwide.

In summary, as the world continues to grapple with ecological crises and dwindling wildlife populations, such innovative methods will undoubtedly contribute to preserving not only North Atlantic right whales but also the delicate ecosystems they inhabit. With the echoes of their calls captured in the randomness of ocean sounds, there remains cautious optimism for a future where the survival of one of Earth’s most endangered marine mammals can be secured.

Subject of Research: Animals
Article Title: Acoustic abundance estimation for Critically Endangered North Atlantic right whales in Cape Cod Bay, Massachusetts, USA
News Publication Date: 21-Feb-2025
Web References: Article DOI
References: Endangered Species Research
Image Credits: N/A

Keywords: Endangered species, Whales, Machine learning, Marine conservation, Bioacoustics