Researchers from the University of St Andrews have gained unprecedented insight into sea mammal behaviour when becoming tangled in fishing nets.
In a paper published today (26th August) in Royal Society Open Science, researchers from the Sea Mammal Research Unit and Scottish Oceans Institute at St Andrews, discovered that their passive acoustic monitoring (PAM) systems deployed on a gill net, had unintentionally recorded a bycatch event. This is thought to be the first time this kind of recording as ever taken place in such unique detail.
The acoustic and movement data from the devices revealed two harbour porpoises foraging near a static fishing net off the coast of Cornwall. One animal then became entangled, the recordings were used to investigate in detail what happened next, as the entangled porpoise attempted to break free, and the two animals communicated. The porpoises spent several minutes foraging close to the net, seemingly able to recognise and avoid it – but researchers speculate that a momentary lapse in concentration, perhaps while chasing prey – led to entanglement. Once trapped, the captured porpoise was able to exert enough force to lift, but not break, the net. During the bycatch event the porpoises exchanged distinct call types, possibly distress signals.
These extraordinary insights could be crucial in developing innovative techniques, like more acoustically reflective nets, to catch animals' attention and make nets more noticeable, new types of net which allow larger, stronger species to break free and could further the development of biomimicry acoustic deterrence devices which send out warning sounds to scare certain species away.
Bycatch – when species become accidentally entangled in fishing gear – is the single biggest direct human induced cause of death in dolphins and porpoises worldwide. In the UK alone, it is estimated that around 1000 porpoises are lost every year after becoming trapped in static nets.
Despite the scale of the problem, capturing a bycatch event in real time, and gaining vital understanding of an animal's behaviour, is extremely difficult.
Lead author, Dr Jamie Macaulay, Senior Research Fellow at the School of Biology and Scottish Oceans Institute, said: "We only monitor a fraction of the thousands of kilometres of fishing nets active in UK waters, so the chances of recording these data at the same time that a bycatch actually happened is very small. Observing an event in such detail obviously brings home the harsh realities of the bycatch problem, but this is a problem that the fishing industry and conservationists all want to solve. By closely collaborating with fishers, we were able to gain valuable insights which may help us come up with new approaches that could ultimately save the lives of thousands of animals."
Dr Macaulay, added: "Static net fishing is an important part of the industry, so it's not about saying 'we must stop using these nets'. What this work, combined with other research, helps us do is gain a greater understanding of how and why bycatch happens which will help us develop and accelerate sustainable and practical evidence-based solutions to reduce it."
St Andrews researchers work closely with fishing communities through the UK Bycatch Monitoring Program funded by DEFRA, as well as organisations like CIBBRiNA, an EU-funded project which aims to minimise bycatch of endangered, threatened and protected species by understanding and balancing the needs of the marine environment and the people who rely on it for their livelihoods.
