Slippery as an eel may be a popular phrase but it turns out they are a lot easier to catch when marine vessels make noise nearby.

In a Global Change Biology paper, researchers from the Universities of Exeter and Bristol found that fish exposed to playback of ship noise lose crucial responses to predator threats - European eels (anguilla anguilla)were 50% less likely to respond to an ambush from a predator, while those that did had 25% slower reaction times.

Those that were pursued by a predator were caught more than twice as quickly when exposed to the noise.  

European eel (anguilla anguilla). Credit: The Open University 

Lead author Dr Steve Simpson, Senior Lecturer in Marine Biology&Global Change at the University of Exeter, said, "Our findings demonstrate that acute acoustic events, such as the noise of a passing ship, may have serious impacts on animals with direct consequences for life-or-death behavioral responses. If these impacts affect whole populations then the endangered eel, which has seen a 90% crash in abundance over the past 20 years due to climate change, may have one more problem to deal with as they cross busy coastal areas."

To understand what may cause this loss of crucial anti-predator behavior, the team also tested physiology and spatial behavior, and found heightened stress levels (increased ventilation and metabolic rate) and reduced lateralized behavior (right-left preferences) when eels were subjected to playback of ship noise. 

Co-author Dr Andy Radford, Reader in Behavioural Ecology at the University of Bristol, explains, "The fact that eels were affected physiologically and spatially suggests that other important functions may also be affected. We focused on anti-predator responses as, unlike impacts on movement or feeding, there is no way to compensate for being eaten after the disturbance goes away."

This study highlights the importance of assessing the scale of impacts of the anthropogenic noise that now pervades many coastal environments. Dr Simpson said, "If we want to effectively manage noise in the marine environment, we next need to assess the spatial scale over which individual animals and populations are affected. This means taking experiments like this one to offshore environments near to real-world noise sources."