While scientists have known for a long time that marine noise, mostly from ships, affects dolphins, whales, and other large marine animals, a new study has found that the noise also affects eels. Researchers with the Universities of Exeter and Bristol are quite concerned about this finding because when eels hear marine noises they lose their instinct to fight.
The researchers studies published in Global Change Biology on August 7, 2014, found that eels who were exposed to the electronic sound of ship noises were 50 percent less likely to respond to an ambush from a predator. Furthermore, they found that the eels were 25 percent slower in responding.
The head researcher on the study is a senior lecturer in Marine Biology and Global Change at the University of Exeter. He says the findings show that the study proves that eels may not respond in ways that would save their lives when ships are in the environment. The number of eels has already decreased 90 percent over the last 20 years. Many scientists believed this drop was due to global changing, but now they are beginning to question that idea. The large number of ships in coastal bay areas may be the main problem or at least an additional one.
In addition to the lack of flight response in the eels, researchers also found that the eels had a higher stress level as exhibited by the animal’s heart beating faster and their oxygen level rising. They also found that the eels had less of a right-left preference, technically lateralized behavior, when they hear ship noises. Dr. Andy Radford points out that “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.”
The researchers say that the next step is to measure the amount of noise in coastal areas.
There are over 800 different species of eel in the world. Eels range in size from barely over 2 inches to over 13 feet. Eels are found in three different types of ocean environments. They can be found in epipelagic environments that are usually located about 650 feet below the water’s surface. They are also found in mesopelagic environments that are located about 3,300 feet below the earth’s surface. Finally, they are found in bathypelagic zones that are located about 13,100 feet below the water’s surface. Researchers believe that those species that live closer to the earth’s surface are most affected.