Until recently scientists knew when adult eels set off for the Sargasso Sea to spawn, but were unable to record the number of eels leaving our rivers on their epic 3,000 mile journey across the Atlantic.
Now, thanks to a hi-tech acoustic camera, the Agency can track the movement of these creatures as they set off on their migration. The device, that uses sound waves (sonar), has been placed in the Huntspill River in Somerset to capture images of eels and data collected will provide a valuable insight into the eel’s mysterious life cycle.
The American-made instrument was originally designed to carry out safety checks on oil rigs detecting hairline cracks on metal surfaces. Acoustic cameras are particularly useful in locations where visibility is poor such as underwater sites and images of near video quality are captured using sonar instead of light waves.
The use of this equipment on the Huntspill is providing the Environment Agency with valuable information on eel numbers. Measuring up to a metre in length, adult eels head out to sea between October and January after growing to maturity in our rivers. Some are up to 20 years old.
There has been a 95% decline in the eel population over the past 30 years as a result of over fishing, pollution, loss of habitat and disease. It is thought changes in ocean currents caused by climate change may also have reduced their numbers.
Eels stop feeding prior to migration and undergo complex physiological changes. Bizarrely, their digestive systems are absorbed into their bodies and replaced with reproductive organs. A number of factors influence the timing of their migration including water temperature, phases of the moon and rainfall.
The acoustic camera on the Huntspill has already produced some excellent images of eels at the start of their migration. Data collected this winter will be compared with a base line survey carried out two years ago when the equipment was first trialled.
Pete Sibley of the Environment Agency commented:
“The introduction of the acoustic camera is our first real chance to record and capture eel numbers by direct observation and increase our understanding of the creature’s mysterious life cycle.”
