LARGE eels in the Hopkins and Fitzroy rivers have been tagged as part of a new study into their migratory habits.
Scientists at the Arthur Rylah Institute made the most of a huge ocean swell down the south-west coast last week and went on the hunt for the short-finned eels to investigate their migratory routes.
"The incredible weather conditions briefly opened the Hopkins River mouth to the sea. This helped the adult migratory eels, which were congregating in the lower river reaches, cross a sand bar and move out to the ocean," DELWP spokesperson Ewan Cook said.
"Eels have an amazing lifecycle, travelling thousands of kilometres as both adults and larvae.
"We believe adult eels can travel as far as the Coral Sea, although the actual location for this spawning is unknown."
To investigate this long distance journey, the scientists have placed 'pop-up' satellite tags onto 16 large eels in the Fitzroy and Hopkins rivers.
"This innovative technology allows monitoring of the eel's movements when the tags release and float to the ocean surface, after which they transmit data to orbiting satellites," Mr Cook said.
"Over the next six to eight months, the tags will record important environmental data such as temperature, depth and light from which the location of the eel can be estimated."
Hundreds of eels were wading in the shallows of the Hopkins River before the ocean passage was opened in partnership with Warrnambool City Council and Glenelg Hopkins Catchment Management Authority.
"In order to maintain healthy river levels and prevent flooding, when required, council excavates the blocked river mouth allowing the river to flow into the ocean," a WCC spokesperson said.
"While flood prevention is an imperative, equally as important is ensuring the artificial opening of the river mouth does not negatively impact marine life.
"When the river mouth is opened, it is predominantly the top layer of water, to a depth of about 1.5m, which washes into the ocean.
"Rigorous water quality testing before the river mouth is opened ensures that when this upper layer of water is discharged, marine life will survive."
The eel tracking project, which runs for three years, is a collaboration between DELWP, the Gunditjmara Traditional Owners and the Glenelg Hopkins Catchment Management Authority.
A world expert in eel ecology and tagging, Professor Kim Aarestrup from Denmark, is also involved in the work.
"Identifying oceanic migratory routes and spawning areas of eels will fill an important knowledge gap," he said.
"It will also help managers address human activities and climate change which affect the eels' habitats."
Find out more about the project here.
Have you signed up to The Standard's daily newsletter and breaking news emails? You can register below and make sure you are up to date with everything that's happening in the south-west.
Sign up for our newsletter to stay up to date.