Scientists in Suffolk have been given a £2.5m grant to examine the reasons why populations of eels are declining.
Eels are the staple food of bitterns and otters
The Centre for Environment, Fisheries and Aquaculture Science (Cefas) in Lowestoft has been given European funding to carry out the research.
Satellite tags will be used to track the fish as they migrate to the Sargasso Sea in the Atlantic to spawn.
Cefas will also gather information using specially-designed tiny data recorders placed inside the eels.
Cefas hopes that knowing more about the fish and its migration habits will shed more light on how to conserve stocks.
Eels are a staple food for bitterns and otters in the rivers of Suffolk, Norfolk and Cambridgeshire and are vital to local ecology.
Dr Julian Metcalfe from CEFAS, who is part of the research team, said although scientists knew where eels spawned, they had little idea about how they got there.
He said: "It's pure supposition because we know where they spawn so they must get there, but (we know) nothing about how they do it."
Data tags would be put inside the fish that would measure temperature and pressure every 10 minutes whilst they swam back through the Atlantic Ocean to the Sargasso Sea.
After spawning the fish dies and the tag is released from the decomposing body.
"The tag then drifts back hopefully to a European beach where hopefully it will be found and someone will send it back to us," said Dr Metcalfe.
"When we get the tag back we can then find out what the fish was doing during its migration," he added.
European eel stocks have been in major decline since the 1970s.