The annual ‘sea run’ of thousands of mature short-finned eels from the mouth of the south-west’s rivers is under way as they make their heroic journey to the warm tropical waters near Vanuatu to spawn,

Hundreds of the eels have been gathering at the mouth of the Hopkins River at night this week as big seas lift the tide over the sandbar at the mouth and give the eels a route out.

A writhing mass of the eels banks against the sandbar waiting for the tide to rise to head out on their epic trip for which they do not return.

Grassmere commercial eel fisherman Tane Quarrell said the eels had been making their run to the ocean for the past two months, later than usual.

The run was usually finished by about Easter but the length of the sea run varied according to the weather, Mr Quarrell said.

He said large-scale tidal movements at this time of year helped sweep the eels towards Vanuatu.

In the Coral Sea near Vanuatu, the male and female eels dive down to great depths where the water pressure forces out their eggs and sperm.

They die in the effort but the eggs are fertilised by the clouds of sperm in the water and they develop into young eels that a reversal in the tidal movements help sweep back to the south-west.

The young eels, known as elvers, then go from the salt of the ocean and swim up the freshwater rivers, climbing up huge obstacles such as the Hopkins Falls to reach waters where they grow until they too make the epic trip to the Coral Sea.

Mr Quarrell said the age at which the eels headed downstream to make their sea run could vary from six years to 25 years.

Mr Quarrell, who has followed on from his late father Graham as a commercial eel fisherman, said the number making the trip this year was down on previous years.

He holds one of the handful of commercial eel licences in the south-west and said he expected to harvest only about four tonnes this year, down on the 10 tonnes his father harvested before the run of lower than average rainfalls years hit this century. 

No commercial eel licences are issued for the Hopkins River and the Glenelg rivers, which are eel breeding areas, but Mr Quarrell works nights fishing the Merri, Moyne, Fitzroy and Surrey rivers.