A jawless blood-sucking eel-like fish has surfaced in record numbers in the River Murray system, a new monitoring program has found.
Ninety-one pouched lamprey and four short-headed lamprey were recorded migrating up from South Australia's Coorong through to the Murray River system between July and October last year – the highest amount ever monitored over winter.
The ancient and native species was feared to be on the brink of extinction after the Millennium Drought.
The Department for Environment and Water's Program Leader for Coorong, Lower Lakes and Murray Mouth Adrienne Rumbelow said the Millennium Drought led to more than three years of disconnection of the Lower Murray river system.
Lamprey are anadromous fish, which means they are born in freshwater, spend most of their adult life in the ocean before they migrate up freshwater rivers to spawn.
"After the drought, probably the next 45 years we were really struggling to find any lamprey in the system and we had some really big concerns about whether we lost a couple of species from the Murray-Darling Basin," Ms Rumbelow said.
Fortunately, more consistent water flows into the Lower Murray River system through to the Coorong and Lower Lakes in the following years led to its recovery, with additional water for the environment aiding the living fossil in its migratory path.
"I think it's a combination of flows at the right time of the year, and then a lot the locks and weirs and anabranches in the River Murray have now got fishways on them," she said.
'Larry' lamprey rockets ahead
The fascinating creatures have been fitted with microchip-like pit tags to allow scientists to track individual lamprey movements.
Recording some of the findings Ms Rumbelow said the fish that travelled the furthest had been nicknamed 'Larry'.
The fastest lamprey was clocked between Lock 3 at Overland Corner and Lock 4 at Bookpurnong, travelling 55 kilometres in one day.
"They only travel at night time as well, so if you just take that travel time as being at night only, then that equates to 4.5 kilometres an hour which is really fast for a little fish," she said.
To collect more data and information on lamprey migration and its recovery the team of scientists is planning to use acoustic tags this season to get more detailed information on each fish's journey.
The current pit tag receivers are located on fishways up to Lock 11 in Mildura but scientists are unable to monitor the fish further upstream.
Ms Rumbelow said acoustic tags would allow the team to put receivers for the tags in more locations across the river system, like anabranches which could provide more detail on the living fossil's journey.
