NPWS staff Peter LeBreton and Andrew Lugg taking details of a bottle-nosed dolphin, one of three found dead in the Clarence River upstream of Grafton.
NPWS staff Peter LeBreton and Andrew Lugg taking details of a bottle-nosed dolphin, one of three found dead in the Clarence River upstream of Grafton. Contributed

Dolphin deaths remain a mystery

THE cause of death of three dolphins found dead on the Clarence riverbank at Seelands remains a mystery.

The Examiner has received numerous calls in the past fortnight about up to eight dolphins swimming in two pods between Memorial Park and Corcoran Park, Grafton.

The sad news about the deaths was confirmed by Lawrence Orel from National Parks and Wildlife, who said one female and two male adults had been found on the reedy banks of Seelands at the weekend.

"A resident in the Seelands area notified us about them," Mr Orel said. "There is no apparent cause as to why they have died."

He said NPWS officers would take samples from the carcasses this week and were hoping analysis might shed some light on the deaths.

"We know dolphins can tolerate fresh water for short periods but can't tolerate it for long periods," Mr Orel said.

Considering the reports of dolphins in Grafton up to a fortnight ago, Mr Orel said the most likely cause of death was the mammals' intolerance to fresh water.

"We don't know why they didn't move back down river … there was no evidence of injury, of boat strike or propeller strike," he said.

Mr Orel said prolonged exposure to fresh water caused problems with dolphins' skin, including infections which led to very pale, light-grey colouring and even the skin peeling away.

"The complications of skin peeling away then lead to internal dehydration which, like in humans, makes them more debilitated."

From this point it was a "very slippery slope", Mr Orel said, because dolphins may struggle to catch prey, their only source of moisture, if they were not fit.

He said the time between a skin infection in a dolphin and death could be three to four days if they remained in fresh water.

"The animals looked as though they had been dead for a couple of days at least; they were quite bloated and were too decomposed to be able to show evidence of this (skin infection)."

Could they have starved?

"It's possible they starved but it's not the most likely possibility," he said.

The carcasses remained on the riverbank as they were too big to move, Mr Orel said.

Long-time Clarence Valley residents yesterday said dolphins and sharks had been seen as far up the river as Copmanhurst in times of high salinity.



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