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Floods force dolphins to leave their river homes


Zoe Satherley
28 May 2009
Dolphins living in our coastal rivers have been forced out to sea because of poor water quality in our river systems, following the recent flooding.

Southern Cross University dolphin researcher Dr Christine Fury, from the School of Environmental Science and Management, said that the dolphins would most likely not return to our river systems for at least several weeks.

“There are two main reasons the dolphins leave the Clarence River and the Richmond River, where we have large resident dolphin populations,” Dr Fury said.

“Firstly, they can’t live for very long in fresh water. Their skin sloughs off and they dehydrate when in fresh water, so with all of the freshwater run-off currently flooding into our rivers, they just can’t physiologically stay in that environment because of their biology.

“It’s the reverse of the human system. If we drink too much salt water we dehydrate and die. If dolphins drink too much fresh water – through their skin – they dehydrate and die.

“The second major reason they leave the river systems is that the fish they feed on also need to be in salt water to survive. So when the fish leave, there is no food for the dolphins.”

Dr Fury said that both dolphins and river fish could be seen living along the plume line which marks the place offshore where the run-off from the rivers meets the salt water of the ocean.

“It’s a clear brown line you can see several kilometres off the coast, which will gradually retreat back westwards to the coast as the seawater makes deeper inroads back into the river systems,” Dr Fury said.

“At this time of year, with the cooler weather, we probably won’t see the major fish kills we have experienced in the summer floods, because there is not enough heat to rot the vegetation that has been washed downstream and deplete the water of oxygen.

“We may get some fish kills but these should not be as extensive as those we see in summer floods.”

Dr Fury said that autumn and winter were not critical breeding or mating times for dolphins, unlike spring and summer months and that although the dolphins would not be happy being away from their river homes, they would adapt to their ocean environment and return as soon as conditions improved.

Photo: Dolphin researcher Dr Christine Fury, who said dolphins were being forced to leave their river homes because of flood impacts.