Southern Cross University Whale Research Centre PhD candidate Christine Fury has spent the last two and a half years studying the habitat use and behaviour of Bottlenose dolphins in the Clarence and Richmond rivers. She has estimated a dolphin population of 65 in the Clarence River and 25 in the Richmond River.
"Nobody has really looked at these dolphin populations before. I know now there are separate populations in both rives that use the river on a daily basis for breeding and general feeding," Ms Fury said.
The dolphins have been sighted up to Grafton in the Clarence River, and up to Coraki in the Richmond River.
The study has found that the dolphins move out of the estuaries during flood events because of poor water quality and lack of food. In one case following a severe flood in the autumn of 2004, a group of dolphins known to inhabit the Richmond River did not return for two months.
"During a flood they are displaced and they have to find food somewhere else. That puts more stress on the dolphins and places them at greater risk from sharks," she said.
"This last summer we have had three or four floods, which means continuing poor water quality."
During floods water quality is adversely affected by lowering pH, dissolved oxygen,
conductivity, water temperature, salinity and increasing turbidity.
"The salinity drops to zero and dolphins are not able to survive in fresh water. The run-off from agricultural land also causes the pH and dissolved oxygen to go down and that is particularly bad for fish, which are the food source for the dolphins," she said.
Ms Fury said improved management of agricultural practices in the catchment areas could improve water quality and benefit estuarine fauna in times of flood.
She said opening the flood gates in the Richmond River on a regular basis, not just in times of flood, would lessen the impact of agricultural run-off during times of flood.
"Opening the gates on a daily basis would disperse the run-off, rather than it collecting and being released in one go during a flood. This is already happening in the Clarence and Tweed rivers and there is better water quality there," she said.
Ms Fury will continue her survey of dolphin habitat use in the two rivers until September.
Media contact: Brigid Veale SCU Communications Manager 02 66593006 or 0439 680 748.