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Thursday 25 May 2006
Study
highlights impact of floods on dolphins
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Bottlenosed
Dolphin
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A new study has found
floods in the Richmond and Clarence rivers are having a
significant impact on dolphin populations, prompting calls for
changes to agricultural and flood management practices.
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.
Source
/ Credit: Southern Cross University
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