Written by Rhonda Oshanek Wednesday, 18 November 2009 13:14
MURDOCH University’s Dr Hugh Finn and his research partners have had a lot of local and international media attention of late, but for an unfortunate reason.
Postdoctoral researcher Dr Finn is studying the local population of bottlenose dolphins in the Canning and Swan Rivers in partnership with Dr Chandra Salgado at Curtin University of Technology and The Swan River Trust.
Since the launch of their new project earlier this year, they have discovered six dead dolphins in the estuaries over the past five months. At least three were young dolphins.
A small group of 20-25 dolphins are year-round residents and therefore subject to the human activities that impact on the health of the estuary. They appear to travel the rivers daily—often into the upper reaches of the estuaries to feed during the incoming tide, and then head out to the ocean to rest on an outgoing tide.
During the project, the researchers will look at photographs of river dolphins to assess skin lesions, use biopsy darts to collect small skin and blubber samples to test for heavy metals and pesticides, and perform necropsies on deceased dolphins to try to determine cause of death.
Necropsies have been performed on four of six recently-deceased dolphins (two were too decomposed to yield useful information) by Veterinary Pathologist Nahiid Stephens at the Murdoch Veterinary School.
Results so far show that the dolphins had suppressed immune systems and were infected with opportunistic pathogens (bacteria, viruses, fungi, yeast and protozoa). While always present, these pathogens would not cause problems for a healthy individual but can harm animals in a weakened state.
Two animals had injuries due to entanglement in fishing lines and two had severe skin lesions.
There were also high levels of Dieldrin in the dolphins’ tissues, a by-product when the pesticide Aldrin breaks down. Aldrin has been banned since the late 1980s due to its carcinogenic, immunosuppressant and neurotoxic effects.
Other compounds present in the tissues in high levels included PCBs and DDT. All of these compounds have a very long half-life in the environment and will not disappear anytime soon.
Previous investigations into significant marine mortality in other areas of the world suggest that the initial immune suppression may be due to a virus, a rapid change in environmental factors (salinity, temperature, pH), long term exposure to contaminants, or even toxic algae or large algal blooms that consume the oxygen in the water. Algae blooms result from the release of nitrogen and phosphorus into the waters draining into the rivers.
The researchers believe it’s likely mortality is due to some combination of these factors but say their conclusions are far from finalised.
Since the dolphin is at the top of the food web, these deaths are a big indicator that things are not well with the Swan and Canning Rivers.
If you’d like to help out with this study, become a volunteer with Dolphin Watch by calling the Swan River Trust River Guardians Program on (08) 9278 0900 or by visiting www.riverguardians.com.
“Dolphin Watch volunteers collect information on dolphins in the Canning River and the upper reaches of the Swan River. This information is very important as we don't have a good understanding of how dolphins use those areas,” says Dr Finn.
Subscribe to this comment's feed
