Vulnerable dolphins in the Central Great Barrier Reef are under threat from exposure to increasing amounts of dangerous contaminants, according to Southern Cross and Flinders University marine researchers.
A new study published in Ecological Indicators sampled pollutants in the blubber and skin of Australian snubfin dolphins and humpback dolphins in the Fitzroy River and Port Curtis in Queensland between 2014 and 2016.
The results were compared to samples collected between 2009-2010. Southern Cross University marine ecologist Dr Daniele Cagnazzi said he was surprised to find that in just five years the concentrations of chemicals and insecticides (PCBs, DDTs and HCB) in both species increased between two and seven times.
With the concentration of land-based pollutants in the Great Barrier Reef increasing over the same period so is the accumulation of contaminants in the favourite preys of dolphins. Dolphins can consume daily six per cent of their body weight in fish. As a result, in dolphins the concentration of contaminants can be up to 200 times higher than what recorded in their prey.
Dr Cagnazzi says 68 per cent of the dolphins sampled had accumulated contaminants above levels that may affect their health and potentially their survival.
“In the Fitzroy River and Port Curtis between 2011 and 2016 three major floods were recorded in the region compared to an average of one every six years before 2011. Extensive flooding in adjacent catchments is the most likely factor responsible for increased distribution of these contaminants into coastal waters,” he said.
The chemicals and insecticides PCB, DDT and HCB are highly poisonous and have been banned in Australia since the late 1970s, but remain commonly detected in Queensland catchments. PCBs are still produced as combustion by-products and released during the recycling of materials and building demolitions. A various range of ‘modern’ contaminants are released into the water from various land sources, such as shipping, coal stockpiles, power station products, landfills, urban development, mining, wastewater, stormwater and tourism. This research analysed a proportion of human-caused contaminants to which dolphin are exposed.
“A large proportion of the sampled snubfin dolphins had pesticide contaminants above thresholds that are associated with a significant higher risk of foetal and neonatal mortality, impaired reproduction and carcinoma, and of most concern the weakened ability of the dolphin immune system to fight off parasites, like toxoplasmosis, as well as bacteria, fungi and viruses. Female dolphins can also transfer most of their contaminants burden, up to 80 per cent, to their first-born calf.”
Flinders University Associate Professor Guido J Parra says climate change models expect rainfall and floods to increase in the Queensland coastal region over coming decades, which in turn exposes dolphins to more potentially harmful contaminants.
“High contaminant levels add to the number of existing threats including climate change, coastal development, underwater noise and vessel disturbances, fishing bycatch and prey depletion faced by these vulnerable dolphin species,” Professor Para said.
“The build-up of these dangerous contaminants can lead to population decline. For example, in South East Asia, high concentrations of various pollutants have been linked to the extinction of the Yangtze River dolphin and the ongoing decline of the Indo-Pacific humpback dolphin.”
“As a result, this could have implications on the long-term survival of entire dolphin populations in Queensland.”
Researchers warn water flowing in the Great Barrier Reef is classified as poor quality, and the Fitzroy River Catchment, the Wet Tropics, Burdekin, Mackay Whitsunday and Burnett Mary catchments have been identified as medium to high-risk for land-based pollutants.
New ports and mining developments are underway in several locations along the Queensland coast and inland which will have an ongoing impact.
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