A study by an international team of marine researchers, including The University of Western Australia, has found dolphin survival and reproductive rates suffered a significant decline following a 2011 marine heatwave affecting around 1,000km of Western Australia’s coastline.
The study, “Long-term decline in survival and reproduction of dolphins following a marine heatwave” published in Current Biology, includes researchers from the universities of Zurich, Leeds and Bristol, and has important implications for marine conservation and mitigating the effects of climate change.
In early 2011, a marine heatwave increased coastal sea temperatures in Western Australia up to four degrees above average. This event led to catastrophic losses of seagrass meadows and fish communities in Shark Bay, a World Heritage area in Western Australia and home to an iconic population of bottlenose dolphins.
Using long-term demographic data from more than 5,000 dolphin encounters in the area between 2007 and 2017, the research team investigated the impact of habitat degradation after this extreme weather event on dolphin survival and reproduction rates. They discovered a decline of more than 12 per cent in survival rates and fewer dolphin calves born after the heatwave.
The researchers suggest the loss of habitat has prevented fish stocks from recovering to pre-heatwave levels, forcing the dolphins to spend more time searching for food. This can mean reduced vigilance, and ultimately, more shark predation on calves. Reduced food availability may also have led to increased mortality of young calves when both the mother’s and the offspring’s nutritional needs could not be sustained.
The study’s senior author Dr Simon Allen, from UWA’s School of Biological Sciences, said while there was an overall decline in dolphin survival rates post-heatwave, the dolphins that used marine sponges as foraging tools, a socially learned technique that helps the dolphins find food in deeper water channels, fared better in comparison to the dolphins that didn’t have the tool-using know-how.
Dr Allen, a principal investigator on the project, said the findings suggested that extreme weather events may be too sudden or disruptive for even highly adaptable animals to respond, leading to negative impacts on dolphin survival and reproduction.
“Researchers are yet to see recovery of seagrass meadows or certain fish stocks and now we find negative impacts on dolphins from just one extreme weather event,” Dr Allen said.
“Given that marine heatwaves are occurring more often in association with climate change this raises serious concerns over the long-term prospects for the dolphin population, commercial fisheries and the ecosystem as a whole.”
The study was funded by grants from the Swiss National Science Foundation, National Geographic Society, Australia’s Sea World Research and Rescue Foundation Inc (SWRRFI), WV Scott Foundation and the AH Schultz Stiftung.
Dr Simon Allen (UWA School of Biological Sciences) 0416 083 653
Simone Hewett (UWA Media & PR Adviser) 08 6488 7975