Marine Heatwaves Threaten Dolphin Survival, Reproduction

A dolphin mother and calf in Shark Bay, Western Australia.

A dolphin mother and calf in Shark Bay, Western Australia. Sonja Wild

New research points to the long-lasting impacts of marine heatwaves — periods of extreme sea surface temperatures — on dolphin populations, reducing survival and reproduction rates. Scientists say the study, published in the journal Current Biology, suggests marine mammals may be more affected by climate change than previously thought.

Led by researchers at the University of Zurich, the study examined the impact of a 2011 marine heatwave in Western Australia’s Shark Bay, a UNESCO World Heritage, that increased water temperatures 4 degrees Celsius above normal for more than two months. The researchers found that the heatwave reduced survival rates of the bay’s dolphin population by 12 percent and caused females to give birth to fewer calves for at least six years following the event. The drop in reproductive success could be attributed to “neglect of calves, increased newborn mortality, delayed sexual maturity, or a combination thereof,” the scientists noted.

The impacts of marine heatwaves on species lower down on the food chain have been well-documented in recent years. A marine heatwave in the eastern Pacific Ocean from 2014 to 2016 caused a record number of tropical sea species to migrate hundreds of miles north to cooler waters. And the 2011 event in Shark Bay reduced the region’s seagrass by 36 percent and caused mass mortalities of invertebrates and fish populations. But up until now, marine mammals were considered largely unaffected by such events.

“Our work raises concerns that such sudden events might have quite negative long-term effects even in groups of marine mammals that are known to adapt usually well to novel environmental conditions,” Sonja Wild, a biologist at the University of Zurich and lead author of the study, said in a statement.