Local dolphins in Australia are being effected by major climate events, a study has found.
Dr Kate Sprogis led a team from Murdoch University’s Cetacean Research Unit to examine the effects of climate variability on the abundance and movements of a resident dolphin population off south-western Australia.
Although there is evidence of how major climate events impact top predators in the open ocean, this is one of the first studies to investigate the effects on a resident, coastal dolphin species.
“The El Niño Southern Oscillation (ENSO) is a large scale climate variation that happens every few years,” Sprogis says.
During El Niño, the trade winds weaken and a pool of warm water gathers on the eastern side of the Pacific Ocean, which causes the Leeuwin Current flowing down the coast of Western Australia to weaken.
The bottlenose dolphin population off the coast of Bunbury have been studied intensively since 2007.
“Dolphin abundance is seasonal, with lows in winter and spring, and highs in summer and autumn,” Sprogis says.
“In the winter of 2009, there was an El Niño event which coincided with a decrease in sea surface temperature and above average rainfall across the region.
“These conditions coincided with a sharp decline in dolphin abundance off the coast of Bunbury.”
Sprogis says bottlenose dolphins in Bunbury are selective feeders and their abundance in coastal waters is likely linked to their preferred prey.
“We believe that dolphins moved away from the area in search of an adequate food supply and, of those that stayed in the area of changing conditions, many found it harder to locate their preferred prey,” she says.
Low salinity waters from the above average rainfall during the El Niño contributed to fatal skin lesions on bottlenose dolphins in Perth’s Swan River, 180 km north of Bunbury.
“Extreme climate events add pressure to species that are already dealing with the complexities of living among coastal human activities,” she says.
“These dolphins are exposed regularly to disturbance by boats, tourism, entanglement and coastal development.
“As global warming progresses, extreme climate events are predicted to increase in frequency and intensity.
“It is vital to keep monitoring coastal dolphin populations in the face of these growing threats.”
This research will be published in the journal Global Change Biology.
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