A new study has warned of the effects of major climate events on local dolphin populations.

A team from Murdoch University has examined the effects of climate variability on the abundance and movements of a resident dolphin population off south-western Australia.

“The El Niño Southern Oscillation (ENSO) is a large scale climate variation that happens every few years,” said lead researcher Dr Kate Sprogis.

“During an El Niño event, 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 in strength.

“The Leeuwin Current plays a central role in Western Australia’s coastal ecosystems.”

Dr Sprogis said that although there is considerable evidence of how major climate events impact top predators in the open ocean, this was one of the first studies to investigate the possible effects on a resident, coastal dolphin species.

The bottlenose dolphin population residing off the coast of Bunbury have been studied intensively since 2007 and the researchers captured the nuances in seasonal variations.

“Dolphin abundance is seasonal, with lows in winter and spring, and highs in summer and autumn,” Dr Sprogis said.

The team was on hand to record the effect of an El Niño accompanied by unusual weather events in 2009.

“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,” Dr Sprogis said.

“These conditions coincided with a sharp decline in dolphin abundance off the coast of Bunbury.

“We found the effects of ENSO were dependent upon the season in which the events occurred.”

Dr Sprogis said results suggested that the decrease in dolphin abundance and movement of dolphins out of the study area was closely connected to the conditions associated with the El Niño event during winter, and its likely influence on dolphin prey.

“Bottlenose dolphins in Bunbury are selective feeders and their abundance in coastal waters is likely linked to the abundance and distribution of their preferred prey,” Dr Sprogis said.

“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.”

Dr Sprogis noted that low salinity waters from the above average rainfall during the El Niño contributed to fatal skin lesions on bottlenose dolphins residing 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 said.

“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 is accessible here.