Australia Weather News

A long marine heatwave has left dugongs facing a critical food shortage in what should be an abundant feeding ground off Western Australia's coast.

Researchers say persistently high ocean temperatures in the Exmouth Gulf, about 1,200 kilometres north of Perth, have scorched half of its seagrass species and could force herds of dugongs into less-sheltered waters.

It adds to the list of flow-on effects from a devastating marine heatwave that has gripped much of the WA coast since September.

"Previously, there were four main species (of seagrass) there," Edith Cowan University research associate Nicole Said explained.

"We've seen that two of those species have been lost, and those two species were the ones that were the preferred food source for dugongs in the Exmouth Gulf."

Seagrass meadows carpeting large areas of the gulf have made it home to the second largest population of dugongs in WA, trailing only Shark Bay to the south.

Ms Said expected the marine flowering plant to be impacted by the warm conditions.

"We're not really sure what will happen from this," she said.

"Will (dugongs) change their preferred food source and start feeding on the species that's done really well?

"Or what we've seen in the past is that dugongs have moved out of the gulf into other areas to feed."

Building pressure

Heatwaves, heavy storms, and cool spells have diminished seagrass stock in the past, pushing dugongs out as pastures rebound — a process that can take two to three years.

Aerial surveys since the 1980s have revealed the gulf's 1,000-strong dugong population tends to migrate towards Ningaloo or Barrow Island when its main habitat is challenged.

Amid a marine heatwave in the summer of 2010–2011, the number of dugongs in the region dropped to a handful, with scientists recording a spike in deaths due to starvation.

ECU megafauna researcher Amanda Hodgson said more frequent and prolonged warming events, like the one underway, could put ecosystems on the verge of collapse.

"We haven't previously considered that Barrow Island area, where dugongs aren't necessarily normally found in high numbers, as an important dugong habitat," Dr Hodgson said.

"We need to consider that there are areas that might not normally represent critical habitat but, in fact, are becoming more critical as these extreme climate events keep happening more often."

Conservation symbol under threat

Dr Hodgson's view is shared by Exmouth local and ecotourism operator Amelia Armstrong.

She described the situation as "horrifying" and called for immediate action.

"This whole system is connected and what we're doing here is going to have ongoing effects," Dr Armstrong said.

Dr Armstrong, who holds a PhD in manta ray research, was among the dozens of Exmouth residents at a community information session the state government's Exmouth Gulf Taskforce held last week.

The taskforce convened its final meeting on the same day, before delivering its report to recently appointed WA Environment Minister Matthew Swinbourn by the end of next month.

In 2021, the state government pledged to create marine parks in southern and eastern portions of the gulf and appointed the taskforce to decide if more areas needed to be protected.

An interim report made public last year recommended the whole of the Exmouth Gulf be conserved.

Dr Hodgson said the present marine heatwave strengthened community resolve to fight for the whole of the gulf to be made a marine park and reduce industrial pressures.

"This is our backyard; we care for it, and it just seems like the community and the environment have just been forgotten about or let down."

Government response

In contrast, residents who attended a community session in Onslow told the ABC they were worried wider protections could hamstring their local economy.

Retiree Felicity Brennan agreed that the gulf's south, which includes a major prawn fishery and marine nursery, should be protected.

But she warned too broad a brush could come at the expense of a town that lacks the same tourist pull as Exmouth.

"This place is a working town," she said.

"I don't see that making the whole thing a marine park is going to affect the temperatures."

Mr Swinbourn defended his government's approach.

"The scale of the heatwave is beyond our small population and large coastline," he said.

"The idea that we're able to address the causes of that heatwave through some small actions that we might take is perhaps … vain, in terms of its hope."

Mr Swinbourn said he was confident the Exmouth Gulf Taskforce could incorporate the early effects of the heatwave into its report, and that the DBCA would continue to monitor its long-term impact.