Ocean heatwave likely killed 30,000 fish off Western Australia coast, government says | Western Australia

A mass fish kill spanning 9km along Western Australia’s Pilbara coast was likely caused by an ongoing marine heatwave, authorities have said.

An estimated 30,000 fish washed up earlier in January at beaches near Gnoorea Point, 50 km south-west of Karratha.

The WA Department of Primary Industries and Regional Development (DPIRD) said it was still investigating the fish kill but believed it “likely that prolonged thermal stress due to the conditions is associated with the deaths”.

Nathan Harrison, an executive director at DPIRD, said the nearshore waters along the Pilbara coast were currently around 31C, which was 2-3C above normal for this time of year.

“A warmer ocean off WA during 2024 has preconditioned a high marine heatwave risk scenario for the summer months when water temperatures naturally increase and peak,” he said in a statement.

Last week, DPIRD issued a strong (category 2) marine heatwave warning for WA’s North Coast and Gascoyne bioregions. In the North Coast, which takes in the Pilbara, sea surface temperatures were 4 to 5C above the long-term average.

There are concerns that the overheated water will cause damage to Ningaloo reef, Exmouth Gulf and Shark Bay, in the Gascoyne. Coral bleaching occurred at Ningaloo in 2022.

Mardudhunera woman Raelene Cooper, a Karratha resident and Murujuga traditional custodian, visited 40 Mile Beach near Gnoorea on Wednesday and described the fish kill as upsetting. “There are still dead animals that have been washed up,” she said.

“It’s quite evident that the water is heating up,” Cooper said, noticing the change while swimming with her family at her local beach. “We’re jumping in and jumping out because the water is so hot – it’s like the water that’s coming out of the shower.”

Marine heatwaves can last from days to months and have devastating impacts on marine ecosystems. One of the WA’s worst marine heatwaves on record, in 2010-2011, resulted in major losses to seagrass and kelp, and impacted abalone and scallop fisheries.

Nearly 90% of marine heatwaves are currently attributable to human-caused global heating. They are expected to increase in frequency, intensity and duration as fossil fuel emissions continue to rise.

Bill Hare, the chief executive of Climate Analytics, said marine heatwaves were known to trigger “extreme low oxygen events, which then create a bigger environmental mess”, though it was not yet clear whether low oxygen contributed to the Gnoorea fish kill.

Mia Pepper, campaigns director at the Conservation Council of WA, said it was a “tragic irony” that the fish had washed up down the coast from Woodside’s North West Shelf gas processing plant, one of Australia’s CO2 biggest emitters.

“The timing and the location of this fish kill should raise eyebrows for most people,” she said, citing the WA government’s recent granting of a 50-year extension to the North West Shelf project.

“We’re not seeing emissions being reduced in in WA … that’s a fundamental policy flaw,” she said, calling for the next state government to limit emissions in line with international obligations.

Paul Gamblin, WA director of the Australian Marine Conservation Society, agreed that there was “a huge dissonance between what we’re seeing in the water and what governments are approving”.

He described it as a “juxtaposition of clear, climate-driven damage and the prospect of multi-decadal, huge fossil fuel projects”.

“We’re talking about places like Scott Reef, [which] has been under bleaching alert over the last few months as well,” he said. A Woodside Energy proposal to bury 4m tonnes of CO2 a year from its Browse gas project underwater would involve drilling wells within about 3km of the reef.

“Government and industry need to start waking up to themselves and dealing with facts,” Cooper said. “There needs to be some accountability.”

The marine heat comes as much of WA continues to swelter in an ongoing heatwave, with extreme heat forecast for parts of the state in the coming days. On 20 January, Geraldton equalled its hottest ever day, with temperatures reaching 49.3C, while January records have also been broken in multiple towns.

Hare said while marine and terrestrial heatwaves were both driven by global warming, their individual causes differed.