A massive fish die-off stretching 9km along Western Australia’s Pilbara coast was likely caused by an ongoing marine heatwave, according to authorities.
In early January, around 30,000 fish washed ashore near Gnoorea Point, about 50km southwest of Karratha. The WA Department of Primary Industries and Regional Development (DPIRD) is investigating but believes prolonged exposure to extreme temperatures played a role in the deaths.
Nathan Harrison, an executive director at DPIRD, noted that nearshore waters along the Pilbara coast had reached approximately 31°C—2-3°C above the usual temperature for this time of year. He explained that the already warmer ocean conditions in 2024 had set the stage for a high marine heatwave risk, particularly during the peak summer months.
Last week, DPIRD issued a strong (category 2) marine heatwave warning for WA’s north coast and Gascoyne bioregions, with sea surface temperatures in the Pilbara rising 4-5°C above the long-term average. Experts fear the extreme heat could harm marine ecosystems, including Ningaloo Reef, Exmouth Gulf, and Shark Bay, which suffered coral bleaching in 2022.
Mardudhunera woman Raelene Cooper, a Murujuga traditional custodian from Karratha, described the fish kill at 40 Mile Beach as distressing. She observed dead marine life still washing up and noted that swimming had become uncomfortable due to the unusually warm water, likening it to shower water.
Marine heatwaves, which can persist for days to months, have severe consequences for marine ecosystems. One of WA’s worst marine heatwaves in 2010-11 caused widespread seagrass and kelp losses and severely affected abalone and scallop fisheries. Experts estimate that nearly 90% of marine heatwaves are now linked to human-caused climate change, with their frequency and intensity expected to rise as fossil fuel emissions continue.
Bill Hare, CEO of Climate Analytics, highlighted that marine heatwaves often trigger extreme low-oxygen events, which can further harm marine life. However, it remains unclear if this factor contributed to the Gnoorea fish kill.
Mia Pepper, campaigns director at the Conservation Council of WA, called it a “tragic irony” that the fish deaths occurred near Woodside’s North West Shelf gas processing plant—one of Australia’s largest CO₂ emitters. She criticized the WA government’s recent decision to extend the project by 50 years, arguing that emissions reduction should be a priority.
Paul Gamblin, WA director of the Australian Marine Conservation Society, echoed these concerns, calling the situation a stark contrast between visible climate damage and the approval of long-term fossil fuel projects. He pointed out that Scott Reef had been under a bleaching alert for months and raised concerns over Woodside Energy’s plan to store CO₂ underwater near the reef.
Cooper called for greater accountability from both government and industry, urging them to acknowledge the scientific realities of climate change.
The marine heatwave coincides with extreme heat across WA, with record-breaking temperatures recorded in multiple towns. On January 20, Geraldton tied its all-time hottest day at 49.3°C. While both land and marine heatwaves are linked to global warming, they have distinct underlying causes, Hare noted.
