Dugong Populations Are Declining in the Great Barrier Reef, Study Finds

Destruction of seagrass habitats and “indiscriminate” gillnet fishing have both contributed to the marine mammals’ dropping numbers, scientists say

A dugong
Adult dugong swimming and feeding in the shallow water of the Red Sea.  Sunphol Sorakul via Getty Images

Numbers of the manatee-like marine mammals called dugongs are steadily dropping in Australian waters around the Great Barrier Reef, per a new report based on 2022 aerial surveys. Among the animals’ biggest threats are gillnet fishing and habitat loss—which climate change and pollution have exacerbated. 

“We observed a decline in overall dugong numbers, with the area of most concern being the southern section of the Great Barrier Reef,” lead author Chris Cleguer, a research scientist with Australia’s James Cook University, says in a statement. “Alarmingly, we observed very few calves in this region, and only two mother-calf pairs spotted in the Gladstone area. Our report reinforces the urgency in addressing threats to dugongs.”

Dugongs (Dugong dugon) live in shallow coastal waters from East Africa to the western Pacific Ocean. Australia is home to the world’s largest dugong population, and they are legally protected by all states and the nation’s federal government. The bulbous gray mammals can grow ten feet long, weigh more than 800 pounds and live for 70 years.

They maintain their massive size by grazing exclusively on seagrass—an adult dugong can devour 64 to 88 pounds of the underwater greenery per day. Because seagrasses are highly sensitive to changes in water quality, dugongs are also easily affected by environmental changes. They are listed as vulnerable on the International Union for Conservation of Nature Red List. Last year, scientists reported that dugongs are functionally extinct in China.

“When seagrass gets disturbed or disappears, dugongs have different options,” Cleguer tells Pat Heagney and Lily Nothling of the Australian Broadcasting Corporation (ABC). “Some might stay in the area and survive, some might stay in the area and not make it because of food deprivation, and some might actually try to move to other areas.”

To get an idea of the large mammals’ abundance in Queensland, a state in northeastern Australia, researchers with James Cook University conduct aerial surveys every five years. Per the most recent report, dugong numbers have declined most steeply among surveyed areas in Hervey Bay, an inlet in southeastern Queensland. There, researchers write, the population has dropped by about 5.7 percent per year since 2005. This statistic may be the result of two major floods in 2022 that destroyed seagrass habitats around the region. 

The researchers also found that the dugong population on Queensland’s eastern coast, between Mission Beach and Bundaberg, is declining about 2.3 percent annually, per the ABC.  

Earlier this summer, the Australian and Queensland governments announced a $160 million package to phase out gillnet fishing in the next few years. These nets, which can be longer than a kilometer, “are indiscriminate in what they catch” and can entangle dugongs, dolphins and turtles, according to a statement from the nonprofit Australian Marine Conservation Society.

The funding is a “fantastic outcome,” Simon Miller, the Great Barrier Reef fisheries campaign manager for the nonprofit, tells the ABC. But he adds the phase-out won’t happen completely until mid-2027. 

“We need urgent action now,” he tells the publication.

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