The Silent Crisis in Pristine Reefs
Off the northwestern coast of Australia, in some of the world’s most pristine and diverse coral reefs, sea cucumbers are rapidly vanishing. Overall populations of these tubular, blobby animals declined by more than half from 2018 to 2023 in the Rowley Shoals, a remote Australian marine park, according to a recent study. Some especially vulnerable species, such as the pineapple sea cucumber (Thelenota ananas) and the hairy blackfish (Actinopyga miliaris), have disappeared across most or all of the monitoring sites there.
Researchers believe a boom in illegal fishing is to blame. Sea cucumber harvesting is prohibited in the Rowley Shoals, and surveys found Australian authorities caught 112 fishing vessels in the area carrying a collective 22 metric tons of sea cucumbers between 2021 and 2023, a figure that translates to roughly 33,000–45,000 animals. This is just the share of illegal fishing that authorities managed to intercept; researchers note that the actual sea cucumber body count is likely much higher.
Widespread Impact Across Australian Waters
The problem isn’t unique to Rowley Shoals. It occurs in reefs across the country’s western and northern waters and has recently been on the rise, according to several researchers, driven by demand for the animals in China and other East Asian countries where they are considered a delicacy and used in traditional Chinese medicine. Illegal sea cucumber fishing spiked in northern Australia in 2024, with fishers targeting sanctuaries and internationally protected species.
Operation LUNAR and Enforcement Actions
The Australian government responded by launching Operation LUNAR at the end of 2024 to crack down on illegal fishing by foreign vessels in the country’s Northern Territory, where the problem is acute, including for high-value sea cucumbers. More than 100 foreign fishing vessels have been intercepted since, according to the Australian Border Force (ABF). Crews of foreign fishermen, primarily from Indonesia, have been arrested for fishing illegally in Australia, their sea cucumber catches confiscated and equipment destroyed.
“Enforcement activity under Operation LUNAR has strengthened ABF’s ability to detect, deter and respond to incursions earlier and more effectively across northern waters,” an ABF spokesperson told Mongabay. The operation reinforces efforts to “safeguard Australia’s marine resources and support the long‑term sustainability of northern ecosystems.”
Vital Nutrient Dispersers at Risk
As long as demand for sea cucumbers remains strong, wild populations of this slow-growing animal could collapse and put the health of entire reef systems at risk in Australia and beyond. “We’re just starting to learn how important they are,” said Monique Hammond, a sea cucumber researcher at Australia’s University of the Sunshine Coast. She explained that these echinoderms recycle detritus, sediment and algae, helping disperse nutrients and improving the strength and resilience of coral reefs, seagrass beds and marine ecosystems broadly. When sea cucumbers disappear, seagrass becomes thinner and weaker, and algal mats can bloom, choking out a reef.
Easy Pickings for Poachers
Because sea cucumbers are harmless to people, generally stationary and tend to gather in groups, they are easy to harvest en masse. Many highly sought species occur on shallow, easily accessed reefs. “You just pick them up, put them in a basket and keep going,” said Teale Phelps Bondaroff, who studies illegal sea cucumber fisheries and serves as research director of the Hong Kong-based advocacy group OceansAsia. With high demand and big profits—for example, the endangered Japanese spiky sea cucumber (Apostichopus japonicus) can retail for more than $3,600 per kilogram ($1,625 per pound)—illegal sea cucumber fishing is a lucrative enterprise.
Indonesia banned sea-cucumber fishing entirely more than two decades ago, and Sri Lanka implemented a permitting system, but the waters between the countries remain a hotspot. Ecuador, including the Galapagos Islands, has also seen illegal sea-cucumber fishing for decades, with populations dropping until the practice is no longer economically viable. Authorities in Japan and Mexico have even reported incidents of diving-related deaths in recent years as fishers dive deeper in search of vanishing sea cucumbers.
The Road to Recovery
Sea cucumber populations often struggle to recover from overfishing. These animals can live for decades and don’t reproduce often. They mate via broadcast spawning, gathering in large groups to release eggs and sperm simultaneously. When an area is left with too few individuals spread far apart, reproduction fails. “It’s really difficult to have any form of sustainable sea cucumber fishery, just because of the nature of the animals,” said John Keesing, a research scientist at the Commonwealth Scientific and Industrial Research Organisation and co-author on the Rowley Shoals survey.
On the other side of the continent from Rowley Shoals, Hervey Bay—part of Australia’s Great Sandy Marine Park—illustrates what happens when fisheries completely collapse. Monique Hammond has spent more than a year searching for the endangered golden sandfish (Holothuria scabra) in Hervey Bay, enlisting dozens of community members and local fishers. They found just two. She hopes a captive breeding program could reintroduce sea cucumbers into the bay, which is noticeably less healthy than surrounding areas that still have the animals.
Experts agree that the better path is to stop overfishing and illegal catches before populations are destroyed. But patrolling Australia’s vast coastline and territorial waters is expensive. “Your chances of not getting caught if you’re an illegal fisherman are unfortunately pretty good,” Keesing said. Still, he stressed the importance of monitoring populations and enforcing regulations, especially in healthy marine parks like Rowley Shoals. “We have some of the last pristine populations of sea cucumbers. Protecting them is paramount.”