Standing atop a 16-foot-high seawall on South Korea’s western coast, Chris Purnell and his colleagues slide mesh bags stuffed with empty oyster shells down onto the sandy mudflats of the Geum Estuary. They then clip the heavy bags to ropes and drag them into the gently lapping waters that run into the Yellow Sea.
Purnell’s aim is for these bags, attached to foam floats and lashed together in clusters up to 80 feet wide, to act as artificial roosting sites for the tens of thousands of migratory shorebirds that traverse the East Asian-Australasian Flyway. Coastal development has deprived these travelers of crucial resting spots, leading to drastic shorebird declines in key stopover areas like this one. “We’re hoping this could be a rapid-response intervention,” says Purnell, wetland birds program manager at Birdlife Australia, a nonprofit conservation organization.
The Yellow Sea coastline provides some of the most important resting and refueling grounds for shorebirds migrating between their breeding sites in China, Russia, and Alaska and nonbreeding habitats in Southeast Asia, Australia and New Zealand. For bar-tailed godwits, the Yellow Sea’s tidal mudflats are the only spot to rest and feed along a 6,000-mile journey. In the past few decades, however, coastal development has gobbled up more than 65 percent of this habitat.
In 2006, for example, the near completion of a 21-mile seawall—the world’s longest man-made sea barrier—cut off a large portion of the rich Saemangeum tidal flat from the Yellow Sea so that the reclaimed land could be used for agriculture, aquaculture, industry and housing. This project caused an area almost seven times the size of Manhattan to become starved of tidal replenishment. As a result, the sea snails and other shellfish that shorebirds snacked on rapidly declined. By 2014, the number of birds annually returning to the site had dropped from more than 250,000 to about 50,000. Returning numbers of endangered birds, such as the spotted greenshank and great knot, were whittled down to a fraction of their 2006 levels. The critically endangered spoon-billed sandpiper nearly vanished from Saemangeum.
Migratory birds then increasingly turned to the Geum Estuary, a site north of Saemangeum that is one fourth of its size. Although they were able to feed along the estuary’s narrow mudflats during low tide, the nearby sand dunes and sandspits they needed for roosting were often submerged during high tide. “You would see 10,000 to 20,000 birds circling the coast and swooping down, trying to find somewhere to land,” Purnell says. “It’s pretty sad, because the birds are meant to get there to rest, refuel and get fatter. And instead, they’re burning more energy.”
To provide some immediate respite and give shorebirds the best chance to reach their breeding grounds, Purnell and his team took inspiration from oyster aquaculture. Many farmers along Australia’s eastern coast raise oysters in floating bags, which he thought could also provide the perfect ocean perch for waterbirds.
In proof-of-concept trials in 2018 and 2019, respectively, Purnell and his team built two such floating islands at Port Phillip Bay and the Hunter Estuary, both in Australia, where the shorebirds arrive at one end of their migration. Each consisted of 120 four-square-foot mesh bags connected by ropes. Foam buoys kept the bags afloat, and the weight of the empty oyster shells made them relatively steady in moving waters. The shells also provided a home for invertebrates to colonize—a bobbing waterbird buffet.
Even though migrating shorebirds did not make much use of the artificial roosts because they had access to their natural ones, the team did see waterfowl and terns landing on the oyster bag platforms. That gave the team the confidence to more thoroughly test the setup with a five-year trial in South Korea. Teaming up with Birdlife International in Asia and officials in Seocheon County, which flanks the Geum Estuary, they deployed three clusters of the artificial floats during the peak northward migration period last April. Then they waited.
But they did not have to wait long. Within mere minutes of installation, birds were landing on the floats. By May 2019, 43 shorebird species—including the endangered black-faced spoonbill and far eastern curlew—were using these platforms to roost. That same month, a surveillance camera recorded nearly 300 individuals huddled on one of the clusters. This instant success surprised Hong-Tae Jeon, an official at Seocheon County’s Cultural and Tourism Division. “We were worried whether shorebirds would use the floating roosts,” he says.
In September 2019, during the peak migration period for returning shorebirds, the number of them roosting on an artificial island spiked to 600. Jeon hopes more will use them in the future, after they become more familiar with the new concept. Purnell envisions the use of artificial roosts in other Yellow Sea coastal areas undergoing rapid development—and possibly along other bird migration routes where sea-level rise may swallow up sandspits and low-lying roosting habitat as the climate warms. The team is scheduled to present results of the first year of the trial in November at the first East Asian-Australasian Flyway Shorebird Science Meeting in South Korea.
While he applauds the oyster-bag initiative, Nial Moores, director of a conservation organization called Birds Korea, points out that there are still many more displaced birds in need of diverse roosting sites. “Floating roosts by themselves are not enough,” he says. Moores notes it is also important to keep in mind the needs of local fishers who rely on the fish these birds may eat. And he cautions that artificial roosts could be used as a justification to continue coastal development. He advocates for active protection and management of remaining habitat.
But Purnell envisions the use of these floats only in situations in which habitat has already been destroyed. “It’s almost like an emergency-relief project,” he says. Over the next four years, his team will continue to monitor how many birds use the roosts and how well the floats and other materials stand up to the elements. Officials from nearby counties have expressed interest in the artificial structures, and results from this early effort could help in the development of a more comprehensive conservation strategy for the region.
In the meantime, Seocheon County officials see the birds congregating on the artificial roosts as an opportunity to generate conservation awareness in the region. This project is helping to generate empathy toward natural resources among citizens, Jeon says, so “we are hoping these floating roosts remain in this region.”