Researchers behind an incentive-based fisheries program in Indonesia have reported a drop in shark and ray bycatch, but also warned of an unexpected rise in the intentional capture of these threatened species.

The program pays some small-scale fishers in Aceh province, on the island of Sumatra, and on Lombok Island to release any live hammerhead sharks (genus Sphyrna) and wedgefish (genus Rhynchobatus) that they catch. While the initiative, designed and implemented by the NGO Kebersamaan Untuk Lautan (KUL), has proved highly successful in reducing bycatch of these fish, it has also created a perverse incentive: some fishers were found to be deliberately targeting hammerheads and wedgefish so that they can release them and claim payment, according to a recently published study in the journal Science Advances.

“Our results do not imply that a pay-to-release program cannot work in Indonesia, but rather they offer valuable insights into how such programs could be more effectively designed and deployed,” wrote lead author Hollie Booth, research associate from the University of Oxford’s Interdisciplinary Centre for Conservation Science in the U.K. (Booth is also the founder and chair of KUL.)

Researchers from Indonesia, the U.S. and the U.K. evaluated the conservation program involving 87 fishing vessels, with 50 operating in East Lombok district and 37 in Aceh Jaya district, between May 2022 and August 2023. The initiative offered fishers in Aceh Jaya payments of 15,000 rupiah (about $1 at the time) for small hammerhead sharks, and 50,000 rupiah ($3.30) for large ones. They also received a fixed rate of 120,000 rupiah ($8) per wedgefish.

In East Lombok, fishers were paid more: 500,000 rupiah ($33) per hammerhead and 2 million ($135) per wedgefish. The study noted that these payment differences were based on local market rates for each species.

According to Booth, the program paid out a total of $4,500 over the 16-month period covered in the study. Funding came from grants, the Geneva-based Save Our Seas Foundation, and the U.K.’S Darwin Initiative, she added.

“Incentive-based programs play a critical role in effective and socially just nature conservation,” Booth said in a press release. “We can’t expect small-scale resource users to bear the majority of the costs of conservation, especially when there are wealthier and more powerful stakeholders causing major negative impacts.

“However, as our study has shown, incentives must be well designed and robustly evaluated to incentivize the right behavior and ultimately deliver positive outcomes for nature and people,” she added.

Booth and colleagues assessed the pay-to-release program using randomized controlled trial, which they called the most rigorous approach to show the effectiveness and quantify the effects of the program. She added that RCTs are particularly important for incentive-based interventions because the expected conservation benefits aren’t unambiguously positive, given the many ways they can influence behavioral change in unforeseen ways, such as hidden information and actions.

“When done well, RCTs give the most trustworthy evidence about whether something works or not,” Booth told Mongabay by email. “[H]owever they remain vanishingly rare in environmental programs, and even more so in marine conservation.”

The expected benefits were apparent, the researchers reported, with 71% of wedgefish and 4% of hammerheads that were caught being released. These results were verified through reviewing the footage taken on provided cameras and submitted by the fishers of the released fish safely swimming away and out of sight.

However, the researchers also found that the program motivated some fishers to increase their catches in pursuit of higher payouts, ultimately undermining conservation goals. As a result, wedgefish mortality dropped by only 25% compared to the control group, while hammerhead mortality rose by 44%.

According to the study, the findings led KUL to revise its incentive-based program. The changes include offering size-based compensation rates, limiting the number of compensated releases per vessel each week, and piloting a gear swap initiative to help fishers avoid catching threatened species altogether.

“It is concerning that so much money continues to be spent on conservation programs without rigorous evaluations of their impacts on biodiversity and socio-economic outcomes,” study co-author Paul Ferraro, a senior researcher at Johns Hopkins University in the U.S., said in the press statement.

Sharks and rays, which are large and long-lived marine animals, rank among the most threatened marine species globally, mainly due to overfishing in both targeted and bycatch fisheries. Indonesia accounts for the highest shark and ray catches of any country. Although international trade in hammerhead and wedgefish is regulated under the Convention on International Trade in Endangered Species (CITES), there are no national laws in Indonesia that govern their capture or domestic use. As a result, domestic fishing of these threatened fish continues unchecked.

East Lombok and Aceh Jaya districts are known for high catches of hammerheads and wedgefish. Fishers in these locations use gill nets and longlines, which are among the most harmful gear types for sharks and rays worldwide. These practices reflect broader trends across Indonesia, where more than 90% of the fishing fleet is small-scale and largely dependent on nonselective nets and lines. In the study villages, hammerheads and wedgefish are also vital to local livelihoods, making a pay-to-release program a potentially effective way to reduce economic barriers to conservation.

Small-scale fisheries are widespread across coastal waters in many countries. Similar legal gaps and economic challenges often lead to the routine capture of threatened sharks and rays, which remain important sources of food and income for many coastal communities.

“This initiative has had a tangible impact on strengthening the livelihoods of small-scale fishers, who form the backbone of coastal life in Aceh Jaya,” Teuku Ridwan, head of the district’s marine affairs and fisheries agency, said as quoted in the press statement.

“We hope that the synergy between implementing organizations, fishing communities, traditional leaders, and local government continues to be strengthened to realize marine management that is just, sustainable, and rooted in local wisdom.”

Basten Gokkon is a senior staff writer for Indonesia at Mongabay. Find him on 𝕏@bgokkon.

See more reporting:

Community-based conservation cuts thresher shark fishing by 91% in Indonesia: Study

Citation:

Booth, H., Pienkowski, T., Ramdlan, M. S., Naira, K. B., Muhsin, Milner-Gulland, E. J., … Ferraro, P. J. (2025). Conservation impacts and hidden actions in a randomized controlled trial of a marine pay-to-release program. Science Advances, 11(17). doi:10.1126/sciadv.adr1000

FEEDBACK:Use this form to send a message to the author of this post. If you want to post a public comment, you can do that at the bottom of the page.