Positive outcomes and insights for scaling from a randomized pilot of a gear exchange program to reduce bycatch in small-scale fisheries

Hollie Booth , Ilham Fajri, Rusdiansyah R, Kusuma Banda Naira, Muhammad Rizal, Luky Adrianto, Julia P. G. Jones

Incentive-based conservation programs offer a promising approach for reducing fishing pressure on threatened species while supporting coastal livelihoods, yet causal evidence remains scarce. Modest budgets and small samples are a persistent challenge to evaluating pilots of novel conservation programs. We conducted a 12-month pre-registered randomized pilot of a gear exchange program in Aceh Province, Indonesia, allocating 11 vessels to treatment (N = 4) or control (N = 7) after 26 months of baseline (pre-treatment) monitoring. Treatment vessels were offered fish traps in exchange for gillnets — associated with bycatch of Critically Endangered elasmobranchs. After comparable pre-treatment bycatch rates, treatment vessels recorded zero bycatch across 306 pilot trips while control vessel bycatch declined but persisted (64 individuals, 890 trips), yielding a 95% reduction in bycatch odds (difference-in-differences odds ratio 0.050 [0.002–0.420]). Net income was also $48.62 higher per trip (95% CI: $37.90–$59.35). Bycatch also declined in controls due to opportunistic shifts towards handlining, meaning effects would have been overstated without a counterfactual-based design. Survey data revealed high acceptability and dual conservation-livelihood motivations. Through our randomized mixed-methods pilot we generated credible causal estimates and mechanistic insights that an uncontrolled pilot could not, demonstrating the value of randomized piloting before scaling.