Reef shark population declines on remote Pacific reefs: inferences from multiple methods in a data-limited fishery

Small-scale fisheries are immensely important for the livelihoods, nutrition, and cultural identities of millions of people, but their impacts are less understood than those of industrial fisheries. On the island of Teraina in Kiribati’s Northern Line Islands, sharks have traditionally been harvested only occasionally for cultural purposes. At the turn of the century, growing access to international markets drove sharp increases in harvests, but the fishery remained small, comprising only 17 fishers in 2013, and a ban on commercial shark fishing and trade was implemented in 2016. To understand the possible impacts of this fishery, we interviewed each fisher, obtaining estimates of catch and effort as early as 1983 and validating these estimates with storehouse inventories. We combined these data with previously published tag-recapture data for grey reef sharks Carcharhinus amblyrhynchos at nearby Palmyra Atoll to inform a Bayesian production model for Teraina’s grey reef shark population. Our model suggests that a small number of fishers and motorized boats could plausibly have driven a significant reduction in grey reef shark abundance on surrounding reefs, declining by as much as 75% in as few as 15 yr. Recent ecological and social surveys confirm that shark populations in the Line Islands are likely severely depleted. These results highlight the vulnerability of sharks and other slow-growing marine megafauna to relatively modest small-scale fishing efforts. As few communities, even those that are relatively geographically isolated, remain disconnected from global trade networks, our research suggests a need for management and trade regulations at trans-national scales.