Small-scale fisheries embedded in global trade networks

Small-scale fisheries are immensely important for the livelihoods, nutrition, and cultural identities of millions of people around the world. However, the impacts of small-scale fisheries on vulnerable marine populations, such as sharks, are less well understood than those of industrial fisheries. Alongside colleagues, I’ve constructed a model to investingate the impacts of a small-scale reef shark fishery, parameterized with data from a Kiribati grey reef shark fishery where reef sharks have been harvested at relatively low rates for cultural and subsistence purposes for generations.

A diagram of our modeling approach - a Bayesian dynamic population model allows us to integrate multiple types of data from fisher interviews with tag-recapture and demographic parameter estimates from nearby Palmyra atoll, enabling inference in a data-limited fishery.

At the turn of the century, growing access to international markets afforded local fishers a new source of income from shark fins and drove sharp increases in harvest rates, but the fishery remained small - comprising only 17 fishers in 2013. To understand the possible impacts of this fishery on the grey reef shark population, we interviewed local fishers, obtaining estimates of catch and effort as early as 1983 and validating these estimates with storehouse inventories. We combined these data with previously obtained estimates of demographic parameters for grey reef sharks at nearby Palmyra atoll, constructing a hierarchical Bayesian Beverton-Holt surplus production model for grey reef sharks on the island of study.

Our model suggests that a small number of fishers and motorized boats could plausibly drive a significant reduction in the abundance of grey reef sharks on surrounding reefs, declining to as much as 75% below carrying capacity in just 15 years since the rise in global shark demand. These results highlight the vulnerability of sharks and other slow-growing marine megafauna to relatively modest small-scale fishing efforts. As few communities remain disconnected from global trade networks - even those that are relatively geographically isolated - our research suggests a need for management and trade regulations at multi-national scales.