Fish for Food and Ecosystem Function : Fisheries, Trade and Key Ecosystem Processes in Coral Reefs

Abstract: Fish is a key source of food and income to millions of people living along tropical coastlines. They also play essential roles underpinning key ecosystem processes in coral reefs. For example, herbivorous fish keep algae in check that otherwise may outcompete corals, reducing the reef’s social-ecological values. New fishing methods and globalization have turned fish into global commodities, threatening the ecological resilience of many reefs. This thesis addresses the delicate balance between social and ecological aspects associated with fisheries and trade with reef fish in Zanzibar, Tanzania. Paper I examines how parrotfish contribute to keeping reefs free from algae and shows a non-linear relationship between fish body size and function, hence illustrating that maintaining large fish individuals on coral reefs is particularly important. Gear-based management (GBM) has been suggested as an alternative to no-take marine protected areas (MPAs) to sustain ecosystem processes without threatening fishers’ livelihood. Paper II investigates fishers’ use of different gears and how these gears select different functional groups of fish. Results indicate that gear restrictions could be used to reduce fishing pressure on particularly important groups of fish, but also that such an approach is far from simple. MPAs and GBM are both restrictions targeting fishers, but with increasing global demand for reef fish, it is neither realistic nor fair to place the sole burden of sustainable fisheries on them. Papers III & IV analyze the value chain of fish, from fishers to traders and consumers. Results show that the Zanzibar fishery targets a wide range of fish species and sizes, intended for different markets. The thesis concludes that a sound understanding of the functional properties of fish and more nuanced approaches to regulate fishing may contribute to the management of reef fisheries, but that sustainable solutions will require that measures are taken far beyond the oceans.