Implications of coral reef degradation for fisheries

Hamilton, Mark and Graham, Nick and Hicks, Christina and MacNeil, Aaron (2024) Implications of coral reef degradation for fisheries. PhD thesis, Lancaster University.

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Abstract

Tropical coral reef habitats are vulnerable to numerous environmental stressors, affecting the ecosystem services they provide. Coral reef fisheries provide livelihoods and a vital source of nutritious seafood for hundreds of millions of people in coastal communities, yet little is known about how reef degradation may impact these fisheries, which this thesis addresses using a multidisciplinary approach. Fish biomass and nutrient production rates were estimated on reefs impacted by coral bleaching. In Seychelles, biomass production increased on reefs recovering to coral-dominated states following coral mortality and eventually exceeded pre-bleaching levels, driven predominantly by herbivorous fishes, while on reefs that became overgrown with macroalgae, elevated production rates relative to standing biomass maintained fisheries productivity. Across four Indo-Pacific locations, reef structural complexity positively impacted fish biomass and nutrient production rates, particularly in the unfished Chagos Archipelago. Collectively, these results suggest that while coral-dominated reefs with little human impact may support more productive fish assemblages, reefs with moderate levels of habitat degradation and fishing pressure can continue to provide crucial provisioning services to people. Interviews with trap fishers in Seychelles revealed that reef degradation could have notable impacts on catches, especially when caused by coral bleaching, however other factors such as increased fishing effort were perceived as the main drivers of declining catches and subsequent changes in fishing behaviour. Reef fish biomass and nutrient availability were highest when coral cover was low in French Polynesia, and people’s consumption of reef and pelagic fish was influenced by their social background. Fish consumption habits varied between islands, with those who had more traditional Polynesian diets rich in fish benefitting from higher nutrient intakes. This thesis demonstrates how the condition of coral reef ecosystems can impact production, extraction, and consumption of fish, and that small-scale fisheries on degraded reefs can remain important sources of nutritious seafood.