Coral reef fish spawning aggregations have been overfished in all tropical regions, some to the point of collapse. However, vulnerability to fishing clearly varies among species and local contexts because some aggregation fisheries have been sustained for decades. My thesis aim was to investigate key factors that confer vulnerability to fishing in aggregating species. Integrating behavioural ecology, fisheries science and socioeconomics, I derived an indicator-based approach for assessing vulnerability to fishing based on intrinsic (biology, behaviour) and extrinsic (e.g. fisher knowledge, gear technology) components, which also served as a conceptual framework for research. Five objectives were identified to examine key indicators, their effects and interactions. Firstly, I examined how fisher knowledge and exploitation of aggregating behaviour varies among case study sites in Papua New Guinea, finding that heterogeneity in knowledge was structured by tenure and gear use, while the development of aggregation fisheries was related to socioeconomic dependency on fishing. Secondly, in Seychelles, I show that vulnerability of a rabbitfish to aggregation fishing varies across the spawning season, likely due to environmental factors (weak currents) that reduce gear efficiency in some months. Thirdly, at a multispecies grouper spawning aggregation site in Papua New Guinea, I demonstrate that variation in vulnerability to the gear (catchability) results from species selectivity and the effects of gear saturation. Fourthly, I show how the costs and benefits of marine reserves protecting either spawning or non-spawning habitats depend on changes to catchability that aggregation formation confers. Lastly, I applied the indicator-based approach to examine vulnerability across a global set of spawning aggregation fisheries. The indicator-based approach provides a tool for managers to assess the risks that spawning aggregation fisheries pose, while findings from my thesis identify key mechanisms that will influence the efficacy of fishing effort controls, gear-based measures and marine reserves that may be considered in managing spawning aggregation fisheries.
Jan emigrated from the UK to the tropical paradise of Seychelles nearly 20 years ago. He worked in fisheries research and management for the Seychelles government and the Indian Ocean Tuna Commission, where he developed an interest in the implications of fish aggregating behaviour for population assessment and management. Jan has led research on reef fish spawning aggregations in Seychelles, Kenya and Tanzania, and is now a director of Science and Conservation of Fish Aggregations (SCRFA).