Author(s): Jan Robinson *, Joshua E. Cinner, Nicholas A. J. Graham
The depletion of reef fish biomass is often attributed to overfishing driven by socioeconomic drivers such as local human population density and distance from reefs to markets -. As changes to these key socioeconomic drivers increase demand for resources, reef fishes with slow life histories, such as groupers (Serranidae), are typically the first to be depleted . However, the rate of depletion will also be influenced by the ability of fishers to locate and exploit fish populations when they are most vulnerable to fishing. Vulnerability to fishing increases when fish aggregate or school and the history of fishing is marked by developments based on exploiting this aspect of fish behaviour -. In the context of coral reefs, the development of aggregation-based fisheries depends on many factors including local knowledge relating to fish behaviour -, the technologies available to fishers - and access to aggregation sites -. It is important to understand the key ecological and socioeconomic drivers controlling the evolution of fisheries for aggregating species if they are to be effectively managed.
The exploitation of reef fish spawning aggregations is an obvious example of fishers utilising knowledge on fish behaviour to target populations when their density has increased. A large number of important food fishes on coral reefs aggregate periodically at high density to spawn -. Spawning aggregations represent attractive fishing opportunities since increases in density typically lead to greater catch-per-unit-effort (CPUE)  and because they are highly predictable in time and space, as evidenced by acoustic telemetry techniques that reveal spawner fidelity to specific sites and lunar periods -. Predictable aggregating behaviour is not, however, confined to reproduction since reef fishes also aggregate at specific times and locations for other functions, such as foraging, resting and shelter -. Fishers regularly target non-reproductive aggregations , , though their vulnerability to fishing has received much less research attention than spawning aggregations.
Regardless of their biological predictability, fisher knowledge of aggregations is heterogeneous and will influence the extent to which aggregations are perceived as predictable and exploited by fishers. Fisher knowledge maybe stratified by factors such as gender, age, location and cultural background , , . For example, Hamilton et al. (2004)  documented how fisher knowledge of spawning aggregations varied by clan both within and between locations in Manus Province, Papua New Guinea. Even if aggregations are predictable and their timing and location are known to fishers, accessibility to sites may be low due to factors such as prevailing weather and remoteness -, while inefficient gear use may constrain exploitation rates . Gender preferences and customary marine tenure that specifies ownership rights among kinship groups may also influence fisher access to fish resources , . Furthermore, fishing effort on aggregations may be constrained by limited market access or fish preservation capacity . Consequently, the vulnerability to fishing conferred by aggregation formation will depend on both fisher knowledge of aggregating behaviour and socioeconomic drivers influencing aggregation exploitation.
Fisher knowledge of...