Dinner with Moray?

In mixed-species groups, moray eels (Muraenidae) can function as focal species, hunting for prey within the deep interstices of reefs and, in the process, flushing out potential prey that are then vulnerable to attack by the moray's companions. On 7 December 2021, we observed an unusually large mixed-species hunting group of piscivorous fishes, composed of 26 bluefin trevally (Caranx melampygus), two black jack (Caranx lugubris), and three whitetip reef sharks (Triaenodon obesus) following a single yellow-edged moray (Gymnothorax flavimarginatus) at dusk along the deep (21 m) reef–sand margin off Manuelita Island in Isla del Coco National Park (Pacific Costa Rica). The moray entered a crevice (indicated by the arrow, in the top image) in an isolated coral framework while the primary hunting group circled the vicinity in both clockwise and counterclockwise directions, and the sharks entered and exited the crevice for about seven minutes before dispersing with only the moray remaining. The association of the hunting group may have enabled its members to encounter disturbed prey and then to provoke the moray to continue swimming and hunting, and thus flush out additional prey at other nearby locations. Current understanding remains limited for how predators determine trade-offs for hunting in groups versus individually, how predators share information related to group formation and dissolution, and what the outcomes of such behaviors are in terms of individual fitness. How short-term mutualisms such as these shape the functional relationships between predators and prey in fish communities is an area in need of enhanced attention, given the existing threats to large predators from overfishing and the need to conserve species interactions as a component of ecosystem management.