When reef fish have to mate at certain time of the year they leave their protected reef to move and gather in large numbers in specific places for spawning. These large aggregations are called spawning aggregations. These large meetings allow them to increase their reproductive success by mixing large amount of gametes at a specific place with multiple partners around. But on the other hand they are also more vulnerable to predation. This therefore can create an incredible opportunity for the predators to get easier food.
During a Navy survey around the lagoon of Moorea (French Polynesia) a large aggregation of fish was observed which quickly attracted a large number of reef predators, the blacktip reef sharks (Carcharhinus melanopterus). The following event demonstrates the hard trade of for these reef fish between maximizing their reproductive fitness and increased predation risk….
Another view below: