About Fish Spawning Aggregations

A reef fish spawning aggregation is a grouping of a single species of reef fish that has gathered together in greater densities than normal with the specific purpose of reproducing; typically such aggregations form at the same place at approximately the same times each year.

The best-known examples are certain species of grouper and snapper, but many surgeonfish, rabbitfish, parrotfish, wrasse also aggregate to spawn. There is a great deal of variability among different species in the dynamics of aggregation formation. For instance, spawning aggregations of some small wrasses may consist of just ten individuals spawning close to their normal home range on the reef, while those of some large groupers consist of tens of thousands of fish that may have travelled over one hundred kilometres to an aggregation site on a particular reef.

There are two classes of spawning aggregation, ‘resident’ and ‘transient’. Both occur at predictable and regular sites and times. In resident aggregations fish only travel short distances to the aggregation sites, and assemble on a regular basis, sometimes almost daily and for extended periods. Such species are generally small in size. Transient aggregations, on the other hand, tend to be formed by larger species physically able to travel greater distances. Transient aggregations usually form for just a few months each year, often for a week or two at a time. As a general rule, transient aggregations are larger, of shorter duration and less common than resident aggregations.