Timing and location of aggregation and spawning in reef fishes

Abstract

Fishes that engage in aggregation spawning do so at specific sites and times and have a wide diversity of spawning strategies. There are some clear distinctions in locations and timing between transient aggregations (TA) and resident aggregations (RA). TAs have larger predatory fishes, occur infrequently, but seasonally largely on or near shelf edge areas. RAs have herbivores and omnivores, are more numerous and occur in both shelf edge areas and inshore regions. Aggregations differ between the Indo-west Pacific (IWP) and tropical western Atlantic (TWA); probably due to current dominated regimes in the IWP due to the higher tidal amplitudes and barrier reef/channel geomorphology. Migration patterns are related to the frequency of spawning. Nearly all TA (and some RA) sites are used by multiple species, either sequentially or simultaneously. Many aggregation sites are stable in location over decades with only slight variation. Spawning at some TAs is now known to occur during periods of low current speed. The entrainment of TA propagules into oceanic circulation after spawning is uncertain with tendencies at some TA sites for retention of propagules. Spawn from RAs is less likely to become entrained into oceanic circulation. Water temperature regimes may be an important determinant of seasonality of spawning and early life history success. Most aggregations occur over a limited temperature range. The daily and lunar timing of aggregation spawning may be related to needs of pelagic life history. Predation on spawning adults is rare while predation of released eggs is common, but neither factor is believed to limit or structure aggregations.