Fish Spawning Aggregations: A Reef Resilience Toolkit Module

Every Aggregation Counts

The network of marine reserves in the Mesoamerican region. Recently, the network was updated to include protection of several FSAs. Most of the reserves shown have minor or no enforcement and exploitation of FSAs continues. © Mesoamerican Barrier Reef Systems Project

Reproductive population dynamics are unknown for practically all FSA-forming species. While the contribution of a single aggregation to annual reproduction output varies by species, recent evidence suggests that individual aggregations represent sub-sets of the entire reproductive population, with some adults visiting the FSA no more than once within a reproductive season1. Moreover, eggs spawned at a particular FSA may not provide recruits to local populations, but instead to reefs positioned “downstream” of the FSA. The protection of every aggregation is paramount, since “upstream” FSAs, often outside local or regional boundaries and protected areas, may form the source of recruits to local reefs. In areas where self-recruitment is high, FSA loss may equate to localized population extinction.

Connectivity of Populations

Questions of connectivity between regions and FSAs, and of the importance of FSAs to local stock replenishment, are currently the subject of much research. The traditional view of connectivity, and FSA site placement, was that spawning occurred at a specific time and location to maximize egg dispersal, reduce predation, and increase the probability of recruitment to new areas. However, more recent work suggests that reefs may be largely self-recruiting, that is, the larvae that settle on the reef are supplied mainly by localized populations,2 and that specific biophysical mechanisms may exist to retain larvae close to their spawning source3. The ongoing work in this area will have important implications for the effective design of marine reserves to protect FSAs.

Currently, there is little management of reef fish spawning aggregations. A recent review of marine reserves showed that only four out of 55 no-take reserves had taken FSAs into consideration in their design4. Of those that have incorporated FSAs into MPA design, most are lacking in enforcement; consequently, the depletion of the reproductive populations for those FSAs continues. The depletion of FSAs often results in substantial impacts to local ecosystems and industry. FSA protection and management urgently needs to be included in the wider context of fisheries management and marine conservation.