Fish Spawning Aggregations: A Reef Resilience Toolkit Module

Biological Factors

A number of methods are available to collect biological data. Many of these methods are discussed in the section on FSA Monitoring. In this section, spawning aggregations are prioritized for immediate management needs according to their biological characteristics.

Massive swirl of spawning fish. Photo © Will Heyman/TNC

Priority FSAs

• Multi-species FSAs
• FSAs declining in abundance
• FSAs where endangered or vulnerable species are spawning

Multi-species FSAs

Protecting multi-species FSAs is a cost-effective method to help reduce mortality of a number of different species, with a single management action. Multi-species FSAs will likely need to be protected year-round rather than seasonally, since species sharing the same site often spawn at different times throughout the year. Monthly monitoring over the year and at varying lunar phases may reveal that single-species FSAs are actually multi-species FSAs.

FSAs in Decline

Declines in FSA abundance can be measured in a number of ways. Extirpated FSAs have rarely been observed to re-establish, while some have shown no recovery for decades. It is not known what happens to the remaining few fish once a site is extirpated. Some speculate that the location of spawning sites is transmitted socially from older generations of mature fish to younger generations of first-time spawners1. The complete disappearance of fish that have previously spawned at a site may prevent socially mediated reproductive cues to be transferred to younger cohorts, thus causing a site to become inactive.

FSAs of Endangered or Vulnerable Species

FSAs are particularly important for endangered species, such as the goliath grouper, Epinephelus itajara, that forms relatively small, seasonal aggregations. The protection of spawning areas and other critical habitats of endangered and vulnerable species should be a high priority for management.

Other Protection Priorities

• Migratory corridors to FSAs
• Critical habitat for early life history stages of spawning species

Migratory Corridors of FSAs

Since some fishes migrate relatively long distances to FSA sites, it is important to determine these routes and incorporate them into protective measures, particularly in areas adjacent to FSAs where concentrations are likely highest, and fish are most vulnerable. Tagging studies, while time consuming and potentially expensive, can provide valuable data on migration patterns. Acoustic tagging is more expensive and additionally requires an array of acoustic receivers installed in the area to record measurements. However, acoustic tagging and tracking studies can provide relatively precise information on the movements of fishes, and have led to important discoveries on the behaviors of fishes2. Scientists use fish tag and recapture studies to determine the range and migration patterns of spawning fishes. Tagging studies can help estimate mortality rates for spawning stock biomass.

Habitat for Different Life Stages of Spawning Species

Fishes may use a wide range of habitats throughout their life cycles. In reef fishes, this may include the pelagic environment, mangrove habitats, seagrass beds, and coral reefs. A disruption in any part of the life cycle is likely to result in decreased reproductive output. In order for management to be effective it must provide for the protection of a variety of different habitats. Many estuary habitats, such as mangrove swamps, are impacted by land-based activities and coastal development3. Therefore it may be necessary to coordinate with terrestrial or other associated agencies to ensure that habitats for all fish life stages are protected.