Fish Spawning Aggregations: A Reef Resilience Toolkit Module

Physical Information

Some general locations where spawning aggregations may occur include the seaward edges of reef channels, promontories, patch reefs and even seamounts. In most locales, these general reef features are quite numerous and it would take far too much time and resources to locate sites by random dives. However, the use of aerial photographs and nautical charts, in combination with fisher interviews or activities, might provide insights into FSA locations within a particular area or region. Gradually, these combined observations may form general patterns that can assist in locating additional FSAs more easily. Some examples are provided from published references, including the following:

• Along the Belize portion of the Meso-American Barrier Reef, several grouper and snapper FSAs have been located at the seaward edge of reef promontories1. Other FSAs for these same species have been found in similar locations in the Cayman Islands and Cuba7. However, not all grouper and snapper FSAs in the Caribbean occur at promontories, so don’t be misled into assuming that physical patterns for one locale are readily transferable to another. While making generalizations might aid in locating FSAs for some species, it can also be counter-productive. Thus, the best strategy is for resource managers to keep an open mind about where FSAs may and may not occur.
• FSAs have been found in relation to a number of geomorphological and hydrological features. Some FSAs have been located on sandy bottoms; in “holes” in the seabed; and on rocky bottoms, reef slopes, seamounts, channels, pinnacles, and shelf-edge areas. Some FSAs occur in areas of rapidly moving currents, while others exist in rather benign locations, often for the same species. Similarly, FSAs may be found in a range of depths. This indicates that we still have much to learn about the physical associations of FSAs, and that it is too early to make generalized statements.

Relationship between seawater temperature (line) and abundance (bars) for cubera snapper. From Heyman et al. 2005

Environmental Cues

For some species, aggregation formation and spawning seem intimately linked to one or a combination of environmental cues, such as photoperiod, temperature, tide and lunar cycle. For example, in Belize, both photoperiod and temperature have been indicated in the timing of seasonal reproductive activity in cubera snapper (Lutjanus caynopterus).1 Similarly, recent assessments of squaretail coralgrouper (Plectropomus areolatus) in the Pacific suggest that temperature and photoperiod are connected to the timing of reproductive activity.2 Nassau grouper spawning in the Caribbean is linked to a very narrow temperature range.3 Reproductive activity for a number of other species of snapper and grouper has been linked to environmental cues,4 and this number is likely to increase as more studies are performed.

The association between (a) photoperiod and (b) sea surface temperature (SST) to (c) reproductive season for squaretail coralgrouper. From K. Rhodes, unpublished

Among reef fishes, probably the most common environmental cue associated with spawning is lunar cycle.5 Many species have a spawning cycle linked to one or more lunar phases. Within a particular species, these phases vary across the species distributional range, similar to spawning season, as shown most notably for the camouflage grouper, Epinephelus polyphekadion.6 For camouflage grouper, spawning may occur along the same general latitude at either full or new moon, depending on locale. Wide seasonal variation is also shown for this species, although no clear trends were associated with latitude. Similar to squaretail coralgrouper in Pohnpei, camouflage grouper FSA formation may be tied to increasing temperature and photoperiod, since these species are known to co-aggregate there.

Recording and understanding linkages between physical conditions and spawning seasonality can provide insight into the predictability of reproduction for some species, and help guide future efforts in identifying FSAs. Knowing when to look is equally important as knowing where to look.

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