Spawning Signs
Fishes that participate in group spawning may also aggregate for feeding or other purposes, such as predator avoidance. Therefore, care must be taken in referring to an aggregation as a spawning aggregation.
Dog snapper spawning in Belize. Photo © Rachel T. Graham
To confirm the reproductive function of an FSA, either direct observation of spawning, or the presence of hydrated eggs is required (histological microscopic observation of post-ovulatory follicles is also used, but requires some specialized tissue preparation). However, confirmation of spawning is often difficult and rarely witnessed, since many species spawn at night, at depths below safe diving limits, or away from reefs in open water. In these events and without access to gonads or histological techniques, verifying that a congregation of fish represents a spawning aggregation is problematic.
In lieu of direct evidence, indirect confirmation using a combination of spawning signs or behaviors can sometimes be used. However, some of these behaviors are also demonstrated during non-reproductive periods, so caution should be exercised, particularly when relying on a single event or behavior to categorize an aggregation. Some behaviors often associated with FSA include:
- Aggregating in numbers higher than those usually observed during non-reproductive periods
- Color changes
- Aggression or territorial displays
- Courtship
While these behaviors are useful for confirming reproductive function, they should generally be used in combination,1 and when efforts to verify reproductive activity by traditional means have been exhausted.
Aggregating or Grouping
Aggregating behavior among fish normally found to be solitary is one of several behaviors potentially associated with reproductive activity. By definition, an aggregation is a concentration of fish in densities three times higher than that observed during non-reproductive periods2. For some grouper, this can mean an aggregation of just a few individuals such as in the goliath grouper, Epinephelus itajara. In other species the aggregation can be hundreds, thousands or even tens of thousands of individuals, as observed for cubera snapper (Lutjanus cyanopterus)3.
Aggregation of Nassau grouper in Belize. Three of the four recorded color variations are apparent: normal (lower right), white belly (front left) and dark phase (upper). These color changes may be associated with spawning but also occur during other non-reproductive periods. Photo © Julie Stockbridge/TNC
Color Change
Some species exhibit color change during spawning, which may be sex-specific. For example, in the squaretail coralgrouper (Plectropomus areolatus), there are six color patterns, and some are sex-specific4. For Nassau grouper (Epinephelus striatus) there are four color patterns. Not all patterns are sex-specific and color change can also be associated with other activities. For example, in camouflage grouper (Epinephelus polyphekadion) similar color changes can be observed during reproduction as well as at cleaning stations. Thus, care must be taken when using color change alone as an indication of reproductive activity.
Aggression or Territorial Displays
Chasing and fighting are behaviors normally associated with territoriality. These behaviors may be heightened during spawning season as the males, in particular, come into close contact. Scars, bite marks, missing patches of skin (e.g., brown-marbled grouper, Epinephelus fuscoguttatus), or frayed caudal rays (camouflage grouper) are often seen in males at the conclusion or spawning. As with color change, aggression and territoriality may not always indicate reproductive activity.
Courtship Behavior
Species-specific spawning behaviors vary greatly, but sometimes include swimming displays, such as repetitive orchestrated movement (e.g., cubera snappers5, tiger groupers, and others), and nuzzling among paired individuals, with fish rubbing against one another6. These behaviors may represent courtship, and are often common within spawning aggregations. As with the aforementioned behaviors, monitors should be careful in associating these behaviors alone with reproductive activity.
Combined Behaviors
When normally solitary fish are found grouped in relatively high densities, display color changes or aggressive behavior (fighting or biting), appear with swollen bellies, and courtship is observed, there is reason to suggest this represents reproductively active fish. Monitoring sites and individuals with regularity, and over time, may provide greater information on the reproductive activity of the species, and confirm that the group of fish represents an FSA.
Resources
The following list of references provides information on reproductive behaviors. Many more are available from ConserveOnline or the SCRFA website.
Introduction to monitoring of spawning aggregations of three grouper species in the Indo-Pacific: A manual for field practitioners (Pet et al. 2006) (download pdf, 3,812k)
Synopsis of biological data on the Nassau grouper, Epinephelus striatus (Bloch, 1792), and the jewfish, E. itajara (Lichtenstein, 1822) (Sadovy and Eklund 1999)
Spawning aggregations of groupers (Serranidae) in Palau (Johannes et al. 1999)
Temporal and spatial trends in spawning aggregations of camouflage grouper, Epinephelus polyphekadion (Bleeker 1849) in Pohnpei, Micronesia (Rhodes and Sadovy 2002)
1 Pet et al. 2005
2 Domeier and Colin 1997
3 Heyman et al. 2005
4 Johannes et al. 1999
5 Heyman et al. 2005
6 Rhodes and Sadovy 2002