14 - Palau: Aggregations

Spawning by Camouflage Grouper, Epinephelus polyphekadion, Observed and Documented in Palaufor First Time in Wild

 Observations of spawning in groupers are relatively rare, and the camouflage grouper is no exception. Its aggregations have been variously documented and monitored since the mid-1990's in Palau. However, observations of actual spawning had not been made there, despite many attempts to observe their spawning at dusk by different observers.

 A recent dedicated effort by Jim Forrest and Jeanette Denby of the yacht "Dancer", based in Palau, offers for the first time solid information regarding the actual time of spawning by the camouflage grouper in the country. In addition to making general observations, Forrest was also able to film grouper behaviour, courtship and spawning for a new documentary being prepared by SCRFA on coastal fisheries and spawning aggregations
in Palau.

Spawning was seen on 11 June and 11 July 2010 (1 day before and the day of the new moon) at Ulong Channel (Ngerumkaol), a well known aggregation site on the western barrier reef of Palau, just after dawn. Spawning occurred after the tidal current had turned from incoming to outflowing. The currents were moderately strong moving out the channel and the grouper spawned over nearly an hour. Most spawnings were by a single pair, but a few group spawnings were also seen. There was not a general flurry of spawning; single pairs spawned at various times. In one case, a second male (“streaker”) swam up to release sperm in the gamete cloud following a pair-spawn. The spawnings occurred a short distance inside the mouth of the channel (30-60 m distance) in water about 12 m deep. The groupers only ascended a short distance, 1.5-2 m, from the bottom. In most cases black snapper, Macolor niger, were awaiting the spawn (they seemed to anticipate the spawn based on behaviour of the groupers) and moved into the newly released gamete cloud within seconds of release, feeding. Predation on a grouper within the aggregation was seen by Forrest when a large moray swam across the bottom, and took a grouper into a hole. Several sharks were attracted by this Camouflage grouper commotion, but did not attempt to seize the struggling fish.

The currents at Ulong Channel are somewhat unusual for a barrier reef channel, perhaps due to its “partial” nature; the channel does not go all the way through the shallow reef and is a net exporter of water, 60% is from lagoon to ocean, while 40% is from ocean to lagoon (import). We plan to reevaluate current observations around early morning times just before the new moon to determine the patterns of current flow when camouflage groupers are spawning. Earlier work by Kevin Rhodes, based on fishing camouflage grouper at hourly intervals during the night and examining the gonads suggested that spawning also occurs during nightime hours, so the time of the tide might be particularly important. Some excellent video footage of camouflage groupers courting and spawning was also included in the BBC Documentary series “South Pacific” in the second episode titled “Castaways”. The documentary purports that the footage of spawning (time and date unreported) was shot in the Solomon Islands, however, an inquiry to the BBC revealed the footage was shot in French Polynesia and bought from a freelance videographer. Attempts to get more information about the location, timing, lunar phase and such have not yet been successful. We will keep tracking this down until we can add another positive observation on camouflage grouper spawning.

Patrick L. Colin
Coral Reef Research Foundation
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