USA: Goliath

Grouper Aggregation and Spawning Research in SE Florida

The Florida Oceanographic Society conducted a preliminary Goliath grouper (Epinephelus itajara) monitoring project during the full moon of September near Jupiter, southeast Florida. The research focused on corroborating the reports of local divers that Goliath groupers were aggregating and possibly spawning at several locations on nearby off-shore reefs. Historically, the Jupiter area was known in the 1950s – 1970s as a spawning area but mangrove habitat loss in the nearby Lake Worth and Indian River lagoons and over-fishing were probably major factors that resulted in sharp declines in numbers of this species that ultimately led to protection by both the Federal government and the State of Florida in the early 1990s.

The one day initial monitoring resulted in 304 Goliath Grouper sightings spread out over five different, adjacent, reef locations. A total of 32 aggregations were counted. Note that aggregation is used to define the collective assembly - within each aggregation were multiple groupings which could be exhibiting different behaviours simultaneously. The largest single grouping consisted of 55 Goliath Groupers. Two-thirds of the sightings were made during the late afternoon with the remaining one-third observed during mid-morning dives. Twenty-eight percent of the Goliath Grouper were large adults with a total length of 180 to 240 cm. Fourteen percent of the groupings consisted of paired adults and 79% of the sightings had three or more Goliath Groupers.

No direct spawning activity was observed but several indirect indicators of possible spawning behaviour were noted. These behaviours include colour changes, chasing, stacking (arrangement of Goliath Groupers wherein one hovers directly above another), and pairing. Eighty-five percent of the Goliath Groupers had a normal coloration pattern. Three percent displayed a bicolor phase with a pale head. Both completely dark and completely pale coloration patterns were also observed.

The Florida Oceanographic Society plans to conduct further monitoring in 2009 by optimizing the survey design to include monitoring during the full moon period in July, August, and September. Timing of the dives close to dusk will also be included in the 2009 monitoring efforts. The SCRFA manual was very valuable in designing the underwater survey form used by the divers. A full copy of the 2008 final report is available at the Florida Oceanographic Society’s web site at www.floridaoceanographic.org.

Mike Phelan
Florida Oceanographic Society
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