Goliath Grouper Aggregations in Florida

in Underwater by Marcelo Krause — January 21, 2011 at 9:54 AM | 0 comments

The Goliath Grouper is the one of the largest fish of the grouper family and can weight as much as 800 lbs. Their range includes the Florida Keys, the Caribbean, practically all of the Brazilian coast as well as Congo to Senegal on the eastern Atlantic. They species is classified as critically endangered by the World Conservation Union (IUCN) and have been protected in the US since 1990, in the Caribbean since 1993 and in Brazil since 2002. Spotting a goliath grouper in Florida in the 80’s and 90’s was really rare.  But after the protection law has been in place the population have slowly recovered. Now 20 years later we can dive in Florida with large grouper aggregations. The aggregations happen at the end of the North American summer during August, September and October.  I have spent 2 days diving near Jupiter, FL with Jim Abernethy’s Scuba Charters. It seems that for some reason the gropers love to hang around artificial reefs. We dove at the wreck of the Zion for the 2 days. The wreck lies on a sandy bottom at 90ft deep and the groupers gathered around the wreck. It was hard to tell how many groupers were there, but I would guess that total numbers could be around 60 to 70. One dive boat that was early at the site told tales of more than a hundred. Most part of the groupers kept a safe distance from the divers, producing a loud “boom” from time to time. These loud noises can easily be heard by divers and seems to be produced by the contraction of a sonic muscle that is connected to the vertebrae and swim bladder. A few fish appeared to have no fear and would let divers approach very close. Like other fishes from the grouper family, the aggregations occur for breeding purposes. Studies show that the reproduction activities occur during the night, with peak times between 01:00 and 03:00. During this time the groupers perform several forays to shallower depths for spawning purposes. The noises also seem to be a spawning indicator, with increase of number of sounds being recorded during the night peak time. Contrary to the Brazilian popular belief, the North-American goliath groupers seem to have less spawning activities during the full moon. The location for the aggregations seems to be connected with the proximity of large mangrove areas, that are essential for the groupers during the early stages of life.  A curious behavior that I so far have not observed in Brazil (maybe due to the usual low visibility in the water) is that many of them seem to like to group together away from the wreck and up in the water column, in the middle of nowhere.

The same aggregations happen in Brazil during the summer. In one day a few years ago I was able to see more than 120 individuals in 4 different dive spots. I plan to write about the Brazilian aggregations on a future post on the blog. For more info on the Brazilian Groupers please visit Meros do Brasil.