JUPITER -- The huge Goliath grouper seemed to be playing peek-a-boo with divers hovering near the wreck of the MG III about 60 feet deep off Jupiter. If the humans swam too close, the giant mottled brown fish backed up deeper into the shipwreck. But if they held still and waited, it edged closer cocking its head to eye them, then opening its cavernous maw so that they could see all the way down to its palate.
Not far away, some other divers creeping up on scores of Goliaths puttering around the wreck heard a deep boom that sounded like an orchestra tympani or the penetrating bass of a rap song. That meant the humans were invading the fishs space, and it was warning them off using vibrations from the muscles attached to its swim bladder.
Far from scared, the divers were elated.
That was so cool, they told one another after surfacing at their charter boat, the Blue Tang.
In a two-tank drift dive that covered three 90-foot-deep artificial reefs the Zion, Miss Jenny and Bonaire followed by the shallower MG III, the dozen divers probably had observed several hundred Goliath groupers. Large schools of the huge, gentle giants began showing up on shipwrecks from Boynton Beach to Stuart in July for their annual spawn, which peaked in August and is expected to extend into mid-October.
Scuba divers come from Florida, the United States and around the world just to see the one-of-a-kind aggregation of huge fish now making a resurgence after nearly being wiped out by overfishing in the 1980s. Since the Goliath fisherys closure in the South Atlantic and Gulf of Mexico in 1990, the population has swelled, prompting some spearfishers and hook-and-line anglers to call for its reopening.
But NOAA Fisheries, the federal agency in charge of managing fish stocks in the United States, and the Florida Fish and Wildlife Conservation Commission have no plans to open the harvest of Goliaths anytime soon. Scientists from the two agencies are expected to begin a stock assessment in 2015 to determine whether they have rebounded enough to allow any take. Chris Koenig, a retired professor from Florida State University, and several colleagues are gathering scientific data for that assessment. A lot of their work is performed in the waters around Jupiter.
Its neat they aggregate in such density, Koenig said. You cant see that anywhere in the world. Now the population is really building. Theyre doing well. Theyre getting up there.
Koenig and his fellow scientists are trying to learn all they can about the giant groupers life history, movements, reproduction and diet. They have caught, tagged, sampled and released more than 400 Goliaths off Jupiter in the past two years including a banner weekend of 80 in three days earlier this month.
Working from captain Mike Newmans commercial boat, Dykoke, the scientists use heavy lines dangling from poly balls and circle hooks baited with chunks of barracuda, jack, and bonito to catch Goliaths on the wrecks. They handline the fish quickly into the Dykokes cockpit and pump saltwater through its gills while they take a sample of the fin rays for aging, biopsy the ovaries and collect sperm, pump the stomach to see what it ate, collect genetic material, and implant streamer and acoustic tags. Occasionally, a fish dies after being worked up, which upsets divers who find it.
But Koenig said his team has lost only three fish in two years a tiny percentage of the 800 that federal and state fisheries managers considered allowing them to kill five years ago in order to take otoliths, or ear bones, for aging. Koenig said they dont need to harvest fish because theyve developed non-lethal techniques for sampling.
Since the mid-1990s, Koenig said, scientists have learned a lot about Goliaths:
• They eat mostly small, slow-moving fish and crustaceans, but very few lobster.
• They are hermaphrodites, harboring sperm and eggs in the same set of gonads in 5-10 percent of fish sampled.
• They can live to their 60s, beginning to spawn at about four feet long.
• As juveniles, they inhabit mangrove estuaries then move out to deeper water when they mature.
• They will travel long distances as much as 180 miles to reach summer spawning sites.
Unknowns include: Do the fish spawn in pairs or groups? Can larvae harvested during spawning be raised in captivity? And what is the exact relationship between size and age?
Koenig urges anglers eager to target Goliath grouper to be patient and accept the findings of scientists.
I get sick of arguing about it, Koenig said. All this misinformation they repeat to each other until it becomes truth. People believe their buddies and not what science tells them. They want their cake now. Its hard getting through to them.