By CHAD CARNEY
© St. Petersburg Times, published September 23, 2001
Sinkholes on the Florida mainland are frequent dive sites for freshwater divers. Most are between 100- and 200-feet deep and many connect to the Floridan Aquifer by a system of caves, often well-charted by technical divers.
Seven sinkholes up to 50 miles offshore from St. Petersburg are found below 110 to 160 feet in the Gulf of Mexico and are only occasionally visited by spearfishermen. Some are "bottom unknown," while others have been explored to depths of 450 feet.
Earlier this month we met with scientist James Cutler from Mote Marine Lab in Sarasota, circling above the largest sinkhole, known as the Green Banana or 50 Mile Spring. The water below is often green but the sink is round, not banana-shaped.
Rumor has it when it was first explored a case of green bananas drifted by and the name stuck.
Cutler brought the R/V Eugenie Clark, a research vessel equipped with a remote operated vehicle. The gulf floor is 160 feet deep at the rim of the sink, so divers have short bottom times and extensive decompression stops before surfacing.
The ROV can stay down as long as needed to shoot hours of videotape with bright surface-powered lights. Tethered to the boat by a 300-foot power and video cord, it found the sinkhole first and made the perfect descent line for us to follow.
Cutler took soil samples from a shelf 10 feet below the rim of the sink, which is about 300 feet across. Plentiful small to medium amberjack schooled above the sink, large tarpon hovered and goliath grouper lurked around the sinkhole's crusty edge.
To the southeast the next location was the South Spring, which drops from 140 feet to an unknown bottom. Mote's crew lowered a water sampling device, reminiscent of the "Dorothy" device from the film Twister.
Cutler said little is known about these offshore sinks, so they are checking for freshwater flow and trying to determine their formation period. On this trip only 69-degree seawater was found. On previous visits schools of 20 to 30 black-tip sharks have been observed above this approximately 75-foot diameter sink.
The Fish Bowl, just a little bigger and to the south, has only a 20-foot drop to the floor 160 feet down. A broken-off rim on one side looks much like a ledge and has held some big black groupers in the past.
The Jack Hole off Bradenton is the best known and second-largest of the seven sinks, with a diameter of about 200 feet. Fishing line and tackle snarl the lip at 120 feet and the bottom drops to 370 feet.
Fishermen often mistake these sinks for wrecks because of the similar reads on their bottom recorders and the common fish caught. Often difficult to locate, they show little slope and no sound echoes from inside the sink.
Just west is the lesser known Donut Hole, a small sink about 20 feet wide that funnels into cracks and crevices to a depth of 145 feet. Many big mangrove snapper join the usual amberjack found here.
The Northwest Pride Sink is about 100 feet across and is 132 deep like the nearby wreck of the Mexican Pride. A buddy reports a straight chimney and a hard bottom at 200 feet, where he once retrieved his dropped speargun. It is also called Russ' Sink, after a drowned spearfisherman.
The 18 Foot Hole, two-thirds of the way to the Middle Grounds, was mistakenly called the 18 Foot Ledge. Actually a large pothole in 108 feet, it opens into a 40-foot cavern with a barely passable crack at the 140-foot deep floor. The hole appears to widen below and the bottom remains a mystery. Sinkhole dives share many of the dangers common to wrecks and caves and should only be attempted with proper training, experience and equipment.
Nitrox is recommended for dives from 120 to 150 feet and trimix at 180 feet and below.
- Capt. Chad Carney teaches scuba and spearfishing and charters out of St Petersburg. Call 727-423-7775 or e-mail firstname.lastname@example.org.