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Four Shark Blue Hole

Cave Type: Ocean blue hole - fault line cave

Location: Grassy Cays, South Andros Island

Length: 600 m plus

Maximum depth: 100 m plus

Description: Four Shark Cave is an offshore ocean blue hole located inside the barrier reef, along the fault line 5 km northwest of Dolly Cays, South Andros. The entrance is a coral rimmed basin about 10 m deep that opens into one of the largest caverns in the Bahamas. This 70 m long, 20 m wide chamber known as the Kalik Cavern extends to 60 m depth. At the far end of the cavern, a narrow crack at 40 m depth descends into a continuation of the fissure with depths from 50 to 105 m or greater. In the entrance zone, the bottom consists of sand and fine white silt. Strong tidal currents exchange reef water with that from the interior of the cave.

Hydrology: Water column profiles were obtained in rear of the cavern using a Hydrolab Water Quality Analyzer. A diver descended with the Hydrolab from a dome in the ceiling at 9 m depth down to 40 m depth. At this point, the Hydrolab was lower on a line to the cavern floor at 56 m. Salinity increased gradually from 35.9 g/l at the top of the dome to 37.4 at 56 m. The general temperature trend in the water column involved a decrease from 27.6 oC at 9 m to 26.0oC at 56 m. The pH decreased from 9.2 at 9 m to 8.6 at 56 m. Dissolved oxygen decreased from 2.5 mg/l at 9 m to 1.25 at 56 m depth. Thus, deeper waters in the cavern are relatively higher in salinity, while lower in temperature, pH and dissolved oxygen.
In order to observe changes in water entering or exiting the cave over the course of a tidal cycle, a Hydrolab was suspended in the water column 15 m inside the cave and left to record data at one minute intervals for 12 hours (8 PM to 8 AM). Open ocean water entering the cave on a raising tide was compared with water flowing out of the cave at the end of the tidal cycle. Ocean water was relatively warmer (31.0 vs. 26.9oC), lower salinity (35.8 vs. 36.5 g/l), lower pH (9.3 vs. 8.9) and higher dissolved oxygen (4.1 vs. 1.0 mg/l). The characteristics of the water exiting the cave at the end of the tidal cycle most closely matched those of water from 14 to 20 m depth within the cave water column. This indicates that even in the cavern zone, cave water is not completely flushed during a typical tidal cycle. Deeper water from the bottom of the cavern and from sections of the fissure beyond the restriction, must consequently have a long residence time within the cave.

Diving Mode: Standard cave scuba

History: First explored by Kevin and Travis Mack, Rob Palmer, Dan Malone, Murray Bilby and Michael Thomas in summer 1996.

Fauna: Due to the presence of strong tidal currents, numerous species of filtering feed invertebrates are characteristically found near the cave's entrance. Encrusting sponges and hydroids are present on the walls at the entrance and also around the crack at rear of the cavern where current velocity increases due to the constricted nature of the passage. Divers exploring the fissure at 70 m depth reported observing numerous troglobitic crustaceans within the cave water column, but, unfortunately, specimens were not collected (Dan Malone, personal communication).  Ostracods, cumaceans, copepods, larval shrimp and nebaliaceans were collected and are currently being identified.

Conservation status: This cave, along with all other blue holes in the South Andros "String of Pearls", has currently been proposed to the Bahamas Ministry of Agriculture and Fisheries as a marine reserve.

References:

  • Palmer, Rob. 1997. Deep into Blue Holes. Media Publishing Ltd., Nassau, Bahamas, 188 pages, 22 figures, 13 maps, 24 color plates.
  • Palmer, R.J., J.M.C. Hutchinson, S.J. Schwabe, and F.F. Whitaker. 1998. Inventory of blue hole sites explored or visited on South Andros Island, Bahamas. Cave and Karst Science, 25(2):97-102, 8 maps.

Contributor: Brian Kakuk, Caribbean Marine Research Center, Bahamas


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