Diving with great hammerheads in Bimini
In March 2019, I had the privilege of SCUBA diving with four great hammerhead sharks off the coast of Bimini. Thank you to Neil Watson’s Bimini Scuba Center for the truly unforgettable day!
The great hammerhead (Sphyrna mokarran) is the largest species of shark in the family Sphyrnidae. They are best known for their relatively straight, square cephalofoil (“hammer head”) and distinctive tall, curved first dorsal fin. They can reach a maximum length of 18-20 feet.
The unique wide-set eyes of sharks in the hammerhead family give them better vision than most other sharks. They also have special sensory organs called “ampullae of Lorenzini”, small pores filled with gel that detect electrical fields in other animals. In great hammerheads, the ampullae are distributed across their wide cephalofoil (head), allowing them to find prey like stingrays that often bury themselves in the sand.
While great hammerheads were once found in tropical oceans around the world, this species is currently endangered. Great hammerhead populations are declining throughout their range, primarily due to fishing and harvesting of their fins.
Luckily, some governments are taking action to protect great hammerheads and other threatened shark species. The Bahamas National Shark Sanctuary was created in 2011, where shark fishing and trade of shark products is prohibited and more than 40 shark species are protected within 654,715 square kilometers of ocean. The Bahamas is sometimes referred to as the “Shark Capital of the World”, and its islands and waters have become a popular destination for tourists from all over the world to snorkel and dive with sharks. Shark related eco-tourism has contributed more than $800 million US dollars to the Bahamas GDP in the past 20 years (source: Atlas of Marine Protection).
In addition to the beautiful great hammerhead sharks, Bimini is home to many, many nurse sharks (Ginglymostoma cirratum). Unlike most other shark species, nurse sharks do not have to actively swim to pump water over their gills and breathe, so they spend most of their time as sedentary bottom-dwellers. As largely nocturnal hunters, they patrol the reefs and suction-feeding for benthic fish and invertebrates.
Fortunately, robust populations of this species remain in many parts of its range. Nurse sharks are an important species for shark research, because they are able to tolerate capture, handling, and tagging without experiencing a severe stress response.
Both nurse sharks and great hammerheads often host remoras, ray-finned fishes in the family Echeneidae with a sucker-like organ that allows them to firmly attach to the skin of larger marine animals (see photos below). Growing up to 2.5 feet long, remoras remove ectoparasites and loose skin from their hosts, which include whales, sea turtles, sharks, and rays.