By Tom Baird
Since sharks range widely searching for prey, at any one time we might find different species of sharks entering St. Joseph Bay following schools of fish or feeding on the rich invertebrate fauna of the bay. However, according to researchers at the Apalachicola National Estuarine Research Reserve (ANERR), there are four species of shark that can regularly be found in St. Joseph Bay. They are the Blacktip Shark (Carcharhinus linbatus), Nurse Shark (Ginglymostoma cirratum), Atlantic Sharpnose Shark (Rhizoprionodon terraenovae), and the Bull Shark (Carcharhinus leucas). None of these is a surprising resident or visitor because all prefer warm shallow coastal waters, especially bays, estuaries, lagoons and river mouths.
The one most likely to be seen by snorkelers and kayakers on the bay is the nurse shark. Nurse sharks can be seen resting on the bottom or feeding on various bottom dwelling mollusks like clams or scallops, crustaceans such as blue crabs, and stingrays. They will also eat coral, algae, and the occasional slow fish. They are generally nocturnal feeders and rest on the bottom during the day. Most sharks need to constantly swim in order to aerate their gills. Nurse sharks are able to pump water over their gills enabling them to remain motionless on the bottom.
Nurse sharks are a fairly docile shark and divers often pull the tail of a nurse shark resting on the bottom, or hitch a ride on their back. They are not known to be aggressive, but will bite if provoked. Their relatively docile nature is fortunate since nurse sharks can reach lengths of 14 feet and weigh over 700 pounds, although the average size is around 7 to 9 feet and 150 to 250 pounds. Nurse sharks have somewhat variable coloration; most are brown or grey-brown, but some are tan or greyish tan and others greyish pink.
Of the four common shark species in the bay, the Bull Shark is no surprise either. Bull Sharks can be found worldwide in warm shallow water along coasts, and range from Massachusetts to Brazil in our part of the world. Bull sharks will even travel up rivers and have been sighted in both the Mississippi and Ohio Rivers. This is a large, stout-bodied shark that can range up to 11 feet in length and 690 pounds, although the average size is around 8 feet long and 290 pounds. Unlike the nurse shark, bull sharks are aggressive and account for most human attacks worldwide, mainly because their preference for warm, shallow habitats puts them in close contact with humans. Usually these are cases of mistaken identity in which a flashing human leg in murky water may resemble a prey species. Nevertheless, these shark bites are rare. Keep in mind that, according to the National Weather Service, your chances of being struck by lightning in a given year are 1 in 750,000, while your odds of being killed by a shark are 1 in 3,700,000. According to the University of Florida’s International Shark Attack File, your chances of even being attacked by a shark are 1 in 11,500,000. You have a greater chance of dying from the flu – 1 in 63. You are more likely to be injured driving to the beach than you are from a shark encounter once you get there.
The Atlantic Sharpnose Shark is our little neighborhood shark, having the smallest range of any of the four common sharks in the bay. They are found only from waters off New Brunswick and Nova Scotia in Canada south to the Yucatan coast in Mexico. They are also rarely found deeper than 30 feet, and are common around Florida and in the Florida Keys. The Atlantic Sharpnose is a small shark averaging about 3 feet, although maximum size goes up to almost 4 feet. Besides fish, this shark will also eat shrimp, crabs and mollusks. It is a common resident of the surf zone and can tolerate lower salinity estuarine conditions, but does not travel up rivers like the bull shark.
Although Blacktip Sharks have a worldwide distribution in warm seas, along the Atlantic coast, Blacktip Sharks range from New England to Florida and around the Gulf to Mexico. They are a very common inshore species around Florida and in the Gulf of Mexico, especially in the spring and summer. As the name implies, this shark has an unmistakable black patch on its dorsal fin, as well as black on the edges of the caudal or tail fin and on the pectoral and pelvic fins. According to the National Marine Fisheries Service, the majority of shark bites in Florida are likely attributable to this species, although there has never been a fatal attack in this region, and this shark is usually considered wary of humans, even somewhat timid. Blacktips reach a maximum length of about 6 feet, but the average size is slightly less than 5 feet.
Sharks in general possess some of the most amazing adaptations of any living creature. They have lateral line receptors that can sense movement in the water, and electroreceptors that detect changes in electrical fields due to the presence of prey. They have highly sensitive smell receptors, and even have the ability to replace teeth throughout their life. If you catch a shark while fishing, gently release the animal. They are important components of the marine food web and researchers are regularly documenting disruptions to marine ecosystems that have resulted from the overfishing of sharks. These predators are necessary to keep our bay healthy and productive, and deserve our respect rather than fear.
Tom Baird has been a fisheries biologist, high school and community college teacher (oceanography and microbiology), director of a science and environmental center, teacher of science and principal in Pinellas County as well as an educational consultant. He retired from the Florida Department of Education and he and his wife divide their time between Tallahassee and Cape San Blas.