The mating actually happens around this time of year, usually between March and June. They are sometimes confused with spinner sharks because both frequently leap and swim out of the water when hunting fish. As the NOAA explains, the big difference is the anal fin on a blacktip shark is white, while a spinner shark's anal fin has a black tip. The NOAA says blacktip sharks can grow to up to six feet long. The oldest known one was 15.5 years old. Atlantic blacktip sharks are found year-round in the Gulf of Mexico. And, in the Atlantic Ocean, they're usually found off the coast of Virginia to Florida, though they have reportedly migrated as far north as Cape Cod in the past, according to the NOAA.