PALM BEACH, Fla. - We see a lot of sharks in the water this time of year. spinners, blacktips, bulls, sandbar sharks.....but what's the difference? Being a surfer and seeing these sharks first hand, has me wondering what kind of sharks I'm seeing swimming below me. Surfers call most of the sharks we see spinners, due to the way they jump out of the water and rapidly spin around. Spinners also have black tips on their fins, which leads to the confusion with the blacktip shark. I've been asked many times "what's the difference between a spinner shark and a black tip shark?"
I contacted the leading shark expert in Florida, Grant Gilmore, and asked him to explain what the difference was.
Spinner Sharks vs Blacktip Shark
(Spinner off Juno Pier, Photo: Nadja Neptune)
"Spinner sharks are easily identified by the jet black pigment on the dorsal surface of the pectoral fin and the somewhat posterior position of the dorsal fin relative to the pectorals. This separates it from the blacktip shark, that also jumps out of the water and spins, therefore, often mistaken for a spinner shark. The spinner also has black pigment on its anal fin that the blacktip does not have. Both sharks are common, though the blacktip is more abundant than the spinners inshore. Surfers appear to call both species "spinners" more often based on their behavior, but shark fishery captures from the beach catch more blacktips than spinners."
Spinner Shark Identification Video by Mark Sampson :
Blacktip Identification Video by Mark Sampson:
(Videos by Mark Sampson)
"Spinners tend to be more abundant some distance out from the beach, blacktips along the beach. Both reach a max size of around seven feet. The black pigment on the blacktip fins is more diffuse and limited to the second dorsal, lower caudal lobe, pelvics and underside of the pectorals. The blacktip snout is more rounded than the spinner and its dorsal fin is larger and more forward, just over the trailing tips of the pectoral."
Bull Sharks vs Sandbar Sharks
(Bull Shark, Photo: Wikipedia)
"I see more and more accounts of "bull" shark sightings that are actually sandbars. Sandbar sharks have very large triangular dorsals, bulls much smaller angled dorsals. Both have rounded snouts. The sandbars are one of the most abundant local sharks in the surf and shallow continental shelf. The are much more heavier than blacktips for the same length fish, though not as bulky as bull sharks. Sandbars have been called "brown" or sand sharks in the past. The accepted common name is sandbar. They were migrating by with the blacktips."
Sandbar shark identification video by Mark Sampson:
"Checking on historical records of migratory times and found that the migration was in the window observed previously, though it can very by several weeks between years depending on weather conditions. Their migratory rate can take them from Florida to Cape Hatteras, and possibly Chesapeake Bay in 7-10 days. Since conditions were so bad father north, I did not blame them for taking their time going further north. They may be able to sense distant meteorological conditions over many miles, as the sharks of Charlotte Harbor likely did with Hurricane Charlie in 2004. The sharks left and the sand sea-trout had the largest spawning party for the entire year. Go figure!"
Sharks vs Humans
While most of the attacks on the east coast of Florida are from Spinners, Black Tips, and Sandbar sharks...Gilmore says humans are not targeted, they are just aggressive eaters and hands and feet kicking from a surf board may resemble their food.
"The four sharks, Bull, Sandbar, Blacktip and Spinner are all aggressive when hungry, the latter two species swimming rapidly in the surf or just off the beaches, and are always around. However, they are small sharks and give way to humans in the water. One day I watched a young bather waving to the NASA helicopter as we flew over at the KSC. She did not know it but she had mullet swimming around her legs attempting to flee several small blacktip sharks trying to catch them. She was completely surrounded, apparently did not know it, and the sharks had absolutely no interest in her. I have also body surfed with blacktips in clear water with no risk. "
Bull sharks are a different story, however they are not common very close to shore, unless you are near an inlet or estuary. Gilmore explains the bull's behavior:
"Bulls are casual swimmers coasting along further offshore, but can be within 300 yards of shore. Bulls have a larger range of dietary preferences and attack larger prey, like bottlenose dolphins and sea turtles, but most often fish. Since their diet
consists of larger prey, they are aggressive with larger prey and humans can fall into that category if they tend to resemble something the bull shark has eaten before. .... Large mature bulls can be aggressive from the standpoint of going after larger prey. "
The most active time is early morning and late evening, experts advise not to go in the ocean at that time. Tough for the dawn patrolling surfers that want to get a sesh in before work. The best advise is always surf/swim with a friend. In cast you do get in trouble, there will be someone there to help, or get help.
If you want more information on our local sharks population, Gilmore recommends the new book on "Sharks of North America" by Jose Castro, 2011 Cambridge Press.
Gilmore says "it is very good in giving migratory habits and biology of these sharks as well as outstanding paintings by Diane Peebles. Well worth the investiment if you are really interested in sharks and likely to be a classic hard to get in the future."