The target that day was cobia. But shortly after departing Fort Pierce Inlet, anglers Carter Andrews and Capt. Ryan Weir found themselves in the middle of a school of sharks.

Airborne sharks.

Jumping, flying, twisting sharks.

"It was incredible," said Weir, who captured the acrobatic display on his cell phone March 14 of what he called "hundreds" of spinner sharks. "We were about a mile off the beach in about 30 feet of water."

At one point, Weir thought a shark might actually fly itself right into the boat.

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Weir, of Chuluota, fishes regularly with Andrews, of Vero Beach, serving often as a camera boat operator for Andrews' television shows. Andrews hosts The Obsession of Carter Andrews airing weekly on Outdoor Channel and the newly launched show Legendary Catch, which began airing last week on Nat Geo channel.

Weir said the day they encountered the spinner sharks, they were trying to find cobia, but came up empty. They decided to see if they could find some tarpon when they saw the spinner sharks on their way to the Boils, a popular fishing spot named for the way water from the nearby St. Lucie nuclear power plant's outflow pipe "boils" to the surface.

More:Sharks are much closer than you may think, especially January through March

"The school was massive, and you really can't tell that from the video," Weir said, "but I'll bet it was over an acre in size."

An acre is 43,560 square feet. There were at least 10 simultaneously airborne sharks in one's field of vision, Weir said.

Truth be told, the sharks could have been blacktip sharks. Both jump into the air when they are feeding on small bait fish. Both are about the same size. Both can have small black coloration on the tips of their pectoral fins. Both are frequently mistaken for each other.

But these sharks certainly could twirl.

Weir shared the video clips on his Instagram page, @captryan461. Weir and Andrews tried casting topwater plugs at the sharks to see if they could get one to bite. None would that day. (However, Weir reported Andrews encountered a similar school off Fort Pierce this week, and he did hook up with a few using a Yo-Zuri Mag Darter plug).

Spinner sharks and blacktip sharks are found along Florida's coastline each winter and spring traveling in large migrating schools. Shark researchers believe by the end of March, the schools are following food sources like bluefish, Spanish mackerel, schools of menhaden and sardines as they push back to the north.

They are not usually implicated in bites on humans. In fact, the International Shark Attack File attributes only 16 bites to spinner sharks, and none fatal. They are likely to be found in the surf zone where surfers and beachgoers can be found recreating in the water.

More:Martin County surfer snagged by shark at Hobe Sound Beach

Spinner sharks reach sexual maturity when males are 4-7 years old and females are 7-8 years old, and they reproduce on a 2-year cycle. They carry their young for 11-15 months and have a litter of six to 10 pups born live at a length of about 22-25 inches.

This year, weather conditions and the presence of bait fish and other food fish have produced many days where the spinner sharks' acrobatic feats have been visible by beachgoers looking offshore, or boaters searching for tarpon, cobia, permit or big jack crevalles.

Why they jump

Why in fact do spinner sharks jump? Well, that's kind of a hard question to answer, says Stephen Kajiura, professor at Florida Atlantic University and director of FAU's Elasmobranch Laboratory.

"Why the sharks jump, we don’t know for sure," he wrote in an email. "There are three different hypotheses have been forwarded to explain this behavior. One suggests that they jump and spin to dislodge parasites and maybe remoras. Another hypothesis is that they jump as a form of social signaling — to indicate that they are there and to provide some sort of group cohesion. The final hypothesis that has been proposed is the the jumps are the result of them rushing to the surface to capture prey, and jumping into the air."

Similar to how great white sharks jump out of the water when they are chasing after seals in South Africa, Kajiura suggested. However, he added, none of these hypothesis have been rigorously tested, so the answer is unknown.

"What is particular interesting is that when one jumps, others often jump as well," he wrote. "That might lead to the social signaling idea. The parasite removal is the simplest explanation and we often see them with remoras so that might be another factor."

Kajiura confirmed the sharks are heading north right now.

"We have seen fewer sharks recently (in his weekly aerial shark migration surveys) so I think that they are moving north." he wrote. "It is about the right time of year to do it and water temperatures were generally warm this year after a cold January, so there is no strong motivation for them to stay here."

Unless it is simply to jump.

Spinner sharks

Length: 5-9 feet, but average 4-5 feet

Average weight: 120 pounds

Range: Worldwide throughout tropical and temperate seas

Food: Small bait fishes, bluefish, mackerel, squid, rays and sometimes smaller sharks.

Birth: Live, about 6-10 pups per birth

Migration: Along Florida's East Coast each winter and spring

Fishing regulations: In Florida, anglers may keep one spinner shark per day measuring a minimum of 54 inches to the fork of the tail. For complete shark fishing regulations go to https://myfwc.com/fishing/saltwater/recreational/sharks/.

Sources: MyFWC.com, Shark Info, Sharks of the Shallows by Jeffrey C. Carrier