Today marks the first day of summer -- which means it's time for sun, sand and surf. But beachgoers still need to be mindful of the fourth "s" -- sharks.Each year there are anywhere between 70 to 100 shark attacks worldwide, resulting in about five to 15 deaths, according to the Florida Museum of Natural History at the University of Florida.The most unprovoked shark attacks last year were in the U.S., the museum said. Within the U.S., most shark attacks occur in Florida.Here are some tips for how to stay safe according to former Green Beret and survival expert Terry Schappert.Reuters via Newscom, FILEWarning signs are placed along the beach to warn swimmers and surfers of recent shark sightings in San Clemente, Calif., May 23, 2017.Stay calmIf you see a shark, don't thrash or scream, Schappert told ABC News in 2015. Just turn around, get out of the water and tell everyone else to get out, he said.Sharks pick up vibrations and smells, but they can't see you most of the time, Schappert said."The more you flail around ... [the sharks] are very attracted to that," Schappert said.Have a planEvery beach-goer should have an evacuation plan, which includes knowing where the closest hospital is, Schappert said."Just think in your head, what would happen ... if someone you love just got bit? What now?" he said. "Don't be paranoid, but have a procedure. Think about how you'd get out of the water, then think about ... the chain of what would happen next.""Try not to freak out," Schappert added. "But know it's a possibility."STOCK PHOTO/ShutterstockA great white shark is seen here in this undated stock photo.Know first-aidMost shark bites are on the limbs, according to Schappert, and when a shark's mouth hits a swimmer's arm or leg, "it's bound to sever an artery.""Shark bites are not smooth -- they're jagged -- which makes the wound worse," he said. And the more jagged the wound, the more it will bleed, so it's important to know first-aid."The best thing you can do for that person is to stop the bleeding," Schappert said, which, if the victim is bit on a limb, means applying a tourniquet.STOCK PHOTO/Getty ImagesTwo male great white sharks swim off of Isla de Guadalupe, Mexico in this undated stock photo.(MORE:Surfer bitten by shark, seriously injured: Reports)(MORE:Newlywed shares details of terrifying shark attack on final day of her honeymoon)(MORE:Hawaii man suffers serious injuries in shark attack)Schappert took ABC News' Matt Gutman swimming in shark-infested waters near the Bahamas in 2014.To properly learn how to fend off sharks, Gutman pulled on 15 pounds of chain mail armour, and then put clothes on top to simulate real people’s finding themselves stuck in shark-infested waters after a plane or a boat crash.Gutman and Schappert then did what experts say not to do: flapping around in waters where sharks were feeding, wearing regular clothing.While they were in the water, Schappert's advice to Gutman was to:Slow down your movementsFast movements give off the signal of prey, he said. Also conserving energy is key to survival in the above scenario.Team upIf there are two people in the water, Schappert recommended treading water back to back to limit the spheres of control by half, to 180 degrees each.Fight backIf the sharks begin attacking, fight them off, Schappert said.He recommended striking the sharks using quick, downward punching motions."All you can do is fight and let them know, 'I am not going down easy,'" Schappert told Gutman.