Federal wildlife protection programs are helping shark populations to rebound, but they aren't the sole reason for the uptick in encounters between sharks and humans.

The growing human population and increasing use of beaches are major factors too, scientists say.

Recent shark attacks in North Carolina and Florida have made headlines as the summer beach season gets into gear. Such attacks have become more common in recent years. The Florida Museum of Natural History's International Shark Attack File says the number of unprovoked attacks has grown in every decade since the 1970s.

Shark researcher George Burgess, who publishes the file, said this decade is almost certain to set a record for shark attacks.

"The fact of the matter is, while shark populations rebound and hopefully come to where they once were, the human population is rising every year," Burgess said. "We're not rebounding, we're just bounding."

Americans made 2.2 billion visits to beaches in 2010, up from 2 billion in 2001, according to a US army corps of engineers estimate. A spokesman for the American Shore and Beach Preservation Association said the figure is likely to still be rising because of the improving economy.

Populations of some shark species have grown due in part to conservation efforts, such as a 1997 US law that prevents the hunting of great white sharks. Dr. Bob Hueter, director of the Center for Shark Research at Mote Marine Laboratory & Aquarium in Sarasota, Florida, said preservation and management have also helped build populations of species like the sandbar shark and blacktip shark.

The Marine Mammal Protection Act of 1972 also has helped to increase the population of seals, a favorite prey of white sharks. In Massachusetts, the growing number of seals has raised concerns in recent years about the animals attracting sharks to beaches favored by humans.

Hueter said the rebounding white shark population justifies vigilance, but he added that it is presumptive to assume there are more shark attacks because there are more sharks in the ocean.

"Sharks are fairly sophisticated. If they are hunting for seals, they are going to concentrate their efforts near a seal colony," he said. "Are you going to go swimming in a seal colony? Of course not."

There were 72 shark attacks worldwide in 2014, three of them fatal, according to the International Shark Attack File. The deadliest recent year was 2011, when 13 of 79 attacks were fatal.

Greg Skomal, a senior scientist with the Massachusetts Division of Marine Fisheries, said encounters with marine animals such as sharks are inevitable as long as people keep visiting their habitat.