Two teens were recently victims of a shark attack… so we dove deep for more information on this topic.

The attacks occurred just 30 miles up the coast from where a 13-year-old girl was bitten by a shark three days earlier. On the basis of the damage suffered by the teens in North Carolina, shark expert George Burgess says a large tiger or bull shark is most probable to blame. Of course, these two species are often found right along the coast and are known to occasionally bite people, says Burgess, who studies attacks at the Florida Museum of Natural History.

A rising number of countries from South Pacific are passing and enforcing bans on shark fishing, and the fish are showing some localized signs of recovery. Basically the overall conservation picture remains dim, especially with illegal fishing.

On Tuesday, officials continued to patrol the area’s beaches and said any shark acting aggressive, like swimming within 100ft from the shore, would’ve been euthanized. That order prompted criticism from shark experts, who said the shark or sharks involved in the attacks were surely long gone. So a long term trend shows an increase in incidents – individual years have such few shark attacks that short term statistical analysis is dicey.

Experts estimate that around 100 million sharks are killed by people in almost any given year, in a haul that many consider unsustainable and which threatens many species.

Sharks reproduce slowly so they are particularly vulnerable to overfishing. By a huge multiple. As pointed out by the Global Shark Attack File, in 2015, there were 29 unprovoked shark attacks worldwide. For example, last year, the world recorded 72 unprovoked shark attacks, down from 75 in 2013.

Quite a few incidents are provoked attacks in which someone is bitten while spearfishing or while attempting to catch a shark or release it from a line or net. Among unprovoked attacks, the fish are most often confusing people with their normal prey, often due to poor visibility.

Surfers are most often attacked, as they spend long periods of time in the water and often splash around like prey. Did you know that a steadily rising human population is also a big factor? Recent attempts to cull great white sharks to reduce attacks on people in Western Australia have met with sharp criticism from scientists. The jury is still out on whether such attempts will actually make a difference.

Quite a few companies have marketed wetsuits and surfboards designed with patterns said to repel sharks, from killer whales to lionfish. Shark culls performed in Hawaii in the 1950s showed no measurable effect on the rate of shark attacks on people, said Chris Lowe, professor of marine biology at California State University, Long Beach, who analyzed the data taken during those culls.

Whenever in line with an analysis by George Burgess, a shark researcher at the Florida Museum of Natural History and the current keeper of the International Attack File, the total number of shark to human interactions occurring in a given year directly correlates with the interval humans spent in the sea. Therefore, this trend doesn’t have anything to do with the relative deliciousness of American thigh meat.

That simple fact could explain why the number of attacks was on the decline.

While limiting their exposure, Americans have likely spent less time in the water since the recession, writes Burgess. Burgess thinks that over fishing worldwide could also mean there are fewer animals out there mistaking a wet suited human for a savory seal.

Shark safety researcher Christopher Neff suggests avoiding swimming during or after storms, that can make the water cloudy and churn up the bait fish that lead to shark feeding frenzies. However, in addition to swimming near the presence of seals and similar prey species or where fishermen have dumped guts, Neff also suggests avoiding swimming at dawn and dusk, for similar reasons.

Australia, who racked up 14 shark attacks last year, comes in second. Certainly, as pointed out by the File, of the incidents in 2011 involving shark teeth sinking into unwitting human flesh occurred in shallow waters off beaches.

Yet, the United States’ share of incidents was the lowest in over a decade between 2001 and 2011, an average of 59% of confirmed, unprovoked attacks took place in waters.

People must remember that swimming in the ocean is always a wildlife experience, says Burgess. So there’s a reason to avoid known shark nursery grounds.