A mile-long stretch of Sunset Beach and Surfside Beach was closed Sunday after an Orange County Sheriff’s Department helicopter spotted three 10 to 12-foot sharks 150-yards off shore.

“It’s a precaution due to the size of the sharks and potential for aggressive behavior,” Michael Diller, a lifeguard at the nearby Seal Beach, tells the Los Angeles Times.

The sighting comes a week after 52-year-old fitness trainer Maria Korcsmaros was bitten by a shark 15 miles south of Sunset Beach. Shark attacks have also been in the news across the world, including in Western Australia, where a 60-year-old diver and a 29-year-old surfer were both killed in separate fatal attacks last week.

“The evidence, some of it anecdotal, seems to be that there are significantly more sharks off our coastline,” premier of Western Australia Colin Barnett told the Guardian. “There seems to be more large sharks, particularly great whites, and they seem to be closer to the beaches.”

Mr. Barnett's assumption is not wrong.

According to the International Shark Attack File, maintained by the Florida Museum of Natural History since 1958, 2015 saw 98 unprovoked attacks – the highest rate on record, surpassing the previous record set in 2000 with 88 attacks.

Researchers say there are two human-induced contributions to the increased attacks: rising human populations and rising ocean temperatures.

The National Oceanic and Atmospheric Administration (NOAA) reports nine of the 10 years with the warmest ocean temperatures have occurred since 2000. This long-term warming, says researchers, could shift the sharks’ range “as much as 40 miles poleward per decade” as they follow their prey’s migration away from the equator. The warming is certainly from human-caused climate change, say scientists, as 93 percent of greenhouse gas warming is absorbed by the world's oceans.

Also, rising human populations means that there are more swimmers venturing into the sharks’ territory each year.

“Sharks plus humans equals attacks,” Dr. George Burgess, program director for the University of Florida’s Program for Shark Research, told UF News. “As our population continues to rapidly grow and shark populations slowly recover, we’re going to see more interaction. We can and should expect the number of attacks to be higher each year. When we visit the sea, we’re on their turf.”

In fact, Florida Museum of Natural History's shark website argues that given the rising number of humans in the water, the rate of shark attacks is declining.

While the total number of attacks each year has increased, they still aren’t as commonplace as many beachgoers might believe. For example, although 2015 was a record-breaking year in the number of attacks, there were six fatalities worldwide compared to the 11 deaths in 2000.

“Although the headlines say ‘attack,’ these are really more of encounters, they are nonlethal,” Dr. Neil Hammerschlag, director of the Shark Research and Conservation Program at the University of Miami, tells The Monitor in February. “It’s important that we don’t create this hysteria that ‘shark populations are on the rise, attacks are on the rise.’ It’s important to remember that these aren’t mindless killers. They are social animals and ecologically important and their populations are in trouble.”

Some scientists and politicians say sharks face a greater threat to existence than humans.

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An estimated 100 million sharks are killed globally each year, say a team of researchers at Dalhousie University in Canada in a 2013 statistical report. Between 6.4 to 7.9 percent of sharks of all species are killed annually, say the researchers, but no more than 4.9 percent can be killed to maintain population stability. Primarily, sharks die from being caught unintentionally as bycatch or they are killed for their fins to feed a Chinese appetite for shark fin soup.

Oceana reports that for every one human killed by a shark, on average, about 25 million sharks are killed by humans.