When someone gets bitten by a shark — as happened to one man on Sunday in Del Mar — it's standard policy to put up signs such as those now standing in the sand, warning visitors to stay out of the water for two days due to a recent shark incident — but there's no scientific reason for that timeframe.
Now, local shark experts are trying to use DNA samples to figure out if they can still detect the presence of the shark who bit the man Sunday morning near 17th Street, and for how long.
"This has never been done before," said Zach Merson, a Shark Lab Field Technician at California State University Long Beach.
On Monday morning, Merson hopped on a boat with lifeguards and headed out about 100 yards offshore to the spot where just one day before a man was bitten several times during a swim training.
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"We were able to recover the wetsuit from the victim and take some swabs along the bite marks to recover DNA," Merson said. "At the same time, we’re taking water samples right off the beach here to see if we can recover white shark DNA as well, just from the environment, and see if we can identify how long this individual shark is remaining in the area."
Merson said Del Mar beach is a nursery habitat for juvenile white sharks, so they tend to gather there for long periods of time. Since 2020, they’ve tagged about 60 juvenile white sharks in this area and about four of those sharks were detected around the time of Sunday's incident.
At its height, Del Mar has had up to a dozen or more sharks here at once, according to Merson.
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"We’re trying to understand more about this individual that was involved, was it part of this aggregation [of sharks] or was it passing through? We’re hoping to use these new genetic technologies to answer some of those questions," Merson said.
Merson says it’ll probably take about a month to determine if they can actually detect white shark DNA in the water. Linking that specific shark will take even longer, as they need enough DNA to identify that specific shark.
Again, this is something entirely new they're trying.
What's the likelihood you'll encounter a shark?
Merson says the high amount of sharks in the water doesn't directly mean there's a high risk of a shark encounter.
"There are sharks here every single day. We’re monitoring them through tagging and tracking and they’re here every day, and the rate of incidents with people is actually no higher at these aggregation sites than it is at non-aggregation sites. So despite there being a lot of sharks, there’s not necessarily an increased risk for people," Merson said.
Why would a juvenile white shark bite a human?
Juvenile white sharks primarily eat things like stingrays, croakers, flat fish, all small creatures that live on the bottom of the seafloor. For them to target something that might be a seal or sea lion-shaped is an uncommon occurrence (like a human), Merson told NBC 7.
"It’s possible that it was an incidence of curiosity. Sharks don’t have hands like we do, so when they encounter unknown objects in their territory, they have to investigate using their mouth, Merson said. So we see them occasionally bite things like kelp and buoys, and we think that’s just some investigative behavior. And unfortunately, an 8 or 9 foot shark taking an investigative bite can be of medical significance to a human.
Despite the incident, scientists are not seeing as many as they have in past years in the area. So it's interesting that the bites happened during a kind of lull in shark activity, Merson said.
