Expert disagrees with Laird Hamilton’s comments about sharks and women menstruating

It’s been a week since Laird Hamilton chatted with TMZ Sports and revealed his thoughts on why there’s such a shark craze in Southern California right now.

As a refresher, this is what Hamilton had to say: “The most common reason to be bitten is a woman with her period, which people don’t even think about that. Obviously if a woman has her period, there’s a certain amount of blood in the water.”

While Hamilton is one of the most highly-respected watermen on the planet, we wanted to dig deeper and see if there was any scientific basis for this thinking.

We spoke to Christopher G. Lowe, Ph.D. professor of Marine Biology at California State University, Long Beach who is also the Director of the Cal State Long Beach Shark Lab to get some answers.

A great white shark. Photo: Courtesy of Elias Levy/Flickr

Are sharks so attracted to blood that a woman on her period is in danger?

I’ve addressed this same question probably for the last four summers. Unfortunately it comes as a bit of a byproduct from the way we’ve educated people on how good sharks can smell in the water. That old saying a shark can detect a drop of blood from a mile away, I think that’s this myth that people have.

The first part of this is the idea that a drop of blood can be detected is pretty different than a drop of blood drawing a shark into a feeding frenzy. Being able to detect something in the water at a very low concentration is very different from changing the shark’s behavior.

So what about Laird Hamilton’s comments then?

He’s a great waterman; a phenomenal surfer. My job isn’t to criticize anybody, but to let people know here’s what we know science-wise.

The thing that Laird said is not untrue in that, yes, sharks can detect blood. But it’s how it affects their behavior. He said that women are more likely to be bitten, which isn’t true. It’s actually the opposite — more men are bitten than women.

Granted, part of that is because more men are in the water, but the argument I use is not just about sharks being able to detect the blood, but it’s about the volume of blood.

So that’s not enough blood to send a shark into a frenzy?

There are more kids swimming along the beaches with skinned up knees, surfers with scrapes and cuts, they’re not women and they’re probably bleeding far more than any woman would who is menstruating. It’s crazy to say that women are more susceptible to be bitten by sharks because of that.

The part that we really have to get back to is, what changes shark behavior? The example I’ve used is we’ve gone out and tried to attract sharks so we can tag them. I’ve dumped 30 gallons of cow and pig blood into the water, and still can’t get sharks to come to the boat.

We’ve got to get past this fallacy of if you’re in the water and a shark is nearby it will attack you. That’s just not true. And also if you’re in the water and you’re bleeding, a shark will attack you — that’s not necessarily true either.

It takes more than that to change the shark’s behavior. The whole idea of a woman on her period being more susceptible to being bitten by a shark because she might leak a little tiny bit of blood just isn’t true.

Are sharks even attracted to human blood then?

Fish blood has different amino acids than human blood. It’s like us smelling barbecue. If you’ve had barbecue, that odor is associated with eating barbecue. The next time you smell it, automatically your stomach starts to rumble, you salivate a little bit, you may want to investigate and move in the direction of where that odor is coming from to see if there’s any barbecue for you.

If there was another thing burning, maybe something like hair, you may be able to smell that, but you may not know what it is and you may not want to go eat it either.

So they may be able to detect it, but they may not necessarily associate it with something they’ve eaten before. Obviously most sharks eat fish, so once they’ve eaten the fish and detect the blood, they then know what that smell means.

There are very few sharks who have eaten people. So even if they detect human blood, they may not associate that with something that they’ve normally eaten.

Do we know what sends sharks into a feeding frenzy?

There is a lot more to it than just blood going into the water and sharks going crazy. That’s the part that we have to get beyond. It’s educating the public about those sorts of things that we as scientists use to make it relatable about how sensitive sharks can smell. We’re learning, but we still don’t really know why sharks bite people.

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