I was watching National Geographic Channel or Discovery, on Saturday night and there was a program on shark attack victims. They had all survived and were telling their story. Some of them were surfers, some were abalone divers and some swimmers. It was a run of the mill shark attack documentary, they had marine biologists on discussing shark behavior, commenting on each attack…the narrator of the show kept saying, "…we still do not know why sharks attack humans…"
This sentence perplexes me. Why do biologists - people who ought to be in the know - wonder why great whites attack humans?
The question itself infers that great whites and other sharks have some discernment in what they are going to eat. Sharks, especially great whites feed on seals and sea lions all the time. They see a human in the water they are going to go and investigate and maybe take a bite to test … or they are going to full on attack. I don’t see a question here…Wondering why great whites attack is like wondering why dogs fetch or why many predatory land mammals give chase if something is running from it. It’s a basic instinct.
Sharks attack because we are their food if they choose to eat us. They don’t care if we come from a boat are wearing a wetsuit and have an air tank strapped to out back. It doesn’t matter…
Do marine biologists really think sharks have some discretion in attacking us because we are human? I would think that if we enter the dinner table of a shark that we are fair game to eat. No?
The idea is that scientist come up with various hypotheses that are testable. Throwing up their hands and saying “it’s just what sharks do” wouldn’t be good science. The idea that a Great White attacks because it mistakes a human for its natural prey or because it’s simply interested in taking a sample is a hypothesis. Some scientist might agree and others might think the shark attacks for other reasons.
I’ve just started the Devil’s Teeth by Susan Casey. The title refers to the Farallon Islands, probably the best place to study white sharks (apparently, scientists don’t like the great part), as the area is protected, as opposed to the other GWS hotspots in S Africa, Oz, and Mexico. So far, it seems we don’t know a whole lot about them.
Well, sharks don’t attack just anything in the water. A number of interesting tests have been undertaken by the PRBO research group and others at Año Nuevo, trying out surfboards with different combinations of colors and surfaces (also squares of carpet) to see what will get attacked and what won’t. I’ll try to dig out any literature I can find on it later.
It’s a really difficult question to get at: what motivates a behavior. The first step is to see what parameters that behavior has - in this case, can we identify what characteristics a target has that a shark will attack? We don’t even have a complete answer to that question yet, although I recall hearing some preliminary results from the experiment mentioned above, I don’t think they’ve done exhaustive testing.
That question becomes more difficult when you can’t keep that animal in captivity - IIRC, the Monterey Bay Aquarium still holds the record for keeping a White Shark, for less than a year still. So no easy experimental program can be undertaken. It has to be an opportunistic program undertaken in conjunction with other research (in this case, PRBO also tags sharks off Año Nuevo.)
We know that sharks do occasionally attack humans. We know they don’t always attack humans in the water, and we know that when they do attack, the humans often survive because the shark does not press the attack. We also know they attack most frequently in areas where other prey may be found - Elephant seal youths, in the case of the “Red Triangle” here off California. The ‘mistaken for seals’ hypothesis fits these conditions pretty well, but it isn’t complete.
What we don’t know are what factors lead up to the shark attack that are different from all the cases in which a shark doesn’t attack. That’s going to take a lot of time and arguments to resolve, and it’s entirely possible that the ‘mistaken for seals’ hypothesis will be overthrown in the process (although I’m personally in favor of it.)
ETA: I hear Devil’s Teeth is a good book, but sometime ask me about the effect that it had on shark research - which wasn’t entirely good.
I agree to an extent. I think "mistaken" for a seal is a misnomer. Sharks engage prey out of instinct…if you threw a fleshy piece of non-discript material and thrashed it around it may get attacked. Humans swimming are prey…I don’t think sharks are differenciating species. That is conjecture of course. It’s interesting to postulate about instinct because it is something that is housed in the most primitive regions of the brain.
I think a shark attacks when several conditions are met, like:
-oject is thrashing (attack)
-object is seal-sized (attack)
-object is beeding (attack)
-object is lighand dark-colored (attack)
Explains why surfers are popular: they look like seals, and are big enough for a significant snack!
I’m not sure that I’d oppose ‘instinct’ and ‘differenciating species’ quite that much; I don’t see any bright line between completely instinctive species and completely rational ones (in fact, I don’t know of any examples of the latter).
I suppose you could argue about whether ‘mistaken for a seal’ is or isn’t appropriate shorthand for ‘appeared to a shark’s senses in a way that triggered an attack behavior that is typically triggered by seals but not typically triggered by more clearly human stimuli’, but it’s fine with me, assuming the context is ‘how can we prevent shark attacks’ rather than ‘discussion of rationality in animal behavior’
To tell if sharks like surfers more than swimmers you’d have to factor in the amount of time that surfers are in the water (a lot), and the depth at which a surfer is located relative to a swimmer (deeper) to figure out if surfers actually are more popular than swimmers. I don’t know that that has been convincingly done.
At crowded beaches there are a lot of swimmers. However, at pretty much every surfable break there are a couple guys out most of the day - very noticible coverage if you drive down the coastal highways in California.
I’ve also heard it argued by a fellow oceanographer, although not a shark researcher, that sharks are like babies; they investigate things by putting the thing in their mouth.
While the answers here are insightful, they seem a bit tangential to the primary reason the narrator says, “We still don’t know why sharks attack humans.” He says it for drama. It’s a TV show, not a scientific journal article, and they’ve got to keep people interested. Imagine if the narration went like this:
“Sharks are predators, and they are often looking for potential meals. Humans sometimes look like potential meals, so sharks sometimes attack them. We don’t know exactly what a human has to be doing to look more or less like a meal, but it’s probably best just to stay clear of shark infested waters until we do know.”
The show would last 17 seconds. They need to fill an hour and then get you coming back for the next episode. So, they cast a mysterious cloud over a rather straightforward situation. Par for the course for television science.
I’ve read that sharks are such efficient predators that if they attacked out of hunger there would hardly ever be anything left of the victim. So is it a territorial aggression thing? Or do they take a bite or two and think, “That’s not a seal; that tastes like shit!”? Some other reason?
I’ve heard that that is a theory as to what’s going on. It explains why they do things like take a single bite and swim off. Great Whites as I recall tend to attack from below, swimming at high speed and just gulping you down in one bite; so the possibility that they are thinking “Ewww, that thing tasted nasty” won’t do you much good.
