Tuna use sharks as back scratchers despite risk of being eaten | Hacker News Reader

Tuna use sharks as back scratchers despite risk of being eaten

newscientist.com

125 pointsrntn46 comments

A tuna is a seriously fast fish. Note that they rub at the back end of the shark, which is the obvious place to go. If the shark gets annoyed the tuna can get away rapidly and get a very decent head start before the shark has turned and got going.

The sharks are probably not bothered about being used for grooming because it is reassuring to have your lunch check in and say hi occasionally.

6,000 camera deployments of two to three hours each. 117,000 individuals seen from 261 species. 106 rubbing behaviour samples spotted. The article doesn't quite get the rest of the stats sorted out, giving two percentages. Let's say there were roughly 50 tuna on shark rubbing sessions.

Some tuna are nails and probably impressing the girly tuna!

I don’t know that adult tuna are at much risk from these sharks. Not only are the tuna much faster, but both species are predictors of roughly the same weight with the sharks tending to be smaller and both preferring to hunt smaller fish.

Younger or weak specimens could be, but yellowfin tuna presumably also occasionally chow down on significantly smaller sharks.

Tuna, Turnips, Trek

Maybe the tuna have a way of knowing whether the sharks they use are hungry. Maybe they choose ones which have eaten recently.

"Jaws just ate Freddy. Sucks to be him, but hey, time for a massage!"

If you have the opportunity I strongly recommend visiting the Tuna tank at the Monterey Bay Aquarium during a feeding. Watching a fish the size of a VW Beetle swim 30 kilometers an hour is incredible.

Many moons ago I lived in Cyprus and rather enjoyed windsurfing. I recall a rather lovely session off Evdhimou beach in around 1986ish. The wind was 4-6 and nearly directly onshore, surf about 3 foot, so ideal conditions for seriously fast blasts for miles before a gybe and then more of the same. I was sailing a Fanatic Bee - semi sinker and a 5.5m2 sail.

I was doing a broad reach at full belt, bouncing over wave peaks, spray everywhere. That beach is very shallow - 1.5m (5') for about 1/2 mile or more and it is also basically quite flat. That means that waves are quite stable when you get there.

I came in from around 2 miles out. I'm hooked in, poised over the water about 18" from my bum doing around 20 knots. I'm perfectly balancing a shit load of forces and feeling absolutely invincible. I then see a dorsal fin rise up out of the water behind me and I came close to voiding my bowels. The Med doesn't have many sharks but there are some. Great whites turn up from time to time.

It was a porpoise.

I ran for around a mile with several porpoises bouncing around in my wake. I would twitch my board and they responded and pissed about in my tiny wake. They would probably prefer a bigger wake to play in but I was the best offer at the time.

There's all sorts of weird relationships between sharks and other fish. Like the fish that live off by performing dentistry for sharks inside their mouths.

https://www.youtube.com/watch?v=V5EszU8yuA8

One of the fish in the piccy in the article looks like a remora - not a dentist, more a general hygienist.

Amazing! The evolutionary pathway of the sharks that didn't chomp and the Cleaner Wrasse that had the guts (or the lack of flight response?) to go near a sharks mouth is astonishing.

There's also a type of shrimp that cleans even human teeth. I first saw it on a dive where our guide casually removed her regulator and they approached quickly. Here's how it looks (not my video):

https://youtu.be/RVNh0liyei8

If this seems strange, remember that tuna have no arms. How else would they scratch themselves?

Seabed, rocks etc.

Ok but that’s far away. What’s next, not carrying all the groceries in one trip?

That's why they risk rubbing themselves on a mincing machine.

I subscribe to New Scientist (actually Dad is currently) and have done so for roughly 35 years. This is not the finest science ever reported.

There will actually be loads of really great science and stuff from these studies but sadly "tuna shags shark" or some other rubbish sells ads n that.

I'm starting to get a bit disillusioned now and might have to pen an "angry of Andover" piece to NS. I'll threaten to cease my subscription (that my dad pays for) and look like a right old prat.

On the other hand, I might simply ask for some decent science. This isn't the best. It sounds novel to start with but rapidly looks like tosh.

What's strange to me is that tuna even feel the urge to scratch themselves

They can't scratch each other either....

Apparently it's to dislodge painful parasites.

The shark seems to be enjoying himself, too, judging from the smile on his face.

This is definitely the most meme-like marine photo I've ever seen

I guess "keep your friends close and your enemies closer" has never been more applicable. Such a strange behavior its hard to see the reasoning. Aren't tunas supposed to be semi-intelligent, as far as fish go? I feel like I remember seeing something like that before?

I guess you didn’t read the article to find the reason

Between this and the Hemingway post the other day, HN seems to have a weird tuna fixation, stay tuned-a

Stay at-tuned

Assuming that of the 108 instances of shark rubs, none got eaten, because the article didn't say otherwise. The title says "despite risk of being eaten" so this data point would be interesting

I wonder how many years of evolution it took for tunas to target the back end of a shark instead of the front.

And how many more years it will take before tunas can grow fingernails and scratch their own parasites off?

Although the article is riffing on "nosh rubs itself on a food blender", there were not really very many samples of that behaviour seen. 106 rubbings in total, some against a shark and some not - unclear, let's say 50. They mention over 100,000 individuals seen.

I'd venture that evolution isn't involved at all and it is simply opportunism that was observed. It's such a rare event that we can't science this one much.

Before you grow fingernails, you need to grow fingers. Before you grow fingers, you need something to wave them around on otherwise they don't do much - that'll be arms (or legs). Fish have been there, seen it, done it (multiple times) and reverted too (multiple times).

I wonder if its a learned behavior versus something instinctual.

> I wonder how many years of evolution it took for tunas to target the back end of a shark instead of the front.

I would not be surprised if they can think and learn by observation. Then there would be no need for evolution.

Sometimes you REALLY gotta scratch that itch

Anyone got a video of this behavior?

It must have been a really troublesome itch to take that risk!

An allegory of partnering with big tech companies.

Except the Tuna have are usually able to get away unharmed after showing their hand to the shark.

Tuna is full of mercury and other human-made environmental toxins, due to it being high in the food chain. So I don't trust that Tuna in their "right mind" would do this. It's like observing human mad hatters and concluding that their behavior is normal

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