How do schools of fish swim in almost perfect unison?

[drmark2000]

With all due respect to our ichthyoid planet-mates, it does seem that most appear to have been toward the back of the line when brains were being handed out.

So, how do schools of fish, small and large, manage to coordinate those sudden, radical shifts in direction that I suppose most of us have seen, at least on nature documentaries. I have seen this phenomenon in real life, and find it awe-inspiring.

I’ve heard that some fish have a line of extremely sensitive nerve receptors on each side. Could this come into play?

And, while on the topic, why do they do this? Is it possibly to confuse potential predators, and that schooling itself creates the illusion of one larger creature rather a lot of smaller, more vulnerable ones? Just guesses.

Thanks!

[Colibri]

The phenomen of flocking and schooling behavior is discussed in my Staff Report: How does a flock of birds wheel and swoop in unison?

Such movements are a prime example of emergent behavior: the behavior is not a property of any individual bird, but rather emerges as a property of the group itself. There is no leader, no overall control; instead the flock’s movements are determined by the moment-by-moment decisions of individual birds, following simple rules in response to interactions with their neighbors in the flock.

[Squink]

Fish, like birds, key their movements off their nearest neighbors:

Reynolds’s boids obeyed three main rules: 1) Avoid collisions. 2) Try to match the speed and direction of nearby boids. 3) Move toward the “center of gravity,” or the mean position, of the nearby boids. An even simpler flock simulation is included among the sample programs shipped with the StarLogo software. At each time step, each bird finds its nearest neighbor among all its flockmates. (If there are multiple nearest neighbors, all at the same distance, one is chosen arbitrarily.) If the chosen neighbor is closer than a predetermined threshold distance, the bird flies in the opposite direction; if the neighbor is farther than the threshold, the bird flies toward it; if the distance is just right, the bird matches the neighbor’s heading. Thus each bird interacts with only one neighbor at a time. This rudimentary model will not win any Oscars, but it creates flocks that do seem recognizably avian.

E Pluribus Unum

[mks57]

It’s an interesting question. In World War I, and “rediscovered” in World War II, the British and Americans found that merchant shipping losses to German u-boats were greatly reduced by using a convoy system. There were loud arguments about whether it was safer for a merchant ship to sail independently or become part of a convoy. Good arguments were made for both points of view. Experience showed that convoys were safer than going it alone.

[Rocketeer]

@mks57

It’s an interesting question. In World War I, and “rediscovered” in World War II, the British and Americans found that merchant shipping losses to German u-boats were greatly reduced by using a convoy system. There were loud arguments about whether it was safer for a merchant ship to sail independently or become part of a convoy. Good arguments were made for both points of view. Experience showed that convoys were safer than going it alone.

It seems to have been determined by the search problem. 80 ships spread out over 80 square miles of ocean means that there’s a better chance that a u-boat, surfacing at random with a lookout in the conning tower, will spot one. Eighty ships bunched together on one square mile of ocean, much less likely to be spotted.

[jawdirk]

I was in Florida this summer, where there are large schools of small transparent fish swimming near the shore. These fish were swimming all around me, spaced only a few inches apart, and occasionally bumping in to me. I have heard that the best way to catch a member of a flock/school/herd, is to single one member out. Looking at the school of fish, I could see that this was almost impossible. By the time you see the individual fish clearly, the school has already surrounded you, and it fills your vision. It was impossible (for me) to pick out one fish from the school – they are constantly swerving in unison, and they all look identical. Just as you start to get a bead on one, the school swerves in unison, and you find that you are now focusing on a different fish a centimeter away from the first fish. It would be challenging enough to catch an isolated fish, but with the visual confusion of thousands of other fish, forget about it. That centimeter is all the fish needs.

To catch fish in a school like that, you need a net or strong suction. Your eyes will not help you.