My guess is that was during -

I think - sardine mating or migrating season, where there are millions of sardines that are in huge schools and everything but the kitchen sink attacks them to eat them.. smaller fish, which bring in larger fish, which bring in sharks, and usually birds attack from the air, as well.. But, no birds in this video that I saw..

Its a total free for all chaotic mess.. Sharks will swim through the sardine "bat ball" and eat every sardine they can.. they then throw up and eat more and that cycle goes on and on..

With exception to the birds (who kamikazi dive bomb into the water to get sardines), watch this and see if it would appear to be what's going on under water..

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Friendship is like peeing your pants.. Everybody can see it, but only you can feel the warmth..