Sailing on Monterey Bay on a dark night, it’s not uncommon to see large areas of ocean flash into phosphorescence as anchovy schools suddenly move, probably away from predators, or as your boat passes through them. It must have been incredible back when the schools were much larger.
Some years ago, during the El Nino years of the 80’s as I recall, I was scuba diving off Carmel in spectacularly clear water at maybe 80-90’ depth when a large school passed overhead. It suddenly became almost pitch dark. As I neared the surface, ascending through them, I had the strange experience of being in the center of a 10-12’ sphere of clear water, surrounded by a bubble of silvery fish.