Phil and I ran into a mess of them a few years ago. We saw them from a distance and they looked like breaking fish, so we trolled into them.
When we realized what they were, I hit the spool releases on all the rods to get under them...and to our complete surprise, there was a school of rock feeding beneath them.
A little tricky reeling them in, but we limited in about 30 minutes.
Hybrid Mode
