I was quite a teen surfer in Hawaii and have seen, first-hand, that same situation i.e., a school of sharks through the in-shore waves!
Needless to say, we all surfed, carefully, clear to the beach on the next set!!
In five years, tho', our 'gang', nor I, ever experienced an actual attack out there. Just the occasional jelly fish sting....
If the seal numbers increased some of us would make our way to shore or find another spot. Most of the guys never cared. Every couple of years someone gets chomped in the Santa Cruz area because they didn't have enough sense to not surf in water filled with seals.
Hawaii has the most and best big wave sites in the country. However, Mavericks is a must see when the north swell is in. The water is ice cold, shallow with rocks and filled with sharks. A 10 foot swell will jack up to 25 feet without any warning. I never miss a chance to get down there when I'm on the west coast.