Any marine mammels near the shore are a bad sign. Sharks like to eat sea lions and dolphins and sea otters. When you see them in the line up it's time to go.
I used to surf at Anno Nuevo State Park in Santa Cruz, and when the ocean got full of the smiley happy critters you could litterally see the sharks circling. Creepy.
Don't wanna be the "weakest link" in the food chain........