Ten percent of the big fish still remain. There are still some blue whales. There are still some krill in Antarctica. There are a few oysters in Chesapeake Bay. Half the coral reefs are still in pretty good shape, a jeweled belt around the middle of the planet. There's still time, but not a lot, to turn things around.
Don't eat shrimp - it's one of the most unsustainable fish. For every pound that's caught, 10 or 20 pounds of other stuff is killed and dumped back overboard. It's the number one killer of juvenile sea turtles in Mexico. Two good sustainable seafood guides that I'd recommend are from the Monterey Bay Aquarium and the Blue Ocean Institute.