If its in-coming the bay waters would not have carried them toward the bridge. If out-going that scenario-sans the sharks-would be possible. As far as sharks go that is a possibility but their bodies would have been discovered after bleeding out. Sharks don't eat people. They bite them. Additionally most of the great whites are out near the Farallon Islands -several miles off the coast although it is not unusual for someone to spot a great white near the coastline up there. In 1957 I was in a free-diving spear fishing contest off Monterey when a patrol boat came by and told us a white was spotted cruising the area. We continued diving and now one encountered the fish.
