© AP Photo/Ben MargotTourists watch sea lions on boat docks at Pier 39 in San Francisco.
Two mysteries surround a huge herd of sea lions that were hanging out on a pier in San Francisco Bay: Why did so many show up, and why did so many leave at once?
Just last month, Pier 39, famous in San Francisco for its sea lions and the throngs of tourists they attract, was groaning under the weight of more than 1,500 of the animals. The record number delighted tourists and baffled experts.
Marine experts suspect the sea lions came and stayed for the food, then left largely for the same reason.
"Most likely, they left chasing a food source," said Jeff Boehm, executive director of the Marine Mammal Center in Sausalito, which runs an information center and gift shop at Pier 39. "It's probably what kept them here in the first place."