The majority of the herd took off, most likely chasing a food source. The ones that are tagged are showing up south of Monterey.
There were more than 1,500 sea lions at Pier 39 up until Thanksgiving, a new record.
Then their numbers dwindled almost overnight.
A spokesperson for the Marine Mammal Center says changes in currents or water temperature may have changed where the food sources are. Sea lions mostly feed on herring in the winter months.
The harbor master thinks they will return in a month or two.