It’s been about a week since the sea lions disappeared and no one is quite sure where they went or when exactly they’ll be back.

San Francisco’s Pier 39 is missing the signature sounds of sea lions. For over 20 years, they have frequented the pier. A common sight is tourists gathering along the area to listen to their loud barks and watch them play.

Now, the view is far less pleasant. Some tourists are still gathering, however the sea lions are nowhere to be found. It’s been about a week since the sea lions disappeared and no one is quite sure where they went or when exactly they’ll be back.

The good news is that experts are hopeful the creatures will return to Pier 39. 4 and a half years ago, the sea lions pulled a similar stunt. In December 2009, they abruptly disappeared.

Marine scientists say sea lions around Fisherman's Wharf sometimes leave their docks during the early months of summer and migrate south, typically to the Channel Islands off the coast of Southern California.

In this year’s migration, all of the sea lions, even the ones that are too young for breeding are gone. In 2009, the creatures returned three months after disappearing, so tourists visiting this summer may have to forgo the sea lion viewing.