Sea lions gather on a floating dock at Pier 39 in San Francisco, California May 4, 2015. Hundreds of sea lions began hauling out on the docks following the Loma Prieta earthquake of 1989, and face no natural predators at the pier. (Photo by Robert Galbraith/Reuters)

People pose for photographs at Pier 39 in front of a floating dock crowded with sea lions in San Francisco, California May 4, 2015. (Photo by Robert Galbraith/Reuters)

Sea lions frolick on floating docks at Pier 39 in San Francisco, California May 4, 2015. (Photo by Robert Galbraith/Reuters)

A crowd of sea lions crowd onto floating docks at Pier 39 in San Francisco, California May 4, 2015. (Photo by Robert Galbraith/Reuters)

Sea lions gather on a floating dock at Pier 39 in San Francisco, California May 4, 2015. (Photo by Robert Galbraith/Reuters)

People gather as a crowd of sea lions lay on floating docks at Pier 39 in San Francisco, California May 4, 2015. (Photo by Robert Galbraith/Reuters)

Sea lions sleep on a floating dock at Pier 39 in San Francisco, California May 4, 2015. (Photo by Robert Galbraith/Reuters)

People take photographs of sea lions crowded onto floating docks at Pier 39 in San Francisco, California May 4, 2015. (Photo by Robert Galbraith/Reuters)

Sea lions gather on a floating dock at Pier 39 in San Francisco, California May 4, 2015. (Photo by Robert Galbraith/Reuters)

Sea lions gather on floating docks at Pier 39 in San Francisco, California May 4, 2015. (Photo by Robert Galbraith/Reuters)

A woman takes a photograph of floating docks of sea lions at Pier 39 in San Francisco, California May 4, 2015. (Photo by Robert Galbraith/Reuters)