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Young males like Sam often are the ones that travel away from groups, looking for food. If they find a new, hospitable habitat, others including females may join and create the basis of a new colony, Gurrola said.

While there is no certain reason for Sam’s appearance in San Francisco, Isadore and biologists working to unlock more clues have some leads to go on.

He could have swam across the bay’s mouth from Marin County, and scat collected from Sam will be analyzed to see if there’s a genetic link to that population. But now, Sam seems to be happy swimming around and munching on small fish, including goldfish discarded in the area.

“We’re just trying to piece things together in a logical way,” Isadore said. “River otters sometimes even stow away on boats, we just don’t know.”