The roughly 2,000-pound Steller sea lion became an internet sensation during his extended stay at the popular waterfront attraction, where he even got his own sign and plush toy from the Marine Mammal Center. Visitors have continued to stop by in hopes of spotting him.
"Of course I know who Chonkers is," one visitor said.
"We have heard of Chonkers," another added.
"We thought we'd stop in and see Chonkers, so we're hoping to see him," a third visitor said.
LIVE: 'Chonkers,' the giant sea lion stealing hearts at San Francisco's Pier 39
But so far, those hopes have gone largely unfulfilled.
"I feel like I heard a few people saying, 'Oh, I think I see him in the back here', but I don't I don't think anybody actually did," one visitor said.
Experts say there could be a natural explanation for his disappearance.
Daniel Costa, professor of ecology and evolutionary biology at the University of California at Santa Cruz, said the sea lion may have moved on to establish territory ahead of breeding season.
"I suspect that he is now at the Farallon Islands, too, right off San Francisco or maybe even Ano Nuevo island," Costa said.
Still, his absence may not be permanent.
"We could see him tomorrow. We could not. We might not see him for months. He might not ever come back," Costa said.
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A spokesperson for Pier 39 said the sea lion has been visiting the area intermittently for about 15 years, usually staying only a few days at a time. This visit was longer than usual, drawing increased attention. Costa said the fact that the sea lion stayed for so long though at Pier 39 is promising.
"He found it to be a of an interesting spot. So, I think we'll just have to wait and see. Anything's possible," Costa said.
Despite Chonker's absence, many visitors said the experience was still worthwhile.
"It's just so great to be on the water. So I'm really not that sad about it. I mean, it's still just a beautiful day, so never a bad time," one person said.
There have also been reports of a lookalike sea lion spotted at the pier, though it's allegedly not another Steller sea lion, but a large California sea lion.