I observed some of the sea lions scooping up small rocks and sand (mostly shell carbonates) and swallowing them.
While diving with sea lions off Hornby Islands in the Salish Sea, British Columbia, I observed some of the sea lions scooping up small rocks and sand (mostly shell carbonates) and swallowing them. I was lucky enough to video one of the sea lions doing it.
In an article published in SEALION-WORLD on sea lion feeding the last paragraph of the article stated:
“There is one aspect that researchers are very puzzled by. They have found a variety of stones in the stomachs of dead sea lions in the wild. They can range from very small pebbles to fairly large sized rocks. It isn’t fully understood if they accidentally consume them while in the water feeding. Some think they may be curious about the rocks and often swallow them on land. This remains a mystery though for them to continue looking into.”
This video footage seems to document at least one way that sea lions may obtain these mysterious pebbles and rocks.
Observations From Members 
Steller sea lion
