At least 10 killer whales were spotted late Sunday afternoon and again Monday off the Palos Verdes Peninsula, stealing the spotlight from migrating gray whales.

They're the same orcas that appeared in the same area on Dec. 10, and a day later off Newport Beach, and the increasing frequency of their visits suggests that transient killer whales are expanding their range into Southern California, possibly taking advantage of an exceedingly abundant sea lion population.

"There's no question that sightings are increasing," said Alisa Schulman-Janiger, who runs the California Killer Whale Project and catalogues individual orcas based on distinct markings. "Especially with the 51s. They seem to have become really fond of this area."

The killer whales spotted Sunday and Monday are from at least two family groups: the CA51s (seven whales) and CA 140s (three whales). These groups are most commonly seen off Monterey in Central California.

Transient killer whales prey largely on marine mammals, especially sea lions, whose population off California has been increasing since 1975. Transient orcas were first documented off Southern California in 1998.

Sightings were sporadic until recently. The CA51s, which often travel with one or two smaller family groups, have been documented in Southland waters at least a dozen times during the last two years.

They're famously boat-friendly, which makes for easy close encounters when they're around.

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