LONG BEACH >> Not 10 minutes after Dan Salas pulled up anchor he spotted an endangered fin whale off the bow.

Next, a pod of common dolphins surrounded his whale-watching boat like a mob of surfers riding the same wave.

Before the 2-hour ride had ended, enthralled passengers also watched two different gray whales spout, roll and dive, one of them a pregnant cow on her way to birth a calf in the sheltered lagoons of Baja.

“This has been a fantastic start to our whale-watching season. We are setting records. This is just the beginning,” Salas said, as he steered his boat full of paid passengers back to Long Beach Harbor on Monday.

The number of whale sightings off the Southern California coast are up, way up, and the chances of seeing one on an excursion this winter are 90 percent, he said. Sightings of gray whales — about 20,000 making their annual migration from the Bering Sea to Mexico — are headed for a second-straight record December, while orcas, known as killer whales, and rare blue whales have also arrived on L.A.’s coast as Christmas week visitors.

The marine mammal explosion — a two-year phenomenon — has dock workers and boat captains buzzing. Scientists are tallying up the higher numbers but can’t settle on the reason for the increase, speculating on warmer waters, more food in the Arctic, or possibly more citizen scientists combing the seas.

Even with a fading El Niño, the waters off the Pacific coast are warmer. “It is hard to say if it is because the waters are warmer. But if you have consistently warmer waters, things will change,” hedged Kera Mathes, marine biologist with the Aquarium of the Pacific in Long Beach.

Warmer waters could have produced more food in the North, where gray whales bulk up for the long journey south, she said.

Orcas have been seen as recently as Friday, she reported. In the last four years, orcas have showed up at the Southern California coast at the end of December mostly for food — a tempting buffet of sea lions, dolphins and even a baby gray whale or two, Mathes said.

If they show up again on Jan. 1, it will mark four straight years ending and beginning with orca sightings in L.A., Mathes said.

Fin whales, an endangered species known for their shark-like dorsal fin and long, slender body, are the second-largest whale species behind the blue whale. Why are they showing up off Long Beach, San Pedro and Palos Verdes?

A new theory postulates a permanent population of fin whales may live off the coast of the Channel Islands, Mathes said.

But the odds-on favorite for a record-breaker lies with the gray whales, whose migratory patterns are set by the calendar and are easier to spot. Last year, the American Cetacean Society’s Los Angeles Chapter counted 364 gray whales, the highest December in 31 years, well more than the previous December’s 191, Mathes said. As of 10 a.m. Monday, the census stood at 326 for this month, just 39 shy of a record.

With about 20 gray whales seen a day, and two days left in the month, Mathes believes there’s a very good chance the record will be broken. “We are on par for another record-breaking December,” she said.

Gitante Serrato, a volunteer with the Cabrillo Marine Museum Whale Watcher Naturalists, said one theory for the higher number of whale sightings is the additional eyes.

“Whale-watching has become a much bigger deal in the last 10 years. More people are out there looking,” said Serrato, a resident of San Pedro. The museum and the aquarium have increased outreach. Also, boats and naturalists have teamed up to enhance the whale-watching experience, she said.

While Salas hopes for more record whale sightings, which can translate into more ticket sales, Mathes wasn’t sure if the December whale rush will carry over into January and February.

Another theory revolves around the clear, dry weather, which increases visibility. If more storms arrive, the count could go down.

Parent Hilary Zachry of Redondo Beach said recent videos about dolphins and whales have sparked interest among family members.

“It is a world-class experience right outside of L.A.,” said Zachry, who along with her young children enjoyed whale-watching Monday aboard Salas’ boat, part of the Harbor Breeze Cruises.

Her friend, Brandy Johnston, also of Redondo Beach, said she preferred her children see whales and dolphins in their natural environment rather than in a tank at Sea World or at a zoo.

On board the boat, she and her children learned about the “footprint” the 80,000-pound gray whale leaves on the surface as it swims beneath the black water. “Also, she was able to see the barnacles on the whales,” she said, pointing to her young daughter staring out the boat’s window.

The mother and daughter watched as the large gray whale dove and surfaced, a spout of water spraying like a puff of smoke above the horizon. In each of the seven dives, the whale arched her back in a roller-coaster motion and pierced the black water, the final dive aided by a flip of her tail or fluke.

“This is much more natural,” Johnston said.