About the length of a small bus, one of the world's biggest sharks may be making a comeback off Ventura.

After basking sharks all but disappeared decades ago, people had reported some sightings off the coast in recent years. Then, this spring, those numbers started to climb.

A spate of sightings were reported recently off Ventura and the Santa Monica Bay, said Christopher Lowe, director of the Shark Lab at CSU Long Beach.

“It has really been 30 years since we’ve seen them in any numbers,” Lowe said.

At one time, basking sharks, known as gentle giants, could be found off California by the hundreds or even thousands. But their numbers plummeted after the 1960s.

The eastern North Pacific population was listed as a species of concern in 2009. Since, researchers have tried to fill in the many blanks on what is known about the elusive fish.

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But there are still a lot of unknowns, including whether the sharks are back to stay or if their numbers will reach historic levels, experts said.

In April, basking sharks started regularly making the list of Island Packers' daily sightings. The boat company ferries people back and forth to Channel Islands National Park and reported seeing as many as 20 of the sharks in one day.

“I hope it’s a sign of comeback,” fisheries research biologist Heidi Dewar said of the increasing numbers. Dewar, with the National Oceanic and Atmospheric Administration, has studied basking sharks for the past decade.

“But given the variability in sightings," she said, "I think we have to wait a few more years before we can say that with confidence.”

What are basking sharks?

Many of the basking sharks seen locally were in the 18 to 25 foot range. But they can get to be 30 feet long, Dewar said.

Similar to baleen whales, they do not have big teeth like some other shark species.

Basking sharks are filter-feeders and tend to feed a lot at the surface, mostly eating tiny plankton about the size of a grain of rice. When they forage, they'll swim with their wide, white mouths open.

"They're these massive, gentle giants sort of mowing the seas," Dewar said. "I think it would be great and help instill a love of the ocean and love of nature the more people who could see them."

It's unclear why their numbers crashed off the West Coast.

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But the sharks were targeted by fisheries in the past and an eradication program in Canada. Off the coast of British Columbia, the sharks were killed to prevent them from getting tangled up in salmon nets.

That practice ended decades ago and the sharks garnered protection, but the population failed to rebound.

Experts also don't know if the sharks moved elsewhere when they disappeared off the local coast.

"That's the challenge in not knowing their full range," Dewar said. "We wouldn't even know where to look."

A surge in basking shark sightings

NOAA used to have a regular aerial surveys that would spot hundreds or even thousands of basking sharks off shore at times.

After they were listed, NOAA launched a research program in 2009 to find out more about them. The agency started a sightings database and got a little funding to tag a few sharks when, or if, they were spotted.

Over two years, they were able to get out four tags on sharks, Dewar said. Two of those tags stayed on for eight months or more.

One of the sharks was tagged in Monterey Bay and swam to the tip of Baja. The second was tagged in the Southern California Bight and went to Hawaii.

That wasn't nearly enough data to identify any patterns, but now, the agency may be getting another chance.

After getting reports of multiple sightings off Ventura this month, researcher Ryan Freedman set off to try to find some and hopefully tag them. His company contracts with NOAA's Channel Islands National Marine Sanctuary.

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About 30 minutes in, he saw one basking shark. Then, he saw three others. The sharks were swimming just north of Santa Cruz and Anacapa islands, Freedman said.

"When you pull up to these fish, you're kind of in awe of how big they are," he said.

He tagged two of the sharks. If successful, the tags will record data over the next eight months or so.

In the meantime, NOAA is asking for the public's help.

Dewar and other basking shark researchers urged the public to let them know about sightings.

If boaters do see a basking shark, she asked that they slow down and give them space to avoid crashing into the large, slow moving species.

"We're very fortunate to have very cool ecology in our backyard," Freedman said. "We hope the public can help us learn more about how and where they are."

What to do if you see a basking shark

To report a basking shark sighting, call 858-546-7023 or email basking.sharks@noaa.gov and provide the date, time and location, as well as any comments.

If a boater spots a basking shark, authorities say to slow down to 6 knots and do not make any sudden changes in direction or speed. If closer than 320 feet, switch your engine to neutral.

Cheri Carlson covers the environment for the Ventura County Star. Reach her at cheri.carlson@vcstar.com or 805-437-0260.

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