Spotting a basking shark off the coast of California is a rare thing after their notable absence for the last 30 years, but a spate of sightings by local fishers and sightseers has experts hoping this may be a sign of a comeback.

Basking sharks are the second-largest fish in the ocean, reaching over 10 meters (33 feet) in length and weighing up to 6 tons. But these gentle giants are no danger to anything but plankton, famously scooping up snacks with their mouths agape.

Although found in every temperate ocean across the world, to see one is pretty special. To spot two in one month, off Santa Monica Bay where they haven’t been seen in three decades, is extremely exciting.

“It was a very special thing,” Captain Skip Rutzick, who runs a yacht charter service, told local newspaper The Argonaut. “I’ve been on the ocean 1,000 times in the last five years and I’ve seen many whales, I couldn’t tell you how many thousands of dolphins, and the very rare ocean sunfish the Mola mola – but to see a basking shark was very special.”

Luckily, the crew managed to capture footage of the sharks. The first sighting was on March 31, off Malibu. Having spotted the telltale dorsal and tail fins as it lazed around at the surface, they followed it at a safe distance for a few minutes before it submerged. The second sighting was on April 20, in nearly the exact same location.

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Amazingly, they’re not the only people to spot these beautiful ocean giants in the area either. A group of 15 sharks was spotted by sightseeing boats off Santa Cruz Island in mid-April, another group of around eight were seen further south in Long Beach, and as many as 10-20 have been seen swimming in the Santa Barbara Channel.

The gentle giants can grow up to 11 meters (33 feet). Martin Prochazkacz/Shutterstock

In the early 1900s, basking sharks numbered in the hundreds, possibly thousands, off the West Coast of the US. But, like many marine creatures, were hunted to near extinction by humans either for their fins and liver, or through eradication programs to clear shipping lanes. And like most sharks, it takes them a long time to repopulate due to low reproductive rates. In 2009 they were added to the IUCN Red List of Threatened Species and in 2010 NOAA identified them as a Species of Concern. To have them back in California waters is making conservationists cautiously optimistic, although a few sightings doesn't mean they have repopulated the area just yet.

And, if after reading this you're thinking about grabbing a boat and whizzing out to Santa Monica or Malibu to see if you can spot these special creatures for yourself, local shark experts are warning people not to.

"You have more risk to them," James Anderson of Cal State Long Beach Shark Lab told NBC. "The risk of boat-strike, or someone harassing them is going to be more of a risk. Try not to get to close to them. Try not to spook them."

If, however, you do spot any, report your sightings to NOAA's West Coast basking shark program, which monitors the movements of these incredible animals, and do your bit to help conserve them.