Basking sharks are making a comeback in Southern California waters (Credit: Greg Skomal / NOAA Fisheries Service / Public Domain)

Since late March 2019, local fishers and sightseers on whale watching excursions along the Southern California Coast have been treated to a rare sight — dozens of school bus-sized basking sharks lumbering through the water. This is the first time the "gentle giants of the sea" have frequented the area in such large numbers in over thirty years.

Basking sharks, the world's second largest fish, are often mistaken for great white sharks because of their similar dorsal fins. However, while the animals, which can measure up to 30 feet in length and weigh over 10,000 pounds, are larger than the feared predators, they are entirely harmless to humans. Similar to the world's largest fish — the whale shark — and the world's largest animal —the blue whale — basking sharks are filter feeders that swim slowly across the water with their mouths wide open to capture unsuspecting krill and plankton.

Passengers aboard an Island Packers Cruise boat watch a basking whale off of Southern California's Santa Cruz Island (Credit: Lotti Keenan / Island Packers Cruises)

The fish, which get their name due to their tendency to feed at the Ocean's surface, were once found in large numbers in the temperate waters of both the Pacific and Atlantic oceans. However, by the 1960s, the shark had almost vanished from ecosystems on the California coast due to excessive and unregulated fishing for its large fins, meat, and liver, which was coveted for its oil. To make matters worse, the Canadian Department of Fisheries and Oceans instituted an eradication effort throughout the 1950s and 1960s, killing basking sharks because they interfered with salmon fishing operations. The majestic creatures suffered a similar fate in European waters. By 2009, the once abundant animals were listed as a vulnerable species on the International Union for Conservation of Nature's (IUCN) Red List of Threatened Species.

What makes reviving the shark's population harder is that marine scientists have very little knowledge of the animals' habitat, behavior, and migratory patterns. While researchers from the US-based National Oceanic and Atmospheric Administration (NOAA) managed to gain some insights from four tagged specimens between 2010 and 2011, they have been unable to tag any more since. Fortunately, this past April, Ryan Freedman and his team from the Channel Islands National Marine Sanctuary off of California's Pacific Coast, managed to deploy satellite tags on two basking sharks in a single day. The researchers, who plan to tag four more sharks if the opportunity arises, hope observing the fish will provide them with more information about the elusive animals.

“These data will help fill gaps in our understanding of basking sharks’ movement, their overlap with fisheries, and how oceanography influences the species’ distribution,” said Heidi Dewar of NOAA Fisheries’ Southwest Fisheries Science Center and the shark conservation project’s lead scientist. “All of this information is vital for the continued management and conservation of these poorly-understood sharks."

A basking shark swims close to a whale-watching boat off of Santa Cruz island (Credit: Kristen Campbell/Newport Coastal Adventure

Though researchers are not sure of the cause of the sharks' resurgence in California waters, many speculate the warming oceans and an increase in plankton, brought on by nutrient-rich rainwater runoff, may be a factor. While Dewar agrees environmental elements may be at play, she is hesitant to draw conclusions. “I wish I had a good answer,” she said. “We definitely know the ocean is changing.”

Regardless of the reason, Dan Salas, chief executive and founder of Harbor Breeze Cruises in Long Beach, California, who has seen the animals five times in his lifetime — three this year — is thrilled at the exciting addition to the roster of Southern California's marine life. "They're like the Loch Ness Monster," he told the Los Angeles Times. "You hear these stories of them, but it's really hard to get a picture!"