Lots of Southern Californians are on the ocean looking for whales this spring, but they might also keep an eye out for basking sharks.
Though sightings of these gargantuan plankton-eating sharks are rare, three were recorded this week: one Tuesday off La Jolla, another early Wednesday morning south of Dana Point, and a third Wednesday near San Clemente Island.
The Wednesday sighting was made just before 7 a.m. by fishermen aboard the Sum Fun out of Dana Wharf Sportfishing. (Videotape of that shark is at the bottom of this post; the image at right is generic, courtesy of Gregory B. Skomal.)
NOAA Fisheries biologist Heidi Dewar said that local sightings of basking sharks tend to increase at this time of year, perhaps because food becomes more abundant.
Basking sharks are the world's second largest fish, next to whale sharks. They're found in temperate oceans around the world and can measure 45 feet. They feed mostly on swarms of copepods and other zooplankton.
Upwelling generated by springtime winds often results in plankton blooms. Boat captains off San Diego and Orange County have noticed vast swarms of shrimp-like krill, which feed on smaller copepods and are part of the same food web.
Basking sharks are among the most mysterious of large sharks. Scientists do not have reliable population estimates and know little about migration patterns. In the eastern Pacific they were once commonly found off Central California and Canada, but were extensively hunted until about the mid-1950s.
In 2010 off San Diego, NOAA Fisheries biologists placed a satellite tag on a basking shark, marking the first-ever satellite tagging of the species in the Pacific. The tag, however, popped off the shark and washed ashore soon afterward.
(Extensive tagging of basking sharks, with color and number identification tags, has been performed off Monterey in Central California by the the Pelagic Shark Research Foundation.)
Since 2010, two other basking sharks were tagged in the region. One traveled to Morro Bay before the tag came off after 53 days. The other swam to Hawaiian waters and biologists were able to track its movements for eight months.
Last year in Monterey, as part of a Stanford University project, a satellite tag was placed on a basking shark that swam to waters off Baja California.
Scientists are striving to learn more and a team from NOAA Fisheries was searching for basking sharks Wednesday off San Diego. Boaters who make a sighting are asked to email information to email@example.com, or telephone (858) 334-2884.