World's Second-Biggest Fish Tracked to Surprising Locale

World's Second-Biggest Fish Tracked to Surprising Locale

Basking sharks, the second-largest fish on the planet, were once plentiful along the Pacific coast of North America, gathering by the hundreds and even the thousands. Now, it's a rare treat to see even one of these ocean giants. Yet within the space of just a few days, satellite technology has offered scientists an unprecedented look at the mysterious wanderings of this elusive fish.

On Feb. 2, a basking shark tagged with a tracking device in June 2011 suddenly checked in near Hawaii — after eight months of silence. The fish, tagged near San Diego, was one of only four basking sharks ever tagged in the eastern Pacific, and the lone shark to keep its tag for such a long time.

"It was really exciting for us," said Heidi Dewar, a research biologist with the National Oceanic and Atmospheric Administration's Southwest Fisheries Science Center in La Jolla, Calif. The roughly 2,500-mile journey (4,000 kilometers) from California to Hawaii is the farthest ever recorded for a basking shark in Pacific waters.

And in addition to revealing where the sharks may go when they leave coastal waters, the tracking device also revealed somewhat startling information about where the sharks like to hang out. Near Hawaii, the colossal fish spent all its time in surprisingly deep seas, lingering in twilit waters 1,600 feet (500 meters) down during the day, and commuting up to a depth of 650 feet (200 m) at night.

Data on the record-breaking trek came just four days after one of the only other tagged sharks also pinged a satellite, this time about 500 miles (800 km) off the coast of Baja, Mexico.

"The location was a bit of a surprise," said Steven G. Wilson, a research associate at Stanford University's Hopkins Marine Station in California's Monterey Bay, where a team tagged the 16-foot-long (5 m) shark in August 2011. Although he expected the shark to have traveled south, Wilson said, he didn't expect to see it so far out to sea.

Both scientists said the tags can't talk to a satellite from underwater, and are programmed to detach from the animals at an appointed time. Once they bob to the surface, the tags transmit reams of data on temperature, depth and sunrise & sunset — information that will allow researchers to plot the latitude and longitude of the shark's wanderings between tagging and satellite check-in. Analyzing the data will require many more weeks of work.

Yet it is work that Dewar says is worthwhile if researchers hope to provide officials with better information on how to protect an enigmatic species that, according to some estimates, has declined by 90 percent in the eastern Pacific. Some data indicate that as few as 300 animals remain in the entire region. 

Basking sharks are enormous fish, second only to whale sharks in sheer size. Despite their ferocious appearance — they swim along the ocean's surface with their giant mouths agape — basking sharks are filter feeders, funneling swarms of microscopic zooplankton down their gullets.

The sharks, declared a species of concern in 2010, haven't rebounded. Data suggest that the sharks can live up to 50 years, yet reproduce slowly, gestating young between 2.5 to 3.5 years, with a lag time of 22 to 35 years between generations.

Both Wilson and Dewar said that basking sharks are far more plentiful and far better studied in the Atlantic, where tracking studies have revealed long, transoceanic journeys. And it was in the Atlantic that Dewar had her own up-close encounter with the species, an experience that has, in part, continued to inspire her research.

"I've jumped in the water with them, and it's pretty amazing," Dewar said. "They're huge and potentially imposing, but they're incredibly docile and kind of peaceful," she said. "Once you make that kind of connection with an animal, it's pretty hard to forget."