West Coast boasts underwater Serengeti, study finds
By Juliet Eilperin,
How many fish can we harvest to feed growing populations without entirely depleting ocean reserves? What kind of damage did last year’s oil spill actually cause to the Gulf of Mexico’s wildlife? And when is it safest to swim in waters that man-eating sharks sometimes haunt? The way to unlock these and other key secrets of the deep: Attach electronic tags to oceangoing creatures and send them out to do the research.
That’s what a team of researchers did in a decade-long project that shines unprecedented light under the waters of the world’s biggest ocean — the Pacific — and proves the worth of a methodology that can be adapted for use elsewhere around the world.
The Census of Marine Life’s Tagging of Pacific Predators (TOPP) project, published Wednesday in the online version of the journal Nature, deployed 4,036 tags on 23 species of ocean predators, a group that includes several seabirds.
It reveals that the eastern Pacific Ocean is akin to Africa’s Serengeti, teeming with wildlife and crisscrossed by migration corridors used by sharks and seabirds. But the census’s greater value might be in advancing knowledge of a largely uncharted underwater world on which we increasingly depend.
“It’s precedent-setting. It’s a tremendous tool for conservation and management,” said Jesse Ausubel, vice president of the Alfred P. Sloan Foundation and co-founder of the Census of Marine Life. “We were literally blind. We can now see. We know what’s underneath now.”
The findings would be “as if from space we can see the people on the D.C. Metro, and not only the D.C. Metro, but the people on Amtrak and at Dulles Airport and Reagan National Airport and BWI,” he said.
Now, for the creatures, “you suddenly see these incredible patterns by these commuters, long distance and short distance,” he said.
For example, shearwater seabirds tagged off New Zealand made a 262-day, 39,790-mile round-trip journey in a figure-eight pattern, the longest animal migration ever recorded electronically at the time.
Elephant seals won another distinction in the project: At 5,492 feet, one seal dove deeper than any other tagged animal in the study.
Seventy-five researchers from five countries collaborated on the project, which cost $20 million to $25 million, analyzing the ocean’s chlorophyll content and tracking the nature of the water through which the predators moved.
“Just off the West Coast may be one of the greatest hot spots for open ocean predators in the world,” said Barbara Block of Stanford University’s Hopkins Marine Station, the lead author of the study along with Daniel Costa, professor of ecology and evolutionary biology at the University of California at Santa Cruz.
In a phone interview, Block said she was struck by how each spring the rich nutrients in the cool water along the California Current, which flows south along the West Coast of the United States, Canada and Mexico, drew an array of animals to the same place. Young bluefin tuna make their way from Japan for the area’s soup of krill, sardines, anchovies and squid, as do leatherback turtles from Indonesia and sooty shearwater birds from New Zealand.
“They have their favorite haunts, they clearly have the places they keep going back to,” Block said. “The upwelling [of nutrients] is so intense there in the springtime it really sets the table for the whales, the tuna and the sharks. They come and lunch at that table, from everywhere in the entire Pacific realm.”
The California Current is “a predictably and persistently productive region” many marine creatures gravitate to over and over again, said Steven Bograd, a research oceanographer at the National Oceanic and Atmospheric Administration’s Southwest Fisheries Science Center and one of the paper’s co-authors.
“We’ve characterized, better than ever before, that it is a really critical area in the life history of these animals,” he said in an interview.
Tagging revealed that several species — including leatherback sea turtles, black-footed albatrosses and salmon sharks — followed similar routes from the western, central or south Pacific to reach the current’s rich resources.
While scientists tracked most animals for less than a year, they followed several tunas, sharks and turtles for longer: in the case of one salmon shark, well more than 31 / 2 years.
Costa said the fact that these different creatures are following the same path helps account for why some of them, including leatherback turtles, get caught by fishing vessels that are targeting other species. In one instance, he noted, the same female elephant seal tagged in 1995 off the island of Ano Nuevo north of Santa Cruz “took the same exact path 11 years later” when researchers tagged her again.
“It’s not genetic; it’s some sort of learned behavior,” Costa said in an interview.
The scientists emphasized that the fact that many of these commutes largely take place within the exclusive economic zones of the United States, Canada and Mexico — the 200-mile stretch from shore that individual countries can govern — means that the three countries can adequately protect these areas.
In the case of sharks, Block said, researchers were able to determine that species with a common ancestor — salmon, white and mako sharks — preferred to spend time in slightly different temperatures. In Alaska, salmon sharks swim in water as cold as 42.8 degrees but can manage in temperatures as high as 53.6 degrees; great whites stick close to the California coast at 53.6 degrees but journey to Hawaiian waters as balmy as 69.8 degrees; and makos inhabit seas as warm as 80.6 degrees.
“We’ve dug inside the guilds down to the species level,” Block said.
The information revealed through electronic tagging, Ausubel said, should compel policymakers to protect these underwater animal meccas: “It’s a joy and a revelation, and it’s also a call to action.”