Pacific Ocean’s ‘corridors of life’

Two broad ocean highways where countless sea creatures migrate, feed, mate and reproduce have been discovered running across the Pacific by scientists tuning in to thousands of radio signals.

The calls have come from electronic tags fitted to the Pacific’s top predators – sharks and whales and the wandering albatross, for example. In all, the 23 most important of those creatures – in the water and the air – have revealed a far more complete picture of the behavior patterns and environments of the ocean’s animals than the fragmentary information known before to science.

The discovery of the two highways is the culmination of a wide-ranging 10-year project involving more than 75 scientists from five nations, including the project’s leaders, Barbara Block of Stanford’s Hopkins Marine Station and Daniel Costa of UC Santa Cruz.

The scientists call the highways “the corridors of life” and “the grasslands of the sea,” and likened them to Africa’s vast Serengeti Plain, where countless species of African land animals live and migrate. The ocean regions are major habitats for the Pacific’s predators and their victims lower on the food chain – indeed for everything down to the krill and plankton of the ocean’s depths.

One is the huge area where the cool, nutrient-rich California Current flows southward from the Arctic along the California and Mexican coast and outward from the near-shore into the deep sea beyond. The other is the broad region known as the North Pacific Transition Zone that crosses from Japan to the coast of Washington.

Twenty-one of the project’s leading researchers are reporting their combined results today in the online edition of the journal Nature.

Tracking migrations

The scientists attached 4,306 tags – many of them holding tiny radio transmitters – to more than 3,500 birds and animals, and followed the seasonal migrations of many of them year after year. The signals sent by the radio tags allowed the scientists to locate many hot spots along the highways where each species gathers regularly to feed and reproduce, and to follow them along their migratory routes.

Sensors in many of the tracking tags gave the researchers complex data on the salinity of the so-called highways and on the area’s light levels and temperatures.

The major goal of the international project – Tagging of Pacific Predators, or TOPP, as it’s called – was to deepen scientific understanding of the Pacific’s biodiversity so that threatened species can be protected internationally and productive fisheries can be managed more effectively, the scientists said.

Although the migratory patterns and habitats of some predators have been reported before, Block and Costa said this was the first time the entire ecosystems of the Pacific’s two great centers of biodiversity have been understood, they said.

“It pulls all the pieces together,” Costa said.

For example, the TOPP report noted that the radio tags show clearly how, when water temperatures are just right, leatherback turtles migrate seasonally from their nesting beaches in Papua, New Guinea, into the California current – many winding up in the waters around the Farallones off of San Francisco.

Shearwaters, long-winged seabirds, reach the California current from New Zealand, and loggerhead turtles migrate annually from Japan, the TOPP project noted.

Tale of two highways

California sea lions live their entire lives inside the California Current, but the TOPP researchers found that elephant seals, sharks, albatrosses, tuna and many other predators migrate and forage in the North Pacific Transition Zone before moving on each year.