Predators of the North Pacific Ocean - among them many sharks, whales, seals and sea turtles - will be forced to swim farther from their food supplies or go hungry as the world's warming climate shifts their normal habitats, a marine scientist has concluded.
Yet the changes pushed by ocean warming may benefit some seabirds and fast-swimming tuna, which are built to forage farther than their competitors, according to a study by Elliott Hazen, a National Oceanic and Atmospheric Administration fisheries researcher affiliated with Stanford's Center for Ocean Solutions.
Climate specialists estimate that average sea surface temperatures will rise from 1.8 to 10.8 degrees by the end of this century, and Hazen and his colleagues have calculated how this could affect predators in two great western regions of the world's oceans.
One is called the North Pacific Transition Zone, a vast area of swirling currents that stretches for nearly 6,000 miles from British Columbia to Japan. Cold, nutrient-rich polar water in the north of the zone lies next to warmer, nutrient-poor water on the south.
The other region lies off the Pacific coast, where the California current flows southward for 2,000 miles from British Columbia to Baja California, and where upwelling water brings rich supplies of nutrients to the surface during most years.
"As the climate warms, many of the sea's top predators will face difficult challenges as they are forced to seek their prey in new locations in distant habitats," Hazen said. "They'll have to travel farther and farther every year just to reach their food."
Predator, prey split
Food for most ocean predators will be moving northward as their habitat in the Transition Zone shifts. At the same time, the ancient migration routes across the ocean for many of those predators will likely remain unchanged. That means that many of those predators, like blue whales, loggerhead turtles, will be left far behind their prey if they don't manage to veer north to find it, Hazen said.
"For species already stressed by overfishing or other human impacts, increased migration time and loss of habitat could be a heavy blow," he said.
Hazen and his colleagues followed the tracks of nearly 2,000 marine animals from 15 different species. They traced where the animals feed, reproduce and migrate through what Stanford scientists have called the "grasslands of the sea" and the "corridors of life."
Those animals carried electronic tags - many of them equipped with tiny radios - that recorded virtually every aspect of their lives, including the temperature and salinity of the sea around as well as their movements. Another group of scientists followed them in a separate Stanford-led international project called TOPPS, for "Tagging of Pacific Predators."
Still another group of scientists developed complicated mathematical models linking the effects of global warming on the habitats of both marine animals and their prey. The warming forecasts came from the United Nations' Intergovernmental Panel on Climate Change.
Using satellite data to locate key habitats for predators and prey, Hazen and his colleagues predicted that as the climate warms, some habitats in the zone will shift northward by as much as 35 percent, or at least 600 miles, before the end of the century.
But as some predators struggle, more mobile marine animals, like swiftly moving species of tuna and sea birds like albatross, will likely benefit because they will face diminished competition for food, Hazen's group suggested.
Predators that live primarily along the Pacific Coast or that migrate into it are likely to be less affected by habitat changes, however, because the upwelling of nutrients in the California Current rarely stops except during particularly strong ocean events called El Niño, Hazen's group said.
The finding were reported in a recent issue of the journal Nature Climate Change.