Other Environmental Themes

Blue Highways

Sea turtles routinely make long journeys across the oceans, but until the 1990s, little was known about their precise movements. That's when researchers began using radio transmitters and satellites to track leatherback turtles in the Pacific, as they made their way southward from a nesting beach in Costa Rica. The researchers learned, to their surprise, that the turtles followed similar paths, year after year, over distances of 1,000 miles or more.

Investigators also discovered distinct turtle migration routes in the Caribbean and Atlantic. Nobody knows exactly what guides the turtles along these corridors, which may simply be narrow ocean bands where food resources are concentrated. "These turtle species have been around for more than 50 million years, which means they've had a long time to figure out the best places to eat," comments Stephen Morreale, a Cornell University zoologist who began following leatherback migrations more than a decade ago.

Although many aspects of "turtle highways" remain mysterious, knowledge of their existence can help focus efforts to preserve endangered leatherbacks. "Narrowing down the area in which we have to be careful can make it easier to protect these animals," Morreale adds.

Other marine pathways have been discovered since—including one in the Pacific that stretches 5,000 miles from Japan to southern California—thanks to satellites that monitor changes in ocean color. Loggerhead turtles, albacore tuna, and elephant seals travel on this "marine superhighway," which is located along a "chlorophyll front"—a transition zone where cold, nutrient-rich waters from the north converge with warmer, nutrient-poor tropical waters. The albacore use the front as an important foraging and migration corridor, feasting on squid and saury along the way. Pacific fisheries also record the highest albacore catches in the same transition zone, pointing up the need to protect species that roam international waters where safeguards are limited at best.

The marine superhighway, the longest of numerous ocean fronts found to date, is popular among marine creatures because of the ready abundance of crabs, jellyfish, and other comestibles. Unlike highways on land, which are fixed in place by asphalt and cement, the location of this highway can shift by as much as 1,000 kilometers, depending on the time of year.