The cold upwelled water is shown in purple and dark blue. This maps shows the locations of two whale sharks that follwed fronts along the north and south boundaries of the coastal upwelling plume off the coasts of Equador and Peru. When the front moved north and south in huge wave-like meanders, the whale sharks followed these meanders like semi trucks negotiating a winding mountain road. Ryan's analysis showed that whale sharks followed this front as if it was an open-ocean highway. This boundary is called the North Pacific Equatorial Upwelling Front. "The whale sharks could have ranged anywhere in the Eastern Tropical Pacific," he said, "but they were primarily following frontal boundaries between warm and cold water."Įxtending across the Eastern Pacific is a distinct boundary between warm water north of the equator and colder water to the south. When Ryan first looked at the whale-shark tracks in relation to the satellite data, he was struck by how consistent the tracks were. Because the Equatorial Pacific is often cloudy, Ryan used a combination of infrared and microwave radiation data from satellites (microwave radiation can pass through clouds). Ryan analyzed day-to-day changes in sea-surface temperature across the entire Eastern Tropical Pacific for the months when the whale sharks were being tracked. Sea-surface temperatures, routinely measured by satellites, can reveal the oceanic features that whale sharks encounter during their large-scale movements. Credit: Jonathan Green/Galapagos Whale Shark Project This was a challenging task because ocean conditions are continually changing and whale sharks are always on the move.Ī whale shark swims over the rocky seafloor near the Galapagos Islands. The researchers contacted Ryan to help them figure out how the whale-shark movements related to ocean conditions. The tagged sharks spent the next four to six months traveling east and west from this location across a 4,000-kilometer expanse of ocean, mostly staying between the equator and five degrees north latitude. This was the first time whale sharks had been tagged in the Eastern Tropical Pacific. In 20, a team of researchers from Ecuador and England attached satellite tracking tags to 27 whale sharks at Darwin's Arch, a remote location about 200 kilometers (125 miles) northwest of the main Galapagos archipelago, and about two degrees north of the equator. This study, recently published in the journal PLoS One, could help in the conservation of these endangered animals.
They discovered that whale sharks in this area spend most of their time cruising along fronts-the dynamic boundaries between warm and cold ocean waters. MBARI biological oceanographer John Ryan recently worked with biologists who have been tracking whale sharks in the Eastern Tropical Pacific Ocean.