Satellite asset tracking technology usually is employed to monitor the movement of high-value assets such as construction equipment or trailers transporting merchandise or other valuable cargo.

Biologists at Stanford University applied that same satellite technology to monitor the movement of salmon sharks in the Pacific Ocean, revealing new details on the sea creatures’ migratory habits and physiology.

“Sharks are declining globally, yet the movements and habitats of most species are unknown,” Stanford biologist Barbara Block said in a statement. Block headed up a team that included researchers from the National Fisheries Services, Monterey Bay Aquarium and the Alaska Department of Fish and Game. The research was conducted as part of the Census of Marine Life, an international network of scientists seeking to understand the abundance and diversity of organisms in the oceans.

To facilitate the study of the salmon shark, the teams used two types of satellite tagging technology. One, known as the Smart Position-Only Tag (SPOT), tracks individual sharks in real time as they migrate. The SPOT tag is attached to the dorsal fin and transmits the animal’s position to satellites when the shark surfaces. Scientists then download the data to track the shark’s day-to-day movements. This information also is available to the public in near real-time on the Web at http://www.toppcensus.org. Stanford did not reveal which satellites in particular are being used to gather the data.

The second satellite technology, called Pop-Up Satellite Archival Tag (PAT), records water pressure, temperature and light while the salmon shark swims. Unlike SPOTs, which remain fastened to the shark, PATs detach from the animal on a preprogrammed date, then float to the surface and begin transmitting date to satellites.

“We combined radio uplinking SPOTs that give us accurate position and data-logging PATs that store information for the duration of the programmed mission,” Block said. “By using two types of tags, we’re able to accumulate a larger data set on the sharks’ habitat and preferences with a greater accuracy than we’ve been able to do before.”

In total, 51 female sharks were tagged between 2002 and 2004 in Prince William Sound in the Gulf of Alaska. The longest distance traveled by an individual shark during the observation period was 11,321 miles over 640 days, equivalent to traveling nearly halfway around the Earth.

In addition to learning about migratory habits, researchers are using the data to help protect shark species. “From these data, we can map areas of high use, visualize shark migration corridors and identify species-specific hot spots where shark population may benefit from increased protection,” Block said.

(Barbara Block, Stanford University, 831/594-2071)