LAKEWOOD, Colo. — Wildlife biologists successfully used "passive transponders" that act as a microchip to track the movement of endangered fish through the Colorado River from Utah's Lake Powell to critical habitat near Rifle, Colo.

Monitoring antennas were installed this month in the fish passage at the Price-Stubb Diversion Dam and became operational Aug. 12. By four days later, the first fish with a "passive integrated transponder" tag used the passage. Data shows the endangered Colorado pikeminnow swam 130 miles during the past year.

Designed by Biomark, the system detects the tags to track if fish are moving up or down the river system. The monitoring provides remote sensing, according to federal wildlife biologists, and is built to withstand the debris and flows of the Colorado River.

Michelle Shaughnessy, project leader for the U.S. Fish and Wildlife Service, said the transponders and monitoring system will help the agency track the type and number of species of fish moving through the fish passage.

"We anticipate receiving important information about all four species of endangered fish from this remotely sensed structure," Shaughnessy said.

The actual fish passage — at 900 feet long — was completed two years ago, allowing fish to bypass the barrier of the dam. By doing so, it restored access to four species of endangered Colorado River fishes: the humpback chub, bonytail, Colorado pikeminnow and razorback sucker. The passage is formed by 190 strategically placed concrete cylinders designed to create better flow conditions for the fish.

Completion of the passage gave the fish access to 50 miles of critical habitat that had been blocked since the 8-foot diversion dam was completed in 1911.

Biologists say because the passage is adjacent to an interstate highway system, the remote sensing provides a safe and effective research tool.