Pelicans and cutthroat

David Sparks Ph.D.

Blackfoot Reservoir, located about 40 miles east of Pocatello, is home to two divergent, yet symbiotic, conservation stories that have been playing out in southeast Idaho for nearly 30 years, leaving Fish and Game biologists to find new innovative ways towards one common solution.

On one side of the coin is the Yellowstone cutthroat trout, a native species in the upper Snake River drainage that have declined in significant portions of their distribution. Their limited numbers have led to decades’ worth of research and management efforts by Fish and Game fisheries and wildlife biologists.

On the other side is another once-threatened species, the American white pelican, competing directly with Yellowstone cutthroat trout recovery efforts.

The Pelican Effect

To survey the number of Yellowstone cutthroat trout in a fishery, one might assume the sole method for gathering this data is by netting the reservoir. Thanks to pelicans (relatively speaking), there is another way.

Fisheries biologists look not just to the water but to the land — specifically, a pelican’s nest — to help assess Yellowstone cutthroat trout populations in the fishery.

“In places where the pelicans are nesting, we can comb the area and scan for PIT tags regurgitated by the pelicans,” said Watkins. “This helps us understand the basic relationship between pelican abundance and fish predation.”

Fisheries staff have estimated that as much as 50 percent of PIT-tagged fish in Blackfoot Reservoir can be consumed by pelicans, which eat 4-5 pounds of fish a day.

“The observed predation has been pretty alarming,” Watkins said. “Monitoring the effect of pelicans is just half the battle at Blackfoot Reservoir. We’re also working on recovering native cutthroat trout toward an objective of 10,000 spawning fish, which takes an understanding of fish survival and population growth rates. Collectively, all these pieces support or inform elements of the state’s pelican management plan.”