Cutthroat and pelicans

Cutthroat and pelicans

David Sparks Ph.D.
David Sparks Ph.D.
F&G biologists work to protect a popular Yellowstone cutthroat fishery from pelican predation

A conservation success story results in conflict at Blackfoot Reservoir

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.

For nearly three decades, Fish and Game staff have been deploying a number of management strategies to find a balance between cutthroat trout and white pelicans. And, in 2022, that work is continuing.

The sky’s the limit

Across the U.S., pelicans were on the decline until around the 1960s. Since the ’80s, pelicans have seen a rise in numbers thanks to reduced pesticide use, increased federal and state protection and adapting to new environments. 

Since the 1990s, pelicans have been breeding consistently at three nesting colonies across Idaho. The abundance of breeding adults increased significantly through the early 2010s and peaked in 2012. Blackfoot Reservoir’s Gull Island, for example, has been a popular pelican destination since as early as 1910. After a partnership with USDA Wildlife Services to rid the island of badgers in 1991 and 1992, pelicans took advantage of the predator-free real estate and began nesting on Gull Island in 1993.

Fish and Game biologists in the southeast region have been focusing their efforts on this conundrum since that year, when there were around just 200 breeding adult pelicans. In 2007, that number had soared to its peak of 3,400, before declining to an average of about 1,100 over the past 5 years.

Since 2010 the statewide breeding population has fluctuated annually. Since 2017, breeding adults have averaged around 4,600. In Idaho, pelicans predominantly forage on abundant populations of nongame fish resulting in non-consequential or acceptable impacts to other resource values and anglers. 

However, pelican predation in some areas has a measurable impact on sport fishing and native trout conservation programs, most notably native Yellowstone cutthroat trout, creating conflict between pelican and fisheries management objectives.

Big birds, bigger problems

“At Blackfoot Reservoir, we’d like to consistently manage pelicans at our plan objective of 700 breeding adult birds,” said Regional Fisheries Manager Carson Watkins. “In recent history we’ve been about double that.”

Seeing the balance of pelicans and Yellowstone cutthroat trout beginning to teeter heavily towards the big white birds, Idaho Fish and Game unrolled its first pelican management plan back in 2009. Since pelicans are a federally protected species under the Migratory Bird Treaty Act, Fish and Game has been working in coordination with the U.S. Fish and Wildlife Service to monitor pelican populations in the Blackfoot River system and to manage predation impacts on the cutthroat trout fishery.

“Managing pelican predation has been a slow, uphill battle,” Regional Wildlife Manager Zach Lockyer said. “They are very intelligent birds — efficient fish-eaters, with a strong fidelity to their preferred nesting areas. Blackfoot is a big, complex system, which complicates managers’ ability to control where pelicans occur in space and time.”

The current American White Pelican Conservation Plan is a tightrope walk — establishing a management framework which keeps pelican populations healthy and viable but also reducing the impact of the colonies on native trout and recreational fisheries. How do you reduce the number of one federally protected species of concern on a body of water while simultaneously recovering the population of native fish species? Fish and Game staff argue there may be a solution.

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