Rainbow Harvest Helps Yellowstone Cutthroats

For the past few years Idaho Fish and Game has been working to slow the impact of non-native rainbow trout on native Yellowstone cutthroat trout in the South Fork Snake River below Palisades Dam. Now anglers are lending a hand in a big way.

To further reduce the effects of rainbows on cutthroats, Fish and Game lifted the limits on rainbow and rainbow-cutthroat hybrids last January and extended the year-round season to the entire South Fork Snake River. Recent fish population surveys in the river indicate that anglers may be starting to make a dent in rainbow trout numbers.

Each year Fish and Game electrofishes (uses electricity to temporarily stun fish) portions of the river to assess overall fish numbers, species composition, and size. According to Jim Fredericks, Regional Fishery Manager, "the 2004 fish population survey was encouraging in that we're starting to see evidence that anglers are reversing the trend of an increasing rainbow population". Non-native Rainbow trout went from being nearly nonexistent in the upper South Fork in the mid-80s to more than 1,300 per mile in 2003, when they outnumbered native Yellowstone cutthroat trout for the first time. In this year's survey rainbow trout had decreased to around 830 per mile.

Fredericks said rainbow trout size indicates that the decreased population was the result of harvest. "A large percentage of the rainbow population was yearling fish--those in the seven- to 10-inch range, compared to last year when there was a greater percentage of 12-to 20-inch fish".

The bad news is that the cutthroat population is still struggling. "Unfortunately, we've seen drought years and the resulting low stream flows in the tributaries lead to weak cutthroat year-classes," Fredericks said. Whereas the rainbow population was made up of a large percentage of yearlings, the cutthroat population was mostly older fish.
Officials are optimistic that 2004 should provide a stronger age-class of cutthroats, and fewer rainbows. Rob Van Kirk, an assistant professor at Idaho State University has worked with Fish and Game to evaluate the effect river flows have on rainbow and cutthroat trout reproduction. Van Kirk believes two things likely favored cutthroat reproduction in 2004. First, the Bureau of Reclamation worked with water users and fishery managers to store additional water in Palisades Reservoir last winter by decreasing winter flows. This stored water was released in the spring to coincide with natural runoff. The high spring flow was designed to hinder rainbow spawning and improve cutthroat reproduction.

Second, the cooler, wetter summer and fall meant much better conditions in the tributary streams which juvenile cutthroat trout depend on. Biologists won't be able to accurately estimate the 2004 age-classes until next fall, when those fish are yearlings.

Fredericks urges anglers to keep harvesting rainbows "Nobody believes we'll ever get rid of rainbows entirely, it's just a matter of keeping them in check."

Many anglers still have a hard time killing wild trout. Scott Yates, Director of the Idaho Water Office for Trout Unlimited sees the need for anglers to help. "Decades of espousing and practicing catch-and-release have made it hard for some people to start harvesting fish," Yates noted. "Nobody is questioning the far-reaching efficacy of catch-and-release fishing and the benefits it provides in terms of protecting quality wild and native trout fishing, but people are realizing there is a time and place for a catch-and-keep ethic, especially when a native trout fishery is at-risk. The South Fork is one of the most unique native trout fisheries in the world, and anglers who are helping to keep it that way ought to feel pretty good about themselves."
 

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