Arctic grayling are a unique fish because remnant populations were native to only two of the lower 48 states-Michigan and Montana. Grayling were apparently isolated in both of these areas by the last period of glaciers, which ended 10,000 to 12,000 years ago. Michigan's grayling were extinct by 1936, but Montana populations continue to persist in a fraction of their historic range. In fact, the only remaining native stream dwelling grayling population in the lower 48 states is found in the Big Hole River in southwest Montana. Declines in Montana's native grayling populations are attributable to:
The Sun River drainage supports two different grayling populations. Neither of these populations are native; rather both originated from introductions by the state of Montana Department of Fish, Wildlife and Parks (FWP). The most unique of these populations does not even reside in a stream or lake, but in the Sun River Slope Canal (also known as Sunnyslope Canal), which transports water from Pishkun Reservoir east to the Fairfield Bench. This population originated from grayling that were initially stocked into Pishkun Reservoir in the late 1930's and early 1940's. These fish eventually flushed out of the reservoir and became established in the canal system. People reported finding grayling in the canal as early as the 1940's, but their presence was not confirmed until 1971 when FWP biologist Bill Hill sampled several .
The fact this unique naturally reproducing grayling population still exists and has persisted for over 60 years in the Sunnyslope Canal is nothing short of remarkable. Flows in the canal can peak at 1,600 cubic feet per second (about half the summer flow of the Missouri River at Craig!) during the irrigation season, and then it almost entirely dries up during the winter months! A special research study completed by a graduate student from Montana State University in 1996 found there were only about 100 fish in this unique grayling population and they complete their entire life cycle (spawning, rearing, feeding) in about the first 5.5 miles of the canal below Pishkun.
But each year many adult and juvenile grayling are lost from this small population once they move further down the canal and/or into irrigation ditches. There are several large drop structures (artificial waterfalls built to control slope and erosion in the canal) that prevent them from swimming back up the canal. Maintaining a bare minimum winter flow is critical to sustaining this population in large holdover pools in the dried-up canal. Greenfields Irrigation District helps these grayling by allowing a slight trickle of flow to leak out of Pishkun Reservoir's outlet gates during the wintertime. Additionally, FWP established catch and release regulations on these grayling to protect the population.
The other grayling population found in the Sun River drainage resulted from ongoing restoration efforts to expand the range of the last remaining ' fluvial' (meaning stream dwelling) population in Montana (and the continental United States). Offspring from Big Hole River grayling were introduced into the North and South Forks of the Sun River above Gibson Reservoir in 1999, 2000, and 2001. Although the area above the falls was not part of the historic range of grayling (recall that the Sun River was historically fishless above the falls at Diversion Dam), biologists felt the excellent habitat, ample stream flows, and absence of some potential competitors (no brown trout and few brook trout) would allow grayling to become established.
Introducing grayling into these waters was no small task. About 6,800 yearling grayling (6 to 8 inches long) were introduced into the North Fork each year, while 4,500 were stocked annually into the South Fork. Because these waters are within the Bob Marshall Wilderness, grayling had to be loaded into coolers and packed in by U.S. Forest Service and FWP horses and mules for many miles. Each pack animal could carry about 100 grayling per trip, so it took numerous trips each year with several pack strings to complete the introduction. Rafts were also used to help disperse the introduced grayling in the South Fork.
Although initial survival was high from these introductions, it was not long before the grayling drifted downstream out of both forks into Gibson Reservoir. Soon after, anglers were commonly catching them in the reservoir, and grayling started to appear in FWP sampling nets in Gibson. Grayling were even sampled in the Sun River below Gibson Dam, and probably several made it all the way to Pishkun Reservoir! It was apparent from FWP surveys and angler reports that grayling were not staying in the North and South forks. Despite our best efforts to establish grayling in the upper Sun River, it is not always easy to predict how fish will respond to a new environment.
Grayling restoration efforts in the Sun River drainage took a different approach in 2004. Biologists working on the Ruby River in southwest Montana experimented with hatching grayling eggs streamside in simple portable incubators. Preliminary results from the Ruby indicated that grayling hatched on-site remained near where they hatched and did not exhibit the tendency to migrate like the yearlings that were stocked in earlier restoration attempts. In spring 2004, FWP used egg incubators in the North Fork of the Sun River on a trial basis. Ten incubators were placed at two different locations in the upper drainage, and approximately 12,000 eggs were equally divided among the incubators. Grayling started hatching within a week, and were completely hatched out and swimming freely in the North Fork of the Sun River just two weeks later. The experiment was very successful-about 90% of the eggs hatched. We do not yet know how well the grayling fry survived their first year, but we plan on increasing our efforts the next couple of years to hatch out 40,000 to 50,000 eggs annually. It is hoped that these efforts will establish fluvial Arctic grayling in the Sun River drainage and help preserve this unique Montana native fish.