A History of Fish Abundance & Compostion in Silver Creek, Idaho

Pre-Settlement Period
According to testimonials from travelers passing through the area, Silver Creek was about 25 feet wide, two feet deep, and so full of trout they could hardly swim. At this time, all trout in the Silver Creek watershed were native redband trout, a variety of rainbow. When all the large marshes were functioning and the watershed was covered with native vegetation, its wildlife and fisheries were highly sought after by Native Americans.

1875 to 1947
With the advent of large numbers of livestock moving into the basin and the soon to follow agricultural practices, the impacts to Silver Creek were evident as early as 1903. Hauk (1947) reported a much wider stream than exists today, with heavily silted tributaries, and a dense trout population compared to other trout streams in the country. Nonetheless, Hauk believed the trout fishery to be in decline, and in response, all the Silver Creek tributaries were closed to fishing from 1934 to 1946. As far back as 1917, Silver Creek was considered by sportsmen to be the most highly productive trout fishery in the country. Even in its more degraded state, Silver Creek and its tributaries (as it is today) supports a valuable and productive trout fishery.

By the 1920s, government agencies were stocking brook trout in the Silver Creek watershed, and by 1947 their numbers made up the highest percentage of trout species in the watershed. From the 1920s to 1930s, McCloud River rainbow trout were stocked in Silver Creek. In later years, the Idaho Department of Fish and Game stocked other varieties of rainbow trout. Unfortunately, these stocking practices are the primary reason that native redband trout no longer survive in the watershed in their pure form.

1947 to 1980
During the 1950s, Silver Creek was intermittently closed to fishing because it was believed that over-fishing was causing the declining trout population. Agricultural reclamation, meanwhile, was eliminating the huge marshes in the tributaries of Silver Creek; however, no data are available to determine the impacts to the trout population from these land conversions. Over the next several decades, various sources reported declines in the fishery. More recently, decreased catch rates and sizes have been documented.

1980 to Date
In the late 1970s, brown trout was stocked in waters with direct access to the Silver Creek watershed. By 1986, brown trout made up 19 percent of the trout population in Silver Creek; by 2004, this figure increased to 60 percent and then leveled off at 55 percent in 2007. As the proportion of brown trout has increased, there has been a concurrent decrease in the proportion of rainbow trout. Due to this indiscriminate stocking, brown trout are here to stay in Silver Creek and are now one of the important trout species in sport fishery.

A 2001 fish population analysis found 2,800 trout per mile in Silver Creek, which is much higher than the numbers found in other trout streams in the country. In fact, trout density (1,573 rainbow/hectare) in Silver Creek was the highest measured for a mixed species salmonid fishery in the United States. Wiley (1977) reported 3 to 6 pound trout were regularly taken by fishermen.

In 2007, IDFG sampled Silver Creek at three locations (Stalker Creek, Cabin, Martin) to evaluate trends in population abundance and structure and estimate rainbow trout and brown trout abundance. Brown trout densities ranged from 308 to 640 fish (>100mm/km) at the Cabin and Martin sites, respectively, while rainbow trout densities ranged from 95 to 1,726 fish (>100mm/km) at the Martin and Cabin sites, respectively. IDFG sampled again in 2010; however, the results will not be available until spring of 2011. Nevertheless, some preliminary observations are:

• The fishery appears to be moving toward a brown trout- dominated fishery ; the upper sections of Silver and Stalker creeks are about 60% brown trout and 40% rainbow, while the lower reaches are about 80% brown and 20% rainbow.
• The shift from rainbow to brown trout dominance is a function of habitat degradation (primarily temperature because browns have a higher tolerance) as well as piscivory.
• Total abundance of trout is not much different from 2007
• Age analysis indicates no year classes have been lost; and, remarkably, some brown trout are 12 to 14 years old.
• Growth rates remain strong, about the same as in previous sampling years
• Species composition has changed with the likely extirpation of mountain whitefish

In 2000, Jack Hemmingway stated that Silver Creek was now better fishing than it was in the 1930s. Brook trout, however, have fewer numbers now than when they were originally stocked over a half century ago. Reports from 1952 to 1997 indicate that fishermen were averaging a catch rate of about one trout per hour. From 2001 to 2007, Gillian (2007) reported a decline in the trout population. It is doubtful that fishing success, per unit of time, in Silver Creek has decreased much over the past 75 years. Trout populations naturally have wide variations in year to year population size and could be the cause of the consistent reports of fish population declines.

In June 1992, the first recorded trout kill occurred at “Point of Rocks” on Silver Creek. This could have been caused by low dissolved oxygen (2.5ppm), high stream temperatures, toxic inputs, a combination of these factors or unknown factors. In June 1994 a second trout kill was reported when dissolved oxygen was 3.2 ppm; however none of these isolated kills had a significant effect on the trout population. Reported fish kills in the Silver Creek watershed are quite rare to date.