South Fork of the Snake Fish Population 2017:
South Fork Snake River 2017 fall population estimates
The Idaho Department of Fish and Game continued annual fish population monitoring at the Conant and Lorenzo monitoring reaches of the South Fork Snake River in the fall of 2017 to evaluate the effectiveness of management actions on the river. Data from these surveys are used in decision making to achieve the goals outlined in the state fish management plan which include preserving the genetic integrity and population viability of native Yellowstone Cutthroat Trout and reducing Rainbow Trout abundance to less than 10% of the species composition at the Conant monitoring reach in the upper river. This is an initial summary of our 2017 data from these reaches and may be subject to change with further review and analysis.
Total trout abundance at Conant changed from 3,758 trout/mile in 2016 to 4,196 trout/mile in 2017, which is close to the 10 year average (2007-2016) of 4,346 trout/mile.
The 2017 estimate for Yellowstone Cutthroat Trout [YCT] was slightly below the 10 year average with 1,424 YCT/mile (10 year average = 1,783).
The Rainbow Trout estimate (1,849 RBT/mile) was above the 10 year average of 1,593 RBT/mile.
The Brown Trout (BNT) estimate (923 BNT/mile), was close to the 10 year average of 970 BNT/mile (Figure 1 and Table 1).
Figure 1. Estimates of fish per mile for Yellowstone Cutthroat Trout (YCT), Rainbow Trout (including hybrids; RBT), and Brown Trout (BNT) at the Conant monitoring reach from 1982 through 2017 with 95% confidence intervals.
Table 1. Point estimates for Yellowstone Cutthroat Trout (YCT), Rainbow Trout and Rainbow x Cutthroat hybrid trout (RBT), and Brown Trout (BNT) per mile with respective 95% confidence intervals for the Conant monitoring reach of the South Fork Snake River from 1982 through 2017.
The Yellowstone Cutthroat Trout estimate for 2016 was 296 YCT/mile, which was lower than the 10-year average of 398 YCT/mile. We estimated there were 1,436 BNT/mile which is near the ten year average for BNT at Lorenzo of 1,521 BNT/mile (see Figure 2; Table 2). For the first time in this 31 year dataset, we were able to get enough RBT to calculate an estimate, which was 43 RBT/mile.
Figure 2. Estimates of fish per mile for Yellowstone Cutthroat Trout and Brown Trout at the Lorenzo monitoring reach of the South Fork Snake River from 1987 through 2017 with 95% confidence intervals.
Table 2. Point estimates for Yellowstone Cutthroat Trout (YCT) and Brown Trout (BNT) per mile with respective 95% confidence intervals for the Lorenzo monitoring reach of the South Fork Snake River from 1987 through 2017.
“I hope the Holiday season finds you all well. I thought you might want to see what the fish counts were like after our fall surveys this year at Conant and Lorenzo. I’ve included a summary with a couple figures and tables. Please feel free to contact me or Dan Garren if you have any questions.”
Regional Fisheries Biologist, Idaho Department of Fish and Game
Upper Snake Regional Office
4279 Commerce Circle
Idaho Falls, Idaho 83402