Fish Population Monitoring. In 2015, FWP conducted electrofishing surveys to characterize abundance and distribution of and other species within the 10 designated sampling reaches (A-E), which include 19.3 miles of mainstem and 8.6 miles in tributaries (Table 7). Additional surveys included 6.4 miles of tributary reaches. A total of 1,509 fish were captured during fall 2015 electrofishing surveys including Arctic Grayling, xxxxx xxxxx, brown trout, rainbow trout, and burbot. During these surveys, 122 Arctic Grayling were captured. Big Hole Tributary Reach Reach Length Kilometers (Miles) Arctic Grayling Xxxxx Xxxxx Rainbow Trout Brown Trout Burbot Miner Creek (B) 0.60 0 77 0 5 10 Steel Creek (D) 2.91 42 188 1 2 35 Deep Creek (E) 1.41 12 47 21 19 4 Swamp Creek 1.75 39 135 0 7 16 North Fork BHR 2.88 0 5 0 25 2 Xxxxxxxx Creek 1.80 7 56 0 2 21 Total 15.95 261 645 22 92 96 Table 7. Total fish captured during FWP fall one-pass electrofishing surveys of the Big Hole Arctic Grayling CCAA monitoring reaches, and other mainstem and tributary reaches. Big Hole River Reach Reach Length Kilometers (Miles) Arctic Grayling Xxxxx Xxxxx Rainbow Trout Brown Trout Burbot Big Hole Arctic Grayling CCAA (A) 1.33 0 124 0 5 4 Big Hole Arctic Grayling CCAA (B) 2.51 0 42 5 167 3 Big Hole Arctic Grayling CCAA (C) 5.83 10 6 5 6 2 Big Hole Arctic Grayling CCAA (D) 3.28 3 2 41 37 0 Big Hole Arctic Grayling CCAA (E) 1.33 0 124 0 5 4 Total 19.3 19 221 53 248 10 The Big Hole Arctic Grayling CCAA document outlines population abundance goals within the Project Area. Based on the 10 CCAA monitoring sites, the index of abundance (CPUE based on cumulative total captures/total distance) for age-1 and older Arctic Grayling will exhibit a positive trend over the 5-year period following execution of the Agreement (FWP and USFWS 2006). Results of age-1 and older Arctic Grayling population abundance trend in the 10 CCAA monitoring sites from 2006 – 2015 are shown in Figure 4.
Fish Population Monitoring. In fall 2020, FWP completed electrofishing surveys to determine Nb in the Big Hole River drainage. Surveys were conducted on 11 reaches over a total of 14.07 miles. A total of 180 young of year (YOY) and 20 Age 1+ grayling were captured during these surveys (Table 7). One hundred-twenty YOY grayling genetic samples were used to calculate Nb. Nb for the 2020 grayling cohort was 208 (95% CI: 167-271; Figure 3). Although point estimates for Nb were lower than the estimate from last year (332.8), they are consistent with the ongoing positive trend in Nb for the Big Hole grayling population. Other species sampled included xxxxx xxxxx, brown trout, rainbow trout, burbot, sculpin, longnose dace, white suckers, and longnose suckers.
Fish Population Monitoring. In 2023, FWP completed 16 miles of electrofishing surveys in 12 waterbodies to determine Nb in the Big Hole River drainage. A total of 147 young of year (YOY) and 56 Age 1+ grayling were captured during these surveys (Table 8). One hundred thirty-seven YOY grayling genetic samples were used to calculate Nb. Nb for the 2023 grayling cohort was 167 (95% CI: 140-205; Figure 3). The 2023 estimate is slightly higher than the median Nb estimated since genetic monitoring began (155.4). Other species sampled included xxxxx xxxxx (Salvelinus fontinalis), brown trout (Salmo trutta), rainbow trout (Oncorhynchus mykiss), burbot (Xxxx xxxx), mountain whitefish (Prosopium williamsoni), Rocky Mountain sculpin (Cottus bondi), longnose dace (Rhinichthys cataractae), white suckers (Catostomus comersonii), and longnose suckers (Catostomus catostomus). Table 8. Xxxxxxxx captured during 2023 electrofishing surveys in the Big Hole River watershed. Reach Name Reach Length (mi.) Grayling YOY Samples Collected Age 1+ Grayling Deep Creek 2.1 0 8 Fishtrap Creek 1.0 0 25 Seymour Creek 0.1 0 0 Squaw Creek Side Channel 0.8 1 7 Xxxxxx Creek Side Channel 1.2 20 1 Xxxxxxx Creek North 0.2 0 0 Xxxxxxx Creek South 0.5 11 1 Xxxxxxxx Creek 2.9 49 1 Steel Creek 2.7 25 7 Swamp Creek 3.0 18 6 Big Hole River-Xxxxxxx 0.5 17 0 Total 16.2 147 56 Table 9. Estimates of family summary statistics and Nb for Arctic Grayling from the Big Hole River. N is number of individuals genotyped. Nb shows estimates of the effective number of breeders, based on 12 microsatellites. LCI and UCI are the lower and upper (respectively) 95% confidence intervals for the Nb estimate from each year. Year N Nb LCI UCI 2007 50 107.1 76.2 171.7 2008 30 77.2 47.6 175.7 2009 128 77.6 66.7 91.4 2010 46 92.4 66.1 146 2011 66 81.9 64.5 108.9 2012 56 289 142.8 5050.9 2013 49 432.7 171.7 ∞ 2014 88 268.4 166.8 614.1 2015 56 181.9 109.2 465.5 2016 51 96.1 68 155.3 2017 63 155.4 103.3 289.7 2018 128 145.2 115.1 191.3 2019 145 332.8 203.7 510.1 2020 119 208 166.6 271.3 2021 119 172 141.2 216.8 2022 144 116.9 102.8 134.3 2023 137 167.2 139.8 205.1 Figure 3. Estimates of the number of effective breeders (Nb) in Arctic grayling from the Big Hole River over time. Error bars indicate 95% confidence intervals.
