Gear Comparison for Sampling Age‐0 Mountain Whitefish in the Madison River, Montana

Abstract

The efficacy of various sampling gears for age-0 Mountain Whitefish Prosopium williamsoni is largely unknown, which makes it difficult to investigate recruitment and early life history dynamics for the species. We compared four gears: seine, backpack electrofisher, minnow trap, and lighted minnow trap. Gears were tested in backwaters, large channels, and small channels in the Madison River, Montana. No age-0 Mountain Whitefish were captured in minnow traps or lighted minnow traps. Mean CPUE of age-0 Mountain Whitefish was higher for seining (0.18 fish/m 2 ; SD, 0.39) than for electrofishing (0.01 fish/ m 2 ; SD, 0.03), and the CV was lower for seining. A broader length distribution was sampled by seining (17-41 mm) than with electrofishing (21-36 mm). Age-0 Mountain Whitefish CPUE in seines was highest in backwaters. In channel sites, Mountain Whitefish presence was associated with areas of still or slow water ≥2 m 2 . Relative to the other sampling gears we evaluated, seining was the most efficient gear for sampling age-0 Mountain Whitefish in a lotic ecosystem.

Reproductive Ecology, Spawning Behavior, and Juvenile Distribution of Mountain Whitefish in the Madison River, Montana

“…Age-0 fish distribution.-In spring 2014, seining (3 × 1.5-m beach seine, 1.6-mm bar mesh) in backwaters, channels, and four tributaries ( Figure 1) was used to describe the distribution of age-0 Mountain Whitefish (defined as hatch date to December 31 of same year, age < 1.0). In 2013, age-0 Mountain Whitefish were patchily distributed and present at ECOLOGY OF MADISON RIVER MOUNTAIN WHITEFISH relatively low numbers in the Madison River (Boyer et al 2017), so we restricted 2014 sampling to habitats likely to have age-0 Mountain Whitefish present. Aerial maps were used to delineate backwaters, 200-m channel lengths (channel > 6 m wide), and 50-m tributary lengths (within 500 m of confluence with Madison River).…”

“…In the field, wadeable sampling sites 50 m in length (that included at least 2 m 2 of slow velocity habitat) were identified in preselected large channel sites. Sample sizes were determined from a power analysis using 2013 seining data (Boyer et al 2017).…”