Geology topics

William H. Horns

Publications and source records attributed to William H. Horns.

2 recordsLinked to original sources

USGS2000

Seasonal changes in ruffe abundance in two Lake Superior tributaries: Implications for control

Since the discovery of ruffe Gymnocephalus cernuus in the St. Louis River in 1987, state, federal, and tribal management agencies have sought to slow its spread to areas outside the western end of Lake Superior. A debate over control strategies highlighted uncertainties about seasonal movements of this species between Lake Superior and its western tributaries. One strategy called for eliminating reproducing populations in tributaries on the periphery of the range using chemical piscicides. That strategy rested on the assumption that ruffe congregate in tributaries during a predictable time of year. This study was designed to explore that assumption. Ruffe collections from the Iron and Sand rivers during 1995 indicated that ruffe were present in those tributaries throughout the summer but that abundance was not highest at the predicted time: June 19–22. Maximum abundance in the Iron River did not coincide with that in the Sand River and did not occur during June 19–22 in either river. The timing of peak abundance was not clearly related to changes in water temperature. Ruffe were present in substantial numbers in Lake Superior during June 19–22 when aggregations in the tributaries had been predicted. These findings do not support the assumption of the chemical control strategy.

North American Journal of Fisheries Management↗

USGS1993

Distribution, abundance, and resting microhabitat of burbot on Julian's Reef, southwestern Lake Michigan

We used a remotely operated submersible vehicle equipped with a color video camera to videotape the lake bed and document the distribution and abundance of burbot Lota lota on a 156‐hectare portion of Julianˈs Reef in southwestern Lake Michigan. The substrates and bathymetry of the study area had been mapped recently by side‐scan sonar. Burbot density determined from videotapes covering 6,900 m 2 of lake bed at depths of 23–41 m averaged 139 individuals/ hectare (range, 0–571/hectare). This density was substantially higher than the highest burbot density (59–95/hectare) reported in the literature. Burbot were present on the lake bed at depths of 23–36 m, but were most abundant near the crest of the reef at 23–28 m, where the water temperature was 8–13°C, their preferred summer temperature range. Substrates in that temperature range on the reef were bedrock, bedrock ridges, and bedrock and rubble. Burbot were most abundant on the bedrock and rubble. Small fish and macroinvertebrates typically eaten by burbot elsewhere in western Lake Michigan were distributed on the reef according to their summer preferred temperatures and were not seen in abundance where burbot density was highest. We saw no lake trout Salvelinus namaycush on Julianˈs Reef, although large numbers of juvenile lake trout have been stocked there annually and temperatures on the reef were in the preferred summer temperature range for lake trout.

Michigan, Wisconsin↗