Lake Herring Spawning Grounds of the St. Marys River with Some Potential Implications for Early Spring Navigation

Abstract

The St. Marys River is a connecting channel between Lakes Superior and Huron and is a thoroughfare for international shipping. An experimental expansion of the navigation season into early spring raised concerns over the effects on the hatch of lake herring Coregonus artedii. Fundamental to assessing the risk is knowledge on location of lake herring spawning grounds and proximity of incubation to navigation. Variable-mesh gill nets were fished from late October through November 1993–1996 between Izaak Walton Bay (above the Soo Locks, in Sault Ste. Marie, Michigan) to lower Lake Munuscong. Presence of ripe, partially spent, and spent female lake herring was used as an indicator of spawning activity. Catch rates of female lake herring in spawning condition were compiled in a Geographic Information Systems database and expressed on three-dimensional graphic plots for visual inspection. A hydraulic-flow model was used to predict the potential short-term dispersion of the eggs from spawning grounds. Within the survey area, four locations were identified as being of the highest spawning use: Baie de Wasai vicinity of upper Lake Nicolet, Garden River vicinity, upper Lake George, and immediately above and below the Rock Cut Channel. The areas of least use by spawning lake herring were the navigation channels and Soo Locks vicinity. These results indicate that spawning lake herring are typically using areas away from navigation. Analysis of the flow model output revealed no relationship between distance traveled by eggs and amount of use by spawning lake herring.