Spring Distribution and Abundance of Larval Fishes in the St. Marys River, With a Note on Potential Effects of Freighter Traffic on Survival of Eggs and Larvae

Abstract

Larval fishes were collected at seven transects in the St. Marys River from late April to late May, 1985, to determine potential effects of extending the winter navigation season on spawning success and survival. Larval lake herring ( Coregonus artedii) 8 to 25 mm occurred in densities of 0 to 1,450 larvae/1,000 m 3 and were most commonly found in shallow water (1 to 2 m). Most lake herring hatching occurred during late April to early May, the first 3 wk after ice break-up, but there was no distinct hatching peak. Lake whitefish ( C. clupeaformis) larvae, 12 to 23 mm, with densities of 0 to 600/1,000 m 3, were most common at 1 m being collected at all transects, except the transect in the Edison Hydropower Canal which passes Lake Superior water into the river. Densities of the two coregonine species were similar to densities observed in important nursery areas of Lake Huron. However, the contribution of lake herring to the river population is not known. Burbot ( Lota lota) larvae were common temporally and spatially, with higher abundances in the channel. Yellow perch ( Perca flavescens) and rainbow smelt ( Osmerus mordax) larvae were absent in April and early May, and abundant in late May. Lake herring, lake white-fish, and burbot have the greatest probability of being affected by the proposed extension of the navigation season through resuspension of sediments, dislodgment of eggs, and premature emergence of larvae.