Using larval fish abundance in the St. Clair and Detroit Rivers to predict year-class strength of forage fish in Lakes Huron and Erie

Larval fish samples were collected in plankton tow nets in spring and summer, 1977–1978 and 1983–1984, in the St. Clair and Detroit rivers which are part of the connecting waterway between Lakes Huron and Erie. Larvae abundance of the major forage fish in the rivers are compared with their year-class abundance, as measured by bottom trawl catches of later life stages in Lakes Huron and Erie. Abundance of rainbow smelt, Osmerus mordax, and alewife, Alosa pseudo-harengus, larvae in the St. Clair River in adjacent years of the 4-year study was correlated with the abundance of yearlings captured in bottom trawls in lower Lake Huron in the spring of the following years. Abundance of locally produced larval rainbow smelt, alewives, and gizzard shad, Dorosoma cepedianum, in the Detroit River in adjacent years was correlated with the abundance oj’ young-of -t he-year captured in bottom trawls in western Lake Erie the following fall. Sampling fish larvae in the main channels of the St. Clair and Detroit rivers thus provided a potential early index of forage fish abundance in the lakes.