J. Great Lakes Res. 21(3):395-399 Internat. Assoc. Great Lakes Res., 1995 NOTE Winter Diet of Lake Herring (Coregonus artedi) in Western Lake Superior Jason Link,! James H. Selgeby,2 Michael H. Hoff,2 and Craig Haske1l 2 ,3 1Department of Biological Sciences Michigan Technological University Houghton, Michigan 49931 2National Biological Service Great Lakes Science Center Lake Superior Biological Station Ashland, Wisconsin 54806 ABSTRACT. Lake herring (Coregonus artedi) and zooplankton samples were simultaneously collected through the ice in the Apostle Islands region of western Lake Superior to provide information on the win- ter feeding ecology of lake herring. Zooplankton constituted the entire diet of the 38 lake herring col- lected for this study. We found no evidence of piscivory, although it has been reported by anglers. Diet selectivities were calculated using a Wilcoxon signed-ranks test and showed a preference of lake herring for larger zooplankton, especially Diaptomus sicilis, whereas the smaller copepod, Cyclops bicuspidatus thomasi, and immature copepod stages were selected against. These data document that overwintering copepods are food for a broad size range of lake herring in winter. INDEX WORDS: Coregonids, zooplankton, winter, fish diet, Lake Superior. INTRODUCTION Lake herring (Coregonus artedi) historically yielded commercial harvests larger than all other species combined in Lake Superior (Hansen 1990). Many lake herring stocks were overfished to near extinction (Selgeby 1982), but in recent years the biomass of lake herring has been increasing in Lake Superior. Efforts stimulated by the federal mandate to restore native stocks have led to the re- turn of this species as the dominant planktivorous fish in terms of both abundance and biomass (Con- ner et al. 1993, Hansen 1990). To properly manage the continued restoration of this species, increased 3Present address: National Biological Service NFRC Columbia River Field Station Star Route Cook, Washington 98605 395 understanding of lake herring biology in Lake Su- perior is needed. Understanding the diet composition and require- ments of an organism is crucial to the effective management of that organism. The diet of lake her- ring has been dominated historically by zooplank- ton during the open-water seasons of the year (Dryer and Beil 1964; John and Hasler 1956; Lang- ford 1938; Pritchard 1930, 1931). However, there is no published information on the winter diets of lake herring in the Great Lakes. Biological events, in- cluding lake herring feeding activity, occur in the winter and may be important even though they are rarely sampled (Bolsenga et ai. 1988). Lake herring feeding during winter may be im- portant to the recovery and maintenance of lake herring populations in this lake. The objectives of our study were to describe the diet of lake herring captured under the ice and to contrast the zooplank- ton in the diet with the zooplankton community of the lake.