Publications

A general model was developed to examine the effects of multiple predators on survival of eggs and fry of lake trout, Salvelinus namaycush, associated with spawning reefs. Three kinds of predation were simulated: epibenthic egg predators consuming eggs on the substrate surface during spawning, interstitial egg predators that can move in rocky substrate and consume incubating eggs, and...

We conducted a three-year mark-release-recapture study of the endangered Karner blue butterfly (Lycaeides melissa samuelis Nabokov) at Indiana Dunes National Lakeshore to describe the butterfly's movement patterns and to assess seasonal changes in the Karner blue's population structure. Estimated mean Karner blue adult life span was less than 3.5 days. Populations exhibited protandry and...

Burrowing mayflies, Hexagenia spp. (H. limbata and H. rigida), began recolonizing western Lake Erie during the 1990s. Survey data for mayfly nymph densities indicated that the population experienced exponential growth between 1991 and 1997. To predict the time to full recovery of the mayfly population, we fitted logistic models, ranging in carrying capacity from 600 to 2000 nymphs/m2, to...

Larvae of the Karner blue butterfly, Lycaeidesmelissasamuelis, feed solely on wild lupine, Lupinusperennis, from the emergence to summer senescence of the plant. Wild lupine is most abundant in open areas but Karner blue females oviposit more frequently on lupines growing in moderate shade. Can differences in lupine quality between open and shaded areas help explain this disparity in...

Lake trout Salvelinus namaycush in nearshore waters of Lake Michigan grow faster than lake trout residing offshore on Sheboygan Reef, which is in midlake. We examined the stomachs of lake trout, spanning ages 1 through 16, caught in both nearshore and offshore environments of Lake Michigan during 1994 and 1995 to determine whether diet differences may be responsible for the difference in...

We present evidence for a hypothesis that the deepwater ciscoes (Coregonus spp.) of the Laurentian Great Lakes were selected for buoyancy-regulation traits that facilitated planktivory on Mysis relict, a crustacean that undertakes extensive diel vertical migration (DVM). We assessed the vertical distribution and behavior of bloaters (C. hoyi) in Lake Michigan with bottom and mid-water...

A study of the reproductive success of lake herring (Coregonus artedi) in the St. Marys River was conducted in the winters and springs of 1994, 1995, and 1996. The St. Marys River connects Lake Superior to the lower Great Lakes making it an important route for ship traffic. Recent pressure by commercial carriers to extend the shipping season by breaking ice earlier in spring, has raised...

Acoustic studies in Lake Michigan found that bloaters (Coregonus hoyi) were less reflective per size than the other major pelagic species. This difference in in situ acoustic backscattering could indicate that the deep-water bloaters have compressed swimbladders for much of their vertical range with related implications on buoyancy. To test this hypothesis, the buoyancy characteristics...

Gillraker number, one of the most important taxonomic characters in the Coregoninae, has been considered genetically determined and not environmentally modifiable. However, laboratory-reared progeny of Coregonus alpenae, C. artedi, C. clupeaformis, C. hoyi, C. kiyi, C. zenithicus, and Prosopium cylindraceum generally had fewer gillrakers than the wild parents from which eggs were taken...

We used bioenergetic models for lake herring Coregonus artedi, bloater Coregonus hoyi, and rainbow smelt Osmerus mordax to estimate consumption of zooplankton,Mysis, andDiporeia in western Lake Superior for selected years between 1978 and 1995. Total invertebrate biomass consumed yearly ranged from 2.5 to 38 g/m2 with nearly 40% consumed between August and October in all years. Copepod...

The age structure of mature lake trout Salvelinus namaycush from the Wisconsin waters of Lake Superior increased following a population recovery that has taken place since the 1960s. As the population aged, it became apparent that scales were unreliable aging structures. Beginning in 1986, we examined both scale and sagittal otolith ages from tagged fish with a known period at liberty...

In 1993, 20 great blue heron (Ardea herodias; GBH) eggs (one per nest) were collected from a colony at the Indiana Dunes National Lakeshore, Indiana (INDU). The eggs were artificially incubated until pipping and were then analyzed for organochlorines, mercury, and selenium. Livers of embryos were analyzed for hepatic microsomal ethoxyresorufin-O-dealkylase (EROD) activity. Brains were...