Timothy B. Johnson

Factors affecting the growth and condition of lake whitefish (Coregonus clupeaformis).

Though declines in the growth and condition of Great Lakes lake whitefish (Coregonus clupeaformis) have been largely attributed to food web disruptions caused by invasive dreissenid mussels, a comprehensive evaluation of alternative hypotheses is currently lacking. Using various statistical approaches, we evaluated 69xa0years of data from the inner basin of South Bay, Lake Huron, considering the role of biological variables (food availability as Diporeia abundance and lake whitefish relative abundance as catch per unit effort, CPUE) versus environmental variables (climate change as growing degree daysxa0>5xa0°C and productive habitat capacity as percent epilimnetic volume, EV) on the condition and early growth rates of resident lake whitefish. Consistently, biological variables (Diporeia abundance, CPUE) best explained changes in lake whitefish growth and condition, respectively, in years when Diporeia data were available. In their absence, environmental variables (EV) best explained early growth rates of lake ...

Spatial Patterns in Assemblage Structures of Pelagic Forage Fish and Zooplankton in Western Lake Superior

We assessed abundance, size, and species composition of forage fish and zooplankton communities of western Lake Superior during August 1996 and July 1997. Data were analyzed for three ecoregions (Duluth-Superior, Apostle Islands, and the open lake) differing in bathymetry and limnological and biological patterns. Zooplankton abundance was three times higher in the Duluth-Superior and Apostle Islands regions than in the open lake due to the large numbers of rotifers. Copepods were far more abundant than Cladocera in all ecoregions. Mean zooplankton size was larger in the open lake due to dominance by large calanoid copepods although size of individual taxa was similar among ecoregions. Forage fish abundance and biomass was highest in the Apostle Islands region and lowest in the open lake ecoregion. Lake herring (Coregonus artedi), rainbow smelt (Osmerus mordax) and deepwater ciscoes (Coregonus spp.) comprised over 90% of the abundance and biomass of fishes caught in midwater trawls and recorded with hydroacoustics. Growth and condition of fish was good, suggesting they were not resource limited. Fish and zooplankton assemblages differed among the three ecoregions of western Lake Superior, due to a combination of physical and limnological factors related to bathymetry and landscape position.

Immediate X-ray-inducible responses from mammalian cells

It has been nearly 6 years since we reported the induction of new proteins in human normal and tumor cells after ionizing radiation. Since that time there has been an explosion of new data and ideas from a number of laboratories regarding the immediate responses of human cells to ionizing radiation. The data are, however, extremely difficult to interpret since researchers are using confluence-arrested, log-phase, normal or tumor cells, and are exposing these to a variety of doses of ionizing radiation. It is especially difficult to interpret data from cells that are exposed to supralethal doses of ionizing radiation. Thus this session of the workshop entitled Molecular, Genetic, and Cellular Basis of Radioresistance at Low Doses: A Case Of Inducible Repair? concentrated on inducible responses (both late and immediate) of human cells exposed to physiological doses of ionizing radiation. A major focus of future research in this field must be directed toward the function(s) of these inducible proteins and the expression of genes in DNA repair, cell cycle progression (especially radiation-induced cell progression delays) and/or cell death, including apoptosis.

Estimation of invertebrate production from patterns of fish predation in western Lake Superior

Abstract We used bioenergetic models for lake herring Coregonus artedi, bloater Coregonus hoyi, and rainbow smelt Osmerus mordax to estimate consumption of zooplankton,Mysis, and Diporeia 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 zooplankton represented the largest proportion of biomass collectively consumed by the three species (81%), although rainbow smelt consumed almost twice as much Mysis as zooplankton. Growth efficiency was highest for rainbow smelt (3.84–16.64%) and lower for the coregonids (1.91–12.26%). In the absence of quantitative secondary production values, we suggest our estimates of predatory demand provide a conservative range of the minimum invertebrate production in western Lake Superior during the past 20 years.

Lake Herring (Coregonus artedi) and Rainbow Smelt (Osmerus mordax) Diets in Western Lake Superior

Abstract We describe the diets of lake herring ( Coregonus artedi ) and rainbow smelt ( Osmerus mordax ) in western Lake Superior during the summers of 1996 and 1997. Both species consumed predominantly (> 71% by number) zooplankton, showing a preference for larger taxa. Diet overlap between the two species was low (Schoeners indexxa0=xa00.42). Mysis was most important in rainbow smelt diets, whereas Diaptomus sicilis was most important in lake herring diets. Rainbow smelt selected larger taxa, and larger individuals within a taxon when compared to lake herring, although rainbow smelt tended to be smaller fish. Fish diets have changed relative to previous studies and may be reflecting changes in the zooplankton community. Continued changes in the fish and zooplankton community will alter predatorprey and energetic pathways, ultimately affecting growth and production of the ecosystem.

Ontogenetic and Seasonal Patterns in the Energy Content of Piscivorous Fishes in Lake Superior

Ontogenetic, seasonal, and sex-related patterns in energy density (J/g wet mass) was studied in burbot (Lota lota), lean lake trout (Salvelinus namaycush namaycush) and siscowet lake trout (Salvelinus namaycush siscowet) collected from Lake Superior in 1996 and 1997. Energy density was strongly negatively correlated with water content for all fishes (r2 = 0.86 to 0.99). For fishes of comparable size, energy density of siscowet (10.8 kJ/g) was significantly higher than lean lake trout (7.8 kJ/g) and both were significantly higher than burbot (5.1 kJ/g). Energy density in spring was higher in lean and siscowet lake trout, and lower in burbot than in other seasons. No significant differences were apparent between sexes within a species. Energy density increased in a predictable fashion with body mass for lean and siscowet lake trout, but varied without trend for burbot. The regression common to the three species (kJ/g wet mass = 36.78 – 0.41(% water), p < 0.001) provides a straightforward method for estimating ontogenetic and seasonal energy density in these fishes.