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Geology topics

T.F. Nalepa

Publications and source records attributed to T.F. Nalepa.

5 recordsLinked to original sources
USGS2010

Declines in deepwater sculpin Myoxocephalus thompsonii energy density associated with the disappearance of Diporeia spp. in lakes Huron and Michigan

The deepwater sculpin Myoxocephalus thompsonii is a glacial relict in the Laurentian Great Lakes that primarily consumes two glacial relict crustaceans, Mysis relicta and Diporeia spp. Deepwater sculpin were collected in Lake Michigan off Little Sable Point (in 2001) and Muskegon, Michigan (in 2001 and 2009), and in Lake Huron off Harbor Beach, Michigan (in 2007) for energy density and diet analyses. These sites and years represented differences in available prey. In Lake Michigan, energy densities of deepwater sculpin in 2001 were similar to those reported in 1969-1971. In contrast, energy content declined at least 26% at Muskegon between 2001 and 2009. Overall, energy density was 31-34% higher at a site with abundant Diporeia spp. compared with two sites without Diporeia spp. Deepwater sculpin diets consisted primarily of M. relicta at all sites, but included 10-17% (dry mass) Diporeia spp. at sites where this crustacean was still abundant. Food biomass in stomachs was higher at sites with abundant Diporeia spp. than at those without Diporeia spp. Deepwater sculpin energy density and food biomass in stomachs were similar between two sites without Diporeia spp. despite differences in abundance of remaining prey, M. relicta. Declines in deepwater sculpin energy density suggest the potential for further effects on other species and changes in the flow of energy through the food web of the Great Lakes. Published 2010. This article is a US Government work and is in the public domain in the USA.

Ecology of Freshwater Fish↗
USGS2006

Energy density of lake whitefish Coregonus clupeaformis in Lakes Huron and Michigan

We collected lake whitefish Coregonus clupeaformis off Alpena and Tawas City, Michigan, USA in Lake Huron and off Muskegon, Michigan USA in Lake Michigan during 2002–2004. We determined energy density and percent dry weight for lake whitefish from both lakes and lipid content for Lake Michigan fish. Energy density increased with increasing fish weight up to 800 g, and then remained relatively constant with further increases in fish weight. Energy density, adjusted for weight, was lower in Lake Huron than in Lake Michigan for both small (≤800 g) and large fish (>800 g). Energy density did not differ seasonally for small or large lake whitefish or between adult male and female fish. Energy density was strongly correlated with percent dry weight and percent lipid content. Based on data from commercially caught lake whitefish, body condition was lower in Lake Huron than Lake Michigan during 1981–2003, indicating that the dissimilarity in body condition between the lakes could be long standing. Energy density and lipid content in 2002–2004 in Lake Michigan were lower than data for comparable sized fish collected in 1969–1971. Differences in energy density between lakes were attributed to variation in diet and prey energy content as well as factors that affect feeding rates such as lake whitefish density and prey abundance.

Environmental Biology of Fishes↗
USGS2003

Temporal variation of energy reserves in mayfly nymphs ( Hexagenia spp.) from Lake St. Clair and western Erie

1. We analysed changes in energy reserves (lipid and glycogen) and length–weight relationships of burrowing mayflies ( Hexagenia spp.) in 1997–99 to compare an established population in Lake St Clair with a recovering population in western Lake Erie of the Laurentian Great Lakes. In addition, we measured changes in water temperature and potential food in both water columns and sediments. 2. Although overall mean values of lipid and glycogen levels of Hexagenia nymphs from Lake St Clair and western Lake Erie were not significantly different, there were differences in seasonal patterns between the two lakes. In Lake St Clair, levels were highest in early spring, declined throughout the year, and reached their lowest levels in fall during all 3 years of study. In contrast, levels in western Lake Erie were lower in spring, increased to a maximum in summer, then declined in fall. Seasonal patterns in length–weight relationships were similar to those for lipid and glycogen. 3. Total lipid as a percentage of dry weight did not increase with developmental stage of nymphs until just prior to metamorphosis and emergence from water. However, the major reserve lipid, triacylglycerols, increased systematically with development stage. In the final stage of development, triacylglycerols declined, probably as a result of energy consumption and its conversion to other biochemical components for metamorphosis and reproduction. 4. Indicators of potential food (algal fluorescence in the water column and chlorophyll a and chlorophyll a /phaeophytin ratio in sediments) suggest that Hexagenia in Lake St Clair have a food source that is benthic based, especially in early spring, whereas in western Lake Erie nymphs have a food source that is water column based and settles to the lake bottom during late spring and summer.

Freshwater Biology↗
USGS2001

Changing abundance of Hexagenia mayfly nymphs in western Lake Erie of the Laurentian Great Lakes: Impediments to assessment of lake recovery?

After an absence of 40 years, mayfly nymphs of the genus Hexagenia were found in sediments of western Lake Erie of the Laurentian Great Lakes in 1993 and, by 1997, were abundant enough to meet a mayfly-density management goal (ca. 350 nymphs m —2 ) based on pollution-abatement programs. We sampled nymphs in western Lake Erie and Lake St. Clair, located upstream of western Lake Erie, to determine the importance of seasonal abundance and life-history characteristics of nymphs (e.g., emergence and recruitment) on density estimates relative to the mayfly-density management goal. Two types of density patterns were observed: (1) densities were relatively high in spring and gradually decreased through late summer (observed in Lake Erie and Lake St. Clair in 1997 and Lake St. Clair in 1999) and (2) densities were relatively high in spring, gradually decreased to mid summer, abruptly decreased in mid summer, and then increased between summer and late fall (Lake Erie and Lake St. Clair in 1998 and Lake Erie in 1999). Length-frequency distributions of nymphs and observations of adults indicate that the primary cause for the two density patterns was attributed to failed (first pattern) and successful (second pattern) reproduction and emergence of nymphs into adults in mid summer. Gradual declines in densities were attributed to mortality of nymphs. Our results indicate that caution should be used when evaluating progress of pollution-abatement programs based on mayfly densities because recruitment success is variable both between and within years. Additionally, the interpretation of progress toward management goals, relative to the restoration of Hexagenia populations in the Great Lakes and possibly other water bodies throughout the world, is influenced by the number of years in which consequtive collections are made.

International Review of Hydrobiology↗