T.A. Edsall | Search USGS

USGS2005

Burrowing mayflies as indicators of ecosystem health: Status of populations in western Lake Erie, Saginaw Bay and Green Bay

The U.S. Environmental Protection Agency and Environment Canada are supporting the development of indicators of ecosystem health that can be used to report on progress in restoring and maintaining the Great Lakes ecosystem, as called for in the Great Lakes Water Quality Agreement between the United States and Canada. One indicator under development is based on burrowing mayflies (Hexagenia: Ephemeroptera: Ephemeridae). We sampled in western Lake Erie, Saginaw Bay (Lake Huron), and Green Bay (Lake Michigan) in spring 2001 at 117 stations covering about 1,870 km 2 of lake bed, to determine the status of nymphal populations of Hexagenia, and to provide information that would further the technical development of an indicator of ecosystem health based on Hexagenia. In western Lake Erie, density and biomass of nymphs were generally highest on fine-grained substrate in offshore waters and were lower on coarser substrates in near shore waters. Nymphs were virtually absent from Saginaw Bay, where only one nymph was collected at 28 stations. Nymphs were collected at only 6 of 48 stations in Green Bay, and density and biomass were highest at the northern end of the bay. Polluted sediments are likely responsible for the absence or low density and biomass of nymphs observed on fine-grained substrates in western Lake Erie, Saginaw Bay, and Green Bay, all of which historically supported abundant populations.

Green Bay, Lake Erie, Lake Huron, Lake Michigan, S↗

USGS2002

The growth-temperature relation and preferred temperatures of juvenile lake herring

Lake herring, Coregonus artedi, were once extremely abundant in the Great Lakes where they functioned as a major trophic integrator, directly linking the planktonic crustacean resource to lake trout. Salvelinus namaycush. Lake herring populations in the Great Lakes collapsed during the middle third of the 20th century due to overfishing, degradation of critical habitat in major production areas, and interaction with exotic species. Fishery and habitat impediments to the recovery of lake herring have been removed, and it may now be possible to reestablish the species in its former habitats in the Great Lakes if adverse interactions with exotic species can be controlled within acceptable limits. To determine the potential for thermal niche overlap and adverse interaction with exotic fishes, juvenile (age-0) lake herring were held in the laboratory at 5, 10, 15, 18, and 21 C, and fed ad libitum for 54 days. The optimum temperature for growth in weight was about 14.5 C, indicating the fundamental thermal niche was 12.5-16.5 C. Fish used in the growth study were also tested in a vertical thermal gradient tank to measure their final preferendum. The final preferendum, 16.5 C, was in close agreement with the optimum temperature for growth and within the fundamental thermal niche. Both the optimum temperature for growth and the final preferendum have been used as measures of thermal niche, but this is the first time both measures were made on the same group of fish. Published information on the fundamental thermal niche, preferred temperatures, thermal habitat use, and feeding habits of alewives, rainbow smelt, and ruffe, indicates they will co-occur in spring, or summer with age-0 lake herring and that collectively they pose a predation threat to small, age-0 lake herring.

Advances in Limnology↗