Status of pelagic prey fishes in Lake Michigan, 2012

David M. Warner; Timothy P. O’Brien; Steven A. Farha; Randall M. Claramunt; Dale Hanson

Abstract

Acoustic surveys were conducted in late summer/early fall during the years 1992-1996 and 2001-2012 to estimate pelagic prey fish biomass in Lake Michigan. Midwater trawling during the surveys as well as target strength provided a measure of species and size composition of the fish community for use in scaling acoustic data and providing species-specific abundance estimates. The 2012 survey consisted of 26 acoustic transects (576 km total) and 31 midwater tows. Mean total prey fish biomass was 6.4 kg/ha (relative standard error, RSE = 15%) or 31 kilotonnes (kt = 1,000 metric tons), which was 1.5 times the estimate for 2011 and 22% of the long-term mean. The increase from 2011 resulted from increased biomass of age-0 alewife, age-1 or older alewife, and large bloater. The abundance of the 2012 alewife year class was similar to the average, and this year-class contributed 35% of total alewife biomass (4.9 kg/ha, RSE = 17%), while the 2010 alewife year-class contributed 58%. The 2010 year class made up 89% of age-1 or older alewife biomass. In 2012, alewife comprised 77% of total prey fish biomass, while rainbow smelt and bloater were 4 and 19% of total biomass, respectively. Rainbow smelt biomass in 2012 (0.25 kg/ha, RSE = 17%) was 40% of the rainbow smelt biomass in 2011 and 5% of the long term mean. Bloater biomass was much lower (1.2 kg/ha, RSE = 12%) than in the 1990s, and mean density of small bloater in 2012 (191 fish/ha, RSE = 24%) was lower than peak values observed in 2007-2009. In 2012, pelagic prey fish biomass in Lake Michigan was similar to Lake Superior and Lake Huron. Prey fish biomass remained well below the Fish Community Objectives target of 500-800 kt, and key native species remain absent or rare.

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David M. Warner, Timothy P. O’Brien, Steven A. Farha, Randall M. Claramunt, Dale Hanson. 2012. Status of pelagic prey fishes in Lake Michigan, 2012. https://pubs.usgs.gov/publication/70160585

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Factors affecting benthic macroinvertebrate health in the City of Roanoke, Virginia, 2020–2023

Major waterways in the City of Roanoke (City) have failed to meet Virginia’s aquatic life designated use since 1996. Segments of the upper Roanoke River lack healthy benthic macroinvertebrate communities which prompted a total maximum daily load (TMDL) study by the Virginia Department of Environmental Quality (VDEQ) to identify the most probable stressor(s) causing the impairment. Excess fine sediment was identified as the most probable stressor impairing benthic macroinvertebrates on portions of the Roanoke River in 2006, and a watershed implementation plan published in 2016 required communities within the impaired watershed to implement projects that would reduce the load of fine sediment entering the Roanoke River. Additional benthic macroinvertebrate sampling and stream habitat assessments along the Roanoke River and Tinker Creek (a tributary to the Roanoke River that flows through the City) revealed continued impaired conditions, and subsequent stressor identification analysis was completed in 2023. Samples collected downstream of the City on the Roanoke River and Tinker Creek generally showed more impaired conditions relative to samples collected at locations upstream of the City. Based on this evaluation, sediment and sediment-bound polychlorinated biphenyls (PCBs) were identified as probable stressors while specific conductance, total nitrogen, and sediment metals were possible stressors in Tinker Creek; however, only a sediment TMDL target was identified to address impaired benthic macroinvertebrate communities. In the Roanoke River upstream of the Niagara Dam, sediment and total phosphorus were identified as probable stressors, sediment polycyclic aromatic hydrocarbons and sediment PCB were considered possible stressors; however, the TMDL target was only for total phosphorus. The City partnered with the U.S. Geological Survey (USGS) in 2016 to continuously monitor water quality and streamflow conditions on a major tributary of Tinker Creek, Lick Run, and by 2020, four similar monitoring stations were installed on the Roanoke River and Tinker Creek near the locations of benthic macroinvertebrate sampling. Monitored parameters included streamflow and/or gage height (water level), water temperature, pH, dissolved oxygen, specific conductance, and turbidity. Turbidity is a measure of the relative clarity of the water and was previously used to model suspended-sediment concentrations at the monitoring stations. The City also contracted Kirk Environmental, LLP (KE) to collect benthic macroinvertebrate samples and stream habitat assessments near the locations of the water-quality monitoring stations. Identified benthic macroinvertebrates were used to calculate the Virginia Stream Condition Index (SCI), a multi-metric index composed of eight biological attributes that represent elements of the structure and function of the benthic macroinvertebrate community that measure diversity, composition, and tolerance to pollution. Study objective: In this report, benthic macroinvertebrate samples and stream habitat assessment scores collected at four locations on the Roanoke River and Tinker Creek by KE and the VDEQ between 2020 and 2023 were compared to measured water-quality and streamflow conditions prior to sampling to evaluate patterns between benthic macroinvertebrate health, water quality, and hydrology.

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Status of pelagic prey fishes in Lake Michigan, 2012

Abstract

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Factors affecting benthic macroinvertebrate health in the City of Roanoke, Virginia, 2020–2023