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Have water quality changes in the Huron-Erie Corridor contributed to increases in Lake Erie sea lamprey populations?
Julia L. Mida Hinderer1, Jean Adams2, David Bennion3, Aaron Jubar4, Fraser Neave5, Matthew Faust6, and Michael Siefkes1
1Great Lakes Fishery Commission, 2100 Commonwealth Blvd., Suite 100, Ann Arbor, MI 48105
2U.S. Geological Survey, Great Lakes Science Center, 223 East Steinfest Road, Antigo, WI 54409
3U.S. Geological Survey, Great Lakes Science Center, 1451 Green Road, Ann Arbor MI 48105
4U.S. Fish and Wildlife Service, Ludington Biological Station, 229 S. Jebavy Dr., Ludington, MI 49431
5Fisheries and Oceans Canada, Sea Lamprey Control Centre, 1219 Queen Street East, Sault Ste. Marie, ON, P6A 2E5
6Ohio Department of Natural Resources, Sandusky Fisheries Research Station, 305 East Shoreline Drive, Sandusky, Ohio 44870
Invasive sea lamprey populations are above target in Lake Erie, and a large larval population in the St. Clair River is hypothesized to contribute to the problem. Historically, the St. Clair River system was heavily degraded and was not thought to support problematic sea lamprey populations. However, recent restoration and remediation efforts have resulted in improved environmental quality in the river. We examined the relationship between changes in water quality in the St. Clair River and larval sea lamprey populations, using existing monitoring data from multiple agencies to analyze trends in dissolved oxygen (DO) and temperature (T) at locations near standard sea lamprey survey sites. Our inability to combine data across agencies limited the spatial and temporal coverage of our water quality data. We did not detect trends in DO or T through time. We also plotted the frequency of extreme events (i.e., high T and low DO) at point source discharges through time. Interestingly, the frequency of these extreme events increased in recent years at several stations, but we were unable to detect long-term trends in the data. We examined trends in Secchi depths in the system through time and did not find clear patterns. Finally, we created Geographic Information System (GIS) layers of habitat restoration sites, sediment remediation areas, former combined sewer overflow (CSO) sites, and former industrial point source pollution discharges. We overlaid these “areas of remediation” with statistically significant larval sea lamprey hot spots (i.e., areas with elevated densities of larval sea lamprey), and although two hotspots were associated with former CSOs or industrial point sources near tributary outflows, we did not find any overall patterns of spatial correlation that would suggest a causal relationship. There was a consistent pattern throughout the time series of within-year hot spots of larvae in the lower St. Clair River just upstream of Harsens and Walpole Islands, and a high outlier site on the upstream end of Stag Island. Sea lamprey surveys could be conducted near the outflows of formerly polluted tributaries in systems of interest, as these were the only areas that appeared spatially correlated with sea lamprey hotspots in this study. We conclude that although our data do not allow us to say that improved water quality or habitat restoration has led to increases in larval sea lampreys in the St. Clair River, other formerly polluted river systems might produce more sea lampreys as they are restored. Agencies must institute consistent, well-designed water quality monitoring to understand how sea lampreys and other undesirable species might respond to changing conditions.