Monitoring of white sucker tumors in Sheboygan AOC: testing spatial history with stable isotopes [CAP_1_2012]
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Purpose

In coordination with WDNR, USGS, and USFWS, this project involves capturing white suckers in the Sheboygan River AOC to assess whether the tumor BUI can be delisted. These tumors are believed to reflect long-term exposure to chemical contaminants in many AOCs. A fundamental challenge in interpreting results from migratory species—such as white suckers—is resolving whether they have resided in the contaminated area, or instead entered the area to breed after spending their lives elsewhere. Chemical tracers are a common approach for assessing the spatial history of migratory fish, and can fruitfully be applied to the Sheboygan context.

Objective

If suckers mix widely, we would expect isotopic ratios to be similar across wide spatial scales. By identifying which invertebrates most closely resemble sucker tissues (after correcting N ratios for trophic fractionation), we can establish where the fish are spending the majority of their time. At a broader scale, both my previous work in northern Green Bay and studies of riverine white suckers (Doherty et al. 2011) indicate that these fish return consistently to the same watershed to spawn every year. If suckers remain close to their spawning watershed throughout the year, we would expect to observe distinct isotopic ratios among populations due to local environmental conditions. Our comparisons to other populations will test whether the Sheboygan River run of white suckers represents a local sub-population that would be exposed to toxicants only in the Sheboygan region, or instead these fish mix freely along the Lake Michigan shoreline before selecting a tributary to reproduce within.

Outcome

In addition to quarterly and final reports, we will provide compiled data and sampling GPS coordinates to WDNR for archiving purposes. The final report will include a full statistical analysis of the spatial scale at which suckers mix along the Wisconsin shoreline of Lake Michigan, with reference to both the Sheboygan and Fox River AOCs.

Study Design

We will use stable isotopes to test habitat use by migrant white suckers, thereby strengthening the potential request to delist that BUI and the Sheboygan River AOC as a whole. Stable isotopes are useful for determining habitat use because the stable isotope ratios of organisms reflect both their diets and environmental gradients. Isotope ratios of consumers reflect their diets in predictable ways (carbon isotopes directly reflect the diet, while nitrogen isotopes increase consistently with trophic level by ~3.4‰ from prey to consumer).We expect to find distinct nitrogen isotopic ratios between the stream and the open lake because agricultural nitrogen inputs create strong isotopic enrichment relative to the natural background in Wisconsin streams (Diebel and Vander Zanden 2009), and the Sheboygan River watershed is 67% agricultural by area. For carbon isotope rations, EPA scientists (Hoffman et al. 2010) identified gradients in carbon isotope ratios along the transition from the St. Louis River to Lake Superior, and my past research has revealed sharp contrasts in carbon isotope ratios between stream biota and lake-dwelling suckers in northern Green Bay. Thus, I expect to find gradients of both nitrogen and carbon isotopes that can be used to identify whether suckers running into the Sheboygan River are residents within the river, the Sheboygan harbor, or Lake Michigan more broadly. If the suckers sampled for tumors include a mixture of river and lake-dwelling fish, we would also be able identify which individuals have spent the most time in the Sheboygan River and harbor compared to dwelling in Lake Michigan, thereby refining the tumor assessment in important ways. This two-pronged approach comparing Sheboygan River suckers to both macroinvertebrates from the Sheboygan region and suckers migrating into other watersheds will enable us to draw inferences about the spatial scale of habitat use by Sheboygan River suckers. Our results will aid in interpreting the significance of shifts in white sucker tumors and other BUIs in the Sheboygan River AOC. Specifically, the argument to delist the tumor BUI will be much stronger if stable isotopes indicate that the Sheboygan population is localized (and thereby subject to contaminants remaining within the river), yet still shows low tumor rates.

Related Reports

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Great Lakes Restoration Initiative
Toxics and Areas of Concern
CAP_1_2012
2012
Proposed
 
Reports and Documents
White Sucker Tumor Proposal
Initial Project Proposal
Sucker Isotope Data
Sucker Isotope Final Report
Sucker Scope of Work GLRI Capacit Grant
Monitoring of white sucker tumors in Sheboygan AOC: testing spatial history with stable isotopes
 
Activities & Recommendations
Monitor AOC Beneficial Use Impairments
In coordination with WDNR, USGS, and USFWS, this project involves capturing white suckers in the Sheboygan River AOC to assess whether the tumor BUI can be delisted.
 
Watershed
Sheboygan River
 
Waters
Sheboygan River
Monitoring Data