Summer 2020 eNewsletter

Featured Research: Modeling Lake Michigan’s Suitability for Asian Carp

Silver carp. Photo Credit: D. O’Keefe, Michigan Sea Grant.

Bigheaded carp are the two plankton-feeding species of Asian carp that were imported to the United States in the 1970s as a means of controlling algal growth in reservoirs and sewage treatment lagoons. The close proximity of bigheaded carp to Lake Michigan has elevated concerns about the impact they could have on the Great Lakes food web, which supports a $7 billion recreational fishery. While their insatiable appetites, flexible diets, rapid growth, and reproduction rates make bigheaded carp a formidable invader, Lake Michigan is colder and has less plankton than the environments where they currently exist, including the Illinois River where they compose 63 percent of the total fish biomass.

Reductions in nutrient loads over the past 50 years and the proliferation of the invasive filter-feeding quagga mussels have transformed Lake Michigan into a plankton desert, which has prompted two questions: 1) Does Lake Michigan have enough food to support bigheaded carp? 2) How do human-caused stressors such as climate change and nutrient pollution affect Lake Michigan’s vulnerability to bigheaded carp?

Satellite MODIS image of Lake Michigan. Photo Credit: NOAA CoastWatch.

To help answer these questions, a team of scientists from CIGLR and NOAA GLERL constructed a model that evaluates Lake Michigan’s suitability for bigheaded carp growth. The work was part of CIGLR Ecological Modeling Data Analyst Peter Alsip’s master’s thesis at the University of Michigan School for Environment and Sustainability. The team’s approach (known as a “growth rate potential model”) measures habitat quality based on water temperature, prey abundance, and bigheaded carp’s physiological requirements for growth. Previous studies indicated that bigheaded carp could only survive in Lake Michigan’s plankton-dense areas, such as Green Bay, but these studies did not account for carp feeding flexibly on different food throughout the water column. The data produced by a 3D lake model allowed the team to build on previous research by evaluating subsurface habitats while also accounting for bigheaded carp’s ability to feed on an alternative prey item, detritus, as well as phytoplankton and zooplankton.

Their results were surprising. By accounting for diet flexibility and subsurface habitat in the model, the research team demonstrated that nearly all of Lake Michigan contains suitable habitat for bigheaded carp. Habitats with greatest potential to support bigheaded carp were located near river mouths and in Green Bay, which agrees with previous studies. However, their research also demonstrates that Lake Michigan’s offshore areas are suitable for bigheaded carp. Although offshore areas offer a relatively low-quality habitat, making them less appealing for resident populations, they may provide migration corridors through which bigheaded carp could spread to more food-rich areas in the lake.

In the next phase of the study, Alsip utilized this model to evaluate how anthropogenic, or human-caused, stressors such as climate change, nutrient pollution, and invasive mussel filtration individually and interactively affect bigheaded carp habitat suitability. Using simulated scenario datasets from the same lake model, the team was able to assess invasion risk for historical, present, and potential future lake conditions.

“We compared model data with recorded lake conditions representative of 2010 to those of the 1980s,” says Alsip. “Lake Michigan experienced heavier phosphorus loads and no invasive mussels in the 1980s, which led to bigheaded carp gaining 8 to 40 percent more weight through the year.” The research team also simulated a scenario with a warmer climate, which lengthened the growing season by increasing the fishes’ foraging activity and limiting food competition with mussels due to prolonged summer stratification of the water column. As suitable habitat increases in time and space, so does the risk of these fishes spreading throughout Lake Michigan and reaching food-rich habitats, such as Green Bay, that will support greater growth.

“Overall, our study demonstrates that Lake Michigan has become less suitable for bigheaded carp since the 1980s, primarily due to strategic phosphorus abatement,” says Alsip. “However, the lake’s vulnerability to these fishes will increase as climate change progresses or if nutrient pollution increases, despite the competitive feeding pressure from dreissenid mussels.”

Related Resources:

• CIGLR Minute: Asian Carp Research (video)
• Invasive Species (webpage)
• Alsip, P.J. 2018. Modeling Lake Michigan’s Suitability for Bigheaded Carps: The Importance of Diet Flexibility and Subsurface Habitat. (thesis)
• Alsip, P.J., H. Zhang, M.D. Rowe, D.M. Mason, E.S. Rutherford, C.M. Riseng and Z. Su. 2019. Lake Michigan’s Suitability for Bigheaded Carp: The Importance of Diet Flexibility and Subsurface Habitat. Freshwater Biology. DOI:10.1111/fwb.13382. (article)
• Alsip, P.J., H. Zhang, M.D. Rowe, E. Rutherford, D.M. Mason, C. Riseng and Z. Su. 2020. Modeling the interactive effects of nutrient loads, meteorology, and invasive mussels on suitable habitat for Bighead and Silver Carp in Lake Michigan. Biological Invasions. DOI:10.1007/s10530-020-02296-4. (article)

Related News Articles:

• Climate warming increases Asian carp threat to Lake Michigan by offsetting quagga mussel ‘ecological barrier’, Michigan News, 7/72020
• Warming Could Lower One Barrier to Invasive Fish Reaching Great Lakes Mussels in the lakes, themselves invasive species, may not be able to outcompete Asian carp for food, as previously thought, Scientific American, 7/8/2020
• Climate Change Would Limit Competition For Asian Carp If Introduced In Lake Michigan, Study Finds: Research Shows Invasive Mussels Won’t Hold Fish At Bay, Wisconsin Public Radio, 7/8/2020