Summer 2019 eNewsletter

Featured Research

Modeling Lake Michigan’s Suitability for Bigheaded Carps

The invasion of several notorious non-native species, such as the sea lamprey and zebra mussels, have transformed the ecological landscape of the Great Lakes. As efforts to understand and minimize the damage of already entrenched invaders continue, the prevention of new invasions has become the strategic priority of invasive species management and has motivated research that identifies which species pose the greatest threat to the Great Lakes. Of the many species being monitored by scientists, perhaps none are more concerning than bighead and silver carp (collectively referred to as bigheaded carp).

Bigheaded carp. Photo Credit: CIGLR.

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. These species escaped into natural waterways, quickly spreading throughout the Mississippi River basin. Bigheaded carp have established dense populations in many rivers, including the Illinois River where they comprise 63% of the total fish biomass. Bigheaded carp disrupt aquatic food webs by voraciously feeding on zooplankton and phytoplankton, limiting the food available to resident plankton-feeding fishes and potentially impacting the larger predatory fish that feed upon them. While they prefer to eat plankton, bigheaded carp will consume alternative foods, such as detritus and bacteria, when plankton becomes less available.

The close proximity of the bigheaded carp population 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. 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 the question: does Lake Michigan have enough food for Bighead and Silver carp to thrive?

Previous research indicated that bigheaded carp could only survive in plankton-dense areas of Lake Michigan, such as Green Bay, but important knowledge gaps persist. These studies only considered the food available at the water surface, though a deep-water layer of algae is common during summer, and did not evaluate the possibility of bigheaded carp feeding on non-plankton food sources.

Figure 1. Map of Bighead carp (left) and Silver carp (right) average habitat quality in the summer (June-Aug) in Lake Michigan with references to major river mouths (triangles with the name of the river) and surrounding cities and states. The map displays colors of Growth Rate Potential, with deeper blues representing areas with lowest habitat suitability for growth and deeper reds represent those habitats that are best suited for growth. Grey habitat within the lake indicates areas where growth potential was negative, and thus deemed not suitable.

To develop a more complete understanding of bigheaded carp invasion risk, Peter Alsip (CIGLR’s Ecological Modeling Data Analyst) and a team of scientists from CIGLR and NOAA GLERL have constructed a model that evaluates the suitability of Lake Michigan habitats for bigheaded carp growth. This approach (referred to as a “growth rate potential model”) measures habitat quality based on water temperature, prey abundance, and bigheaded carps’ physiological requirements for growth. The detailed data produced by the model allowed the team to evaluate habitat quality throughout the entire lake, including subsurface environments, while also accounting for the ability of bigheaded carp to feed on an alternative prey item, detritus, as well as their preferred prey: phytoplankton and zooplankton.

Not surprisingly, the model indicated that habitats with greatest potential to support bigheaded carp were located near river mouths and in the algae-rich area of Green bay, which agrees with previous studies. However, in contrast to previous studies, they also found suitable offshore habitat for Bighead carp (Figure 1) due to the added considerations of diet flexibility and subsurface food sources. While a majority of Lake Michigan’s offshore areas are suitable for Bighead Carp, they are relatively low in quality, which will make it less appealing for the fish to reside there for extended periods. However, the suitability of offshore habitat may provide migration corridors through which bigheaded carp could spread to more food-rich areas in the lake.

Using the same approach described above, Peter is currently conducting research to understand how meteorology, lake-wide phosphorus loads, and invasive mussel filtration affect bigheaded carp habitat suitability. This new study seeks to understand how these stressors individually and interactively influence the vulnerability of Lake Michigan to bigheaded carp.

“Our new study is exciting because it could provide a basis for understanding how a warming climate will affect Lake Michigan’s suitability for bigheaded carp in the future. It will also help explain how past changes in nutrient loads and invasive mussels have shaped habitat suitability as we understand it today,” says Alsip.



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)

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