If you’ve read the news regarding the Great Lakes at any point in the past decade or two, you’ve likely heard that those big water bodies are under constant, imminent threat from two sources: invasive Asian carp and blue-green algae. While invasive bighead and silver carp have so far failed to establish a population in any of the lakes, algal blooms are common sights for anglers and boaters.
Using remote sensing and bioenergetics, the study of energy’s movement through living systems, researchers from the U.S. Geological Survey have determined that enough algae exists in Lake Erie to sustain both of the carp fish, were they to establish a foothold. The results of the study, published in the Journal of Great Lakes Research, show that satellite imagery and bioenergetics offer useful tools for fishery managers and researchers.
“Bioenergetics models have been used for a plethora of other fishes,” said Karl Anderson, fish biologist with the USGS and lead author of the paper. “It is a common tool used by fisheries biologists to try to estimate how big a fish will get. It has a huge, huge literature background.”
The paper’s authors employed a model developed for a 2010 study on the suitability of the Great Lakes for Asian carp, but improved it with more species-specific parameters. For instance, the 2010 study’s authors used tilapia energy density as a stand-in for that of Asian carp. The researchers compared results from their updated model with existing reports on carp growth and found that their updates made for a very accurate tool.
“Using our study, we were able to show that Lake Erie, in fact, provides a very large area of adequate food for bighead and silver carp,” Anderson said.
The model relies on a range of parameters, including water temperature, fish energy density, food availability and how much food an individual fish can consume. Once the appropriate calculations are performed, the model can determine what algae concentrations are needed for invasive carp to maintain their body weight and grow in Lake Erie.
Remote sensing via satellite imagery enabled the researchers to determine algae concentrations without performing timely and expensive in-situ sampling. But Anderson warns that satellite observations can only measure algae concentrations in the top meter of the water column. Different algal species exist at different levels in the water column, potentially indicating a larger food source for Asian carp than the study recognizes.
“When it comes to our predictions here, we are literally just scratching the surface,” Anderson said.
Determining other parameters required a slightly more hands-on approach. To measure energy density in the carp, Anderson collected fish from different rivers, froze them, then ground the fish into a “homogenous consistency, much like hamburger,” before testing the resulting paste for caloric content.
“Of course, then you have to dry the sample, which causes the whole building to smell like baked fish,” Anderson said, laughing. “They did not like me very much that summer.”
While Anderson is pleased with the efficiency of the improved model, he notes that it leaves out a few key variables. It doesn’t consider predation or the energy cost required for reproduction and other activities such as quick, evasive swimming.
Still, researchers say their updated model is useful for comparing the invasion potential for each of the Great Lakes to help inform management decisions.
“This study demonstrates a tool that natural resource managers can use to evaluate whole lakes,” Anderson said.