In past decades, the variety of both native and non-native species in Lake Michigan has changed and complicated its waters. Recently, the presence of mussels has created clearer lake water. Though seeming advantageous, it has harmed the Great Lakes environment and the people using it.
The history of Lake Michigan is a cycle of invasion and a resulting struggle to maintain its food web. In the 1940’s, Lake Michigan first encountered problems with invasive sea lampreys. These eel-like creatures attach to large predatory fish and slowly drain their blood. Due to the sea lamprey’s presence, indigenous fish populations like lake trout have drastically declined.
Research fishery biologist, David Bo Bunnell, of the US Geological Surveys Great Lakes Science Center, said, “They pretty much devastated native lake trout, lake white fish and other native species that were already suffering from overfishing.”
Without these large predatory fish, another non-native species, the Alewife, was able to infest the lake. These saltwater fish were able to sneak into this new environment and overpopulate, causing more management problems due to their large die offs during spawning season.
As Alewife populations exponentially increased, coastal managers were left with no choice but to introduce more non-native fish to combat the problem. In the 1960’s, King and Coho Salmon were stocked and brought into the Great Lakes environment. Having a diet mainly consisting of Alewives, the salmon drove down Alewife populations and promoted more sport fishing. Rick Bentley, a former fishing industry worker said, “They’re a very strong fish and they offer a fight…it might take 15 to 20 minutes to bring them in.”
Soon after the arrival of salmon, a new species entered the Great Lakes ecosystem: mussels. Quagga and Zebra mussels, which can thrive in various habitats, feed off phytoplankton and filter water. Their arrival to the Lakes’ already populated waters caused a crash to Alewife populations as food became scarce and predation by salmon increased. In Lake Huron, disappearance of Alewife populations due to invasive mussels drove salmon away to other lakes such as Lake Michigan.
Today, mussels in the Great Lakes continue to be a problem despite their benefits of filtering and clearing lake water. Lake Michigan, in particular, struggles with continuous changes to the fish populations and is beginning to face the same challenges Lake Huron faced.
Yu-Chun Kao, a post-doctoral scientist at Michigan State University, studied Lake Huron’s collapse and explored the effects of the mussel population and nutrients on the Great Lakes ecosystem. Kao’s studies showed that salmon are very vulnerable to lake environmental changes and hypothesized that as mussels overpopulate the lake, salmon populations will likely decline. Additionally, his studies suggested that Lake Michigan could possibly support a diverse ecosystem of mussels, salmon, and other lake trout, but it would require tightly controlled stocking and research to ensure adequate food for all species.
When it comes to stocking the Great Lakes, the Jake Wolf Memorial Hatchery in Topeka, Illinois, has worked with the state to create a better more stable lake ecosystem for both the wildlife and the fishing industries. The hatchery raises 15 species of fish and has continued its practice each year since 1984. More recently with the fluctuating conditions, stocking has required more calculation and collaboration with other states bordering the lake.
In 2006, scientists estimated that the population of Alewives in Lake Michigan weighed 10,000 metric tons. In 2016, all fish populations combined in the Lake were estimated to weigh 11,000 metric tons, reflecting the decrease in the Alewife populations in the last decade. As a result, fish managers at the hatchery have cut stockage of salmon from 3.3 million in 2013, to just 690,000, as of last year.
Mussel populations have not only affected salmon, but their presence raises a concern for the future of Lake Michigan. While mussels have succeeded in clearing Lake Michigan’s waters, their manifestation has also changed the quality of the lake bed. As mussels continue to feed, the bottom of the lake becomes polluted with feces, which react to sunlight and are converted into an algae called cladophore. This increased production of cladophore could attract another non-native species to Lake Michigan, such as the Asian Carp.
The future of Lake Michigan and the fish industry that depends on it is still unclear. For fishermen like Bentley, the sport of fishing has drastically changed to adjust to the environmental shifts in the lake. The arrival and overpopulation of mussels creates fear for the future ecosystem of the Great Lakes. For now, mussel populations seem to have plateaued, but continued research will need to be done on Lake Michigan’s ecosystem to monitor for major fluctuations and any other upcoming changes.
[Source: Chicago Tribune]