The food chain that nourishes life on land is much like the food chain that nourishes life in Lake Michigan. Organic creatures feed small invertebrate creatures, which in turn feed larger vertebrate creatures, which in turn feed the largest of vertebrates-humans.

Steve Pothoven, who works next door to Coast Guard Station Muskegon at the National Oceanic Atmospheric Administration’s (NOAA) Lake Michigan research center, laughed when I used this simple comparison but admitted it was an accurate comparison at that. Well, I thought it was a lot more user friendly than the scientific terms he threw at me like microscopic Bythotrephes , Cercopages , and similar words that caused many of us to pursue majors other than biology and medicine.

Steve, 29, certainly is one who apparently can handle such words, earning a master’s degree from the University of Minnesota in fisheries with an undergraduate degree in biology. He currently works for the Great Lakes Environmental Research Laboratory (GLERL), which is part of the National Oceanic and Atmospheric Administration. GLERL’s main laboratory is located in Ann Arbor.

Steve and other GLERL researchers spend weeks underway on Lake Michigan aboard the University of Michigan’s 80-foot research vessel "Laurentian", and NOAA’s 65-foot "Shenehon".

GLERL researchers monitor the health of the Lake’s food web in order to provide baseline data to managers of natural resources and policy makers in the Great Lake region. Their research holds particular interest for sport fishermen who pursue yellow perch, salmon and trout.

The food chain for yellow perch, salmon and trout starts with basic organic creatures called microscopic phytoplankton, or in simpler terms- algae. Small invertebrates called Diporeia that live in the Lake’s bottom sediments feed on the algae, these spineless creatures in turn provide food for small prey fish such as alewife, bloater, whitefish and juvenile yellow perch. Of particular interest to sport fishermen is the alewife, which is the main food source for the salmon.

Recently GLERL scientists have noted a drastic decline in the invertebrate Diporeia in Lake Michigan, which in time could affect the alewife and thus the salmon population. The reason Diporeia invertebrates are declining could be because of zebra mussels. When Zebra mussels invaded the lake in the late 1980’s, they rapidly multiplied and began to compete with Diporiea invertebrates for algae. The zebra mussels’ aggressive filter feeding consumed algae at a much greater rate than Diporeia invertebrates and by 1993 Diporeia numbers had declined to nearly zero in water depths less than 150 feet in the southern portion of the lake. The decline has continued to spread into northern areas of the lake.

Declines in Diporeia could force fish to use alternate food sources that may not contain as much energy as Diporeia. This could result in lower fish growth or reduced reproduction output, which will ultimately affect the food quality and quantity available to predator fish such as salmon, lake trout, and adult perch. GLERL researchers like Steve are monitoring Diporeia population numbers and how fish populations are responding to the loss of major food items.

Their findings are not encouraging. According to Steve, GLERL scientists discovered quagga mussels in Lake Michigan in June 2000. This exotic mussel is related to the zebra mussel, but can reproduce in deeper water depths than zebra mussels. The quagga mussel could affect the offshore waters in a manner similar to what has occurred in the near shore areas since zebra mussels arrived. This means that there may be a lower potential for production of invertebrates and in turn lower production of prey fish in the future, which would ultimately affect salmon and lake trout production.

In addition to zebra and quagga mussels competing at lower food chain level, there are two other exotic species that arrived in Lake Michigan via ship ballast water in the 1980’s- the spiny water flea and fish-hook flea. These species possess long spines and are frequently found in clumps on fishermen’s downrigger lines. These spiny creatures compete for the same algae, as juvenile yellow perch do. In addition to direct competition, their long spines prevent small fish from feeding on them. Larger yellow perch and alewife, however, are able to include the spiny water fleas in their diet, although the large spine does not appear to be readily digestible and may reduce the nutritional value of these species.

So what does this all mean regarding Lake Michigan’s fish population including the huge salmon school? Well, that question remains to be answered, but Steve will admit that it does offer a potential problem that needs to be closely monitored. For certain, without the vigilant efforts of GLERL researchers, serious threats to the food web system like zebra mussels and the like hold little chance of being abated.

As for now, GLERL is spearheading a project to evaluate the effectiveness of regulations that will require ships to flush ballast tanks with salt water prior to entering the Great Lakes. This practice is intended to kill fresh water organisms picked up in foreign ports.

By stopping the import of foreign species into the lakes fresh water ecosystem, the advance of zebra mussels and other alien species that threaten the Lakes delicate ecosystem will be abated.

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Boat Smart is now on the Internet: www.boatsmart.net (includes Lake Michigan water temperatures and local weather).

Use channel 16 for emergencies, and channel 9 for calling fellow boaters.