By Dr. Joel Hoffman
|In July 2011, scientists and educators from around the Great Lakes will be aboard EPA’s Lake Guardian research vessel to research environmental conditions in Lake Superior, and share their stories.|
On Saturday night we hit a rough patch of weather. As the waves climbed towards 6-8 feet tall, we were forced to stop our scientific sampling at about 3 AM and search for a safe harbor. We found calm waters inside the Keewenaw Waterway, a shipping canal that cuts through the Keewenaw Peninsula (a prominent peninsula that extends far into Lake Superior in the south-central portion of the lake) and were forced to lay low in the port of Houghton, Michigan until the conditions were calm enough to return to work. After the storm passed, we continued sampling along the east side of the Keewenaw Peninsula, in the center of Keewenaw Bay. It was not long before it was apparent that the storm had changed the character of the lake. Before the storm, there was a large pool of warm surface waters (warm for Lake Superior is 65°F) extending 60-70 feet down that was sitting atop very cold (37°F), denser water at the bottom of the lake. After the storm, the the surface water was quite a bit colder (55-60°) and gradually became colder with depth.
Sampling began shortly after dark and the evening’s station provided some exciting views and some exciting science. After deploying the manta trawl to sample for plastics floating on the surface of the lake, our teacher-scientist team stood in the bow of the boat and watched a northern lights display. It was spectacular.
We then deployed the tucker trawl to catch fish larvae – young fish that have yet to develop all their adult features such as fins and scales. Away from shore in nearly 200 feet of water, we captured the young of burbot (also called eelpout or lawyer fish), a freshwater cod species. Although we think of these deep, cold waters as being harsh for life compared to the warm, shallow, more productive coastal environment, the young burbot appear to thrive in the colder conditions. While the adults live close to the bottom and eat fish (they can be found in the deepest portions of Lake Superior – over 1300 feet deep!), their young live close to the surface, feeding on a diet of fatty plankton. This is a wonderful example of how all the lake is connected – that a species could starts its life in the upper few feet of the lake and complete its life in its greatest depths.
About the author: Dr. Joel Hoffman is a research biologist in EPA’s Mid-Continent Ecology division, and. the head scientist for the 2011 Lake Guardian Shipboard and Shoreline workshop on Lake Superior.
Editor’s Note: The opinions expressed in Greenversations are those of the author. They do not reflect EPA policy, endorsement, or action, and EPA does not verify the accuracy or science of the contents of the blog.