MDNR Fisheries Biologists make amazing discovery in their own back yard
“Five years ago, we were doing a large lake survey on Elk Lake, and pulled in some lake trout and they just looked different, like something special” said Jory Jonas, a research biologist with the Charlevoix Fisheries Research Station. The fish the DNR had netted seemed more bullet shaped with the dorsal fin set further back on the body and they had a different coloration. These observations led Jonas to have genetic analysis performed on samples from 25 fish. The results showed these lake trout had more similarities to Lake Superior genotypes than to current hatchery brood stock or to lake trout stocked in Elk Lake during the 1980’s. They had other unusual traits as well. When water temperatures drop to 46-52 Degrees F in the fall, it’s spawning time for lake trout. Typically, lake trout prefer shallow rocky bars to drop their eggs that hatch in four to five months and require oxygen rich water. The Elk Lake fish laden with eggs, however, are in 100 feet or more of water along the western side in the lake’s central basin, leading to speculation that they may be related to one of the deepwater forms that used to exist in Lake Michigan. It’s believed that their Lake Michigan counterparts succumbed to over fishing and the sea lamprey and became extinct in the 1950’s. “Any lake trout that you catch in Lake Michigan today, with the rare exception, is from a hatchery,” said Jonas. Since Elk Lake was dammed off from the Grand Traverse Bay starting as early as the 1860’s, and fish passage was all but eliminated by the turn of the century, these trout may have remained genetically isolated for over 100 years.
With help from Laura Mathews, a Central Michigan University biology student working on a Masters degree, Jonas embarked on an extensive study of the lake trout in Elk Lake this fall. “How do eggs survive in up to 180 feet of water on a clay bottom, where does the oxygen come from?” questioned Jonas. However, studying fish in very deep water is a difficult task. Current DNR long-term temperature monitors in Elk Lake are located in water that is too shallow. Capturing fish with nets in water this deep is also difficult. The researchers want to avail themselves of underwater robotic technology being used to capture fish in the Great Lakes and plan to start bottom mapping with high tech sonar equipment that can differentiate bottom substrates starting next summer. So far 130 fish have been tagged and released. Subsequent net drops were successful but only two tagged fish have been recaptured, indicating the population size may be large. Jonas hopes to get help from local fishermen. If you catch a tagged lake trout, the DNR would like you to send the date, location of capture, length of the fish and the tag (if kept) or tag number (if released) to the Charlevoix Great Lakes Station or report the information on the following website; http://www.michigandnr.com/taggedfish/
For additional information, fishermen may call (231) 547-2914.
Great Lakes fisheries managers believe there used to be six to nine different strains of lake trout in Lake Michigan that disappeared in the 1950’s. The strains that have been planted since have struggled to reestablish themselves due to reproductive issues such as poor egg hatching and poor survival of fry. “A lot of fingers get pointed at alewives, round gobies and rusty crayfish eating lake trout fry”, Jonas said. “Bottom line is, we don’t know why they are having these issues.” Fisheries managers had been traveling to other States where historic Lake Michigan strains were exported in the past to look for reproductively successful populations and now they may have found one in their own back yard. Jonas recently submitted 50 additional samples from Elk Lake to a geneticist to be compared to scale samples from Lake Michigan genotypes. If sufficient similarities exist it may lead to an attempt to create a hatchery brood stock. “If that is successful, it would reintroduce genetic diversity that we can’t find anymore,” said Jonas.
