Where are the tullibees?
A small, silvery, iridescent fish that lurks in some area lakes is on the decline.
Tullibees, also known as cisco or lake herring, typically weigh about one to two pounds, but can get up to 5-pounds, 12-ounces. They feed on insects, small fish, small crustaceans and zooplankton. Tullibees are also considered an important part in the diets of large predators such as northerns and walleyes.
As members of the trout and salmon families, tullibees are cold blooded and have a low tolerance to high water temperatures. This trait is the reason they are only found in cool, deep lakes with a good supply of oxygen.
Some lakes that fit these requirements in the Alexandria lakes area include the chain of lakes, Lake Bergen, Lake Minnewaska, Lake Osakis, Lake Ida, Lake Miltona and Rachel Lake.
Dean Beck, who is the supervisor with the Department of Natural Resources (DNR) fisheries department in Glenwood, said that the central lakes area is on the southern fringe of the tullibee's range.
The termocline, or middle water layer of a lake, is where the tullibees prefer to live. This layer is cool, yet it contains a conducive amount of oxygen for these fish. Shallow lakes that are highly productive and don't have a deep thermocline won't support tullibees.
A recent concern to those who monitor tullibee populations has been their decline in numbers.
An article from the DNR's Minnesota Conservation Volunteer publication by Darby Nelson states, "According to [Pete] Jacobson [a DNR fisheries biologist], the lakes at greatest peril are along the forest-prairie transition zone form Annandale through New London-Spicer then up through Alexandria and Fergus Falls."
Beck said that, locally, when the DNR does its annual fish surveying, it doesn't catch many tullibees. The few that they do catch does show a decline, however. "We don't catch many regardless," he reiterated.
Tullibees' low tolerance to high water temperatures "may be part of their demise or stress," said Beck. Global warming and climate changes may be partly to blame for rising water temperatures. Beck added that these changes in the environment have caused the depth of the thermocline to increase - bringing the tullibees' ideal habitat closer to the surface and warmer temperatures.
Another requirement for tullibees - an adequate oxygen supply - may be more directly attributed to human habits.
"We're speeding the lakes' aging," Beck emphasized.
The Conservation Volunteer magazine said that phosphorus and other nutrients enter lakes, via run-off from watersheds. Lakes that are rich in these nutrients have more algae and aquatic life. In turn, this vegetation depletes the oxygen supply, leaving less for the tullibees and other fish.
Alexandria and the surrounding area, have so many lakes that any impurity is almost certain to find its way into a lake or river. For this reason, it is particularly imperative that people take care of the watershed.
Beck offered such suggestions as upgrading septic systems, minimizing soil exposure (to prevent erosion) and eliminating pet waste.
Other preventative measures include leaving lakeshore wetlands alone so they can filter pollutants and refraining from using fertilizers with phosphorus.
Warmer weather in the summer months also decreases the amount of oxygen in the water. This causes die-offs of tullibees in some lakes. Beck said this situation tends to be less common, but there is still the fact that die-offs are occurring.
"Tullibees are good indicators," Beck said. Because they are so sensitive to changes in temperature and oxygen levels, tullibees are often one of the first species to drop out.
"If you have tullibees in a lake, you know things are pretty good. If they are declining, you know something is wrong,"' said Jacobson in the Conservation Volunteer magazine.
One thing that has been done for area lakes to help give the tullibee population a chance is to close fall gillnetting. Beck said this practice used to be more common and it's hard to find a gillnet anymore. Anglers put a gillnet in shallow water in the fall (when the tullibees are in their spawning mode) and catch dozens of fish. The only lakes that still allow it in the Glenwood/Alexandria area are Lake Ida and Rachel Lake. Beck said that they are working to close the fall gillnetting on these lakes, too.
Some anglers still catch tullibees the old fashioned way - by casting out a line. Beck said that this doesn't pose nearly as much of a threat as water quality and temperature.