SHEBOYGAN, Wis. -- Try to imagine Lake Michigan in the 18th century.
Before man-made channels eased the way for transoceanic shipping, before aquatic invasive species flooded in, before byproducts of the industrial revolution began to pollute its waters.
From the records available, the Big Pond's ecosystem was dominated by one top predator, the lake trout.
More than a dozen cool-water species such as walleye and northern pike were associated with bays and tributaries.
And further down the food chain, at least seven species of ciscos were known to exist.
It would be unwise to dismiss the smaller fish as mere food for bigger species. The ciscos also helped distribute energy from shallow to deep waters.
In fact one of them -- the lake herring, known to scientists as Coregonus artedi -- was the most abundant species in each of the Great Lakes, according to scientists.
The lake herring also was one of the most, if not the most, important commercially-caught fish species in Lake Michigan through the 19th century.
But populations of the ciscoes generally collapsed during the middle of the 20th century because of overfishing, interactions with invasive species such as alewife and rainbow smelt and loss of spawning and rearing habitat, according to research cited in "Ciscoes of the Laurentian Great Lakes and Lake Nipigon," by the Great Lakes Fishery Commission.
Five of the ciscos are now completely gone from Lake Michigan. Only the bloater chub and the lake herring remain.