DULUTH (AP) — Minnesota fisheries managers are concerned about the future for herring on Lake Superior.

At a time when demand for the fish has increased, biologists worry not enough young herring are surviving.

Commercial fishermen who ply the waters off Minnesota's North Shore have caught a lot fewer cisco, or lake herring, in recent years.

Minnesota Department of Natural Resources fisheries chief Don Pereira says at least on the western arm of Lake Superior, the herring population "is not in a healthy state."

Pereira says cisco are vital to both whitefish and lake trout, which eat herring or herring eggs to survive.

The fragile cisco population has led Minnesota fisheries managers to impose conservative limits on fishermen. But in Wisconsin, there hasn't been any cisco limit.