Cisco, also known as lake herring, were once the primary prey fish in Lake Erie and supported the largest commercial fishery in the Great Lakes. The population collapsed in the 1920’s due to over-fishing, habitat loss, pollution, and the introduction of non-native species like rainbow smelt. By the 1960’s cisco were virtually gone from Lake Erie and are now considered extirpated. Since their collapse, Lake Erie has undergone many changes, both positive and negative, to the extent that the lake e