Analysis of recent declines in cisco (Coregonus artedii) populations in several northern Wisconsin lakes
Lakes of northern Wisconsin are primarily glacial kettles; many are unconnected to other surface waters. Since the glacial retreat, when cisco probably were present in most of these lakes, the proportion of cisco lakes has decreased. Only 14 \% of Vilas County lakes larger than 30 ha have been reported to contain cisco, and in the past 25 years this figure has declined further, Among our four study lakes, the species has disappeared complerely from Allequash Lake and is nearly gone from Big Muskellunge. Both these lakes offer marginal cisco habitats; however other lakes with equally poor conditions still have thriving cisco populations. In another of our lakes, Sparkling Lake, cisco are being displaced by invading populations of rainbow smelt (Osme17ls mordax). This is in contrast to the dominance patterns reported for the analogous European species (Coregonus albula and Osmerus eperll1nus). Cisco abundance may also be decreased by walleye (Stizostedion vitreum).