J. Great Lakes Res. 31:267–276 Internat. Assoc. Great Lakes Res., 2005 Sculpin Community Dynamics in Lake Michigan Charles P. Madenjian 1,* , Darryl W. Hondorp 2 , Timothy J. Desorcie 1 , and Jeffrey D. Holuszko 1 1 U. S. Geological Survey, Great Lakes Science Center 1451 Green Road Ann Arbor, Michigan 48105 2 Cooperative Institute for Limnology and Ecosystems Research University of Michigan National Oceanic and Atmospheric Administration, Great Lakes Environmental Research Laboratory 2205 Commonwealth Boulevard Ann Arbor, Michigan 48105 ABSTRACT. Two hypotheses have been proposed to explain the dynamics of sympatric populations of deepwater sculpin (Myoxocephalus thompsonii) and slimy sculpin (Cottus cognatus). The first hypothesis is that slimy sculpins negatively affect survival of deepwater sculpins, and therefore deepwater sculpins coexist with slimy sculpins only when a keystone predator, lake trout (Salvelinus namaycush), is abun- dant. According to the second hypothesis, changes in the abundances of the sculpins are driven by inter- actions with fishes other than sculpins. To evaluate both hypotheses, we applied regression analyses to long-term observations on abundances of both sculpin populations in Lake Michigan during 1973–2002. For slimy sculpin abundance, we considered the predation effect by lake trout and the effect of deepwater sculpins on slimy sculpins. For deepwater sculpin abundance, we considered the effect of alewife (Alosa pseudoharengus) on deepwater sculpins, the predation effect by burbot (Lota lota), and the effect of slimy sculpins on deepwater sculpins. An information criterion was used to select the best regression model explaining the temporal trends. The best model to explain trends in slimy sculpin abundance was the model that included the lake trout predation term only. The best model to explain trends in deepwater sculpin abundance was a model including the alewife and burbot predation terms. Thus, a negative effect of slimy sculpins on deepwater sculpins was not essential in capturing the sculpin community dynamics. Therefore, our results supported the second hypothesis. Further, our results supported the contention that control of the alewife population was a prerequisite for restoration of deepwater sculpin populations. INDEX WORDS: Deepwater sculpin, food web, predation, restoration, slimy sculpin, species inva- sions. INTRODUCTION Brandt (1986) proposed that the dynamics of deepwater sculpin (Myoxocephalus thompsonii) and slimy sculpin (Cottus cognatus) populations in the Laurentian Great Lakes were regulated by the pres- ence of a keystone predator, lake trout ( Salvelinus namaycush). The basic premise for his hypothesis was that slimy sculpins, through competition with or predation on juvenile deepwater sculpins, ex- erted a negative effect on the survival of deepwater sculpins. Therefore, deepwater sculpin and slimy sculpin populations would coexist only when the abundance of lake trout was sufficiently high. * Corresponding author. E-mail: cmadenjian@usgs.gov When abundance of lake trout remained too low for a sufficient amount of time, deepwater sculpin would be extirpated. To support his hypothesis, Brandt (1986) presented data showing habitat over- lap between slimy and deepwater sculpin in Lake Michigan. Citing other studies, he also documented that the diets of the two sculpin species were simi- lar, and that slimy sculpin is the preferred food of juvenile lake trout. Finally, he argued that deepwa- ter sculpin was extirpated from Lake Ontario during the 1950s because lake trout had been absent from the lake for too long a period of time. Others have argued that the dynamics of deepwa- ter and slimy sculpins in the Laurentian Great Lakes were driven by interactions with non-sculpin 267