UlaTristan UlaIchthyologyDr. Miner10/12/05Mark-Recapture and Population Characteristics by Depth in Rusty Crayfish (Orconectes rusticus)in the Portage RiverIntroductionOver the past few years, studies have been conducted to better understand the habitat and niche of the rusty crayfish (Orconectes rusticus). The varying substrate properties of a river bed have shown to effect crayfish distribution based on predation and size. Crayfish on sand beds were found to be smaller (based on carapace length) and preyed on more frequently than larger crayfish in stone or macrophyte habitats. (Kershner M. W., 1995, Smily P.C., 2000) Additionally, depth also has an effect on crayfish distribution which was measured with the initial capture. Size has been seen to be relative to depth, in that as the water depth increases, the size of the crayfish increases. (Englund, 2000). It was expected that there would be a correlation between depth and carapace size. A mark-recapture study was performed to calculate population size. The purpose of this method is to study the distribution and population size in a 13m X 26m riffle in the Portage River. By marking the crayfish initially caught and releasing them back into the riffle, the population was calculated from the Peterson Method and the density was found using the area of the riffle.