Effects of Stream Channelization on Fish Populations in the Buena Vista Marsh, Portage County, Wisconsin

Fish populations from 6-8 year old ditches and 52-62 year old ditches within the Portage County Drainage District were compared with populations in adjacent portions of natural streams. Two study areas were selected, the upstream zone of good brook trout ( Salvelinus fontinalis) habitat and the other downstream in marginal trout waters where white sucker ( Catastomus commersoni) were more numerous. Each area included new ditch, old ditch and natural stream , all of similar discharge. Estimates of annual production by brook trout, population and biomass estimates of brook trout and white sucker, and total catch records for other fish species were derived from electrofishing samples in June, August and September, 1974 and April-May, July and September, 1975. A creel survey was conducted during the 1975 trout season. Loss of year-round instream cover through channelization limited brook trout density, which reduced annual production by brook trout to 28.8 kg/ stream km in the upstream new ditch study area as opposed to 72.2 kg/km in the upstream old ditch and 65.5 kg/km in the upstream natural stream. Angler success was also reduced, from 1.03 trout/hr in the upstream old ditch and 1.05 trout/hr in the upstream natural stream to 0.26 trout/hr in the upstream new ditch o Approximate equality of these parameters in the upstream old ditch and natural stream indicated that recovery of natural channel morphology and trout carrying capacity was nearly complete after 60 years. Midsummer water temperatures reached upper lethal levels for brook trout in the downstream ditches, where current velocity was reduced and white sucker were abundant. Mottled sculpin (Cottus bairdi} were consistently absent from the upstream new ditch and scarce in the downstream new ditch. Natural stream had the greatest number of fish species in both study areas (12 upstream and 18 downstream), and new ditch had the fewest (9 upstream and 11 downstream).U. S. Fish and Wildlife Servic