Fisheries Research Report No.1801, 1973

Michigan Department of Natural Resources
Fisheries Research Report No.1801,1973
Food Interrelationships of the Mottled Sculpins, Cottus bairdi, and Juveniles of the Rainbow Trout, Salmo gairdneri,
in a Tributary of Lake Superior

Paul R. Hannuksela

Abstract.-Young rainbow trout and sculpins occupy similar habitat in many Michigan streams, and thus may compete for available food. To examine this possibility, I investigated the production and food habits of coexisting populations of the mottled sculpin and juveniles of the rainbow trout, in relation to the standing crop of bottom fauna in a small tributary of Lake Superior. Production of age-0 and age-I rainbow trout from June to August 1970 was 2. 8 g/m². Mottled sculpin, of ages I and II, produced 1. 5 g/m² during the same period. The bottom fauna was composed mostly of Tendipedidae, Hydropsychidae, Rhyacophilidae, Limnephilidae, Baetidae and gastropod. The mean standing crop of bottom fauna was 9.4 g/m². The rainbow trout and the mottled sculpin had similar diets; bottom organisms were eaten in approximate proportion to their abundance in the stream. No mutual predation occurred between the two fishes. The low total food consumption of 1. 9 times the mean standing crop of benthos indicated that detrimental food competition probably did not occur between rainbow trout and molted sculpins.