Michigan Department of Natural Resources
Fisheries Research Report No.1877, 1980
Population Dynamics of Trout in Some Streams of the Northern Lower Peninsula of Michigan
Howard Gowing and Gaylord R. Alexander
Abstract.-Standing crop, growth rates, and production were computed for trout in 14 streams located in the northern lower peninsula of Michigan. These waters lie in a region with soils which have a high infiltration rate and ground-water recharge. They have the prerequisite flow and temperature regimes, along with carbonate hardness, to be classed as good trout streams. The streams varied in width from 4. 7 to 33. 9 m and in mean discharge from 0.42 to 4.95 m3 per second.
One stream contained brook trout only, three contained brown trout almost exclusively, and 10 streams had two or more species of trout. Rainbow trout were present in four of the streams. In 9 of the 10 streams having more than one trout species, brown trout, on the average, comprised 68% of the total standing crop (kilograms per hectare). Of the 10 streams containing brook trout, 3 had fall standing crops of this species no greater than 2.4 kg per hectare. Total fall standing crop of all trout averaged 85. 1 kg per hectare. Standing crop per unit area was not related to size of stream based on discharge.
Trends in survival of brown and brook trout differed in that the latter showed better survival the first summer but poorer survival the third year and thereafter. At age 0 and older, brown trout attained a greater length and weight than brook trout with differences tending to increase with age. Brown trout lived longer than brook trout. Relatively few brook trout survived to age IV whereas brown trout commonly survived to age VII. The average annual production of brown trout populations was 81. 6 kg per hectare, brook trout populations 24.0 kg per hectare, and rainbow trout populations 8. 5 kg per hectare. Production of trout) all species combined and all streams combined, averaged 95.4 kg per hectare. The average P/B ratio, based on the fall standing crop, was 1.04 for brown trout, 1.68 for brook trout, and 1. 72 for rainbow trout. For all trout combined it was 1.13.
On six streams censused for angling, the fishing ranged from 160 to 75 6 hours per hectare or an average of 5 12 hours per hectare . Anglers cropped between 25 and 378 trout per hectare and from 4. 1 to 37. 7 kg per hectare. Harvest represented 4-37% of the annual production. Potential production of trout in six streams was also estimated on the basis of natural mortality (M) in the absence of fishing mortality (F). This tended to increase production values, more for brown than brook trout. Streams were rarefied on a basis of annual production per unit area (grams per hectare), per unit area per annual discharge (grams per hectare per cubic meter per year), and per unit length per annual discharge (grams per kilometer per cubic meter per year) which indicated a greater efficiency of water use and productivity of trout in small streams compared to large streams.