Michigan Department of Natural Resources
Fisheries Research
Report No.1800,1973
Changes in Fish Species Composition in the Au Sable River,
Michigan, from the 1920's To 1972
John Scott Richards
Abstract.-An ichthyological
survey was made of the Au Sable River and it; tributaries, as part of a broader
study of current economic developments within the watershed and the capacity of
the river to absorb the impact of an increase in human population and the
accompanying exploitation of resources, without undue deterioration of
environmental quality. Fishes have an important role in recreation, and the
composition of the fauna will reflect changes due to environmental abuse such as
reduced water flow, increase in temperature, chemical pollution, over-enrichment
by nutrients, over-fishing, and others. Fortunately a careful fish survey was
made on the river about 50 years ago by Carl L. Hubbs and associates. I repeated
the same survey during the summer of 1972, duplicating the gear, river sites,
dates and time, as closely as possible. Collections taken in 1972 were compared
with the Hubbs' collections by three approaches: (1) a species analysis, (2) a
faunal resemblance index, and (3) species diversity; the latter two involve
statistical procedures. Hubbs took 45 species; I took 44; 37 species were the
same. Judging from abundance of coldwater species and from the. statistical
indices, the river system has improved as "trout water" in the central
cold-water area: the lower half of the North Branch and Big Creek, the lower
half of the South Branch, and the Main Stream from Grayling to the South Branch.
On the other hand, quality of trout water has deteriorated above Grayling in
both Main Stream and East Branch, in the headwaters of the North Branch, and
from Cooke Pond downstream. Most of the river from the South Branch to Cooke
Pond has changed little as trout water. For the immediate future, measures which
would lower the water temperature during summer months would be favorable to
trout fishing, especially in those stream segments where there has been some
deterioration during the last 50 years.