The Big Water

Tucked away in the pine forest of Northeast Lower Michigan is one of the state’s most unique river reaches, the 23-mile stretch of the Au Sable River below Mio Dam. If you have a yearning to experience "Big Water" this is the place to visit, with stream widths approaching 200 feet and depths to float your hat. It is most easily fished by boat, but anglers can wade most shore areas; just don’t expect to cross the river very often. It also has a reputation for brown trout, BIG brown trout!

The uniqueness of this section of river is, in large part, its magnitude. It is the largest cold water river in the Eastern United States boasting an average annual discharge at Mio of more than 1,000 cubic feet per second (cfs). In addition, this section has the highest free flowing gradient of any Michigan stream in its class, nearly 4.5 feet of drop per mile of stream.

Unfortunately, along with all of these unique attributes some problems exist. These are associated primarily with the presence and operation of one of Consumer Energy’s hydroelectric projects, Mio Dam. As with nearly all dams, the problems include changes in water quality, elevated stream temperatures, changes in natural flow patterns, disruptions in the transport of sediment and woody debris, promotion of competing fish species, and barriers to upstream and downstream fish movement. Even in the face of all these obstacles, this river can still produce an exceptional trout fishery, but only with the assistance from fisheries managers.

The most obvious symptom of the problems is exhibited in the trout’s inability to maintain a self-sustaining population. Fisheries managers have addressed this problem for many years by stocking yearling brown and rainbow trout. Stocking rates and trout strains have varied through the years and so has the fishery. The fishery did earn a reputation, not for numbers of trout, but for large trout. It is not uncommon to hear reports of 30-inch browns being landed each year. Angler reports indicate that the fishery had its most recent peak during the 70’s and early 80’s with gradual declines noted during the late 80’s and 90’s. The low stocking rates during that period were no longer able to sustain a high quality fishery. It was suspect that changes in the strain of trout stocked helped lead to poor survival.

Fisheries managers reacted to this problem with an intensive effort to restore the fishery by replacing lost woody debris, repairing eroding banks, and changing trout stocking strategies. The focus of this article will relate to trout stocking as it is addressing the immediate needs of the trout fishery. To improve survival of trout stocked, new strains of brood stock were obtained for propagation in the state’s hatchery system. These strains were obtained from stocks of trout that demonstrated improved survivability in the wild. In addition, the numbers of trout stocked were increased to mimic the reproductive dynamics of self-sustaining stocks found upstream near Grayling. Historic stocking levels were in the range of 10 to 30 yearling trout per acre, and the new estimated stocking levels needed to be increased to 200 yearlings per acre. These stocked trout were split between brown and rainbow trout to add diversity to the fishery. This new stocking strategy began in 1998 and will continue annually through the year 2003. Unfortunately, there is considerable cost associated with stocking these fish. It costs the State of Michigan and its licensed anglers $70,000 per year to stock these fish, hence this management action will only be considered temporary as it addresses only the symptom and not the actual problem.

Due to the considerable investment in this fishery, Michigan Department of Natural Resources, Fisheries Division, is committed to evaluating the success of these management activities through trout population surveys and angler creel surveys. These surveys began in 1999. Initial results of the juvenile trout surveys indicate that natural reproduction is occurring, but young-of-year (YOY) trout are not surviving through the summer. Population estimates conducted on the overall trout population place the total trout biomass at 28 pounds per acre (brown trout - 18lbs/ac, rainbow trout -- 10lbs/ ac). Size and age distribution of the brown trout is excellent with 14 percent of the fish over the 15-inch size limit and seven age classes represented in the population. The growth rates for brown trout are 2.4 inches above the state’s mean growth index. Size and age distribution for rainbow trout is also good, but with a younger overall population. Fifty two percent of the rainbow trout population is larger than the 12- inch size limit with three-year classes present in the population. Growth rates are 4.1 inches above the state’s mean growth index. Creel census results are not available yet, but will be reported in future issues.

It appears that our management actions are on track and the fishery is responding as expected. Evaluation will continue over the next several years with a goal to raise the trout standing to 60 pounds per acre and an ultimate goal of a self-sustaining trout population. In addition, a three year water quality study is nearing completion by Consumers Energy. This study was agreed as part of their 40 year operational license issued by the Federal Energy Regulatory Commission. Findings from this study will be used to identify water quality issues associated with the operation of Mio Dam. Hopefully we will then be able to address our juvenile trout survival concerns. RWOL

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