Manistee river tributaries as potential Arctic grayling habitat

Background/Question/Methods

The Manistee River was one of the last rivers in Michigan to support a population of Arctic grayling (Thymallus arcticus). It is believed that as a result of degraded habitat conditions, overfishing, and interactions with introduced fish, graylling were no longer found in the Manistee river after the early 1900s and Michigan waters after 1936. Attempts to reintroduce Arctic grayling into MI, most recently in 1991, were unsuccessful, but issues such as disease may have limited the success. Grayling are a species of great importance for tribal heritage and their restoration would also be desirable for recreation. A renewed interest in Michigan grayling lead to the assessment of environmental conditions of tributaries within a 12.9-mile section of the Manistee River to determine if suitable conditions existed. We collected data for a suite of abiotic habitat metrics from 23 sites distributed across 8 tributaries within the Manistee watershed. Data collected included basic water parameters (temperature, dissolved oxygen, pH), streambed substrate composition based on pebble counts and bulk methodology, areal measurements of channel geomorphic unit, and stream velocity measurements. These values were compared to literature values and current conditions of rivers with Arctic grayling populations.

Results/Conclusions

Although much of the historic grayling habitat in the region was disturbed during the era of major logging around the turn of the 20^th century, preliminary analysis of data shows that some important abiotic conditions within Manistee River tributaries are within the range of conditions that support current populations of Arctic grayling. Most tributaries surveyed contained the deep pools that grayling have been found to use as refuge.  Fifteen of the sites (within 7 tributaries) were composed primarily of pebbles (4-256mm) and the remaining 7 sites were dominated by fine substrates (sand, silt, clay). Eight sites had pool:riffle ratios between 0.27 and 1.51, and eight sites contained at least 30% pools by area. Basic water parameters, streambed substrate compositions, and channel geomorphic units were within the ranges of those found for populations of Arctic grayling persisting in Montana, Alaska, and Canada. For the metrics analyzed thus far, suitable potential grayling habitat does exist in Manistee River tributaries.  As part of the larger project, these data will be combined with biotic conditions to determine if the tributaries could support the reintroduction of Arctic grayling and which tributaries are most suitable.