A Summer on the Manistee River
The Michigan DNR Fisheries Division, in partnership with the Little River Band of Ottawa Indians, and other partners are moving forward on a plan to reintroduce Arctic Grayling (grayling) to select Michigan streams. The Manistee River system was chosen as the initial focus area for this effort because it historically held large populations of grayling, presently contains 1000s of miles of high-quality coldwater habitat, and has many interconnected tributaries to accommodate grayling migrations among tributary and mainstem river reaches. Looking at MDNR survey records for the Manistee, it was apparent that many tributaries of interest lacked recent surveys. In addition, habitat and fish survey information needed for assessing stream reaches for grayling reintroduction were often not collected, or collected using different methods. This makes comparisons among stream reaches difficult or impossible.
A key to successful reintroduction of grayling is finding a stream or set of streams where habitat conditions are suitable for each life stage of grayling (egg, fry, juvenile, adult), where densities of predator and competitor species will not pose too much of a problem, and where connections exist between habitats to accommodate any seasonal movements of grayling that might occur. Clearly, this is a complicated issue, and it should be no surprise that previous reintroduction efforts have failed. To increase our chances of successfully re-establishing grayling in Michigan, a well-thought out process is needed to prioritize streams for reintroduction efforts and to guide collection of data for evaluating potential reintroduction reaches.
A substantial grant from the Consumers Energy Foundation spurred our efforts to address the issues described above and enabled collection of field survey data in the upper Manistee River system in summer 2017. With the grant monies, we hired Dr. Cameron Goble (who studied grayling as part of his recently completed Ph. D. program at Michigan Technological University, MTU) to lead field survey efforts, along with two summer field assistants hired through and housed at the Au Sable Institute, which is located in the upper Manistee watershed. A meeting was held among MDNR fisheries research and management biologists, LRBOI biologists, and representatives from MTU & the Au Sable Institute in March 2017 to identify potential reintroduction streams that lacked the comprehensive surveys needed for assessing their suitability. Twenty-five reaches were initially selected for surveys, and are identified with stars on the map below.
Prior to this, MDNR research staff began to flesh out a prioritization framework that could integrate data on key measures of stream habitat, fish community attributes, and stream network connectivity to assess the suitability of a given reach for each life stage of grayling and the grayling population overall. A prioritization framework is useful because it provides a transparent explainable process (which facilitates collaboration); uses clearly-defined quantitative ranking criteria; enables comparisons of streams within and among river systems; can show where information gaps still exist; can be adapted or updated as info gaps are filled and we learn more; and can potentially incorporate existing standardized survey data. In February 2017, MDNR Fisheries Division, LRBOI, and researchers from MTU met to flesh out the prioritization framework, specifically to: 1) identify the relative importance of egg, fry, juvenile, and adult components of habitat for grayling reintroduction success in Michigan; 2) identify and prioritize key field parameters characterizing habitat at each life stage; 3) to review MDNR habitat survey protocols with respect to these parameters. We learned that MDNR’s Status and Trends Random Site protocol surveys could be used to adequately characterize what the group thought were key aspects of habitat for each life stage. MTU and MDNR researchers met later to assign suitability values to measured values for each parameter that was deemed important for each life stage of grayling based upon group consensus. This process enabled us to turn survey data into a rating score for each life stage, allowing quantitative comparisons among river reaches and prioritization of their suitability for grayling. With knowledge of how surveys would be conducted (using Status and Trends Random Site protocols), and how data would be summarized and used, we were ready for a productive field season.
Field surveys began in mid-June, once the target streams had reached mid-summer flow levels, and concluded in late July. Each survey followed MDNR’s Status and Trends Random Sites protocols, which provide specific instructions of how much of the reach to sample and how to go about assessing habitat and fish communities. Surveys involved quantification of many stream characteristics: stream channel depth, width, and substrate; habitat type (riffle, pool, run); stream edge habitat; stream bank stability; riparian landcover types; coverage by instream aquatic plants and wood habitat types; stream flow rate; abundance of all fishes by species and size class; hourly stream temperature measurements; and anecdotal observations of amphibians and reptiles. Each survey typically took one full day. Every stream held brook trout, brown trout, or a combination of both species, with trout densities varying among sites.
Data were entered into MDNR’s survey database the Fish Collection System for archiving and generation of summaries of the habitat parameters measured. The summary values were entered into a secondary database connected to the prioritization framework to provide estimates of how suitable habitat in each reach is for egg, fry, juvenile, and adult grayling. A detailed report describing the prioritization process, scoring criteria for habitat parameters deemed most important to each life stage of grayling, and scores by life stage for each of the tributaries sampled in 2017 (and other tributaries where suitable data were previously available) is being prepared for submission to a peer-reviewed scientific journal.
In addition to assessing the suitability of habitat for grayling, we are exploring differences among study reaches in the degree to which they would allow unrestricted movements of grayling to other habitats within the river system. Streams that allow such movements are referred to as having high connectivity, meaning that access is unhindered by dams, waterfalls, or impassable culverts at road crossings. Grayling are noted for being highly mobile in stream environments in Montana and the northern portion of their range, though in his studies of Michigan grayling, Vincent (1962) referred to them as non-migratory in the state. Connectivity was identified as a major component of Michigan’s prioritization framework for grayling, contributing 19% to the overall score (predator-competitor densities contribute 44% and habitat for all life stages represents 38%). We are currently examining the utility of the web-based tool FishWorks for characterizing connectivity of stream reaches in the Manistee system and elsewhere.
The biological data collected during the 2017 surveys will be incorporated into the prioritization framework, enabling rating of stream reaches for each life stage based on habitat, co-occurring fishes (predators or competitors), and connectivity. At this point, we are still working to develop quantitative criteria for rating reaches based upon how dense populations of resident brook trout, brown trout, or other species that may potentially be problematic for grayling. We are approaching the biological questions in part through a grant-funded study to look at predation rates on grayling fry and eggs by juvenile brook trout and brown trout in an artificial stream environment, as well as competition between young grayling and resident trout. Ideally, we would like to supplement these controlled, observation-based studies with field surveys that provide quantitative relationships between densities of co-occurring grayling and resident trout of various ages and sizes. Once these relationships are described, we will be able to use the fish survey to rate how suitable individual reaches are for each life stage of grayling based upon each reach’s habitat conditions, existing fish community, and connectivity to other habitats. We hope that this knowledge will enable managers to target reintroduction activities to locations where we think there is the greatest likelihood of success.