How many stocked steelhead returning to Michigan rivers are still unmarked?
Anglers have been tracking catches of steelhead with and without fin clips. Most stocked steelhead in Michigan rivers now have an adipose fin clip, but some do not.
Since 2018, steelhead stocked in Michigan waters have been marked with an adipose fin clip as part of the Great Lakes Mass Marking Program. Due to the complex life history of steelhead, it can be difficult to interpret what the ratio of clipped to unclipped fish in your catch really means.
Stocked steelhead typically smolt (turn silver) at Age 1, migrating downstream to one of the Great Lakes to feed soon after they are stocked. Wild steelhead can spend one, two, or even three years in streams before smolting and leaving the stream to feed in a big lake environment. Growth is much slower in the stream environment, so biologists draw a distinction between “stream age” and “lake age” when interpreting how age influences the growth rate and size of steelhead.
Michigan steelhead can live for up to eight years, with up to six summers spent growing in the big lake. Steelhead stocked as spring yearlings in 2018 have now spent four summers in the Great Lakes. Steelhead stocked before 2018, which have spent 5 or more summers in the big lake, are mostly unmarked*.
For spring 2022, this means the majority of steelhead returning to Michigan streams will have an adipose fin clip if they were stocked. According to Jory Jonas and Ben Turschak, research biologists with Michigan Department of Natural Resources, 24.3% of mature steelhead harvested in Lake Michigan were old enough to be unmarked in summer 2021. Recent models also estimate that 11.4% of steelhead harvested in summer 2022 will be old enough to be unmarked if they were stocked.
We do not have detailed information on harvest in rivers, but we can assume that the breakdown of river fish ages will be similar to that of mature fish in Lake Michigan. Since mortality occurs both as a result of fishing and the stress of spawning over the course of the steelhead run, estimated proportions from the previous summer and next summer can be used as high and low estimates for streams, respectively.
What this means about the steelhead you catch
If you are catching a mix of clipped and unclipped steelhead in your favorite Lake Michigan stream during the spring 2022 season, you can get a rough idea of how many unclipped fish were stocked based on these proportions. For every twenty clipped steelhead you catch, you can expect to catch two to five unclipped steelhead that were stocked without being marked. This will change over time, and for the fall 2022 – spring 2023 season you can expect to catch one or two unclipped stocked steelhead for every twenty clipped steelhead caught. Outside the Lake Michigan watershed, these estimates may not be perfect, but they should give you a rough idea of what to expect.
How you can get involved
Michigan Sea Grant launched the Michigan River Steelhead Project in 2020 to allow steelhead anglers to report their catches online. By recording fin clips and lengths for every steelhead you catch, you can help biologists learn more about how natural reproduction and stocking contribute to fishing success in rivers around Michigan.
It is not too late to sign up online and record data for trips taken from now to the end of the spring run. Catches can be recorded using the Great Lakes Angler Diary website or apps for iOS and Android. A new dashboard feature allows you to quickly calculate %Clipped, catch rate, and the average size of fish you catch, so don’t forget to update your app if you are already participating!
Fishery professionals with Michigan DNR and other agencies regularly participate in Zoom meetings to share updates with anglers as part of this project. You can register online for our next meeting, which is scheduled for Wednesday, May 25 from 7 p.m.-8:30 p.m. The online meeting will also include fishing reports from teams around the state.*Skamania stocked in the Manistee River prior to 2018 were marked with a right ventral clip. Spring yearling Michigan winter steelhead stocked in the Manistee River prior to 2018 were mostly unmarked, but roughly 20,000 per were marked with an adipose clip and coded wire tag (CWT) in 2016 and 2017. Fall fingerlings stocked in the Manistee River in 2017 were also marked with an adipose clip and CWT.
Michigan Sea Grant helps to foster economic growth and protect Michigan’s coastal, Great Lakes resources through education, research and outreach. A collaborative effort of the University of Michigan and Michigan State University and its MSU Extension, Michigan Sea Grant is part of the NOAA-National Sea Grant network of 34 university-based programs.
This survey report was prepared by Michigan Sea Grant Extension Educator Daniel O’Keefe under award NA180AR4170102 and SUBK00013473 from the National Oceanic and Atmospheric Administration, U.S. Department of Commerce through the Regents of the University of Michigan. The statement, findings, conclusions, and recommendations are those of the author(s) and do not necessarily reflect the views of the National Oceanic and Atmospheric Administration, the Department of Commerce, or the Regents of the University of Michigan.