How to interpret steelhead fin clips

Since 2018, yearling steelhead stocked in U.S. waters of the Great Lakes and tributary streams have been marked with an adipose fin clip, but that doesn’t mean anglers can easily determine where their fish was stocked or if it is wild.

A steelhead fish
If your steelhead has a fin clip or other mark, it was definitely stocked. Beyond that, there are few absolutes. With restrictions on in-person interactions and tight budgets we will be relying on anglers for eyes on the water. Help us take advantage of the unprecedented scope of the steelhead mass marking program and encourage your friends to participate in a Great Lakes Angler Diary stream team for your favorite river!

Over the past few years, anglers on Lake Michigan and Lake Huron have been able to tell at a glance whether Chinook salmon are stocked or wild. Thanks to the efforts of the U.S. Fish & Wildlife Service’s Great Lakes Mass Marking Program and collaborating state agencies, virtually all of stocked Chinook salmon caught from 2014 to 2020 were marked before leaving the hatchery. Anglers could spot wild-spawned fish easily by looking for the adipose fin. If a Chinook salmon had its adipose fin it was almost certainly wild, while stocked fish had been marked before stocking by clipping off the adipose fin and (usually) inserting a microscopic coded wire tag (CWT) in the snout.

In 2018, mass marking efforts began to focus on steelhead. This means that anglers are now starting to see more fin-clipped steelhead in catches from the Great Lakes and in rivers where steelhead run. Due to the life history of the steelhead and the variety of different strains and marks used by different management agencies around the Great Lakes, interpreting the meaning of marks on steelhead is much more difficult than Chinook salmon.

The life of a steelhead

Steelhead typically spend two to three summers in the big lake before spawning, with around 90% of the steelhead run in Michigan rivers being made up of Age .2 and Age .3 fish. Some steelhead (young precocious males called ‘skippers’) run after spending only one summer in the big lake, and certain strains are more likely to return at Age .4.

The decimal point is used in describing steelhead because steelhead also spend a significant portion of their life in their natal stream or hatchery before entering Great Lakes waters. The number before the decimal point applies to the stream-age of the fish, and the number after the decimal point refers to lake-age.

Most wild steelhead spend two summers in the stream, but some spend one or three years in the stream environment before smolting and moving to Great Lakes waters to feed. The vast majority of hatchery steelhead are stocked as yearlings in the spring (Age 1.0) because survival is much higher if fish are held in the hatchery for a year. Nearly all of these fish smolt almost immediately upon being stocked. However, some hatcheries have excess fish available when the young steelhead outgrow their living quarters, and these are sometimes stocked as fall fingerlings (Age 0.0) despite low survival.

Unlike salmon, steelhead do not necessarily die after spawning. Repeat spawning is possible, but not as common as some people might assume. In the Little Manistee River, around 20-30% of the run is comprised of repeat spawners. Although you might think that this would mean steelhead can live to a ripe old age, they typically spend about the same amount of time in the big lake as a Chinook salmon. A study of steelhead runs on three rivers found that Age .5 fish accounted for only 2% of steelhead in the Grand River and even less on the St. Joseph and Manistee rivers.

For anglers, all of this means that most of the steelhead showing up in streams for the Fall 2020 and Spring 2021 runs will be marked if they were stocked. Since stocking of mass-marked steelhead began in 2018, all returning fish of Age .1, .2, and .3 will have an adipose fin clip for the 2020-2021 river fishing season. Older stocked fish of Age .4. and .5 may or may not have a mark since some agencies were marking certain strains of steelhead in certain rivers before 2018. Fall fingerlings have also been stocked without marks in certain locations since 2018, although these probably contribute little to fisheries.

A smorgasbord of strains

According to the Great Lakes Fishery Commission’s Fish Stocking Database, at least eight different strains of steelhead and rainbow trout have been stocked into Lake Michigan, Lake Huron, and their tributaries since 2014. These include Michigan winter (Little Manistee), Skamania, Ganaraska, Ganaraska/Normandale, Chambers Creek, and Wild strain steelhead that are artificially spawned and reared in hatcheries, along with Arlee and Eagle Lake strains of rainbow trout. Rainbow trout and steelhead are the same species, but steelhead strains are descended from stocks that migrate from the Pacific Ocean into stream environments to spawn, while rainbow trout stains are descended from strictly freshwater stocks.

Michigan winter steelhead originate in the Little Manistee River, which has hosted naturally reproducing steelhead since the late 1800s. The state of Michigan uses this strain almost exclusively in Lake Huron, although smaller numbers of Eagle Lake strain rainbow trout are also stocked in thumb-area harbors to provide nearshore fisheries. Ontario stocks a strain of steelhead from their Ganaraska hatchery into Lake Huron tributaries, along with the progeny of wild fish – although it is rather confusing to refer to this stain of stocked fish as “Wild” strain.

In the Lake Michigan basin, the state of Michigan has stocked both Michigan winter and Skamania steelhead in recent years. The Skamania strain has its origins in a hatchery of the same name in Washington. Skamania are more likely to run during summer months and typically live a little longer than other strains, with many fish returning at Age .4.

Indiana also stocks Skamania strain steelhead, along with Michigan winter fish. Illinois has stocked both Skamania steelhead and Arlee strain rainbow trout since 2014. Wisconsin has also stocked Skamania and Arlee into the Lake Michigan basin in recent years, along with Chambers Creek steelhead and steelhead strains from the Ganaraska and Normandale hatcheries in Ontario.

In the Lake Superior watershed, Michigan winter steelhead are the only strain currently being stocked in Michigan waters while Minnesota stocks Knife River strain steelhead. Prior to 2018, Minnesota was also stocking Kamloops strain rainbow trout prior to 2018. Volunteer anglers submitted scale samples to the Steelhead Genetics Project, which found that Kamloops trout interbred with steelhead producing hybrids with reduced fitness. As a result, Kamloops stocking was discontinued, but Kamloops rainbow trout stocked in 2017 could still be caught in Lake Superior.

What do the marks tell us?

If your steelhead has a fin clip or other mark, it was definitely stocked. Beyond that, there are few absolutes. Unmarked fish are not necessarily wild, since steelhead from year-classes before 2018 were not being mass marked and some agencies have continued to stock unmarked fall fingerlings.

Different agencies have used different marks for the same strain of fish, so the only way to get a definitive answer on the strain and stocking location of a marked fish is to submit the head or snout for CWT extraction.

Here is a short list of common marking patterns found on Great Lakes steelhead and rainbow trout, which might provide some clues. This list does not provide a complete overview of marks present on steelhead, but it is based on available data from the Great Lakes Stocking Database 2014-2018 and the Michigan Fish Stocking Database in 2019.

steelhead fin marks

Adipose (AD)

This is the most common external mark, and most (but not all!) steelhead with an AD clip will also have a coded wire tag in the snout. The AD clip has been used on every strain of steelhead and rainbow and by every state and provincial agency that stocks fish into Lake Michigan or Lake Huron, although not all agencies mark all strains with the AD clip alone. For example, Indiana marks Skamania steelhead with the AD clip as the only external mark while Wisconsin and Michigan now include additional external marks for Skamania.

Adipose and Right Ventral Fin (ADRV)

In 2018 and 2019, Skamania planted into Michigan’s Manistee River were marked with both the adipose and right ventral clip along with CWTs. The same mark combination was used for Ganaraska strain steelhead stocked into the Root and Kewaunee rivers in Wisconsin in 2018, but Ganaraskas stocked into other Wisconsin rivers received only the AD clip. Kamloops rainbow trout stocked by Minnesota in the French River in 2017 also received ADRV clips, while Kamloops stocked in the Lester River during the same year received adipose and left ventral (ADLV) clips.

Right Ventral (RV)

Prior to 2018, Skamania planted into the Manistee River were marked with a right ventral fin clip. This was before the mass marking program began to focus on steelhead, so these older Skamania do not have an adipose fin clip or coded wire tag. Ventral fin clips have also been used at select stocking sites in Ontario.

Adipose and Right Maxilla (ADRM)

Wisconsin marked Skamania stocked into the Root and Kewaunee rivers with an adipose clip and removal of the tip of the right upper jaw bone (maxilla) in 2018.

Adipose and Left Maxilla (ADLM)

Chambers Creek strain steelhead were stocked into the Root and Kewaunee rivers with adipose and left maxilla clips in 2018. Unlike Skamania, the Chambers Creek strain is also stocked in other Wisconsin rivers with only the AD clip.

Right Maxilla and External Tag

A small number (631) of adult Knife River steelhead were stocked into McQuade Harbor on the north shore of Lake Superior by the State of Minnesota in 2018 sporting both a right maxilla clip and external Floy tag. These fish also have an internal PIT (passive integrated transponder) tag but do not have the adipose fin clip or coded wire tag (CWT) used on yearling steelhead.

Which fish contribute to the run in your favorite river?

Despite the difficulty of interpreting steelhead marks, you can learn a lot about the balance of naturally-spawned and stocked fish in your favorite fishing hole over the next few years. If your catch is dominated by unmarked fish, it is an excellent indication that steelhead are finding good spawning habitat and cold, clear water somewhere nearby.

The Great Lakes Angler Diary website and app for Apple devices (search “GL Angler Diary” in the App Store) provide a way to record your marked and unmarked steelhead catches.

All you need to do to share data with biologists and managers working to improve the fishery and stream health is:

  • Register on the website or by using the GL Angler Diary app
  • Record data for each stream steelhead trip taken during the 2020-2021 season
  • Measure each steelhead to the nearest quarter inch
  • Check each steelhead for marks
  • Record whether the fish was kept or released
  • Take a short survey at the end of the season

This year more than ever the fishery needs your help. Stream fisheries are always difficult and expensive for biologists to survey because anglers are spread out over so many river miles and access points. With restrictions on in-person interactions and tight budgets we will be relying on anglers for eyes on the water. Help us take advantage of the unprecedented scope of the steelhead mass marking program and encourage your friends to participate in a Great Lakes Angler Diary stream team for your favorite river!

If marked fish are showing up in good numbers, you can also help biologists figure out where they are coming from by submitting the heads or snouts of AD clipped steelhead and other salmonids for CWT extraction. The Great Lakes Salmon Initiative, Captain Chuck’s II, Moonshine Lures, and Michigan DNR are providing an extra incentive for this with $100 gift card giveaway (see details).

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 report was prepared by Michigan Sea Grant under award NA180AR4170102 from the National Oceanic and Atmospheric Administration, U.S. Department of Commerce through the Regents of the University of Michigan. The statements, 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.

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