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The life, history and biology of steelhead - part two/Biological Bits

May 25, 2012
By Tom Rozich , The Daily Mining Gazette

Last month my column was Part I of a two-part column about the history of steelhead (also known as rainbow trout) in Michigan and Houghton County. This month will look into their life strategy and biology in their adopted home of the Great Lakes.

Steelhead or rainbow trout (Oncorhynchus mykiss) are in the Pacific salmon genus, with the Chinook or King, coho or silver, chum or dog, sockeye or red, and pink salmon. They were placed here by scientists who determined they were taxonomically (naturally related) most like the Pacific salmon, over 10 years ago. Prior to that, they were in the genus "Salmo," along with the brown trout and Atlantic salmon. Factually, they belong in the genus Oncorhynchus, being native to the same waters as the five species of Pacific salmon, evolving along with them. So how were they able to adapt from a life in the salty waters of the Pacific Ocean to the purest water on Earth in our Great Lakes one asks? Biologists who first brought them here did not really know either, but suspected since the ocean run steelhead spent part of their life in fresh they had a chance! Experiment over, as they have adapted very well to the Great Lakes fresh water environment, you lucky steelhead anglers!

Steelhead are spring spawners, unlike their salmon cousins, which spawn in the fall. They begin their spawning migration in October and continue all winter, with the peak being in April. The steelhead run is in two stages, the late fall/winter migration and the late winter/spring run. These fall fish enter coastal streams in large numbers typically when there is a high water event and are the first to spawn in March or April, when stream temperatures reach 40 degrees Fahrenheit.

This water temperature also triggers the main spring run, with the peak of spawning being in mid-April. Steelhead continue to spawn into May and I have observed spawning fish in mid-June in the Pere Marquette River. Once spawning is complete, not all steelhead die, unlike their salmon relatives, but rather return to the Great Lakes to feed, regain energy and do spawn multiple times. Steelhead also continue to feed while in streams, another difference from their salmon relatives, making them an easier target for anglers.

The average female will deposit 4,000 eggs in gravel areas. The eggs lie in the gravel for 30 to 40 days incubating and hatch during May and June. Once hatched, the young steelhead begin feeding on zooplankton (microscopic animal life) and aquatic insects (mayflies, stoneflies, caddis flies, etc.). The young steelhead are called "parr" and remain in their natal streams for one, two or three years. Most remain two years (84 percent), 15 percent stay one year, while 1 percent stay three years, in Lake Michigan tributaries. Lake Superior streams are different, as late 1980's research on the Big Huron River showed. This study showed, on average, 43.5 percent of the smolts were Age I and 56.5 percent were Age II. No Age III smolts were found in the study. The length of their stream residency is dependent on how fast they grow.

Steelhead parr must stay in streams until they reach the magical size of eight inches or more, which ensues good survival in the fish-eat-fish world of the Great Lakes. Once they reach sufficient size, they "smolt" or out migrate to one of the five lakes, all of which have steelhead populations. The parr factually undergo a physical change, called "smoltification," turning silver as a newly minted dime, which is their protective coloration for life in our Great Lakes. The peak of the steelhead smolt migration is mid-May and generally associated with a rain (high water) event.

In the Great Lakes, they feed on terrestrial insects and other fish, growing and gaining energy for the spawning run. Steelhead remain in the Great Lakes from one to four years before returning to their natal (birth) streams for the first time. Males tend to return at an earlier age, while females stay longer, as it takes more time and energy to produce eggs. A "typical run" is made up of 5 percent Age I, 24 percent Age II, 58 percent of Age III and 13 percent Age IV or older fish. All of the Age I steelhead are precocious males, which steelheaders call "skippers." This is because of their tendency to jump, jump, jump (or skip) across the top of the water when hooked.

Previously, I stated steelhead can and do spawn multiple times, unlike their Pacific salmon cousins, which all die after spawning. How do we determine this fact? Through reading the scales fish lay down annuli or rings on their scales, much like a tree, as they grow. A skilled scale reader, which is both an art and a science, can gain a wealth of information about a steelhead's life by simply "reading" or interpreting the scale. They can tell if it is a wild or hatchery fish, how many years it spent in the Great Lakes before spawning the first time, and how many times it spawned!

The number of repeat spawners ranges from 30 to 55 percent, depending on the river, so if you do release them, they can live to spawn again. Females make up the highest percentage of repeat spawners. In the Big Huron River study, females made up 75 percent of the repeat spawners! The oldest steelhead I ever observed was a female from the Pere Marquette River, Lake County, Michigan. She was a wild fish that spent two years in the river before smolting. She then spent three years in Lake Michigan before coming back to spawn for the first time. Finally, when we scale sampled her and "read" her life history, she was coming back to spawn for the fifth time, making her 10 years old. Fantastic! Those are the kind of genes that are most desirable in our wild steelhead populations.

So, if you choose to harvest a steelhead for the table, a male would be the better choice. Go Fish and Bon appetit!



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