Steelhead, rainbows and 'sneaking'

By John McMillan

A few days ago, after some of my favorite rivers had reopened to angling, I made the 40 minute drive to Forks, Washington, to fish for cutthroat.

The river (which shall go unnamed) was slightly tannin-stained due to recent rains. Fortunately, those rains had boosted streamflows and cooled water temperatures. I worked the caddis through a couple of pockets and landed two small cutthroat, both gilded in yellow and sprinkled with pepper. They were beautiful fish.

Then, half-way into a short choppy run, I had a large boil at the caddis. I missed, so I recast and the fish struck again, and again, before it eventually rolled onto and over the fly.

Based on my adrenaline level after three strong runs and the amplitude of the head shakes I was certain I had stumbled onto a rare Olympic Peninsula wild summer steelhead. However, my thoughts wavered a bit after I was able to tease the fish out of the main current, rather than use brute force, which my experience suggested would be necessary if it were a wild steelhead. Perhaps a hatchery steelhead?

But the final few strips of line revealed not at all what I had anticipated. Splashing around my knees was a large trout. Duped, but in a good way.

I held the fish in the water and admired it closely. It was clearly a male resident rainbow trout, perhaps 18” long. Very large for the river I was fishing. In fact, I have fished that river thousands of times over almost twenty years and have only landed a handful of similarly sized rainbows. He was a rare cat.

Overall, resident rainbows are not very common on the Olympic Peninsula, nor in most of the streams draining the Coast Range in Washington and Oregon. Coastal cutthroat are typically the predominant resident trout on the coast.

On the other hand, resident rainbows are common in streams draining the Cascade Range and into the interior Columbia River, and are probably more numerous than steelhead in many of those populations. They are similarly abundant in much of California, although less so in rivers with significant anadromy.

That rainbows are common in some areas and not in others raises some interesting questions. Such as: Why do some fish become rainbows and others steelhead? What about stream temperatures and climate change—how will steelhead respond?

You will find answers to these questions in this Science Findings piece by Geoff Koch featuring research from the United States Forest Service and other agencies. It is an excellent article and recommended reading for anyone wanting to better understand why rainbow and steelhead do certain things and what that ultimately means for the persistence of the species.

Back to the large male rainbow. Most rainbow trout on the Peninsula are male. There are a couple of reasons for this. First, more females tend to become steelhead than males because they can achieve a really large size in the ocean. A larger size is more important to females than males, because larger size equates to a greater number of eggs (the more you have, the greater the chance of one of them surviving to adulthood). Size is important to males too, but even a small male has enough sperm to fertilize millions of female rainbow eggs.

Second, small resident rainbow males can hide from larger aggressive steelhead males and dart in at the last second to fertilize eggs just as they are released by the female. This is called “sneaking.”

Small male rainbows sneaking fertilizations with female steelhead is more common than most anglers realized. In some populations over 50% of the returning steelhead may be fathered by small resident males.

So don’t judge or hate on the little guys. They are critical to the persistence of steelhead populations. From the evolutionary perspective of a large female steelhead, which may rather mate with another steelhead, we might say it is better to have danced with a less desirable partner than not to have danced at all.

So next time you are out fishing, treat wild rainbows you catch with respect—they might be the next generation’s steelhead.

 

John McMillan is a fisheries biologist and the Science Director for TU's Wild Steelhead Initiative. Click on this file to read one of his published reports on the steelhead-resident rainbow connection: AFS_McMillan et al 2007 steelhead.pdf

Photos by Curtis Reed, John McMillan, and Dave Neal.