Boulder Mountain Fly Fishing/Cutthroat Comparison

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Cutthroat Comparison

The two sub-species of cutthroat trout available to fly fishers on the Boulder Mountain in 2012 are the Bonneville cutthroat [Oncorhynchus clarkii utah] and the Colorado River cutthroat [Oncorhynchus clarkii pleuriticus]. The composite photographs on this page are intended to illustrate the dramatic differences in these two sub-species of cutthroat trout. No matter where you go on the Boulder Mountain you are likely to encounter either or both of these beautiful cutthroat.

As you can clearly see in the image above, the markings of these two trout are quite different. The Bonneville cutthroat on the top is pale in comparison to the Colorado River cutthroat on the bottom. The Bonneville cutthroat has more of a silver base with bronze highlights. The gill plates on the male Bonneville cutthroat will become reddend with maturity and during the spawn. The Colorado River cutthroat exhibits much more coloration overall in both males and females, with males becoming extremely bright after maturing and especially during the spawn. In fact, the mature male Colorado River cutthroat trout is unsurpassed for his vivid colors among all other trout in north America.

These two mature male cutthroat, the Bonneville cutthroat on top and the Colorado River cutthroat on the bottom shown in the image above are very different in overall coloration and also the way they are built. The Bonneville cutthroat shows less red and tends to be a bronze color over most of its body. The mature male Bonneville cutthroat has a red gill cover. The mature male Colorado River cutthroat is very red over much of it's body especially the underside and has a pronounced kype to it's lower jaw.
You can also see the difference in the two immature cutthroat in this image below. Even at this young age and small size it is very apparent that the Colorado River cutthroat is much brighter than the Bonneville cutthroat.

Visually, the difference between the three sub-species of cutthroat trout in the image below is not what you would call extreme. The Bonneville cutthroat on top, followed by the Colorado River cutthroat in the middle and the finally the Yellowstone cutthroat on the bottom. They are all distinct sub-species for sure. However, these three images were selected for their obvious similarities and then made into a composite image to illustrate that sometimes these three sub-species can be difficult to identify when caught independently without another sub-species readily available for a side to side comparison. When you look at this particular composite image the difference is fairly subtle but still it is not difficult to tell them apart with some experience at catching them.

The image below shows two trout that look very much alike, yet one is a Bonneville cutthroat and the other a Yellowstone cutthroat.

Both of the trout in the image above are mature males. Each has a bronze coloration. Each has a similar spot pattern and red gill plates. The Yellowstone cutthroat on the bottom has more spots concentrated nearer the tail than the Bonneville cutthroat on the top.

One of the distinguishing features of cutthroat trout is the presence of sharp teeth not just in the upper and lower jaws, but also at the base of the tongue. These are called basibranchial [hyoid] teeth.

When you catch a mature cutthroat trout of any sub-species, while removing the fly from it’s mouth, take the time to observe the gill arches and the base of the tongue towards the rear of the mouth. You will see these basibranchial teeth. The mature male Yellowstone cutthroat in the image below has an impressive set of teeth. These sharp teeth have a dual purpose. One is for securing food and the other is for fighting with other males during the spawn. It is obvious that this trout has seen his share of fighting due to the presence of many scratches on his head from other male cutthroats.

You may also feel them by gently rubbing your finger over their tongue. However, you risk getting bitten anytime you put your fingers into any large trout’s mouth! The image below shows a mature male Rainbow trout [Oncorhynchus mykiss]. This trout appears to have a similar set of teeth used for the same dual purpose as the cutthroat. Some rainbows will have basibranchial teeth on the base of the tongue as this trout has. This would be an indication of some cutthroat influence due to hybridization, in other words a cuttbow.

Cutthroat trout have a tendency to become piscivorous after they reach maturity. That is if there are other small fish available to them within their environment . In the case of the lakes of Boulder Mountain they may not be eating their own young due to their inability to spawn successfully for lack of proper spawning habitat, but they are provided ample opportunity to eat small fish whenever the airplane swoops in and delivers another batch of fingerlings.

These fingerlings can be new cutthroats, brook trout, splake and or tiger trout depending on the lake. The small trout in the image above is a newly stocked splake delivered airmail by UDWR. This piscivorous nature is common to all mature trout and that includes rainbows which are closely related to cutthroats.

If suitable spawning habitat is present in a lake on the Boulder Mountain where cutthroat and rainbow trout are both present, then there will be a good chance of hybridization occurring between them. This has happened in the past and the result was cuttbows, a hybrid. This rarely occurs on the Boulder Mountain these days as most of the lakes and their tributary streams have been treated numerous times and restocked with only cutthroat and other unrelated species and no rainbow.

There are lakes with both cutthroats and rainbows such as Blind lake shown in the image above, but Blind lake has no obvious tributary streams that would facilitate successful spawning of either of these two closely related species.

The image above shows the tails of a Bonneville cutthroat on the left and that of a Colorado River cutthroat on the right in a side by side comparison. They are similar, although the color of the Colorado River is more red especially on the belly and the adapose and anal fin.

The image above shows the undersides of the Bonneville cutthroat on the left and the Colorado River cutthroat on the right. Both are males caught in June and appear to be very different. The mature Colorado River Cutthroat below is much easier to distinguish in the field overall due to it’s spectacular coloration, especially the males during the spawn. Mature males will keep much of this deep red color most of the year. However, this bright color really intensifies during the months of May and June.

The image below shows a mature Yellowstone cutthroat trout [Oncorhynchus clarkii bouvieri]. The mature male Yellowstone cutthroat can sometimes be extremely colored.

The Yellowstone cutthroat trout [Oncorhynchus clarkii bouvieri] were stocked into the lakes and beaver ponds on southern Utah's Boulder Mountain and the Aquarius Plateau for many decades. The Utah Division Of Wildlife Resources [UDWR] began stocking these beautiful cutthroat here as early as 1945 by some accounts, perhaps even before that time. This early stocking of these trout and also the Brook Trout [Salvelinus fontinalis] was usually done the hard way, by wildlife officers on horseback leading pack animals. The trout fingerlings were loaded into milk cans and hauled up the rugged trails to the backcountry lakes and beaver ponds. The state of Utah finally began using airplanes to stock trout in 1956. The Yellowstone Cutthroat have been known to exceed five pounds in weight by the end of their fourth season in the lakes and beaver ponds on Boulder Mountain after being stocked as fingerlings. The fertile ecosystem of these sub-alpine lakes and beaver ponds provides an abundance of food for growing trout. Over-wintering has always been a problem for the Yellowstone Cutthroat and other species of trout in some shallow lakes here. However, where they have been stocked in lakes with deeper holes and percolating springs, they have faired well with many holdover fish. When the Yellowstone Cutthroat reach maturity in the lakes of Boulder Mountain, they will usually top three to four pounds or more. The replacements for the non-indegenous Yellowstone cutthroat, the Bonneville cutthroat and the Colorado River cutthroat have also proven to grow to large size here.

Some mature male Yellowstone cutthroat will be extremely bright in the first part of June, which is the peak of their spawn. This mature male Yellowstone cutthroat in the image above is beyond red, nearly purple!

If you have never caught Bonneville cutthroat or Colorado River cutthroat and would like to experience the thrill of catching and releasing many of these beautiful native trout, then this is the place to do it. Although Yellowstone cutthroat trout have not been stocked anywhere on the Boulder Mountain for many years now, there are a few left. It is still possible to catch all three species on the same trip, but not very likely in the same lake. If you would like to book a guided trip to fly fish for cutthroat this season, keep in mind that space is definitely limited and plan on booking early.

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