Cutthroat Taxonomy - How do I count my trout?

One question I often get about Cutthroat Trout has to do with how many species/ subspecies there are. For someone that is trying to catch all of the varieties of Cutthroat, this is an important consideration as it sets the basis of overall quest and planning excursions. What I hope to do here is break down what I see as the the three classification systems that are commonly used. I am going to label these as the Behnke System, the Trotter System and the Western Native Trout Challenge System - these are my names for them and do not represent official names.

How many types of Cutthroat are there? That depends who you ask...

1. The first system that I will cover is the Behnke System as it is the oldest and perhaps the most broadly accepted of the classification systems. This classification was developed by Robert Behnke, who used traditional taxonomic and meristic (scale counts, fin rays, gill rakers, chromosomes etc.) characteristics to classify trout. This system is covered in the 2002 essential book Trout and Salmon of North America as well as the excellent 2008 book Cutthroat: Native Trout of the West and breaks Cutthroat Trout (a single species) into four major lineages (Coastal, Westslope, Yellowstone and Lahontan). Within these lineages, the Yellowstone is considered to have 6 additional minor subspecies and the Lahontan has 4 additional minor subspecies for a total of 14 subspecies of Cutthroat Trout. This is the classification that I once used for my website before transitioning to the Trotter System covered next.

Behnke Classification: (Italics for "minor" subspecies)

1. Coastal Cutthroat
2. Westslope Cutthroat
3. Lahontan Cutthroat
4. Paiute Cutthroat
5. Humboldt Cutthroat
6. Willow-Whitehorse Cutthroat
7. Alvord Cutthroat (presumed extinct)
8. Yellowstone Cutthroat
9. Snake River Finespotted Cutthroat
10. Bonneville Cutthroat
11. Colorado River Cutthroat
12. Greenback Cutthroat
13. Yellowfin Cutthroat (presumed extinct)
14. Rio Grande Cutthroat

2. The Trotter System is based on genetics and is covered in the 2018 book Cutthroat Trout - Evolutionary Biology and Taxonomy. This book has multiple contributing authors from the scientific community and is very dense on the science. Based on the latest genetics, it lays out the reasoning for breaking Cutthroat Trout into four species: Coastal, Westslope, Lahontan and Rocky Mountain Cutthroat similar to the major subspecies of the Behnke system. These fish are recognized as distinct species as major subspecies are not recognized as a valid unit for classifying animals under current taxonomic guidelines. With the exception of Coastal Cutthroat, each of these species has its own subspecies for a total of 25 subspecies of Cutthroat Trout. 

There are a number of differences in this system with the most noticeable being the 9 subspecies of Westslope Cutthroat. These subspecies were not recognized by taxonomic or phenotypic traits, but their uniqueness is apparent at a genetic level. 

The next change is the addition of the Quinn River Cutthroat to the Lahontan line, based on their genetic distinctiveness. Based on the Behnke system the Quinn River Cutthroat were typically consider to be part of the Humboldt Cutthroat line. 

There is also major splitting among the Yellowstone/ Rocky Mountain Cutthroat line. First instead of Yellowstone Cutthroat, the Rio Grande Cutthroat provides the scientific name for this species as it is the first subspecies to receive a scientific name. Next, the Snake River Fine Spotted Cutthroat are no longer consider a unique subspecies due to their genetic similarity to Yellowstone Cutthroat (nearly indistinguishable). Additionally, Bear River Cutthroat are broken apart from the Bonneville Cutthroat.  Genetics indicate the Bear River Cutthroat are more closely related to Yellowstone Cutthroat than to Bonneville Cutthroat, as the Bear River was once a tributary to the Snake River. Finally the Colorado River Cutthroat is broken into three subspecies, the Green River Cutthroat (also known as the Blue Lineage), Colorado River Cutthroat (aka Green Lineage) and the San Juan River Cutthroat. 

A key element to note with this system is that while its based on the latest science, it has not yet been accepted by the American Fisheries Society and as such is subject to change as our scientific understanding improves. Also most of the "new" subspecies from this system are not yet recognized by management agencies which either follow the Behnke system or the Western Native Trout Challenge system.

Trotter Classification: 

1. Coastal Cutthroat
2. John Day Westslope Cutthroat
3. Neoboreal Westslope Cutthroat
4. Coeur d'Alene Westslope Cutthroat
5. St. Joe Westslope Cutthroat
6. NF Clearwater Westslope Cutthroat
7. Eastern Cascades-Clearwater Westslope Cutthroat
8. Clearwater Headwaters Westslope Cutthroat
9. Salmon River Westslope Cutthroat
10. Missouri River Westslope Cutthroat
11. Lahontan Cutthroat
12. Paiute Cutthroat
13. Humboldt Cutthroat
14. Quinn River Cutthroat
15. Willow-Whitehorse Cutthroat
16. Alvord Cutthroat (presumed extinct)
17. Yellowstone Cutthroat
18. Bear River Cutthroat
19. Bonneville Cutthroat
20. Green River Cutthroat (Blue Lineage Colorado River Cutthroat)
21. Colorado River Cutthroat (Green Lineage Colorado River Cutthroat)
22. San Juan River Cutthroat
23. Greenback Cutthroat
24. Yellowfin Cutthroat (presumed extinct)
25. Rio Grande Cutthroat

3. The Western Native Trout Challenge System is a classification system based on how the various fisheries management agencies classify Cutthroat Trout and does a considerable amount of lumping compared to the other two systems. For anglers trying to complete the Western Native Trout Challenge, this is the classification system they will be using. The classification based on this system is most similar to the Behnke system with a bit of additional lumping. The main lumping occurs with Lahontan Cutthroat, with only the Paiute Cutthroat being separated as a distinct subspecies. The Paiute Cutthroat were recently reintroduced to their native range, which is currently closed to fishing, so they are not eligible for the West Native Trout Challenge. This primarily has to do with the fact that the Endangered Species Act listing for Lahontan Cutthroat Trout lumped all of its subspecies (minus the Paiute) under it as a single subspecies. Additionally, like the Trotter system, the Snake River Fine Spotted Cutthroat is removed from this classification. 

Western Native Trout Challenge Classification: (Italics for subspecies that are extinct or do not count towards the Western Native Trout Challenge)

1. Coastal Cutthroat
2. Westslope Cutthroat
3. Lahontan Cutthroat
4. Paiute Cutthroat
5. Yellowstone Cutthroat
6. Bonneville Cutthroat
7. Colorado River Cutthroat
8. Greenback Cutthroat
9. Rio Grande Cutthroat
10. Yellowfin Cutthroat

So which list is the right one to follow? Scientifically, the Trotter system is the most robust and the one that I have chosen to used. However, ultimately which system an angler choses to follow is really a matter of opinion depending on the level of challenge that they are looking to pursue.