Rainbow and Redband Trout Taxonomy - How do I count my trout?

Following up on the classification of Cutthroat Trout, I wanted to do my best to cover the classification of Rainbow/ Redband Trout. While Cutthroat taxonomy is a bit tricky and inconsistent, the classification of Rainbow and Redband Trout is in many ways even more challenging. As such, this post is going to be much longer than the one for Cutthroat. 

Just like Cutthroat Trout, there are multiple ways to interpret Rainbow and Redband Trout classification

Unlike most Cutthroat subspecies, that have clear delineations often associated with watershed boundaries, Rainbow Trout subspecies typically have zones of transition making clean classification systems challenging at best. Even where clear watershed boundaries do exist in the Northern Great Basin of Oregon, past connections to other watersheds complicate classification. In many cases this has resulted in secondary contact between forms of Rainbow and Redband Trout resulting in transitional forms. The lower Klamath River is a clear example of this, where the fish in the lower river represent a mixture of Coastal Rainbow Trout and Klamath Lakes Redband genetics. As with Cutthroat, I am going to present Rainbow Trout classification as three systems, the Behnke System, the Genetics based system that I use one my website and the Western Native Trout Challenge System. 

For the purpose of this post, I am not including any of the Rainbow Trout like trout of Mexico or Gila and Apache Trout. There are at least 12 distinct forms of Mexican Trout, all of which originated from the Rainbow /Redband Trout lineage, likely involving two to three distinct colonization events. Long isolation has resulted in significant differences from Rainbow/ Redband Trout further north and suggest that many of these trout could be considered distinct species. Similarly, Gila and Apache Trout both represent and ancient divergence from the Rainbow Trout lineage, occur long enough ago that they are distinct from Rainbow and Redband Trout as well as the Mexican Trout and represent their own lineage.

Behnke Classification: (Italics for "sub populations")

The classification system for Rainbow and Redband Trout developed by Robert Behnke is covered the  in the outstanding book Trout and Salmon of North America.  Behnke's system is based on traditional taxonomic methods that account for physical differences, such as phenotypic traits (spotting or coloration) scale counts, vertebrate counts etc. These methods were excellent for their time and are still useful, but often miss linkages that genetics work picks up. Based on taxonomic methods, Behnke recognized 9 subspecies of Rainbow /Redband Trout native to the United States, with two additional subspecies found outside the United States, the Kamchatkan Rainbow Trout and the Baja Rainbow Trout of Mexico. Both of these forms are closely related to the Coastal Rainbow Trout. 

Coastal Rainbow Trout account for a single subspecies that stretch from Alaska all the way to Southern California. The presence of sea-run Coastal Rainbow Trout (i.e. steelhead) has resulted in genetic exchange between populations of Coastal Rainbow resulting in the large continuous range of the subspecies. The next lineage is the Columbia Basin Redband Trout, which similar to Coastal Rainbow Trout have had significant genetic exchange between populations due to the steelhead life history. Columbia Basin Redband Trout are found east of the Cascade Mountains in the Columbia Basin, in the Fraser River basin upstream of Hells Gate and in the Athabasca River east of the continental divide.

The next group of Redband Trout Behnke lumps as a single subspecies known as the Great Basin Redband Trout. He acknowledged that there is significant diversity among these fish an that they likely derived from multiple sources, but his lumping differs significantly from the Genetic system. In the upper Sacramento watershed Behnke recognized two subspecies of trout, the Sheephaven Creek Redband Trout and McCloud River Redband Trout, which we will see also differs from the genetic method. The remaining Rainbow Trout subspecies are consistent between Behnke's classification system and the other two systems that were are discussing here. The Eagle Lake Rainbow Trout is a unique isolated lake adapted population likely deriving from a mixed Coastal Rainbow and Redband ancestry. Similarly the Kern River Rainbow Trout is thought to arise from a mixed ancestry of Golden Trout and Coastal Rainbow Trout. It is important to note that historically Golden Trout were considered a distinct species and there are still some that recognize them as such. 

1. Coastal Rainbow Trout
2. Columbia Basin Redband Trout
3. Great Basin Redband Trout
1. Fort Rock Redband Trout
2. Harney-Malheur Basin Redband
3. Catlow Valley Redband Trout
4. Klamath Basin Redband Trout
5. Chewaucan Redband Trout
6. Warner Lakes Redband Trout
7. Goose Lake Redband Trout
4. McCloud River Redband Trout (also associated with fish found in the Pit and Feather Rivers)
5. Sheephaven Creek Redband Trout
6. Eagle Lake Rainbow Trout
7. Kern River Rainbow Trout
8. Little Kern Golden Trout
9. California Golden Trout

Subspecies outside the United States

1. Kamchatkan Rainbow Trout 
2. Nelson's Trout or Baja Rainbow Trout

Genetics Based System: (Italics for "sub populations")

The Behnke system did a good job of classifying Rainbow and Redband Trout, but evidence has suggested some changes to the classification of several of the Redband Trout forms. While there is still significant work to be done with the genetics of Rainbow and Redband Trout a few recent studies have provided significant clarity regarding the relationships of these fish. Genetics work suggests that Behnke's classification of Coastal Rainbow Trout and Columbia Basin Redband Trout may not be as straightforward as originally thought. With a 2000 study (here) suggesting the core of the Rainbow and Redband Trout lineage originated in California and northern populations predominately originated from glacial refuges in the Columbia Basin (Redband Trout) and on Queen Charlotte Island (Coastal Rainbow Trout). The genetics work also suggests that mixing of these two lineages appears to be more extensive than suggested by traditional taxonomic methods, however a more recent study (here) supports the subspecies divide at the Cascade crest. Like Behnke genetics work does not subspecies level distinction for the Athabascan Rainbow Trout (here) and has indicated that the Athabascan Rainbow Trout is very closely related to Redbands in the upper Fraser River. Additionally, studies show that both the Kamchatchka Rainbow Trout (here) and the Baja Rainbow Trout (here) are genetically very closely related to Coastal Rainbow Trout. 

A notable study that deviates from the Behnke system was conducted by Ken Currens, Carl Schreck and Hiram Li, titled the Evolutionary Ecology of Redband Trout. Based on the results of this study the Northern Great Basin Redband Trout should be broken out into multiple lineages. First the Redband Trout of the Harney-Malheur Basin and Catlow Valley (determined in this study) group with the Columbia Basin Redband Trout. Next the Goose Lake, Chewaucan Basin and Warner Lakes Redband Trout all group with the McCloud River and other Redband Trout of the Northern Sacramento Basin. A major difference comes up with the Klamath Basin Redband Trout, which appear to have two to three separate forms. There are two groups with subspecies level differences in the basin, one in the headwaters of the Williams, Sprague and Sycan Rivers (Klamath Headwaters Redband Trout) and another group associated with Klamath Lake. A third group in select tributaries of the upper basin aligns with the steelhead populations in the lower river, which appear to be a mix of Redband and Coastal Rainbow trout as mentioned in the Behnke section. The other major difference is the distinctiveness of the Fort Rock and White River Redband Trout. Both of these groups align most closely with the Columbia Basin Redband Trout, but have diverged enough due to long isolation and possible past contact with the Klamath Redband Trout that they should be consider distinct subspecies. Additionally, the Sheephaven Redband Trout are now recognized to just be a population of McCloud River Redband Trout that have experienced significant a genetic bottleneck, but are very closely related to other McCloud River Redband populations (see here).

1. Coastal Rainbow Trout
2. Columbia Basin Redband Trout
1. Harney-Malheur Basin Redband
2. Catlow Valley Redband Trout
3. White River Redband Trout
4. Fort Rock Redband Trout
5. Klamath Lakes Redband Trout
6. Klamath Headwaters Redband Trout
7. McCloud River/ Sacramento Redband Trout
1. Pit River Redband Trout
2. Goose Lake Redband Trout
3. Chewaucan Basin Redband Trout
4. Warner Lakes Redband Trout
8. Eagle Lake Rainbow Trout
9. Kern River Rainbow Trout
10. Little Kern Golden Trout
11. California Golden Trout

Western Native Trout Challenge System

The Western Native Trout Challenge classification system is by far the most simplified of the classification systems with significant lumping. In fact, the 9 to 11 subspecies recognized by the other two classification systems are reduced to just 6. The most notable changes off the bat is that only a component of the Coastal Rainbow Trout subspecies are included, as the Alaskan Rainbow Trout. The classification of Alaskan Rainbow Trout as a distinct subspecies is not recognized by the science but instead is a categorization strictly for the challenge. The most significant lumping is with the Redband lineages, where all of the forms are lumped into a single Interior Redband classification. 

1. Alaskan Rainbow Trout
2. Interior Redband Trout
3. Eagle Lake Rainbow Trout
4. Kern River Rainbow Trout
5. Little Kern Golden Trout
6. California Golden Trout