Western North American Naturalist Volume 68 Number 1 Article 8 3-28-2008 The case for humboldtensis: a subspecies name for the indigenous cutthroat trout (Oncorhynchus clarkii) of the Humboldt River, Upper Quinn River, and Coyote Basin drainages, Nevada and Oregon Patrick C. Trotter Seattle, Washington Robert J. Behnke Colorado State University, Fort Collins Follow this and additional works at: https://scholarsarchive.byu.edu/wnan Recommended Citation Trotter, Patrick C. and Behnke, Robert J. (2008) "The case for humboldtensis: a subspecies name for the indigenous cutthroat trout (Oncorhynchus clarkii) of the Humboldt River, Upper Quinn River, and Coyote Basin drainages, Nevada and Oregon," Western North American Naturalist: Vol. 68 : No. 1 , Article 8. Available at: https://scholarsarchive.byu.edu/wnan/vol68/iss1/8 This Article is brought to you for free and open access by the Western North American Naturalist Publications at BYU ScholarsArchive. It has been accepted for inclusion in Western North American Naturalist by an authorized editor of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. Western North American Naturalist 68(1), © 2008, pp. 58–65 THE CASE FOR HUMBOLDTENSIS: A SUBSPECIES NAME FOR THE INDIGENOUS CUTTHROAT TROUT (ONCORHYNCHUS CLARKII) OF THE HUMBOLDT RIVER, UPPER QUINN RIVER, AND COYOTE BASIN DRAINAGES, NEVADA AND OREGON Patrick C. Trotter1 and Robert J. Behnke2 ABSTRACT.—In the early years of his research on the native trouts of western North America, Behnke (1960, 1966, 1979) observed consistent differences in certain meristic characters between the cutthroat trout of the Humboldt River drainage and those from the Truckee, Carson, and Walker river drainages of the Lahontan Basin, and proposed that the Humboldt trout be recognized as a distinct subspecies. He coined the subspecies name humboldtensis, but a formal description was never published. Here we again present the early evidence for subspecific distinction of the Humboldt drainage cutthroat trout, and add more recent findings from the fields of population genetics and Pleistocene and recent zoogeography that support this interpretation. Based on this evidence, we offer a formal description of the cutthroat subspecies Oncorhynchus clarkii humboldtensis and map its likely historical distribution. Available meristic and zoogeo- graphic evidence indicates that the native trouts of the upper Quinn River, Nevada and Oregon and the Coyote Basin of Oregon should be included with humboldtensis as well. Keywords: Humboldt cutthroat trout, Oncorhynchus clarkii humboldtensis, description, historical distribution, Humboldt River, Upper Quinn River, Coyote Basin, Lahontan Basin. During the early years of his research on utah) and other cutthroat subspecies. When the native trouts of the genus Salmo (now On - he included 35 specimens collected from the corhynchus) of western North America, Behnke west side of the Lahontan Basin and 32 spec- (1960, 1966, 1979) found that specimens of imens collected from the Humboldt River cutthroat trout (Oncorhynchus clarkii) from drainage in this analysis, the program differ- the Humboldt River drainage on the east side entiated them with 100% accuracy. of the Lahontan Basin in Nevada consistently The consistent difference in gill raker num - differed in certain meristic characters from ber is particularly significant in that having specimens from the Truckee, Carson, and numerous gill rakers facilitates feeding on Walker river drainages on the west side of the plankton in lakes (Martin and Sandercock 1967, basin in California and Nevada. One difference McCart and Anderson 1967, Zaret 1980, Mc - was in lateral-series scale counts: 120–160 Phail 1984). This character is indicative of a scales in the lateral series in Humboldt speci - lacustrine evolutionary history for trout of the mens versus 150–180 scales in the lateral series Truckee, Carson, and Walker River drainages, in Truckee, Carson, and Walker river speci- most likely in association with pluvial Lake mens. But the major distinction was in the Lahontan into which these drainages dis- number of gill rakers: collections from Hum- charged during the Pleistocene Epoch. The boldt drainage populations consistently aver- Humboldt River system also drained into Lake aged 2–4 fewer gill rakers (–x = 21) than popu- Lahontan during high stands of the pluvial lations from the Truckee, Carson, and Walker lake, but the significantly lower number of gill river drainages (–x = 24). Hickman (1978) also rakers in the cutthroat trout of the Humboldt observed these consistent differences. As part drainage points to a fluvial rather than lacus- of his study of the taxonomy of the native trout trine evolutionary history. of the Bonneville Basin, Hickman (1978) Based on the consistent differences in mer - developed a discriminate function computer istic characters and the distinctly separate evo- analysis of 16 characters to quantify differences lutionary pathways implied by the differences between Bonneville cutthroat trout (O. c. in gill raker number, Behnke (1966) proposed 14926 26th Ave. S., Seattle, WA 98108-2018. E-mail: [email protected] 2Professor Emeritus, Department of Fishery, Wildlife and Conservation Biology, Colorado State University, Fort Collins, CO 80523-1474. 58 2008] THE CASE FOR HUMBOLDTENSIS 59 50 45 40 35 30 25 20 Number of Specimens 15 10 5 0 18 19 20 21 22 23 24 25 26 27 28 Gill Raker Count henshawi, N=161 humboldtensis, N=137 Fig. 1. Number of gill rakers in Oncorhynchus clarkii humboldtensis versus O. c. henshawi (data from Behnke 1966: table 8). that the cutthroat trout of the Humboldt River drainage cutthroat trout and add more recent drainage be recognized as a separate sub- findings that confirm his original interpreta- species, humboldtensis, to distinguish it from tion. At this time we offer a formal description the cutthroat trout of the Truckee, Carson, and of the cutthroat subspecies humboldtensis and Walker river drainages, which had already been also a rationale for mapping its historical dis- described and named henshawi by Theodore tribution to include not only the native cut- N. Gill and David Starr Jordan in the 2nd edi- throat trout of the Humboldt River drainage of tion of Jordan’s Manual of the Vertebrates of Nevada but also those of the upper Quinn River the Northern United States (Jordan 1878) based drainage of Nevada and Oregon and the Coyote on specimens from Lake Tahoe in the Truckee Basin (also known in older publications as the River drainage. Behnke originally coined the Whitehorse Basin) of Oregon. name humboldtensis in 1963 for a monograph, Behnke’s (1960, 1966, 1979) comparisons of The Rainbow and Cutthroat Trouts of North Humboldt drainage cutthroat trout with the America, that he had written with P.R. Need- cutthroat trouts of the Truckee, Carson, and ham that year. However, that monograph was Walker river drainages began with museum withdrawn from the publication process in 1964 specimens collected by J.O. Snyder from 1911 following Needham’s death, so the name and to 1915 (see Snyder 1917) and continued with formal description of the Humboldt subspecies collections he made himself in 1961, 1962, were never published. Behnke used the name 1963, and 1972. In total, Behnke’s collections again for the Humboldt Basin subspecies in comprise more than 200 specimens from 27 his doctoral dissertation (Behnke 1966), but as localities all across the Humboldt River drain - a nomen nudem (= a name without descrip- age. Figure 1 is a chart of gill raker counts of tion), and in his subsequent publications 137 Humboldt drainage specimens and 161 (Behnke 1979, 1992, 2002), he opted to refer Truckee, Carson, and Walker river specimens to the Humboldt cutthroat trout simply as an from Behnke’s 1961, 1962, and 1963 collections unnamed subspecies. (data from Behnke 1966: table 8) that illus- Here we reiterate Behnke’s early evidence trates the distinct difference between the 2 for the subspecific distinction of the Humboldt sets of populations in just this 1 character. The 60 WESTERN NORTH AMERICAN NATURALIST [Volume 68 humboldtensis data are left-skewed, with a downstream reaches), significantly fewer than mean value of 21 gill rakers and a mode of 22. in O. c. henshawi, which typically has 150–180 The henshawi data are just slightly right- scales in the lateral series. Scales above the skewed, with a mean of 24.2 gill rakers and a lateral line, 26–45. Gill rakers, 18–24 (–x = 21), mode of 24. The null hypothesis that these significantly fewer than the 21–28 (x– = 24) distributions were drawn from the same over- typical of henshawi. Pyloric caeca numbers vary all population was rejected (α = 0.05). across the range but average 50–60 in most Although allozyme electrophoresis studies populations; however, the type specimen from (Loudenslager and Gall 1980, Gall and Loud - the South Fork Little Humboldt River has 45 enslager 1981, Bartley et al. 1987, Williams pyloric caeca, and trout native to Hanks Creek, 1991, Bartley and Gall 1993) have generally a Mary’s River tributary in the Humboldt drain - shown little variation within and among Lahon- age, average 65 pyloric caeca. Basibranchial tan Basin cutthroat populations, the study of teeth, 1–14, fewer than in most samples of Williams (1991) did find sufficient allozyme other cutthroat subspecies. The type specimen variation between Humboldt drainage popula- has 11 basibranchial teeth. Body colors are tions and populations from the Truckee, Carson, generally dull in humboldtensis, a trait it and Walker river drainages to justify his conclu- shares with henshawi, and are typically brassy, sion that the 2 forms should be set apart from coppery, or burnished silver with some ten- one another. Studies of mitochondrial DNA dency toward yellow. Rosy pink tints often (mtDNA) variation (Williams and Shiozawa appear on the sides and on the opercle. The 1989, Williams 1991, Williams et al. 1992, 1998) ventral region is white to gray and the lower also reveal small but significant differences fins are typically brownish with sometimes among these populations.