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TAXONOMY AND DISTRIBUTION OF THE BULL TROUT



157





FIGURE 5. Most posterior gill raker of first arch, right side (ventral view, left; dorsal view, right)
from (A) Salvelinus confluentus, UMMZ 17248, 285 mm, Flathead L., Montana; (B)
Salvelinus malma, UMMZ 128983, 312 mm, King Cove, Alaska Peninsula. Photograph
by the author.




FIGURE 6. Body form and pigmentation in Salvelinus confluentus (A) UMMZ 188857, 134 mm,
juvenile, trib. Clearwater R., Montana; (B) OSUM 25212, 235 mm, juvenile, trib. S. Fork
Flathead R., Montana. Photograph by the author.



158 CALIFORNIA FISH AND CAME

mists. The light-colored spots of 5. confluentus are normally smaller than the
diameter of the pupil of the eye, yet large enough to be seen on a fish in clear
water. Typically, they cover most of the back and are best developed around
the dorsal fin. Suckley (1860) and Campbell (1882) noted these light-colored
spots on the back of the bull trout.

Other Meristic Characters

The range of variation in numbers of vertebrae, gill rakers, and pyloric caeca
were about the same in S. confluentus and S. malma, with almost a complete
overlap between the two species. The mean numbers of pyloric caeca differed
by less than two (Table 6). 5. confluentus has a relatively high number of
vertebrae (mean of 64.8) compared to other Salvelinus taxa from the Pacific
basin (Table 7). Southern S. malma has a mean of 62.9. The increase in number
occurs in the precaudal series (36 in S. malma vs. 39 in S. confluentus) and
probably is correlated with the piscivorous habits of S. confluentus. Other fish
eaters, such as species of Esox, have a long abdominal cavity to accommodate
large prey.

The bull trout is characterized by a slightly lower number of gill rakers than
other North American Salvelinus. The number was found to range between 14
and 20 in S. confluentus with a mean of 16.6. For malma the range was 14 to
23 with a mean of 18 (Table 8).

Osteology

The skeleton of Salvelinus confluentus offers an impressive set of characters
that fully separate this species from S. malma. It was an examination of an
osteocranium of a specimen from Flathead Lake that first led me to suspect that
the bull trout was different from the Dolly Varden.

The external morphology of the head described previously is related to the
features of the cranial skeleton. The distinctive features found are consistent in
samples taken from the various drainages where the bull trout occurs. These
characters have been carefully checked by dissecting preserved material, radio-
graphing nearly 100 preserved specimens, clearing and staining, and by examin-
ing dried skeletal preparations. The latter have been used for purposes of
illustration. A comparative osteological study of the head skeleton in certain
Salvelinus, including S. malma from the western Pacific basin, has been pub-
lished by Shaposhnikova (1971). This should be referred to in comparing 5.
confluentus with S. malma.

The articulated cranium shows: 1 I a flattened skull roof; 2) an elliptical orbit
with a longitudinal axis much longer than the vertical; 3) a large cavity behind
the orbit which was occupied bv the adductor muscle of the lower jaw, and 4)
massive jaws with strong teeth ( Figure 7A). The jaw teeth are best developed
on the premaxilla, dentarv, and anterior end of the maxillary alveolar shaft. The
latter is curved with its dorsal margin covered posteriorly by a sigmoid-shaped
supramaxilla.

The large area for attachment of the adductor mandibulae muscle is made
possible b\ expansion of the lateral h\ omandibular surface ( Figure 8A ) . Because
of this expansion, the hyomandibular is one of the most diagnostic of all the
cranial elements. Among the Salvelinus investigated, the lake trout, Salvelinus
namaycush, has a similar hyomandibular.



TAXONOMY AND DISTRIBUTION OF THE BULL TROUT



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FIGURE 7. (A] Osteocranium oi Sahefotus confluentus, UMMZ i""J458, head length 112 ..

Flathead L, Montana; (8) neurocranium of same individual in dorsal, ventral, and
lateral views.



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af - = :r" "•-•' ~~£ ~£a. . :: .£- ~g c" : a - " • "-_- :.-'-t : ';":i; "5. ~~a ~a
has given rise fee ~any ridges pits ties as • - a- z^sing the pores of

:~£ i-cacc :a :a~a :o ce £ £ -• ccr. :-ces ace .e the surface.

- ; with the hyo^ a - d oular, the supraethmoid is also highly diagnostic for the
bull trout (Figo'e 9 nstead of being sharply divide: " twop a is I head and
posterior extension) by a pronounced constriction, as in S. malma. the lateral
margins of the bone are near parallel posteriorly and then aper gradually
ard the inter or end The head - the bone is marked b . jst a slight lateral
£\ca~5 :r ace: ~a f .'. a. a eg :~£ ate'a ~a r 2 - 3rr "re ~eac a-c cere' -
extension of the f_ca£:hmoid in S. confluentus are more elongated than in $
vufaa and in this respect the) a: z'Dach the condition ir 5 lamay :^sh. The
a-:£- :- ~a-g-s c* :~e as:£-c -^ :: i£fS£s ;*' :-e c-£~a- a£ a::ac^ a \- 1 :-e
s _ p -a£:hmoid ~ £a c a — a '£ correspondingly lengthened in 5. confluentus. Again.
this is a character a sc -ound in t H - a- £ trout

!>£-£_ 'ocranium is depressed in comparison to that of other Safveiinus, with
the parasphenoid only slightly flexed (Figure "3 5. malma possesses a well-



164



CALIFORNIA FISH AND CAME






FIGURE 9 Comparison or supraethmoids in Sa/vethus mj/mj \-C and Sa '■elinus confluentus
(D-f). not drawn to same scale MMZ 126507 286 mm, female. karluk R.,

• • A • aska; \B ] L MMZ - 0c:5 J 383 mm. female Unalaska I. Alaska: (C) UMMZ
To>: -nm remale Unalaska I. Alaska- ID) UMMZ 159333 227 mm, male.
Morrison I. Brit. Co! - IE) UMMZ 172458 est. 490 mm Flathead L Montana
' ' " ' "."- : ; est 420 mm Flathead L Montana.



developed flexure in the parasphenoid which is consistent with its deeper neuro-
cranium. The lateral profile of the neurocranium showing these characteristics
can usuallv be seen in radiographs taken with the specimens King flat on their
sides

When observing the palate in 5 confluentus this species, like 5. malma
(Morton and Miller 1954K does not show a well-developed toothed platform



TAXONOV^- AND DISTRIBUTION OF THE BLLL TROUT 165

on the vomer. The form of vomerine teeth usual - tshallovt \. Sometimes
these teeth are arranged in a single trar - - . ~here is a ell-

f loped gap between the palatine and vomerine tooth rows. This is a consist-
ent feature of S. confluentus riereas in S. malma it is variable.

HYBRIDS

Two of nine specimens of bull tro~: I v.'Z 188652 I taken from Long Creek.
Lake Co.. Oregon, in the upper Klamath basin were identified bv me as hvbrids
with brook trout. Salvelinus fontinalis < Figure 10 > . The hvbrids had much darker
pigmentation over the head, bodv, and fins than the other seven specimens, the
dorsal fins were mottled, and the lower fins were tricolored. Light spots on the
flanks were uniformly smaller than those on the flanks of the bull trout. The
maxillary bones of the upper ja . re long and straight, a characteristic of the
brook trout. Vertebral counts for the hybrids were intermediate • both with t_

"r r eas the Long Creek bull trout ranged from 64 to 66. with a mean of 65.
According to \ idyko\ 1954 brook trout ha\ e 58 to 62 \ ertebrae with a mean

r 9.5. The branchiostegal ray count was high. 13 and 14 on the left side, like
that of the bull trou' whereas brook trout usualK have 11 on the left side
ko\ 195- * of the Long Creek specimens, including the two hybrids,
possessed basibranchial teeth.

Hvbridization between the bull trout and the brook trout has also been men-
tioned b\ Paetz and Nelson I97C to occur in the Clearwater Riser drainage
• \iberta.

Two possible hvbrids between S. malma and 5. confluentus were identified
from lakes in the Skeena River basin. British Columbia. The first individual
L \'\'Z 159328 203 mm. ferr is taken from Swan Lake. It resembles 5.

confluentus in the number of branchiostega s 27 and \ ertebrae i66> but is
more like S. malma in number of gill rakers 2 ind mandibular pores i "
Gill raker charateristics are intermediate between S. malma and S. confluentus.
In head form and maxillary shape, the hybrid also resembles S. malma. The
second specimen L \'\'Z ' 5 ^333. 188 mm, female' from Morrison Lake -
similar in appearance to the Swan Lake individual, especiallv in its head mor-
phologv . It has 24 branchiostegals. 6~ \ ertebrae. 20 gill rakers, and 1 5 mandibular
pores. Like the first specimen, the gill rakers are also intermediate in shape and
structure between those of S. malma and those of S. confluentus.

DISTRIBUTION

Salvelinus confluentus is distributed in a north-south belt along the Rocky
Mountain and Cascade ranges of northwestern North America I Figure 1 }. The
area stretches from lat 41" \ to lat 60 c \ or slightK be\ond. Localities plotted
are about equallv distributed on both sides of the Continental Divide between
lat 50 ; and 60 = N. Major river drainages involved in the distribution pattern on
the Pacific slope are: The McCloud in the upper Sacramento River basin of
California; the upper Klamath in Oregon; the Snake in Oregon, Idaho, and
Nevada; the Columbia River throughout its length; the Pend Oreille; the Clark-
Fork of Idaho and Montana, including the Flathead; the Kootenav Riv er of British
Columbia; the Fra- er of British Columbia, plus Puget Sound iri "ington.

and the Skeena and Taku rivers of British Columbia. In the Bering Sea drair _
thev are found in the headwaters of the Yukon at the boundarv between British



166



CALIFORNIA FISH AND CAME







FIGURE 10. Two hybrid Salvelinus confluentus X S. fontinalis (below) compared with two 5.
confluentus (above); all from same catch by W. Seegrist, Long Cr., Lake Co., Oregon.
Photograph by the author.

Columbia and the Yukon Territory. No specimens were examined from the Nass,
Stikine, or Alsek drainages of the Pacific slope of Canada. McPhail's ( 1 961 ) data
indicate bull trout are in Bowser Lake of the Nass drainage.

On the east side of the Continental Divide, S. confluentus is found in the
headwaters of the South and North Saskatchewan rivers of the Hudson Bay
drainage in Alberta and in headwater areas of the Athabaska, Peace, and Liard
rivers of the MacKenzie system in Alberta and British Columbia, the latter
draining to the Arctic Ocean.

The distributional pattern of S. confluentus is largely the result of headwater
migration and drainage crossover by stream capture. In the northern half of its
range this has occurred following the retreat of the last continental ice sheet.
Stream capture of the upper Columbia tributaries by those of the Saskatchewan
enabled the bull trout to cross to the east side of the Continental Divide along



TAXONOMY AND DISTRIBUTION OF THE BULL TROUT 167

with Salmo clarki and Prosopium williamsoni. Lindsey (1964) has explained
transfer of fishes from the upper Fraser to the Peace River by a drainage block
at the time the continental ice sheet was retreating from northern British Co-
lumbia. It is possible that S. confluentus entered the Taku River by means of
migration along the coastal waters, but other species entered the Taku from the
east through the Liard tributaries or from the Liard via the Yukon headwaters
without any coastal connections (McPhail and Lindsey 1970). S. confluentus is
known from collections prior to 1900 to have entered coastal waters in Puget
Sound, Washington.

Because the bull trout is so generally distributed throughout the Columbia
River basin and because this basin borders others where the bull trout is found,
it is likely that this species originated there. Transfer to drainage basins in the
southern part of its range, such as the Klamath and Sacramento, may have
occurred during or following the last glaciation, but it is possible this distribution
follows an older pattern, as suggested by the isolated occurrence of 5. confluen-
tus'\n the upper reaches of the Sacramento, Klamath, and Snake rivers. However,
according to R. Behnke (Colorado State Univ., pers. commun.) the occurrence
of S. confluentus in the Snake River drainage above Shoshone Falls ( Hubbs and
Miller 1948) is most likely the result of headwater transfer from the Salmon River
drainage.

The distribution of the bull trout corresponds in many ways to that of the
mountain whitefish, Prosopium williamsoni. The latter species differs in having
reached the headwaters of the Missouri drainage in northwestern Wyoming and
western Montana. It also has crossed into the Bonneville and Lahontan basins.
The mountain whitefish is not known from the headwater tributaries of the
Yukon drainage where the bull trout is present (Scott and Crossman 1973).

There is a possibility that S. confluentus was present at an earlier time in the
Bear River of the Bonneville basin. Rostlund (1951) indicates a species of
Salvelinus was known in these waters before 1850. If this is true, it may also have
entered the Lahontan basin, as did Prosopium williamsoni, but has since disap-
peared. The retreat of S. confluentus from the southern extremes of its range is
occurring today as it probably has in the past. The gradual change in climate
since Late Pleistocene with subsequent loss of water once supplied from moun-
tain glaciers and snowfields has been a major factor in eliminating habitats where
the bull trout can survive. Once a prominent species in the McCloud River of
the Sacramento system in California, the bull trout has gradually declined since
the late 1800's and is now close to extirpation. Modifications of the river by man
may have accelerated the rate of decline.

Since Livingston Stone first called attention to the bull trout of the McCloud
River in 1872, very few specimens from the McCloud have been deposited in
museums. Fifteen are known to me, including one probably taken on Stone's
initial tour of the McCloud. The old USNM specimens were originally preserved
in alcohol without fixation in formalin; several are in such a poor state of
preservation that they cannot be removed from their glass container. Two speci-
mens (USNM 15549) labeled Wye-dai-deek-it, the original Indian name for the
bull trout in the McCloud Valley, were collected by Stone in 1874. Seven (in-
cluding one skeleton ) were sent by Stone to the USNM between 1 875 and 1 881 .
Five specimens were taken singly between 1938-1975; one came from the Mt.
Shasta Hatchery at Mt. Shasta in 1956; three small individuals, taken on hook

3—77343



168 CALIFORNIA FISH AND GAME

and line between 1938 and 1950, are housed in the California Academy of
Sciences; a larger adult taken on hook and line July 19, 1975, is in the collection
of the California Department of Fish and Game (CDFG 0513). The exact loca-
tions of capture of Stone's bull trout are not known, although they were probably
taken in the vicinity of the trout hatchery on Green's Creek ( Wales 1 939 ) where
set lines were placed to catch rainbow trout.

Wales (1939) presented testimony that the bull trout formerly occurred in the
upper Sacramento River in the vicinity of Dunsmuir, Siskiyou Co., and in the Pit
River near the mouth of Squaw Creek, Shasta Co. Jordan (1907) listed upper
Soda Springs on the Sacramento River as a locality, but Evermann and Bryant
(1919) stated the McCloud River is the only stream in California in which the
bull trout is known to be native.

Campbell (1882) reported bull trout occurred in the McCloud River from its
mouth upstream to Big Springs. Big Springs is a source of melt water from
snowfields on Mt. Shasta, which yields a nearly constant flow of 7 C (45 F) water
(Wales 1939). Although Campbell had fished the entire McCloud River, he
never took bull trout above Lower Falls (3.2 km above Big Springs) where he
reported water temperatures from 15.5 C to 21 C (60 F to 70 F). Downstream
at the fish hatchery on Greens Creek (now inundated by Lake Shasta), Campbell
reported water temperatures of 13 C to 15.5 C (55 F to 60 F) at midday in the
hottest weather, and from the hatchery up to the Big Springs the river got "one
degree colder about every 10 to 12 miles for the distance of 65 or 70 miles."

The early records from Oregon and Washington indicate the bull trout was
once more widely distributed on the Pacific side of the Cascade and Coast
ranges than it appears to be today. Specimens taken from Puget Sound by Jordan
and others in the 1880's are assignable to either 5. confluentus or S. malma. The
head of Suckley's (1858) type of Salmo confluentus is a bull trout taken from
a Coast Range drainage (Pullayup River) that empties into Puget Sound. Cope
(1879) reported one of the earliest records for Salvelinus confluentus from the
Klamath basin; this is the only previously published record based on an actual
specimen from that basin. The earliest confirmed record for S. confluentus is the
specimen collected in 1854 from The Dalles on the lower Columbia River. In
contrast, this species was not collected from the Snake River drainage of Nevada
until much later (Miller and Morton 1952).

DISCUSSION

I have attempted to provide evidence for the separation of S. confluentus from
S. malma, particularly in that part of the range of S. malma southward from
southern Alaska on the eastern side of the Pacific basin in North America. The
systematics of S. malma throughout its range, including Alaska and the North
Pacific basin, is lengthy and complicated and will be treated elsewhere.

There are valid reasons for considering the bull trout a full biological species:
1 ) The character states investigated which separate S. confluentus from S. mal-
ma are constant throughout a broad geographical area occupied by S. confluen-
tus. 2) Stability is further indicated by the fact that variation of all characters
investigated is minimal when compared to other recognized species of Sal-
velinus. 3) Even though the ranges of 5. malma and 5. confluentus overlap in
the Pacific slope drainages from northern California to southern Alaska, there is
no evidence of introgression in the material studied.


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