Coexistence of Two Species of Sucker, Catostomus, in Sagehen Creek, California, and Notes on Their Status in the Western Lahontan Basin

Volume 49 Number 4 Article 10

10-31-1989

Coexistence of two species of sucker, Catostomus, in Sagehen Creek, California, and notes on their status in the western Lahontan Basin

Lynn M. Decker University of California, Berkeley

Follow this and additional works at: https://scholarsarchive.byu.edu/gbn

Recommended Citation Decker, Lynn M. (1989) "Coexistence of two species of sucker, Catostomus, in Sagehen Creek, California, and notes on their status in the western Lahontan Basin," Great Basin Naturalist: Vol. 49 : No. 4 , Article 10. Available at: https://scholarsarchive.byu.edu/gbn/vol49/iss4/10

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 Great Basin Naturalist by an authorized editor of BYU ScholarsArchive. For more information, please contact [email protected], [email protected]. COEXISTENCE OF TWO SPECIES OF SUCKER, CATOSTOMUS, IN SAGEHEN CREEK, CALIFORNIA, AND NOTES ON THEIR STATUS IN THE WESTERN LAHONTAN BASIN

Lynn M. Decker 1

Abstract. —The observed distribution and relative abundance of two morphologically similar species of sucker, Catostomus, have shifted dramatically over the past four decades in Sagehen Creek and nearby streams in eastern California. The mountain sucker, C. platyrhynchus, formerly abundant and more numerous than the Tahoe sucker, C. tahuensis, has become relatively rare and during this study was consistently less abundant than the Tahoe sucker at all eastern California sites in 1983. Similar shifts in abundance were not seen at the three Nevada sites. Behavioral observations and data on spatial and temporal patterns of habitat use, collected in Sagehen Creek between May and September 1982 and 1983 using a snorkel survey method, indicate nearly complete overlap between mountain and Tahoe sucker habitat use and an absence of any agonistic behavioral interaction between species. The decline of the mountain sucker in these areas is likely the result of an interaction of loss of habitat due to reservoir construction and destructive management practices. These changes may have led to the elimination of isolating mechanisms between the two species and may be increasing the opportunity for introgressive hybridization.

The mountain sucker, Catostomus platy- In 1982, distribution, abundance, habitat rhynchus, and the Tahoe sucker, C. tahoen- use, and behavioral interactions were ob-

sis, co-occur in Sagehen Creek and other served and quantified in Sagehen Creek to streams in the Lahontan drainage basin of determine possible mechanisms allowing the eastern California and west central Nevada continued coexistence of these two sympatric (Moyle 1976). They are morphologically simi- species. During this time, the mountain lar, and natural hybrids occur (Hubbs et al. sucker was extremely scarce, whereas earlier 1943, Smith 1966). The more widely dis- surveys found the mountain sucker to be tributed mountain sucker has been consid- equally as abundant as or more abundant than ered a product of Catostomus evolution, spe- the Tahoe sucker (Flittner 1953, Gard and cialized for cool waters, rapid currents, and Flittner 1974). Collections in nearby streams rocky substrates (Smith 1966). The Tahoe also turned up few mountain suckers. In 1983 sucker, endemic to the Lahontan Basin, is I began an intensive survey over a full sum- considered a stream generalist and reaches mer season to determine the distribution, greatest size and numbers in lakes and reser- abundance, habitat use, and behavioral inter- voirs (Willsrud 1966, Vigg 1978, Marrin et al. actions of both species in Sagehen Creek, and 1984). Although superficially similar, the an extensive survey of other sites where both mountain sucker differs from the Tahoe sucker species had been previously located, to deter- in morphologic trophic specializations (Smith mine if the change in relative abundance 1966), including small terete bodies, reduc- was widespread. These results provide back- tion of swim bladder size, and lip and jaw ground data essential for evaluating the pros- modifications for scraping diatoms and algae pects for continued coexistence of these two from rocks. Moyle (1976) indicated that the species in light of the extensive modification two species probably segregate spatially in of their habitats (primarily reservoir construc- streams, the mountain sucker being more tion), which has occurred over the last four abundant in upper stream reaches and the decades. Tahoe sucker more abundant in lower stream Study Areas reaches; when the two species are found Principal Study Stream: Sagehen Creek together, the mountain sucker is thought to concentrate in riffle sections while the Tahoe Sagehen Creek is in the Tahoe National sucker inhabits pools. Forest, 12.1 km north of Truckee, California

Forest and 'Department of Forestry' and Resource Management, University of California, Berkeley, California 94720. Present address: Pacific Southwest Range Experiment Station, Forest Service, U.S. Department of Agriculture, Box 245, Berkeley, California 94701.

540 October 1989 Decker: Sagehen Creek Suckers 541

STAMPEDE RESERVO

89 TO TRUCKEE

Fig. 1. Location of the principal study site at Sagehen Creek. California, and the extensive comparison sites from previous surveys (inset: = Sagehen Creek, Little Truckee River, Prosser ( !reek, Martis Creek; O = tributary to the Carson River; • = Hot Creek; A North Fork of the Humboldt River).

(Fig. 1). It originates from a series of small Survey Map, Hobart Mills, California, NW/4 springs at an elevation of 2,256 m on the east Truckee Quadrangle. The reach was marked side of the Sierra Nevada. Prior to the tilling of into 12 sections, 100 m each, making location Stampede Reservoir in 1969, Sagehen Creek of observations more easily quantifiable. Sec- meandered an estimated 20.3 linear km tions were numbered beginning at the up- of the added as through several small meadows, a riparian stream end reach and were the reservoir level decreased. Elevations at corridor of lodgepole pine (Pinus contorta), the section markers were referenced to the mountain alder (Alnus tenuifolius), aspen known surface level elevation of the reservoir, groves (Populus tremuloides), and finally a and altitudinal differences along the stream larger meadow area with scattered lodgepole gradient were determined with an Abney pine and willow (Salix spp.), before joining level. the Little Truckee River at an elevation of The stream meanders through a series of 1,768 m. At capacity, the reservoir inundates runs with side pools and shallow riffles. The about 4.8 linear km and, due to the braided upper 400 m is shaded by lodgepole pine, and nature of the channel, 10.6 of the original 12.0 the lowermost 800 m is open meadow with km of stream habitat in this area. occasional willow clumps on the bank edges. The study reach, located in the lower The streambed is low gradient (1%), and the meadow area, was chosen after preliminary substrate is mostly gravel and cobble de- observations in 1982 because it contained the posited on the lacustrine sediments of former majority of the sucker populations, its boun- Pleistocene Lake Truckee. Stream depths in daries were well defined by beaver dams late July (mean daily discharge, 0.54 m /sec) above and Stampede Reservoir below, and ranged from 0.03 m in riffle sections to ap- few obstacles would be encountered in proximately 1.7 m in the deepest pool. Aver- obtaining data by a snorkel survey method. age depth from 25 cross sections was 0.35 m, The reach is 1,200 m in length and is con- and average width was 5 m. The water was tained in Sec. 3, T18N, R16E, and Sees. 34 clear and visibility was 2 m or greater on all and 35, T19N, R16E, of the U.S. Geological snorkel observation davs. 542 Great Basin Naturalist Vol. 49, No. 4

In addition to Tahoe and mountain suckers, Carson River under Ricci Road Bridge cross- seven other species of fish inhabit the study ing. Sec. 23, T16N, R21E, Nevada Depart- reach either as residents or migrants: moun- ment of Transportation map 6-12, 1980. Ele- tain whitefish (Prosopium wiUiamsoni), rain- vation 1,463 m (est.). This tributary flows into bow trout (Oncorhynchus mykiss), brown the Carson River at the 1942 (Hubbs et al. trout (Salmo tratta), brook trout (Salvelinus 1943) survey site. fontinalis), Lahontan speckled dace (Rhin- Hot Creek, Eureka Co., Nevada. Sec. 9, ichthys osculus robustus), Lahontan redside T28N, R52E, Nevada Department of Trans- (Richardsonius egregius), and Paiute sculpin portation map 4-5, 1959. Elevation 1,585 m (Cottus beldingi). (est.). This site was the same as that of Hubbs etal. (1943). from Extensive Site Comparisons North Fork of the Humboldt River, Previous Surveys Elko Co., Nevada, at Interstate 80 bridge Little Truckee River, Sierra Co., Califor- crossing between Elko and Wells, Nevada. nia, 100 m upstream of the Highway 89 bridge Sec. 3, T38N, R57E, Nevada Department of crossing 18 km north of Truckee, California, Transportation map 3-4, 1976. Elevation in Sec. 20, T19N, R16E, U.S.G.S. Truckee, 1,585 m (est.). This site was the same as that of California-Nevada 15 min. Quad. 1955. Ele- Hubbs et al. (1943). vation 1,877 m. This site was the same as that ofHubbsetal. (1943). Methods Sagehen Creek, Sierra and Nevada cos., Principal Study Stream: Sagehen Creek California, two sections within the 1.2-km reach above Stampede Reservoir. Sees. 34 Distribution and abundance. —Surveys and 35, T18N, R16E, Sec. 3, T19N, R16E, to estimate the total distribution and abun- U.S.G.S. Truckee, California-Nevada 15 dance of suckers within the entire 1,200 m min. Quad. 1955. Elevation 1,815 m (est.). Sagehen Creek study reach were completed These are two of three sites (Stations VII and once every two weeks from 7 June to 30 Au- IX) used by Flittner (1953) and Gard and Flit- gust 1983 and again on 22 September 1983. tner (1974). The third site and possibly por- Number, age class (juvenile or adult), and tions of the lower section (IX) surveyed in location of each surveyed individual were 1983 are inundated by Stampede Reservoir. recorded. Additional observations were made Prosser Creek, Nevada Co., California, 50 of the composition of fish assemblages when m below the Highway 89 bridge crossing 7.2 fish appeared in groups and of characteristics km north of Truckee, California, Sec. 22, of the habitat. T18N, R16E, U.S.G.S. Truckee, California- High water on 7 June and 22 June made Nevada 15 min. Quad. 1955. Elevation 1,756 visibility poor. Surveys were therefore com- m. This site is about 1.7 km upstream from the pleted by electrofishing from the bottom to 1942 old highway bridge survey site (Hubbs et the top of the study reach using a Smith-Root

al. 1943), which was inundated when Prosser Type V backpack electrofisher. Remaining Reservoir was impounded in 1963. The differ- surveys were completed by snorkel survey ence in elevation between the 1942 and 1983 (Goldstein 1978).

sites is about 50 m. Observations were made while I pulled Martis Creek, Nevada Co., California, slowly upstream along the bottom in a shallow reach below Martis Reservoir (Moyle and switchback pattern looking for fish at the Vondracek 1985). Sees. 5 and 8, T17N, R16E, banks, near or under obstructions, among U.S.G.S. Truckee, California-Nevada 15 min. rocks, in riffles, and in the mainstream. By Quad. 1955. Elevation 1,740 m (est.). This this method, I observed fish upstream with-

site is below the 1939 survey area (Alex J. out having an obvious effect on their behavior. Calhoun, California Academy of Sciences, Environmental factors. —A U.S. Geo- San Francisco, unpublished data), which was logical Survey stream gauging station, 7.9 km inundated when Martis Reservoir was im- below the headwaters of Sagehen Creek, pounded in 1971. measures the discharge from a drainage area 2 Tributary to the Carson River at Dayton, of 27.2 km (Fig. 1). Continuous stage and Lyon Co., Nevada. The tributary enters the discharge records have been collected since October 1989 Decker: Sagehen Creek Suckers 543

December 1953. Stream temperature is re- tat factors between the two species for each corded at the Sagehen Creek Field Station by observation. a Taylor continuous recording air and water Behavioral observations. —Throughout thermograph, calibrated monthly. Stream the study, I observed at each site the species, temperatures also were taken in the study number, and size of associated fish, and any reach with a Taylor pocket thermometer for interaction among fishes. In 1982 I observed comparison with temperatures at the field sta- fish by snorkeling at sites in the study reach tion. Reservoir level elevation was provided for two to five 30-minute intervals on seven by the U.S. Bureau of Reclamation. A water- different occasions. In 1983 fish were ob- 30- stage recorder with a mercury-column ma- served for to 45-minute intervals in the study reach three separate occasions. In nometer located at Stampede Dam has been on addition, over the two-year study period, 434 in operation since August 1969. separate observations of behavior were col- Microhabitat USE. —Microhabitat use of lected in association with the microhabitat- the two sucker species was quantified in Sage- use measurements. hen Creek in both 1982 and 1983. Fish were For comparison, the diel behavior and ac- located using the snorkel survey method de- tivity patterns of both species of sucker were scribed. The following data were recorded for quantified in an underwater stream observa- each fish observed: stream section (riffle, tion tank at the Sagehen Creek Field Station, pool, pool-run edge, or run), general location where flows and water depth are regulated at offish description of site, water tempera- and the top and bottom of a diversion channel. ture, water velocity taken at fish snout (focal The observation area was 9.1 x 2.6 m. with a point velocity), water velocity taken at 0.6 grillwork at each end to keep the fish inside. total depth (mean water column velocity), Dividers were also used to confine fish in water column at fish (maximum depth of three enclosures, each roughly 3.0 X 1.2 m, depth), distance from the water surface to the next to the glass. Artificial cover was provided fish (focal point depth), substrate composition by floating a small piece of plywood in each 2 in the fish, and in a 0.25 area beneath amount enclosure. type of aquatic vegetation including an esti- Fish were captured by electrofishing in mate of filamentous algae cover on the stream Sagehen Creek and nearby Little Truckee bottom, amount of shade, and description and River, and were then transported to the field proximity of the closest cover. station in chests containing cooled stream Water current velocities were measured to water. Fish were weighed, measured, and the nearest 0.3 cm sec with a Gurley Pygmy placed in the enclosures for a two-day acclima- Current Meter mounted on a top-setting wad- tization prior to the observations. Three sets ing rod. Depths were measured to the near- of observations were made of the behavior and est 3 cm directly from the rod. I estimated activity of the two species between 21 July and visually the substrate size composition based 6 September 1982. The first two sets were on a modified \\ entworth particle size scale composed of twelve 4-hr periods (twice cover- (Bovee and Milhous 1978). ing the full 24 hrs). conducted over two Because of time constraints and the scarcity 2-week periods. The final set was composed of of fishes in the reach during many sample twelve 2-hr periods (once covering a full 24 periods, I used an opportunistic (thus nonran- hrs) of observation over one week. In the first dom) sampling scheme to collect microhabitat two sets I recorded behavior and activity of measurements. Measurements were taken sys- Tahoe suckers at three densities: 1, 5, and 6 tematically, working from the bottom to the fish per enclosure (0.3, 1.4, and 1.7perm"). In top of the reach between the hours of 1100 the final set I recorded the interaction of and 1500 and quantifying microhabitats as Tahoe and mountain suckers in two mixtures: fish were encountered. These measurements 2 Tahoe and 4 mountain suckers, 5 Tahoe were taken independently of distribution and suckers with 1 mountain sucker, and, for com- abundance surveys. The Spearman's rank cor- parison. 6 Tahoe suckers alone. These densi- relation is used as a descriptive tool to dis- ties were similar to observed densities in play and compare similarity of the ranked lower Sagehen Creek for similar areas where frequency distributions of various microhabi- suckers commonly occurred in groups ranging 544 Great Basin Naturalist Vol. 49, No. 4

Table 1. Temporal distribution, abundance, and group size of suckers within the Sagehen Creek study reach from 7 June to 22 September 1983 (* indicates that fishes were present only in a diversion of the main stream). October 1989 Decker: Sagehen Creek Suckers 545

10 24 7 21 5 19 2 16 30 13 27 MAY JUNE JULY AUG SEPT STUDY PERIOD 1983

Fig. 2. Temporal abundance of suckers in the study reach with corresponding measurements of mean daily discharge and maximum and minimum daily stream temperatures at University ol California s Sagehen Creek Field Station.

21 June surveys, mean daily discharge decreased and stream temperatures increased. Correspondingly, the number of Tahoe sucker adults observed increased to 73. On 22 June, Tahoe suckers were observed spawning in an open gravel riffle at the 790-m mark.

Mountain suckers were first observed in the reach on 19 July, when one individual was found. By the following survey of 2 August, the observed number of mountain suckers increased to 37, and Tahoe sucker juveniles also appeared in the reach (Fig. 2). Tahoe sucker juveniles occurred in groups with, and were always more abundant than, the similarly sized mountain sucker adults. Observed numbers of mountain sucker (37) and Tahoe sucker adults (154) peaked on 2 August. Numbers of juvenile Tahoe suckers peaked (75 individuals) in abundance on 16 August. As individuals counted began to decline, stream temperature was also declining (Fig. 2). Mountain 546 October 1989 Decker: Sagehen Creek Suckers 547 range ofeach habitat factor. As neither species 1 FISH occurred off the stream bottom, no apprecia- 2.0 r ble correlation occurred between depth-use I (r = (/> distributions s .427; p < .05). 1.0 In both 1982 and 1983, algae on the sub- u_ strate became evident during the second DC UJ week of July. Prior to this time only Tahoe Q. j£i JL suckers were present in the stream, and no LU algal cover beneath fish was observed. Com- 5 FISH 2.0 parison of estimated algae cover after the second week of July showed no difference (p > .05) between mountain sucker and Tahoe a 1-0 h sucker sites in 1982 but some difference be- UJ Q. tween sites in 1983. In 1982, mean algae cover cL. = C/5 m ^ y a for mountain sucker sites was 81%(S.D. 11; LU n = 8) and for Tahoe suckers, 61% (S.D. = 41; 6 FISH n = 85). In 1983, mean algae cover was 73% > 2.0 r (S.D. = 14; n = 31) and 49% (S.D. - 35; n = H 181) for mountain suckers and Tahoe suckers, O

< 1.0 h respectively. I Both species were distributed in pool, pool- run edge, or run habitats; no suckers were _B 0001 0401 0801 1201 1601 2001 found in riffle sections (Table 2). Of habitats 0400 0800 1200 1600 2000 2400 where Tahoe suckers occurred, 41% were in TIME PERIODS (HOURS) pool habitats, 39% in runs, and 20% in pool- run edges (Table 2). Mountain suckers most Fig. 4. Activity patterns of Tahoe and mountain suckers at three density levels in the stream observation tank often occurred in pool-run edges (49%), with (bars = the mean total activities per minute per fish; 33% in pool and 18% in run habitats (Table 2). shaded portions feeding activity per minute per fish; Behavior. —Both Tahoe and mountain vertical lines the highest value for each time period). suckers rested on the bottom of the study Each 4-hour period represents 18 observation times. The reach near some type of cover during the ma- results are based on 71 .3 hours of observation. jority of daylight hours. Feeding was seldom observed until early July, and then only in the ning just after dawn (Fig. 4). Both species afternoon. The arrival of mountain suckers in appeared more active at night. Feeding inten- the reach was coincident with increased algal sity was greatest during this time, and the fish abundance on the substrate, and mountain moved in less tightly structured groups. suckers were observed feeding substantially Feeding-related activity accounted for a ma- more often than Tahoe suckers. Mountain jority of the 81.3 hours of activity observed: suckers and juvenile Tahoe suckers almost 74.6% for solitary suckers, 54.2% for the always were observed together in the reach, 5-sucker group, and 62.5% for the 6-sucker where they rested side-by-side on the stream group. bottom. Agonistic encounters were never Extensive Collections and observed during this study. Historical Comparisons Besults from the stream observation tank reinforced results of daylight observations The Little Truckee Biver, Sagehen Creek, made in the study reach. Both species were Prosser Creek, and Martis Creek differed sig- highly gregarious. They rested side-by-side, nificantly (chi square p < .05 [Steel and Torrie often touching under the provided cover. This I960]) in relative abundance of Tahoe and behavior occurred in both mixed- and single- mountain suckers from early surveys (Table species groups. When movement occurred, 3). Tahoe suckers were previously estimated the group acted as a unit, regardless of its to be more abundant than mountain suckers make-up. Activity patterns fluctuated at low only at the Little Truckee Biver site (47% levels from early afternoon until early morn- Tahoe, 44% mountain, and 9% hybrids in ing, with a 6-hour period of less activity begin- 1942 [Hubbs et al. 1943]); but in 1983, Tahoe 548 Great Basin Naturalist Vol. 49, No. 4

Table 3. Long-term changes in relative abundance of Tahoe and mountain suckers at seven Lahontan Basin locations. Sources are HHJ: Hubbs et al. (1943); LMD: Lynn M. Decker, unpublished field notes; GAF: Flittner (1953); DCE: Don C. Erman, University of California, Berkeley, unpublished data; PBM: Peter B. Movie, University of California, Davis, unpublished data; AJC; Alex J. Calhoun, field collection provided by California Academy of Sciences, San Francisco. Collection methods are S = seine, E = electrofisher, P&D = pump and drain. October 1989 Decker: Sagehen Creek Suckers 549 controlled by a diversion structure upstream upstream migration of the mountain sucker and during most irrigation seasons may re- but not the Tahoe sucker. Unlike Tahoe suck- main dry continuously for several weeks (Jim ers, which survive very well in lakes and Curran, Nevada Dept. of Wildlife, Fallon, reservoirs (Willsrud 1966, Vigg 1978, Marrin personal communication). et al. 1984), mountain suckers are thought to The California streams surveyed had one prefer moving water and have rarely been change in common—reservoirs had been con- reported from lacustrine environments even structed. Sagehen Creek and Little Truckee when they inhabit tributary systems (Snyder River now flow into Stampede Reservoir 1983). However, my results in Sagehen Creek (filled in 1969), Prosser Creek flows into showed that mountain suckers leave the Prosser Reservoir (filled in 1963), and Martis stream and presumably enter the reservoir in Creek has been bisected by Martis Reservoir late summer, as do Tahoe suckers. Upstream migration in early (filled in 1971). Martis Creek and the Prosser summer is probably coincident with spawning, Creek system were also subject to California and the few adults apparently found sufficient Department of Fish and Game stream poison- spawning habitat below the pond sequence. ing operations. Martis Creek was poisoned Expanded upstream movement of the last in 1977 (Peter B. Movie, University of Tahoe sucker may result from interaction be- California, Davis, personal communication), tween density-dependent factors and the and Prosser Creek was poisoned last in 1984 availability of suitable stream habitat. It ap- (Lynn M. Decker, personal observation). peared that as seasonal abundance of Tahoe Sagehen Creek has undergone little physical suckers increased in the reach, their upstream change upstream from the reservoir (Erman distribution also increased. Tahoe sucker 1973), while some channelization and bank abundance (Erman 1973; Don C. Erman, restructuring took place in 1982 at the Little University of California, Berkeley, unpub- Truckee site. Livestock grazing has been com- lished data) and size (Marrin et al. 1984) in- mon at all sites. creased after filling of the reservoir. Density- dependent intraspecific interactions when Discussion population levels were high may have caused the Tahoe sucker to expand its distribution Marked changes in the observed distribu- upstream where it remained once suitable tion of suckers in and abundance Sagehen habitat areas were reached (Don C. Erman, Creek have occurred since Stampede Reser- University of California, Berkeley, personal voir was filled in 1969 (Erman 1973). By 1975 communication). Mountain suckers have de- some Tahoe sucker individuals had colonized creased in abundance and now remain only in upstream areas far above their original range. the remnants of their former habitat. The species is now apparently a permanent Flittner (1953) estimated the population of inhabitant of areas above the range deter- suckers in Sagehen Creek (1951-52) at 3,308 mined from 1952 to 1969 (Gard and Flittner individuals, 49% of which were mountain 1974) and above the range of the mountain suckers, 38% Tahoe suckers, and 13% consid- sucker. In contrast, mountain suckers occur ered hybrids. In 1983 the estimated maxi- no further upstream than they did in 1951 mum population in the sampled reach of (Flittner 1953) and are consequently now con- Sagehen Creek was 280 suckers; 40 (14%) fined to only 12% of their historical longitudi- mountain suckers (adults) and 240 (86%) nal distribution in Sagehen Creek. Tahoe suckers (155 adults and 75 juveniles). Gard and Flittner (1974) speculated that Because suckers migrated in and out of the the upstream limits of both species were influ- stream, the relative abundance of sucker spe- enced by gradient and substrate, but recent cies changed over time during the study pe- upstream movements of Tahoe suckers tend riod. Thus, an overall decline in suckers in to discount this hypothesis. If the Tahoe Sagehen Creek seems to have occurred as sucker is not limited by these factors, then it is well as a change in the relative abundance of unlikely that the mountain sucker would be so the two species, with the mountain sucker limited. It is possible but unlikely that the now comprising a relatively small proportion long complex (approximately 2 km) of beaver of the population as compared to its 1951-52 dams and ponds above the study reach deters levels. 550 Great Basin Naturalist Vol. 49, No. 4

In the limited distribution of the mountain spawned earlier. The possibility also exists sucker, habitat use almost completely over- that the smaller Tahoe suckers moving into laps that of the Tahoe sucker, and I was unable the stream with the mountain suckers were to document resource partitioning based on hybrids. microhabitat preference. Although mountain Distribution and abundance data from suckers possess specialized morphological Sagehen Creek and three local streams show characteristics that seem adaptive to living that populations of the mountain sucker are and feeding in riffles and swifter current now extremely limited and suggest that spe- areas, they were never found in these habi- cies may have become vulnerable to local tats. The arrival of mountain suckers into the extinction; at best, mountain suckers are cer- stream was, however, coincident with the in- tainly rare in these areas. Similar shifts be- crease in algae available on the substrate. tween years in relative abundance of suckers Mountain suckers were observed feeding sub- were not evident at the eastern Lahontan stantially more often than the associated Basin sites in Nevada. The differences be- Tahoe suckers. Sites with more algae were tween regions are possibly due to an inter- apparently selected by the mountain sucker, action of reduced and altered habitat and de- and this difference may reflect the presumed structive management practices in the moun- heavier use of diatoms and algae by the mountain sucker areas in eastern California. tain sucker than by the Tahoe sucker (Hauser In Sagehen Creek and three other nearby 1969, Marrin 1980). It seems unlikely, based stream, the impoundment of reservoirs seems on my observations, that the food resource in to have reduced the habitat area of the moun- Sagehen Creek was limited or that one species tain sucker and may have eliminated former prevented the other from feeding in an area, mechanisms isolating it from the Tahoe suck- as both species were present at these sites and er. The inundation of lower Sagehen Creek neither inter- nor intraspecific agonistic en- may also have contributed to the Tahoe sucker counters were observed in the stream or overwhelming the mountain sucker in these stream observation tank. Resource partition- areas, thereby increasing the probability of ing was perhaps not evident because of the genetic swamping (Hubbs 1955). current low density of fishes and abundant The loss of a sucker species due to intro- algae. gressive hybridization has been documented

The comparatively high degree of observed by Andreasen (1975). Although I have not hybridization for the Lahontan Basin—13% determined whether the proportion of hy- reported by Flittner (1953) compared with 1% brids in the Sagehen Creek population has predicted by Hubbs et al. (1943)—indicated increased since 1951, it seems doubtful that a previously that isolating mechanisms may population of 40 individuals—down from have been incomplete in Sagehen Creek. If 1,630 (Flittner 1953)—can persist much lon- former isolating mechanisms existed, such as ger. In two years of observation, young-of- segregation along a longitudinal gradient or the-year mountain suckers were absent in on a microhabitat level, results of my study Sagehen Creek and in the three other local show that they may now be functionally streams. Such was not the case at the eastern nonexistent. To some extent, temporal segre- Lahontan Basin sites in Nevada. It also seems gation may limit the time of spatial overlap unlikely that the reservoirs harbor large popu- between the two suckers, as documented for lations of the mountain sucker, since they other sympatric sucker species (Nelson 1968). have yet to be noted in collections by other Mountain suckers were absent when Tahoe researchers. suckers were spawning. A smaller size class (110-140 mm total length) of the Tahoe Acknowledgments sucker, however, moved into the stream with similarly sized adult mountain suckers and The research described here is based on was present and abundant at sites when my thesis presented to the Department of mountain suckers appeared ready to spawn in Forestry and Resource Management, Univer- mid-August. It is possible that the Tahoe sity of California, Berkeley, in partial fulfill- suckers present were ripe, even though large ment of the requirements for the Master of Tahoe suckers (160-220 mm total length) had Science degree. Financial support was in part October 1989 Decker: Sagehen Creek Suckers 551

from the University of California Agriculture Sierra counties, California. Unpublished thesis, University of California, Berkeley. 150 Experiment Station, the Wildlife and Fish- pp.

Gard, R , and G A Flittner 1974. Distribution and eries Graduate Student Fund, and the Paul R. abundance of fishes in Sagehen Creek, California. Fund. Living and laboratory facili- Needham J. Wildl. Manage. 38: 347-358. ties were provided at the Sagehen Creek Goldstein. R M 1978. Quantitative comparison of sein- Field Station during fieldwork portions of the ing and underwater observation for stream fishery surveys. Prog. Fish-Cult. 40: 108-111. study. Special thanks go to D. Erman for pro- Hauser, W J 1969. Life history of the mountain sucker, viding the opportunity as well as support and Catostomus platyrhynchus, in Montana. Trans. guidance during all phases of the research, Amer. Fish. Soc. 98: 209-215. and to P. Moyle who initially sparked my Hubbs. C L 1955. Hybridization between fish species in nature. Syst. Zool. 4: 1-20. interest in native fishes. R. Miller generously

Hubbs, C L . L C Hubbs, and R E. Johnson 1943. provided copies of his field notes from early Hybridization in nature between species of surveys of the Lahontan Rasin. M. Rrereton, catostomid fishes. Contrib. Lab. Vertebr. Biol. V. Landrum, S. Martin, R. Wagner, M. Univ. Michigan 22: 1-69. Marrin. D. L. 1980. selectivity Yoder-Williams, and M. P. Yoder-Williams Food and habitat use by introduced trouts and native nongame fishes in helped with fieldwork. D. McCullough, L. sub-alpine lakes. Unpublished thesis. University Maxwell, P. Moyle, G. Nelson, M. Power, of California, Berkeley. 87 pp. and an anonymous reviewer made helpful Marrin, D L, D C Erman, and B Vondracek. 1984. comments on various drafts of the manuscript. Food availability, food habits, and growth ofTahoe sucker, Catostomus tahoensis, from a reservoir and a natural lake. California Fish Game 70: 2-8. Literature Cited Moyle, P B 1976. Inland fishes of California. University of California Press, Berkeley. 405 pp.

Andreasen. J K 1975. Systematics and status of the Moyle, P B , and B Vondracek 1985. Persistence and family Catostomidae in southern Oregon. Unpub- structure of the fish assemblage in a small Califor- lished dissertation, Oregon State University, Cor- nia stream. Ecology 66: 1-13.

vallis. 76 pp. Nelson, J S. 1968. Hybridization and isolating mecha- Bovee, K. D., AND R. T. Milhous. 1978. Hydraulic simu- nisms between Catostomus commersonii and C. lation in studies: instream flow theory and tech- macrocheilus (Pisces: Catostomidae). J. Fish. Res. nique. Instream Flow Information Paper 5, Fish Board Canada 25: 101-150. and Wildlife Service OBS-7S/33. 131 pp. Smith. G R 1966. Distribution and evolution of the

Dauble, D D , AND R H Gray 1981. Comparison of a North American fishes of the subgenus Pantos- small seine and a backpack electroshocker to eval- teus, genus Catostomus. Univ. Michigan Mus. uate nearshore fish populations in rivers. Prog. Zool. Misc. Publ. 129: 1-133. Fish-Cult. 42: 93-95. Snyder, D E 1983. Identification of catostomid larvae in Decker. L M 1984. Distribution, abundance, and coex- Pyramid Lake and the Truckee River, Nevada. istence of two species of sucker (Catostomus) in Trans. Amer. Fish. Soc. 112:333-348.

Sagehen Creek, California, and their status in the Steel, R. G. D , and J H Torrie. 1960. Principles and western Lahontan Basin. Unpublished thesis. procedures of statistics. McGraw-Hill, Inc., New University of California, Berkeley. 40 pp. York. 480 pp. Erman, D. C. 1973. Upstream changes in fish populations Vigc, S 1978. Vertical distribution of adult fish in Pyra- following impoundment of Sagehen Creek, Cali- mid Lake, Nevada. Great Basin Nat. 38: 417-428. fornia. Trans. Amer. Fish. Soc. 102: 626-629. Willsrud, T 1966. A study of the Tahoe sucker, Flittner, G. A. 1953. The composition and distribution of Catostomus tahoensis. Unpublished thesis, San the fish populations in Sagehen Creek, Nevada- Jose State College, San Jose, California. 78 pp.