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jpeg Tom Kennedyı
Biology Department, University of Nevada-Reno, Reno, NV 89557-0015
ıCurrent address: U.S. Fish & Wildlife Service, Nevada State Office, 4600 Kietzke Lane, Bldg. C-125, Reno, NV 89502-5093
The Warner sucker is endemic to the Warner Basin, located in south-central Oregon, extreme north-east California, and extreme north-west Nevada. It is part of a relict fauna that was isolated in the Pleistocene during the last pluvial period roughly 15,000 to 17,000 years ago when Lake Warner was formed (Hubbs and Miller 1948, Snyder et al. 1964). Warner suckers occur in Twelvemile, Twentymile, and Honey Creeks, and their associated tributaries as well as remnant lakes in the Valley when filled (fig. 1). Streams are considered the most dependable and critical habitat for persistence of Warner suckers as lakes routinely desiccate roughly every thirty years.
Figure 1. click for map ( 27KK jpeg)
Warner suckers use low to moderate- gradient stream reaches for spawning and rearing (Williams et al. 1989). Some are year-round stream residents and reach maturity at three to four years of age when approximately 130 to 160 mm in length (standard length) (Coombs et al. 1979). Historic records indicate that large spawning runs of suckers and redband trout (Oncorhynchus mykiss ssp.) would ascend tributary streams in the spring and spawn in areas with clean, coarse gravel (Coombs et al. 1979). In streams, larvae drift-feed on zooplankton and small insects near the water surface, then switch to foraging on algae and associated benthic food items (detritus and macroinvertebrates) when two months old and approximately 25 to 30 mm total length.
In 1985, Warner suckers were listed as threatened by the U.S. Fish & Wildlife Service due to observed declines in range and numbers, introductions of piscivorous game fishes into lakes, and modifications of stream habitat (White et al. 1990). Critical habitat was designated and includes low-gradient sections of Twelvemile, Twentymile, Snyder (tributary to Honey Creek), and Honey Creeks, as well as part of the spillway canal north of Hart Lake.
Water diversions and dams were originally installed in Warner Valley streams 150 years ago by Irish settlers for agricultural crops and cattle ranching. Although some efforts to allow fish passages over dams have been done, other dams without ladders could be preventing spawning migrations of adult suckers from occurring. In addition, since diversion channels are not screened, young life stages of suckers might become trapped in irrigation ditches. Water management for crop production may conflict with requirements of developmental stages of Warner suckers as well.
Recent investigations have focused on drift and survival of sucker larvae in low to moderate- gradient streams.
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jpeg Warner sucker larva.
Rollie White photo
In 1992 and 1993, we studied drift ecology of Warner sucker larvae to determine if downstream transport limits juvenile recruitment (Kennedy and Vinyard submitted, Kennedy and Olsen 1994). Peak flows in Twentymile Creek ranged from 74 ft³ secı in April 1992 (Fig. 2) to 4,970 ft³ secı in March 1993 (Fig. 3), and were indicative of variation in discharge of Warner Valley drainages over the past thirty years.
Figure 2
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jpeg Twentymile Creek at 74 ft³/secı
Figure 3
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jpeg Twentymile Creek at 4,970 ft³/secı
By July 1992, all lakes in the valley floor had desiccated (Fig. 4), but refilled up to Campbell Lake in 1993 (Fig. 5).
Figure 4
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jpeg Dry Warner Basin, 1992
Figure 5
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jpeg Filled Warner Basin, 1993
Although recruit losses of other western Catostomids is suspected to occur from entrainment in diversions downstream of spawning areas, Warner sucker larvae may have developed resistance behaviors to avoid drifting since downstream habitat is unreliable. We hypothesized that propensity for larvae to drift may be an evolutionary adaptation for a species depending on reliability of suitable rearing habitat downstream. Low catches of sucker larvae in drift nets (zero in 1992 and two in 1993) supported this hypothesis (Fig. 6). We also experimentally entrained larvae in high mid-channel currents and tracked drift responses by snorkeling (Fig. 7).
Figure 6
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jpeg Drift netting for larvae
Figure 7
Our results suggest Warner sucker larvae minimized traveling downstream by exploiting available cover. We also recorded diel positions of larval groups and found that groups were positioned significantly closer to shore during nocturnal hours in 1993 than in 1992 where velocities were typically lowest. Other Catostomid larvae may have evolved drift resistance patterns such as these due to instability of downstream habitat.
To test this hypothesis, we collected information on larval drift of the twenty-five western Catostomids. In all cases in which aquatic habitat has been unreliable since the Pleistocene due to desiccation or salinity intrusion events, the four native species of Catostomids avoid drifting as larvae. Additional data on larval drift patterns of the other Catostomids for which information is not currently available will help identify the consistency of this relationship.
We also studied survivorship and distributions of sucker larvae in the same years and compared survivorship patterns in relation to food availability to other data published on Catostomid larvae to indirectly assess whether food may be limiting survival of Warner sucker larvae (Kennedy et al., in prep., Kennedy and Olsen 1994). Although environmental conditions were dissimilar, survivorship curves of Warner sucker larvae in lower Honey Creek for 1992 and 1993 were not significantly different and showed low recruitment to juvenile size classes both years (< 10% and < 3%, respectively). Drift was sampled with a 500 µm net at the water surface where larvae fed. Microhabitat observations showed larval groups inhabited stream locations with low water velocities, abundant submerged vegetation, and highest potential prey densities. However, computed potential food densities where Warner sucker larvae occurred were below rations required for sufficient survival in another related species, C. commersoni.
We propose starvation may be reducing population size of threatened Warner suckers in some areas. Current irrigation procedures for alfalfa production during summer months may conflict with survival of drift-feeding larvae in low-gradient stream sections of the Warner Valley. Reductions in microhabitat velocities occurred after boards were placed across a diversion weir in both years at the downstream end of the study area to impound water for irrigation use later in the summer. It is not known whether the other seven weirs further downstream are managed in the same manner, but this practice may reduce drifting prey availability by altering natural streamflow in Honey Creek. Water impoundment in low-gradient areas could be timed differently to avoid conflicting with drift-feeding larvae. This measure could help to improve recruitment success of Warner sucker progeny in similarly managed areas.
Coombs, C.I., C.E. Bond, and S.F. Drohan. 1979. Spawning and early life history of the Warner sucker (Catostomus warnerensis). Unpublished report to U.S. Fish & Wildlife Service, Sacramento.
Hubbs, C.L. and R.R. Miller. 1948. The zoological evidence: correlation between fish distribution and hydrographic history in the desert basins of western United States. Pp. 17-166. In: The Great Basin with emphasis on glacial and postglacial times. Bulletin of the University of Utah Vol. 30.
Kennedy, T.B., G.L. Vinyard, and T.F. Hart, Jr. In prep. Food limitation in larval Warner suckers (Catostomus warnerensis), Lake County, Oregon.
Kennedy, T.B. and G.L. Vinyard. Submitted. Drift ecology of western Catostomid larvae with emphasis on Warner suckers (Catostomus warnerensis). Environmental Biology of Fishes.
Kennedy, T.B. and M. Olsen. 1994. Drift ecology of Warner sucker larvae (Catostomus warnerensis) and lake recolonization by native and exotic fishes of the Warner Valley, Oregon. Oregon Natural Heritage Program, The Nature Conservancy.
Snyder, C.T., G. Hardman, and F.F. Zdenek. 1964. Pleistocene lakes of the Great Basin. U.S. Geological Survey Miscellaneous Geologic Investigations Map 1-416.
United States Fish and Wildlife Service. 1985. Endangered and threatened wildlife and plants; determination that the Warner sucker is a threatened species and designation of its critical habitat. Vol. 50, No. 188.
White, R.K., T. Hoitsma, M.A. Stern, and A.V. Munhall. 1990. Final report on investigations of the range and status of the Warner sucker, Catostomus warnerensis, during spring and summer 1990. Submitted to: U.S. Bureau of Land Management, Oregon Dept. of Fish and Wildlife, U.S. Fish and Wildlife Service.
Williams, J.E., J.E. Johnson, D.A. Hendrickson, S. Contreras-Balderas, J.D. Williams, M. Navarro-Mendoza, D.E. McAllister, and J.E. Deacon. 1989. Fishes of North America, endangered, threatened, or of special concern: 1989. Fisheries (Bethesda) 14(6): 2-20.
Tom Kennedy: U.S. Fish & Wildlife Service, Nevada State Office, 4600 Kietzke Lane, Bldg. C-125, Reno, NV 89502-5093
Threatened Fishes of the World, Warner sucker. Jack E. Williams
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