8117 - Laserfiche WebLink

Home Browse Search

Razorback sucker Spawning of razorback sucker, like Colorado squawfish and humpback chub is associated with changes in the hydrograph. Razorback sucker spawn on the ascending limb of the hydrograph (Figure 7, from Tyus and Karp 1989). As with the Colorado squawfish, razorback sucker are known to use n'llo primary spawning areas, one on the Green River near RM 311 and the other in the Yampa River just above the confluence with the Green River. Individuals have been observed to move as far as 100 river miles to a specific spawning site (Tyus and Karp 1990, and Modde et al. in preparation). Movement to the spawning bar appeared more related to discharge rate than temperature (Figure 8). As with Colorado squawfish, the pattern of the hydrograph rather than absolute flows tend to initiate movement to spawning locations. However, in 1995 fish implanted with radio transmitters were observed to move to the spawning locations in late April, but, larvae were not collected downstream until June when water" temperatures exceeded 140 C (Fish and Wildlife Service unpublished data). Thus, although adults seem to be attracted to the spawning sites by discharge, spawning may not occur until temperatures reach approximately 140 C (Tyus and Karp 1990). In general, the spawning requirements of all three listed species, known to reproduce it the Yampa River is determined by the combination of flows and temperature, both of which are related. The spawning activities of these fish were influenced more by the pattern of flow: Le. rise or drop in the hydrograph, in any given year than a specific magnitude of flow. Each species migrates and spawns at a different stage of the hydrograph (Figure 9). Therefore, the occurrence of a natural hydrograph is an important feature to the reproductive success of endangered fishes and represents a rationale as to why the largest natural populations of Colorado squawfish (Tyus 1991) and razorback sucker (Lanigan and Tyus 1989, Modde et al. accepted for publication) occur in waters influenced by the Yampa River hydrograph. It appears that temperature and the shape of the hydrograph have a greater influence on behavior relating to the initiation of spawning activity than the magnitude of the hydrograph. However, it is the magnitude of the flows which influence the geomorphology of the river and effect habitat availability. Thus, although fish appear to cue to specific patterns of the hydrograph, the magnitude of the hydrograph is responsible for creating available spawning, nursery and adult habitat. Association of Nonnative Fishes with Native Fishes Native fishes were reported to be more abundant than nonnative fishes in the canyon reaches of the Yampa River than in either the upper (RM > 54 or lower reaches (RM < 1.8) (Figure 10. Appendix 2). Among all Yampa Canyon (RM 1.8 to 14