6012 - Laserfiche WebLink

Home Browse Search

• Limiting Factors Temperature - Natural spawning was observed in January 1980 at Dexter NFH at a temperature range of from about 10 to 15°C and eggs were observed on cleaned gravel areas O.b to 1.2 m in diameter. Douglas (1952) observed spawning razorbacks in Lake Havasu at 14 to 18°C. Razorbacks were observed spawning over gravel areas at 15°C and eggs and larvae were collected in Senator Wash Reservoir, Imperial County, California (Medel-Ulmer 1981). Hatching success of eggs spawned at Dexter was poor due primarily to the poor condition of the eggs as they came from the female. Incubation of eggs was at about 17°C. At these temperatures, on about the sixth day after hatching the larvae began to rise to the surface and start feeding. Toney ( ) found- they grew about I mm/day, reaching 60-70 mm TL 68 days after hatching. Growth of juveniles was highly variable in the hatchery; in their fifth year (1980) they ranged in size from 150 to 400 mm TL, i.e. the maximum growth rate was about 80 mm per year. Tests of razorback juveniles ( 300 mm) at Utah State University showed they preferred 23-24°C which is similar to those temperatures preferred by juvenile Colorado squawfish, humpback chub and YOY bonytail chub (Appendix). However, there was considerable variation between individual razorback preferences (12-29°C) but not unlike that observed for the other fishes tested. Slightly higher temperatures (+2-3°C) were selected in the nighttime periods. Swimming ability of .the razorbacks was tested at various tempera- tures. Overall, the razorback sucker was a poorer swimmer than the Colorado squawfish, humpback chub and bonytail chub. Temperature was not found to significantly (P=0.5) affect swimming times for the razorback, although Figure shows that at 20°C they could swim for approximately one hour at a velocity of 0.4 m/sec which is higher than those recorded at I2 or 26°C. The fish's unwillingness to swim in face of the current was a factor in making the data highly variable. This caused the differences between temperatures to be insignificant. McAda and Wydoski (1980) found three probable spawning sites in the Yampa River where the water velocity was 1 m/sec and the temperature ranged from 7 to 16°C. One fish implanted with an ultrasonic transmitter was observed spending most of its time in slower water (0.42 m/sec) venturing into faster water at times where contact was usually lost. Total Dissolved Solids - All life stages seem to fair well at TDS levels up to 750 mg 1, that of Willow Beach NFH water. No studies or other records are available by which to approximate the preferred or avoidance levels. Food - No young razorbacks were collected by our field teams and, therefore, no stomach analysis data was available. Other authors (Jonez and Summer 1954; Banks 1964; Vanicek 1967) reported finding algae, plant debris, ephemeropters, trichoptera, diptera and chironomid larvae in the stomachs of razorbacks.