Laserfiche WebLink
Survival of Trout Planted in the Tailwater <br />Harvest, use, and yield reached record levels in 1981, 3 years after <br />the penstock modification became operational. The record yield of <br />111 kg/ha (99 lb/ac) in 1981 was not sustainable, and angler use and <br />success rates fell in subsequent years. The outstanding success <br />experienced by anglers in 1981 was due to the combination of warmer water <br />temperatures, which stimulated the tailwater's productivity, and <br />exceptional survival of trout fingerlings planted in 1980, an estimated <br />30% of which were harvested during 1981. No other stocking of fingerling <br />trout during the 1978-1982 study period produced second year creel <br />returns of more than 8.2%, and even the 1980 stockings contributed <br />significantly for only two years. <br />The successful fingerling stockings of 1980 were introduced earlier <br />and at larger mean TL than any other cohorts; thus, by winter 1981 many <br />of these fish may have recruited to the adult (larger than 250 mm) life <br />stage. Trout that were larger than 300 mm when tagged prior to the <br />winter of 1982 experienced much higher angler tag returns the next summer <br />than those less than 300 mm TL. Sampling in Dinosaur National Monument, <br />Colorado, downstream of the study area, demonstrated that some trout <br />emigrated downstream from the tailwater during winter to habitats that <br />were marginal for trout. The emigration appeared to be largely confined <br />to juvenile trout. Creel statistics for stocked fingerlings suggested <br />that winter natural mortality of juvenile trout ranged near 90% in most <br />years. Natural mortality of adult trout, based upon angler catch curves, <br />appeared to be much lower than that of juveniles. <br />Instability of the sportfishery and disappointing survival rates of <br />stocked fingerlings were the result of the interactions of factors <br />-3-