3135 - Laserfiche WebLink

Home Browse Search

29 were taken from Morrow Point Reservoir in routine gillnetting during 1971, and losses of small salmon through the Blue Mesa turbines were also found in 1973. To determine if significant losses of these fish were occurring, marked-fish studies were instigated. One disadvantage of the fluorescent markings is that the marks cannot be seen, unless fluoresced under black light (3600A). Because of this, some rainbow were finclipped so fish could be detected easily in the field. Wiltzius (1971) described the technique and methods used to mark rainbow trout with fluoescent pigment in 1967-1971 at Blue Mesa Reser- voir. Rainbows from the 1971 markings showed less retention than those in previous years, so when the markings for the present study were initiated in 1974 considerable testing of equipment, pressures, distance above fish, etc. was done in an attempt to improve this marking technique. It was found that the pressure delivered in the 1971 marking was inade- quate for proper retention of granules. Subsequently, a system was developed and described by Wiltzius and Smith (1976) which was believed could result in extremely high percentages of permanently fluorescent- marked rainbow trout. Recent findings by Mueller (1977) in Wyoming in- dicate that 82 percent of a fluorescent-marked rainbow lot retained pigment for 42 mo. Our working system uses greater pressures and pigment appli- cation, which should result in higher percentages than the Wyoming study. Our new system was used to mark all of the scheduled rainbow fingerlings stocked from Hotchkiss National Fish Hatchery into Blue Mesa Reservoir during 1974-1976 and in Silverjack Reservoir in 1974. Sampling of the rainbow trout harvest from Blue Mesa Reservoir in 1975-1977, using 30 watt ultraviolet lamps in a darkened area at the boat ramps, was used to determine percent retention of the marked groups. In general,