7157 - Laserfiche WebLink

Home Browse Search

2.1 The Southwestem Naturalist vol. 29, no. I TARU: I.-Number uf field wllectiulls. Upper Colorado River drainage (Colorado). 1979-81. Numbers ill parentheses represe71t tlumber of collections which contained one or more squawfish larvae. Culuradu Yampa Gunnison While TOIaI 1979 155(2) 33(0) 59(0) 247(2) 1980 114(1 I) 215(9) 46(0) 375(20) 1981 319(1) 519(11) 81(0) 94(0) 1013(12) Total 588(14) 734(20) 114(0) 199(0) 1635(34) Spawning dates were determined using calculated ages of field collected larvae. Larval age was estimated by comparison with data derived from Hamman's (1981) hatchery study. Hamman's hatchery SllK:k were progeny of parents collected from the Colorado River, and Yampa rivers, C.olorado and the Green River, Utah. Spawners were maintained at normal river water temperatures and. with the exception of one group which was injected with carp pituitary extrat't. spawned spontaneously. Hatchery water temperature varied belween raceways during hatching and larval growth and. in one instance. a temperature drop of 13-I40C was recorded. We determined larval growth rate (m) for time of hatching up to 45.0 mm TL from the slopes of linear regression analyses for three size increments i.e. 7.0- approximately 15.0 mm 1'1., > 15.0 - approximately 30.0 mm TL, and > 30.0 - approximately 45.0 mm TL. Growth rale varied (rom 0.35 (r = 0.93), 0.36 (r = 0.99), to 0.40 mm/day post-hatching (r = 0.99), respectively. In those cases where the smallest and/or largest individual in a field sample were collected on more Ihan one dale of a sampling trip. the earliest date was used fOf the purpose of determining lhe earliest possible spawning date. The calculated ages permitted a projeclion of both the earliest and latest spawning dates both for a given collection period and the year as a whole. The following equations were derived to estimate the range of larval ages in a collection: A. [(Lmi. - HSmu) + m] + HT mi. = larval age (days) B. [(L.... - HSm..) + m] + HT.... = larval age (days) where: Lmi. = total length (mm) of lhe smallest individual ina colleclion Lmu = lotallenglh (mm) of the longest individual in a collection HS.... = maximum hatching size (7.5 mm totallenglh) (Hamman. 1981) HSmi. = minimum hatching size (6.0 mm totallenglh) (Hamman. 1981) HT.... = maximum hatching time (6.0 days) (Hamman. 1981) HT mi. = minimum hatching time (3.75 days) (Hamman. 1981) m= growlh rate (0.35. 0.36, 0.40 mm/day) RESULTS.-A total of 1,635 larval fish collections were made in the Colorado portion of the upper Colorado River basin in 1979-1981. The rarity of Colorado squawfish larvae is reflected by the fact that they occurred in only 2.6% (34 of 1,322) of collections made in the mainstem Colorado and Yampa rivers (Table I). No squawfish larvae were captured in 313 collections in the Gunnison and White Rivers. Number per collection ranged from 46 in one Colorado River sample (km 243.9, 13 Aug 1980) to a single individual in 12 samples in both rivers combined (Tables 2 and 3). Mean number per kilometer varied from 0.09, 0.87 to 0.01 (1979- 1981) in the Colorado River, and 0.24 to 0.18 (1980 and 1981) in the Yampa River. Squawfish larvae were typically found in relatively low-velocity (:50.3 m/sec) shallow (0.06-0.3 m) shoreline concavities. Water temperatures at time of collection ranged (rom 190C (July, 1980) to 260C (August, 1981). In the Colorado River, squawfish larvae were collected in a stretch from km 245.7, near Lorna (Mesa County). to km 212.2 in the vicinity of the Colorado-Utah State line (Table 2). The largest single collection (46