8022

• UCREFRP Catalog Number: 8022
• Author: Muth, R. T., et al.
• Title: Reproduction and Early Life History of Razorback Sucker in the Green River, Utah and Colorado, 1992-1996.
• USFW Year: 1998.
• USFW - Doc Type: 34,
• Copyright Material: NO

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laboratory study to validate patterns of increment deposition in otoliths of captive larval
razorback suckers reared under fluctuating water temperatures demonstrated that ages of wild
larvae could be accurately estimated (K. Bestgen, Larval Fish Laboratory, personal
communication). All specimens collected in 1995 and all remaining in 1993 samples after
selected specimens had been removed for mitochondrial DNA analysis were analyzed.
Subsampling of individuals was necessary for 1994 and 1996 collections because of the large
numbers of specimens available for otolith aging.
The number of fish in each subsample per collection was determined from results of a
computer simulation subsampling routine performed on a frequency distribution of ages of
razorback sucker larvae in a large sample (N = 56) collected on 30 May 1994 from the middle
Green River. All larvae in that sample were aged, and individuals were allocated to a categorical
frequency distribution of ages that ranged from 8 to 20 d; the median age (13 d) and standard
deviation (2.57) were assumed to be representative of other large collections. To determine how
many larvae were required in subsamples to achieve that standard deviation, subsamples of 10,
15,20, or 30 individuals were randomly drawn, with replacement 1,000 times each, from the
frequency distribution and the average standard deviation was calculated for each subsample
size. Average standard deviations for sub samples with 20 or 30 individuals were 2.52 or 2.79,
respectively. Accordingly, for all other 1994 and 1996 samples, subsample sizes were set at 25
individuals for collections with more than 100 razorback sucker larvae and 25% of the total
number of razorback sucker larvae in samples with 100 or fewer individuals. Randomization
was accomplished by assigning each larva in a sample an unique number from 1 to N and using a
random number table to select individuals.
For aging, otoliths were removed from specimens and mounted on numbered glass slides
in either immersion oil (left lapillus and sagitta from larvae 13 mm TL or smaller) or
thermoplastic cement (left lapillus from larvae 14 mm TL or larger); sagittae in larger larvae
were elongated and difficult to age. The maximum diameter of each otolith was measured at
1000X magnification under a compound microscope fitted with a calibrated ocular micrometer.
Otoliths mounted in immersion oil were aged without further preparation, whereas otoliths
mounted in thermoplastic cement were ground on one side with wet-dry sandpaper and lapping

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