9560

• UCREFRP Catalog Number: 9560
• Author: Valdez, R. A.
• Title: A Generalized Interactive Model to Predict Floodplain Habitat Area Needed to Recover the Endangered Razorback Sucker in the Upper Colorado River Basin - Floodplain Model Version 5.1.
• USFW Year: 2004.
• USFW - Doc Type: Logan, UT.
• Copyright Material: NO

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Juan River subbasin.
3.2 Sex Ratio

A sex ratio of 3 males to 1 female is used in the recovery goals for razorback sucker, and
is believed to represent effective sex ratio for the species (Lentsch et al. 1998). The floodplain
model allows the user to input up to eight sex ratios, ranging from 1 to 8 males per female.
3.3 Length-Weight Relationship
A length-weight relationship for wild razorback sucker is not available in published
literature. A relationship for adult females was developed for use in this model from 44 fish
captured in the Upper Colorado River during 1979-81 (Valdez et al. 1982). These fish range in
size from 432 mm to 635 mm TL. This length-weight relationship for females is used in the
model to predict fish weight from specified lengths in order to compute number of eggs
deposited by all females in the population.
3.4 Fecundity
The relationship of female fish weight to fecundity was derived from documented egg
counts of wild specimens captured and examined (McAda and Wydoski 1983; Minckley 1983;
Marsh [unpublished]; Minckley et al. 1991), and from hatchery stripping operations (Hamman
1985). Two relationships were developed; total ova produced by fish of a given weight, and ova
produced per kilogram offish weight. The former relationship was used because it provided.a
better estimate from weight of females determined from a length-weight relationship.
From the relationship of fish weight to number of ova, it was detennined that female
razorback sucker at maturity, or 400 mm TL, weigh about 844 g and carry about 10,464 ova, or
about 7,370 ova/kg. Average weight for the summary of fish included in the relationship was
1,272 g with 63,645 total ova and 49,838 ova/kg. Maximum weight was 1,618 g with 142,686
total ova and 100,624 ova/kg.
3.5 Survival of Eggs and Larvae
Survival of eggs and larvae are user-specified input variables and can range from 0 to
100%. Data on survival of eggs and larvae are ~vailable from field observations in lake
environments (Bozek et al. 1984), hatching success under hatchery conditions and pond culture