7152

• UCREFRP Catalog Number: 7152
• Author: Holden, P. B.
• Title: Relationship between Flows in the Yampa River and Success of Rare Fish Populations in the Green River System.
• USFW Year: 1980.
• USFW - Doc Type: Logan, Utah.
• Copyright Material: NO

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using numbers of fish caught as an index to successful reproduction,
is supported by Vanicek (1967), as well as by Holden (1973), Holden
(1977), Holden and Crist (1978), and Holden and Selby (1979). These
studies show that strong year classes, as indicated by the location
of many young-of-the-year, can be followed and that the cohort re-
mains strong in future years. collections. Likewise, poor years are
reflected later by low catches of juveniles.
Care must be used in direct interpretation of numbers of young
fish indicating reproductive success unless effort expended, and type
of sampling, is known. Sampling with inadequate equipment, or in the
wrong habitats, can result in capture of low numbers of young squaw-
fish in river sections where they are fairly common. Squawfish juve-
niles prefer certain habitats, and are most abundant in these types
of habitat (Holden 1977). Therefore, sampling a rather short reach
of river may produce very small numbers because few preferred habitats
exist in that reach. Therefore, it is impractical to utilize numbers
of fish caught as a direct index of reproductive success. Rather, it
is more reasonable to consider two levels of success, good and poor.
Good success is defined as years where squawfish young-of-the-year
were found fairly commonly for the effort expended, and/or when a
cohort (year class) is commonly found at Ages I, II, or III. Poor
success is defined as year classes when few young or juveniles are
found even though sufficient effort is expended. The major method of
determining when an age group is "common" or when "few" fish are
caught is to compare years of known effort. Therefore, in the tables