8003

• UCREFRP Catalog Number: 8003
• Author: Haynes, C. M. and R. T. Muth.
• Title: Identification of Habitat Requirements and Limiting Factors for Colorado Squawfish and Humpback Chubs ‎(January 1, 1981 to June 30, 1982)‎.
• USFW Year: 1982.
• USFW - Doc Type: SE-3-4,
• Copyright Material: NO

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were excluded during the random site selection but which-were sampled
due to the wide variety of habitat types available. "Special" sections
(e. g., Black Rocks) were relatively short river reaches which were
exhaustively sampled due to the enormous variety of habitat features
available at these localities.
Catch-per-unit-effort was defined as number per species per unit area (m 2).
Area was determined utilizing sein dimensions and length and width of the
individual sein haul. Substrate composition was determined for each
sample (Appendix A). Fish specimens were identified and assigned to 10 mm
total length (TL) size increments. Larval forms which could not be
identified in the field were preserved in 10% formalin and returned to
the laboratory.
Beginning in May (1982), ichthyoplankton nets were employed in the Black
Rocks area (Colorado River) to evaluate larval drift. Nets were approximately
4 m in length with a rectangular opening of 1.5 square meters. Mesh size
was 560 U. Analyses of these samples will be initiated during fall-winter,
1982.
Estimates of spawning periods were made using length-frequency information
(i.e. number x 10 mm size group) in addition to indications of adult
ripeness (i.e. color, tuberculation, gravidness). In addition, squawfish
spawning date estimates were determined utilizing calculated ages based
upon data derived from Hamman's (1981) hatchery study. Larval growth rate
(m) was determined for time of hatching up to 45.0 mm TL from the slopes
of linear regression analysis for three size increments (i.e. 7.0 - ±15.0 mm
TL, > 15.0 - ±30 mm TL, and > 30.0 - ± 45.0 mm TL). Growth rate varied
from 0.35 (r = 0.93), 0.36 (r = 0.99) to 0.40 mm/day post-hatching (r = 0.99),
respectively. The ages derived from the following equations permitted
a projection of both the earliest and latest spawning dates for both a
given collection period and the year as a whole.
A' [(Lorin - HSmax) ~ m] + HTmin = larval age (days)
B. C(L~x - HSmin) ~ mJ + HTmax = larval age (days)
Where: Lorin = total length (mm) of smallest individual in a collection
1'max = total length (mm) of largest individual in a collection
HSmax = maximum hatching size (7.5 mm TL) (Hamman, 1981)
HSmin = minimum hatching size (6.0 mm TL) (Hamman, 1981)
HTmax = maximum hatching time (6.0 days) (Hamman, 1981)
HTmin = minimum hatching time (3.75 days) (Hamman, 1981)
m = growth rate (0.35, 0.36, 0.40 mm/day)
Colorado Sq_uawfish. Larval Colorado squawfish were identified utilizing