8159

• UCREFRP Catalog Number: 8159
• Author: Trammell, M. and T. Chart.
• Title: Aspinall Studies
• USFW Year: 1999.
• USFW - Doc Type: Annual Assessment of Colorado Pikeminnow Larval Production in the Colorado River, Utah 1992-1996 \
• Copyright Material: NO

Table 7. Pearson's correlations between larval abundance and fall catch rates of Colorado
pikeminnow (CPM) from Interagency Standardized Monitoring Program (ISMP) and
Nursery Habitat (NH).
Fall catch rates of Pearson's correlations
age 0 CPM rz coefficient, and probabilityp
Yeaz ISMP NH ~ . ISMP #/100 NH
#/100 m2 #1100 mZ P . m2 #/100 m2
1992 3.96 3.77 WW +0.18 +0.22
(#/1000 m') 0.77 0.72
1993 4.88 2.44 WW +0.25 +0.33
~sh/hour 0.68 0.59
1994 4.33 0.38 MO +0.12 +0.09
(#/1000 m') 0.85 0.89
1995 2.9 0.21 MO +0.57 +0.52
#fish/hour 0.31 0.36
1996 20.8 14.27 NH +0.97
#/ 100 mZ 0.005
The relationships between larval abundance and juvenile abundance were compared
between the larval drift sampling sites and ISMP Reach 2 and the nursery habitat reaches (Table
7). The Pearson's correlation coefficients were low, and not significant, because the relationship
was skewed by the 1995 results (Figure 12). In most years larval abundance was fairly indicative
of juvenile abundance, but in 1995 juvenile abundance was low despite high larval densities.
When 1995 was removed from the regression for Moab catch rates, the correlation improved
considerably, to rz = 0.92.
The most interesting case in this five year study was in 1995. Although 1995 had good
larval production levels (Moab fish/hour catch rate was 2"~ highest), it also had the lowest catch
rates of juveniles in the two fall sampling studies. The pikeminnow were estimated to have
spawned relatively late (July 11 to August 22) and therefore would have had the fewest number
of days between average hatch date and fall collections in early October (estimated to be 50
days). Thus, the loss of that cohort occurred in a relatively short time frame.
Many factors other than Iarva1 production may influence year class strength, such as
summer and fall flows, water temperatures, habitat availability and presence of competitive and
predacious fish species. In 1995, several of these factors could have negatively affected the
abundance of juveniles in the fall. In 1995, the average August and September flows were higher
than the other years of the study. Trammell and Chart (1998) showed that high peak and summer
flows resulted in a reduction in available nursery habitat in 1995. This suggests increased
potential for drifting larvae to be transported past the nursery habitat areas because sufficient
habitat to retain the fish had not developed.
The length and quality of the growing season for age 0 Colorado pikeminnow is a
function of the timing of reproduction coupled with the water temperatures. Total lengths of
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