7226 - Laserfiche WebLink

Home Browse Search

~-. 800 700 H 600 Z W 5~ J J 400 H 300 Q zoo ~ ioo Northern pike I Largemouth bas j~ I ~-• 1 ~- .~ I ~' I Colorado squawfish ,' I ~ (River) 'I / '~`._ q Colorado s uawfish (Pond) Z ~ 4 5 6 7 8 9 10 11 YEAR OF LIFE FIGURE 2. Comparison of growth rate of Colorado squawfish from the upper Colorado River basin (Vanicek and Kramer 1969, Seethaler 1978) with these characters for northern pike and largemouth bass (vertical bars are the median 50 percent of the values provided for these latter species by Carlander 1969, 1977). Also shown is growth of Colorado squawfish in a pond near Grand Junction, Colorado (Osmundson, 1986). The dashed line on the curve for pond fish is projected growth. adjacent upper Colorado River, the short growing seasons provided by upper basin rivers were implicated as the cause of slow growth of Colorado squawfish therein. Growing season for Colorado squawfish doubtless was longer in downstream regions of former range, but how rapid growth there might have been is unknown because squawfish were extirpated from these areas before such life-history information could be collected. An understanding of the relative length of growing seasons provided by these former habitats can be obtained, however. Black and Bulkley (1985) studied the relation between temperature and growth of Colorado squawfish with excess food. Our least- squares analysis of their Table 1 data suggested no growth will occur below about 14 C. If we assume the growing season is when water temperatures exceed 14 C, that of the present-day upper basin Colorado River is less than five months whereas those of the historic middle and lower river were about six and eight months, respectively (Figure 3). Similarly, the Osmundson (1986) pond -110-