data by age and, inexplicably, males were not 100% 

 mature at any length (Fig. 3). 



Discussion 



The transplanted walleye population of the John 

 Day pool of the Columbia River grows at a rate ap- 

 proaching the highest previously reported (Fig. 4). 

 Concomitant with rapid growth these walleye are 

 very fecund (Ikble 3) and mature at an early age 

 (Fig. 3). We suggest that these life history charac- 

 teristics result from the combination of a favorable 

 temperature regimen and a nonlimiting food supply. 



High growth rates are generally found in walleye 

 populations of more southerly latitudes where higher 

 temperatures and longer growing seasons occur. 

 Figure 4 contains data from Norris Reservoir, TN 

 (Stroud 1949), Lake Gogebic, MI (Eschmeyer 1950), 

 Lac la Ronge, Saskatchewan (Rawson 1957); as well 

 as the composite high and low length-at-age values 

 reported by Colby et al. (1979). Relative to the 

 latitude of the John Day pool (lat. 45°55'N), Norris 

 Reservoir is south (lat. 36°15'N), Lac la Ronge is 

 north (lat. 55°07'N), and Lake Gogebic is at approx- 

 imately the same latitude (lat. 46°47'N). The mean 

 growing degree-days (GDD) above 5°C (GDD >5°C) 



1 2 3 4 5 6 7 8 ^^»?3t?»'^«^..<?3>3U'?D'5>-j 



Age 



Fork Length (Midpoint o( 50mm increments) 



Figure 3.— Percent mature walleye by age and length and by sex for 

 specimens collected in the John Day pool of the Columbia River, April- 

 September 1980-81. Curves were drawn by eye (Sample size in 

 parentheses.) 



800 

 700 



-g 600 



E 



£ 500 



c 



« 



-J 400 



a 



t- 300 

 200 

 100 



6 7 8 

 Age (Years) 



10 



11 



12 13 



Figure 4.— Comparison of length-at-age for walleye from the John Day 

 pool, Columbia River; Norris Reservoir, Tfennessee (Stroud 1949); Lake 

 Gogebic, Michigan (Eschmeyer 1950); Lac la Ronge, Saskatchewan 

 (Rawson 1957) and the composite high and low values reported by Colby 

 et al. (1979). Numbers in parentheses are the mean growing degree-days 

 above 5°C, John Day value is from Anonymous (1969), all others are from 

 Colby and Nepszy (1981). 



704 



