Figure l. — Columbia River drainage. 



creased significantly. From 1973 through 1978 

 fewer than 15 juvenile walleye were taken per year, 

 whereas in 1979, several hundred were taken with 

 similar fishing effort. Early in the season, an exact 

 count was not possible because many of the small 

 fish (<40 mm TL) fell through the mesh of the net 

 [12.7 mm (V2 in) stretched measure]. In 1979, 

 young-of-the-year walleye was first taken in the 

 gatewells in July and continued to be taken until 

 sampling was suspended in mid-December. 



Walleye normally spawns at water tempera- 

 tures between 5.6° and 11.1° C (Scott and 

 Grossman 1973). Hatching occurs in 21 d at water 

 temperatures of 10°-12.8° C (Niemuth et al. 1972). 

 Water temperatures at John Day Dam rose from 

 6.2° to 13.8° C during April and May 1979. At these 

 temperatures one would expect hatching to extend 

 through May, producing fry in the 40 mm class by 

 early July. 



Water temperatures in John Day Reservoir dur- 

 ing the summer were near optimum for excellent 

 growth of juvenile walleye. Huh et al. (1976) re- 

 ported the growth of young-of-the-year walleye to 

 be temperature dependent, with optimum growth 



occurring at 22° C. Water temperatures in John 

 Day Reservoir fluctuated between 19° and 21° C for 

 a 10- wk period extending from early July through 

 September. 



Total length of juvenile walleye increased an 

 average of 11 mm/wk from July to October (Figure 

 2). This compares very favorably to the 13 mm/wk 

 reported by Wolfert (1977) for walleye in Lake 

 Erie. Mean length of young-of-the-year walleye in 

 John Day Reservoir at the end of the 1979 growing 

 season was 226 mm. Average weight by this time 

 was 87.4 g (0.19 lb). Total length at the end of the 

 growing season was only slightly less than re- 

 ported for walleye in Lake Erie (Wolfert 1977) and 

 considerably greater than lengths reported in 

 Lake Gogebic, Mich. (Eschmeyer 1950); Red Lake, 

 Minn. (Smith and Pycha 1960); and Oneida Lake, 

 N.Y. (Forney 1966). Growth of young-of-the-year 

 walleye in John Day Reservoir slowed steadily in 

 November with declining water temperatures. 



The presence of a larger number of walleye in 

 the gatewell samples during 1979 indicates that 

 the abundance of juvenile walleye appears to be 

 increasing. The potential impact on salmonid 



568 



