1977, Johnson 1961) and that egg survival over a silt or sand 

 bottom was poor (Priegel 1970, Johnson 1961) . 



The percent of eggs collected in water 76 cm or deeper on the 

 Intake gravel bar during 1977, 1978, and 1979 varied inversely with 

 river discharge during peak spawning. This discharge was 7,800, 

 9,000, and 13,000 cfs for the 3 respective years. Seventy-one, 

 48, and 30 percent of all eggs sampled during 1977, 1978, and 1979, 

 respectively, were collected at depths of 76 cm or more. During 

 1977 the minimum velocity where eggs would be expected to occur, 72 

 cm/s (90% confidence level) was 60% higher than the two subsequent 

 years which had higher flows during April. Apparently more walleye 

 (sauger) were spawning in deeper, swifter sites in 1977, a year of 

 low flow. 

 Predicted Preferred Spawning Flows 



A water surface profile program was used to predict hydraulic 

 parameters at the four Intake egg transects (Graham et al. 1979). 

 These hydraulic parameters were used to predict the amount of top 

 width (almost identical to wetted perimeter) present at various 

 flows which met spawning criteria at each cross-section. The 

 criteria used for 1977 were a mean water velocity between 70 and 96 

 cm/s, a depth not less than 46 cm, and a cobble or pebble 

 substrate. The criteria used for 1978 and 1979 included: a mean 

 water velocity of 42-96 cm/s, a depth not less than 30 cm, and a 

 cobble or pebble substrate. 



Because of wider velocity and depth intervals, the total top 

 width available for Stizostedion sp. spawning was greater for the 



89 



