other Yellowstone River Sites 



Walleye were found spawning at 14 sites in the mainstem of the 

 Yellowstone in addition to the area downstream from Intake 

 diversion dam in 1980. Most of these sites, all small compared to 

 the Intake spawning area, were located adjacent to gravel islands 

 or along gravel shores at the head or mouth of dry side channels. 

 The physical criteria (depth, substrate, and velocity) at these 

 sites were very similar to that at the Intake gravel bar and 

 probably played a role in the selection of these sites by walleye. 

 The velocities where eggs were collected ranged from 76 to 134 cm/s 

 with a mean of 95.2 cm/s (Table 18). Depths ranged from 61 to 91 

 cm and substrate was usually cobble or pebble with one site being 

 fine pebbles. Sites where spawning occurred were runs along the 

 source or mouth of dry side channels or along small gravel islands 

 (Figure 24) . 



Flows which would result in favorable spawning habitat on the 

 Intake gravel bar should also result in favorable spawning 

 conditions at these other spawning areas. Flows in 1980, when 

 these sites were discovered, were within the range determined 

 favorable for Intake. 



To maintain the integrity of the unique mainstem spawning 

 areas, channel maintenance flows are required during the high water 

 period. Islands and side channels are formed and maintained as a 

 result of a period of highwater or "flood flow" (Leopold et al. 

 1964, Martin 1977). Peterman (1979) suggested that this flood flow 

 is 52,000 cfs ad should occur at a frequency of twice every 3 



100 



