reduction in the number of fish in the river, thereby decreasing fishinq 

 success of these birds. The eventual effect would be a reduction in the 

 populations of these species present on the river during migration and 

 possibly during the breeding season. 



If flow reductions during the summer result in stagnation of some back- 

 waters, it is possible that these areas could serve as brood-rearing and 

 feeding areas for ducks. Because the present scarcity of brood-rearing 

 habitat is thought to limit duck nesting on the river, this could result in 

 higher breeding duck populations along the river. 



Water withdrawals during the nesting season from late March through May 

 would probably reduce goose nesting success through increased nest predation. 

 Merrill and Bizeau (1972) stated that maintained releases of 16,000 cfs from 

 Palisades Dam on the Snake River prevented goose nest predation yet did not 

 produce nest flooding. High run-off periods on the Snake before dam 

 construction produced high nest losses due to flooding, such as now occur 

 under similar conditions on the Yellowstone. 



Water withdrawals which cause a decrease in available goldeneye food 

 species (bottom-dwelling invertebrates and algae) or in food supply would 

 cause a decrease in goldeneye populations. 



Alterations in channel morphology which result in a reduction in the 

 number of islands might lower the beaver (Castor canadensis) populations, 

 which are highest in the braided sections of the Yellowstone (Martin 1976). 

 In some areas, such as the Hysham-to-Bighorn section, geese frequently nest 

 in dense willow stands which have been thinned by beaver. If beaver populations 

 were to decline following flow alterations, the increased density of bushy 

 cover on some islands could discourage goose nesting on sites previously 

 uti 1 i zed 



Water withdrawals concentrated during the high sediment load period 

 from May through July could alter silt deposition patterns and result in 

 island stabilization in some areas. If open bars and small islands which 

 are currently open and deviod of vegetation become stabilized, these sites 

 would be less attractive to loafing waterfowl, resulting in a possible 

 reduction in the numbers of migrant waterfowl which stop in the lower Yellowstone 

 Valley. These open bars and islands also serve as territorial defense sites 

 for breeding ducks and geese, and loss of them could decrease those breeding 

 populations. Water withdrawals concentrated in late summer and early fall 

 could further dewater the river at a time when flows historically have been 

 low. The dewatered channel would provide extensive loafing areas for ducks 

 and geese and secure fishing sites for herons. These areas would be more 

 secure than those presently available due to the distance of the birds loafing 

 along the water's edge from the edge of the riparian vegetation. For herons, 

 the impact on the fish populations resulting from low flows in the fall and 

 winter would nullify the benefit of improved fishing sites. 



The increased acreage of agricultural land in the Yellowstone Valley 

 would probably attract more migrant field-feeding ducks and geese in spring 

 and fall. This would probably be more apparent in sections of the river which 



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