98 



FISHERY BULLETIN OF FISH AND WILDLIFE SERVICE 



I /oor' 



Figure 1. — Redd making. Female digging. 



Figure 2. — Typical currents in a redd. 



silt a short distance downstream. This material 

 spreads out in a flat semicircle at first; then, as the 

 digging upstream proceeds, it collects into a loose 

 pile called the tailspill. With more digging, the 

 redd assumes a long oval shape about twice the 

 length of the salmon and several inches deep. 

 The prespawning digging of the redd may go on 

 for as many as 5 days. 



At the beginning of the spawning stage, the nest 

 is ready for the eggs. All loose gravel and fine 

 material have been removed from the pot, or 

 center of the redd, whose shape is such that any 

 current in the bottom flows upstream (see fig. 2), 

 then upward and outward. Usually there remain 

 in the pot large stones too heavy for the fish to 

 move far, and the crevices between these rocks 

 provide excellent lodgment for the eggs. Males 



are constantly present now. The female alter- 

 nately digs at the redd and settles back into the 

 depression to release eggs. A male then moves 

 quickly alongside the resting female, as in figure 3, 

 curves his body against hers, and releases sperm 

 in a small milky cloud that settles briefly in the 

 bottom of the redd where the eggs are lodged. 

 The newly deposited eggs are thus surrounded by 

 sperm and eventually fertilized. Excess sperm is 

 carried slightly upstream along the bottom of the 

 redd and gradually carried away by the current. 

 During the spawning stage the redd increases 

 considerably in length and depth, and appears to 

 move upstream as a result of the continued digging 

 at the upstream wall and the filling in of the tail- 

 spill area. 



The postspawning stage begins after the female 



