distances of 10 or more feet, it has 

 been established that waterfalls of 

 this height will quite effectively 

 block the upstream migration of 

 most salmon. Even a waterfall of 

 5 or 6 feet will stop the majority of 

 salmon unless water-flow conditions 

 are ideal. Fish ladders for salmon 

 at dams rarely require the fish to 

 leap a vertical distance of more than 

 2 feet, and most ladders are so ad- 

 justed as to permit the fish to swim, 

 rather than jump, a rise of about 

 1 foot. 



Upon arrival at the spawning 

 area the female deposits her eggs in 

 a nest, or redd, which she digs in 

 the gravel of the stream or, in some 

 instances, in shallow lake-shore wa- 

 ters. Burner (1951) describes the 

 characteristics of the redds, as well 

 as their preparation and the activi- 

 ties of the fish : 



During the prespawning state, the fe- 

 male salmon is green, that is, the eggs are 

 neither ripe nor loose in the ovaries. 

 Males are seldom in attendance, and are 

 frightened away by the female, who re- 

 pels all intruders of either sex. The fe- 

 male digs the redd as she turns on either 

 side, at an angle of about 45° to the cur- 

 rent, head upstream, body arched, and 

 makes a series of violent flexions with 

 body and tail. The tail strilies gravel oc- 

 casionally and the strong-boiling current 

 created carries gravel and 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 tail- 

 spill. With more digging, the redd as- 

 sumes 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 re- 

 moved from the pot, or center of the redd, 



the shape of which is such that any cur- 

 rent in the bottom flows upstream then 

 upward and outward. Usually there re- 

 main in the pot large stones too heavy 

 for the fish to move far, and the crevices 

 between these rocks provide excellent 

 lodgement for the eggs. Males are con- 

 stantly 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, 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 sur- 

 rounded by sperm and eventually fer- 

 tilized. Excess sperm is carried slightly 

 upstream along the bottom of the redd 

 and gradually carried away by the cur- 

 rent. During the spawning stage the redd 

 inci-eases 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 

 tailspill area. 



The postspawning stage begins after 

 the female finishes depositing her eggs. 

 Males are no longer attentive. The fe- 

 male is gaunt and spent, but she 

 continues to dig at the gravel with ever- 

 weakening efforts until she dies. This 

 postspawning digging, which may con- 

 tinue for 10 days, becomes shallow, off 

 center, and ineffective. The area of the 

 nest is increased without (after the first 

 day at least) adding to the protection 

 of the eggs. 



Each salmon female produces 

 from 2,000 to 5,000 eggs, the number 

 depending upon the s^^ecies and size 

 of the fish. The time required for 

 the eggs to hatch is regulated by the 

 temperature of the water. One 

 measure that was devised by Seth 

 Green for brook trout was 50 days 

 at 50° F., and plus or minus 5 days 

 for each degree less or greater than 

 this average. This formula can be 

 applied only as a general guide for 

 salmon. Newly hatched fish, called 



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