CHARACTERISTICS OF SPAWNING NESTS OF COLUMBIA RIVER SALMON 



107 



without delay to the lake and live there at least a 

 year before migrating seaward. 



Blueback-salmon redds are perfect models of 

 the nests made by larger salmon of other species. 

 The extent of the redd and the size of the gravel 

 chosen are scaled down to the size of the blueback. 

 The number of redds measured, the average size, 

 and the gravel composition are shown in figure 

 56, circles K, L, M, and N. The gravel composi- 

 tion was 90 percent or more of medium and small 

 size, with the small gravel (about the size of a 

 golf ball) predominating. The stream-tjrpe blue- 

 back redd contained a small pot of larger stones 

 to receive the eggs, had a loose tailspill, and was 

 oval. The lake-type redd in the shallows near 

 shore in Osoyoos Lake (Okanogan River water- 

 shed) was larger and of irregular shape; because 

 there was no current, the female would dig all 

 around the edge of the nest. As there were rela- 

 tively few of the lake-type redds, none were 

 measured. 



REDD SIZE AND INTERREDD SPACE 



In general, for all species of salmon the size of 

 the redds varies in direct proportion to the size 

 of the salmon comprising the run, and in inverse 

 proportion to the size and cementation of the 

 gravel in the stream. The redds made in slow 

 water are larger and more circular in outline, but 

 as a rule are not as deep as those made in rapid 

 water where the hydraulic force helps move the 

 gravel. 



On crowded spawning gravels of riffles and 

 rapid runs, some chinook redds overlapped slightly 

 end-to-end because the long tailspill of one redd 

 would be disturbed by the female working 

 directly downstream from it. Only a few redds 

 overlapped laterally. As a matter of fact, few 

 redds of any species were made exactly side by 

 side, but occasionally the redds would form diag- 

 onal rows across the streams. For the most 

 part, the female chinook salmon was vigorously 

 averse to the presence of another female im- 

 mediately upstream from her nest, or one digging 

 directly at the side of her nest, until her own redd 

 was well under way. 



The natural tendency of the female salmon 

 to guard the privacy of the redd area made for 

 fairly regular spacing. The more or less sym- 

 metrical oval shape of most nests was an addi- 

 tional space factor. The salmon redds in a 



crowded stream area do not fit into each other 

 like the parts of a jigsaw puzzle, but have spaces 

 between them nearly as great as, or greater than, 

 the areas of the nests themselves. This interredd 

 space varies with the species and also with such 

 physical factors as population pressure, composi- 

 tion and gradient of stream bottom, and water 

 velocity. The ratio of interredd space to redd 

 size appeared to be less for chum salmon and 

 silver salmon than for the other species studied. 

 The contiguous and in some cases superimposed 

 construction of chum-salmon redds may have 

 been the result of overpopulation of the limited 

 spawning areas available in the streams examined. 

 Population pressure noticeably decreased the 

 interredd space of silver salmon in Beaver Creek 

 at the upper limit of spawning, where the stream 

 was wide enough for only one or two redds. 



In the Kalama River, the large rubble made 

 for smaller redds, but interredd spacing was 

 about the same as elsewhere — presumably because 

 the nest radius to be defended remained the same 

 for chinook salmon of a given size. In quiet-water 

 areas, both redd size and interredd spacing were 

 proportionately greater than the redd size and 

 interredd spacing in stretches of rapid water 

 where the stream bed had considerable gradient. 

 In rapid water, the spawning salmon were busier 

 with redd digging, so that fewer "dog-fights" 

 occurred. Their distribution on the spawning 

 gravels was more or less uniform, resembling the 

 typical spawning-stream population of moderate 

 riffles. 



In general it was noted for chinook salmon that, 

 wherever sufficient spawners were present to 

 utilize virtuaUy all the usable gravel, the interredd 

 space amounted to nearly three times the area 

 occupied by the redds. Thus, the total average 

 area necessary for a pair of spawning fish was 

 about four times the area of the average redd. For 

 other species, the space factor was somewhat less 

 than that for chinook salmon. It is believed, 

 however, that to arrive at a conservative figure 

 for the number of pairs of salmon that can satis- 

 factorily utilize a given area of gravel suitable 

 for spawning, the area should be divided by four 

 times the average size of the redds. Thus, a 

 pair of spawning summer or fall chinook salmon 

 would require approximately 24 square yards of 

 suitable gravel; spring chinook salmon, 16 square 

 yards; silver salmon, 14 square yards; chum 



