SALMON AND TROUT IN ALASKA. 99 



The coho, perhaps in its effort to reach low temperatures, frequently 

 continues up the small streams to a point where the bottom material 

 is coarse. In Steelhead Creek it passes humpbacks and dogs on the 

 gravelly lower part of the stream and spawns in the rough upper por- 

 tions. In all the small Alaskan streams it doubtless occupies the 

 sockeye beds later in the season and perhaps does some damage, but 

 the greater part of the run spawns below those beds and in creeks not 

 entered by the sockeyes. Cohos, like the smaller species, while mak- 

 ing their way upstream or when frightened out of the "nest," may 

 frequently be seen in water too shallow to cover them. Whether these 

 "nests" are excavated in shallows where the original depth is less than 

 that of the fish, or whether the small amount of water is not more 

 usually due to a fall in the stream subsequent to the fish's entr}^, has 

 not been fully ascertained. 



Humpback and dog salmon may often be seen spawning on the 

 same beds, but in general the former is more frequently seen on finer 

 bottoms and in shallower water, while the more powerful dog salmon 

 sometimes occupies bottoms of coarse gravel in some depth of water. 

 The humpback is said sometimes to fail to get beyond the reach of 

 high tide in the selection of its spawning place. 



DEPOSIT OF EGGS. 



The deposit of spa-svTi on riffies and in small streams, where it is most 

 subject to the action of floods and frost, at first sight seems to be poor 

 economy. But the necessities are twofold, first, aeration, and second, 

 protection from light and enemies. In water of much depth relative 

 to volume the bottom current is retarded, with the result that fine 

 sediment is deposited and th? circulation through the gravel or other 

 material is impeded if not entirely cut off. If the eggs were placed in 

 such a region of little current, they would not be carried from under 

 the mother fish and the material for covering and protecting them 

 would not be carried down over them, hence any such movement as 

 the spawning fish now makes would only lead to stirring up eggs and 

 gravel, with the result of destroying the first spa^vn within a few days 

 after its deposit. For this reason the lake spawning of the sockeye 

 must be of less proportionate value. 



The action of the spawning fish in breaking away the gravel by means 

 of forcing the body and tail against it achieves the double purpose of 

 working the sex product down to the genital opening and of setting 

 the fine gravel and sand in motion to cover the eggs. When first 

 extruded the contents of the egg envelope do not quite fill it, the egg 

 is soft and will bear considerable rough handling. Its specific gravity, 

 only slightly greater than the water, holds it to the bottom, but allows 

 it readily to drift along with the current. Upon finding an early lodg- 

 ment the osmotic absorption of water "freezes" it to the object 

 against which it rests, and any drifting particles of sand not heavy 



