408 
BULLETIN OF THE BUEEAU OF FISHERIES 
in time, a fairly reliable determination of the correlation existing between the size 
of the escapement — that is, breeding population — and the number of the resulting 
progeny. On a 'priori grounds, however, it could be anticipated that this correlation 
would not be perfect, since there are various environmental factors which doubtless 
affect the rate of mortality throughout the life of the salmon from the time the eggs 
are laid until sexual maturity is reached and the fish return from the sea to spawn. 
A few clear cut cases are known in which enviromental conditions have destroyed 
the effect of large spawning escapements. Of the various factors which may affect 
survival in the ocean we know, at present, very little, but it seems rather probable 
that conditions in the sea are much more constant than in fresh water. Certainly 
such factors as the water conditions at the time of spawning and during 4he incuba- 
tion period, the abundance of enemies and competitors, and the abundance of natural 
food organisms in the lakes bear directly upon the ultimate success of breeding. 
The Karluk watershed, which is situated in the western part of Kodiak Island, 
is occupied by the Karluk River, Karluk Lake, Thumb Lake, O’Malley Lake, and a 
considerable number of tributary streams of various sizes and which together con- 
stitute very important breeding grounds for the red salmon. The spawning escape- 
ments since 1921 have varied from about four hundred thousand to approximately 
two and a half millions. Gilbert and Rich (1927) estimated that well over 1,000 
million red salmon eggs were deposited in the lakes and streams of this watershed 
during the spawning season of 1926. 
The young red salmon derived from the eggs deposited in this watershed spend 
some time in Karluk Lake, where they are almost exclusively plankton feeders; they 
migrate to the sea in the spring of their second to fourth year. The great majority 
of them leave the lake in the spring of their third year. By far the larger number of 
them mature in their fifth year and return to spawn at that time, so they spend ap- 
proximately half of their lives in the lake and half in the sea. The lake, therefore, 
plays a very important role as a nursery for the young red salmon, and this fact has 
led to a general assessment of its physical, chemical, and biological status. The 
Karluk system is of special interest in this connection since it is generally recognized 
that, for its size and the area of its suitable spawning grounds, it is unusually pro- 
ductive. It has maintained a large run over a long period of intense exploitation — 
a run that is still considered one of the best of the whole of Alaska outside of Bristol 
Bay where there are numerous streams and lakes all of which are much larger than 
those of the Karluk system. Those engaged in the salmon investigations at Karluk 
have spent some time each year on the spawning grounds making such studies of the 
conditions as were possible in such an isolated locality and with the limited time 
available. Particular attention has been paid to conditions on the spawning beds, 
but the obvious importance of a knowledge of conditions in the lakes led to the col- 
lection of the data which form the basis of this report. 
PHYSICAL AND CHEMICAL DATA 
LOCATION AND PHYSICAL FEATURES OF LAKE 
Karluk Lake lies in latitude 57° 24 ' N. and longitude 154° 5' W. The lake is 
long, narrow, and straight sided, with a prominent bay, the Thumb, situated about 
the middle of the east side. (See fig. 1.) Three small islands help to separate the 
Thumb from the main part of the lake. The main axis of the lake lies in a general 
north and south direction and its maximum length is 19.6 kilometers (12.2 miles); 
