Fishery bulletin of the Fish and Wildlife Service - NOAA

FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 267
in the water of the same streams, on the same dates, above the area where spawning
and spawned-out salmon were found. Furthermore, a part of the salmon spawn
along the beaches of the lake and eventually die, and the carcasses, together with the
carcasses which drift downstream into the lake from the tributaries, decompose and
the phosphorus contained therein becomes available to the phytoplankton. A
shortage of phosphorus in the lake water would inhibit the growth of all forms of
phytoplankton.
It is apparent from a study of the chemical analyses of the lake water and of the
stream waters that both phosphorus and silica are being absorbed, during the summer
months, by the phytoplankton as fast as they become available, for otherwise
the concentration of these chemicals in the lake water would approach that found in
the streams. Since the concentration of these chemicals in the lake water during
most of the summer was less than a measurable amount, it is evident that they must
be limiting factors in the production of the phytoplankton and may possibly be
affecting indirectly the growth and survival of the red salmon Engerlings of Karluk
Lake.
CHANGE IN AGE COMPOSITION OF THE POPULATION
The percentage occurrence of the various age groups in the population, as determined
from a study of the scale samples (tables 3 to 16), appears to be changing
from year to year. However, a direct comparison of one year's data with another
cannot truly represent the change, if any, since a given year's run is composed of
the progeny from the escapements of several years.
To determine whether or not a change has been taking place in the age composition
of the population, it is necessary to compare the age composition of the escapements
with the age composition of the fish returning from the respective escapements.
The age compositions of the escapements for a series of years are presented in table
18, and the age compositions of the returns from the escapements appear in table 25.
The percentage of 58 fish in the escapements for the years 1922 and 1924 to 1929,
inclusive, was 59.3, 76.0, 66.8, 81.1, 70.8, 56.9, and 34.8 while the percentage of 53
fish in the returns from these escapements was 50.0, 49.3, 41.2, 52.5, 45.2, 39.5 a,nd
42.0, respectively. There was a lower percentage of 58 fish in the return than there
was in the escapement for every year with the exception of 1929. A similar condition
is found to exist if the returns from the spring and fall escapements are considered
separately.
The pairs of percentages for the 64 age group for the years 1922 and 1924 to 1929,
inclusive, are as follows (the first figure being the percentage of the 64 group in the
escapement for a given year and the second figure being the percentage of the 64
group in the return from the escapement): á.0:11.3; 10.5:22.8; 15.8:39.3; 7.6:33.2;
6.Í : 29.4; 9.0:20.3; 35.1:27.7. In all years except 1929 there was a greater percentage
of the 64 group present in the return from the escapements than there was in the
escapements.
In considering these two major age groups there appears to be a decrease in the
relative abundance of one, and an increase in the relative abundance of the other.
It thus becomes of interest to determine if a change is taking place in the length of
ocean residence and in the length of fresh-water residence of these fish.