24 DEPARTMENT OF THE NAVAL SERVICE 
7 GEORGE V, A. 1917 
It will be seen from the tables that during the three months, December, January 
and February, the average temperatures differ little, but are lower than during the 
other months, while the greater portion of the retardation of growth takes place during 
January, February, and March. November, during which there was no evidence of 
check except during the last few days, was colder, on the average, than March, and 
had a lower minimum. October was almost as warm as April, and yet retardation is 
evident on occasion almost to the end of April. There are only 4-1 degrees of differ- 
ence between the average of October and January, and only 2 degrees between the 
average for November and January. There may be that much difference between the 
temperature at the surface and at a depth of 5 fathoms (in table II there is a difference 
of 3-6 degrees shown thus for September 9), and 5 fathoms would certainly not be too 
great depth for a salmon to reach. Doubtless there is a maximum, an optimum and a 
minimum temperature for growth, but it is scarcely probable that if the optimum is 
reached at 13 or 14 degrees, 7 degrees would be at or near the minimum, and it it were, 
8-6 degrees, the average for March, should be far enough away from that minimum to 
show a definite increase of growth instead of showing a continuation of the minimum. 
Tf the check is due to the lowering temperature, one would naturally expect that 
the change should take place in all of the fish of the same species in the same region at 
or near the same time, and yet some have close rings beginning on November 27, 
while others have little or no sign of them on January 5; some have got over the check 
on March 17, while others retain it on April 22. Between these dates in the two cases 
there is a period of time equal to almost half of the time during which all show retarda- 
tion. Again, if the check is due to the lowering temperature, all in the same vicinity 
should have checks of nearly the same width, but instead there is a great variation from 
one or two rings to six or seven. The variation occurs in the individuals in one year 
class as much as in any of the others, and after the first year is over the individuals 
that migrate as fry are affected in the same way as those that migrate as yearlings. 
Nothing shows better the entire lack of relation between rate of growth and tem- 
perature than the graphs for each for the entire year. In making a graph for the 
growth rate, the average percentage of the total growth for the year was taken for 
each half-month. As the new growth for the year starts about April 1, that is taken fox 
the basis of calculation. In the graph for water temperature (surface) the average 
for each half-month was taken also. The graph showing the percentage of the year’s 
growth completed during each half-month is also given. 
The curves for growth rate and temperature are so unlike that they are scarcely 
comparable. The greatest growth rate is in. May, the highest temperature in August, 
by which time the growth rate has become materially reduced. The growth curve has 
a sharp ascent from the first of April until the middle of May and a very gradual 
descent for the rest of the year; the temperature curve has a gradual ascent from 
January until August and a gradual descent for the rest of the year. Half of the 
total growth, for the year takes place during April, May and June, before the tempera- 
ture has nearly reached its greatest height. During the next two and a half months 
another quarter is added, leaving but a quarter for the next six and a half months, but 
by the middle of September the temperature has decreased very little. 
It may be remarked here that there is no indication of a total cessation of growth 
during January, February, and March, such as Lea says occurs in the North Sea her- 
ring. The growth is very much retarded but does not cease entirely. The width of 
the winter bands shows this to be true. 
Taking all of these points into consideration, it can scarcely be maintained that 
temperature has any very definite primary effect on rate of growth. 
Tables somewhat similar to those given for temperature could be given for den- 
sity or salinity during the same period, but as they cover ground so similar it does not 
appear to be necessary. Suffice it to say that there seems to be just as little direct 
relation between salinity (as far as the limits in the waters of the strait of Georgia are 
concerned) and growth rate, as there is between temperature and growth rate. 
