460 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [34] 
About 100 or 200 small salmon should be measured in the sea, and near 
the mouths of the Rhine, at a certain season of the year, if possible in one 
certain month (as the length does not always remain the same). These 
fish would certainly—as to their length—be classed among those the 
catching of which is forbidden by law; but the result would justify an 
exception; as the arrival of the great mass of the young fish is limited 
to a certain season of the year, the different migrations would show on 
the curves constructed from such measurements, like annual rings. So 
far all attempts to obtain such a determination of the age by the mark- 
ing of young salmon have been in vain. But even supposing that fish 
thus marked are caught again, the result of the statistical method is 
much more valuable, because it alone ‘can select from among the numer- 
ous exceptions and variations which doubtless occur in the conditions 
of life of these fish with absolute certainty, those fundamental rules on 
which everything depends. 
Irom these and other reasons, to be considered later, I prefer to 
designate the time which elapses till the young salmon’ had been 
transformed from a small fish into the St. Jacob’s salmon simply by ¢; 
and by introducing this unknown quantity to designate the following 
determination of the age of the fish as the more probable one in most 
cases in as far as fish which participate in all migrations are con- 
cerned: 
Migration of the young salmon to the sea ...-..- 1 year. 
Kirst spawning period of the St. Jacob’s salmon: 
Smallispecimens. 4544).8.7756- ob Wiese hous 1+ ¢ years. 
hares Specimens +8224. Sete hls tee eee ee 2+ ¢ years. 
Second spawmins period. f5 85 se ee eee eee 3+tand 44 ¢ years. 
Phird spawning periods: 0), 2 Adeeee eee 5+¢ and 64 ¢ years. 
The curve indicating the sizes of the females is much easier to under- 
stand than that of the males. Here, likewise, three elevations may be 
noticed. Hemale salmon of the first migration are very rare near Basel, 
and the data had to be supplemented by measuring St. Jacob’s salmon 
from Wesel (September 23 to October 13, 1879). Here the females are 
likewise in the minority; the Wesel salmon referred to (which were, 
distinguished by the length of their nose) showed one-fourth females 
and three-fourths males. 
The curves of the second and third immigration are very distinetly 
Shown in the Basel salmon of both years. I am inclined to ascribe the 
considerable breadth of all three curves, just as with the male fish, first 
of all to differences of age in the first immigration which return at every 
succeeding migration, and to other differences of the intervals between 
the years of migration; and only in the second place to individual differ- 
ences of growth. Attention should also be directed to the circumstance 
that the maxima of the three curves are not, as with the males, equi- 
distant from each other, but that the proportion of the first distance to 
the second is as 10 or 11 to 7, or 3 to 2. Its proportion to the distance 
