HOMING INSTINCT OF PINK SALMON 
35 
occupies the central area of the scale. This band is terminated at its outer border 
by a narrow band of closely set growth rings or the winter band (W.B.). The second 
band of widely spaced growth rings, i. e., those laid down in the life of the salmon dur- 
ing its second spring and summer in the sea, immediately follows the winter band 
(IV. B.) and terminates at the margin of the scale. 
The growth rings on the Duckabush River pink-salmon scale shown in figure 10 
likewise may be divided into the three characteristic bands. The first band of widely 
spaced growth rings is, however, not very distinct since the rings near its center are 
in such close proximity that they form a rather definite incidental band of closely 
spaced rings ( I.B. ). The winter band of closely spaced growth rings (W.B.) and the 
succeeding second band of widely spaced growth rings are on the other hand very 
distinct and well marked around the circumference of the scale. This incidental 
band of closely spaced rings (I.B.) that occurred in the life of the salmon during its 
first spring and summer in the sea is no doubt due to a temporary retardation in its 
rate of growth. The occurrence of such aberrations on the scales of the Pacific salmon 
was recognized by Gilbert (1913, p. 5), who says: 
Thus it comes that the surface of the scale is mapped out in a definite succession of areas, a 
band of widely spaced rings always followed by a band of closely crowded rings, the two together 
constituting a single year’s growth. That irregularities occur will not be denied, and this is natural, 
inasmuch as growth may be checked by causes other than the purely seasonal one. 
Had not the scale in figure 10 been known to have come from a pink salmon that 
matured at 2 years of age, it would still be illogical to assume the incidental band of 
closely spaced rings (I.B.) to be a true winter band. Such an assumption would mean 
that the salmon bearing this scale spent 3 summers and 2 winters in the sea and ma- 
tured at 3 years of age. This, however, would be impossible since the pink salmon 
runs in the streams on Hood Canal and along the Strait of Juan de Fuca occur only 
on alternate years. Hence the salmon composing these runs must mature at 2 or 
some multiple of 2 years of age. 
Since the pink-salmon runs in the Duckabush River occur only on the odd years, 
it is impossible for any of the pink salmon in this stream to mature at 3 years of age. 
In order to check the possibility of any of the pink salmon in this stream maturing 
at 4 years of age, the run in this stream was examined for individuals bearing the marks 
in the summer of 1933. No marked salmon were found in the 1933 run and every 
fish was examined carefully at the time it was spawned artificially by the hatcherymen. 
The runs of pink salmon in Snake Creek occur every year, hence the 1933 run in 
Snake Creek was examined in order to check the possibility of the pink salmon in 
this stream maturing at 3 years of age. The salmon run in this stream was examined 
in the same way that it was examined during the summer of 1932. No marked 
pink salmon was found in the 1933 run. There was, however, a number of pink 
salmon with deformed and missing adipose fins found in this run, which is further 
evidence that pink salmon with missing adipose fins due to natural causes are not 
infrequently found in the runs. 
There is still other evidence which indicates that the pink salmon mature at 
2 years of age. In 1913 and 1915 large shipments of eyed pink-salmon eggs were 
sent from the Pacific coast to the fish hatcheries in the New England States. These 
eggs were hatched artificially and in the spring of 1914 and the spring of 1916 the 
fry were liberated in a number of streams along the coast. In the summer and fall 
