GROWTH AND MATURITY OF SALMON IN THE OCEAN 
43 
even though they would have matured during the year in which they were taken. 
For instance, many of the fish with ocean nuclei captured dm'ing May and June, 
and which have been considered as mature, would, in all probability, not be ready 
to enter the river until August or September, and would be feeding and growing at 
a rapid rate during the interval. Gilbert has shown, in his paper on the salmon of 
Swiftsure Bank, that maturing cohoes taken at that point increased nearly 100 per 
cent in weight during July and August, just prior to their entry into fresh water 
for the purpose of spawning. On account of the range in the age at maturity of the 
Chinook salmon, it is impossible to get as reliable figures for this species. It will 
presently be shown, however, that there is a distinct increase in length of the chinooks 
taken outside the mouth of the Columbia diu-ing the season. In the case of the 
4-year fish with ocean nuclei — the age group that contains the greatest number of 
maturing individuals — the length increases from about 80 cm. at the opening of 
the season to over 90 cm. by the close of the summer season on August 25. Since 
the weights vary as the cubes of the linear dimensions, this increase in length indi- 
cated an increase of nearly 50 per cent in weight during the summer. At this rate 
a fish weighing 16 pounds at the opening of the season on May 1 would weigh 24 
pounds by the end of August. The 3-year fish with ocean nuclei increase in length 
from about 60 cm. to about 75 cm. during the season. This indicates an increase 
of approximately 95 per cent in weight, a figure quite similar to that given by Gilbert 
for the cohoes, which are also 3-year fish. 
In resume, this inquiry into the relative maturity of the chinook salmon taken 
in and near the Columbia River has established the following facts: (1) The fish 
found in the river are, with very few exceptions, mature; that is to say, they have 
definitely left the ocean and entered upon their spawning migration. A very few 
fish taken in the extreme lower end of the Columbia River estuary, and only under 
exceptional tidal conditions, are immature; that is, they will not mattn-e and spawn 
during the year in which they are taken. (2) In contrast with this condition it 
has been shown that the fish taken in the ocean near the mouth of the Columbia 
River contain varying proportions of fish that will not mature for at least one more 
year. (3) These immature fish taken in the ocean belong mainly to the following age 
groups, arranged in the order of relative abundance: Third year, ocean nuclei; 
second year, ocean nuclei; third year, stream nuclei; fourth year, ocean nuclei; 
fourth year, stream nuclei; and fifth year, stream nuclei. (4) The percentages of 
mature and immature fish taken at different times during the fishing season have 
been determined, and it has been shown that a very high percentage (approxi- 
mately 90 per cent) of the fish taken in the ocean during the early part of the season 
are immature. The proportion of immature fish gradually lessens as the season 
advances, until in August nearly 90 per cent of the fish taken are maturing. There 
is some indication that in September there is a return to the conditions found in 
May — a high percentage of immature individuals. 
ABUNDANCE OF THE VARIOUS AGE GROUPS 
The variations in the percentages of the various age groups taken inside the 
river at different times during the season are striking, especially when compared 
with similar data for the fish taken in the ocean. Table 9 gives for each collection 
