GROWTH AND MATURITY OF SALMON IN THE OCEAN 
17 
In a preliminary report dealing with the subject of this paper (Rich, 1921a) 
the writer made the following statement: 
The determination of the age by means of scale studies will not alone give a sufScient index 
to the degree of immaturity since there is such a wide range in the age at which these fish reach 
the spawning stage — from 2 to 6 years. If the percentage of individuals of different ages among 
the mature fish were constant, it would be possible, from a determination of the percentage of 
fish of different ages taken by troll and purse seine in the ocean, to estimate the percentage of fish 
of different degrees of maturity. This, however, is not the case. The percentage of fish of the 
various age groups varies greatly at different times among the mature fish and also among those 
taken in the ocean. Presumably these variations, at least among the mature fish, are due quite 
largely to racial differences, but our present knowledge of the various races of chinook salmon is 
far too limited to aid in segregating the races from mixed lots. Even if our knowledge of the races 
were complete it might well be that they could not be identified and segregated accurately and 
fully enough to serve this purpose. It is apparent that some other means than the determination 
of the age is necessary in order to learn the percentages of mature and immature fish taken in 
the ocean and their relative maturity. 
It has been found, as will be subsequently showTi in detail, that the size of the 
eggs gives a fairly accurate means for determining how soon the females will mature. 
During a field trip to Monterey, in 1915, it was noted that there was considerable 
variation in the size of the ova, and a series of egg samples was collected. It was 
thought that from a study of the eggs something might be learned of the percentage 
of mature and immature fish taken by troll in Monterey Bay. These eggs were 
collected from the cleaning tables and no attempt was made to collect data and 
scales from the fish from which the eggs were taken. Nothing was done with this 
collection until the summer of 1918, when the matter was again brought up for 
consideration. On examining the samples, the fact became apparent that several 
reasonably distinct sizes of eggs were to be found, which presumably represented 
different degrees of maturity. (See Table 23, p. 86.) In order to secure more 
complete data, another collection was made at Monterey in the summer of 1918, 
and in this case measurements and scales vv'ere secured along with the egg samples. 
The study of this collection confirmed the earlier observations as to the presence 
of fairly distinct size groups of eggs, and the examination of the scales showed 
a high degree of correlation between age and the size of the eggs. (Table 25, p. 87.) 
Extensive collections have since been made from the fish taken by troll ofi^ the mouth 
of the Columbia River, and it has been found that, while the determination of 
maturity is not as simple a matter as it had first appeared, the general features 
will hold good. 
It is obvious that this method is applicable only to the females and no method 
has yet been devised for accurately determining the relative maturity of the males. 
It was thought at first that the percentage of males of various degrees of maturity 
could be calculated with reasonable accuracy from the percentages of males and 
females found among the mature fish in the stream if once the percentage of mature 
and immature females taken outside was known. If it were not for disturbing 
factors this could easily be determined, /or each separate age group, by means of the 
following proportion : Percentage of males taken inside : percentage of females 
taken inside : : percentage of males taken outside which are mature : percentage of 
females taken outside which are mature. It has been found, hovrever, that the 
A 
