GROWTH AND MATTTrITY OF SALMON IN THE OCEAN 53 
The study of the fish of this age group taken in the river is complicated by the 
fact that two quite distinct races are found running simultaneously during the latter 
part of August and September. A discussion of the racial differences observed among 
the chinook salmon has not been attempted in this paper, but in this particular case 
the differences are so striking that a failure to segregate the two races would be mis- 
leading. Tables 19 and 20 on pages 82 and 83 give the length-frequency distribu- 
tions in detail for two large collections made, respectively, on August 22 and Sep- 
tember 12, 1919. An examination of these tables will show that the length-frequency 
distributions of the 4-year fish with ocean nuclei are distinctly bimodal. The 
bimodality is apparent, not only in both collections but also in the two sexes of each 
collection, as well as in the distribution in which males and females are combined. 
The cumulative evidence of these facts points strongly to the fact that two distinct 
races are present. Additional evidence of a very satisfactory nature, which sup- 
ports this interpretation, is available from the scales. Two quite different types of 
scales are found among the fish of this age group : One, typical of the smaller fish, is 
characterized by a comparatively small ocean nucleus, which is usually not sharply 
defined from the succeeding growth of the second year, and the winter bands of the 
second and third years are relatively close together. The type that is associated 
with the larger fish has a distinctly larger nucleus, which is usually well set off from 
the rest of the scale. The second and third winter bands are more widely separated 
and are frequently less sharply marked than those of the other type. Figure 41 
illustrates the scales of the first type — associated with the smaller sized fish — and 
Figure 42 illustrates the scales of the second type. The evidence given by the length- 
frequency distributions and by a careful study of the scales indicated that there was 
very little overlapping in the sizes of these two races, and consequently the line of 
separation has, somewhat arbitrarily, been set at 90 cm. All of the fish above 
this size have been considered as belonging to the larger race, and all below it as 
belonging to the smaller race. The overlapping of the two races is quite obviously 
so slight that there will be little error in making this assumption. In the text figure 
the two races have been shown separately in the last two collections. Both races 
were included in the calculation of the trend. 
FISH IN THEIR FIFTH YEAR, OCEAN NUCLEI 
It has been shown above that there were comparatively few fish of this age group 
taken outside the river, although it is well represented among the fish taken inside. 
It is significant, therefore, that the trend, as determined from these relatively inade- 
quate data from outside, is quite similar to the trends as determined for the other 
age groups found among the fish taken outside, which were much more adequately 
represented. On the other hand, the trend for the fish taken inside is reversed, the 
larger fish occurring during the early part of the season, althoiigh the group is well 
represented both as regards number of individuals and number of collections. The 
deviations from the line of the trend are again greater in the case of the fish taken 
inside the river. These features are shown in Figure 17. 
