Fishery bulletin of the Fish and Wildlife Service - NOAA

FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 275
migrate seaward. At the end of the migration period a part of this population is
present in the lake. These fish remain for another year and obtain more growth. In
the fourth year, the largest individuals remaining in the lake proceed seaward, the
time of appearance in the migration being correlated with their size. The slowest
growing individuals of the entire progeny which have not migrated remam in the lake
for another year and then migrate seaward in their fifth year.
The older fish are of a larger average size than those of lesser age and their larger
size is due to the longer growing period that precedes migration. Fish in the older
age groups are usually the slower growing fish of the progeny from a particular spawning.
Thus, the urge to migrate seaward is related to the size and growth rate of
fingerlings, and it appears that environmental conditions that affect the growth of the
fish during the time spent in the lake also affect the tune at which the fingerlings
migrate to the ocean.
The data on the percentage of males in the samples of migrants which were examined
to determine sex are presented in table 28. The males and females were
equally represented. Grouping the 3- and 4-year fish, it was found that the total of
11,080 fish examined consisted of 5,557 males and 5,523 females. The slight variations
in the sex ratios from year to year are probably due to chance because there is
no significant statistical difference in the ratios.
TABLE 28.—Number of 8-year and 4-year migrants examined and percentage of males in the samples
1925
1926
1927 . ..
1928
1929
1930
1931
1932
1933
1934. . _
Total
Year
Number of
3-year fish
examined
£70
448
211
491
318
1,308
1,764
1,286
646
802
7, 804
Number of
males
296
232
115
262
168
659
831
632
320
401
8 916
Percentage
of males
51.9
51.8
54.5
53.4
52.8
60.4
47.4
60.3
49.5
50.0
60 18
SEX RATIOS OF ADULT FISH
Number of
4-year fish
examined
72
160
144
224
287
674
277
833
626
90
3 276
Number of
males
40
71
75
127
161
335
132
401
262
47
1,641
Percentage
of males
The sex ratio of the adult fish is in marked contrast to that of the seaward migrants,
Data on the percentage occurrence of males in the samples for the years 1922 and 1924
to 1936 are presented in table 29, arranged according to the length of time spent in
the ocean. The percentage occurrence of the males decreases with increased ocean
residence. All of the zero-ocean fish 8 are males. The average percentages of males
in the one-ocean fish, of varying .periods of fresh-water residence, range from 100
percent to 75 percent. The average percentages of males in the two-ocean fish range
from 02 percent to 32 percent, while the average percentages of males hi the threeocean
fish of varying fresh-water residence range from 38 percent to 35 percent.
• Fish which spend only a few months In the ocean and return as mature flshln the fall of the same year in which they migrated
seaward.
65.6
47.3
62.1
56.7
66.1
61.3
47.6
48.1
48.0
52.2
60 09