Biology of the Aku — Brock 
95 
TABLE 1 
Year-Class Modal Lengths in Centimeters at Various Mean Dates 
mean 
SAMPLING DATES 
YEAR-CLASSES 
(dated by PRESUMED YEAR OF ORIGIN) 
NUMBER OF 
FISH MEASURED 
1943 
1944 
1945 
1946 
1947 
1948 
1949 
1950 
Sept. 15, 1946 
80.36 
74.40 
43.74 
2,311 
Dec. 8, 1946 
81.46 
75.96 
51.95 
3,463 
July 3, 1947 
79.30 
68.10 
43.96 
5,364 
Feb. 25, 1948 
78.00 
61.88 
429 
June 28, 1948 
79.74 
71.79 
43.79 
3,136 
Dec. 8,1948 
80.00 
74.64 
57.68 
160 
Aug. 16, 1949 
79.50 
71.89 
46.20 
588 
Dec. 26, 1949 
73.84 
53.78 
853 
July 12, 1950 
71.91 
44.08 
4,878 
Dec. 24, 1950 
74.21 
53.59 
1,266 
July 4, 1951 
68.13 
44.21 
8,409 
Total 30,827 
pies were taken from such portions of the 
catch as, according to the captain of the vessel 
making the landing, had come from a single 
school of fish. 
Acknowledgments 
The field work for these studies was done 
by the employees of the Division of Fish and 
Game who deserve much of the credit for 
the results. Mr. W. Van Campen and Mr. J. 
P. Welsh took a large share of the length 
measurements. Mr. T. Shimizu took those 
length measurements from single school sam- 
ples for 1949 , 1950 , and 1951, and Mr. F. W. 
Loo, statistician for the Division of Fish and 
Game, contributed to the statistical analysis 
herein. Dr. A. L. Tester of the University of 
Hawaii has offered a number of constructive 
suggestions. The fishermen, boat owners, and 
others engaged in the aku fishery have been 
most helpful. The officials of Hawaiian Tuna 
Packers, Ltd., have been, at all times, co- 
operative and interested in the program. 
AKU LENGTH FREQUENCIES 
The length measurements are plotted in 
Figure 1 and are grouped into units covering. 
for each length frequency curve, approxi- 
mately a 6-month period. This grouping was 
selected for two reasons: (1) To insure the 
inclusion of an adequate number of measure- 
ments in each group, and (2) to make it 
convenient to plot, with the first considera- 
tion in mind, the length frequencies on an 
approximately uniform time scale. Some in- 
dications of the factors which made it seem 
best to place the length data in a few com- 
paratively large groups will be given later. 
The length data, as plotted in Figure 1, 
have a feature of considerable interest— the 
apparent progression of modal groups through 
the fishery with time. Such a group entering 
the fishery during the summer months at a 
modal length of 40 to 50 centimeters may be 
identified with a modal group of 55 to 60 
centimeters which appears in the winter fish- 
ery, and in turn with a modal group of 68 
to 72 centimeters which occurs in the follow- 
ing summer months’ catch. There is an 
additional group at a modal length of 79 to 
80 centimeters sometimes represented in the 
summer landings which may represent a 
group of fish a year older. 
If it is assumed that these modal groups 
represent year-classes, the following interpre- 
