Biology of Wahoo — IVERSEN AND YOSHIDA 
371 
Fig. 1. Wahoo captured by surface trolling in the Line Islands. 
used in the open ocean, but some longline 
stations were occupied as close as 5 to 10 
miles from land. 
Length measurements were made in milli- 
meters, using calipers. The fixed arm was 
placed on the tip of the upper jaw with the 
mouth closed, and the sliding arm of the 
caliper was placed at the fork of the caudal 
fin, being careful to depress the fleshy flap 
(Marr and Schaefer 1949: 242). Weights were 
taken in pounds, using a steelyard rigged to 
a davit on the deck of the vessel. Some diffi- 
culty was encountered in accurately weighing 
the fish when the vessel was under way, but 
most weights were taken when the vessel was 
in smooth waters or at anchor. 
In preparing length-frequency distributions 
the lengths were first combined in 4-cm. 
groups and then smoothed by a moving aver- 
age of three. Modal groups in these distribu- 
tions are defined as the size classes with the 
highest frequencies in the smoothed distribu- 
tions. Where several adjacent size classes are 
similar in height after smoothing, the center 
of these size classes is designated as the mode. 
Stomach contents of the fish were recorded 
in the field as soon as possible after the fish 
were captured. The few parasites returned to 
the laboratory for examinations were pre- 
served in 10 per cent formalin. 
Measurements of ova for spawning and 
fecundity analysis were made with a dis- 
secting microscope, employing a micrometer 
eyepiece measuring in units of 0.023 mm. 
The eggs were not perfectly symmetrical, so 
to avoid selection the "diameter” measured 
was the distance between two lines of the 
micrometer tangent to the eggs, the microm- 
eter being held in one position during a series 
of measurements, following the method of 
Clark (1934: 7). 
AVAILABILITY 
Wahoo do not appear to form large com- 
pact schools. This simplifies the problem of 
