34 
PACIFIC SCIENCE, Vol. IX, January, 1953 
associated with direction and distance of haul 
(Tester, 1951: 332). 
Each haul was made in precisely the same 
manner. The current meter was read; the net 
was lowered over the side; the ship’s speed 
was increased from 0 to about 2 to 3 knots 
so that the upper edge of the mouth of the 
net was towed about 15 cm. below the surface 
of the water at a distance of about 25 meters 
astern. During the first haul in each set of 
three, the temperature was read to the nearest 
tenth of a degree (C.) from a freshly-scooped 
bucket of sea water, and a sample of sea water 
was taken for later chlorinity determination 
in the laboratory. At the end of exactly five 
minutes, the ship was stopped, the net was 
hauled alongside by hand, the current meter 
was re-read, the net was thoroughly washed 
from the outside with a power hose, it was 
hauled aboard, the cod end was removed and 
the contents placed in a quart jar with the 
usual care in rinsing, washing, etc. The jar 
was then labelled and formalin was added to 
make a solution of approximately 10 per cent. 
In the laboratory, the plankton was placed 
in Petri dishes, sorted by eye and by low 
power dissecting microscope, and all nehu 
eggs and larvae were removed and counted. 
The larvae were subsequently checked for 
correct indentification under higher magnifi- 
cation and were measured to the nearest 0.1 
mm. from the tip of the closed lower jaw to 
the base of the tail, using an ocular micro- 
meter. Chlorinity of the water samples (p.p.- 
m.) was determined by the Mohr method. 
The Atlas current meters were standardized 
by determining the number of revolutions 
made in towing them at slow speed (about 3 
knots— equivalent to about 3-7 revolutions 
per second) back and forth over a known 
distance between two buoys. There was close 
agreement between the calibration of the two 
meters, one of which was used for about 18 
months and the other for the remaining 6 
months. Calibration was undertaken but once 
rather than at intervals during the period of 
use. It is believed that this negligence led to 
no great error as (a) the meters were kept 
oiled, (b) the jewel bearings remained intact, 
and (c) there was no indication of a pro- 
gressive change in the number of revolutions 
per 5 -minute haul over the period of use. 
As the hauls were standardized in time, the 
variation in volume of water strained from 
haul to haul was relatively small. Adjustment 
of the egg counts to a standard volume of 
water (100 cubic meters— a rough average of 
the actual volume strained per haul) was 
made, although it did not greatly alter the 
counts nor influence the major conclusions 
drawn from unadjusted data. The adjustments 
were made according to the following formula 
which is similar to that of Ahlstrom (1953: 6) : 
r 100 E 1,369.072 E 
h s = = 
R.a.p. R 
where E s is the number of eggs adjusted to a 
volume of 100 cubic meters of sur- 
face water; 
E is the number of eggs per haul; 
R is the number of revolutions of the 
meter per haul; 
a is the area of cross-section of the 
mouth of the net (0.19635 square 
meters) ; 
p is the length of the column of water 
needed to effect one revolution of 
the meter (0.372 meters). 
The adjustment was not made for the larva 
count as the numbers involved were small and 
in most cases remained unchanged when the 
adjusted values were rounded to the nearest 
whole number. The unadjusted data may be 
considered to represent the number of larvae 
per 100 cubic meters of surface water. 
RESULTS 
Variation with Substation 
Adjusted egg counts at Substations A, B, 
and C ranged respectively from 0 to 1,661, 
0 to 1,722, and 0 to 2,617, with grand arith- 
metic means of 60.6, 61.8, and 81.1 eggs per 
100 cubic meters for the 207 sampling days 
