+s ial
eoallen
Ppiankton
Survey
*Hanato TSURUGA and Harumi TOZAWA
Meee
tmouth and 450 cm in length.
The front portion
Sreisted of a cotton minnow net, 350 cm in length,
mien average mesh of 1.6 x 1.9 m.
The back portion
Meted of bolting silk, LOO cm in length, with an
;
mate mesh of 0.3 mm.
ing the run in the waters adjacent to Christmas
hd, 6 net tows on the surface and 11 tows at a depth
SO\m were made for 1 or 2 hours immediately after
faat a speed of 2-3 knots. Eleven tows on the
e.were made during the runs between Tokyo and
u in the same manner mentioned above.
portion of the plankton samples obtained from
tow was measured for activity, aboard the ship.
der was placed in a 10% formalin solution and
for radiochemical analysis.
éplankton sample, 30-50 g in wet weight, was
1 the muffle furnace after being dried at 110°C.
i
:f
i
sample of the ash was placed in a stainless
g> mm in diameter and 8 mm deep, and the gross
Muapectivity measured with a conventional G-M counter.
menting efficiency, based on a 7°Zr-75Nb standard
Meeetor samples 1 to 11, and 6.3% for samples 12
meyorrections were not made for the activity derived
B.. Results are shown in Tables 1 and 2.
Bross # -radioactivity of the plankton ranged from
dpn/0.5¢ of ash, and seemed to be approximately
ea
momo that of plankton from Japanese waters.
Activity
guples from the Equatorial Countercurrent showed an
200f—
19
tt
oS
So
w)
meee Of 632 dapm/O.5¢ of ash in 4 samples.
This was
meuly higher than the average of
341 dpm/O. 5g of ash
Meeweenples from the North Equatorial Current or 361
mda8 of ash in 9 samples from the South Equatorial
Tar
*
etokal. Regional Fisheries Research Laboratory
E
_49~
Pe