Plankton Catcher — Bary ET AL. 
57 
or numerous series of hauls, in order to assess 
the versatility and reliability of the catching 
power of the unit. A conventional type of net, 
of 50 cm. diameter (Bary, 1956), was twice 
fished alternately in horizontal tows wdth the 
catcher, and other horizontal tows have been 
made with the latter. Some vertical tows with 
the catcher have been compared with collec- 
tions from a Nansen- type closing net. When- 
ever a net has been included during trials with 
the unit, the bucket has been examined for 
plankton. 
The range of organisms and the quantities 
collected are most encouraging. Several of the 
smaller species of pelagic fish, fish larvae, 
squid, and larger euphausiids and shrimp have 
been captured. Also, common forms such as 
copepods, chaetognaths, salps, and larval 
decapods are collected, sometimes in high 
numbers. When the catches of the 50-cm. net 
and the catcher were roughly equilibrated for 
differences in size of mesh, area of mouth, 
and distances towed, the catcher was believed 
to have collected a greater quantity of larger 
organisms, including fish and shrimp, than 
the net. Collections made during the vertical 
hauls with the 70-cm. Nansen-type of net and 
the catcher were similar in the range of organ- 
isms captured. Specimens are alive (except 
fish larvae) and quite undamaged at towing 
speeds up to 8 kt. 
Although test hauls with the catcher are 
few, those made to date suggest it collects a 
representative range of organisms — a range 
which may be comparable with that taken by 
the 70-cm. Nansen closing net. 
OPERATION 
A "high-speed” plankton sampler, as well 
as being towed at fast rates, must also be 
quickly and easily handled on deck, recovered 
from, launched, and lowered to the level at 
which it is to be towed, and emptied of its 
catch. 
On raising the present catcher from a hori- 
zontal tow, the depressor is lifted onto a hook 
attached to the ship’s side (not necessary in 
calm water), and the rear end of the catcher 
is rested in the crotch on the guard rail (Fig. 
6) ; the meter is read (or the smoked cylinder 
renewed), and tail and net are removed. A 
second net and frame can then be slipped into 
the body and the tail replaced. The unit is 
lifted over the side and while hanging free of 
the rail, the valve is opened. The depressor is 
then freed, and the whole is lowered into the 
water. For a team of three (one working the 
winch), the time taken on this routine is about 
two minutes. The ship may continue to steam 
at from 6 to 8 kt. The used net is washed 
down with sea water from a hose and the 
catch preserved; the net is then ready for the 
next tow. < 
To reach the required depth of a horizontal 
tow, the catcher is allowed to dive on an 
almost free-running winch, and a length of 
wire is veered equivalent to 2.5 times the 
depth (a ratio of approximately 1:2.5 was 
found to apply up to 100 m., but may not 
do so at greater depths. The depth-flow meter 
provides a check on the depth reached.) Mean- 
while the ship may continue underway, alter- 
ing speed to the towing speed, if necessary. 
At the end of the tow, the catcher is closed 
by messenger, recovered, and the usual rout- 
ine followed. 
In vertical tows with a single unit (no tows 
with multiple units have been made), the 
routine is similar. Additionally, the wire is 
released from the after bracket before the tail 
is lifted onto the rail, and is replaced again 
before lowering. The terminal sinker need not 
be lifted, but may require steadying with a 
strop or boat hook in rough weather. 
Lowering for the vertical tow is rapid when 
compared with a Nansen -type of net. It is 
necessary to brake the winch to a vertical 
speed of about 4 kt. so that a strain is main- 
tained on the wire, otherwise the catcher may 
dive nose first (see earlier). The haul is as 
rapid as the winch permits, or as is desirable. 
At depths below 750 m., delays of a minute 
or two are necessary, before commencing to 
