Numbers of organisms 



Each plankton sample was examined in 10- 

 ml. portions under a low -power binocular 

 microscope, and the fish eggs, fish larvae, 

 and amphioxi were removed and counted. The 

 wet volumes of plankton were then determined 

 by displacement (drained plankton placed in 

 graduated cylinder containing a known volume 

 of 5 percent buffered formalin) . 



Numbers of organisms other than fish eggs 

 and larvae and amphioxi were estimated by 

 counting those in aliquot portions of a sample 

 and adjusting the counts to the entire sample 

 volume. The procedure was as follows: (1) 

 the sample was stirred thoroughly, and a 10 

 ml . portion removed, by dipping with a 10 ml . 

 beaker, to a dish marked with a centimeter 

 grid; (2) the more numerous organisms were 

 counted in six preselected centimeter squares, 

 and the less numerous ones counted in the en- 

 tire dish; (3) the portion was then returned to 

 sample jar, the sample stirred thoroughly, 

 and a second 10 ml . portion removed; (4) the 

 second portion was treated in same manner as 

 the first; and (5) the counts were averaged and 

 then adjusted to the entire sample volume by 

 multiplying by the appropriate factor. Num- 

 bers of the various organisms per cubic meter 

 of water strained were calculated by dividing 

 sample totals by volumes of water strained. 



Continuous Plankton Sampler 



Plankton samples were also taken with a 

 continuous sampler designed by Albert W . 

 Collier, Jr , Chief, Gulf Fishery Investiga- 

 tions, Fish and Wildlife Service. A descrip- 

 tion of this sampler has not been published, 

 but general construction details and operation- 

 al procedure will be presented here . Figure 3. 

 The sampler consists of a circular trough 

 divided into eight compartments, and is driven 

 by an electric motor at the rate of one revolu- 

 tion per eight hours. Extending down from 

 each compartment is a tube fitted at its lower 

 end with a clamp which holds a 1 -1/4" No . 1 

 silk filtering disc . A reverse bend in the dis- 

 charge tube below the clamp retains sufficient 



water to cover the silk, thus preventing 

 filtered organisms from drying out. Sea 

 water is pumped from a sea chest located 

 several feet below the ship's water line, 

 through a standard water meter, and into the 

 sampler . As the sampler trough revolves, 

 each compartment receives water for one 

 hour . After one revolution of the trough 

 (eight hours), a timer switch shuts off the 

 sampler and pump motors. The filtering 

 discs are then removed, preserved in 5 per- 

 cent formalin, and replaced with new silks. 

 Each revolution constitutes a "run' . The 

 sampler is permitted to run continuously, 

 except for the time needed to change silks and 

 when the ship is entering or leaving a harbor 

 (where sand and silt may jam the water meter) . 



The flow of water into the sampler is 

 regulated according to the density of planKton 

 encountered (in shallow waters phytoplankton 

 plugs the filtering disc rapidly if flow is not 

 reduced) . A pressure gauge in the line be- 

 tween the meter and the sampler provides for 

 uniform adjustment of the flow. From 50 to 

 100 gallons of water pass into each compart- 

 ment during the hour it receives water. 



The silks are examined individually, and 

 counts made of all organisms present . The 

 counts are then adjusted to "Number per 

 cubic meter of water strained" . The position 

 of the ship at the time the center of each com- 

 partment is reached is accepted as the loca- 

 tion of sampling for the compartment involved. 

 Generally, the trough does not matce one 

 revolution in exactly eight hours, and the time 

 for each compartment is adjusted accordingly. 



Dip -netting 



Dip -netting for larval and juvenile forms 

 of fish was conducted on station when seas 

 and weather conditions permitted. Dip nets 

 used were 18 inches in diameter, lined with 

 1/4-inch nylon mesh, and were fitted with 12 

 foot bamboo handles . Spot and floodlights 

 were used at night to attract fish. In general, 

 dip-netting at night under the lights proved 

 more productive than dip -netting during the 



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