14. Copper tube with outlets for each rubber tube 

 ( 13). Water to operate the subsampler comes 

 through a large-diameter garden hose and 

 pistol-type hose nozzle (not shown) attached to 

 this tube. 



15. Overflow tube attached to the outside of the 

 cylinder (3). The cut edges of a longitudinal 

 section of Plexiglas tubing are bonded to the 

 cylinder from the overflow intake to the bot- 

 tom of the base (1). Below the base the tube is 

 not sectioned (i.e., left intact) so a drain hose 

 can be attached to it. 



16. Aluminum window screen covering overflow 

 intake; bottom of intake opening is level with 

 the top of the vanes (8) when they are raised. 



17. Rubber stopper in drain hole below spout. 



Also omitted from the diagram are "stops" on 

 the bottom edges of the vanes (which prevent the 

 vanes from pulling through the false floor) and 

 spongy, foam gaskets attached to the doors with 

 rubber cement. 



Subsampling Procedure 



In subsampling, one pushes the inner cylinder 

 (6) with the attached vanes down until it rests on 

 the base; in this position the tops of the vanes are 

 even with the top of the false floor so that the vanes 

 and floor form a single flat surface. The entire 

 sample is then placed on the false floor. The hose 

 nozzle trigger is squeezed fully open, squirting 

 water rapidly through the rubber tubing. (Nor- 

 mally, the space below the false floor is still filled 

 with water from previous use.) Some of the water 

 rises through the three vane slits in the false floor, 

 thereby inhibiting downward passage of the 

 smaller specimens; most of the water squirts out of 

 the upper tubes, causing the water above the false 

 floor to swirl rapidly. Turbulence thoroughly 

 mixes the sample as both sample and water re- 

 volve. When the water almost reaches the bottom 

 of the overflow intake, the inner cylinder (6) and 

 attached vanes are quickly raised as far as possi- 

 ble so that the locking pin (7) slides farther 

 through its hole in (6) and over the top edge of (4); 

 simultaneously, the hose nozzle trigger is re- 

 leased. The sample has now been divided into 

 three parts equal to about 0.2, 0.2, and 0.6 of the 

 whole. 



The entire subsampler is next tilted on its 

 hinges (2) in preparation for emptying. If a 0.2 

 subsample is desired, only one door is opened and 



492 



the contents of that compartment flow through the 

 spout (12) into a sieve. (To avoid bias, the user 

 should always open the same door first. Occasion- 

 ally fish balance on top of the vanes; the user can 

 avoid personal bias by always pushing the fish so it 

 falls headfirst.) Opening both doors produces a 0.4 

 subsample and the remainder of the material in 

 the subsampler constitutes a 0.6 subsample. The 

 0.6 subsample is removed by first taking out the 

 0.4 subsample and then lowering the vanes as far 

 as they will go. The 0.6 subsample may then be 

 washed into a sieve below the spout. ( When remov- 

 ing any subsample, it is easier to wash the or- 

 ganisms out of the subsampler than to pick or push 

 them out.) A wide variety of subsample ratios can 

 be obtained by sequentially subsampling subsam- 

 ples (e.g., 0.8 x 0.2 x 0.2 = 0.032). 



Small organisms do occasionally fall through 

 the vane slits into the space between the base and 

 the false floor. Such losses are normally insig- 

 nificant compared with the total number being 

 subsampled, but they are noticeable through the 

 Plexiglas. These organisms may be recovered by 

 washing them out through the drain hole plugged 

 by the rubber stopper (17). 



No special leveling of the subsampler is re- 

 quired for proper operation; it may be mounted on 

 any reasonably level surface such as a table top or 

 laboratory bench. 



Discussion 



The subsampler is useful for estimating both 

 total numbers in a sample and the total length- 

 frequency distribution. If the total sample is not 

 first separated by species, one should at least make 

 a thorough scan of the sample, before subsam- 

 pling, to remove any unusually large or odd spec- 

 imens. As stated by Hightower et al. ( 1976), these 

 can later be added to the total estimate, which is 

 derived by extrapolating the subsample results. 

 However, subsampling can give erratic results for 

 inconspicuous species present in small numbers. 

 Therefore, I think it usually is best to first sepa- 

 rate the total sample into individual species, and 

 subsample only the abundant ones. For each of 

 these species, a subsample is first taken, and its 

 weight and that of the remainder are obtained by 

 the spin-dry method described by Herke (1973). 

 (In contrast to plankton, preserved fishes and 

 many crustaceans can be easily and precisely 

 weighed without damage by using the spin-dry 

 method.) All organisms in the subsample are then 



