through the strainers, 

 considered in turn. 



Each of these will be 



Fragmentation of organisms 



When organisms have to pass through a 

 1.27-cm. pump whose impeller turns at 3,450 

 r.p.m. and then through a 120-m. hose with 

 internal cables, fragmentation is possible. 

 Estimates of abundance will be low if a large 

 portion of the animals are so severely damaged 

 that they become unrecognizable or are torn 

 into parts which may then pass through the 

 mesh of the strainer. The percentage of frag- 

 mented organisms, as indicated by the number 

 of damaged specimens among the first 100 of 

 four kinds counted, were as follows: 



Percentage 

 fragmented 



Organisms 



Copepods (various spe- 

 cies & stages) 



Sardine eggs ( Sardinops 

 caerulea ) 



Sardine larvae ( Sar- 

 dinops caerulea ) 



Brine shrimp ( Artemia ) 



Size 

 <0.3 mm. long 



1.7 mm. diameter 



5 mm. long 



10 mm. long, used 

 for testing 



92 



49 



Only a small percentage of the small 

 copepods and stage VI and VII sardine eggs 

 (Ahlstrom, 1943) were damaged. Damaged 

 copepods were slightly crushed but easily 

 recognized. The perivitelline membranes of 

 some eggs were ruptured, but the embryos 

 remained intact. 



Sardine larvae and brine shrimp suffered a 

 high percentage of fragmentation. Nearly all of 

 the sardine larvae were headless but the bodies 

 were not injured. They are probably too fragile 

 to pass the impeller uninjured. Fragmented 

 brine shrimp were headless, and the bodies 

 often mutilated. Brine shrimp also are probably 

 too large and fragile to pass the pump un- 

 damaged. 



General inspection (no counts made) showed 

 that chaetognaths, 6 mm. long, and doliolids, 

 1 mm. long, remained in good condition, but 

 many euphausiids, ostracods, and fish larvae 

 were damaged. The pump described he re should 

 not be used for sampling fragile organisms or 

 organisms longer than 5 mm. Diaphragm, 

 air lift, or centrifugal pumps with larger 

 chambers offer possibilities for sampling 

 larger organisms. 



Uneven Transport of Organisms Through 

 the Hose 



Because friction and turbulence prevent 

 water from flowing evenly through the hose, 

 the transport of organisms is not uniform. 

 This uneven transport can cause contamination 

 of samples by mixing organisms that were 

 collected from different strata in a vertical 

 series. Two trials indicated the differences in 



the transport of organisms through the hose. 

 In each test the pump was placed in a large 

 container so that it recirculated water through 

 the system and back into the container. Known 

 numbers of dead adult brine shrimp, 1 cm. 

 long, were introduced simultaneously at the 

 pump intake and retrieved in a series of 

 samples after passage through the hose. Ten 

 consecutive 100-liter samples and a final 500- 

 liter sample were collected in small nets with 

 mesh aperture of 0.75 mm. Sampling started 

 immediately after introduction of the shrimp. 

 One hundred shrimp were used in one trial, 

 and 50 in the other. 



Table 1 presents the frequency distribution, 

 percentage frequency, and cumulative percent- 

 age of shrimp for the series. The number of 

 shrimp retrieved rather than the number 

 introduced forms thebase of these percentages. 

 Only 129 of the 150 shrimp used in the two 

 trials were recovered. A few were probably 

 lost in handling but the major loss was due to 

 fragmentation, a factor which was not antici- 

 pated. Only heads were counted but some may 

 have become unrecognizable or may have 

 passed through the mesh. It was presumed that 

 few if any shrimp remained in the hose after 

 the passage of 1,500 liters of water. 



The frequency distribution shows that most 

 of the shrimp remained together but some were 

 separated by more than 800 liters of water 

 pumped (table 1, column 4). The small num- 

 ber of shrimp that appeared in the second 

 sample of each trial must have been carried by 

 the swifter central core of water. They reached 

 the outlet even before the calculated volume of 

 the hose, 250 liters, was replaced once after 

 introduction of the shrimp. The majority of the 

 shrimp appeared in the third sample; all the 

 shrimp would have appeared in this sample if 

 transport of organisms had been uniform. The 

 remainder, 24.1 percent, were detained for 

 varying periods, probably by eddies. 



Table 1. — The number and percentage of simultaneously introduced 

 brine shrimp recovered in 10 consecutive 100-liter samples and 

 a final 500- liter sample, after passage through the pump and 

 hose 



1 The percentages are based on the 129 shrimp retrieved. 



