the two groups of animals are not qualitatively 

 different. The number of organisms adhering 

 to the screening of the funnel was about 20 

 percent of that in the cod end, which means 

 that the funnels must be washed after every 

 sampling period and all residue must be in- 

 cluded with the sample. 



VERTICAL DISTRIBUTION OF SARDINE 

 EGGS AND LARVAE AND 

 OTHER ZOOPLANKTON 



After the initial testing of the pump we found 

 an exceptionally high concentration of sardine 

 ( Sardinops caerulea ) eggs and larvae in Sebas- 

 tian Vizcaino Bay, Baja California. This pro- 

 vided an excellent opportunity to test the gear, 

 because eggs float passively in the water and 

 eggs and larvae were so abundant that only rela- 

 tively small amounts of water had to be strained 

 to detect changes in vertical distribution. 



A vertical series was taken at lat. 28° 01.7 

 N., long. 114° 25.4 W. on August 26, 1964, 

 between 1925 and 2237 hours P.s.t. while the 

 vessel Black Douglas was anchored in 45 m. 

 of water. Two 500-liter samples were taken at 

 each 5-m. level from the surface to 35 m. 

 The system was flushed with 500 liters of water 

 at each depth before sampling was started but 

 was not flushed between samples from the 

 same depth. According to table 1, a flushing 

 volume of 500 liters removes at least 82 

 percent of the organisms that remain in the 

 hose from a previous depth. 



Salinity and temperature of the water from 

 each level were measured. Comparison of the 

 temperatures with a BT tracing made after 

 sampling indicated that the hose was nearly 

 vertical. 



The sardine eggs and larvae were identified 

 and counted, and stages of development of the 

 eggs were determined according to the criteria 

 of Ahlstrom (1943). All eggs except one were 

 either stage VI or VII; as the water temperature 

 was 20.7° C, they must have been spawned 

 the previous night (Ahlstrom, 1943). Many of 

 the larvae were headless, but enough 

 characters remained for reliable identifica- 

 tion. Most were between 4 and 5 mm. long. 



The numbers of sardine eggs and larvae 

 and of chaetognaths and doliolids in each 

 sample are given in table 2 with temperatures 

 and salinities. Temperature and salinity pro- 

 files and mean numbers per cubic meter for 

 each level appear in figure 5. The BT tracing 

 obtained immediately after sampling is shown 

 in figure 6. The eggs were abundant and uni- 

 formly distributed, 42 to 46 per m. 3 , in the 

 upper levels where temperature .and salinity 

 were uniform. The water temperature, 20.7° 

 C, is near the upper limit of the spawning 

 temperature range, but according to Ahlstrom 

 (1954) it is typical of off-season spawning 

 temperature in Vizcaino Bay. Egg abundance 

 dropped significantly to ll/m. 3 at the 15-m. 

 level. The BT tracing (fig. 6) indicates that 

 this depth was near the upper boundary of the 

 thermocline. Water samples from this level 

 showed a 0.1° C. drop in temperature and a 

 0.02 p.p.t. rise in salinity. At the 20-m. level, 

 the egg concentration was only 2/m. , and at 

 greater depths none were found. 



The larvae were uniformly distributed, 32 to 

 35/m. 3 in the upper 10 m., but at the 15-m. 



Table 2 . --Temperature , salinity, and numbers of sardine eggs, 

 sardine larvae, chaetognaths, and doliolids for pairs of 

 500-liter samples in the vertical series 



[Temperature and salinity were taken only in the first sample 

 of each pair; all counts are total except for doliolids which 

 were estimated from one-fourth aliquots] 



P 20 



6 6 

 6 i 

 —a ;- — 



,-°*' 9~~ ~ 



o--'' • a 



1 



i i 



14 



16 IS 



TEMPERATURE 



20 

 •C. 



33.67 33.71 33.75 

 SALINITY %. 



ZJ 



20 40 



EGGS / M 3 



] ] 



20 



D- 



40 



100 200 



CHAETOGNATHS / M 



300 

 3 



600 1200 1800 

 DOLIOLIDS / M. 3 



Figure 5. — Vertical distribution of temperature, salinity, and the numbers of sardine eggs, sardine larvae, 

 chaetognaths, and doliolids per cubic meter. The horizontal line represents the beginning of the thermocline. 



