FISHERY BULLETIN: VOL. 79. NO. 4 



Sampling times (EST) 



e 



o 

 o 



0) 



700 



600 - 



500 - 



400 - 



O 300 - 



0) 



E 



200 - 



100 



L 



o 



::^ 



-a 



iD" 



FIGURE 7. — Average number of At- 

 lantic whiting eggs from spawning 

 to hatching plotted by developmental 

 stage and time of day. based on collec- 

 tions made during the vertical distribu- 

 tion study of ichthyoplankton in the 

 Middle Atlantic Bight, July 1974. 



Developmental stage 



the eggs were spawned. According to Stokes' law, 

 Atlantic whiting eggs would have a rising velocity 

 of 1.18 m/h or about 3.5 m during the 3-h interval 

 between samples. Based on this and the fact that 

 newly spawned eggs were taken primarily in the 

 and 4 m nets, the adults were spawning in the 

 upper 10 m of the water column. 



An overall mean of 30 Atlantic whiting larvae/ 

 100 m^ was taken during the cruise. The numbers 

 of larvae showed significant differences for all 

 three primary factors (depth, time of day, and 

 days) (Table 2). In general, the number of larvae 

 caught increased with increasing depth (Figure 

 3). Significant numbers of larvae may have oc- 

 curred below our 30 m sampling depth. A com- 

 parison of the numbers of larvae taken in the 15 

 and 30 m tows at various times of day (Figure 8) 

 shows that more larvae were caught at 30 m 

 during the day, while at night many more larvae 

 were taken at 15 m. In general, more larvae were 

 caught at night; however, on day 3 more were 

 taken in the daytime. The larvae either avoided 

 the nets more effectively in the daytime or more 

 larvae migrated upward into the range of the 

 nets at night. 



Figure 9 shows the average lengths of larvae 

 caught at 15 m and at 30 m. During the daytime, 



the 4.5 mm larvae were at 15 m while 6.5-9.2 mm 

 larvae stayed at 30 m. At night, large larvae (6-9 

 mm) were at both 15 and 30 m, probably mixing 

 with the small larvae, some of which may have 

 sunk between 1800 and 0000 h, based on the de- 

 crease in mean length at 30 m and the increase 

 in mean length at 15 m. 



1800 2100 0000 0300 



SAMPLING TIMES (EST) 



0900 



Figure 8. — Mean percentage of Atlantic whiting larvae at 15 m 

 relative to larvae at 30 m by time of day from the vertical 

 distribution study of ichthyoplankton in the Middle Atlantic 

 Bight, July 1974. 



716 



