YELLOWTAIL FLOUNDER OFF NEW ENGLAND 



221 



Table 42. — Numbers of yellowtail eggs and larvae taken on the May 10-18 cruise in 1929 

 [Weighted to basis of 20-minute tow with 1-meter net] 



and bottom (fig. 26). (In these shoal waters at 

 this time of year the upper 50 meters or so are 

 nearly isothermal.) The lowest temperature re- 

 corded in any of the stations where eggs were 

 taken was 4.8° C. at the bottom off Montauk 

 Point. Evidently spawning had been proceeding 

 prior to this April cruise when temperature con- 

 ditions of 5° to 7° C. prevailed. 



Recalling Bigelow's observation that hatching 

 occurred in about 5 days at 10° C, we may deduce 

 that hatching would require between 5 and 10 days 

 at these lower temperatures of 5° to 7° C. Since 

 larvae were found on April 18 that were several 

 days old, it is apparent that spawning must have 

 started in this area in early April at the latest. 

 Size of the larvae during the April and May 

 cruises (tables 43 and 44) provides a clue, how- 

 ever, that hatching had not long preceded the 

 April cruise. During this cruise, the larvae 

 ranged from 2 to 6 mm. in length, the bulk of them 

 being about 3.5 mm. These larvae were smaller 

 than those encountered during the May cruise, 

 when the larvae ranged from 3 to 11 mm. in 

 length, and were mostly 4 to 6 mm. 



The close agreement in distribution of eggs and 

 larvae suggests that hatching was completed and 

 that the larvae had assumed their bottom-dwelling 

 existence before much of the horizontal drift oc- 

 curred. If this were not so we would expect a dis- 



placement in the centers and boundaries of the 

 egg and larval distributions. Assuming that 

 hatching was completed and the larvae had de- 

 scended to the bottom, we may then note that the 

 southernmost contingent of eggs and larvae off 

 Virginia and Delaware disappeared from the sur- 

 face waters by the time the temperature had risen 

 above 11° C. Presumably, the eggs found in this 

 area on April 17 to 19 had hatched and the larvae 

 had descended to the bottom by May 14 to 16, 

 when these southern stations were revisited. 



At a station off Fire Island where yellowtail 

 larvae were particularly abundant on May 17 and 

 18, 1929, a special series of tows was made, to de- 

 termine vertical distribution of the larvae ( table 

 45). It may readily be seen that at all times the 

 greatest number was located near the 10-meter 

 level, but considerable numbers were taken during 

 the night at the surface and at the 5-meter level. 

 Relatively few were taken at any time at the 20- 

 and 35-meter levels. This suggests some diurnal 

 dispersion upward from the 10-meter level. Con- 

 siderable differences are also apparent in the num- 

 ber of larvae taken during the night hauls — nearly 

 twice as many larvae being obtained in the mid- 

 night series as were taken in the noon series, 

 whereas morning and evening series were inter- 

 mediate. Since there is no evidence that larvae 

 retreated to levels below the net, it appears likely 



