YELLOWTAIL FLOUNDER OFF NEW ENGLAND 



219 



Interpretation of the survey data would be 

 easier if we had more information on the dura- 

 tion of the egg and larval stages. Bigelow and 

 Welsh (1925) report that hatching takes place in 

 5 days at a temperature of 10° to 11° C. They 

 judge further, from the stage of development, 

 that the larvae descend to the ocean bottom when 

 14 mm. long, although Perlmutter (1939) re- 

 ported that postlarvae caught in the bottom trawl 

 ranged up to 12.6 mm. in length. This does not 

 agree with Bigelow and Welsh's observation of 88 

 pelagic larvae 6.5 to 19 mm. long caught in a tow 

 net off Sandy Hook on August 1, 1913. We con- 

 clude from these facts that the yellowtail may go 

 to the bottom at lengths less than 12 mm., or even 

 more than 19 mm., depending on conditions, but 

 we remain ignorant of the duration of the larval 

 period. 



Horizontal distribution, of eggs and larvae in 

 1929. — The plankton hauls during 1929 were made 

 with nets, either 1 meter or V2 meter in diameter, 

 towed horizontally at various levels at an average 

 speed of 1.2 knots. The forepart of the nets had 

 29 to 38 meshes per linear inch, the rear part 48 

 to 54 meshes. For purposes of this paper, the 



hauls have been reduced to a standard basis of 

 20-minute tows with 1-meter nets. 



During the April and May 1929 cruises, eggs 

 and larvae of the yellowtail flounder were the 

 dominant vertebrate form in the plankton (tables 

 41 and 42). The number of eggs taken ranged up 

 to 37,000 at one station in April and to 79,000 

 in a tow in May. The eggs were taken on the 

 April 12 to 24 cruise from the offing of Currituck, 

 Va., to the northeasternmost stations off Block 

 Island (fig. 26), but there was an impressive cen- 

 ter of distribution off the coasts of northern New 

 Jersey and Long Island. During the May 10 to 

 18 cruise, the southern limits of distribution of 

 the eggs had moved about 150 miles to the north- 

 east and a similar though less extensive movement 

 was apparent in the principal center of the distri- 

 bution, although a secondary center remained off 

 Atlantic City. Distribution of the larvae corre- 

 sponded closely to that of the eggs in both the 

 April and May cruises though, of course, the num- 

 bers of larvae were markedly smaller. 



The southern and offshore limits of the distri- 

 bution of eggs in the April cruise agree 'well with 

 the position of the 7°-C. isotherm at both surface 



Table 41. — Numbers of yellowtail eggs and larvae taken on the April 12-24 cruise in 1929 

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



