HORIZONTAL DISTRIBUTION, GROWTH AND DYNAMICS OF DISPERSAL 353 



There is also the possibiUty, and we cannot ignore it, that the larvae, to a certain degree at least, 

 can resist the surface drift. Bishai (i960) has shown experimentally that 1-5 day old herring are 

 not entirely passive drifters, that they respond positively to current, orientate themselves against 

 it, and try to resist it by swimming upstream, keeping station for at least an hour in face of a 

 current with velocity between 0-58 cm. /sec. (0-013 rnile/hr.) and 1-03 cm./sec. (0-023 rnile/hr.). At 

 higher velocities they drifted with but not so fast as the current. Day old herring (average length 

 6-5 mm.)^ subjected to a current of 7-60 cm./sec. (about 4 miles a day) drifted along at an average 

 rate of only 4-2 cm./sec. 



LONGITUDE 



ADOLESCENT 



FURCILIA 6 



5 



1. 4 



3 



2 



I 



ADOLESCENT 



FURCILIA 6 



5 



I. 4 



■I 3 



|> 2 



I 



ADOLESCENT 



FURCILIA 6 



5 



M 4 



" 3 



M 2 



" I 



ADOLESCENT 



FURCILIA 6 



■ ■ 5 



4 



ADOLESCENT 



FURCILIA 6 



5 



4 



00° 00° 01° 02° 02° 03° 04° 05° 05° 05° 06° 13° 14° 15° 16° 17° 20° 



+ 



JULY 



Scale per cent I I I 



^ O 50 100 



AUGUST 



+Tf^f 



Scale per cent 



TT 



Scale per cent 



"JH- 



SEPTEMBER 



Scale per cent 



TTTTTTT" 



' ,L . I Scale per cent OCTOBER 



NOVEMBER 



T 

 f 



LONGITUDE 

 ADOLESCENT 

 6 FURCILIA 

 5 

 4 

 3 

 2 



ADOLESCENT 



5 FURCILIA 



5 



4 



3 



2 



I 



ADOLESCENT 



6 FURCILIA 



5 



4 " 



3 " 



2 " 



I 



ADOLESCENT 

 5 FURCILIA 

 5 

 4 



ADOLESCENT 

 6 FURCILIA 

 5 " 



4- 



Fig. 105. Developmental condition of the young winter and spring swarms in Weddell East, showing the 



swarms in the west, the younger in the east. 



older 



The southern or East Wind zone. Whereas in the Weddell stream the larval growth-rate can be 

 followed with some degree of precision throughout the whole year, in the East Wind drift it can only 

 be followed with certainty from January to April (p. 321, Fig, 83), the onset of winter conditions 

 in May preventing further access, or at any rate further effective access,^ to these high latitudes 

 for the rest of the year. For 8 months, from May to December, they remain largely frozen over 

 and it is not until January of the following year, 1 1 months after the earliest recorded major East 

 Wind rising (p. 310, Fig. 74), that the developmental condition of the i-year old swarms en- 

 countered then permits some estimate to be formed of what the larval growth-rate below the winter 

 ice might be, and of how long the young first year swarms in the extreme cold and prevailing 

 darkness of their wintry environment exist in a purely larval, or principally larval, developmental 

 phase. 



' This is about the average length of the Second Furcilia o E. superha. 



^ Certain narrow strips of the extreme northerly reaches of the East Wind zone are in fact occasionally accessible in May 

 (p. 348, Fig. 102). Such parts as remain open, however, lie for the most part (p. 346, Figs. 100 and loi) outside the main 

 East Wind region of larval abundance. 



41 



