Fishery Bulletin 98(1) 



Females 



190 m 



100 leO loo 360 300 360 400 



480 m 



Ida aoo >6o 300 



630 m 



100 wo 200 260 SCO 360 400 



Mantle length ^mm) 



Males 



Age structure 



190 m 



190 m 



200 260 300 360 



480 m 



480 m 



630 tn 



630 m 



wo 160 100 260 300 360 400 



1 



Mantle lengtti (mm) 



Hatching month 



Figure 6 



Length-frequency and hatching month compositions (age structures) of Ulex argentinus at different depths of the fishery region of 

 45-47°S outside the EEZA between 21 and 30 April 1991. Symbols are the same as in Figure 4. 



hatching-month compositions were practically similar 

 to those for the continental slope (630 m) at 45-47°S 

 and shelf (190-210 m) of 51-52°S. However, in spite 

 of the similarity in modal length both in males and 

 females in the last case, most of the females were 

 mature in 45-47°S, whereas those at 51-52°S were 

 still maturing (Figs. 5 and 8). 



Discussion 



Stock structure dynamics 



Studies of the length-at-age structures for immature, 

 maturing, and mature squid (separately! of both sexes, 

 with a 10-day interval, revealed in detail the intrapop- 

 ulation structure dynamics and migratory patterns of 

 /. argentinus during the January-April feeding period 

 on the Patagonian Shelf Previous investigations, in 

 which length-at-age data were pooled separately for 



each sex, revealed only general patterns in the age 

 structure dynamics of/, argentinus (Rodhouse and 

 Hatfield, 1990; Uozumi and Shiba, 1993). 



Stock structure of winter-hatched /. argentinus was 

 rather stable during the feeding period (January- 

 April). After massive immigration of June- and July- 

 hatched squid into the region 45^7°S from the end 

 of January through the beginning of February, prob- 

 ably from an area farther north on the Patagonian 

 Shelf (Hatanaka, 1988; Parfeniuk et al, 1992), the 

 age structure of squid remained rather stable until 

 the middle of April. During each 10-day period, from 

 four to five month classes were observed, similar to 

 the number obtained from the jigging fishery data 

 (Uozumi and Shiba, 19931. Predominance of monthly 

 classes changed gradually fi'om June-hatched squid 

 in February to July-hatched squid in March-April. 



A considerable portion of the June and July-hatched 

 squid continued their southward feeding migrations 

 and reached 47-49°S by the end of February, which 



