Arkhipkin; Intrapopulation struaure of I/lex argentlnus during its feeding period over the Patagonlan Shelf 



became the most abundant in catches, as in the middle 

 of January. During the second and third 10-day peri- 

 ods of February, hatching-month composition was the 

 same as that of January, with June- and July-hatched 

 squid predominating. However during the third 10-day 

 period, the number of large mature females (280 mm 

 ML) increased considerably (Fig. 4). 



In March, the hatching-month composition of the 

 /. argentinus catch was approximately similar to that 

 of the second 10-day period of February; June- and 

 July- hatched squid were the most abundant. The pro- 

 portion of July-hatched squid increased by the end of 

 March with a corresponding decrease in June-hatched 

 squid. Modal sizes of males increased from 220-230 

 mm ML in the beginning to 230-240 mm ML at the 

 end of the month. Length composition of females was 

 bimodal (240-250 and 290-300 mm ML). The pro- 

 portion of immature females decreased, whereas the 

 proportion of mature females increased by the end of 

 March (Fig. 5). 



In April, hatching-month composition of/, argenti- 

 nus caught over the shelf edge (170-190 m depths) 

 remained almost similar to that of the second and 

 third 10-day periods of March; July-hatched squid 

 were predominant. Almost all males were mature. 

 Immature females disappeared from catches in the 

 first and second 10-day periods of April, but were 

 caught in small numbers in the third 10-day period. 

 At the beginning of the month, the length composition 

 of both maturing and mature females was bimodal 

 (260-270 and 300 mm ML). During the second 10-day 

 period, large maturing and mature females (310 mm 

 ML) began concentrating over the shelf edge, whereas 

 medium-size females (270-280 mm ML) were still 



dispersed (Fig. 6). These concentrations caused 

 another increase in CPUE for the fishing fleet (Fig. 

 2). During the third 10-day period of April, large 

 mature squid (females of 310-320 mm ML and 

 males of 270 mm ML) appeared in deeper waters 

 over the continental slope, and they became most 

 abundant at 480-630 m depths. Medium-size squid 

 (maturing females of 280 mm ML and mature males 

 of 250 mm ML) remained over the shelf edge (Fig. 6). 



Region 47-49°S During the first 10-day period of 

 February, the length composition of males was uni- 

 modal (230 mm ML) and most of these males were 

 mature. Among females, two different modal groups 

 occurred in the catches: immature June-hatched 

 females (220 mm ML) and maturing and mature 

 April- and May-hatched females (260 mm ML). 

 Large catches of June- and July-hatched squid were 

 evident between the second 10-day period of Feb- 

 ruary and first 10-day period of March (Fig. 2). 

 Hatching-month compositions did not change sig- 

 nificantly in this period, June- and July-hatched squid 

 were caught almost in equal proportions. Mature 

 males increased slightly in length from 230 to 240 mm 

 ML. The proportion of immature females decreased 

 and that of maturing and mature females increased 

 by the second 10-day period of March (Fig. 7). 



Region 51-52°S Hatching-month composition was 

 similar between the third 10-day period of March and 

 second 10-day period of April; July-hatched males and 

 females were predominant in catches. Length compo- 

 sitions were unimodal for both sexes. Except during 

 the third 10-day period of March when about a third of 

 males were maturing, most of the males were mature, 

 and their sizes increased from 260 mm ML at the end 

 of March to 280 mm ML at the end of April. Females 

 grew more rapidly in length than did males (from 

 280 to 320 mm ML). They matured quickly; imma- 

 ture females prevailed at the end of March, whereas 

 maturing females were predominant at the end of 

 April. During the third 10-day period of April, age 

 composition of/, argentinus changed owing to a high 

 proportion of August-hatched squid (Fig. 8). 



Comparative comments 



Simultaneous sampling in the regions of 45^7°S and 

 47^9°S between February and March and in the 

 regions of 45-47°S and 51-52°S between March and 

 April enabled a comparison of both length and hatching- 

 month compositions of/, argentinus in these regions. 



Hatching-month compositions were almost similar 

 in the regions of 45-47°S and 47^9°S during the 

 same 10-day periods (Figs. 4, 5, and 7). Modal sizes 



