Fishery Bulletin 98(1) 



period that takes place in waters off Brazil and Uru- 

 guay in August-September (Leta, 1987; Santos and 

 Haimovici, 1997); a juvenile period that takes place in 

 shelf and oceanic waters off Uruguay and Argentina 

 in September-December (Biiinetti, 1988; Parfeniuk 

 et al., 1992); a feeding period that takes place on the 

 Patagonian and Falkland Islands shelves in January- 

 April (Brunetti, 1988; Hatanaka, 1988); a prespawn- 

 ing period that takes place on the shelf edge and slope 

 off Argentina and Uruguay in May^uly (Hatanaka, 

 1986, 1988; Arkhipkin, 1993); and a spawning period 

 that takes place in shelf and slope waters off north- 

 em Argentina, Uruguay, and Brazil in July-August 

 (Brunetti, 1988; Santos and Haimovici, 1997). Squid 

 aggregate and are fished mainly during their feeding 

 period on the shelf, as well as during their prespawn- 

 ing period on the shelf edge and slope (Nigmatullin, 

 1989b). 



Stock structure dynamics of /. argentinus during 

 their feeding period on the Patagonian Shelf were 

 studied both in the fishery region of 45^7°S outside 

 the EEZAand within the FICZ by using data obtained 

 fi-om Japanese jigging vessels (Rodhouse and Hat- 

 field, 1990; Uozumi and Shiba, 1993). It was found 

 that the age composition of /. argentinus catches 

 changed between January and April owing to the grad- 

 ual migrations of feeding schools of these squid. Ear- 

 lier hatched squid immigi'ated to and emigrated fi-om 

 the fishery region earlier than later hatched groups 

 (Uozumi and Shiba, 1993). Squid of the former group 

 had slower growth rates than those of the latter group 

 (Rodhouse and Hatfield, 1990). Data from trawling 

 vessels showed that, during the prespawning period, 

 winter-spawned /. argentinus made active northward 

 migrations from the southern Patagonian Shelf along 

 the continental slope of Argentina. Squid migrated 

 in waves of abundance, consisting of 2-4 successive 

 monthly generations. Males moved 2-3 weeks earlier 

 than females of the same monthly group (Arkhipkin, 

 1993). 



An analysis of length-frequency distributions of /. 

 argentinus showed that the jigging fishery had a 

 higher selectivity for squid than did the trawl fishery 

 (Koronkiewicz, 1995), and therefore data from the 

 trawl fishery reflected the natural population distri- 

 bution far better than those from the jigging fishery. 

 In the present report I examined the stock structure 

 dynamics of/, argentinus during the January-April 

 feeding period, using both data from two research 

 vessels and two commercial trawlers (both fishing 

 within the fishery) and statolith aging techniques, 

 and comparing these stock structure data with those 

 obtained by the Japanese jigging fishery both within 

 and outside the EEZA. Together with the data obtained 

 during the prespawning period (April-June) (Arkhip- 



-40°S 



-4i°S • 



-44°S 



-46°S 



-48°S 



-50°S 



-52°S 



-54°S 



-64''W -62°W -60°W -58°W -56°W 



Figure 1 



Sampling locations of Illex argentinus off (circles I and 

 within ( triangles ) the Exclusive Economic Zone of Argen- 

 tina (EEZA) in the southwest Atlantic in January-April 

 1991. 



kin, 1993), the results of the present study make it 

 possible to reconstruct the full picture of the stock 

 structure dynamics of/, argentinus during the entire 

 fishery period. 



Materials and methods 



Data on the Ai'gentine shortfin squid, Illex argentinus, 

 for the present study were collected during four exper- 

 imental surveys carried out in the fishery region of 

 45-47°S outside the EEZA by the Soviet research ves- 

 sels A«c/mr and Volzhanin (2700 GRT) and within the 

 EEZA (in 47^9°S and 51-52°S) by the fishing trawl- 

 ers Petropavlovskaya krepost and Batiliman (4000 

 gross registered tonnage [GRT] ) between January and 

 April 1991 (Fig. 1). Trawls were conducted with differ- 

 ent types of rope trawls with a mean horizontal open- 

 ing of 60-75 m and mean vertical opening of 40-50 

 m. Trawls were made in the superficial water layer 

 at night and near bottom in the daytime at bottom 

 depths ranging from 140 to 190 m in January-March 



