AGE, GROWTH, STOCK STRUCTURE AND MIGRATORY RATE OF PRESPAWNING SHORT-FINNED SQUID ILLEX-ARGENTINUS BASED ON STATOLITH AGING INVESTIGATIONS

Biological and fishery features of the waves of abundance of Illex argentinus in three fishery regions - 52-degrees-S (shelf with 180-230 m depths in exclusive economic zone of Argentina-EEZA), 46-degrees and 42-degrees-S (continental slope with 600-800 m depths off the EEZA) in April-June 1990 were studied. According to age analysis of 629 statoliths made aboard, age-length structure of each wave of abundance were determined. In April-June active spawning migrations of I. argentinus were observed from feeding grounds located in limits 50-52-degrees-S along the continental slope northwards through 46-degrees and 42-degrees fishery regions. Only winter-hatched squids (hatched from June to September of the previous year) took part in migrations which were observed as waves of abundance in all three regions. Each migratory wave of abundance consisted of 2-4 successive monthly generations. The start of spawning movement was corresponded with the age and maturity state of the squid. Squid of all monthly generations began migrating from the 52-degrees-S region at a mean age of approximately 250 days, passed through 46-degrees-S at mean age 280 days and through 42-degrees-S at mean age 295 days. Males migrated 2-3 weeks earlier than females of the same generation. Rates of somatic growth were very low during migrations from 52-degrees to 46-degrees-S (RDGR - 0.13% mantle length (ML) in mature males and 0.2% ML in maturing females). During movement from 46-degrees to 42-degrees-S and, obviously further, mature squids practically ceased somatic growth. Estimated rate of migrations was 23.2-28.9 km day-1 (including current velocity), or 26-30 cm s-1 (0.47 body length s-1). Spawning was considered to occur on the continental slope of Uruguay and Brazil north of 35-degrees-S in July-August. Methodical approaches of efficient determination of squid age, growth and stock structure by means of investigation of squid biological features and statolith microstructure in each distinguished wave of abundance were elaborated.