Illex argentinus: life cycle, population structure, and fishery

Since the establishment of the Falkland Islands Conservation and Management Zone (FICZ) in 1986, catch and effort data for Illex argentinus have been reported to the Fisheries Department of the Falkland Islands Government, and observers have collected biological data aboard commercial vessels fishing within the zone. I. argentinus are caught in the FICZ between March and lune. Early in the season the fishery is concentrated to the north of the FICZ and later spreads to approximately 52-53°S. By June the fleet has shifted to the northwest of the zone. Catches and catch rates peak early in the season and decline thereafter. Male squid recruit into the fishery at a modal mantle length of about 200 mm and grow to about 300 mm by the end of the season, and females recruit at approximately the same size and grow to some 350 mm. For both sexes this is generally in agreement with data derived from growth increments in the statolith. At the time of recruitment, males are more sexually mature than females. Maturation in both sexes proceeds with growth and most squid migrate out of the fishery about one month before the estimated peak time of hatching of the next generation. Squid maturing early in the season are smaller than those maturing later. Data from the fishery are consistent with the hypothesis that the spawning grounds of I. argentinus are towards the north of the Patagonian Shelf, that eggs and larvae develop in the Brazil Current, and the squid then spread over the shelf to feed, grow, and mature. There is evidence that squid on the spawning migration follow the northerly flow of the Patagonian Current to the west of the Falkland Islands.