A comparison of the fishery biology of three Illex coindetii Vérany, 1839 (Cephalopoda: Ommastrephidae) populations from the European Atlantic and Mediterranean waters

Three populations of the short-finned squid Illex coindetii were simultaneously sampled and studied from the Southern Celtic Sea and Bay of Biscay, Portuguese waters and Greek Seas, during a EU funded project (FAIR CT 1520). Dorsal mantle length (DML) ranged from 24 mm to 360 mm and body weight (BW) from 2.4 g to 1630 g. Modal progression analysis (MPA) indicated a female life span of 13–18 mo and in male life span of 11 mo. Length-weight relationship was found to be positively allometric for males and negatively allometric for females in all three populations. Sex ratio did not differ significantly from 1:1 over the entire sampling period. Differences among the three populations were observed for the following life-cycle parameters: (1) males from the Portuguese waters had significantly different length-weight slopes from those from the remainder areas; (2) size at full recruitment was determined at 110 mm in females from the Portuguese waters whereas in females from the Southern Celtic Sea and Bay of Biscay and from the Greek Seas was 170 mm; (3) female recruitment peaks were recorded only during autumn in samples from the Southern Celtic Sea and Bay of Biscay while in those from the Portuguese waters and the Greek Seas the recruitment peaks were recorded at various seasons; (4) maturing and mature males were found abundantly over the entire sampling period in the samples from the Southern Celtic Sea and Bay of Biscay and the Greek Seas whereas in those from the Portuguese waters maturing and mature males were at higher percentages than immature ones only during spring and summer; peaks of the Gonadosomatic index, calculated for mature females from the Southern Celtic Sea and Bay of Biscay, were scored from February to April of 1998 and 1999 and during September of 1998 while in the samples from the Greek waters during April and August 1998 and during January and May 1999; (5) L50 (mantle length at which 50% of the individuals are mature) values estimated for both females and males from the three studied areas were gradually decreased from the North Atlantic to the Mediterranean; (6) length data suggest that females from the Greek Seas potentially mature at two modal sizes while those from the remainder areas show only one modal size at maturity. Environmental variables (sea surface temperature and chlorophyll-a concentration) were correlated with some of the biological indices of the I. coindetii populations. Finally, results on biological indices of the I. coindetii are compared with those calculated for its congeneric species I. illecebrosus, I. argentinus as well as with another European ommastrephid species Todaropsis eblanae.