Reproductive biology of the short-finned squid Illex coindetii (Cephalopoda, Ommastrephidae) of the northeastern Atlantic

For the purposes of this study, 5 311 post recruit of Illex coindetii were collected from the fishery on the Galician shelf, with sizes ranging from 32 to 379 mm dorsal mantle length (ML). Samples were taken monthly from November, 1991 to October, 1992. Sexual maturation, spawning season and population structure of Illex coindetii were analyzed. The spawning season extended throughout the year reaching a peak in July-August, with size at first maturity in males, 128 mm ML and in females, 184 mm ML. Males mature at a smaller size and attain lower size (279 mm ML) than females (379 mm ML). The sex ratio of the whole population sampled was slightly biased towards males, nevertheless monthly variations observed and the ratio obtained(1.09 : 1) does not suggest that there is spatial segregation by sexes in the fishing ground. From the total sample, 185 males and 281 females, covering the whole range of ML's, were randomly separated out to calculate maturation indices. A correlation between the subjective scales and the values of these indices was established in both sexes. The nidamental gland length proved to be a reliable parameter for distinguishing between stages of maturity in females. The fecundity of the species varied between 3 500 and 285 000 oocytes, (the most frequent range being from 30 000 and 200 000 oocytes) in the ovary and the oviducts. The principal axis of the vitellogenic oocytes and eggs varied between 0.8 and 1.2 mm. It was estimated that 1 g of eggs in the oviduct contained 2 331 +/- 912 eggs. The number of spermatophores in the spermatophoric sac varied between 81 and 1 555, and it was observed that the number and the length of the spermatophores tended to increase with size of the males. Illex coindetii may be considered as an intermittent spawner.