THE LIFE-HISTORY OF LOLIGO-FORBESI (CEPHALOPODA, LOLIGINIDAE) IN SCOTTISH WATERS

The population biology of the loliginid squid Loligo forbesi is descri bed from monthly samples taken from the Scottish fishery (1990-1992). Length-frequency distributions are complex, particularly in males, wit h several size modes present in each month. Growth rates appear to be variable, with no single equation describing the growth of all putativ e microcohorts. Length-weight relationships vary in relation to maturi ty stage, and a decrease in size-adjusted mantle weight in later matur ity stages indicates the diversion of resources from somatic to reprod uctive growth. The sex ratio among recruits is biased towards males bu t becomes increasingly biased towards females as the animals mature, T here is an extended breeding season, from January to May with a peak i n February-March, and two pulses of recruitment, in April and in July- September. Results are broadly consistent with the previously establis hed view of this species as having a 1 year life-cycle. There is limit ed evidence for the existence of a separate offshore population, breed ing earlier than the main coastal population and with wide interannual fluctuations in abundance. However, improved information on distribut ion is required to test this hypothesis.