The life history of Loligo forbesi (Cephalopoda: Loliginidae) in Scottish waters

The population biology of the loliginid squid Loligo forbesi is described from monthly samples taken from the Scottish fishery (1990-1992). Length-frequency distributions are complex, particularly in males, with several size modes present in each month. Growth rates appear to be variable, with no single equation describing the growth of all putative microcohorts. Length-weight relationships vary in relation to maturity stage, and a decrease in size-adjusted mantle weight in later maturity stages indicates the diversion of resources from somatic to reproductive growth. The sex ratio among recruits is biased towards males but becomes increasingly biased towards females as the animals mature, There is an extended breeding season, from January to May with a peak in February-March, and two pulses of recruitment, in April and in July-September. Results are broadly consistent with the previously established view of this species as having a 1 year life-cycle. There is limited evidence for the existence of a separate offshore population, breeding earlier than the main coastal population and with wide interannual fluctuations in abundance. However, improved information on distribution is required to test this hypothesis.