The population size structure of Loligo is complex and unstable. Size and age are not consistently related, consequently length-based assessment methods are not generally applicable. Multivariate analysis of morphometrical data, and isozyme elecrophoresis, shows that Loligo forbesi populations from the coastal waters of mainland Europe are rather homogeneous, but that those from the Azores are a distinct stock. Loligo forbesi and L. vulgaris are annual species with a peak of seasonal maturity and breeding in the winter (December-May) throughout the geographical range. Sexual maturity occurred at two distinct size classes, more obviously in males than females. This was not explained as different ages at maturity but suggested alternative growth rates perhaps arising genotypically, or from different migratory strategies or ecological conditions. Males grow larger than females, mature about 1 month earlier and recruit earlier to the fishery. Female fecundity estimates vary between 1000-23000 eggs but are not strongly related to body size. Egg size frequency distributions suggest a protracted, batch-spawning mode of egg laying. There is seasonal recruitment to the fishery but in some areas two periods of recruitment may not be compatible with the timing of breeding.
Fish, including many commercially important species were the dominant prey of Loligo. Squid of all types are eaten by fish, seals, cetaceans and seabirds, although quantitative estimates of consumption by these trophic levels were low. Catches of squid by European countries and from EC north east Atlantic waters have been rising over the period 1980-90. Currently this catch supplies only a minor component of the European market for squid, the balance is made up by imports. The squid catch in the northern part of the range shows wide fluctuations in abundance by area and by season. The applicability of assessment methods for these stocks is limited by inadequate and inaccurate statistical information, and because nearly all of the catch arises as a by-catch from finfisheries. Potential for increasing the catch and applying possible management methods lies in placing greater emphasis on developing directed fishing by alternative fishing methods, or by selected area and season.
A new collaborative European project on cephalopod fisheries in the north east Atlantic has started (1993-95). This will investigate stock structure and interactions by genetic methods; make direct estimates of growth and the use of biochemical indices of growth and condition; continue to collect population data, fishery statistics and reproductive assessments; larval and pre-recruit surveys will be evaluated; age determinations, based on daily increments of statolith growth, will be introduced and used to test hypotheses on population structure and life cycle biology as well as facilitate the use of age-based assessment methods.
See also: Fisheries Research 21, 1-314.