This paper explores effects of environmental variability on the life cycle of the chokka squid, Loligo vulgaris reynaudii in South Africa, particularly the effect of physical and chemical influences on adult distribution, and the availability of spawning aggregations to the local jig fishery. The following hypotheses are presented: 1) temperature, dissolved oxygen and currents have a direct effect on the demersal distribution of adult chokka on the feeding grounds, but this is restricted to the west coast where environmental conditions are more extreme relative to the south coast, 2) chokka catches increase in proportion to the extent of coastal upwelling, 3) spawning behavior along the inshore regions (<50m) is strongly influenced by turbidity near the seabed. High turbidity forces the spawning popuation to lay their eggs in deeper waters, and are thus not available to the jig fishery. 4) El Niño – Southern Oscillation (ENSO) events are linked with large fluctuations in the availability of spawning squid aggregations to the inshore jig fishery.

Martialia hyadesi were collected from fishing vessels at the Antarctic Polar Frontal Zone (APFZ) and the Patagonian Shelf Edge (PASE) during the 1989 austral autumn and winter. Squid were measured, weighed, assigned a maturity stage and the paired statoliths were removed. Statolith sections revealed concentric growth rings using light and scanning electron microscopy. Counts of these putative daily micro-growth increments were made directly and by an estimating procedure. Energy dispersive (ED) and wavelength dispersive (WD) x-ray analyses of Sr and Ca content were made on subsamples of statolith sections. Estimated increment counts, which were generally higher than direct counts, were adopted for routine application. Back calculated hatching dates showed that a single cohort, with a relatively narrow size range, was sampled in each geographical area. Back calculations suggested that M. hyadesi at the APFZ had hatched in the austral winter and those at the PASE had hatched in the spring. At the PASE, growth rate was estimated to be some 30% higher than at the APFZ and PASE squid were more mature at a given age. The hypothesis that the Sr:Ca ratio along the growth axis of the statolith contains information on thermal history was examined. Sr:Ca ratios in the statolith fell in the range 0.009–0.017 and varied systematically but this variation did not apparently relate to season and ratios were not significantly different between geographical areas. A consistent feature was a relatively low Sr:Ca ratio at the time of hatching. According to the Sr:Ca thermometer hypothesis this is consistent with spawning in relatively warm water but it could equally be due to depositional differences during early statolith growth. The Sr:Ca thermometer hypothesis could neither be confirmed nor rejected by the data but there is evidence that strontium varies systematically with age in the squid statolith.

Recent studies of Falkland Islands seabird diets have found that Gonatus antarticus is a major prey item for a number of penguin species. Rockhopper (Eudyptes chrysocome), gentoo (Pygoscelis papua) and Magellanic (Spheniscus magellanicus) penguins breeding in the Falklands are estimated to consume several thousand million Gonatus per annum, with mean dorsal mantle lengths of 28–42 mm. Aspects of the distribution and growth of the G. antarcticus stock in the vicinity of the Falkland Islands are discussed.

Ommastrephid squids undergo remarkable morphological change during the transition from planktonic paralarvae to adults. These changes are characterized by changes in the relative growth of body dimensions and mark phases and stages in post-embryonic development. The following morphometric characters of paralarval and juvenille Illex argentinus ranging in size from 1–55 mm ML were measured: dorsal mantle length (ML), mantle width (MW), head width (HW), eye diameter (ED), right arm lengths (AIL) (AIIL) (AIIIL) (AIVL), proboscis length (PL), proboscis division (PD), fin length (FL), fin width (FW), right tentacle length (TL), club length (CIL), dactylus length (DL) and carpus + manus length (CML). The relative growth of AIL, AIIL, AIIIL, HW and ED, showed discontinuities at c. 14 mm ML, while AIL, AIIL, AIIIL, AIVL, FL, and TL showed other discontinuities at c. 28 mm ML. These discontinuities seem to be related to the activity and ability of the animal to obtain food and survive in different environments. At an early phase (1–14 mm ML), there is a rapid development of the arms, suckers and fins. In the second stage (14–28 mm ML) there is a rapid development of the tentacles and clubs. In the third (>28 mm ML), the juvenile grows more in length in relation to other body parts. No morphological change, besides the proboscis division, takes place at the end of rhynchoteuthion stage. This may indicate the necessity for re-evaluation of the paralarval phase in Ommastrephidae.