Although never seen in nature, gelatinous egg masses up to 1 m in diameter containing 10,000
to 100,000 eggs have been produced in captivity by female Illex illecebrosus swimming in mid-water in the 15 m diameter Aquatron pool. When incubated at temperatures between 13 and 26°C these masses produced viable hatchlings whose behaviours were observed and recorded. The hatchlings sink at 5 mm s-1, swim vertically at speeds up to 26 mm s-1, hover and avoid both the surface and
the bottom. Metabolie rates estimated from rates of yolk utilization and calculated values for swimming costs were used to predict " critical periods'' or survival times for unfed hatchlings in various temperature and activity regimes. Theseare discussed in relation to the hypothesized role of the Gulf
Stream in distribution of the hatchlings of this commercially important but still poorly understood squid species. Potential benefits from vertical migration are suggested and a comparison with Loligo
opalescens made
