Early life growth of the short-finned squid, Illex illecebrosus (Mollusca: Cephalopoda), was reconstructed from periodic increments deposited on the gladius structure of squid collected in the Gulf Stream/Slope Water front and the Scotian Shelf. The general effects of environmental changes and lifestyle transitions in the variation of size-specific gladius growth was investigated. The offshore growth was exponential and at least six size-specific growth phases were distinguished. Paralarval growth ended at approximately 10 mm gladius length (GL). An important change in growth at 30–40 mm GL was associated with the shift from the macroplanktonic to micronektonic habitats and the transition from the Gulf Stream to Slope Water. The approximation to the Scotian Shelf/Slope Water Front was suggested as related to a growth transition at 68 mm GL. A change to linear growth occurred after the nektonic lifestyle was attained on shelf waters (90 mm GL).