Sepia apama have a life span of 1-2 years. Not much is known about their life history outside of the breeding season. Breeding takes place during the austral winter (May to September), when hundreds of thousands of animals aggregate in northern Spencer Gulf to mate and lay eggs. Recent research based on analysis of growth increments of cuttlebones suggests that Sepia apama has two alternative life cycles (for both sexes). The first involves rapid juvenile growth during the first summer after hatching, with maturity reached within 7–8 months. These individuals return to spawn in their first year as small individuals. The second life cycle involves much slower juvenile growth during the first summer, with maturity deferred until their second year, when they return to spawn as much larger individuals.
Hall, K. C., A. J. Fowler, and M. C. Geddes. 2007. Evidence for multiple year classes of the giant Australian cuttlefish Sepia apama in northern Spencer Gulf, South Australia. Rev Fish Biol Fish 17: 367-384.
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