In general, the sex ratio in the populations is thought to be 1:1. However, there is a highly skewed male-biased operational sex ratio in the spawning aggregation (up to 11:1). This is the highest known among cephalopods. The change in the S. apama sex ratio during the spawning season (from more to less skewed towards males) suggests that males arrive before females at the start of the season. Therefore, males may not aggregate in response to a concentration of females, but rather at a particular location or habitat type. Recent genetic evidence (using allozyme electrophoresis, microsatellites and mitochondrial nucleotide sequences) has revealed three major genetically distinct groups of Sepia apama. It has been recommended that each of these groups be managed separately to preserve genetic diversity.
Hall, K. C. and R. T. Hanlon. 2002. Principal features of the mating system of a large spawning aggregation of the giant Australian cuttlefish Sepia apama (Mollusca : Cephalopoda). Mar Biol 140: 533-545
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