Batch or trickle: understanding the multiple spawning strategy of southern calamary, Sepioteuthis australis (Mollusca : Cephalopoda)

Abstract

Many cephalopods are ‘multiple spawners’; however, we know little about the timing and dynamics of egg production. This has implications for the allocation of energy to reproduction, lifetime fecundity and subsequent recruitment. The current study aimed to determine if Sepioteuthis australis (Quoy and Gaimard, 1832), which spawns multiple times, produces mature oocytes for deposition in a continuous trickle or in larger discrete batches. Throughout a spawning season, developmental stages were assigned to the ovaries of each female by combining macroscopic and histological analyses of the oocytes. Half of the females (46%) showed a significant peak in oocytes at one of the maturation stages, indicating that females were developing eggs in batches. It was hypothesised that the remaining females were also batch spawning, given that the oviduct weights of the remaining females (54%) were high and the other measured biological characteristics were similar to those of the females showing a peak in oocyte stage. Average batch fecundity declined over the 3-month spawning season, but total egg numbers in the ovary increased, suggesting that females might have deposited small batches more often during December. As reproduction requires large allocations of energy, understanding how females distribute reproductive effort throughout their lives is crucial to understanding the behaviour of populations, individuals and their offspring.