Extended and spatially asynchronous reproductive periodicity in a harvested, warm-temperate rocky-reef gastropod (Turbinidae)

Turban snails are targeted for their high-quality meat and, consequently, are often subjected to heavy harvesting pressure. Managing recreational and small-scale fisheries is challenging, partly due to a lack of biological data underpinning certain regulatory measures. This study aimed to fill current knowledge gaps on the reproductive cycle of the recreationally and culturally harvested Australian turbinid, Turbo militaris. The objectives were to investigate the reproductive timing of T. militaris in New South Wales (NSW) and identify likely environmental drivers of reproductive periodicity. Oocytes and gonads were sampled from wild animals monthly over 15 months at two sites separated by ~500 km. Analysis of oocyte size frequency and gonadosomatic index revealed that T. militaris has a pattern of extended reproduction, which is synchronous between sexes. Turbo militaris was ripest during summer, and spawning appears to have occurred over multiple events, although primarily during winter. Reproductive timing was associated with environmental explanatory variables, including sea surface temperature, wave height, salinity, phytoplankton and nitrate concentration, together accounting for 81% of the variation in oocyte size frequency and 67% in the gonadosomatic index. Reproductive periodicity was correlated with wave conditions and phytoplankton concentrations inconsistently between sites, indicating that the effect of some environmental conditions may be unpredictable or site-specific. Reproductive timing was asynchronous between two sites in the NSW fishery, posing challenges for designing seasonal fishing closures and community-based harvesting rules. Spatial closures for species with spawning over extended timeframes, or spatially asynchronous reproductive cycles, are potentially more suitable for achieving fisheries management objectives.