Fishery Biology and Ecology of the Marine Snail, Turbo militaris

Kate Seinor

doi:10.25918/thesis.462

Demands for the ocean’s resources have risen alongside expanding populations, underscoring the need for improved management. A sound understanding of a target species’ biology and ecology is pivotal to effective fisheries management. However, research is often limited in small-scale fisheries and for invertebrates. Turbo militaris is a large rocky-reef gastropod endemic to the east coast of Australia across ~ 8° of latitude. Turbo militaris is harvested by cultural, recreational and commercial fisheries for its high-quality meat and large size. Efforts to manage T. militaris stocks are currently hampered by data deficiency, especially regarding life-history. Consequently, this work aims to increase the knowledge base on T. militaris, thereby providing a valuable case study for informing other gastropod fisheries. A shell-drilling and gonad-biopsy procedure was developed as a non-lethal method for reproductive sampling in T. militaris. Reproductive periodicity in T. militaris was assessed at two locations spatially separated by ~3° of latitude, using gonadosomatic index measures and oocytes obtained using the drill-biopsy method. T. militaris showed prolonged reproductive activity, with peak ripeness in warmer months and spawning over multiple events, mainly in winter. Reproductive timing was asynchronous between locations and linked to environmental variables such as sea surface temperature. A mark-recapture study was conducted to assess the mobility and growth of T. militaris at subtropical and temperate locations along eastern Australia. Movement patterns were similar across rocky shores; displacement distances were localised and non-directional, with limited upshore-to-downshore mixing. These findings suggest that harvested intertidal populations are not readily replenished, and unsuitable habitats may inhibit snail movement confining adult snails to each rocky shore. Thus, heavy harvesting may considerably impact local populations, especially for snails in shallow areas, while deeper habitats may be safeguarded due to limited accessibility. Turbo militaris grows rapidly and can live up to 10 years. Growth varies latitudinally, with temperate snails growing faster, attaining a larger average size, having higher natural mortality and a shorter lifespan than subtropical snails. This indicates a potentially higher turnover for the temperate populations and thus a greater resilience to stress, whereas the subtropical snails may be more susceptible to overfishing or other environmental impacts due to slower recovery. Sexual maturity was attained by temperate snails in less than one year and within two years for subtropical snails, allowing approximately 1.5 years for temperate snails and 4.4 years for subtropical snails to reproduce prior to entering the fishery. Therefore, current minimum size limits offer suitable protection across the fishery to ensure population replenishment. Should further management be required, decreased bag limits or total allowable catch for commercial fisheries may be necessary, especially in subtropical regions. Furthermore, due to limited adult movement and extended, asynchronous reproduction, spatial protection in favourable habitats would be suitable for reducing harvesting impacts and safeguarding existing adult populations. This research has substantially enhanced our knowledge on the biology and ecology of T. militaris. Turban snails are ecologically important and are valuable fisheries resources with cultural significance. By addressing data deficiencies on T. militaris, this research provides empirical data that supports the management of this important, spatially restricted species.

Fishery Biology and Ecology of the Marine Snail, Turbo militaris

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Fishery Biology and Ecology of the Marine Snail, Turbo militaris

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