Latitudinal variation in age and growth of a harvested, rocky-reef gastropod (Turbinidae)

Abstract

In Australia, the military turban Turbo militaris Reeve 1848 is culturally, commercially and recreationally fished. Fishery regulations include a bag limit of 20 snails and a minimum legal-size limit of 75 mm. Yet, there is limited biological knowledge to inform management. Mark−recapture surveys were used to assess growth and develop age-and-growth models for T. militaris at two subtropical (29.4 °S and 29.8 °S) and two temperate (both 32.7 °S) rocky shores in eastern Australia. Growth varied between subtropical and temperate regions separated by < 400 km. Temperate snails attained a larger asymptotic size than subtropical snails (108 mm vs 94 mm), a greater growth coefficient (K) (0.57 y⁻¹ vs 0.29 y⁻¹), a higher rate of natural mortality (M = 0.57 y⁻¹ vs 0.37 y⁻¹) and shorter lifespan (T_max = 5 years vs 10 years). Sexual maturity (37 mm, 95 % CI: 35–39 mm) was attained by temperate snails at 0.7 years (range: 0.7–0.8 years), allowing ∼1.5 years before entering the fishery. In contrast, subtropical snails reach sexual maturity at 1.7 years (range: 1.6–1.8 years), having ∼4.4 years before reaching the harvestable size. Our findings indicate that current minimum legal-size limits are appropriate across the fishery for ensuring population replenishment. Yet, climate change may impact the growth pattern of T. militaris. The fast-growth and shorter lifespan of temperate snails suggests greater resilience to environmental stressors due to higher population turnover. In contrast, subtropical snails likely have slower population recovery, reflecting greater vulnerability to stressors or depletion by overfishing.