Vine, N.G.Mzozo, Ziyanda Brightness2026-08-172026-08-172024-10Mzozo, Z.B. (2024) Factors influencing the larval settlement of abalone (Gastropoda: Haliotis midae): considerations for stock enhancement and ranching. PhD thesis. Alice: University of Fort Hare.http://hdl.handle.net/20.500.11837/4826PhD thesisThe South African wild abalone, Haliotis midae, is essential for critical commercial fisheries; however, the population has declined significantly over the past four decades due to overfishing and poaching. This thesis was developed in response to the decline of wild abalone stocks and the high costs associated with seeding juvenile abalone to help improve the wild population. Concerns over these costs have led to increased interest in seeding abalone larvae, as millions can be produced in a basic hatchery, resulting in lower expenses. A series of hatchery-based and ocean-seeding experiments were conducted to establish baseline methods and make recommendations for enhancing or ranching competent H. midae larvae. In one hatchery experiment, the impact of temperature on the development and settlement of H. midae larvae was assessed. The results indicated that both larval development and settlement improved with every 2°C increase in temperature within the range of 14°C to 22°C. Therefore, it is recommended that larvae be seeded at temperatures between 20°C and 22°C to potentially increase settlement rates and shorten the settlement period. The study also investigated the effectiveness of chemical and biological cues in improving the settlement and metamorphosis of competent H. midae larvae before their release into the ocean. It was found that settlement cues were only effective when water flow was turned off, and the highest settlement rates occurred with a combination of potassium chloride (10 mM KCl) and biological cues from Nitzschia sp. diatoms. However, all treatments exhibited lower settlement responses when water flow was present. This suggests that chemical cues may not be effective if larvae do not receive them until they are fully settled. Continuous exposure to an inducer until metamorphosis, achievable in a hatchery but not in the ocean, did enhance settlement. This finding highlights the potential for application within the hatchery environment. Tagging released larvae is fundamental for evaluating the success of a seeding program. In a hatchery experiment, bright and persistent epifluorescence marks were successfully induced in H. midae shells using calcein (25 mg.L-1 for 24 hours) without negatively affecting the survival or settlement of the larvae post-immersion. To evaluate the viability of using abalone seeding as a tool for ranching and stock enhancement, competent, fluorescent-stained H. midae larvae were released at three sites less than two meters apart in Noordhoek (Gqeberha) along the Eastern Cape coastline. Although the density of the released larvae (2.22±1.09 m²) was lower than that of wild abalone (37.96±7.45 m²), the growth rate of the released abalone was not hindered. Results from this pilot study demonstrate that releasing hatchery-reared H. midae larvae has the potential to support abalone ranching and enhance the wild abalone population along the Eastern Cape coastline. While the technique requires further refinement, these findings provide a foundational methodology for implementing the release of H. midae larvae in this region.enaquacultureSowingAbalone cultureAbalone populationsAbalonesThesis