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Estimating variation in growth of Haliotis laevigata across a sea ranching operation in south-western Australia

Mundy, David (2020) Estimating variation in growth of Haliotis laevigata across a sea ranching operation in south-western Australia. Honours thesis, Murdoch University.

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The use of aquacultured individuals to restore and rebuild fisheries, i.e. aquaculture-based-enhancement (ABE), is increasing globally to maintain seafood supplies and increase production of depleted species such as abalone (Haliotidae, Halioits). Sea ranching is one form of ABE that is very prominent in China, Korea, and Japan, and has recently been developed for Greenlip Abalone, Haliotis laevigata, in Flinders Bay, south-western Australia. Ocean Grown Abalone (OGA) contract the production of juvenile abalone by 888 Abalone’s hatchery at Bremer Bay and transport them to Flinders Bay where they release them onto artificially created habitats (Abitats). Production from this sea ranching facility has now reached 55 tonnes year-1, 41% of the 2018 total production from all Western Australian capture abalone fisheries.

This thesis investigated the performance of released abalone on the OGA sea ranch by tagging hatchery raised individuals to: (i) estimate growth in shell length and total weight and how this varies across the lease (different “lines” of Abitats) in relationship to water temperature and dissolved oxygen, (ii) investigate whether growth differs between the hatchery and the ocean phases, and (iii) evaluate whether a mark laid down after moving from the hatchery to the ocean environment (hatchery mark) provides a good estimate for the size of seeding and can be used to calculate the growth of harvested abalone. Other morphometric measurements of harvested abalone were also documented including shell length (SL), shell width (SW), shell depth (SD), total weight (WT), and foot weight (FW), with correlation conducted between each of these variables.

Three cohorts of abalone were tagged and released onto Abitats on different lines on the lease and one cohort was released on different artificial structures (“Flatpacks”). One of the cohorts was tagged in the hatchery and retained for 74 d before release, while the other cohorts were released immediately after tagging. Individual growths rate in SL and WT from the size at tagging and the size at harvest were calculated, with a one-way ANOVA showing that growth across the sea ranching lease was homogenous i.e. did not differ significantly among lines (SL: P = 0.17, WT: P = 0.42), with overall growth rates for SL of 2.318 mm month-1 and WT of 2.403 g month-1. Logger data from three lines on the sea ranch showed similar patterns of variation in water temperature and dissolved oxygen between 20th March 2020 and 31st May 2020 and did not appear to differ significantly. A paired T-test for individual abalone found that growth rates did not differ significantly between the hatchery and ocean phases for either shell length (T73 = 1.3, P = 0.209) or weight (T16 = 1.4, P = 0.173), with an overall growth rate of 1.964 mm month-1 for the hatchery and ocean phases which projects an expected time of 2.5 years (30.5 months) to reach 100 mm and 3.8 years (45.8 months) to reach 130 mm shell length after seeding onto Abitats at ~40 mm shell length. This time to length projection is shortened to 2.2 years (25.9 months) to 100 mm and 3.2 years (38.8 months) for abalone to reach the 130 mm harvest target using the growth rate from tagged abalone across all lines sampled (2.318 mm month-1).

The first apparent application of shell morphometric analyses to Greenlip Abalone found that the mean SL:SD and mean SL:SW ratios differed significantly among lines (P = 0.016, P = 0.010, respectively) but the differences in ratios were small (0.33, 0.04) and unlikely to be biologically significant. The hatchery mark at harvest was a linear predictor of the SL at seeding, with high statistical significance (P < 0.001, n = 178) and the hatchery mark accounting for 50.6% of the variation in SL at seeding.

The results from this Thesis provide the first quantitative growth estimates of individual Greenlip Abalone from the OGA sea ranching site in Flinders Bay, south-western Australia. Highlighting the importance of continuing estimation of growth rates and meristic measurements, the remaining tagged abalone will provide valuable information about growth throughout the entire ocean phase for sea ranching, by the evaluation of growth rates through maturing size ranges as the abalone reach harvest size. Potentially, this could be incorporated into future monitoring procedures for OGA commercial operations to provide accurate measurements of growth across the whole lease.

Item Type: Thesis (Honours)
Murdoch Affiliation(s): Environmental and Conservation Sciences
Supervisor(s): Loneragan, Neil and Admiraal, Ryan
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