Publication Date

10-2007

Series Number

166

Publisher

Department of Fisheries, Western Australia

City

Perth

ISBN

1 921258 10 1

ISSN

1035-4549

Abstract

A preliminary assessment of stock enhancement of Haliotis laevigata (Greenlip abalone) in Western Australia was undertaken with the release of 6,000 abalone near Augusta in 2004. The objective of the project was to obtain quantitative data on the likelihood of enhancement, as an additional management tool to TACs and size-limits, being successful in natural habitats in Western Australia. Baseline surveys coupled with an assessment of growth and survival of released 1+ and 2 + animals were undertaken at 12 sites within Flinders Bay, Augusta. Overall survival was 19% for 1+ age abalone and 27% for 2+ animals after 9 months. However, habitat had a significant effect on survival, with survival in high quality habitats being 35% for all animals. Mean densities of animals less than 96 mm shell length (1- 3 years age) increased five-fold in the 12 months between the baseline surveys, and the post-seeding survey.

Total cost of stock enhancement (production + release) was higher for 2+ animals compared to 1+ animals, but reduced with increasing numbers released. Maximum economic efficiency was gained with a release of 500,000 + animals, which cost $0.39 per 1+ animals, and $1.02 for 2+ animals. To ensure maintenance of existing genetic diversity of wild stocks, an enhancement rate of 35% of natural recruitment to the breeding stock was evaluated. Being within the expected variation in natural recruitment, this rate is considered unlikely to result in density-dependent effects on mortality and growth.

Under this scenario, a maximum annual release of 2.5 million 1+ animals, or 1 million 2+ animals to the state-wide stocks of Haliotis laevigata could be sustained. Yields from this release would be 35 – 40 t (meat weight) at estimated survival rates. At the current landed value ($126 / kg meat weight), a 14 tonnes (20%) annual increase in commercial catch is required for a break-even return on costs of enhancement. Similar estimates were also derived for smaller genetic zones. From a cost-benefit analysis, 2+ and 1+ releases were similar in performance. The options are: 1) a larger grow-out program and a smaller enhancement program will yield higher and less variable survival (2+ releases); 2) a smaller grow-program, and a larger release program, for lower overall survival (1+ releases).

A test case for commercial enhancement was proposed, and includes appropriate biological, environmental, and genetic targets against which success can be evaluated. If implemented, this programme would require annual monitoring, and a maximum annual release of 137,000 × 1+, or 53,000 × 2+ animals for a 5 – year period so that success can be gauged against natural variability in recruitment.

A larger experiment is required to critically investigate the effect of habitat on survival, and supply robust estimates of growth and survival to optimise the bio-economic analyses. The method described may be useful for populating depleted areas that are known to be productive, but subject to low recruitment. However, enhancement into the natural habitat should only be implemented as an activity that is integrated into wild-stock management, and subject to the existing suite of performance indicators currently used to manage the fishery. It also needs to explicitly recognise other risks, such as the possibility of disease introduction.

Number of Pages

40

Keywords

Stock enhancement, Haliotis laevigata, Greenlip abalone, Western Australia, Seeding, Hatchery-produced abalone, Wild stock management

Disciplines

Aquaculture and Fisheries | Marine Biology | Natural Resources and Conservation | Natural Resources Management and Policy

Download

Share

COinS