File(s) under permanent embargo
The fisheries biology of the Tasmanian stocks of Haliotis rubra
thesisposted on 2023-05-27, 17:03 authored by Prince, Jeremy Duncan
The fishery for Haliotis rubra or blacklip abalone is Tasmania's most valuable fishery, with a landed value of approximately $50 million in 1988. Despite the fact that catch rates have remained relatively stable since 1970, commercial abalone divers in Tasmania are expressing grave doubts about the long term sustainability of this fishery. The aim of this study was to document the biology of H. rubra and the nature of the fishery in order to re-assess the fishery biology of this species, and current methods of stock assessment. For this purpose, a broad ranging study of the structure and dynamics of the pre-recruit, and recruited, abalone populations has been completed. The ramifications of the results of this study have been explored using a model which simulates the dynamics of a single unit stock of abalone. Finally, in the light of these results I have re-assessed historical trends in catch per unit effort within the Tasmanian abalone fishery. These results show that the structure of7-J. rub-ra-/populations is more dynamic than generally recognized, with high levels of recruitment and mortality amongst juveniles. Juveniles are cryptic, emerging onto the surface of the reef where they are vulnerable to commercial exploitation, as they mature. The emergent adult population is relatively stable being characterized by lower levels of growth and mortality. On a spatial scale of 10-100 m the adult population is relatively mobile, exhibiting patterns of movement which could lead to aggregation and dispersion in response to changes in population pressure. In contrast the scale of larval dispersal is apparently restricted to lO's of meters. These results suggest that the scale of a unit stock in this species can be measure on the scale of lOO's of meters and explain the spatial heterogeneity which is characteristic of abalone stocks. Commercial divers have a high degree of knowledge about the spatial distribution of abalone and target known aggregations of stock. Divers allocate their effort according to a range of priorities, one of which is the expected catch rate. When this characteristic of the fishery is combined with the biology of the species it is apparent that, on the spatial and temporal scale of commercial catch and effort data, catch rate is unlikely to be a reliable index of stock abundance. A re-assessment of the catch per unit effort data confirms the conclusion, that a wide range of factors determine catch rate trends in the commercial fishery. For this reason standard methods of stock assessment are not applicable to the fishery. Developing new techniques of stock assessment and management, based on survey data and detailed knowledge of the relationship between stock and recruitment offers the best long term hope for managing this fishery.
Rights statementCopyright 1989 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s). Library has additional copy on microfiche. Thesis (Ph.D.)--University of Tasmania, 1990. Includes bibliographical references