Growth and movement of the South African abalone Haliotis midae: A reassessment

Abstract

Growth rates of a number of Haliotis midae populations around the South African coast were studied by means of tagging. These populations ranged from the cool waters of the western coast to the more temperate environment of the eastern Cape. Standard von Bertalanffy growth curves were fitted and growth parameters derived. These ranged from 0.19 to 0.25 for K, the average rate at which L_∞ is approached, and from 156 to 173 for L_∞, the average theoretical maximum length. These indicate far higher growth rates than were previously published for this commercially fished species, and the reasons for this difference are discussed. The expectation that growth rates would be fastest in the warmer eastern Cape waters was not realized, there being no significant difference in growth between the Bird Island population on the eastern coast and the Robben Island population on the western coast. These new growth parameters indicate that H. midae in the commercial fishery grounds is attaining sexual maturity some four years earlier, and the minimum legal size some five years earlier, than previously considered. This has considerable significance for modelling studies presently underway.

Movement of a small population of adult H. midae was studied over a three-year period, after which 47% of the original abalone were still present on the study site. Of these, 81.5% still occupied exactly the same position on the rocks. This indicates that H. midae that have located an optimum habitat, and that are not disturbed, tend not to move.