STUDIES ON SOUTHERN AUSTRALIAN ABALONE (GENUS HALIOTIS) .16. RECRUITMENT, HABITAT AND STOCK RELATIONS

The dynamics of a population of the greenlip abalone, Haliotis laevigata, was studied from 1978 to 1990 in Waterloo Bay, South Australia. During this period the fishery was closed from 1982 to 1986 and the size limit was increased in 1986. The spatial distribution of recruitment (measured as the abundance of the 2+ age class) was correlated during every year of study with a complex gradient comprising water movement, habitat complexity and predator density, and for six years of the study with depth. Recruitment in the six years from the closure was 2.7 times higher than that in the preceding seven years. The intensity of aggregation of the adult (greater than or equal to 4 years) fraction of the population varied with density and habitat complexity. Under intense fishing, aggregations were fewer and smaller. This paper weights stock abundance according to a model relating intensity of aggregation with fertilization success and presents a stock-recruitment relation for the Waterloo Bay population. The curve is a classical Ricker type showing compensation at high stock sizes. This curve indicates that below adult densities of about 0.15 to 0.2 m(-2) the population is increasingly vulnerable to recruitment failure and ultimately to collapse.