PATCH DYNAMICS AND EFFECTS OF EXPLOITATION ON ABALONE (HALIOTIS-IRIS)POPULATIONS

Simulation modelling based on surveys of two populations of Haliotis i ris explored the effects of exploitation on the abundance of individua ls and the frequency of aggregations (patches). The two populations co nsidered had contrasting exploitation histories (zero and high) and di ffered in the frequency of small patches (<5 individuals) and large pa tches (>4 individuals). Assuming that fishers harvested only large pat ches, a low proportion of the available patches was fished except in t he case of the unfished population in which only 50% of individuals we re of harvestable size (empirical estimates indicated that about 65% o f the populations considered in the simulation were of harvestable siz e). Such fishing behaviour may apply to other abalone fisheries. The r esults of low effect of fishing on patch density can explain why the s ize composition of abalone is insensitive to exploitation rate. The re latively low impact of intense fishing on the patch frequency means th at population surveys would have only a low chance of detecting a chan ge in the population structure.