ESTIMATING THE ABUNDANCE OF ABALONE - THE IMPORTANCE OF PATCH SIZE

A method to assess the patch frequency and so derive estimates of rela tive abundance and biomass for populations of Haliotis ii-is is descri bed. The eight populations of H. iris surveyed from southern New Zeala nd comprised mostly small patches (less than or equal to 4 individuals ). Larger patches were comparatively infrequent but their frequency va ried among populations. Application of patch-frequency data to estimat e relative abundance was validated with direct counts and a comparison with the collection rates from timed searches. Relative abundance, re lative biomass and density were estimated from patch-frequency data. T hese measurements were more precise and less time consuming than direc t estimates df density. The relatively short time per survey allowed r eplication, giving surveys the power to detect the changes in the freq uency of patches expected to result from commercial fishing. A survey method to examine juvenile abundance is also described: abundance was weakly correlated with the frequency of large patches. The relative ab undance of juveniles varied among H. iris populations possibly because of differences in wave exposure between habitats.