SMALL-SCALE SPATIAL VARIATION IN GROWTH, SIZE AT MATURITY, AND YIELD AND EGG-PER-RECRUIT RELATIONS IN THE NEW-ZEALAND ABALONE HALIOTIS-IRIS

Tag-recapture studies revealed differences in the growth rate of Halio tis iris between headlands and bays separated by as little as 200 m. I ndividuals off headlands had a significantly higher incremental growth and reached a higher maximum size than those in bays. These results w ere consistent with observations of the size composition of H. iris wh ich showed that few individuals of harvestable size (> 125 mm shell le ngth) were found in bays. Differences in the growth rate of H. iris ma y account for the apparent differences in the size at onset of maturit y: individuals off headlands, and from a fast-growing population off W ellington, reached reproductive maturity at a smaller size compared wi th those in bays. Yield-per-recruit modelling showed greater yields fr om headlands than bays, but egg-per-recruit modelling revealed more eg g production was conserved in bays than off headlands. Yields could be increased from bays by decreasing the minimum size to 110 mm. Egg- an d yield-per-recruit models were sensitive to the natural mortality rat e (M = 0.03, 0.05 and 0.10 compared). The results show that parameters important in the management of commercial fisheries for abalone can v ary over small distances: such variation should be incorporated in man agement strategies for abalone fisheries.