Tag-recapture studies revealed differences in the growth rate of Haliotis iris between headlands and bays separated by as little as 200 m. Individuals off headlands had a significantly higher incremental growth and reached a higher maximum size than those in bays. These results were consistent with observations of the size composition of H. iris which showed that few individuals of harvestable size (> 125 mm shell length) were found in bays. Differences in the growth rate of H. iris may account for the apparent differences in the size at onset of maturity: individuals off headlands, and from a fast-growing population off Wellington, reached reproductive maturity at a smaller size compared with those in bays. Yield-per-recruit modelling showed greater yields from headlands than bays, but egg-per-recruit modelling revealed more egg production was conserved in bays than off headlands. Yields could be increased from bays by decreasing the minimum size to 110 mm. Egg-and yield-per-recruit models were sensitive to the natural mortality rate (M = 0.03, 0.05 and 0.10 compared). The results show that parameters important in the management of commercial fisheries for abalone can vary over small distances: such variation should be incorporated in management strategies for abalone fisheries. M9S027

Growth data for the New Zealand abalone Haliotis iris were collected from 30 sites around the New Zealand coast by tag–recapture methods. Most data were collected to provide input into abalone stock assessments within discrete management areas, but had not been examined to determine the nature or extent of any large-scale patterns that might be useful to fishery managers. Sites spanned more than 10° of latitude and were subject to a large range of wave energies and temperatures. Mean monthly sea surface temperature (SST) and wave energy were estimated for each site and a generalised linear regression model was used to examine the relationship between variables. Size-at-maturity was also examined at ten sites. Initial length of abalone explained 35% of the variation in incremental growth, and a further 19% was explained by maximum SST, which also explained 60% of the variation in asymptotic length. Fastest growth was generally in areas with lower mean monthly maximum SST, and sites with the slowest growth had the highest mean monthly maximum SST. Size-at-maturity decreased with increasing temperature. The implications of these broad patterns upon abalone fisheries management strategies are discussed.

Experimental studies of post-settlement abalone (Haliotis iris Martyn) indicate that wave exposure and conspecific adults may be important sources of mortality. In aquarium studies, exposure of post-settlement abalone to grazing by sea urchins (Evechinus chloroticus) and starfish (Patiriella regularis), animals common in the subtidal habitat of H. iris, resulted in similar survival to control treatments (no grazers). However, in the presence of conspecific adults, the survival of post-settlement juveniles was approximately half that of control treatments. The major cause of mortality was evidently pedal smothering by adults. Similar results were obtained in field studies in which survival of recently settled abalone was greater in the absence of conspecific adults. Field studies also revealed that the differences between two bays exposed to contrasting wave action were a significant source of variation in post-settlement mortality. Survival of recruits was greater in the sheltered bay compared with the bay exposed to ocean swells.

No abstract

The growth and reproductive patterns of abalone are central to an understanding of the dynamics of their populations, and provide essential input into many of the stock assessment models currently used as the basis of assessing the sustainability of the fisheries. At present, most of this knowledge is obtained by tag-recapture methods, which are time consuming, often expensive and potentially confounding. The aim of the present study was to determine whether variations in the ratios of oxygen and carbon isotopes in the shells of Haliotis iris can be used to determine age, growth and reproductive patterns. Isotopic analyses of H. iris shells indicated that oxygen isotope profiles within the shells reflected ambient water temperature at the time of shell precipitation, and that these profiles could be used to determine age and growth patterns. To match the variation in isotopic ratios with ambient temperature cycles, we also adopted the novel approach of fitting a growth function to the data sets. The method should allow the collection of abalone growth information over the finer scales more appropriate for the rational management of abalone fisheries. Variations in the ratios of carbon isotopes showed no consistent patterns and, unlike some mollusc species, did not appear to be useful predictors of reproductive status at length.