Population biology of paua (Haliotis iris and Haliotis australis) along the Wellington South Coast, New Zealand

Abstract

Aspects of the demography of Haliotis iris and Haliotis australis were examined over a 12-month period during 2003 from sites along the south coast of Wellington. The counts, sizes and the rates of growth, mortality, movement and recruitment of H. iris and H. australis were examined. The study determined species-specific and site-specific differences in paua numbers, with H. iris found at higher abundance than H. australis at all sites. The counts of both species were generally higher in the eastern sites (closest to Wellington Harbour) compared to western sites on the south coast, with both species most abundant at Princess Bay and Palmer Head. Aggregative behaviour was examined and found to be common in H. iris, with approximately 60% of individuals aggregating in patches of 2-16, but was less common for H. australis with approximately 30% aggregating. Aggregation was also shown to increase significantly during the winter period for H. iris. Count and size estimates were compared to an earlier study completed on the south coast of Wellington (Pande, 2001) and no significant difference in count data was found between the two periods, but a significant difference in mean size of H. iris was observed due to larger numbers of smaller paua sampled in this study. Population abundances from mark-recapture data indicated higher abundances of H. iris than H. australis at each site. Estimated survival rates were low for March-May and high survival rates were observed during September-November. Mortality estimates derived from size frequency distributions gave low values (Z<0.2 per year) for both species compared to other species of abalone. Growth parameters from von Bertalanffy and Gompertz growth models were estimated from mark-recapture data and length-frequency cohort analysis. Differences were found between species and differences in growth rates of H. iris but not H. australis were found between sites and time periods. H. iris at Red Rocks had a markedly slower growth rate than at other sites, and growth rates of H. iris decreased over winter and increased during spring and summer. Seasonal differences in recruitment were also observed with an increase in juvenile H. iris abundance during May and July. A relationship between juveniles and adults was identified, with more juveniles found at sites with larger adult population sizes. The results will be useful as baseline data for the proposed Taputeranga Marine Reserve for the south coast of Wellington and will contribute to determining how effective reservation status is on paua counts, size and biology in the future.