Abundance of large toheroa (Paphies ventricosa Gray) at Oreti Beach, 1971–90, estimated from two‐dimensional systematic samples

Abstract

The population of toheroa (Paphies ventricosa Gray) at Oreti Beach, South Island, New Zealand, was until recently considered relatively minor in comparison to those of the North Island west coast beaches. It is now the sole remaining toheroa population in New Zealand to support recreational toheroa gathering. This paper analyses count data from 22 systematic surveys of large toheroa (> 8 cm) at Oreti Beach between 1971 and 1990. A variance estimator appropriate to two‐dimensional systematic surveys is developed to enable computation of confidence intervals for these abundance estimates. It is concluded that the recreational harvest taken during open days can not be reliably estimated by pre‐ and post‐harvest surveys and should instead be determined from inspection and enumeration of open day participants. At current population and harvest levels the impact of occasional open days at Oreti Beach is slight; however, the high annual variability of toheroa populations and the uniqueness of this one remaining harvestable stock suggest a need for continued population surveys.

Keywords:

• abundance
• Mesodesmatidae
• toheroa
• systematic sample
• variance estimator