Abundance, distribution, and size structure of toheroa (Paphies ventricosa) at Ripiro Beach, Dargaville, Northland, New Zealand

Abstract

The distribution of toheroa (Paphies ventricosa Gray) beds, and the abundance and size structure of toheroa at Ripiro Beach, Dargaville, New Zealand, were determined by a two-phase stratified sample survey. The first phase was undertaken in February and March 1999 and the second phase in June 1999. The first phase located and sized 45 toheroa beds, and stratified the beds according to the observed density of siphon holes. A total of 53 transects were sampled. The transects were run perpendicular to the shoreline and positioned systematically within each stratum. Along each transect the sampling of beds was done at 5 m intervals using a 1 x 0.5 m quadrat. Outside of the beds, sampling was done at 10 m intervals. The total number of toheroa ?75 mm (previous minimum legal size) was estimated to be 3.3 million with a standard error of 480 000. This abundance of legal-sized toheroa is roughly comparable with numbers last seen at Ripiro Beach in the late 1960s. The total abundance of toheroa of all sizes was estimated to be 113.5 million with a standard error of 33 million. It appears that there has been good recruitment of 0+ toheroa on Ripiro Beach and the abundance of toheroa of all size ranges has greatly increased since the previous survey in 1974.