NIWA conducted the most recent surveys of toheroa on Ninety Mile Beach in 2000 (Morrison &
Parkinson 2001) and 2006 (Morrison & Parkinson 2008) using two-phase stratified random designs.
In each year, the beach was initially stratified before the survey by traversing the beach looking for dense siphon holes (‘pock-marked’ sand, putatively denoting toheroa beds) and by limited exploratory digging. The beach was divided into strata representing different (putative) toheroa densities and/or areas along the beach. Subsequently, two-phase stratified random sampling was undertaken using transects orientated down the beach slope, with 0.25 m2 quadrats dug at 10-m intervals down each transect