suitable only for surveying beaches that contain dense beds of toheroa which can be positively
identified by the nature of the siphon holes on the surface of the sand. The attributes of toheroa and tuatua siphon holes must be easily distinguished, and, equally importantly, the pre-survey stratification should immediately precede the main survey sampling to avoid problems of toheroa movement over time (e.g., with wave and storm action). Stratification using this approach is problematic because the presence of surface siphon holes appears to vary depending on environmental conditions. In the 2006–07 surveys of toheroa at Dargaville Beach and Muriwai Beach, Akroyd et al. (2008) found that the location and density of toheroa beds identified by siphon holes in the pre-survey stratification had changed considerably by the time the full surveys were conducted.