Based on the low abundance of toheroa at Ninety Mile Beach in 2006 (Morrison & Parkinson 2008)
and on more recent observations by local iwi, we predicted that the abundance of toheroa in 2010 was likely to be very low, and the existence of dense beds of toheroa was unlikely. Tuatua and toheroa are known to exist in the intertidal zone at Ninety Mile beach, and both species exhibit surface siphon holes under appropriate conditions. We considered that a pre-survey traverse of the beach looking for siphon holes would not be a cost-effective basis for stratification in 2010. We decided that resources allocated to a pre-survey exploration would be better invested in sampling during the full survey.
We considered that stratification of the beach was appropriate for the 2010 survey, but based our stratification on prior information on the historical distribution and abundance of toheroa (and tuatua) at Ninety Mile Beach, rather than on pre-survey observations of siphon holes.