Photographs from P. parvivipara and P. vivipara habitat, and graph of P. vivipara population trends.

Trends from the largest P. vivipara population at Pitt Water. Each point is the mean of adult densities from numerous sampling events over each 2 year period. During 1976-83 a fixed 1 m² quadrat was sampled (Prestedge 1998) while a different method was used from 2001-04 involving 25 m transects being sampled across the site (Ecomarine 2014). Other survey types (timed-search) have also found large population declines (see section 2.).