The influence of habitat characteristics on toheroa Paphies ventricosa

The surf clam toheroa (Paphies ventricosa) is endemic to New Zealand, where it inhabits the intertidal zone of exposed sandy beaches in North and South Island regions. This species is of great cultural importance, and has a long history of supporting customary, recreational and commercial fisheries.

Population declines have led to the closures of all fisheries, except customary take. Factors contributing to the declines have included changes in land use and habitat characteristics. The present study assessed the toheroa population at Oreti Beach (Southland) in 2014, and some of the habitat characteristics that may influence the distribution and abundance of this species.

The population of large toheroa appeared stable in 2014, but the estimated number of juvenile toheroa was about one third of the previous estimate in 2009. A marked change in 2014 was the increase in the occurrence of gravel, with 24% of all quadrats containing gravel, whereas no gravel or stones were recorded previously.

Statistical modelling indicated a negative association between juvenile toheroa and the presence of gravel, and between juvenile toheroa and ghost shrimp (Biffarius filholi) burrow density. The influence of these habitat characteristics on juvenile toheroa may affect recruitment to the adult population.