Distribution and abundance of toheroa (Paphies ventricosa) on Ninety Mile Beach, March 2000
- Author
- Morrison, M.; Parkinson, D.
- Year
- 2001
- Journal / Source
- New Zealand Fisheries Assessment Report
- Publisher / Organisation
- Ministry of Fisheries
- Number
- 20
- Month
- May
- Pages
- 13
- ISBN / ISSN
- 1175-1584
- Summary
- A population survey of toheroa on Ninety Mile Beach, Northland, was undertaken during March 2000. The area was stratified through examination of the beach for dense siphon holes (denoting toheroa beds) and limited exploratory digging every 1 km. The beach was divided into seven strata, representing different toheroa densities andlor areas along the beach. A two-phase, stratified random survey was undertaken using transects orientated down the beach slope, with 0.5 m2 quadrats dug at 10 m intervals down each transect. The population size of toheroa over 14 mrn in length was 51.6 million (c.v. 19.8%), the highest abundance ever recorded fiom the beach. A further 10.2 million toheroa under 15 rnrn (c.v. 26.9%) were present. However, only 1 million (c.v. 40.6%) were 75 mm or greater, with only 2 animals over 99 rnrn being sampled. Most of the population was composed of juveniles less than 40 rnm in length, probably representing a 0+ cohort. Given an historical tendency for high mortality rates to follow large recruitment events, it is unknown whether this large recruitment event will translate into high adult toheroa abundance over the next 2 to 3 years. Ongoing monitoring of this cohort would be invaluable in assessing what post-recruitment factors (sources of mortality) are operating to keep adult population densities to low levels, relative to historical abundances.