Recruitment in tuatara

Some appreciation of recruitment processes in tuatara, Sphenodon punctatus (Reptilia:Rhynchocephalia) and the habitat requirements of small juveniles is essential to the long-term management of surviving natural populations. It is also important that this information be acquired while a large and relatively secure breeding population, such as the one on Stephens Island, still exists.

A survey of juvenile habitats and dispersion on Stephens Island in the summer of 1987-88 has provided input to DOC plans for revegetating the island, and a framework for the census of juveniles <140 mm snout-vent. This work utilized a unique opportunity arising in December 1987, when tuatara nests located 12 months earlier by Dr M.B. Thompson (VUW) to monitor incubation conditions, became available to monitor hatching. It was also an ideal chance to intercept hatchlings and examine dispersal movements, since both the nests and the hatchlings are otherwise very difficult to locate. A number of these juveniles were tracked individually using cotton thread attached to the tail, or by radiotelemetry using miniaturized transmitters implanted in the body cavity.

Tracking data combined with population counts and meteorological records, provide guidelines for management of the habitat, and appropriate timing and methods for census. Information on clutch sizes and egg mortality, (MEM & Dr M. Thompson, VUW) in conjunction with new understanding of female reproductive cycles (Dr A. Cree, VUW), and of habitat quality in relation to population densities (Dr J. Gillingham, CMU), provides a basis to estimate annual production and compare this with field data. A modelling approach is necessary to estimate survival beyond 4-S months when the hatchlings start to burrow, since part of the population (depending on time of year and weather) then becomes "hidden" underground.