Tuatara with banding
Adult tuatara range from about 300 g to 1 kg.
They are the only surviving members of the order Sphenodontia, which was well represented by many species during the age of the dinosaurs, some 200 million years ago. All species exept for the tuatara declined and eventually became extinct about 60 million years ago.
Tuatara are therefore of huge international interest to biologists. They are recognised internationally and within New Zealand as species in need of active conservation management.
Tuatara once lived throughout the mainland of New Zealand but have survived in the wild only on 32 offshore islands.
These islands are characteristically free of rodents and other introduced mammalian predators which are known to prey on eggs and young as well as compete for invertebrate food.
The islands are usually occupied by colonies of breeding seabirds. These seabirds contribute to the fertility and the richness of invertebrate and lizard fauna which tuatara need to survive.
Recent advances in the captive incubation and raising of tuatara have allowed the species to be translocated to a further four islands that they presumably inhabited in the past. The ability to eradicate rodents from islands has also enhanced these efforts.
Tuatara on Stephens Island
Species of tuatara
Until quite recently two species of tuatara were recognised and one of these was considered to comprise two subspecies.
The northern tuatara (Sphenodon punctatus punctatus) present on islands from the Bay of Plenty north, and the Cook Strait tuatara (S. punctatus) an unnamed subspecies present on Takapourewa (Stephens Island) and the Trio Islands in Marlborough Sounds.
The other species was the Brothers Island tuatara (S. guntheri) known naturally from one small island in Marlborough Sounds. In 2009 research examined DNA and allozyme data for all populations and concluded that tuatara is best described as a single species that contains distinctive and important geographic variants.
There are three kinds of rats in New Zealand. The kiore have been here for at least 1000 years. These typially weigh about 100 grams and resemble large mice. Adult tuatara can co-exist with kiore but it seems that tuatara eventually die out where kiore are present.
Several clues suggest that the kiore may have been nest robbers - taking eggs as well as small hatchlings. Being slow breeders the tuatara cannot make up for losses.
There were probably few, if any, tuatara left on the North and South Islands by the time European settlers arrived in New Zealand
The larger Norway rats weight up to 450 g. Norway rats and ship rats (up to 200 g) arrived in New Zealand with European visitors and settlers. These rats are nature's 'vandals', eating and destroying whatever is available, and becoming prolific breeders when food is plentiful.
Tuatara male, Poor Knights Islands
Rats are considered the most serious threat to the survival of tuatara because they are easily transported as stowaways on boats and usually the first alien animals to arrive unnoticed in new places.
Islands with rats have few nocturnal invertebrates or reptiles. Even the rats have to rely on seeds, fruits and other plant material for food because there is little else.
Mice are less devastating, but also damage natural communities by eating seeds and small insects that native reptiles and birds normally eat.
Low genetic diversity
A less obvious, but very significant threat to tuatara survival is the low genetic diversity of the species. Low diversity has implications for how well animals are placed to cope with future climate change and also for the viability of newly established populations.
Low genetic diversity is often associated with vulnerability to new pathogens and low reproductive success for example. This low genetic diversity is now spread across small and isolated islands reducing further the ability to cope with future environmental change.
Scientific research is particularly relevant to the conservation of tuatara, and has recently established how changes in incubation temperature of the eggs influences the sex of the hatchlings.
Conservation initiatives focus on keeping existing habitats free of rodents and re-introducing them to new, rodent-free islands.
Captive animals play an important part in conservation, education and research. Animals can be seen at some of these locations such as Southland Museum, Willowbank in Christchurch, Natureland in Nelson, Wellington and Auckland Zoos, and several other institutions.
DOC has produced a conservation recovery plan for tuatara and a plan for their captive management.
You can help
The continued conservation of tuatara relies largely on public goodwill in preventing rodents establishing on their island refuges.
On most islands this means complying with the 'no-landing' rule but on others (such as Matiu and Tiritiri Matangi) the public should be vigilant in ensuring no pests go ashore with them.