Changing taxonomy and the need for supplementation in the management of re-introductions of Brothers Island tuatara in Cook Strait, New Zealand

Summary

Brothers Island tuatara (Sphenodon guntheri), once considered a distinct species confined to a tiny founder population on North Brother Island in New Zealand's Cook Strait, were reintroduced to three predator-eradicated island sanctuaries, Titi Island in 1995, Matiu/Somes Island in 1998, and Long Island in 2007, using wild adults and captive-reared juveniles hatched from eggs collected on North Brother Island and raised for three to six years before release with toe-clip marking and artificial burrows. Intensive post-release monitoring recaptured 63% of Titi Island founders and 60% of Matiu/Somes founders across repeated survey trips through 2007, finding all founders had grown significantly since release, some juveniles reaching near-adult size, and confirming reproduction on both islands: an unmarked juvenile captured on Titi in 2007 and a discovered nest on Matiu/Somes whose eggs were incubated off-island and the hatchlings later returned. However, recent genetic research revealed that the taxonomic distinction underlying the program is unwarranted, since all tuatara are now considered a single species, while North Brother Island itself shows high inbreeding and low diversity, casting doubt on its suitability as a source population; population models suggest at least 70 adults would be needed per founder group to preserve genetic targets over ten generations, a threshold none of the three releases met. Major difficulties included tuatara's long generation time complicating short-term assessment and the difficulty of recapturing cryptic juveniles in dense scrub. The project rates itself Successful, citing confirmed survival, growth and breeding at multiple sites plus strong public education value at accessible Matiu/Somes Island.