Between 2014 and 2018 a mark-recapture/ resighting study was conducted to ascertain the size of the population of New Zealand storm petrel (Fregatta maoriana) at their breeding grounds on Hauturu, Little Barrier Island, New Zealand. A total of 415 New Zealand storm petrels were captured and marked with individual colour bands using acoustic playback and night-time spotlighting on Hauturu. Two mark-recapture models were developed using the recaptures of banded birds on land and the at-sea resightings of banded birds attracted to burley on the Hauraki Gulf near Hauturu. The land- based model suggests a current population of 994 (range 446–2,116) individuals whereas the at-sea model suggests an estimate of 1,630 (range 624–3,758) individuals. The discrepancy between these models likely lies in the bias of on-land captures towards juvenile birds constituting >50% of birds caught. We consider the at-sea model most representative of total population size. Logistic population growth models anchored by on-land and at-sea population estimates suggest pre-rat eradication populations of New Zealand storm petrel of 323 and 788 individuals respectively.