Flesh-footed shearwater population monitoring and estimate 2024/25
This is the final report for POP2024-02 Flesh-footed shearwater population monitoring 2024/25. Published August 2025.

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POP2024-01: Flesh-footed shearwater population monitoring and estimate: 2024/25 (PDF 8,461K) 

Summary

This report presents the population monitoring and population estimate findings from the final year of the toanui/flesh-footed shearwater (Ardenna carneipes) research carried out by Wildlife Management International Ltd. (WMIL) for the 2024/25 breeding season on Ohinau and Mauimua/Lady Alice Islands. 

During the 2024/25 season, WMIL monitored 294 and 306 study burrows on Ohinau Island andLady  Alice Island respectively. Of these 72.8% (n=214) and 59.8% (n=183) were breeding burrows for Ohinau and Lady Alice respectively. WMIL were able to identify 88.3 % (189 of 214) breeding birds in burrows on Ohinau Island and 84.2% (n=154) on Lady Alice Island. Determining breeding success was not a deliverable for this season. For both islands, breeding occupancy of study burrows has declined over time.

During the 2024/25 season, 227 adult flesh-footed shearwaters were banded on Ohinau Island and 52 on Lady Alice Island. No chicks were banded this season. On Ohinau 4.0% (n=44) of chicks, which have been banded since monitoring began, have been recaptured at the colony. This includes five individuals from the 2015/16 cohort, two individuals from the 2016/17 cohort, three individuals from the 2017/18 cohort, six individuals from the 2018/19 cohort and one individual from the 2021/22 cohort. On Lady Alice Island 17% (n=48) of the 280 banded chicks from the 2016/17-2018/19 cohorts have been recaptured back at the colony. Of the 76 individuals resighted since Andrea Booth’s study from 2000-2009, five individuals were detected breeding for the first time this season.

Two population surveys were carried out this season, each within a single sub-colony on each island. On Ohinau the Pōhutukawa colony was surveyed again, and on Lady Alice Island, LA1 colony was surveyed, to obtain estimates of population size and trends for these sub-colonies. The same transect start locations and bearing directions that were originally carried out during the first island-wide surveys (Ohinau: 2017/18, Lady Alice: 2018/19 breeding seasons) and second island-wide surveys (Ohinau and Lady Alice: 2023/24 breeding season) were used. The surveys carried out this season thus represent a repeat of the survey methods that were first obtained for each sub-colony.

For the two population surveys (labelled as the ‘2017/18 repeat’ and the ‘2023/24 repeat’) that were carried out in the Pōhutukawa colony on Ohinau Island, 14 (of the original 15) and 20 (of the original 20) transects were completed. This covered a survey area of 560 m² and 800 m², respectively. From these surveys WMIL estimates that there are 227 (75-378, 95% CI) and 220 (90-350, 95% CI) occupied flesh-footed shearwater burrows in the Pōhutukawa colony from the 2017/18 and 2023/24 re-survey, respectively. However, by combining both surveys and increasing the sampled area to 1,266.43 m², the combined population estimate for the Pōhutukawa colony is estimated at 238 (128-349, 95% CI) occupied burrows. This combined estimate for the Pōhutukawa colony represents a percentage decrease of 16% (est. % average change at -10% (95% CI: -52, 82)), since last year’s population estimate for this colony of 282 (139-425, 95% CI) occupied burrows, and a 44% percentage decrease (est. average % change at -39% (95% CI: -69, 44)) since the first estimate in 2017/18 at 423 (173-673, 95% CI) occupied burrows.

For the two population surveys (labelled as the ‘2018/19 repeat’ and the ‘2023/24 repeat’) that were carried out in the LA1 colony on Lady Alice Island, 59 (of the original 60) and 60 (of the original 60) transects were completed. This covered a survey area of 2,314 m² and 2,400 m²), respectively. From these surveys WMIL estimates that there are 490 (358-622, 95% CI) and 364 (246-483, 95% CI) occupied flesh-footed shearwater burrows in the LA1 colony from each resurvey, respectively. Again, by combining both surveys and increasing the sampled area to 4,326.97 m², the combined population estimate for the LA1 colony is estimated at 420 (327-512, 95% CI) occupied burrows. This combined estimate for the LA1 colony represents a decrease of 16% (est. average % change at -17% (95% CI: -41, 29)) since last year’s population estimate for this colony of 502 (315-689, 95% CI) occupied burrows, and a 48% decrease (est. average % change at -47% (95% CI: -60, -28)) since the 2018/19 estimate of 809 (565-1054, 95% CI) occupied burrows, and a 52% decrease (est. average % change at -51% (95% CI: -63, -33)) since the first population estimate took place in the LA1 colony in 2017/18 at 871 (630-1,112, 95% CI) occupied burrows.

The reasons contributing to these declines are unknown but likely due to mortality from accidental bycatch by fisheries, plastic pollution, and climate change impacts. Low adult survivorships could therefore be the key driver of these declines. Continuing to gather long-term datasets will be vital to this and WMIL recommend these results are used to produce actionable conservation management measures for this long-lived seabird, before declines push the colonies to an irreversible point.

Recommendations include:

  • Continue population monitoring on Ohinau and Lady Alice Islands with 200 breeding study burrows monitored annually over two expeditions (Dec/Jan and Apr/May).
  • A survival analysis be undertaken to estimate adult survival on each island.
  • There is continued, focused effort to band and recapture as many flesh-footed shearwaters on the surface and in burrows on both islands.
  • Titi Island, Marlborough Sounds, be considered as a potential future monitoring location.
  • An island-wide population estimate on Ohinau Island be undertaken in five years.
  • Continued sub-colony surveys at LA1 on Lady Alice, Pohutukawa on Ohinau Island
  • An island-wide population estimate on Lady Alice Island be undertaken in five years.
  • An island-wide population estimate on Titi Island be undertaken as soon as possible.
  • Other breeding colony sites be considered for population surveys.
  • The conservation threat status of toanui/flesh-footed shearwaters be reviewed under the New Zealand threat classification system in light of these findings.

Publication information

Lamb, S., Ray, S. 2025. TLamb, S; Ray, S. (2025). Toanui/flesh-footed shearwater population monitoring and estimates: 2024/25 season. Unpublished Wildlife Management International Technical Report to the Department of Conservation.