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Marine Ecology Progress Series

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MEPS 670:223-238 (2021)  -  DOI: https://doi.org/10.3354/meps13763

Projected impacts of climate change, bycatch, harvesting, and predation on the Aotearoa New Zealand tītī Ardenna grisea population

David Fletcher1,*, Jamie Newman2,8, Sam McKechnie2,9, Corey Bragg3,4, Peter Dillingham5, Rosemary Clucas2,10, Darren Scott2,11, Sebastian Uhlmann2,12, Phil O’B. Lyver6, Andrew M. Gormley6, Stewart Bull4, Kayne Davis4, Renata Davis4, Riki Davis4, Tane Davis4, Lania Edwards4, Jane Kitson4, Tina Nixon4, Michael Skerrett4, Henrik Moller7

1David Fletcher Consulting Limited, Karitane 9471, Aotearoa New Zealand
2Department of Zoology, University of Otago, PO Box 56, Dunedin 9054, Aotearoa New Zealand
3Tokona te Ao - Tribal Economies, Te Rūnanga o Ngāi Tahu, 25 College Street, Dunedin 9012, Aotearoa New Zealand
4Rakiura Tītī Islands Administering Body, PO Box 316, Invercargill 9840, Aotearoa New Zealand
5Department of Mathematics and Statistics, University of Otago, PO Box 56, Dunedin 9054, Aotearoa New Zealand
6Manaaki Whenua Landcare Research, PO Box 69040, Lincoln 7640, Aotearoa New Zealand
7Centre for Sustainability, University of Otago, PO Box 56, Dunedin 9054, Aotearoa New Zealand
8Present address: Parliamentary Commissioner for the Environment, PO Box 10 241, Wellington 6143, Aotearoa New Zealand
9Present address: Pacific Community, BP D5, 98848 Noumea, New Caledonia
10Present address: 1 Meremere Street, Timaru 7910, Aotearoa New Zealand
11Present address: 359 Oreti Road, Invercargill 9879, Aotearoa New Zealand
12Present address: Flanders Research Institute for Agriculture, Fisheries and Food, Fisheries and Aquatic Production, Ankerstraat 1, 8400 Ostend, Belgium
*Corresponding author:

ABSTRACT: Many factors have contributed to a decline in the tītī (sooty shearwater) Ardenna grisea population in Aotearoa New Zealand since at least the 1960s. The relative impacts of Southern Oscillation Index (SOI) variation, bycatch, predation, and traditional harvesting by Rakiura Māori were recently estimated in a study fitting population models to data from the period 1976-2005. Annual mean SOI was related to both adult survival and fecundity. We used the results from that study to project abundance of tītī under a range of management strategies and future SOI scenarios, based on 41 climate models. Projections over the period 2019-2070 showed marked variation across the climate models. When the proportion of chicks harvested and the level of depredation by weka Gallirallus australis were set at their historical means and the proportion of birds killed in bycatch was set at an upper bound based on current estimates, the probability of a decline ranged from 0.30 to 1.00, across all climate models. When both bycatch and depredation by weka were set to zero, the probability of a decline ranged from 0.11 to 1.00, across all climate models. Our results suggest that future abundance of tītī in Aotearoa New Zealand will depend to a large extent on SOI conditions over the coming decades. As climate-model uncertainty makes reliable prediction of future SOI conditions difficult, adaptive management is likely to be the best option for Rakiura Māori, the kaitiaki (environmental guardians) of the Rakiura Tītī Islands, to maintain sustainable tītī harvests.


KEY WORDS: Harvest management · Population projection model · Southern Oscillation Index · Sooty shearwater


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Cite this article as: Fletcher D, Newman J, McKechnie S, Bragg C and others (2021) Projected impacts of climate change, bycatch, harvesting, and predation on the Aotearoa New Zealand tītī Ardenna grisea population. Mar Ecol Prog Ser 670:223-238. https://doi.org/10.3354/meps13763

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