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MEPS prepress abstract   -  DOI:

One-hundred-and-forty-one-year stable isotope record suggests changing distributions but little shift in trophic positions within a resident northern New Zealand seabird community

M. J. Rayner, B. J. Dunphy, K. Lukies, N. Adams, M. Berg, L. Kozmian-Ledward, M. H. Pinkerton, S. J. Bury

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ABSTRACT: Globally human population growth, its associated pollution and the vast scale of industrialised fisheries are having negative impacts on oceanic food webs, affecting top predators, such as seabirds. We used stable isotope (δ15N and δ13C) analyses of feathers to investigate the contemporary structure and long-term changes in a near-shore community of five seabird species in Northern Aotearoa, New Zealand. Feathers were collected from museum specimens or live individuals (between 1878 and 2019) in the Tikapa Moana, Hauraki Gulf, a marine habitat increasingly threatened by overfishing and urbanisation. To tease out the effects of baseline ecosystem versus seabird distributional changes we analysed muscle isotope values of forage fishes collected over 43 years (1976 – 2019) and provide isotopic data from contemporary prey species sampled within the region. Contemporary δ15N and δ13C values were consistent with existing data on diet and foraging distribution of the five seabird species. Values of δ15N declined in only one of five species studied suggesting for the other species there was little change in their trophic position over time. However, δ13C values declined in three species and a lack of change in the δ15N and δ13C values of forage fish suggests this change is reflective of a behavioural shift in birds’ distribution. However, changes in isotopic baselines over the sampling period cannot be ruled out and requires further investigation. Results demonstrate the value of stable isotope analyses of contemporary and archived samples as a cost effective, non-invasive method for monitoring of coastal seabirds in a changing world.