Long‐term dietary shift and population decline of a pelagic seabird — A health check on the tropical Atlantic?

Research output: Contribution to journalArticle

Authors

  • Bernard Hughes
  • Colin Wearn
  • Roger Dickey
  • Judith Brown
  • Nicola Weber
  • Sam Weber
  • Vitor Paiva
  • Jaime Ramos

Colleges, School and Institutes

Abstract

In the face of accelerating ecological change to the world's oceans, seabirds are some of the best bio‐indicators of marine ecosystem function. However, unravelling ecological changes that pre‐date modern monitoring programmes remains challenging. Using stable isotope analysis of feathers and regurgitants collected from sooty terns (Onychoprion fuscatus) nesting at a major Atlantic colony, we reconstructed a longterm dietary time series from 1890 to the present day and show that a significant dietary shift occurred during the second half of the twentieth century coinciding with an apparent population collapse of approximately 84%. After correcting for the “Suess Effect,” δ13C in feathers declined by ~1.5‰ and δ15N by 2‰ between the 1890s and the present day, indicating that birds changed their diets markedly over the period of population decline. Isotopic niches were equally wide before and after the population collapse but isotopic mixing models suggest that birds have grown ever more reliant on nutrient‐poor squid and invertebrates as teleost fish have declined
in availability. Given that sooty terns rely heavily on associations with sub-surface predators such as tuna to catch fish prey, the rapid expansion of industrialized fisheries for these species over the same period seems a plausible mechanism. Our results suggest that changes to marine ecosystems over the past 60 years have had a dramatic impact on the ecology of the most abundant seabird of tropical oceans, and highlight the potentially pervasive consequences of large predatory fish depletion on marine ecosystem function.

Details

Original languageEnglish
Pages (from-to)1383-1394
Number of pages12
JournalGlobal Change Biology
Volume25
Issue number4
Early online date3 Feb 2019
Publication statusPublished - Apr 2019

Keywords

  • Ascension Island, bio-indicators, carbon-13, marine ecosystem function, nitrogen-15, onychoprion fuscatus, sooty tern, South Atlantic, stable isotope, Onychoprion fuscatus