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

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 long‐term 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.

Localised anthropogenic wake generates a predictable foraging hotspot for top predators

“…Likewise, it has been suggested that hydrodynamic forces around hard structures could modify prey availability, thereby increasing a seabird’s rate of energy acquisition 51 . While our findings suggest that terns exploit the flood wake of a device, an overall ecological (population-level) benefit through increased individual energy acquisition can only be determined when accounting for parameters relating to, e.g., foraging success, prey profitability, and breeding performance 51,52 .…”

Getting to grips with wildlife research by citizen scientists: What role for regulation?

“…(a co-author of this paper) at the University of Birmingham and since then they have published 16 peer-reviewed scientific papers and a book (e.g. Bolton et al, 2012 ; Reynolds et al, 2019 ). Working closely also with the Ascension Island Government and the University of Exeter (Cornwall Campus) in the UK, they have also provided invaluable seabird tracking data towards the August 2019 designation of the largest marine protected area (MPA) in the entire Atlantic and taken ownership of the Biodiversity Action Plan (BAP) on the island, providing a Species Action Plan (SAP) for the sooty tern ( Onychoprion fuscatus ) and the brown noddy ( Anous stolidus ).…”

Tunas off northwest Africa: The epipelagic diet of The Bigeye and Skipjack tunas

“…Impacts are not only observed directly on their prey but can produce cascading effects on other marine species and communities. For example, the increase in tuna fishing activity in the 1960's in the eastern tropical Atlantic Ocean and the consequent decline of tuna populations in that area is thought to have caused a shift in the diet and a dramatic decline of the once massive Sooty tern Onychoprion fuscatus population of Ascension island which depends on interactions with sub-surface predators to locate and catch prey (Reynolds et al, 2019).…”