No way home: collapse in northern gannet survival rates point to critical marine ecosystem perturbation
- PDF / 1,503,157 Bytes
- 10 Pages / 595.276 x 790.866 pts Page_size
- 99 Downloads / 155 Views
ORIGINAL PAPER
No way home: collapse in northern gannet survival rates point to critical marine ecosystem perturbation David Grémillet1,2 · Clara Péron3 · Amélie Lescroël4 · Jérôme Fort5 · Samantha C. Patrick6 · Aurélien Besnard7 · Pascal Provost8 Received: 27 March 2020 / Accepted: 5 November 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Seabirds are one of the most threatened of all bird groups, with a marked community-wide decline across the last decades. Yet, some seabird species are more resilient than others, and it is essential to study under which conditions even these highly resilient organisms are affected by global changes. Here, we report such a case in northern gannets (Morus bassanus). Using global location sensors (GLS), demographic and stable isotope analyses, we performed a long-term study of the migration biology and inter-annual survival of gannets breeding on Rouzic Island in Brittany, France. Across 2006–2015, our analyses showed that the birds spent the inter-breeding period off Western Europe, in the Mediterranean or off West Africa. There were no inter-annual trends in the use of these different areas, but isotopic analyses suggested food competition between gannets and industrial-scale fisheries. Crucially, we found a precipitous decline in the return rates of birds equipped with GLS, from 100% in 2006–2007 to less than 30% after 2015. This decline was consistent with a marked decrease in inter-annual survival probabilities for ringed adult gannets, from > 90% in 2014–2015 to 75,000 pairs; (Murray et al. 2015)) facing the North Sea near Edinburgh. Yet, at the southern margin of their distribution range in the Eastern North Atlantic, gannets recently displayed worrying ecological signals. Specifically, long-term monitoring of their southernmost breeding location on Rouzic Island (Brittany, France) in the Western English Channel demonstrated that, after 70 years of population growth, breeding numbers stagnated around 20,000 pairs from the early 2010s, to then decline gradually (Le Bot et al. 2019). This trend was observed even though there is still abundant available breeding space for gannets on Rouzic, and in the absence of noticeable disturbance or predation by invasive species at this protected breeding site embedded into the National Natural Reserve of the Sept-Iles archipelago. Fifteen years ago, we noticed that gannet foraging effort at Rouzic was disproportionately large for a colony of this size (Grémillet et al. 2006). This already pointed to food limitation. More recently, it has been proposed that the EU ban on the disposal of fishery wastes at sea would deprive
13
Marine Biology
(2020) 167:189
scavenging seabirds, including gannets, from an essential food source (Bicknell et al. 2013). Using Rouzic gannet body condition measurements, stable isotope analyses of their trophic status and GPS-tracking of their movements at sea across 2005–2017 (Le Bot et al. 2019), we demonstrated that gannets fed either on natural prey or fishery wast
Data Loading...
