Environmental Predictors of Seabird Wrecks in a Tropical Coastal Area.

Davi Castro Tavares,Salvatore Siciliano,Jailson Fulgencio De Moura

doi:10.1371/journal.pone.0168717

Abstract

Beached bird surveys have been widely used to monitor the impact of oil pollution in the oceans. However, separating the combined effects of oil pollution, environmental variables and methodological aspects of beach monitoring on seabird stranding patterns is a challenging task. The effects of a comprehensive set of oceanographic and climatic variables and oil pollution on seabird strandings in a tropical area of Brazil were investigated herein, using two robust and innovative methods: Generalized Linear Mixed Models and Structural Equation Modeling. We assessed strandings of four resident seabird species along 480 km of beaches divided into 11 sampling areas, between November 2010 and September 2013. We found that increasing the distance from the nearest breeding island reduce the seabird stranding events. Storm activity and biological productivity were the most important factors affecting the stranding events of brown boobies Sula leucogaster, Cabot’s terns Thalasseus acuflavidus and kelp gulls Larus dominicanus. These species are also indirectly affected by warm tropical waters, which reduce chlorophyll-a concentrations. Beach surveys are, thus, useful to investigate the mortality rates of resident species near breeding sites, where individuals are more abundant and exposed to local factors associated with at-sea mortality. In contrast, conservation actions and monitoring programs for far-ranging seabird species are needed in more distant foraging areas. Furthermore, beach monitoring programs investigating the impact of oil pollution on seabirds need to account for the effects of environmental factors on stranding patterns. The present study also demonstrated that seabirds inhabiting tropical coastal waters are sensitive to climate conditions such as adverse weather, which are expected to increase in frequency and intensity in next decades.

Highlights

Seabirds are among the most vulnerable groups of marine vertebrates, with 97 of the 346 living species globally threatened, and the populations of 162 species showing declines [1, 2]
The present study demonstrated that seabirds inhabiting tropical coastal waters are sensitive to climate conditions such as adverse weather, which are expected to increase in frequency and intensity in decades
We demonstrate that the combination of environmental conditions, such as increased sea surface temperature, reduced biological productivity and adverse weather, is affecting seabird mortality at tropical sites

Summary

Introduction

Seabirds are among the most vulnerable groups of marine vertebrates, with 97 of the 346 living species globally threatened, and the populations of 162 species showing declines [1, 2]. These organisms are sensitive to habitat alterations and anthropogenic disturbances, and, for this reason, are used as indicators of environmental quality and health [3,4,5]. Seabirds die at sea and their corpses are subsequently deposited along beaches. Since it is impossible to monitor seabird deaths at sea, mortality is evaluated based on carcass deposition patterns along beaches.

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Discussion

Conclusion