Temporal and Spatial Distribution of Mercury in Gulls Eggs from the Iberian Peninsula

We examined how coastal mercury contamination varied spatially and temporally across the Iberian Peninsula by measuring mercury concentrations in the eggs of the sentinel biomonitor yellow-legged gull (Larus michahellis). Samples were collected from eight colonies that ranged from the Atlantic across the south and northern areas of the Mediterranean. We also measured Hg residues in eggs of the one of the most endangered gull species in the world, the Audouin’s gull (Larus audouinii) from the Ebro Delta, where colonies of yellow-legged and Audouin’s gull co-occur. Fresh eggs were collected in 2009 and 2016 and samples were pooled from each colony for analysis. Mercury concentrations in yellow-legged gulls ranged between 0.4 and 2.8 mg/kg dry weight (dw); although there were no significant differences in concentrations between sampling periods, significant differences were found between colonies. Higher concentrations were associated with northern Mediterranean colonies (Columbretes and Ebro Delta), likely due to proximity to emission sources, circulatory marine currents and diet composition. Mercury concentrations in yellow-legged gull eggs were lower than those reported to result in impaired hatching. Residues in Audouin’s gull eggs from the Ebro Delta were significantly higher (4.0–5.6 mg/kg dw) than those in yellow-legged gull from the same location, probably associated with dietary differences. Mercury levels in Audouin’s gull were ten times above the benchmark suggested to reduce nest success by 10%. Overall, these results raise concern for adverse health impacts in this protected seabird species and further investigation in Audouin’s gull eggs from the Ebro Delta is recommended. © 2018, The Author(s).

From Spain, we acknowledge the Islas Atlánticas National Park, Refugio de Caza de las Islas Chafarinas, Illes Medes Natural Park, Delta de l’Ebre Natural Park, Columbretes Islands Natural Park, Montgrí, les Illes Medes i el Baix Ter Natural Park, that authorized our work. From Portugal, we acknowledge Maria Felisbina Quadrado and Sofia Batista from the Portuguese Environment Agency (APA), Department of Water Resources for the support; Lurdes Morais from Portuguese Protected Area of Berlengas-Portuguese Institute for the Conservation of Nature and Forests (ICNF) for the sampling permission. The Servei de Protecció i Gestió de la Fauna (Catalan Government) and Direcció General de Medi Natural i d’Avaluació Ambiental (Generalitat Valenciana) are acknowledged for sampling permission. National and Natural Park´s staff are acknowledges for their help in the gull eggs collection and transport. We are especially grateful to Javier Zapata (Chafarinas), José Antonio Fernández-Bouza and Vicente Piorno (Atlantic Islands), Juan Jiménez (Generalitat Valenciana), Miguel Ángel Monsalve Dolz (Equipo de Seguimiento de Fauna—VAERSA, Generalitat Valenciana), Francesc Vidal and Antoni Curcó (PN Delta de l’Ebre) for their enthusiasm, implication, logistic support, and valuable contributions to the project. Dr. Jacob González-Solis, Dr. Dani Oro, Javier Zapata, Cristina García and Marc Bosch are acknowledged for aiding in the sampling campaigns carried out in 2009. This study was financed by the Spanish Autonomous Organism of National Parks [Projects 2012/768 and 2009/038]. R. Ballesteros is acknowledged for his help in preparing the egg material for Hg analysis. From UK, this work was supported by the Natural Environment Research Council as part of the CEH programme delivering National Capability.

Peer reviewed