Contaminantes ambientales persistentes y su influencia sobre el éxito reproductor en una colonia de gaviota de Audouin (Ichtyaetus audouinii) en el mediterráneo occidental

Abstract

The Audouin's gull (Ichthyaetus audouinii) is a medium size Larid that breeds in the Mediterranean mainly on the Spanish coast where more than 85% of its worldwide population stock is found. This explains the importance of studies about the factors that threaten its conservation. The presence of contaminants (heavy metals and organochlorine compounds) in samples of different seagull (adult and chicks) tissues from four Mediterranean reproduction colonies between the 0º and 3º East longitude, was investigated between 2001-2011; Grosa Island (Murcia), Torrevieja (Alicante), Ebro Delta (Tarragona) and Moltona Island (Balearic Islands). Level of heavy metals (Zn, Cd, Pb and Cu) in chicks blood samples, feathers (adults and chicks) and eggshells, were analyzed by anodic stripping voltammetry (DPASV), while Hg in blood and feathers by atomic absorption spectrophotometry, using a direct mercury analyzer. The analysis of organochlorines in egg content was performed by gas chromatography with electron capture detection (GC-ECD). Prior to the toxicological studies, thermal stress in chicks, the perinatal mortality and sex ratio in the colony of Grosa Island were evaluated. It was verified the absence of thermal stress in the chicks due to handling at the time of sampling, and the perinatal mortality events occurred between the day of the laying and the first 7 days of the chicks' life (90% of the cases). The sex ratio showed a higher proportion of males than females (1.63: 1). This proportion was higher as the productivity of the colony increased. Tissue analyses showed that, in the Grosa Island the chicks Pb and Cd levels were higher than those of Torrevieja and were above those described by some authors in healthy birds. On the other hand, Hg and Zn levels were higher in Torrevieja colony, where the chicks reached worrying concentrations, associating this metal as well as Zn with the loss of productivity of the colony, although the latter to a lesser extent. The analyses of heavy metals in the eggshells showed that the metals were detected in this tissue according to Zn> Cu> Pb> Cd. Pb and Cd concentrations were higher than those found by other authors in the eastern Mediterranean for the same species. A significant negative correlation was observed between Cu-egg size, and Pb-shell weight. The presence of DDE, HCB, dieldrin and 21 PCBs congeners were detected in the eggs. The results showed that this species is exposed to abnormally high levels of DDE, dieldrin and PCBs. This study showed a pattern of decreased exposure to PCBs "target", in the Western Mediterranean, a 50% for every 10 years and that exposure is more related to feeding habits than to geographic location. DDE levels above 11,80 µg/g were established as NOEL in relation to thinning of the shell. Pb, Zn and Cu concentrations in chicks feathers from Grosa Island and Hg from Torrevieja, suggest that the exposure in the Southeastern Spanish coast is higher than Ebro Delta, and it was verified that females eliminate more metallic waste from their body through the feathers than through eggs laying.