First assessment of the ecotoxicological status of Cuvier's beaked whale (Ziphius cavirostris) in the NW Mediterranean Sea

Cuvier's beaked whale (Cbw) is one of the least known species in the world. The Mediterranean subpopulation is ranked as Vulnerable (VU) in the “IUCN Red List of Threatened Species”, considering both the declining population trend both the low number of mature individuals estimated in the basin. While effects of underwater noise, known to be one of the main threats to the species, are being widely investigated, the ecotoxicological risk of the species is still unknown. The objective of this study is to investigate for the first time the ecotoxicological status of Cbw in the NW Mediterranean Sea (Pelagos Sanctuary). The levels of organochlorine compounds (PCBs), polybrominated diphenyl ethers (PBDEs), and related biomarkers responses (induction of cytochrome's P450 CYP1A1 and CYP2B isoforms) were investigated in 22 skin biopsies from free-ranging organisms. This sample set represent about the 20% of estimated size of the resident population in the area which has been monitored during the last fifteen years. All the animals were sexed and categorized into three different age classes (juveniles, subadults, adults) by both the estimated size and coloration patterns. CYP1A1 and CYP2B protein activity show different trends among different age groups and between sex. The contaminants analysis highlight that the average abundance pattern for the target contaminants was PCBs>PBDEs and the concentration values are linked to age and sex, with males showing higher levels (∑PCBs 23.77 mg/kg l.w., ∑PBDEs 0.516 mg/kg l.w.) than females (∑PCBs 8.08 mg/kg l.w.,l ∑PBDEs 0.172 mg/kg l.w.). 80% of sampled cbw had PCB concentrations above the toxicity threshold for physiological effects in marine mammals, suggesting a potential effect on this mediterranean population fitness. This study represents an important step forward in our understanding of the effects of toxic compounds in combination with other known or suspected threats to this population of Cuvier's beaked whale.