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Shannon dolphins under threat from Persistent Pollutants

The bottlenose dolphins living in the Shannon Estuary are the least contaminated in Europe, a new study has shown, but levels are still above the toxic threshold thought to impact on their health and reproduction.

A new study just published in Scientific Reports ( explored levels and trends in organochlorine residues in a number of populations throughout Europe including bottlenose dolphins and killer whales in Ireland. Biopsy samples from 8 dolphins resident in the Shannon Estuary were included in the study, which is the largest study of persistent pollutants in dolphins in the world. The results showed that although many of the most toxic organochlorines are no longer produced, concentrations in a range of species and populations throughout Europe are so high to impair reproduction and in some cases could lead to the extinction of these populations.

A bottlenose dolphin mother and calf in the Shannon Estuary, Ireland

Dr Simon Berrow, Project Manager with the Shannon Dolphin and Wildlife Foundation, based in Kilrush, Co. Clare and lecturer on the Applied Freshwater and Marine Biology degree in the Galway-Mayo Institute of Technology, who was one of the co-authors in the study, said “it's quite shocking, pollution concerns have decreased in recent years as many of these chemicals are no longer produced and other issues such as climate change, fishing and acoustic trauma have become greater conservation issues in Europe for dolphins and other marine mammals. However, this study shows the threat pollution poses to our coastal species has not gone away and indeed is far greater than we expected”.

Organochlorines such as poly-chlorinated biphenyls (PCBs) were manufactured from the 1920s, but were banned in the UK in 1981 and in the rest of the EU in 1987. However less than 10% of the total PCBs manufactured have entered the marine environment so it is imperative we prevent more entering through, for example, leakages from landfill and re-suspension during dredging. Once these persistent pollutants have entered the marine environment, there is practically nothing that can be done to remove them. We are creating a toxic time bomb!

PCBs have been shown to have a wide-ranging impact on human and animal health, from links to cancer, to suppressing the immune system and causing reproductive failure. PCB contamination seems to have a marked effect on breeding success and is particularly an issue for calves. When a mother is lactating, up to 90% of her PCB body burden can be passed into the calf across the placenta and through the milk, leading to death of the calf. In highly contaminated populations it may take a number of calves to die prematurely, to lower the concentrations in the mother to levels where a new calf may be viable.

Mother and newborn calf in the Shannon Estuary

Dr Berrow added “we provided samples from bottlenose dolphins in the Shannon Estuary to this study and although we are pleased that concentrations in the Shannon dolphins were the lowest in Europe, the levels were still well above the toxicity threshold which leads to serious impacts”. Tissue samples from a killer whale stranded in Cork were also analysed and levels in this individual were some of the highest concentrations recorded anywhere for this species in this study.

Lead author on the study Dr Paul Jepson, who is a wildlife veterinarian from the Zoological Society of London, said “our findings show that, despite the ban and initial decline in environmental contamination, PCBs still persist at dangerously high levels in European dolphins, probably the highest in the world right now, by some way”.

It is essential that the threat persistent pollutants such as these organochlorines pose is taken seriously and all efforts are taken to ensure none enter the marine environment. Dr Berrow warned “that this is just the tip of the iceberg and if we looked at the concentrations of other contaminants such as polychlorinated dibenzofurans, polychlorinated dibenzo-p-dioxins and the brominated flame retardants we would discover our dolphins and whales are swimming in a cocktail of persistent pollutants having unknown but potentially catastrophic effects on them and other marine life”.

Dr Berrow added “the number of calves born in the estuary each year ranges from 6-10 which we feel is quite healthy, but how many would be born if levels of persistent pollutants were below the toxic threshold? I guess we will never know!

The full paper is entitled PCB pollution continues to impact populations of orcas and other dolphins in European waters
By Paul D. Jepson, Rob Deaville, Jonathan L. Barber, Àlex Aguilar, Asunción Borrell, Sinéad Murphy, Jon Barry, Andrew Brownlow, James Barnett, Simon Berrow, Andrew A. Cunningham, Nicholas J. Davison, Marielten Doeschate, Ruth Esteban, Marisa Ferreira, Andrew D. Foote, Tilen Genov, Joan Giménez, Jan Loveridge, Ángela Llavona, Vidal Martin, David L. Maxwell, Alexandra Papachlimitzou, Rod Penrose, Matthew W. Perkins, Brian Smith, Renaud de Stephanis, Nick Tregenza, Philippe Verborgh, Antonio Fernandez and Robin J. Law. Scientific Reports | 6:18573 | DOI: 10.1038/srep18573


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