A recent study of organochlorine levels (pesticides, PCBs etc) in bottlenose dolphins from the Shannon estuary has shown that although concentrations are elevated they are not at levels thought to compromise the health of the dolphins.
Dr Simon Berrow co-ordinator of the study said ‘ultimately all our industrial, domestic and other discharges end up in the sea and if we want to try and understand what effects our activities are having on the environment, we should look at the marine environment and animals that live their’.
Background
Persistent pollutants are ubiquitous in the marine environment. Dolphins are marine top predators and may bio-accumulate pollutants through the food chain. High concentrations of organochlorines (especially Polychlorinated Biphenyls (PCBs)) have been associated with reproductive failure in marine mammals.
The Shannon estuary is the site of the only known resident group of bottlenose dolphins in Ireland and has been designated a candidate Special Area of Conservation under the EU Habitats Directive – the only one for dolphins or porpoises in Ireland. As part of a long term programme to try and identify the main threats to the health and status of the dolphin in the estuary a study of persistent pollutants was carried out.
This study was carried out by the Shannon Dolphin and Wildlife Foundation in collaboration with the Marine Institute, University of Aberdeen, Dalhousie University in Canada and the British Antarctic Survey.
Tissue samples from resident dolphins were obtained by using biopsy darts, which are fired into the dolphin from a crossbow. These darts take a small sample of skin and blubber for analysis. This was the first time biopsy sampling of dolphins has been attempted in Ireland and was carried out under licence from Dúchas.
DNA from the skin was used to sex the dolphin sampled and blubber was used to determine the concentrations of 11 PCB congeners and seven organochlorines (mainly pesticides).
Results
Eight dolphins were sampled (6 male: 2 female). Mean concentrations for all organochlorines were greater in males with maximum concentrations of DDE, trans-nonachlor and PCB con-geners 153 and 138. This is typical of marine mammals in Europe.
Conclusions
The results from this study showed that levels of persistent pollutants are higher in bottlenose dolphins from the Shannon estuary compared to harbour porpoises and common dolphins sampled outside the estuary but similar to white-sided dolphins mass stranded in Co Mayo.
Concentrations were similar to bottlenose dolphins sampled in Scotland but much lower than levels reported from the Mediterranean Sea.
Dr Simon Berrow co-ordinator of the study said ‘Although levels of pollutants were elevated they were below levels thought to compromise the health of dolphins and are not thought to be a major threat to bottlenose dolphins in the Shannon estuary’.