Concerns have been raised to the health and long term future of Bottlenose dolphins (Tursiops truncatus) resident off the coast of Cornwall.
A research project between Exeter University and Cornwall Wildlife Trust analysed statistics related to the number of sightings and the numbers of dolphins in each group spotted as well as records of strandings going back to 1991.
This showed worryingly that 20 years ago 66% of cetacean sightings of the peninsula were of Bottlenose dolphins compared to just 27% in 2008, while at the same time average pod size has shrunk from 18 to just six6. The study also noted that despite calves being regularly seen the population was still shrinking.
The reasons behind this decline is unclear with pressure from fishing on their food sources one potential cause, but a study published in August points to pollution being a major contributing factor.
Higher than usual instances of the potentially lethal Brucella ceti bacteria have been found in dead, stranded Bottlenoses in the last six years with half of the eight specimens found being infected.
However in the rest of England and Wales there were no cases of the bacteria in the 15 dead dolphins recorded between 1989 and 2008 and only one case was reported in the 36 dolphins examined in Scotland during the same period.
The scientists believe there may be a correlation between the presence of the bacteria and the extremely high levels of polychlorinated biphenyls (PCB's) found in the blubber of two of the dolphins, one of them having the highest level recorded in the species in the UK for 20 years.
PCB's were once commonly used in paints, adhesives and fire-retardants amongst other things but have been banned due to their toxic nature. Despite this they still persist in the marine environment and have been linked with damage to immune systems and fertility in cetaceans.
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