Pollutants banned 40 years ago found in local dolphins' skin

Thursday 19 September 2019

Dolphins may be delighting people with more frequent visits to local waters in recent years – but a new study has made a worrying revelation about the level of pollution they've been exposed to.

A survey of bottlenose dolphins – the type most commonly spotted around the Channel Islands – found record high levels of mercury in their blubber and skin, as well as toxic pollutants banned as many as four decades ago.

The study was carried out by a team of scientists aiming to plug a research gap, as no toxicological data was available on bottlenose dolphins in the Normano-Breton Gulf (NBG), which is the largest European community of such dolphins, “despite their proximity to urban and industrial activities”. 

They therefore concluded it was critical to carry out such a research “for risk assessment and long-term management” of the species.

Pictured: The survey was carried out in the Normano-Breton Gulf (NBG).

Having analysed samples of skin and blubber from 82 bottlenose dolphins, the research group said organochlorinated contaminants were among the compounds most commonly found.

Such contaminants were banned in the 70s and 90s, but the scientists explained that their persistent chemical properties mean that they can travel far and remain in water for many years, as well as penetrating deep ocean fauna.

The study concluded that local bottlenose dolphins have higher concentrations of these contaminants in their blubber than other groups in European waters.

The mercury concentrations in the skin were also among the highest concentrations observed in this species and very close to the concentrations previously described for the bottlenose dolphins in the Mediterranean Sea and from the Florida coastal Everglades - two sites known for their high contamination levels. 

“Our data suggest a high exposure of the NBG bottlenose dolphins linked to their high trophic position and their diet, which is composed of mackerel,” the scientists said. 

Pictured: The team analysed biopsy samples of skin and blubber from 82 bottlenose dolphins.

The scientists said the conservation of the bottlenose dolphins – which are protected by the Habitats Directive in European waters - requires the creation of special areas of conservation as well as for strict protection.

They noted that human activities are increasing in the Gulf and that noise pollution, disturbance by tourism activities and by catch could pose a threat to the dolphins.

Highlighting that bottlenose dolphins have declined in the northeast Atlantic, the team said the last member of a resident bottlenose dolphin population in Arcachon (France) died 18 years ago while a group in Portugal (Sado Estuary) has declined due to low calf survival over several decades. 

They “strongly recommend” the Normanno-Breton Gulf becomes a “special area of conservation (cSAC) candidate” in a bid to preserve what they describe as “the last large European population of bottlenose dolphins.”

The news comes as dolphin sightings around the Channel Islands have hit their highest levels in years. Seafaris alone reported 364 separate sightings in all of 2018 - a 30% rise in around five years.

"The Seafaris staff are renowned for their eagle eyed vision, and maybe we are getting slightly better at spotting them, but it is safe to say the Channel Islands bottlenose dolphin population is increasing," the team wrote in a blog.