Dolphins: Devastating skin disease caused by decreased water salinity linked to climate change

A devastating skin disease affecting dolphins — which can leave up to 70 per cent of each of their bodies covered in lesions — is linked to climate change, a study found.

US and Australian experts found that ‘freshwater skin disease’ is associated with an increase in the frequency and intensity of storm systems.

Storms can bring in such vast quantities of rainwater that they decrease the salinity of coastal waters until they become freshwater, in which the dolphins cannot live.

The resulting skin condition — first identified in Louisiana in 2007 but since been spotted in coastal areas around the globe — causes patchy and raised lesions.

The long-term outlook for those with the skin disease is poor — and particularly so in cases where the animals suffered from prolonged exposure to freshwater. 

Outbreaks in recent years have been recorded in the US states of Alabama, Florida, Louisiana, Mississippi and Texas — and along the coast of Australia.

In each case, the location in question had recently experienced a sudden and drastic decrease in the salinity of the coastal waters.

A devastating skin disease affecting dolphins — which can leave up to 70 per cent of each of their bodies covered in lesions, as pictured — is linked to climate change, a study found

A devastating skin disease affecting dolphins — which can leave up to 70 per cent of each of their bodies covered in lesions, as pictured — is linked to climate change, a study found

Researchers believe that the first recorded outbreak — which was detected in 40 bottlenose dolphins living in Lake Pontchartrain, a brackish estuary near New Orleans — was caused by storm waters left from 2005’s Hurricane Katrina.

‘This devastating skin disease has been killing dolphins since Hurricane Katrina, and we’re pleased to finally define the problem,’ said paper author and pathologist Pádraig Duignan of the The Marine Mammal Center in Sausalito, California. 

‘With a record hurricane season in the Gulf of Mexico this year and more intense storm systems worldwide due to climate change, we can absolutely expect to see more of these devastating outbreaks killing dolphins.’

According to the researchers, coastal dolphins can accommodate mild changes in seawater salinity — such as occurs seasonally — but they are not a freshwater species and suffer when waters are not sufficiently saline. 

Severe cyclones and hurricanes — especially if they occur frequently and following periods of drought — can deliver such unusually large volumes of rain that they turn coastal waters into essentially a freshwater environment.

In the wake of major storms like Harvey and Katrina, these conditions can last for as long as months — with devastating effects for local dolphin populations.

Storms can bring in such vast quantities of rainwater that they decrease the salinity of coastal waters until they become freshwater, in which the dolphins cannot live. The resulting skin condition — first identified in Louisiana in 2007 but since been spotted around the globe — causes patchy and raised skin lesions, as pictured on this bottlenose dolphin from Australia

Storms can bring in such vast quantities of rainwater that they decrease the salinity of coastal waters until they become freshwater, in which the dolphins cannot live. The resulting skin condition — first identified in Louisiana in 2007 but since been spotted around the globe — causes patchy and raised skin lesions, as pictured on this bottlenose dolphin from Australia

As average global temperatures continue to rise thanks to man-made climate change, experts predict that extreme storms will be a more regular occurrence. 

This, the researchers warned, will in consequence result in more frequent and severe outbreaks of freshwater skin disease in impacted coastal areas.

The findings of the study has major implications for the current outbreak in Australia, the team added — which is impacting the rare and threatened Burrunan dolphin — and could help experts to diagnose and treat the affected animals.

The long-term outlook for those with the skin disease is poor — and particularly so in cases where the animals suffered from prolonged exposure to freshwater. Pictured, a researcher examines the corpse of an adult female bottlenose dolphin, covered in lesions, found near the mouth of the Mitchell River near Lake King in Western Australia

 The long-term outlook for those with the skin disease is poor — and particularly so in cases where the animals suffered from prolonged exposure to freshwater. Pictured, a researcher examines the corpse of an adult female bottlenose dolphin, covered in lesions, found near the mouth of the Mitchell River near Lake King in Western Australia

‘The findings in this paper will allow better mitigation of the factors that lead disease outbreaks for coastal dolphin communities that are already under threat from habitat loss and degradation,’ Dr Duignan said.

‘We hope it is the first step in mitigating the deadly disease and marshalling the ocean community to further fight climate change,’ he concluded. 

The full findings of the study were published in the journal Scientific Reports.

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