In late November 2014 an oil slick was reported off the coast of Thailand, suspected to be coming from offshore platforms in the Gulf of Thailand. A member of a local marine and coastal resource conservation club said that another spill inn February had killed 10 dolphins and a number of other marine animals. He also reported seeing dolphins swimming in the area of that earlier slick.
It is possible that these dolphins were exposed to oil during the earlier spill and did not survive the secondary effects to the lungs and liver, similar to the dolphin mortality event that is being investigated as possibly related to the Deepwater Horizon event. As acute effects are not often seen in cetaceans (whales and dolphins) the chances of the deaths being related to the latest spill are lower.
It is also possible, however, that the dolphins were victims of local fishing practices, which include taking dolphins that were accidentally entangled in their nets and maintaining them in aerated tanks on their boats for sale to aquariums. Not all dolphins would survive the entanglement in the nets and others might not survive in the system on the fishing boats. These dolphins would likely be thrown overboard.
Neither of these theories have been proven as no post-mortem examinations have been done on the animals. And, while the animals may have oil on them when they wash ashore, the oil exposure could have occurred after the animal died as the body drifted through oiled areas.
Proving cause of dolphins' death can be difficult without resources and interest
To prove oil exposure as the cause of death, expensive and extensive testing is needed. Samples of internal organs and blubber would need to be tested for non-oil contaminants to eliminate possible exposures to other pollutants that could have similar effects. Any oil found would need to be fingerprinted to determine where it came from as there are a number of oil rigs in the Gulf of Thailand and significant shipping traffic through the region.
Dolphins that have been caught in fishing net will usually have some injuries or marks on the body from the net rubbing their skin. There might also be injuries from rough handling during removal from the nets. Should an animal wash ashore with evidence of both oil and net entanglement, it would be difficult to determine whether the oil played any part in the death of that animal.
Without dedicated oiled wildlife response organisations in place, cause of death is often not determined, leaving people to speculate based on minimal information. The presence of the oil is, however, a valid cause for concern for local marine life.
Oil slick pollutes southern beach. Bangkok Post. 19 November 2014. Accessed online 24 November 2014
Another dolphin found dead; villagers point finger at hunters (Thailand).The Ocean Update. Accessed online 24 November 2014