Moving even further east, we stay on the continent and hear from Dr Dove and her work on the remaining population of Irrawaddy dolphins in the Mekong River ... as you'll read the news isn't positive and urgent action is needed to save these remarkable animals. (You can also learn more by visiting Dr Dove's FaceBook page "Help save the Mekong Irrawaddy dolphins from Extinction")
The Mekong River Irrawaddy dolphin (Orcaella brevirostris) population inhabits a 190km stretch of the Mekong River between Cambodia and Lao PDR. This population has been listed as critically endangered on the IUCN Red List of Threatened Species since 2004.
Since mortality monitoring commenced in 2003, the dolphin population has suffered 93 deaths of which over 60 percent were calves under two weeks old. Research carried out by Dr Verné Dove over the past 3 and a half years has found that the dolphins have high levels of environmental contaminants (DDT, PCBs, & Mercury) in their system, which has depleted their immune system, rendering them defenseless against disease. In addition a disease agent known as Aeromonas hydrophila has been identified as the main cause of death in several of the neonatal dolphins and older dolphins. These findings are significant as the latest population abundance monitoring surveys, reveal that there are only approximately between 64 and 76 Irrawaddy dolphins remaining in the Mekong River, with this figure declining each year with an annual average mortality of 13 dolphins. This is a drastic decline in numbers, as only 30 years ago locals report seeing thousands of dolphins.
Dr Verné Dove a veterinarian from Australia with a strong marine mammal background, and a Masters in Conservation Medicine, joined WWF-Cambodia as a volunteer in 2006. She volunteered for 3 years before being given a consultancy position in late 2009.
Her main research focus has been determining the high cause of mortality in the Irrawaddy dolphins, particularly in neonatal calves. In addition to undertaking necropsies on all the dead dolphins, she has also done research on population monitoring including abundance, movement and
distribution; behaviour assessment; looking at the effect of eco-tourism; water quality monitoring; toxicology and acoustic work.
In September 2008 Dr Dove completed a Master’s Thesis dissertation which summarised all her scientific findings. These findings were made public in a report issued by WWF-Cambodia in June 2009. She revealed that pollution in the Mekong River has pushed the local population of Irrawaddy dolphins to the brink of extinction. Her hypothesis was that environmental chemicals found in high levels in dolphin samples, for example DDT, PCBs and Mercury have all acted synergistically to reduce the immune systems capability of warding off disease. She also hypothesised that limited genetic diversity due to inbreeding was possibly another factor contributing to the dolphin deaths, as inbreeding depression can further reduce the immune’s systems ability to function effectively. Aeromonas hydrophila and several other opportunistic bacterial disease that were identified as contributing to the cause of some dolphin deaths would not normally be fatal unless the dolphin’s immune systems were suppressed.
The source of some of the environmental contaminants may involve several countries through which the Mekong River flows as these pollutants particularly the pesticides are widely distributed in the environment. However some contaminants such as Mercury, may be from local gold mining activities in Cambodia. These findings are worrisome as the same pollutants may also pose a health risk to human populations living along the Mekong that consume the same fish as the dolphins.
The Mekong River dolphins are isolated from other members of their species and unless a recovery project is undertaken to reduce the very high and unsustainable mortality level, this population will become functionally extinct in the not too distant future. There is still a small window of opportunity to save this population, but time is running out.
Some further reading for you ...
http://www.divshare.com/folder/547250-3de to download:
• The dolphin necropsy report in Khmer and English
• Broadcast quality footage of the dolphins swimming the Mekong River at Cambodia.
http://www.panda.org/wwf_news/multimedia/photo/irrawaddy_dolphin.cfm to download:
• High quality photos of the dolphins playing in the Mekong River in Cambodia.