Māui dolphin toxicology and disease research
IntroductionResults of research into levels of pollution and toxoplasma infection in Māui and Hector’s dolphins.
In 2009, DOC contracted Massey University to do some research into the levels of pollution found in Māui and Hector’s dolphins. This involved testing samples from Māui and Hector’s dolphins that had either washed up or been caught in fishing nets in the previous few years (all the Māui dolphin had washed up).
The researchers were looking particularly for pesticides like DDT and organochlorines. Dolphins like Māui and Hector’s are particularly at risk because they live in coastal waters where these pesticides end up after being washed down rivers and other waterways.
Relatively high levels of these chemicals were found in both Māui and Hector’s dolphins. However, none of the dolphins examined had concentrations of chemicals high enough to cause a reduction in fertility or a reduction in their immunity. The levels were certainly not high enough to cause death.
There are other pollutants in the environment which could potentially be having an impact, but at this stage it seems unlikely that they are a major cause of decline in the dolphins.
A 2013 study by Massey University found 7 out of 28 (25%) of Hector’s and Māui dolphin that were found beachcast between 2007 and 2011 died due to toxoplasmosis (5 of 25 Hector’s dolphins and 2 of 3 Māui dolphin). Further testing showed that of dolphins that died of other causes, 61% were also infected with Toxoplasma. This disease can cause death, behavioural changes, still births and reduced reproductive rate.
Toxoplasma infection occurs through ingestion of either infectious oocysts (hardy thick-walled spores that are able to survive for lengthy periods outside of a host) or tissue cysts, and can occur in all warm-blooded species. Wild and domestic felids are the only source of infectious oocysts, which are shed in the faeces of infected cats, particularly newly-infected kittens. The main source of infection for dolphins is likely to be through freshwater run-off from surfaces contaminated with cat faeces.
Massey University has been contracted by DOC to further investigate Toxoplasma gondii infection in Hector’s and Māui dolphin, with the particular focus to characterise the source and route of entry into the marine environment for an atypical strain. Clarification of the pathway of toxoplasma infection will enable better management decisions to be made, and recognition of the role of this infectious disease in dolphin mortality will strengthen the case for control measures aimed at eliminating preventable causes of death.
Massey University will also continue with ongoing necropsy of Hector’s and Māui dolphin carcasses from bycaught or beachcast animals and screen for a range of diseases that may have an effect on the population.