Māui dolphin toxicology and disease research

Toxicology research

In 2009, the Department of Conservation (DOC) asked Massey University to investigate pollution levels in Māui and Hector’s dolphins. Researchers tested samples from Māui and Hector’s dolphins that had either washed up on beaches (beach cast) or been caught in fishing nets. All the Māui dolphin samples came from animals that had been beach cast.

The study focused on harmful chemicals like DDT and organochlorine pesticides, which can build up in coastal waters where these dolphins live. These pollutants often enter the ocean through rivers and stormwater run-off from land.

The results showed relatively high levels of these chemicals in both Māui and Hector’s dolphins. However, none of the dolphins had concentrations high enough to affect their fertility, weaken their immune systems, or cause death.

While other pollutants may still be present in the environment, current evidence suggests that chemical pollution is unlikely to be a major cause of the dolphins’ decline.

Disease research

A 2013 study by Massey University found that 7 out of 28 (25%) Māui and Hector’s dolphins that were found beach cast between 2007 and 2011 had died from toxoplasmosis – a disease caused by the parasite Toxoplasma gondii. This included 5 Hector’s dolphins and 2 Māui dolphins. The study also showed that 61% of dolphins that died from other causes were infected, suggesting that exposure to the parasite is widespread. Toxoplasmosis can lead to death, changes in behaviour, stillbirths, and lower reproductive success.

Dolphins can become infected with Toxoplasma gondii by swallowing infectious oocysts – hardy spores (eggs) shed in the faeces of cats, especially newly infected kittens. Oocysts are tough and can survive in the environment for long periods. The most likely way dolphins are exposed is through freshwater run-off that carries infectious oocysts from land into the ocean.

To better understand this threat, DOC has contracted Massey University to investigate the source and route of entry of Toxoplasma gondii into the marine environment, particularly focusing on lethal strains.

Understanding how Toxoplasma enters the marine environment will help guide better decisions to protect dolphins. Recognising the role this disease plays in dolphin deaths also strengthens the case for taking action to reduce preventable risks.

Disease surveillance programme

The current surveillance programme builds on earlier work and aims to establish long-term monitoring of key pathogens affecting dolphin health. The focus is on Toxoplasma gondii, Brucella spp., and morbilliviruses, all of which can cause serious illness or death.

Surveillance findings so far:

Toxoplasma gondii (the parasite that causes toxoplasmosis)

• 135 tissues from 28 dolphins tested between March 2022 and June 2025.
• 11 dolphins (39%) tested positive for Toxoplasma DNA.
• One Māui dolphin (H315) died from toxoplasmosis; the others had latent infections.
• Archived tissues from dolphins H333–H347 will be tested next.

Brucella spp.

• 54 tissues from 27 dolphins tested.
• No positive results to date.

Morbillivirus

• Initial tests showed possible positives, but further analysis suggests no current infections.
• Massey University is developing a new testing protocol to improve accuracy.

Read the full report (PDF, 255K)