Threats not caused by people
Find out more about threats to Maui's dolphins not caused by people.
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Disease
Predation
Weather
Disease
An assessment of health of Hector's dolphins during a 2004 trial tagging study at Banks Peninsula found that most results were within expected ranges or not significantly different when compared with similar species.
The major result was the diagnosis of Brucella abortus (or a similar organism) in one tagged animal. Brucella is a pathogen of terrestrial mammals that can cause late pregnancy abortion, and has been seen in a range of cetacean species elsewhere. In 2006 Brucella was identified in a dead Maui's dolphin and this could potentially have serious ramifications for this critically small population.
Whale lice are found on freshly dead dolphins and at close range they can be seen on living dolphins as small dark brown spots, but do not appear to cause any harm. Several species of nematodes and lungworms have also been found in Hector's and Maui's dolphins. There is no evidence that these parasitic infections could have caused death.
Pneumonia has been noted in several Hector's dolphins, and may have played a role in the deaths of the animals. This may be indicative of accumulation of other stressors (not normally lethal on their own) that lead to pneumonia in these dolphins.
Predation
The dolphin's main natural predators are thought to be sharks and killer whale. There are three shark species around New Zealand that are suspected to consume Maui's dolphin - great white, blue, and broad-nosed seven-gilled sharks. Mako sharks and bronze whaler sharks are unlikely to constitute a serious risk for Maui's dolphins.
There are two reported instances of white sharks eating Maui's dolphins off the North Island's west coast. In both instances it is unknown if the dolphins were killed by the shark or scavenged after the dolphins died.
A seven-gilled shark caught in the Manukau Harbour was found to have Maui's dolphin remains within its stomach. Due to the small size of the shark it is presumed to have scavenged the remains.
Apart from sharks, other likely natural predators of Maui's dolphin are orca/killer whales (Orcinus orca), which are present in the coastal waters of New Zealand.
Weather
Extreme weather conditions have been thought to cause the separation of calves from their mothers, resulting in the death of the calf.
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