2010-2011 abundance estimate

Maui's dolphins

In 2010, DOC began field work in collaboration with the University of Auckland and Oregon State University to obtain a new abundance estimate.

The use of DNA profiles to identify individuals and estimate abundance was chosen because of the potential to get more information about the individual dolphins, such as the size of the parental generation (‘effective population size’ – this gives an indication of the loss of genetic diversity), how many are males and how many are females, how much they move around over both the short (days) and long (year) term and more.

From February to March in 2010 and 2011, the research team collected samples from a total of 41 different individuals. Some individuals were sampled more than once and by examining how many of the same dolphins were resampled in the second round of research against the number of new individuals sampled, a revised abundance estimate can be calculated.

Key findings:

• The abundance of Maui’s dolphins of over 1 year of age for 2010-11 was estimated to be 55  with a 95% confidence interval of 48 to 69 (this means that the researchers are 95% confident that there are between 48-69 Maui’s dolphins over the age of 1).
• Utilising genetic samples from Maui’s dolphins available from 2001-07 and the current 2010-11 sampling period the rate of change for the population from 2001-11 could be estimated. The result suggests a slow decline over the past decade (-3% per year), although this trend could not be confirmed with 95% confidence.
• In 2010, DNA fingerprinting of the samples collected showed that there were two South Island Hector's dolphins swimming with the Maui's dolphins. In 2011 one of those Hector's dolphins was sampled again in a similar area. This is the first record of this occurring.
• Although there is no record that the female Hector’s dolphin have interbred with Maui’s dolphins, it is possible that they can and this might enhance its genetic diversity.
• An individual dolphin moved about 80km in less than three weeks, with others moving in the vicinity of 30km before being sampled again. This indicates that the individuals remaining in the population can still mix amongst themselves and are not restricted to small isolated groups only.
• It seems that there are at least as many females as males in the population. Of the 41 individuals sampled, 25 were female and 16 were male. Having more females in a population usually gives the best chance of the species recovering. 

The data from this report is not directly comparable with earlier aerial surveys (see 2005 estimate) because of the different methods used, but the reports both highlight that the population is very small and are indicative of a recent decline.

Maui's dolphin abundance estimate report (PDF, 3,061K)

2005 estimate

This estimate, published in 2005, was made from extensive aerial surveys by Otago University in 2004. The researchers then used a statistical model to come up with the estimate. This suggested that there were around 111 dolphins left (the 95% confidence interval was 48-252).

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