Maui's dolphin abundance estimate
Find out about the work DOC has done to estimate the size of the Maui's dolphin population.
2010-2011 abundance estimate
In 2010, the Department of Conservation 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 individual dolphins. This allows us to derive information such as “effective population size” (which estimates the effective number of breeding adults in the parental generation), gives an indication of genetic diversity, estimates how many are males and how many are females, how much they move around over both the short-term (i.e. days) and long-term (months/year) and more.
During two austral summers (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 was calculated.
Maui dolphin survey, west Coast of the North Island between Kaipara harbour and New Plymouth
- 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 female South Island Hector's dolphins swimming with 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 evidence that these female Hector’s dolphins have interbred with Maui’s dolphins, it is possible that they can. This could enhance the genetic diversity of the Maui’s dolphin population.
- 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)
This abundance estimate, published in 2006, 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 (with a 95% confidence interval of 48-252).
back to top