The use of DNA profiles to identify individuals and estimate abundance was chosen because of the importance of subspecies identification and the potential to get more information about individual dolphins.
This allows us to derive information such as:
- 'effective population size' (estimates the effective number of breeding adults in the parental generation)
- 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.
The 2015-16 and 2010-11 abundance estimates used DNA profiles while the 2006 estimate used aerial surveys.
2015-16 abundance estimate
In 2015 DOC and Ministry for Primary Industries, in collaboration with Auckland and Oregon State Universities, began a repeat of the abundance estimate of Māui dolphins.
The previous estimate was carried out in 2010 and 2011 summer seasons, and estimated there were approximately 55 individuals aged 1+ years.
The revised population estimate was carried out over two summer seasons, 2015 and 2016. The 2015 and 2016 field reports are available below.
- The abundance of Māui dolphins over 1 year of age was estimated to be 63 with a 95% confidence interval of 57 to 75 (this means that the researchers are 95% confident that there are between 57-75 Māui dolphins over the age of 1 year)
- Over both years a total of 92 biopsy samples were collected from a total of 51 individual dolphins
- 32 of these individuals were females
- 17 individuals were sampled in both years
- 49 individuals were identified as Māui dolphins
- 2 individuals were identified as Hector’s dolphins, one of which was sampled in the previous surveys (2010/2011), and a male Hector’s was sampled in both 2015 and 2016.
The 2015 and 2016 field seasons were successful in matching the effort of the 2010 and 2011 surveys with a comparable number of surveys, duration of the survey period and coverage of the primary known habitat for Māui dolphins.
The results of this abundance estimate will be used to inform the review of the Hector’s and Māui dolphin Threat Management Plan in 2018.
Estimating the abundance and effective population size of Māui dolphins using microsatellite genotypes in 2015-16, with retrospective matching to 2001-16:
Māui dolphin biopsy sampling survey field reports and preliminary results:
2010-2011 abundance estimate
In 2010, DOC began field work in collaboration with the University of Auckland and Oregon State University to obtain a new abundance estimate.
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.
- The abundance of Māui dolphin of over 1 year of age for 2010-11 was estimated to be approximately 55 with a 95% confidence interval of 48 to 69 (this means that the researchers are 95% confident that there are between 48-69 Māui dolphin over the age of 1).
- Utilising genetic samples from Māui dolphin 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 Māui dolphin. 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 Māui dolphin, it is possible that they can. This could enhance the genetic diversity of the Māui 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 2006 estimate) because of the different methods used, but both the reports highlight that the population is very small and are indicative of a recent decline.
Estimating the abundance and effective population size of Maui’s dolphins using microsatellite genotypes in 2010–11, with retrospective matching to 2001–07 (PDF, 3,061K)
The 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).
A new abundance estimate for Maui’s dolphin: What does it mean for managing this critically endangered species?
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