Hector's DolphinsHector’s dolphins are a rare dolphin species that inhabits coastal waters around New Zealand up to a depth of 100 meters. They are not only the smallest and rarest marine dolphin species, but also one of the best studied dolphins in the world.
Fishing is their main threat (commercial and recreational gillnetting, and trawling). Scientists estimate that there were about 30,000 Hector's dolphins in the 1970s. Now there are just over 7,000. One of its two subspecies, the Maui's Dolphin, has a population of less than 50. Although some measures have been taken (most notably the closures introduced in 2008), Hector’s dolphins are still declining. Maui's DolphinsThis subspecies of Hector’s dolphins survives only in a remnant population off the North Island’s West (WCNI) and is facing imminent extinction.
Ninety percent of Maui’s dolphins are already gone. Maui’s dolphins number less than 50 individuals. This is down from their previous estimate of 111 older than one year, in 2005. This number equates to less than 20 breeding females, so every animal is precious beyond measure. Scientists from the University of Otago have calculated that Maui’s dolphins can only cope with one human induced death every 5-7 years, but we know that only recently two Maui’s dolphins died within a few months of eachother. Also looming large are new threats, such as the world’s first large-scale power station in prime habitat of the last surviving Maui’s dolphins. The Crest Energy development is to consist of 200 massive turbines, each measuring over 20m in diameter and was pushed through by the New Zealand Minister of Conservation despite strong local opposition and objections from experts. ► Watch a Maui's dolphin on video |
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2012 estimate put Maui's dolphin population at just 55 individuals
13th March 2012 - New Zealand's Department of Conservation (DOC) announced today that the number of Maui's dolphins above the age of one has reached an all time low between 48-69 individuals, with a mostly likely point estimate of 55. The report is the result of a study conducted by DOC in collaboration with the University of Auckland and Oregon State University between March in 2010 and 2011. In a novel approach, the researchers used the animals' genetic profile to calculate the new abundance estimate.
In what biologists call a mark and recapture technique, biopsy samples were colleced from a total of 41 different individuals, some of which were sampled more than once. By comparing how many dolphins were sampled again in the second round of the study with the number of samples from new individuals it is possible to calculate an population size estimate.
DOC states that "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."
DOC's key findings:
In what biologists call a mark and recapture technique, biopsy samples were colleced from a total of 41 different individuals, some of which were sampled more than once. By comparing how many dolphins were sampled again in the second round of the study with the number of samples from new individuals it is possible to calculate an population size estimate.
DOC states that "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."
DOC's 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 researchers are 95% confident that there are between 48-69 Maui's dolphins over the age of 1).
- Comparing genetic samples from Maui's dolphins from an earlier period between 2001-07 with the current 2010-11 sample suggests a slow decline over the past decade (-3% per year), although this trend could not be confirmed with the usual statistical 95% confidence limit. .
- In 2010, DNA fingerprinting 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 to show that female Hector's dolphins have interbred with Maui's dolphins, it is possible that they can, which might enhance their genetic diversity.
- One Maui's dolphin moved some 80km in less than three weeks, with others moving around 30km before being sampled again. This indicates that the remaining individuals can still mix amongst themselves and are not restricted to small isolated groups .
- There seem to be at least as many female as male Maui's dolphins. Of the 41 individuals sampled, 25 were female and 16 were male. Having more females in a population usually gives the best chance of recovery.
DOWNLOAD DOC's 2012 Maui's dolphin abundance estimate report (PDF, 3061K) Otago University scientists Liz Slooten and colleagues carried out extensive aerial surveys of Maui's dolphins in 2004. They used a high-wing plane and a team of four experienced observers to toothcomb Maui's dolphin habitat. This line-transect survey resulted in a population estimate of 111 dolphins (95% confidence interval 48 - 252 individuals). Download this paper by clicking on the image. |