Endangered Māui dolphins appear to have changed their diet, scientists say.
Tiny skin samples collected from the animals for almost 30 years, between 1993 and 2020, showed chemicals indicating changes in prey, potentially caused by the creation of a marine sanctuary and an El Niño weather event.
Associate Professor Emma Carroll, a co-author of the paper, said the results help give a better idea of how Māui dolphins could respond to more drastic environmental changes.
"Overall this is good news for the Māui dolphin ... they are able to find their preferred prey and so far they are adapting when conditions change," she said.
Read more about dolphins: Rose Davis' first person account of helping rescue a pod of stranded dolphins on Waiheke Island recently.
The species is on the brink of extinction, with only as few as 54 adults alive.
The researchers also believe the dolphins were likely at their "thermal limit" in the area they currently live in, so big changes were likely to be needed.
"We really are hoping that they can keep adapting," Carroll said.
"That's something that [we'll be] looking at in the future; how will climate change and increasing warm events like La Niña change their food, their ecosystems, and the distribution of these dolphins."
The timing of the changes shown in the skin samples provide clues as to what was going on when the dolphins changed their diet.
From 2008 onward, the pods' diet became less diverse, coinciding with the point that a marine sanctuary in their range restricted fishing along a 40 kilometre stretch of Tāmaki Makaurau's west coast.
Lead author of the paper Courtney Ogilvy, a PhD student at the university, said Māui dolphins mostly eat small fish, less than 10cm, such as ahuru cod, red cod and sprats. The skin samples couldn't tell the scientists exactly which species the dolphins eat - just that the range of species narrowed.
"We think that the sanctuary increased the amount of food available to the dolphins," Ogilvy said.
"That meant they were able to get more of their preferred prey, and not work so hard to get many different types of food."
The dolphins also changed their diet notably in 2015 and 2016 - but just temporarily.
That change matched the timing of an El Niño weather event in 2015 and 2016, when fish that would not normally be found so abundantly in their area would have become more common due to changes El Niño could have on water temperatures and current changes.