University of Auckland: Endangered dolphins’ diet may have changed for the better

New Zealand’s Māui dolphin, the world’s most endangered marine dolphin, changed its diet during the past 30 years, research shows.

Scientists checked tiny skin samples collected from the dolphins between 1993 and 2020 for microchemical markers revealing diet.

Turns out the dolphins’ meals became less diverse from 2008, when a marine sanctuary restricted fishing in their habitat, which stretches along 40 kilometres of Tamaki Makaurau’s west coast.

“We think that the sanctuary increased the amount of food available to the dolphins,” says the lead author of the paper, Courtney Ogilvy, who’s a PhD student at Waipapa Taumata Rau, University of Auckland. “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 scientists’ analysis doesn’t reveal exactly which types of fish were consumed, just the breadth of diet. (Māui dolphins typically eat fish smaller than 10 centimetres in length, dining on species such as ahuru, red cod and sprats.)

The dolphins seem to be eating more of their preferred prey since a marine sanctuary was introduced in 2008
A temporary change in diet occurred during the El Niño weather event in 2015 and 2016.

“Dramatic climate events like El Niño can change water temperatures and currents, meaning that fish from different regions can move into the dolphins’ habitat,” says co-author Professor Rochelle Constantine. “As you really are what you eat, this change is reflected in the microchemical markers in the dolphin’s skin.”

The microchemical markers are called stable isotopes.

“Overall this is good news for the Māui dolphin,” says co-author Associate Professor Emma Carroll. “They are able to find their preferred prey and so far they are adapting when conditions change.”

Now, the scientists plan to investigate how climate change will alter the dolphins’ habitat.

“We know they are likely to be at their maximum thermal limit, so increasing ocean temperatures may eventually shift the distribution of the dolphins and their preferred prey,” says Professor Constantine.

Located only in Aotearoa, the number of Māui dolphins aged a year or older may be as few as 54, according to the latest estimate.

The Marine Mammal Sanctuary, on the west coast of the North Island, Te Ika-a-Māui was established in 2008 and expanded in 2020.