By Otago Marine Science 29/07/2020

Professor Steve Dawson

Scientists from the University of Otago, working with colleagues from around the world, have found that New Zealand right whales are doing much better than right whales in other parts of the world.

The research was published as the feature article in the journal Marine Ecology Progress Series. Southern right whales are starting to bounce back from the impact of whaling. They are still not exactly common, numbering 10,000–15,000 individuals. But each individual whale is fat and healthy!

Mothers in poor condition tend to have much skinnier calves

By contrast, the North Atlantic right whale is teetering on the brink of extinction, with about 410 individuals remaining off the east coast of North America. Shipping and fishing continue to kill these whales through collisions with vessels and whale entanglement in fishing gear such as lobster pots. Other impacts include noise pollution and a reduced availability of their main food, copepods.

This new research has shown that North Atlantic right whales are visibly thin and unhealthy, which makes them less likely to breed successfully, accelerating their current decline.

The international team of scientists measured the body condition of individual right whales, off North America, Argentina, Australia and New Zealand. All teams used photography from drones. Right whales feed on dense shoals of tiny copepods, building up their fat reserves in the summer to migrate inshore in winter to breed. In the last stages of pregnancy, and for the first months of suckling, females don’t feed at all. So, how “fat” they are is crucial to their ability to support the pregnancy, and the fast-growing calf.

The study measured 523 whales, including 74 from New Zealand. It is the most comprehensive assessment of the body condition in any whale species, and involved 18 researchers from 12 institutes in five countries. The Otago University team includes Professor Steve Dawson, Senior lecturer Will Rayment, and students David Johnston and Eva Leunissen. Our pilots, Steve and David, took most of the photographs in Port Ross at the Auckland Islands, south of New Zealand. Eva wrote the computer programme used to measure whales from photographs taken by all of the teams, in New Zealand and internationally.

Healthy female right whale and calf, in Port Ross at the Auckland Islands

The bad news is that North Atlantic right whales were clearly in the worst condition, much thinner than any right whales in other parts of the world. Undoubtedly this has consequences for reproduction in this critically endangered population.

The good news is that the New Zealand whales were in excellent condition. We always thought that “our” right whales looked fat and healthy, but this study proves that point. On average the mums nursing their calves in New Zealand waters had a 25% higher body condition index than their counterparts in the North Atlantic. This probably reflects lower impacts from fishing and shipping in the Southern Ocean compared to the North Atlantic.

It was great to be part of this right whale project, with scientists around the world joining efforts. The plight of the North Atlantic right whale is a wake-up call for us all. When right whale numbers start increasing around the mainland of New Zealand, we will have to make sure that fishing and shipping do not cause the same impacts seen in the North Atlantic.