Solving the great NZ whale mystery
28 July 2020
Opinion: Emma Carroll is on her way to the Auckland Islands to try to unfold the mysteries of where tohorā go when they leave sub-Antarctica, and their ocean routes.
At the end of July, in the depths of winter, I’ll be travelling to one of the most remote and inhospitable places on earth to try and solve one of the great mysteries of New Zealand’s southern right whale.
This Southern Ocean Research Partnership expedition, part of my Royal Society of New Zealand Rutherford Discovery Fellowship at the University of Auckland, is headed to the sub-Antarctic Auckland Islands. At Port Ross, a sheltered harbour at the northern tip of the Auckland Islands, New Zealand’s southern right whales, tohorā, breed in these icy cold waters over winter before heading back to summer feeding grounds. They make this migration each year.
For us humans, the journey to the Auckland Islands is pretty exciting. Although the 25m research yacht ESV Evohe is pretty comfy, as we make the 500km dash down from New Zealand to Auckland Islands, we will be sailing across an ocean notorious for big seas and high winds - but it will be worth it to be part of one of the largest gathering of whales anywhere in the world.
We have come here to try and answer one of the big whale mysteries: where do tohorā go when they leave the sub-Antarctic and which route do they take to get there? To help answer that question we’ll be using some of the most sophisticated scientific technology available, including satellite tracking technology, DNA analysis and microchemical analyses.
But first, let’s rewind about 200 years. When Europeans arrived in New Zealand it’s estimated that about 30,000 tohorā could be found in the waters of Aotearoa New Zealand. Their slow swimming speed, rotund bodies containing lots of whale oil, along with a curious and docile nature, helped earn them their name: they were the ‘right’ whales to kill. Hunted almost to extinction in their coastal calving grounds as well as their offshore migratory paths and summer feeding grounds from the early- to mid-20th century, the slaughter was so relentless numbers had plummeted to perhaps just 40 tohorā by 1920.
Amazingly, they clung on. When sightings in the subantarctic became more numerous in the 1990s, University of Auckland scientists Scott Baker and Nathalie Patenaude launched an expedition to see if the population was recovering. Based on their work and subsequent studies by myself and Simon Childerhouse at the Cawthron Insititute, tohorā are thought to have recovered to about 2000 whales by 2009. We think it could have doubled since then. What this means is whales as far as the eye can see in the Port Ross – in 2008 we counted 200 tohorā there in a single day – and I’m hopeful that now we will see even more.
But the last 10 years have been difficult for right whales in Australia, South Africa and South America. These populations have been reproducing much less often, and worse, in South America a lot of calves have died, washing up on beaches by the dozen. One of our best guesses is that females aren’t getting enough kai to breed or to look after a calf once it’s born. Southern right whale mothers have one baby every three years on average, and nurse their calf on milk so dense with fat it’s like toothpaste. Females fast over winter as they raise their young, while calves can grow up to a metre a month. We think that the key to understanding the slow-down in population recovery is to understand where and on what these whales are feeding, as decreasing food could lead to fewer babies.
However, their feeding grounds could be just about anywhere: historical records show them east of New Zealand or near Antarctica during summer, while two whales tracked offshore from the Auckland Islands in 2009 went west to a rich feeding ground south of Australia. This region is too big to send a ship - instead we get the whales to take a bit of tech with them and check up on them using satellites. These ‘satellite tags’ allow us to digitally follow the whales for up to a year (as long as the tag stays on). We’ll find out if they pass through the Great South Basin which is an oil and gas exploration area, how many head to northern to New Zealand or to Antarctica. This is the information we need for further protection of these whales in coming decades.
The second tool is a microchemical marker, which we get from a small bit of whale skin about the size of a finger nail. This will tell us what broad-scale area of the ocean the whale has been feeding in, and along with DNA from the skin, which whānau it belongs to.
Family relationships are important in mammal research. It works like it would if you were trying to identify family relationships at a wedding: at a small wedding your chance of finding two people from the same family is much higher than if 200 attended. From this method we can estimate the size of a population.
For the past decade I’ve dreamed about getting back to the Auckland Islands to see how tohorā at Port Ross are doing. In this wild and remote place, one of the world’s great wonders takes place as these whales gather to breed or just hang out. I can’t wait to see to see them again.
As well as helping fund this research, marine conservation organisation Live Ocean has launched a whale sighting campaign around mainland NZ to help add to our knowledge about where these whales go. For more information on the research or how to report a sighting go to www.liveocean.com
Dr Carroll will give updates of her trip on the Live Ocean blog and also on her own website Whale DNA Lab
Dr Emma Carroll is a senior research fellow in the School of Biological Sciences.
This article reflects the opinion of the author and not necessarily the views of the University of Auckland.
Used with permission from Newsroom Solving the great NZ whale mystery 28 July 2020.
Alison Sims | Research Communications Editor
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