Scientists have analysed chemicals in the skin of southern right whales to give new insights into the animals' distribution, as well as long-term environmental changes in the Southern Ocean.
The research was published this week in Proceedings of the National Academy of Sciences (PNAS). [https://www.pnas.org/doi/10.1073/pnas.2214035120]
The scientists from the US, Australia, Argentina, Brazil, South Africa, Europe, UK, and Aotearoa New Zealand measured the amounts of various carbon and nitrogen isotopes in 1002 skin samples taken between 1994 and 2020.
Concentrations of these isotopes vary between different marine locations and animals feeding in an area retain that isotopic fingerprint in their skin. It takes up to six months for the isotopes to show up in a whale's skin and so scientists can pinpoint where the animals were six months earlier.
"Despite their large size, whales can be very hard to track," says Professor Robert Harcourt, a marine scientist at Macquarie University, and one of the authors of the paper. "Using this technique, we have been able to piece together a map of where the southern right whales have travelled across the Southern Ocean."
The study shows that over the years the whales' foraging grounds have shifted reflecting the changing distribution of the whales' prey. This change appears to be recent and driven by climate change.
Analysis of 2614 whale-catch records from 1792 to 1968 suggests that historical southern right whale foraging grounds were largely stable in mid-latitudes.
"These results suggest that climate change has driven recent shifts in the distribution of southern right whales," Professor Harcourt says.
Not all populations have reacted uniformly.
The southern right whales in the South Atlantic Ocean and southwest Indian Oceans travel to Antarctic waters less often, probably as there are fewer krill there.
In the southwest Pacific, however, whales still head south at certain times of the year, suggesting krill are still plentiful in that ocean.
"An important aspect of this study is that it shows that climate change doesn't mean one thing everywhere and it is causing different effects in different parts of the ocean," says Dr Emma Carroll, from New Zealand's University of Auckland Waipapa Taumata Rau, lead author of the paper.
"This could help prioritise areas where conservation efforts should be focused," says Professor Harcourt.
"This study has shown the critical importance of understanding how wide-ranging animals are adapting their movements as climate change fundamentally alters ocean structure and where they may find their prey.
"Ongoing research includes satellite tracking of individual animals from the major populations along with continued tissue collection, further refining our understanding of important ocean regions for these magnificent ocean giants."
Professor Harcourt led the Australian arm of the study, collaborating with researchers from 36 countries. The first author, Solène Derville, is from Oregon State University, the US and the French Institute of Research for Sustainable Development, Nouméa.
"This was a great global collaboration," says Dr Carroll. "This sort of work is just not possible without the input of many people around the world."
