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Southern right whales have shifted their foraging grounds

An international team of scientists has recently analyzed chemicals in the skin of southern right whales in order to clarify how these animals are distributed and to better understand long-term environmental changes in the Southern Ocean.

The researchers measured the amounts of several carbon and nitrogen isotopes in 1,002 skin samples collected between 1994 and 2020. Since the concentrations of these isotopes vary between different marine locations, animals feeding in specific areas retain that isotopic “fingerprint” in their skin. Due to the fact that it takes about six months for the isotopes to become ingrained in the whales’ skins, scientists can use this method to pinpoint where the animals were approximately half a year earlier.

“Despite their large size, whales can be very hard to track,” explained study co-author Robert Harcourt, a marine scientist at Macquarie University. “Using this technique, we have been able to piece together a map of where the southern right whales have traveled across the Southern Ocean.”

The analyses revealed that over the years the whales’ foraging grounds have shifted, most likely due to the changing distribution of the whales’ prey. Since investigations of 2614 whale-catch records from 1792 to 1968 suggests that southern right whale foraging grounds were largely stable in mid-latitudes, the changes the experts identified appear to be quite recent and are most probably driven by global warming.

However, not all southern right whale populations seem to have reacted uniformly. For instance, while those in the South Atlantic Ocean and southwest Indian Oceans travel to Antarctic regions less often – probably since there are currently less krill there – in the Southwest Pacific whales still head south during certain periods, suggesting krill remain 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,” said study senior author Emma Carroll, a biologist at the University of Auckland. This finding could help prioritize areas where conservation efforts should be focused.

“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,” Harcourt concluded.

The study is published in the journal Proceedings of the National Academy of Sciences.

By Andrei Ionescu, Staff Writer

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