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Shifting ocean conditions influence Chago whale migrations

A new population of blue whales known as “Chagos” pygmy blue whales was discovered in the Indian Ocean last year. They were found incidentally while monitoring nuclear bomb tests. 

Researchers from UNSW Sydney analyzed 18 years of recordings and found that Chango whale song frequency has increased over the years. The experts hope that this indicates the species is rebounding after near extinction due to hunting. 

“We discovered different seasonal patterns of the whales on the west and east side of the island. We found that first of all, the amount of whale songs is increasing over the study period at both sites,” said study lead author Lyra Huang.

“Secondly, they are mainly on the south-eastern side from September to November, and they then migrate to the north-western side and stay until February.”

“Our analysis shows that these movements are related to environmental factors such as sea surface temperature and food availability.”

The researchers also discovered that Chagos migrate from the south-eastern side to the north-western side of Diego Garcia Island in the Indian Ocean. Corresponding author,  Professor Tracey Rogers, explains their migration,

Our earlier research picked up these same whale songs up as far as Sri Lanka and across as far as the Western Australian coastline. This means these whales migrate across the Indian Ocean, which is really unusual for blue whales as they generally move north and south to and from Antarctica, but these guys are going east to west, and back again.” 

“We see high concentrations of chlorohpyll-a [an indicator of krill] on the south-eastern side of the island which corresponds with times when there are more whale songs recorded there, but no correlation at the north-western side.” 

“This tells us that the whales are most likely feeding on that south-eastern side and then migrating past the western side of the island.”

Currently, Chago whale populations are doing well, and the researchers are interested in how climate change will affect them. 

“Oceanic conditions in the Indian Ocean are predicted to change under future climate scenarios,” said Rogers. “So, it’d be really interesting to see how this newly discovered population is going to fare into the future – is that going to be better for them or will it be not as good? But at the moment, things seem to be going really well for them.”

This study has been published in Frontiers in Marine Science.

By Erin Moody , Staff Writer

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