It was a whale of an evacuation. Actually, two.

In what experts said was among the most complex marine mammal rescue ever undertaken, the pair of beluga whales were extricated from an aquarium in the battered city of Kharkiv in eastern Ukraine and transported to Europe’s largest aquarium in Valencia, Spain, on Wednesday morning.

As Russian aerial bombardments of Kharkiv, Ukraine’s second-largest city, have intensified, the evacuation of Plombir, a 15-year-old male, and Miranda, a 14-year-old female, came just in time, marine mammal experts said.

“If they had continued in Kharkiv, their chances of survival would have been very slim,” said Daniel Garcia-Párraga, director of zoological operations at Oceanogràfic de Valencia, who helped lead the rescue.

Belugas, whose natural habitat is the Arctic, need cold water to survive. The devastation of the power grid in Kharkiv meant that the aquarium there had to rely on generator power, making it challenging to keep the waters cooled.

At the same time, the whales’ diets were halved recently amid shortages of the 132 pounds of squid, herring, mackerel and other fresh fish the pair needed daily, Dr. Garcia-Párraga said. Ukrainian caregivers were even considering using discarded fish from restaurants and markets.

And in recent weeks, bombs exploded close enough to ripple the waters of their home at the NEMO Dolphinarium. As the conditions grew more precarious, the Ukrainians decided the whales required evacuation.