International scientists criticised on Friday a Russian plan to release 10 captive killer whales into the Sea of Japan rather than return them to their original habitat, saying it could endanger the mammals’ lives.

The plight of the orcas, which are being held with 87 beluga whales in cramped conditions in a bay near the port of Nakhodka, triggered an international outcry, with celebrities such as actor Leonardo DiCaprio joining a petition that raised nearly 1.5 million signatures calling for their return to the ocean.