A person's voice is also impossible to disguise. After Pavlovich's voice was processed by the voice changer, it sounded somewhat shrill, and once transmitted over the radio, there was no need to worry even if the voice was recorded.
Now the Nisshin Maru was bound to sink, but the other two whaling ships, one behind the Nisshin Maru and the Arctic Sunrise, separated by two ships, the Avenger certainly couldn't reach it, and the other one was blocking right in front of the Arctic Sunrise, with its bow aimed at the Avenger.
Of course, Pavlovich wouldn't actually attack the Arctic Sunrise, but a strong attitude and wording were indispensable. To sink the remaining two whaling ships, it was necessary to get the Arctic Sunrise to leave; otherwise, the torpedoes were very likely to mistakenly hit the Arctic Sunrise.