At approximately 01:32:50 on the Blu-Ray you
can clearly see a diver releasing the mechanical
whales. He is on the far right side of the
screen, you can make out his head, body and
left hand. He is visible for a good 8-9 seconds !
If you have a different media source, it's during
the Bird of Prey decent. You see a closeup of
Kirk, followed by a closeup of Uhura and Gillian,
then a close up looking down on the harpoon. It's
in the following scene.
I've seen this movie a hundred times and
can't believe I've missed this all these years !