What did the probe and the whales say to each other?

Question

In Star Trek IV: The Voyage Home, the survival of Earth depends on a mysterious probe having a conversation with humpback whales.

McCOY: Well, dammit? You think this is its way of saying 'Hi there' to the people of the Earth?

SPOCK: There are other forms on intelligence on Earth, Doctor. Only human arrogance would assume the message must be meant for man....

What was the message?

This isn't answered in the film itself, and the topic is never revisited in Star Trek episodes or other films. But perhaps there are screenplay notes (preferable), novels, or comics that elaborate on the probe's message.

I do not believe that the conversation is an exchange of random sounds without meaning given this:

KIRK: Spock, could the humpback's answer to this call be simulated?

SPOCK: The sounds, but not the language. We would be responding in gibberish.

In other words, the premise of the film relies on the assumption that something specific was being communicated.

As best as I can tell, Memory Alpha and Memory Beta's entries on the probe have no information germane to this particular question.

Answer 1

The film's official novelisation contains a version of events that includes a translation of the probe's conversation with the whales. Apologies for the length of the quote:

[Probe] Why did you remain silent for so long?

They [The whales] tried to explain, but it reacted in surprise and disbelief.

Where were you? it asked.

We were not here, they replied, but now we have returned. We cannot explain, traveler, because we do not yet understand all that has happened to us.

By "us," the traveler understood them to mean themselves as individuals and all their kind for millions of years in the past. By their song it recognized them as youths.

Who are you? it asked. Where are the others? Where are the elders?'

They are gone, the whales sang, with sadness. They have passed into the deep, they have vanished upon white shores. We alone survive.

Your song is simple, the traveler said, chiding. It was not above petulance. Where are the tales you have invented in all this time, and where are the stories of your families?

They are lost, replied the whale song. All lost. We must begin again. We must evolve our civilization again. We have no other answer.

The traveler hesitated. It wondered if perhaps it should sterilize the planet anyway despite the presence of the untaught singing youths. But if it began a new evolution here, the planet would be silent at least as long as it would take the traveler to circumscribe the galaxy. The traveler would have to endure the pain of the world's silence. Organic evolution required so much time. Besides, the traveler possessed very little cruelty. It could consider destroying the young singers, but the conception caused great distress. It abandoned the idea.

Very well, it said. I shall anticipate young stories.

Fare thee well.

The traveler fell silent. The whales bid it farewell. The traveler collected its energy. It ended its interference with the patterns of the blue-white planet. It ceased to power the violent storms ravaging the surface. It sought its usual course, oriented itself properly, and sailed on a tail of flame into the brilliant blackness of the galaxy.

Answer 2

For completeness, I do have a copy of the novel Probe mentioned by N_Soong in a comment. What it has to say is fairly little, but consistent with the STIV novelization. From the prologue:

In the waters of hundreds of worlds it had found primitives who held the promise that, in another million years, they might be able to Speak, might become capable of learning the True Language.

The blue world the entity had recently departed had held such primitives for millennia. Time and again it had returned, listening to their evolving story, etching their rudimentary recitations into its crystalline memory, observing, prompting them in the direction of Speech. But then they had fallen silent. No amount of calling, no intensity of prodding, had brought forth a response until, finally, the creators' instructions had said: Prepare the world for new life. [...] But the instructions had barely begun to be implemented when the primitives had reappeared, had raised their planet-bound voices in joy. [...] When questioned, they would speak only of enclosed spaces and chaos and then freedom.

So the probe was doing something it had done before, establishing contact with the whales of the planet to say hello, exchange stories, and evaluate their progress. The content of its message was just a greeting, then a more urgent "hello, anyone there?". When it finally made contact at the end of the movie, the exchange was "Hey! You weren't there and now you are! What happened?" "We were somewhere else, and now we're here! Some stuff happened but we don't know what it was!" "Well, okay then."

Answer 3

I always thought that because Spock believed he had "successfully communicated their intentions", the Whales were in turn able to relay the story of being saved by these more evolved humans thus convincing the probe to spare the planet.

Answer 4

Spock performed a Vulcan mind-meld and learned from the whales that the reason that the probe was destroying the Earth was that the probe had made an earlier trip past earth and had learned from the whales that they were endangered due to mankind harpooning them. The probe promised to return at a later time and avenge the whales deaths if they had been hunted to extinction.