20 years after the fact, so, again, I doubt it had any real influence other than maybe to make people realize humpback had been heavily hunted past-tense.
You're completely misunderstanding the passage you quoted. It says the moratorium was introduced
in 1966, but that just means it was proposed. That proposal was rejected
by the International Whaling Commission multiple times over the following two decades, and the threat to the whale population got progressively worse over that time. That's why the peak of the "Save the Whales" movement was in the '70s and '80s. That's why The Voyage Home
was made in the first place. I mean, think it through. Would they have made a movie in 1986 warning about the threat of extinction to the humpback whales if it hadn't been seen as a genuine risk at that time?
Here's the article you should've read:
After growing pressure from member nations, in 1979, the IWC established the Indian Ocean Whale Sanctuary as a practical conservation measure. Three years later, in 1982, the IWC adopted a moratorium on commercial whaling, which took effect in 1986 and allowed for scientific research whaling. When Japan resumed whale hunts under the auspices of a research program, some anti-whaling countries and organizations criticized the moratorium's loophole for continued commercial whaling.
In 1994, the IWC created the Southern Ocean Whale Sanctuary in Antarctica to protect whales in their breeding grounds. Two additional sanctuaries were proposed in 1998 by anti-whaling nations, but they failed to get enough votes in the IWC.
So the moratorium didn't even start to take effect until the same year The Voyage Home
came out. And it was an imperfect solution with some big loopholes. A number of countries, including Japan, have never stopped whaling, and some humpback populations remain endangered today.