To be fair that chart only starts in 1900, so you can't see 18th century here. And in the wikipedia page of this chart it says "By 1900, bowhead, gray, northern humpback and right whales were nearly extinct, and whaling had declined". But also in the original phrase "peak of the whaling industry" speaks not just about number of whales killed, but size of the industry as a whole, amount of people involved. Because with new tech I suppose those massive killings in 1960's required much fewer people.