Are you serious? Because a pig or calf can be bought for a few hundred bucks, few thousand tops, and raised in a suburban back yard. Because there is zero chance they are keystone species.

An adult sperm whale weighs over 100 tons and eats about a ton a day. Do you not see the practical implications of that with regards to irreversible damage?

Edit: missed the sustainable part of your post. Whaling afaik can't be sustainable because the demand in Japan is high enough that whale populations simply can't replenish fast enough. They have a very slow reproductive and nurturing cycle.