Per stuff read in the National Geographic the number of kills allowed to Alaska natives is quite limited and a lot of the blubber is used as food due to it’s very high caloric value, needed in that type of climate in the winter. Also the best lamp oil was the lightest fraction of the spermacetti from the head cavity of the Sperm whale I believe. Heavier parts were used for spermacetti candles, considered some of the best candles but I have no idea how they were actually made or how spermacetti was refined for candle and lamp oil use. So far as I can tell the Japanese are the only country currently taking Sperm whales and it is only something like 10 per year.