 During later years, from 1972–73 onward, increasing numbers of lactating females with young were taken.In fact, during the end of the 1972–73 season, the catch of lactating females with young was 45% of the catch.The more destructive periods of Soviet whaling generally were accompanied by the taking of large numbers of females with calves (despite mothers with calves being protected by IWC regulations) and such practices caused sperm whale populations in the southern hemisphere to collapse over just a few years from 1965 to 1980.