How many young does a whale give birth to at one time?
Most of the larger whales have a very low reproductive rate: females only have a single calf every 2-4 years. With very small populations, this low rate of reproduction means that it may takes decades for some species to recover to their former population levels. Even under the best conditions, it will take over a hundred years for the right whale to recover.
For some species of whales, the calves are born during the part of the annual cycle when the animals are in warmer waters, and the adults are not feeding. Unlike dolphins and porpoises, a calf spends a relatively short period of time with its mother. Calves usually become independent within a single year. During that time, a calf gains weight very rapidly. Whale milk is very rich, and a blue whale calf may gain almost 200 pounds per day.