That question may be really hard to answer since many whales are very secretive and unless there are people out counting them the actual number is not available. Even those born in captivity can be difficult because there are some aquariums around the world that do not release this information and even still capture whales from the wild.

The whales stay pregnant for nearly a year.This allows the babies to get very large before they are born. They may be one third to one half the lengths of their mothers. Then they live off their mothers milk for about another six months while she teaches them the basics of being a whale. This takes a lot of energy from the mother, so she may only have one baby every 2-3 years. This means that populations can only grow very slowly. Since there are many species of whales, and they are hard to observe, no one really knows the average number born per year.