The Antarctic blue whale can weigh up to 400,000 pounds and stretches to 98 feet in length. The underwater call of the sperm whale, the earth’s loudest, registers at 230 decibels.

In fact, just two blue whale births have ever been documented — off South Africa in 1911, and off Sri Lanka in 1946. And sightings of calves are remarkably rare, falling far below what should be ...