The catalog contains pictures of 392 individuals, some of which are known to be dead. Others are presumed dead, after having not been seen for six or more years. Researchers estimate there are a minimum of 290 northern right whales left, and Knowlton says the number may be closer to 330, as some of the animals that have gone missing for six years may still be alive. No one has ever documented the entire northern right whale population in a single year. Researcher darts a right whale to collect a skin sample.
Genetic research suggests there are also some right whales that have never been photographed.
Using DNA from skin samples, Brown and her colleagues have determined that some right whales are the offspring of whales that have never been documented, and are not included in the photographic or genetic right whale catalogs. Genetic studies have also shown the whales are sufficiently genetically diverse that the population stands a good chance of recovering, if individuals are not lost to ship collisions and other accidents. But there are other problems that are slowing recovery for the species. While a northern right whale is capable of having a calf every three years, the average time between calves is now up to about five years. Meanwhile, related southern right whales, which have rebounded to a healthy population around 7,000, are having calves nearly every three years.