It is not known for certain how long a whale may live after completing
its growth. At the present time, commercially important species seldom
attain physical maturity before being captured. Many whales which are
captured are measured for scientific study. Such measurements also keep
the whalers from taking undersized juveniles. Whales apparently do not
live to be very old. Fifty years appears to be the best current estimate
of a life span.
[Illustration: Back of a gray whale showing barnacles and barnacle
scars. _Courtesy of Scripps Institute of Oceanography._]