Current Scientific Inquiry
Life Expectancy
Life expectancy is another very useful statistic for population studies. The whaling industry has no easy way of finding this out because whaling never gives an individual whale the chance to attain old age. Perhaps we can eventually determine life expectancy for the gray whale if it can continue to be protected from whaling. By counting the number of babies produced each year, and knowing the life expectancy, We might indirectly obtain the number of whales which die before they have realized their life expectancy. This number should represent the surplus on which whaling could be based. A further study would be necessary to determine what percentage of the surplus could be diverted to the whaling industry.
Age Determination
The problem of aging whales is an important one, and one to which much thought has been given. Actually, it is desirable to know at what age sexual maturity occurs; at what age physical maturity; at what age reproduction is no longer possible, and lastly, the age at death. In addition, we need to know the gestation period and the average number of pregnancies of which the female is capable. Many of these statistics can be obtained from the examination of a freshly killed whale. Such age determinations are made on every specimen which comes aboard the factory ships and also at the shore stations. There is some doubt as to the accuracy of some of these. Physical maturity is delayed in whales for many years, and it is judged complete when the cartilaginous end plates fuse to each vertebrum (backbone). After fusion, further lineal growth is impossible and after this time whales have been noted to shrink slightly each year.
The other structures which a biologist collects for aging are the ovaries of the female whale. These are sliced across into half-inch slabs, and the number of exposed grayish masses are counted. There is one of these structures produced for each pregnancy, and they persist as scar tissue throughout the life of the whale. These structures are functional during pregnancy and nursing and are responsible for a successful pregnancy. A count of these gives the investigator the total number of offspring which have been produced. If one assumes that the whale has not missed an opportunity to produce a baby, the count of these gives the age, assuming one knows the age of sexual maturity and the maximum length of bearing.
In recent years other structures have been tried for aging, so that males might also be aged, as well as females past the reproductive period. The best structure is the cylinder of wax which fills the outer canal of the ear leading to the eardrum. This enlarges as the whale grows, and the growth is marked by banding very similar in appearance to tree rings. Slicing the plug, the rings can be exposed and counted. There are produced but two rings a year. Toothed whales can be aged by sawing the teeth in half and noting the banding. Baleen also is periodically enlarged, but this is more difficult to check.
Distribution and Population Rise
The whaling industry spends a few weeks before the whaling season and at the end, hunting whales with a much lighter gun which implants a numbered cylinder deep in the skin of the whale. Each whale so marked is logged as to the species and the latitude and the longitude, and lastly, the date. Should the marked whale be processed in any succeeding season, a second entry is completed giving the date and place of capture. These records are used to determine the migration routes and the degree of intermingling of adjacent populations. The ratio of marked whales to unmarked whales allows the estimation of the probable size of the whale population. The length of time elapsing until a marked whale is recovered is an indication of the intensity of whaling.
Unlike the situation in the fishing industry where the reproductive potential of the fish is more than adequate to repopulate quickly, in the whaling industry the reproductive potential is small. Only one-fourth of the population can contribute replacements each year, and then only a single baby. Of course, each offspring has a reasonable chance of reaching maturity, whereas with fish only a very small number achieve adulthood.
One might expect that whales would be less affected by the fluctuations in environmental conditions, but this is only a surmise. We do not know as yet how to ascertain whether the food of whales is ever inadequate. Certainly the fact that baleen whales do best around the polar seas suggests that climatic fluctuations of the magnitude and duration of those producing the ice ages, may have profound effects on them.
We can only hope that man will learn to exploit whales in such a way as to take only the surplus and leave the main stock, creating thereby a perpetual resource. Man can best profit esthetically and scientifically by leaving the gray whale free of whaling as a control population.
Gray whale making a deep dive. Photograph by T. J. Walker.
Gray whale spouting. Courtesy Scripps Institute of Oceanography.