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. [Illustration: Gray whale making a deep dive. _Photograph by T. J. Walker._] [Illustration: Gray whale spouting. _Courtesy Scripps Institute of Oceanography._] Appendix Scientific names of all North American cetaceans with common names most in use. Maximum size indicated. Region: (A) Atlantic Ocean, (P) Pacific Ocean, (C) Circumpolar _Common Name_ _Size-Region_