THE NATURAL HISTORY OF WHALEBONE WHALES

Abstract

Summary(1) The whaling industry has provided both the facilities and the stimulus for modern research on the general biology of whales. The principal methods of investigation are (a) anatomical examination, (b) observations at sea, (c) the marking of whales, (d) analysis of the statistics of the whaling industry, (a) The whalebone whales are migratory animals, inhabiting high latitudes in summer where food is plentiful, and moving into warmer waters in winter where there is little or no food, but where breeding takes place. The Greenland right whale does not move far from the Arctic regions and is not found in the southern hemisphere. The black right whales of the north and south do not migrate far and are separated by a wide tropical belt. The humpback migrates from the polar ice to the equator, and frequents tropical coastal waters in the winter months. In the southern hemisphere it is segregated into several communities which have separate migration routes, and between which there can be little interchange. Blue and fin whales undertake less regular and extensive migrations. They are not segregated like the humpbacks, but show a slight tendency to concentrate in the same regions. Grey whales inhabit the North Pacific and undertake regular migrations along the coasts of North America and in Japanese waters. There is less information on the distribution of the sei, lesser rorqual, pigmy right, and Bryde's whale. (3).Certain planktonic Crustacea form the principal food of the whalebone whales. In the Antarctic they feed virtually exclusively on the shoals of Euphausia superba. In the northern seas the diet seems to be more varied. Meganyctiphanes norvegica is probably the most important food organism in the North Atlantic, but further investigations are needed. Little food is taken in winter, though fish and small quantities of other Crustacea are sometimes eaten. (4) Examination of the reproductive organs and measurements of foetuses at different times of year show that breeding mainly takes place in winter and that the period of gestation is about a year. Normally one young is born at a time, and the usual interval between successive pregnancies is probably two years. This applies to blue and fin whales, but other species are probably similar. Blue and fin whales are believed to become sexually mature in about two or three years. The old corpora lutea of the ovaries persist and accumulate, and constitute the best indication so far found of the age of an adult whale. There is some evidence that the rate of increment is about one per year, but this again needs confirmation. The largest recorded number is fifty‐four. Indications of periodic growth in the baleen plates constitute a new method of determining the ages of young whales. The rate of growth is faster in the anterior than in the posterior part of the body. (5) Whalebone whales are more plentiful in the southern than in the northern hemisphere. The sexes are nearly equal. The existing ratio of blue, fin and humpback whales is estimated to be of the order of 15, 75 and 10 respectively in the Southern Ocean, but no estimate has yet been made of the absolute numbers in the populations. Most whaling is carried out by the Antarctic pelagic factories, and little is done now in the northern hemisphere. The stocks of blue and humpback whales have been depleted by the modern industry, but fin whales have been less affected, and progress has been made in the international regulation of whaling. (6) In the future it will be necessary to continue research to some extent on the same lines as before, but new or modified methods could be developed, and aircraft and modern technical devices might be used with advantage.