OCEANIC MAMMALS 527 



In the southern oceans, the investigations of recent years 

 show that the migrations of the humpback are seasonal. In 

 the southern summer they have a "feeding migration" to the 

 southward, and then in the southern winter they migrate to- 

 ward the Tropics for breeding. "Parturition and pairing 

 occur mainly in tropical and subtropical waters. On its north- 

 ward migration the species regularly crosses the equator, at 

 least on the west coast of Africa, for a distance of about 10 of 

 latitude. Occasional migration of individuals from the schools 

 of the southern hemisphere to those of the northern hemisphere 

 is extremely probable" (Matthews, 1937). There is evidence 

 that in the Northern Hemisphere there is migration north- 

 ward in the northern summer, and southward toward the 

 Tropics in autumn and winter, at a time when the southern 

 schools would be in the reverse state of movement, so that 

 much mingling of the two groups would be less likely. 



The investigations of the Discovery Committee show that 

 sexual maturity is reached at an age of 20-22 months, and 

 breeding first occurs at the end of the second year after birth. 

 Humpbacks probably breed once in two years, although oc- 

 casionally pregnancies may occ\ir twice in three years. The 

 period of gestation is about 11 months; the single young at 

 birth is about 4.5-5 meters long; it nurses for about five months 

 and is weaned when about 7.5-8 meters long. The pairing 

 season in the case of the southern schools is mainly from August 

 to November, chiefly in September so that the peak of births 

 falls in August, with a season from July to September. 



Matthews (1937) further points out that "the great destruc- 

 tion of the stock of Humpback whales during the last thirty 

 years is attributable solely to excessive slaughter both during 

 the feeding and breeding migrations. The stock can only re- 

 turn to its former abundance, on which modern whaling in the 

 south was founded, if the Humpback whale is afforded com- 

 plete and world- wide protection for a long period of years. If, 

 thereafter, the stock is to be maintained, catching would have 

 to be carefully controlled, and restricted to the whaling grounds 

 of the far south. " By the International Agreement of June, 

 1937, it is forbidden to take humpback whales of less than 35 

 feet in length, while calves and suckling whales, or adult 

 females accompanied by them, are not to be killed. 



