Notes on the Sexual Cycle of the Pacific Cetacea of the Genera Megaptera and Balaenoptera

Abstract

Relatively little is known regarding the life history of the larger Cetacea. The data are scattered and very fragmentary. It is not known at what age or size the young whale becomes sexually mature and whether breeding is seasonal or occurs throughout the year. The duration of gestation and lactation are not known and the opinions on these matters, some of which are supported by scattered bits of evidence, differ greatly. It was with the hope of extending the data on some of these questions that the present investigation was undertaken. Through the courtesy of Dr. B. W. Evermann, director of the California Academy of Sciences, and Joseph Mailliard, curator of mammalogy and ornithology, the writer spent the last three weeks of August, 1925, at the shore whaling station of the Californa Sea Products Company at Trinidad, California. Only nine whales were taken during this period, owing to stormy weather and an apparent scarcity of whales in that vicinity. Three male and two female finbacks, Balaenoptera physalus, and three male and one female humpbacks, Megaptera nodosa, constituted the catch. Measurements, based on those of Andrews' were taken of all whales. Samples of the stomach contents and specimens of external and internal parasites were collected for study by specialists, but the particular object of this investigation was to seek evidence regarding the reproductive cycle by an examination of the reproductive system of both sexes. So far as is known to the writer no attempt has been made to solve the sexual cycle of Cetacea by a study of the histological characteristics of the testes and ovaries. The method and results of such studies for the smaller mammals are well known. The territory of the whaling operations from the Trinidad station during the period of this investigation extended over an area having a radius of about seventy-five miles. Animals which were brought to the station for flensing had been dead on an average for ten to twenty hours. Despite this fact, the tissues which were fixed in 10 per cent formol showed a fair state of preservation, and a satisfactory examination was possible.