Abstract

Dall’s porpoise, Phocoenoides dalli (True), is commonly encountered over the continental shelf of North America and in offshore and pelagic waters of the western and eastern North Pacific Ocean. This striking black and white porpoise is characterized by great speed and a cone-shaped splash it makes when surfacing to breathe. Because of its great speed in the wild, making it extremely difficult to capture alive, and its hyperactivity resulting in high mortality after capture, much important information remains to be disclosed of the basic components of its life cycle.

At our laboratories, situated at the head of the Monterey Submarine Canyon, the continental shelf drops off sharply only a few miles from shore to depths in excess of 1000 fathoms. Offshore and pelagic waters thus are close at hand, and we have been able to study this little known species of porpoise throughout the year. An intensive study of Dall’s porpoise was undertaken to learn as much as possible about this species in its natural environment. This study was conducted in Monterey Bay for a period that extended over 30 months. My conclusions are based on observations of animals at sea and on specimens collected during this period as beach-cast dead animals or animals taken in the wild. Specimens were available for every month of the year. In this paper, much of the literature relevant to the natural history of this species is reviewed, and new information gathered during our long-term study is presented for the first time.