Ecological Aspects of Reproduction of Marine Mammals

Abstract

The cetaceans fall into two main categories: balaenopterid (baleen) whales and odontocete (toothed) whales. The former are all large whales, but the second category comprises a range from the large sperm whale (Physeter macrocephalus), down to the small marine harbour porpoise (Phocoena phocoena), and also a number of small freshwater river dolphins. The distinction between the two categories is important because the ecology of baleen whales incorporates a regular annual cycle of seasonal migration, often over long distances involving changes of latitude, and feeding, such as the southern blue, (Balaenoptera musculus), fin (B. physalus), and humpback whales (Megaptera novaeangliae), (Lockyer and Brown, 1981). The entire life history, and in particular the reproduction, is geared to this cycle (Mackintosh, 1965), and results most often in a two-year reproductive interval. The odontocetes represent a variety of life styles, some specialised to adapt to seasonal changes, but not as rigidly as the baleen whales (Gaskin, 1982). Odontocetes may have protracted inter-birth intervals of 3–5 years e.g. sperm and pilot whales (Globicephala spp.), but may also reproduce annually e.g. harbour porpoise. All cetaceans spend all their lives in water and produce a single calf each pregnancy.