Marine Biology (2+1)

Reproduction

           Cetaceans have extremely low reproductive potentials, which makes them particularly vulnerable to habitat or environmental change. Populations are thought to be separated into stocks, with individuals only moving between stocks when stocks are large or overlapping. For small, reproductively isolated stocks of cetaceans, recovery from harvesting or environmental damage is very slow. The number of Beluga Whales in the St. Lawrence estuary does not appear to be increasing despite the protection provided to  them for several years. Right whales, which occur in Nova Scotia waters, are also endangered— only about 325 identified individuals remain of the North Atlantic stock. The number of Humpback  Whales appears to be increasing, though they are still considered endangered or threatened. Blue, Fin, Humpback, Minke, Right, and Sperm whales are all designated as protected species by the International Whaling Commission (IWC), and harbour porpoises are considered threatened.

          Most species of whales take several years to reach sexual maturity. The gestation period ranges from ten to sixteen months, and normally only a single calf is born. Lactation lasts for six to ten months for baleen whales and twelve to twenty-four months fortoothed

  whales. Calving intervals for most species are from two to three years, though it varies from one to seven years, depending on the species . Natural mortality rates of whales are low but damage due to human activities is significant. Stranding data and recent studies on right whales show that collisions with ships are responsible for a large proportion of whale deaths.