Friday, January 1, 2010

Marine Mammals of the Eastern North Pacific

The Eastern North Pacific has many marine environments from warm tropical to cold temperate waters, and the shallow continental shelf to deep ocean canyons. Various marine mammals have adapted to survive and in each of these environments. Beaked and sperm whales spend their time in the deep ocean. Most dolphin species favor warmer waters, while a few prefer it cooler. Porpoises avoid the tropics altogether. Harbor seals stay near the temperate coast, as do sea otters.

Some marine mammals, especially large baleen whales migrate from productive cold-water feeding areas in the north to warm tropical / subtropical habitats for birthing calves. The southern migration for most whales begins in late autumn. Northward migrations begin in early spring. Humpback whales travel the open ocean in their migration, where gray whales keep close to shore. The northern fur seal migrates from the Bering Sea to Southern California, while the Guadalupe fur seal stays south of Point Reyes California. Elephant seals feed in the Gulf of Alaska and visit California and Baja beaches twice a year, once to pup and breed, and once to molt.

Many marine animals congregate where upwelling occurs. Upwelling is a natural phenomenon in which cold, nutrient-rich water from the depths is brought to the surface by a combination of Earth’s rotation, prevailing winds, ocean currents. These nutrients foster the growth of phytoplankton (small plant life) which are eaten by zooplankton, which feeds larger fish, attracting a variety of marine life. Many marine mammals return annually to these places of high productivity. The upwelling zone in the Eastern North Pacific begins in near-coastal waters off the Pacific Northwest and extends south into Baja California. During periodic El Nino events, prevailing winds subside and upwelling ceases, resulting in warmer sea surface temperatures in the temperate North Pacific. Under these conditions, plankton exhaust the nutrients in the near- surface water layers.

Marine mammals are classified into three orders: Carnivora (otters, polar bears, seals, sea lions, walrus), Sirenia (sea cows), and Cetacea in two suborders: Mysticeti (baleen whales) and Odontoceti (toothed whales, dolphins, porpoises). Most families of marine mammals including the sea otter to the largest blue whale can be found in the Eastern North Pacific.