Monday, August 8, 2011

Life of Gray Whale

Life of Sea | Gray Whale (Eschrichtius robustus) | Gray whales live at the surface of the ocean near the coastline but dive to the bottom to feed. They are often sighted in the eastern and western North Pacific and along the North American Pacific Coast between the arctic and the equatorial lagoons of Baja California, Mexico. The gray whale has also been spotted in the North Atlantic Ocean, as well as in the Arctic Ocean. Gray whales make an extraordinarily long migration from the Arctic Ocean (northwest of Alaska in the Chukchi Sea) to the Baja peninsula off Mexico, and back each year.

Gray whales have streamlined body and narrow tapered head. The arched upper jaw slightly overlaps the lower jaw. The upper jaw is dimpled with each containing a stiff hair. The gray whale's throat has 2-5 grooves which are 1.5 m in length. Their dark skin has gray patches and white mottling and often contains many scratches, patches of barnacles, and orange whale lice (amphipods feeding on whale skin and damaged tissue such as a wound). Newborn calves are dark gray to black and some have distinctive white markings. 

Gray whale has no dorsal fin but two-thirds of the way back on its body is a prominent dorsal hump followed by 6-12 knuckles along the dorsal ridge that extend to the flukes (tail) which is 3.7  m across, pointed at the tips and deeply notched in the center. Gray whale flippers are paddle-shaped and are also pointed at the tips. Adult males are 13.7-14 m in length with adult females measuring slightly more. Both sexes reach weights of 27,200-36,300 kg. 

Gray whales feed on small crustaceans such as amphipods, and tube worms found in bottom sediments. Gray whales feed primarily during the summer months of long daylight hours in the cold Arctic waters of the Bering and Chukchi seas. To feed, the whale dives to the sea floor, turns on its side (usually to the right), and swims forward along the bottom of the sea, forcing its head through the top layer of sediment along the sea floor. It is there that the whale scoops up its invertebrate prey as well as gravel and mud, leaving a trail behind. The whale then surfaces, straining the sediment through the baleen, which permits only the food to remain in the mouth to be swallowed.

Gray whales are very agile swimmers. They can swim in even relatively shallow water without running aground.  They also breach, jumping partially out of the water and falling back at an angle, splashing and making a loud noise. This may help clean off some of the encrustations of parasites (barnacles and whale lice) or in communicating with other Gray whales. Killer whales, the large sharks , and humans are their predators. Killer whales hunt Gray whales off the Pacific Northwest coast near Oregon, USA. Skin parasites attach themselves to the head area, back, and blowhole area also.

Gray whales live in small pods of about 3 whales, but the group may have as many as 16 members. Large groups (up to hundreds of whales) form in feeding waters, but these are loose, temporary associations. They do not form long-term bonds.  Gray whales are often observed approaching small boats in the shallow lagoons where they calve and mate and actually allow humans to touch them. The reason why remains unclear but some believe it is out of curiosity whereas others believe it may be due to the sound of the boats motors and that they are being defensive of their calves by checking out the intruders.

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