The grey whale (Eschrichtius robustus) name comes from the grey patches and white mottling on its dark skin. These whales undertake one of the longest migrations of any mammal, some traveling over 10,000 miles round trip each year from their Arctic feeding grounds to the birthing lagoons of Baja Mexico. It is also known as the grey whale, grey back whale, Pacific grey whale, or California grey whale. The grey whale is a baleen whale, having approximately 300 baleen plates which hang from their upper jaw. Grey whales are bottom feeders and forage in shallow coastal waters. The baleen plates which are made of keratin, allow them to filter food from surrounding waters.