The eastern North Pacific gray whale undertakes the longest known migration by any mammal. Each spring, gray whales journey 12,000 miles, from Mexico's Baja Peninsula to the Bering and Chukchi Seas. Kodiak lies along their migration route, and Kodiak Whale Fest celebrates their annual return. There are two gray whale populations: the eastern North Pacific and the critically endangered western North Pacific population of Asia. A third population in the northern Atlantic became extinct in the 18th century. The eastern gray whale population is estimated to be 20,000 to 22,000 animals. Eschrichtius robustus reaches a maximum length of 50 feet and has a lifespan of 50 to 60 years. The lack of a dorsal fin distinguishes them from most other whales. Gray whales inhabit shallow coastal waters, where they feed by scooping sediments from the sea floor and filtering out amphipods, tube worms and other small animals. A single whale can turn over 50 acres of sediment in a season of feeding. The churned mud is oxygenated and mixed with the nutrient-rich waters, thus preparing it for the next season. Erosion from logging and agriculture can adversely impact gray whales by choking life from sediments. The eastern population of gray whales winters in the warm waters of the Baja Peninsula, where they breed and calve. The protected lagoons provide security for calves from sharks and killer whales, their chief predators. Calves nurse for seven to eight months and can consume up to 50 gallons of milk per day. The protective behavior of mothers for their calves prompted early whalers to call them "devil fish." Gray whales are sexually mature at 5 to 11 years of age and display complex mating behavior. Gestation lasts one year, and females calve every other year. Males and single females are the first to leave the wintering grounds, departing in February and March. Nursing mothers wait until their calves have built up sufficient blubber to withstand the cold northern waters. Pregnant females and females with newborn calves are the last to begin the two to three month journey north, departing late March to mid-April. During the migration, they swim day and night without sleep. Gray whale sightings in the Ugak Bay area during summer and winter months have led to speculation that Kodiak has a small resident population. Biologists have yet to determine if this is a discrete population, or a case of individuals periodically lingering in the area. There is a small year-round population in the Straits of Juan de Fuca, between Washington and Vancouver Island, and approximately 2,000 gray whales summer along the coasts of Oregon and California rather than undergo the complete northward migration. Observers on the NOAA ship Oscar Dyson sighted five gray whales Friday, three miles off long island. That is the largest group reported this spring.