The migration of salmon along the river is one of nature's most exciting dramas. But for the five species of Pacific salmon (Chinook, chum, coho, pink and sockeye), it is a long, arduous and desperate race against time, in which every obstacle takes its toll. Pacific salmon belong to a group called anadromous fish that includes Atlantic salmon, sturgeon, lamprey, shad, herring, cutthroat trout and rainbow trout. These species hatch and live the first part of their lives in freshwater, then migrate to the ocean to spend their adult lives, which can last anywhere from 6 months to 7 years. When they reach sexual maturity, they return to their native freshwater stream to lay their eggs. Pacific salmon make the round trip only once, but some Atlantic salmon can repeat the cycle multiple times. Migration between freshwater and saltwater occurs during every season of the year, depending on the latitude and genetic characteristics of the fish. Groups of fish that migrate together are called runs or stocks. Salmon spawn in virtually all types of freshwater habitats, from intertidal areas to high mountain streams. Pacific salmon can swim hundreds, even thousands, of miles to return to the stream where they were born. However, only a small percentage of salmon live to reach their natal stream or spawning grounds. Males that survive the journey are often gaunt, with grotesquely humped backs, hooked jaws and battle-ravaged fins. Females are engorged with a pound or more of eggs. Both have large white patches of bruised skin on their backs and sides. Because salmon don't feed once they leave the ocean, some will die along the way because they don't have enough stored body fat to make the journey. Many will be trapped in fishermen's nets. Those who escape the nets may have to swim in polluted waters near cities. Many must make their way over electric dams, leaping from one small pool to another along cascades of concrete steps called fish ladders. In tributary streams, waterfalls and rapids are steep and fast enough to take out all but the strongest. Otters, eagles and bears chase salmon in shallow ripples. Once in the spawning grounds, the fish fight each other: females against females for a place to nest, males against males for available females. The female builds her nest, called redd, by shaking the gravel of the bottom with her fins and tail, and bending ...... half of the paper ...... the almonds belong to the National Maritime Fisheries Service of Department of Commerce. The U.S. Fish and Wildlife Service and other federal and state agencies also have recovery responsibilities. The largest of the Pacific salmon, the chinook (Oncorhynchus tshawytscha), weighs on average about 24 pounds when it returns to its natal river to spawn, most after 2 to 3 years. sea. Chinook is the least abundant of the Pacific salmon. Coho salmon (Oncorhynchus kisutch), the fourth most abundant fishery in the Pacific, is the number one sport fish. It spends only one winter at sea, returning the following autumn to lay its eggs. When fully grown it averages about 10 pounds. Sockeye salmon (Oncorhynchus nerka) makes up about 25% of the West Coast catch, while chum salmon (Oncorhynchus keta) makes up about 13%. Both follow similar migratory paths in the Pacific and reach a common weight of about 12 pounds before returning to their natal river to spawn. The pink salmon (Oncorhynchus gorbuscha), the smallest of the Pacific salmon, weighs in.