<P> The salmon also undergo radical morphological changes as they prepare for the spawning event ahead . All salmon lose the silvery blue they had as ocean fish, and their colour darkens, sometimes with a radical change in hue . Salmon are sexually dimorphic, and the male salmon develop canine - like teeth and their jaws develop a pronounced curve or hook (kype). Some species of male salmon grow large humps . </P> <P> Salmon start the run in peak condition, the culmination of years of development in the ocean . They need high swimming and leaping abilities to battle the rapids and other obstacles the river may present, and they need a full sexual development to ensure a successful spawn at the end of the run . All their energy goes into the physical rigours of the journey and the dramatic morphological transformations they must still complete before they are ready for the spawning events ahead . </P> <P> The run up the river can be exhausting, sometimes requiring the salmon to battle hundreds of miles upstream against strong currents and rapids . They cease feeding during the run . Chinook and sockeye salmon from central Idaho must travel 900 miles (1,400 km) and climb nearly 7,000 feet (2,100 m) before they are ready to spawn . Salmon deaths that occur on the upriver journey are referred to as en route mortality . </P> <P> Salmon negotiate waterfalls and rapids by leaping or jumping . They have been recorded making vertical jumps as high as 3.65 metres (12 ft). The height that can be achieved by a salmon depends on the position of the standing wave or hydraulic jump at the base of the fall, as well as how deep the water is . </P>

How many miles inland does a sockeye salmon travel to spawn
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