Bear Eating a Salmon
Photo courtesy of the National Park Service |
Once the salmon start upstream toward the spawning grounds, they do not feed but derive energy from stored fats. The distance salmon travel upstream to spawn varies. The average spawning trip distance is about 150 miles. The longest known spawning trip length is from the Bering Sea to Lake Teslin in Canada, a total distance exceeding 2,400 miles and a 2,200 foot elevation gain (Migdalski 116-117).
On the way upstream, the salmon face fishermen, fish ladders, waterfalls, and more predators in addition to the challenges they faced on their way downstream earlier in their lives. Humans may have also built more dams or increased river pollution.
Sport Fishermen
Photo courtesy of the National Park Service |
Although salmon do not feed on their way upstream, they can be caught by skillfully presented fishing tackle. In clear water, where the salmon can be seen, it is not uncommon for a fisherman to present his lure dozens of times before sparking the fish's interest enough to take the offering.
Fish Ladder
Photo courtesy of the Corps of Engineers, Portland District |
Fish ladders are built to provide salmon with a way around hydroelectric dams and other obstructions. They are made of a series of pools arranged in a stair step fashion. Water falls from step to step, and salmon must jump from one pool to the next to reach the top. Salmon must jump up small waterfalls in rivers the same way that they climb fish ladders. Salmon can actually climb waterfalls which are higher than they can jump by swimming and leaping upward through the strong current using their powerful tails.
The predators salmon face on their journey upstream include bears, wildcats, and eagles. The bones and scraps of salmon left in the forest by these animals fertilize the forest and help it grow.
Male Sockeye Salmon
Illustration courtesy of the U.S. Fish and Wildlife Service |
As the salmon travel upstream, they undergo color changes. The males' silvery colors transform into brilliant colors, probably to attract females. The males also develop hooked snouts to the point of sometimes overlapping the lower jaw and certain species develop humps on their backs. The females also change in color but not to such brilliant shades. Each species has its own spawning colors, which vary from greens and browns to lavenders and dark reds.
These physical changes are caused by changes in the salmon's fat composition, skin pigmentation, blood chemistry, enzymes, and hormones (Steelquist 43). At this stage, they are more susceptible to disease.
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