So That the Race May Live

So That the Race May Live

Every species of animal life is remarkable in its own way, but those that astound us most are the ones whose behavior is not directed at satisfying their own immediate needs. For some animals instinctive behavior often involves extreme hardship and self—denial, merely to provide the best possible odds for the next generation. Such creatures deserve our admiration; the salmon is one of them.

Salmon will swim great distances, often against violent currents, to spawn in the precise stream in which they were born. This group of fish matures in the ocean, where some individuals may grow to lengths of four feet. At the appropriate season they seek out freshwater and begin a most frenzied swim upstream. They buck the swift currents of rapids and leap waterfalls as high as ten to fifteen feet. Considering that salmon may weigh more than seventy pounds, this is quite a feat. Nor does their skill and prowess stop there; the fish must constantly defy the waiting carnivores, usually bears, which rank salmon among their gustatory favorites. Throughout their frantic swim upstream they never pause, not even for food. The digestive system of the Pacific salmon degenerates, and they never eat again. During this incredible journey they change appearance as their silvery scales turn into a characteristic red.

For the Pacific salmon the journey ends when they find the stream in which they were born. But the most amazing salmon are those that swim up the Yukon River. The fish usually swim the entire length of the river, over 1,000 miles, seeking the water of their birth. Experimentation has shown that the salmon are able to locate their birth stream through an extraordinary sense of smell! When the Yukon salmon reach their destination, the eggs are laid and fertilized. Their task in life now completed, the noble fish simply retire from life, never to see their young or to return to the sea. The newborn salmon swim downstream to the open sea, where they will mature; thus the cycle of life is repeated and the race lives on.

The Atlantic salmon undergoes the same frenzied swim upstream to its place of birth. But unlike its Pacific counterpart, the new parents do not die; instead they return to the sea and resume whatever ventures they normally pursue. The young eventually follow their parents to the sea. There they will mature and repeat an instinctive cycle that seems to defy the very basic laws of survival.

A number of animal groups besides the Pacific salmon instinctively make the supreme sacrifice to preserve the race. Among them are several species of the female octopus. Nature has programmed her to self—destruct after she lays her eggs; it is then that the optic gland secretes a substance that induces appetite loss. Therefore, instead of hunting for food, she spends her last month of life constantly protecting her nest. In this manner her brood is assured of a good chance of survival — while the mother calmly starves to death.

From the book: 
Our Fascinating Earth