Noting the complex relationships between salmon and other organisms, many believe the massive death toll will have far-reaching consequences for river ecosystems.
Adult salmon live in the ocean for several years before swimming hundreds of miles through rivers and streams using a powerful sense of smell to locate the same waters where they were born. There the salmon spawn, burying their eggs in the gravel. The adult fish die soon after, leaving their carcasses behind, enriching the riverâ€™s ecosystem.
Dr. Peter Moyle, fish biologist with the Department of Wildlife, Fish and Conservation Biology at University of Californiaâ€“Davis, said this "feedback loop" is crucial to the entire river ecosystem. Salmon carcasses increase the productivity of freshwater, including the number of insects that juvenile salmon feed on when they emerge from their nests.
But their influence, said Moyle, does not stop at the riverâ€™s edge.
Moyle explained that salmon "fertilize" the trees in areas where salmon spawn. In turn, the trees shade the streams, keeping them cooler, and fallen trees in the stream provide a habitat for young salmon. "So, the enhancements by the dead salmon improves the environment over all for future generations," Moyle said.
Salmon also provide a source of food for a variety of animals, including bears, raccoons, opossums, eagles, vultures and even other salmon. Moyle added that the reproductive cycles of some animals, including mink and otters, coincide with the salmonâ€™s return, providing a reliable food source as they raise their young.