Salmon Die

By Bill Hauser

Salmon deposit eggs during summer that incubate until mid-winter when the fish hatch as alevins and, in spring, become free swimming fry. After some development and growth, they become juveniles called parr or fry until they become smolts that migrate to the ocean. In the ocean, they grow and mature until they migrate back to freshwater to spawn. After salmon return to their stream of origin, they spawn and die.

And then they die.

Is that the end?

No. After salmon die, their carcasses provide food directly to more than a hundred other vertebrates, including other fishes such as rainbow trout, sculpins, and juvenile salmon; mammals such as bears and mice; amphibians, reptiles; and, birds such as eagles and gulls. (In the Kenai River, one estimate showed that rainbow trout gained 70% of their annual growth during the several months of the year when salmon are spawning and dying.) In addition, many aquatic insects such as caddis fly larvae feed on the carcasses. These carcasses become an invaluable part of the food chain.

Indirectly, these carcasses do even more. In the process of rotting, nutrients from the bodies are released into the water to become fertilizer that stimulates the food web from the bottom up. These nutrients are called marine derived nutrients or, simply, MDN because these nutrients – most importantly – nitrogen and phosphorous – are accumulated while the salmon feed in saltwater and are distinguishable from freshwater nitrogen and phosphorous by a chemical analysis. The MDN are stored in the bodies of salmon, transported to freshwater, and released. Some scientists refer to salmon as bags of fertilizer with propellers.

The MDN become dissolved in the water and can be traced into the groundwater and into the riparian zone, trees and other vegetation overhanging the stream. Some flows downstream to a sockeye salmon rearing lake. Here, they stimulate growth of microscopic algae which, in turn, provide food for the next generation juvenile salmon.

In southcental Alaska, most rivers are supported by rainfall, snowfall, and ice melt; i.e., distilled water. If no salmon are found in a stream, the water remains quite sterile and unproductive – which translates into poor native fish populations.

One scientist calculated that the anadromous fish returns in Washington and Oregon is only about 3% of what it had been prior to installation of dams and other barriers and habitat loss. After scientists made this determination, they analyzed salmon carcasses and compounded pellets to drop in streams. This helped to fertilize the streams but not as well as when they dropped frozen salmon carcasses from hatcheries into streams from bridges. Studies demonstrate that in streams in Alaska with spawning salmon, the basic food chain origins and aquatic insects are 25 times greater than in streams without spawning salmon.

Simply put, salmon make a tremendous contribution to our lives and to Alaska and to other fishes and to the entire ecosystem.

The king is dead, long live the king.