The Miraculous Nature of Salmon
Text by Liz McKenzie and Photos by Richard Nelson
The Nature of Salmon
Imagine thousands of bright silvery salmon crowded side-by-side in a shallow freshwater stream, all facing into the current. In the ocean nearby, dense schools of salmon are circling, finning, and leaping above the surface.
Imagine the sheer power and single-minded purpose to swim up miles and miles of rivers and streams and tiny streamlets—often in just a few inches of water and over endless rocky obstacles. Some salmon even manage to fling themselves up the torrents of rapids and over cascading waterfalls.
Through these herculean feats of navigation, strength and determination, salmon return to the place of their birth for the spawning ritual…to give life and then die.
This is just one part of the fascinating life cycle of Pacific salmon—a story that’s been repeating itself since long before humans appeared on the earth.
Ancestors of the salmonid family appeared around 50 to 100 million years ago in Northern Europe. Today there are seven species of Pacific salmon, including five that spawn along the North American coast, as well as steelhead, and the masu salmon, which lives in Asian waters.
The five species of salmon in Alaska—chinook, coho, sockeye, chum and pink—are believed to have evolved from a common ancestor with steelhead (also called rainbow trout). Our modern Pacific salmon have been around for a very long time, appearing 4 to 6 million years ago.
Chinook salmon, also called kings, are the largest, averaging 20 to 40 pounds and measuring about 3 feet long; but they occasionally weigh as much as 100 pounds. Some chinooks make the longest migrations of any salmon.
Coho, or silver salmon, average 8 to 10 pounds, and 24 to 30 inches. These powerful fish are known for their ability to jump waterfalls and are prized by fishermen for their vigorous fighting when hooked.
Sockeye, or red salmon, are esteemed for their rich, oily bright red meat. They are smaller still—4 to 8 pounds and 18 to 24 inches in length. Shimmering silver in the ocean, they turn vibrant red on the spawning grounds.
Chum, or dog salmon, is the most widely distributed Pacific species. They spawn in rivers and streams throughout coastal Alaska and far up into the interior. The second biggest Pacific salmon, chums range from 7 to 18 pounds and up to 32 inches long.
Pink salmon are the smallest and most abundant species—3 ½ to 4 pounds and up to 2 feet long. Pinks are also known as “humpies” for the distinctive hump that forms on the backs of males in their spawning streams.
Endings and Beginnings
All pacific salmon are anadromous—part of their lives are spent in fresh water and part in salt water. They hatch in fresh water and spend varying amounts of time in a river system or lake before heading to the ocean, where they grow and mature, and then finally returning to their birthplace in fresh water to spawn.
The length of time Pacific salmon spend at sea varies from species to species, but they all have one thing in common—every fish dies after spawning.
But the end of one generation is the beginning of the next. Down in the gravel beds in waterways throughout Alaska, millions upon millions of pinkish-orange eggs house the miniscule, growing, soon-to-be fish.
When the eggs hatch in late winter or spring, tiny, eel like salmon, called alevins emerge and hide in the streambed gravels, with their egg sacs still attached. The nutrient rich egg sac will nourish them in relative safety. After the egg sac is completely absorbed the small fish—now called fry—move up into the greater world of the stream where they find clear, cold, oxygen rich water.
Life of Fry
Once they leave the gravel beds, fry are more vulnerable to predation, but nature has provided them with dark, vertical stripes (called parr) for camouflage. Only pink salmon, which move quickly out into salt water, won’t develop these markings.
Each salmon species is adapted to a particular rearing habitat, so the young fish can live in the same waterway without competing for food and cover.
Young sockeyes prefer the relative calm of lakes and ponds. Chinooks hang out along vegetated banks of rivers and streams where the currents are slower moving. Cohos seek out narrow tributaries, beaver ponds, lakes and other still water to grow until it’s time to move into the ocean.
Another way that salmon avoid the pressure of competition is by spending different amounts of time in fresh water. For example, cohos stay for 3 to 5 years, chinooks for 1 to 2 years, and sockeyes from 1 to 4 years, while pinks and chums head for the ocean soon after coming out of the gravel. At this point, pink salmon are just over an inch long, yet these tiny creatures swim out into the vast saltwater world.
The Great Ocean Circuit
At the final stage of preparation for their adult lives at sea, the little salmon move into the current that helps them move downstream to estuaries—where freshwater mixes with sea water and reedy vegetation offers some safety. The fry are now called smolts and they are going through an amazing physiological transformation—changing from fresh water to a life in salt water.
Once salmon move into the open sea, they are even more vulnerable to predators like bigger fish, seabirds, sea mammals and of course, humans.
Why would a fish take such a risk? The answer is simply food. Rivers and streams, while providing aquatic insects for very small fry, can’t support the tremendous growth of adult salmon. Remember that king salmon can grow to be 40 pounds or more. Even the small pink salmon need to gain many times their smolt weight to become 4-pound adults.
What’s for dinner for salmon in the great gyre currents of the North Pacific Ocean? A variety of food including zooplankton, crustaceans, tunicates, shrimp and krill, mollusks, squid and small fish.
All five species of Alaska’s salmon stay out in the Pacific Ocean feeding, growing, and maturing—but the amount of time at sea varies with species and stock. Pinks and chums have the shortest time in salt water, from 6 to 18 months. Sockeyes stay in the ocean for 1 to 4 years, chums from 3 to 6 years, and chinooks are at sea for 2 to 7 years.
The Journey Home
Eventually, even the long-lived chinook salmon feel a genetically programmed pull towards home. Most Alaskan salmon spawn from midsummer through fall, but the exact timing varies from one species to another. For example, some Kenai Peninsula chinooks arrive very early, reaching their home streams in May. On the other hand, Chilkat River chums are very late, spawning in November and December. Even within a species there is a lot of variation
How do salmon find their way back to the place of their birth after a year or more living far out in the North Pacific Ocean?
Biologists think that salmon may navigate using the earth’s magnetic field—and possibly by other cues such as the ocean currents and the position of the sun—but then when they get close enough, they use an acute sense of smell to detect their natal stream.
Once they’ve located the waterway of their birth, salmon make an arduous journey back home—sometimes even to the same small patch of gravel where they hatched from a tiny egg.
How far will a salmon travel upstream to reach home? The record spawning migration is for chinook salmon—about 2,300 miles up the Yukon River.
It is not unusual for some salmon to spawn in a stream or river different from their birthplace. This adds diversity to the genetic pool and allows salmon to populate new areas—for example new rivers formed when glaciers retreat
Love in the Gravel
As they make their way upstream, salmon undergo tremendous physiological changes. They do not eat, but survive for weeks or even months on their stores of fat. They also change color before entering freshwater or as they migrate upstream. Sockeye salmon turn bright scarlet and chum salmon develop a wavy rainbow of vertical striations on their sides.
The body shapes also change as salmon approach their spawning grounds. For instance, male pink salmon develop a large hump on their backs and a distinctive hooked jaw. Male chum salmon develop long, curved canine-like teeth, which might explain why they’re often called “dog” salmon.
On the spawning ground, a pair of sockeye salmon in the center of a large circular nest or redd.
Once a female salmon has reached her spawning area, she’ll scoop out a shallow bowl in the gravel by vigorously fanning her tail. Males often crowd close to her and try to bump other males out of the way, so they can be the closest when she lays her eggs.
After preparing her nest in the gravel—called a “redd”— the female lays hundreds or thousands of eggs and the dominant male quickly moves in to release a whitish cloud of spermy “milt”. Then the female uses her tail to cover the eggs with sand and stones, and eventually she moves on to create several more redds.
Each male can fertilize a number of redds, often with several different females. The number of eggs that a female can produce is staggering; for example a chinook can lay 3,000 to 14,000 eggs. Even the much smaller pinks can produce up to 2,000 eggs
The Gifts of Salmon
Once the work of depositing and fertilizing eggs is complete, salmon literally give their lives for the next generation. Their bodies add important nutrients to the stream, providing food for the insects and other tiny organisms that the young salmon will feed on. Salmon carcasses also supply vital nutrients to plants that give cover to young salmon in the streams and lakes.
But that’s only part of the story.
Studies along the entire North Pacific coast have shown that salmon are a keystone species for both aquatic and terrestrial ecosystems…important for the health of streams and rivers, for estuary meadows and forests, for animals in the nearby ocean, and for entire animal communities on the land.
Dead and dying salmon feed mammals, birds, and insects. These animals carry bits of salmon carcasses up onto the land, and they also deposit fertile droppings. This remarkable process ensures that nitrogen and other nutrients, carried in the bodies of salmon from the far reaches of the ocean, help to enrich the soils, feeding trees, shrubs, and other plants that in turn shelter and sustain the animals.
And humans, too, are a part of this complex web of life. Salmon are essential for Alaska’s subsistence, sport, and commercial fisheries; they provide economic benefits worth billions of dollars every year; they are a vital element in the lifestyles and cultures of communities along the entire North Pacific coast; and they provide healthy, nutritious food for people all over the world.
Salmon have declined or disappeared in many places where they once filled the rivers each year. Alaska is one of the last places where they remain abundant. These amazing creatures depend on humans to carefully manage fishing, to protect watersheds from damage, and to keep the oceans healthy.
If we treat salmon responsibly, they can feed us, enrich our lives, and support our communities for generations long into the future.
Salmon depend on people and people depend on salmon. If we take care of the salmon, we are also taking care of ourselves.