Teacher Resource 3: The Salmon Life Cycle (In Depth)
Recommended for grades 4-8
Key Elements of Lesson 3:
- Salmon have a complex and far-reaching life cycle which takes them thousands of miles, from fresh water to the ocean and back.
- Salmon face many hazards and challenges along the way, both natural and human-made.
Outcomes of Lesson 3:
- Students will be able to describe in detail how adult returning salmon successfully lay, fertilize, and protect their eggs.
- Students will be able to describe specific stream and stream bed requirements that will ensure successful incubation of eggs, and the several hazards they face during this fragile stage.
- Students will be able to describe and draw (ADD A DRAWING COMPONENT) the development of eggs to sac fry to fry.
- Students will be able to describe the hazardous downstream journey of smolts and the physical changes that take place as they transition to salt water.
- Students will be able to describe how the salmon diet changes as they mature in the ocean.
- Students will be able to indicate on a map where Puget Sound watershed salmon migrate in the ocean (ADD THIS DRAWING COMPONENT).
- Students will be able to describe our understanding — as well as our theories — of how salmon are able to navigate and return thousands of miles to find home.
- Students will be able to describe general external physical changes to male and female salmon as they re-enter freshwater and migrate upstream.
- Students will be able to describe the challenges adult returning salmon face during their upstream migration, both natural and, more often, human-made.
- Students will be able to describe in general terms what salmon carcasses contribute to the stream and forest ecosystems.
Reading Passage: Tyee’s Magnificent Journey
As you began to learn in Lesson 2, a hen builds a shallow depression in the gravel of a stream bed — which we call a redd (her nest) and deposits thousands of eggs into it. A buck, swimming alongside her, immediately fertilizes the released eggs as they drop into the redd. The hen quickly moves just upstream and, with a strong whip of her tail, flips up gravel to cover the eggs, burying them. It is important that the eggs remain hidden from predators and locked down to prevent them from being washed downstream by the current.
To incubate successfully, the eggs depend on cold, clean, oxygen-rich, flowing water to percolate (flow through) the gravel in which they are buried. The gravel must remain clean, with very little sediment (small particles) in order to allow the eggs to “breathe” the oxygen-rich flowing water. The flow also carries away waste product, which is important. Water temperatures must remain cold — between 40 and 65 degrees F (Fahrenheit). Salmon are cold-water fish and do not easily tolerate temperatures above 68 degrees F.
During the first month of incubation, the eggs are fragile and even a slight disturbance might destroy them. They are susceptible to many dangers:
- Silt can smother them. Silt is fine sand or clay, eroded from the earth’s surface as water runs downhill. When trees and vegetation are removed from the land or destroyed (by construction, logging or wildfire), the land is exposed to the forces of nature. With enough rainfall, water carries sediment downhill, coloring the water brown as it picks up particles of earth. Streams and rivers turn muddy brown with suspended sediment. These fine particles eventually settle to the bottom as silt. Silt fills the empty spaces between rocks and gravel — where salmon eggs are buried and incubating. Too much silt can devastate eggs by smothering them.
- High stream flows during heavy rainfall can scour (drastically erode) stream beds, tumbling gravel and eggs downstream, killing the eggs.
- Predators feed on eggs. As they forage the stream bed for food, their movements through the gravel can crush or trap the buried eggs.
- Low water levels. During long periods of dry weather, water flows in smaller streams can drop so low that stream side channels — which flow when water is plentiful — can run low and even stop flowing. Many of these side channels are used by salmon to spawn, and those redds can become isolated in side pools, cut off from the flowing stream. The side pools are small and vulnerable to warming by the sun. Without incoming flow, eggs and developing young salmon may suffocate as oxygen in the small pools is used up and not replenished.
Gallery: Eggs & Alevins
On average, only about 10 percent of the eggs deposited in a redd survive. For survivors, after roughly a month of incubation, head and body regions begin to develop and eyes begin to show.
Within a few months, in late winter or spring, the eggs hatch and are called sac fry, or alevin. A sac fry is a fragile creature with huge eyes and a large yolk sac protruding from its belly. The orange sac contains a balanced diet of proteins, carbohydrates, minerals and vitamins. Sac fry remain in the gravel and live off their yolk sac, growing rapidly for one-to-three months.
By remaining under the gravel, sac fry are protected from most predators and other hazards. They continue to rely on clean, porous (lots of spaces in-between) gravel to allow flow of oxygen-rich water.
By late spring and summer, when surviving sac fry have absorbed all of their yolk sac, they must emerge from the gravel to find food. They are now about one inch long and are called fry. Fry feed on plankton and small insects and rely on good streamside cover (such as overhanging trees, grasses, and shrubs as well as woody debris such as logs and dead branches) for protection from predators and keeping the water cool. Fry stay in shallow pools near the edge of the stream where the current is not too strong. They are easy prey for trout and other large fish as well as birds.
When the young fish reach the size of a human finger, they are called — appropriately enough — fingerlings. They now have vertical marks (parr marks) along their silvery sides to help them hide from predators. They continue to grow rapidly.
When they reach approximately four to six inches in length, instinct drives them to migrate downstream toward the ocean. They are now called “smolts.” They travel mostly at night to avoid predators who hunt by sight. Interestingly, most smolt drift backwards downstream, with their head facing upstream.
Throughout this migration, they are confronted by many hazards, including potentially low water in streams, reservoirs which interrupt the natural downstream flow of water, predatory birds from above, dams and other man-made changes to the river channel, and predatory fish and mammals. Ample water flow is a critical factor during downstream smolt migration. High flows mean higher survival rates.
Up to 90 percent of salmon that hatch never reach the sea.
Survivors that reach the estuary — where river water mixes with the sea — experience big changes to their body as they make the remarkable transition from freshwater to saltwater. (Imagine having to adjust to drinking ocean water?! Hint: it would kill us.) This physical change is called smoltification. Their parr marks disappear and their bodies become silvery but also “counter-shaded” (dark above and light below) which will help them avoid ocean predators. Once adjusted, they head out to sea as young salmon.
INSERT A SMALL SECTION HERE THAT DISCUSSES LIFE IN AN ESTUARY.
Gallery: Fry, Fingerlings & Smolts
The amount of time salmon spend in freshwater varies by species:
- Chinook are interesting::
- “Yearlings” spend a year in freshwater.
- “Sub-yearlings” spend just a few months to 6 months.
- Coho and sockeye spend a year or more in freshwater.
- Pink and chum migrate soon after emerging as fry!
Dams drastically alter the natural flow of river systems. The reservoirs behind dams present challenges and dangers: 1) smolts must now navigate across a human-made lake, which critically delays their progress, and 2) as they do so, they are vulnerable to lake predators, both fish and birds. Many smolts are eaten in the journey, and survivors are significantly delayed in reaching the estuary, which can critically impact their transition to saltwater. Dams themselves present hazards: 1) smolts are injured and killed as they pass through hydroelectric turbines or 2) fail to find human-made passageways downstream. Some pass into unscreened irrigation ditches and become stranded in farm fields.
The amount of time that salmon spend at sea varies by species:
- Chinook, Sockeye and Chum: spend 3 to 5 years at sea.
- Coho: most spend 3 years at sea.
- Pink: spend exactly 2 years at sea.
The sea is rich in food sources and salmon grow rapidly. Phytoplankton (microalgae — tiny plants — that float in the water wherever light is able to penetrate) are the first food source for young salmon. Ocean temperatures have much to do with how much phytoplankton is available.
Warmer water reduces the amount of phytoplankton, and therefore greatly impacts the survival of young salmon at sea. HOW IS IT THAT WARM WATER REDUCES PHYTOPLANKTON???
As they grow, their diet evolves to shrimp and krill. Some species move on to herring, sand lance, anchovy and others. However, they also face encounter predators, such as sharks, orcas, other marine mammals, and commercial and recreational fishers.
Where Do Issaquah Salmon Go? (INSERT A MAP)
- Most Puget Sound salmon (including those reared at the Issaquah Salmon Hatchery) emerge from the Strait of Juan de Fuca and enter the Pacific Ocean, following the British Columbia coast north.
- Some salmon turn south and live off the Oregon coast.
- A few remain in Puget Sound. Chinook that stay in the Puget Sound are referred to as “Blackmouth“, based on the black gumline characteristic of Chinook. Blackmouth used to support a significant winter sportfishery, but the numbers of these Chinook have declined greatly in the last decade.
The Alaska Current
Of the majority of salmon who swam north in the Pacific Ocean, Chinook swim as as far as the Aleutian Islands of Alaska. They travel down-current in what is called the Alaska Current — which is a huge counterclockwise circular current nestled under Alaska and the Aleutian islands. INSERT PICTURE. Swimming downcurrent makes their journey easier as they cover long distances. This current is important because it upwells (brings up from below) nutrients from deeper waters. These nutrients feed the phytoplankton, forming a strong basis for life in the oceanic food web, in which salmon can thrive. Unfortunately, as global warming occurs, less nutrient-rich water is brought to the surface, providing less food to salmon. EXPLAIN WHY THAT OCCURS. IS THERE LESS CURRENT?
How Long Do Salmon Stay in the Ocean?
It varies by species:
- Chinook: 3-5 years
- Coho: 3 years
- Sockeye: 3-5 years
- Pink: 2 years
- Chum: 3-5 years
Returning salmon are referred to as “1 salt fish” if they return after one year in the ocean, then “2 salt fish”, and so on. A typical 12-pound Chinook returning to the Issaquah Salmon Hatchery is a 3 salt fish, while a 20 pound Chinook is likely to be a 4 salt fish. The largest Chinook on record weighed 127 pounds, and is speculated to have been at least a 9 salt fish!
Growing to Maturity
While in the ocean, salmon concentrate on feeding and adding to their body mass, especially fats. These fats will be their energy reserves for what will be a long, difficult upstream migration to spawn. These fats are also why animals, such as orcas, sea lions, sharks and humans love salmon, because these fats make salmon delicious to eat.
Once their body matures to a certain point, instinct drives them to reverse course and begin the journey back to their home stream. The salmon who swam north in the Pacific Ocean will now swim against the Alaska Current. Salmon off the course of Oregon head north for their return journey.
What is it exactly that signals to salmon that it is time to leave the ocean and start the migration back to the Puget Sound? What drives their urge or knowledge to turn back? It is instinct and hormones — the biochemicals within mature animals that drive the urge to reproduce. [I NEED TO RESEARCH WHETHER THE TRIGGERS FOR THIS CHANGE ARE KNOWN.]
How Salmon Navigate: the Science and the Mystery
Scientists have studied the navigation of salmon in the ocean for decades, and although a great deal is known, there are still mysteries to unravel.
It is known that salmon can detect the Earth’s magnetic field and that tiny changes in this magnetic field will cause our returning “northern” salmon to travel down the British Columbia coast — either east of Vancouver Island via the Strait of Georgia, or on the west side of Vancouver Island — to enter the Puget Sound via the Strait of Juan de Fuca.
It has been speculated that salmon may navigate by the position of the stars. However, given that there are generally 200 or more overcast days per year in the northern Pacific Ocean, this seems unlikely.
Finally, it is well known that when salmon approach their natal (home) stream, they navigate by smell. Every stream has a unique smell, made up of minerals that are dissolved in the watershed, and other microorganisms, such as algae. For example, even the coal pollutants from abandoned coal mines in Squak and Tiger Mountains lend a distinctive smell to Issaquah Creek. Young salmon learn those smells and use them to guide them home.
LET’S UPDATE THIS GALLERY CAPTIONS TO WALK THE USER THROUGH THE DIFFERENT VISIBLE PHYSICAL CHANGES. While salmon are developing as they travel northward in the Pacific Ocean, their reproductive organs – eggs sacs in the females, testes in the males – are very small. However, as instincts and urges drive them to reverse course and head home, salmon begin to go through remarkable physical changes, particularly as they re-enter the freshwater. Their skin thickens and bones soften. The changes that males go through are the most physically obvious and dramatic, developing hooked jaws, sharp teeth and, in some species, bright colors. We explore these in great detail in our “Salmon Identification” lesson, but a few examples include:
- Chinook take on a darker color, usually a dark brown with enlarged black spots, and some of the males develop red highlights on their sides.
- Coho become much more colorful, with the males sometimes developing very red sides.
- Sockeye develop red bodies and green heads.
- Pink males develop particularly large humps. (Males of all species develop humps, but pinks are the most pronounced, which explains their other name: humpies.)
- Chum develop blotchy, vertical stripes across their sides.
Gallery: Changes in Migrating Salmon
But there is another remarkable change going on inside a female salmon’s body: she is converting body mass (stored fats and muscle) to create thousands of eggs inside her, all of them rich in fats and protein. By the time a female approaches her spawning grounds, 20% of her body weight is eggs.
Interestingly, some salmon return as very small adults, usually weighing less than a pound. These are referred to as “jacks” and may have never even left the Puget Sound. They are sexually mature and capable of fertilizing eggs. Just like their larger brothers, they die after they spawn. Also interesting is that the vast majority of these “early returners” are male (hence the name “Jack”) and very rarely does a female return early. When she does, she is called a ‘Jill’. They are very rare.
Once in Fresh Water, They Stop Eating
After almost constant eating throughout their lives, salmon do a remarkable thing when they re-enter fresh water: they stop eating. Remarkably, they will complete their entire upstream migration and spawning while living entirely off of their fat reserves. The length and arduousness of their upstream migration actually vary by species, with Chinook claiming the long-distance prize:
- Chinook: INSERT CONTENT HERE
- Coho: INSERT CONTENT HERE
- Sockeye: INSERT CONTENT HERE
- Pink: INSERT CONTENT HERE
- Chum: INSERT CONTENT HERE
How do Chinook do it? The answer is: the farther a salmon has to travel upstream, the more stored body fat it requires. Chinook have evolved to be a “fatty” fish (prized for their delicious flavor, by the way) designed for long-distance upstream migration. And even among different runs of Chinook, those whose spawning grounds are hundreds of miles upriver have evolved to be fattier Chinook, allowing them to make the particularly long journey. This is to say: not all salmon of the same species are necessarily alike. You will learn in upcoming lessons that salmon have evolved and become specialized for their home streams.
The Endurance and Hardship of Upstream Migration
As salmon swim past the river estuary on their way upstream, they face a new series of challenges that will test their endurance. Dams built for hydroelectricity, flood control and water supply can block passage upriver. While most dams now have fish ladders to enable salmon to bypass the dams, simply finding them demands part of a salmon’s limited energy resources. Reservoirs behind the dams delay their upstream progress as their migrating instincts are confused by the still water. As they continue to make their way upstream, landslides and log jams can present unexpected new barriers. Waterfalls and rapids challenge salmon and test their endurance. Salmon often suffer visible injuries, adding to the many challenges. Anglers (fishers), bears, other mammals, and eagles take salmon along the way. When flows become too low for upstream migration, salmon may be delayed and must wait in holding pools until there is enough flow to enable upstream passage. Water temperatures may increase as they wait in these pools, creating conditions that promote disease outbreaks among fish. Delays decreases their chances for successful spawning.
When salmon finally arrive at their natal stream and are ready to spawn, the female (or hen) searches for a suitable place for spawning and then prepares a nest, called a “redd”. Swimming on her side and using her tail, she digs a 12 to 18-inch depression in the gravel of the stream bed. DESCRIBE HOW MALES COURT THE HEN. She then deposits between 3,000 to 5,000 bright pink eggs into the redd, and as she does so, the buck quickly fertilizes the eggs with milt (a milky white substance containing sperm). The hen moves upstream of the redd and, with her tail, she flips gravel back over the eggs to bury and protect them.
She remains with her redd for her remaining few days, defending it from disturbance by other hens. The buck swims off, possibly to fertilize eggs of other hens.
They survived a remarkable journey full of challenges and hardship which took them thousands of miles in order to propagate the species. Within just a few days, both the hen and buck die. Their carcasses drift downstream and decay, contributing nutrients to the stream and the ecosystem that gave them life.
INSERT A GENERAL DISCUSSION OF WHAT SALMON CARCASSES CONTRIBUTE TO THE ECOSYSTEM.
Coming up next is a reading passage titled Tyee’s Magnficient Journey which follows the life cycle journey of a Chinook hen — from the salmon perspective. Consider which of the following learning activities are appropriate for your student age group:
- Older students:
- Have them read only part of Tyee’s Magnificent Journey (perhaps up to where Tyee enters the Columbia River on her return journey); complete the Learning Activity Game Hooks and Ladders and then have them write the remainder of the story in their Salmon Journal.
- Younger students: read the story to the students, pausing to discuss each “stage” in the salmon life cycle. Consider listing all the things salmon need to complete each stage.
- Any age: Have your students draw and label the life cycle stages of Tyee in their Salmon Journal. Use different colors for freshwater and saltwater stages.
- Any age: have students record Tyee’s journey on the map provided (map is not to scale). They can do this as they read, or return to the story after they read it to get the needed information. The story notes the months and years Tyee passes points identified on the map. Have students use colored pens or pencils to trace where Tyee goes, one color for her downstream and ocean journey, and another for her return trip (change colors when she begins her journey back to the Columbia River). Also have them note the month and year these points are passed, such as “in red – September 1998” and “enters ocean – June 2000,” using the same color as the journey trace. Use any year to start you want. If she is conceived in September of 1998, she:
- should be passing lower Granite Dam in April 2000
- should enter the ocean in June of 2000
- should pass Sitka, Alaska in August of 2001
- should pass Anchorage, Alaska in October of 2001
- should begin the return trip to the Columbia River in July of 2002
- should enter the Columbia River in March of 2003
- should be back in her home stream to spawn in September of 2003.
You could also use a map drawn to scale to trace Tyee’s route; this allows you to calculate the number of miles traveled between each point. A large classroom map can also be used with colored yarn to trace Tyee’s route.
The salmon life cycle truly is remarkable. In this reading passage, you will follow the journey of one salmon through all stages of her life. You will view the enduring challenges that salmon face through her perspective. We hope you enjoy it and gain some perspective of your own.
A miracle. That’s what indigenous peoples called the vast runs of salmon that returned each year from the ocean. Returning to the streams where their lives began from a huge ocean, these fish were great and magical spirits. Even today, the life cycle of a salmon seems miraculous. The long journey that salmon make from the gravel in their birth stream to deep into the Pacific Ocean and back again is full of dangers and requires almost unimaginable endurance.
Salmon lay between 3,000 and 5,000 eggs in a nest in the stream gravel. But did you know that, on average, only two fish return from all those eggs? If the water level in their stream drops too low, thousands of eggs can be wiped out. Birds, bigger fish, bears, seals, and sea lions take their share of salmon. Nature has provided for this loss by enabling salmon to lay these thousands of eggs.
But nature alone cannot make up for what people have done to salmon. Dams block large areas of the wild salmon’s spawning grounds. Roads and towns have been developed around and over salmon streams. Logging and farming practices have fouled rivers with sediment. As did pollution from cities, factories, and houses. Moreover, technology makes catching salmon too easy. Salmon runs have grown smaller and smaller.
Today, some types of salmon are in danger of disappearing forever. The Pacific Ocean and the great river systems that empty into it are no longer the kind of homes they once were for Pacific Northwest salmon. Eventually, people have begun to recognize that something had to be done to help them. A law called the Endangered Species Act was created, and it helped people to see that many kinds of salmon were in danger of being lost forever. Today, many people are working hard to help salmon survive.
To understand what needs to be done to help salmon, it is important to understand the remarkable life cycle and journey of a salmon. This story — about just one female Chinook salmon, “Tyee the Lucky” — will help you understand. It is told from Tyee’s perspective.
THE CYCLE BEGINS
High in the mountains of central Idaho, a creek too small to have a name runs cold and clear. Thousands of years in the past, great melting ice sheets left a U-shaped valley with a gravel floor. The gravel can still be seen on the creek bottom.
It is September. Leaves are yellow and brown, and frost covers everything along the stream bank. The first snowfall is not far away.
A reddish-brown female Chinook salmon lies just under ripples of rushing water. She is battered and exhausted. She seems to be resting, perhaps waiting for something. Another salmon appears. He is darker, with cream- colored splotches on his body. He moves next to her, facing upstream as she is. These salmon are mating, or spawning.
They are Chinook salmon, also called “tyee” or “king” salmon. They are the largest and live the longest of any Pacific Northwest salmon. The female lays about 5,000 bright pink eggs in a depression in the gravel (called a redd), which she has dug with her tail. Then the male moves in to fertilize the eggs. Finally, the female moves just upstream. With her tail, she kicks up pebbles that drift down over the eggs, hiding and protecting them.
Now the eggs are protected from sunlight, strong currents and hungry animals. For the next four weeks or so, the eggs remain hidden in the gravel. If the redd is not disturbed the eggs will remain safe.
In a few weeks, the eggs begin to change. Inside each living egg, a head, eyes, and a body begin to take shape. Somewhere among this closely packed redd lies Tyee the Lucky. Salmon don’t usually have personal names, but this female is special. Read on to find out why she is called “lucky”.
Tyee is lucky that the water rushing through the gravel in the redd is only about 55 degrees Fahrenheit – perfect for a salmon. Warmer water could end her life early. She’s lucky, too, that there have been no sudden torrents of heavy rain and resulting floods that could scour the stream bed, removing her gravel protection.
Upstream from Tyee’s redd, many riffles of water running over rocks mixes air into the water, giving it a rich oxygen supply. Without oxygen, the eggs would die.
Ducks and other birds, raccoons, and larger trout love to eat salmon eggs. But Tyee is hidden and protected in the stream gravel. Tyee the Lucky.
Tyee’s stream is a healthy one. It had been spared from heavy logging years ago because it was hard to get to. Then, not long ago, the stream and its banks were protected by laws passed to save salmon habitat. Before that, streams all around it had not been so lucky.
In one creek about the same size, a mining operation once ripped up the stream bed. Even though that was years ago, loose soil from the mining is still carried downstream by rainwater. This soil, or silt, covers the graveI in the stream, cutting off the stream’s oxygen-carrying water to the eggs. The eggs suffocate.
On another stream, grazing cattle trampled the stream bank, muddying the stream and filling the gravel beds with silt. Pesticides (chemicals used to kill insects) were used on farm crops upstream and poisoned eggs and fish. Now, people are busy trying to bring this stream back to health. Cattle have been fenced out of the stream, and farmers using pesticides are being more careful, and some have stopped using them entirely. This stream is “on the mend.”
In other streams in the watershed, people logged all of the trees, right up to the stream banks. As a result, these streams no longer have shade to cool the water. Many are choked with debris. Some streams have lots of silt from logging and road building. But in some areas of the watershed, people are working to repair this damage. It will take time to repair all of it, and the job seems almost impossible. Laws were passed to make sure that people protect streams, no matter what kind of work they are doing.
In small streams where salmon spawn and hatch, people are working to restore damaged streams. They are planting as well as leaving trees and shrubs along the banks to keep the water cool and provide food for the insects that live in the stream. They are placing logs and boulders in the stream to create places for fish to hide and grow. They are protecting the stream water from pollution. Almost everybody helps pay for the work, through electricity rates and taxes. Many people even volunteer their own time and money to do these jobs.
Tyee doesn’t know about all the damage or the work underway to repair it. She is still an egg. Her stream is healthy. She is lucky.
FROM EGG TO FRY
It is winter at Tyee’s redd. Snow covers the ground. All is white except the stream itself. Thin ice sheets cling to the banks of the stream. Little can be heard except the soft gurgle of the stream. Nothing seems to be alive. But in the gravel, things are happening.
By Valentine’s Day, the surviving eggs alive have hatched. The hatchlings stay under the gravel. Tyee has transformed herself into a small creature called a sac fry (alevin). Her eyes are huge compared to the rest of her body.
An orange sack, called a yolk sac, hangs from her body. The yolk sac contains all the proteins, carbohydrates, vitamins, and minerals she needs to grow. As she grows, the sac gets smaller.
One night in March, Tyee gets an urge to slip upward through the gravel. She emerges into the stream as a tiny fish, called a fry. Her eyes are still bugged out, and she is tiny — about the size of a fir needle. She stays away from the direct sunlight, in shallow pools near the edge of the creek where the current is not strong. Tyee darts around, feeding on tiny creatures. She is quicker than most – a good thing to be, because as she feeds, she is easy food for other fish, ducks, and herons. Tyee the Lucky.
Some fry start their migration to the ocean as early as May or June. The creek gets shallow in July. Tyee lets the current take her downstream. She is in no hurry, and stops along the way under root wads, fallen trees, and boulders. These places make good resting and feeding stops. By the time the first Fall raIns come in October, she is in the Middle Fork of the Salmon River. ADD A MAP HERE.
By September, Tyee has grown to a fingerling (small salmon, about the size of your finger). She is well over three inches long. Scales protect the length of her body. Over the scales, a slime layer of mucus has formed to protect her from disease and help her slide through the water. She has developed faint, oblong marks along her silver-colored sides to help hide her from predators.
Tyee is big enough now to be a real hunter. She snaps up mosquitoes and other insects that come near the water surface. She nabs an ant unlucky enough to have fallen into the water.
Her mouth helps her eat and breathe. She takes in water through the mouth and forces it out through the gills on each side of her head. The feathery gills contain blood vessels which – just like your lungs in air – take up oxygen from the water.
Tyee doesn’t have ears, but she can hear well. Low-frequency sounds vibrate through the water to a row of small holes along each side of her body. These holes open to nerves that let her “hear” danger coming. Salmon also have nares (pronounced “nair-eez”) which are not quite nostrils but do enable an extraordinary sense of smell. They can smell predators and food.
Tyee can smell home too. As she travels farther from where she emerged from the gravel, she is also memorizing/learning how to get back. Salmon can return to the stream of their birth using this learning. We call this homing, but we don’t yet understand how it works. Somehow, the smell, taste, or some other thing about the water in Tyee’s stream becomes lodged in her memory.
INSERT A PHOTO OF A KINGFISHER HERE. So far, life for Tyee has been mostly good. But she has been chased by more than one large fish. In August, a kingfisher perched on a branch above her took aim and headed straight for her. Thanks to her large eyes and quick reactions, she darted away before he got to her.
Not every young salmon is so lucky. In fact, only about 15 percent of the eggs in her redd make it through the fry stage. That’s 750 salmon of the original 5,000 eggs. And conditions for her brothers and sisters were better than average, given that she came form a healthy stream.
THE DOWNSTREAM JOURNEY
As Tyee begins the winter of her first year, her growth slows. There is not as much food, and she doesn’t seem to be as hungry. As the snow falls, she waits for another spring. In April, it finally comes. Snows begin to melt and spring rains begin. The water level rises and the runoff sweeps young salmon downstream.
Tyee lets the water do the work. She travels with her head upstream as the water carries her toward the unknown. Traveling at night to avoid predators, she feeds on midges (small flies), worms and snails. She is changing both inside and out, preparing for her life in salt water. Her body is ready for the migration. She is at the salmon life stage where she is known as a smolt.
She enters the Salmon River, then the Snake River — a larger river that forms the border between Idaho and Oregon. Other smolts from other streams join her in a mass migration to the sea. The Snake River rushes her along, then suddenly the current is almost gone. It is April, and Tyee has entered the reservoir (man-made lake) for Lower Granite Dam.
This is the first major barrier to her migration to the ocean. Before dams were built, the trip to the ocean from her home stream might have taken three or four weeks. But the dams had slowed the water, and now the journey takes closer to two months. Downstream, more dams await: Little Goose, Lower Monumental, and Ice Harbor on the Snake River. When the Snake joins the Columbia River, four more dams await: McNary, John Day, The Dalles, and Bonneville. All of these dams were built in the 1900s. The dams have been good for people. They have been devastating for salmon.
Dams make electricity by holding back the river water in large reservoirs, then letting it run through turbines (machines that generate electricity from falling water). Falling water spins the turbines to make the electricity. This is a clean and cheap way to provide power for people. Dams also store water for cities and to provide irrigation water for crops during the dry season. They also control flooding. Rivers no longer run free. Some dams have locks which allow barges to pass up and down the river, carrying goods and crops.
But from Tyee’s standpoint, dams are both difficult and deadly. The reservoirs behind the dams have little current, and her trip to the ocean takes much longer. Predator fish such as walleye and bass are waiting to make a lunch out of her all along the way. Her predators thrive in the slower water created by the dams.
Just passing a dam is difficult for Tyee and her kind. At lower Granite Dam, a fish screen catches her just in time and guides her away from the whirling blades of the turbines.
At another dam, the water is high and one spill-way is open. (A spillway allows water to spill over or around a dam.) Tyee is stunned for a short time after a fifty-foot drop over the spillway. She regains her senses just in time to escape from a gull waiting for her above the churning water. Tyee the Lucky.
Tyee’s luck holds as she travels down the Columbia River toward the ocean. Many of her kind were not so lucky. At each of the eight dams she has passed, 10 to 15 percent of the salmon smolts don’t make it. It is a staggering number that shows just some of what dams have done to salmon in Washington state.
People are working to make the trip easier for salmon. Newer and better screens are being installed at the dams. Water releases at the dams are being timed to provide faster flows down the river when the smolts are traveling through. Some of the smolts are even collected at Lower Granite Dam, placed in a barge full of water, and given a free ride down the river. They are released below Bonneville Dam.
INSERT THE TYEE MAP.
After passing Bonneville Dam in late May, Tyee finds herself once again in a flowing river. She passes between the cities of Portland and Vancouver. Here, the water tastes different. In cities, rainwater hits rooftops, paved streets and parking lots. Instead of soaking into the ground, water quickly runs off these surfaces and into the nearest storm drain and into the river.
Pollution is carried with the water. Grit from rubber tires, detergent from washing cars, fertilizers from lawns and gardens, and even used anti-freeze and oil from cars has been washed from roads and driveways into the river. Tyee is glad to get past this part of her trip.
More smolts from other rivers and streams continue to join her in the journey to the sea. The river is full of life.
What’s this!? Suddenly the current seems to be going the “wrong way.” The water, again, tastes different. Tyee has reached the Columbia River estuary, where the river meets the sea. Here, twice each day, the incoming tide pushes seawater back up the river. The estuary is rich in new kinds of food: algae, crab larvae, shrimp and small fishes.
Tyee stays in the estuary for about two weeks. She still has to be careful. She is only six inches long, and must stay out of the way of larger fish in order to survive. Pelicans and other fish-eating birds thrive in the estuary. In the slack water of the estuary — when the tide is turning and water movement has slowed — Tyee joins other smolts near the surface of the water. They jump out of the water as high as they can, but not to catch food. People don’t know why they do this. Perhaps it is to celebrate their lucky trip from their “home streams” to the sea. Tyee should celebrate. She is one of only 300 left of the 5,000 eggs laid by her mother. Tyee the Lucky.
THE GREAT OCEAN
One night, after a warm, clear day in June, Tyee feels the urge to begin the next stage of her life. She rides the night tide across the Columbia River bar and swims into the great Pacific Ocean. She will not see this place again for three years.
In the sea, there is new food to catch. At first, Tyee’s diet is mostly zooplankton – tiny animals in the ocean water. Later, she finds shrimp and other animals. Her body takes up the color of the shrimp, changing the color of her flesh from white to pink. Anchovies, herring and other fish are added to her diet.
Sea birds, tuna and larger salmon are everywhere, hungry to make a meal out of her. But she survives and grows. She heads northward, past the Strait of Juan de Fuca. She now weighs about a pound and a half.
Suddenly, she finds herself in a thick group of all sizes of fish. The group is being drawn together by a huge net. The bottom of a fishing boat can be seen above. Tyee slithers among the trapped fish in the net. She just manages to slide through one of the openings in the net. She has been saved only by her small size. A new predator – people – will be after her now. She has grown large enough to be valuable to both sport and commercial fishers.
For as long as there have been people and fish, humans have taken fish for their own use. The indigenous peoples of the Pacific Northwest used salmon for food and many other things. To them, the salmon was a spirit, a link between the natural world and the world of people. They were in balance with the salmon.
Today, many more people live in the Pacific Northwest. There has been rapid growth, and with it, the need to catch more salmon. As people got better and better at catching salmon, they also damaged the places where salmon lay their eggs and are reared. Dams drastically reduced the number of salmon traveling both up and down the river. Soon, the supply of salmon was not enough.
People argued about the causes of poor salmon runs. They blamed each other. Today, all the people who value salmon are beginning to see that they have to work together to save the salmon.
Tyee is helped also by fishing regulations. These laws set limits on how many fish can be caught, when they can be caught, and where and who can catch them. But Tyee doesn’t know about all this. She swims northward to the northern tip of Vancouver Island.
Tyee is now a clever hunter, eating whenever she can. She doubles her weight every three months in her first year in the ocean. By August of her second ocean year, she passes Sitka, Alaska, and weighs 12 pounds.
One of the great mysteries of salmon is how these fish know where to go when they arrive at the ocean. By tagging fish and tracking them in the ocean, scientists have learned that Chinook salmon stay fairly close to shore. But very little is known about how they navigate. Tyee may use the angle of the sunlight in the water, water temperatures, the earth’s magnetic field, or ocean currents to find her way. Or it could be that the information needed is imprinted in her genes. Whatever it is, Tyee knows without ever having to learn.
Coho, chum and sockeye salmon all have different ocean travel routes than Chinook. Some stay within the island groups off British Columbia in more protected waters. This is what Tyee does, swimming up to 15 miles each day. After two years in the Pacific – the third year of her life – she passes Anchorage, Alaska.
Tyee is a large adult. She weighs 21 pounds, and is two-and-one-half feet long. She has a blue-green back and silvery-white belly. The two-tone coloring makes it more difficult for predators to see her. From above, she blends with the dark ocean waters; from below, she blends with the bright sky.
By now, she knows sea lions by sight and smell. She has been chased by them often, as well as orcas. But she survives. Tyee the Lucky.
During July of her third year in the ocean, Tyee turns around and heads south. Her trip back down the coast is farther out to sea, about 200 miles. She is heading back to the Columbia River. Tyee knows where to go. She is swimming with the current now, and is able to cover roughly 30 miles each day.
Not all kinds of salmon stay in the ocean three years. Each one has its own time of return to fresh water. Sockeye spend two or three years in the ocean. Coho remain for a shorter time. Chinook may stay in the ocean as many as five years before heading back upriver, but most stay two or three years.
Not all Chinook enter the river at the same time of year. There are spring, summer and fall Chinook. These runs of Chinook are named for the time they enter the river from sea.
Tyee is a spring Chinook. Just before Easter in her third year at sea, she returns to the Columbia River mouth. Firm and plump, with pink meat, she is at the prime of her life. She weighs 28 pounds and is over three feet long. She is not the biggest fish there, but she is large. She carries scars from her adventures in the ocean. Behind the large fin on her back are tooth marks from a sea lion that just missed. A row of sea lice (parasites) clings to her body, but she is strong and healthy.
As Tyee moves up into the estuary, she does not know that a short gillnet season just ended. Once again, she avoids danger from people’s nets. But she is not through with people just yet.
Sport anglers are fishing in a number of “hot spots” in the upper estuary. Tyee would be a prize catch.
Tyee snaps at what looks like an anchovy. The anchovy has two hooks in it. A line is attached. Her first reaction is to dive deep and to swim away from the pull of the line. This sets the hook even deeper in her jaw.
Her deep dive doesn’t seem to work. She rises to the surface, slashing and twisting. She jumps out of the water twice to rid herself of the hook. When she rests, she can feel herself getting pulled closer to the boat. She dives again, then rises, trying to get loose. The hook is working loose. If she has enough strength left, she may be able to keep the fight going.
After 20 minutes, Tyee is very tired. Perhaps her luck has run out. The boat is close now. She can see a large silver hoop with green nylon netting moving towards her. With one mighty leap and a twist of her body, Tyee rises out of the water. The hook tears loose. She lies on the surface for a moment, then rolls and swims down with what little strength she has left. She becomes “the big one that got away”. Tyee the Lucky.
THE RACE TO THE REDD
Tyee wastes no more time in the lower Columbia River. The rains have swelled the river, urging Tyee in a race upriver. Against the current, she has one purpose – to get back to her home stream and spawn. Eggs are growing inside of her.
She is no longer interested in food. Even though she might snap in anger at an angler’s bright lure, she is not hungry. She has stored up enough energy to make it all the way to Idaho. Now, it is time to use that energy.
In late April, she finds the entrance to the fish ladder at Bonneville Dam. She climbs the stairs of water. She passes an underwater window where a human counts her as Chinook number 61,346. There will be more Chinook behind her.
She passes into the reservoir. The slack water confuses her for a time, but she finds the ladder at The Dalles Dam. Along the way, there are more anglers and nets. She avoids both, but continues to use her energy reserves and gets thinner.
As she passes forks of rivers and streams, she uses her homing instincts to show her the way home. She says “no” to the Deschutes, the John Day and the Umatilla. But the Snake River “smells” right to her, and she leaves the Columbia. One hundred and fifty miles later, she comes once again to the Salmon River. She waits a few days for rain to make the river “right.” Inside her, eggs are ripening. Her stomach is empty from not eating for a month.
Tyee finds the Middle Fork of the Salmon and turns into it. A week later, she finds her creek without a name. After traveling about 900 miles downstream, 4,000 miles in the ocean, and another 900 miles to return here, she has returned home with a precious cargo.
A five-foot waterfall is all that stands in the way of reaching her goal. After all that’s happened, it seems impossible that Tyee could leap twice her length. But she does.
Four of her redd-mates have already arrived. She is the last. Only nine adults from the original 750 fry made it back to the Columbia River. Two of those ran into a gill net, and couldn’t back out. Another was caught by an angler’s hook. And another became confused by a dam and died of exhaustion trying to find a way through the concrete.
The five are not only the luckiest, they are also the fittest. They alone will pass on these traits to the next generation of Chinook.
THE FINAL ACT: SPAWNING
Males and females pair off to spawn. There are three males and two females, so there is much chasing and nipping as the males try to get a good position around the females. One of the Chinook males is a jack. Jacks return to spawn earlier than other adults. He’s smaller than the other males, but he is able to spawn if the full-sized males don’t make it back to the spawning area.
The big males are dark and blotchy and have hooked snouts. They think the jack is nothing but a bother. When he drifts into the territories they have set up, they send him scampering upstream. After a while, he gets the idea that he is not wanted here.
Tyee ignores all this action. She has her own job. She builds a redd.
She chooses a spot where the gravel is fine (WHAT DO THEY MEAN BY FINE??? HOW SMALL ARE WE TALKING HERE?) and clean. With her tail, she begins sweeping gravel aside. She scoops out a kind of trough, a depression, in the shape of her body and twice as long. She tests it by settling into the trough. Then she moves upstream and swishes more gravel around the redd until it feels just right. The redd has a ridge on the downstream edge where she can rest.
Meanwhile, the two males begin a courtship “dance” around Tyee and the other female. They circle slowly. They come close and move away again. This goes on for hours around Tyee and her sister, resting in their redds.
Finally, a male swims beside Tyee and just upstream from her. His body presses hers against the ridge of the redd. Both seem to shudder. Tyee trembles. Pink eggs come out of her and drift into the redd. Almost immediately, a white cloud of sperm, or milt, comes out of the male and covers the eggs. This fertilizes the eggs, beginning the whole cycle again.
Tyee, with one last tired effort, rises from the redd. Just upstream, she swishes her tail. The action of her tail lifts small pieces of gravel from the bottom and into the redd. Fine gravel now covers and protects the eggs.
Leaves on the trees on the stream banks are yellow and brown. It has been five years since our story began. Tyee the Lucky has finally come home. In a few days, she dies. Her body decomposes, providing food for the smaller animals in the stream that she once fed on as a fry. With death comes life. The journey of Tyee the Lucky is complete.
You now have a greater understanding of the salmon life cycle. At the end of Lesson 1, you answered five questions for which you did not have all the answers. You hypothesized. On a new page in your Salmon Journal, reflect on your earlier hypotheses with what you now know. (Note: some questions will be answered in upcoming lessons.)
Title this page in your Salmon Journal:
Updates to My Lesson 1 Hypotheses
Write a shorthand version of each question for which you have new information. Then describe what you know now. For example:
Q1: What makes for a good redd:
Then write down what you now know that will help you give a better answer to the question. Explain how this agrees or disagrees with your original hypothesis.
Do this for each of the questions from Lesson 1 for which you have new/updated answers.
We will continue to reflect back on your Lesson 1 hypotheses (as well as make new ones) in upcoming lessons.
Hooks & Ladders is an instructive, fun, physical game in which students immerse themselves in the salmon life cycle and the hazards of the journey. It is a teaching tool that also includes class discussion and decisions throughout the game to optimize salmon returns.
In this game:
- Students will experience, first-hand, many hazards that salmon face throughout their life cycle.
- Students will experience, first-hand, the decision-making process that fish managers (people who make policies to protect and maintain salmon populations) must make in their efforts to maximize the number of returning salmon.
Salmon face many obstacles throughout their life journey, but in this diagram, we focus on the variety of “animal hazards” that confront them (including humans). Are you familiar with all of these predators? We challenge you to learn more about them on your own.
LET’S INSERT A SECTION OR AN ASIDE ON SEALS/SEA LIONS, SINCE THE PROBLEM IS A MAN-MADE ONE AS A RESULT OF DAMS AND LOCKS.
LET’S ADD MORE PREDATORS TO THIS GALLERY (IS PREDATORS A SUITABLE TERM??? IS SUSPECT IT’S NOT A GOOD CATCH-ALL. PREVIOUSLY WE USED CONSUMERS, BUT I DON’T LOVE THAT WORD.). LET’S ALSO TURN THIS INTO A TEACHING GALLERY REGARDING EACH OF THE PREDATORS.