Sunday, 1 May 2011

Report Text_Salmons

Salmon

The Incredible Traveling Fish

Salmon is the common name for several species of bony fish of the family Salmonidae. The family also includes several fish called trout. Salmon live in the cold freshwater and sea waters in and around the North Pacific and North Atlantic Oceans. Salmon make one of the most incredible journeys of all animals. They leave their homes after they hatch and sometimes travel several thousand kilometers.

Atlantic and Pacific Cousins

There are two groups of salmon. One is the Atlantic salmon. It lives in the North Atlantic Ocean between North America and Europe. It travels up rivers that meet the sea on these two continents. Five species of Pacific salmon live in the North Pacific Ocean. Like the Atlantic salmon, they live in the ocean and also in the rivers of western North America and eastern Asia.
Salmon
Salmon are anadromous fish. This means they spend part of their lives in freshwater and part of their lives in the salty ocean. Salmon hatch in streams and rivers and then swim to the ocean where they eat and grow. They swim back to the river or stream where they were born to lay eggs.
©Brandon Cole

Food Coloring

Salmon get their striking orange-red color from eating tiny orange arthropods such as krill and shrimp. The coloring can vary from almost white to deep red. A salmon’s color depends how many and what kind of arthropods it gobbles up.

The Incredible Journey

The salmon is an anadromous (uh-NAD-droh-muhss) fish. This means that it spawns in freshwater but spends much of its life at sea. When an Atlantic salmon reaches the age of two, it leaves its home in the North Atlantic. It begins a migration to the same place in the river or stream where it was born. It spawns and then returns to the ocean for two years. After building up its strength, it leaves the ocean and returns to the rivers to spawn yet again.
Did You know?©GLOBIO.org
For Pacific salmon, the journey may take two to four years. When they reach their freshwater birthplace, females lay their eggs and malesfertilize them. Unlike Atlantic salmon, the Pacific salmon do not make a return journey to the ocean. After spawning, Pacific salmon die in the streams, rivers, and lakes where they were born.
Exactly how salmon find their way is a mystery to scientists. Some experts think salmons’ sense of smell helps them find and reach their destination. Others believe salmon have a kind of compass in their brains that guides them.

Built to Travel

Salmon swim and leap more powerfully than most fish. Their bodies are also designed to travel long distances.
Click on this strong swimmer to discover more.
©M.Durham/GLOBIO.org

The Journey of a Lifetime Begins

A salmon begins as a pea-sized, orange-colored egg laid in the gravel bottom of a cold freshwater stream or lake. After 50-150 days, the salmon hatches and swims a little. The egg sac stays attached to the belly like a little yellow balloon. In the first days, a salmon baby, called alevin or sac fry, will get all its nutrients from the egg sac. Its body absorbs the egg sac after a few days. Then, the fry must begin finding food itself. Small arthropods are the most common food for fry.

Young Salmon: Parr for the Course

Salmon Growth Chart©GLOBIO.org
Salmon soon develop dark bars on their sides and become much more active predators in the river. The young fish are called parr during this stage. They will remain parr for one to three years. This is a dangerous time for them. Parr often get eaten by birds, other fish, snakes, frogs, and other predators. But some parr survive. When they reach a size of about 15-20 cm, they start swimming toward the ocean.

To the Ocean!

Smolts are salmon that are old enough and large enough to leave the river and swim into the ocean. Their bodies go through an amazing change. They adapt so they can live in the salty water of the ocean. Smolts travel in large schools for protection but many never make it to the ocean. They get eaten by larger fish, orca whales, sea birds, bald eagles, and other predators. Before the salmon returns to its birthplace in two to four years, it will travel 1,600–5,000 km.

Salmon and People

For centuries, native peoples along the Pacific Coast of North America have fished for and eaten salmon. Native American legends andceremonies celebrate the importance of the salmon to the peoples’ survival and to the whole food chain. A common Native American legend describes the salmon as a people. When the Native American people became hungry, they asked the Salmon People to help them. The chief of the Salmon People finally agreed.
Harvesting Salmon Eggs
People harvest salmon eggs and raise them in fish hatcheries until they are parr. The parr are then released into the ocean to become adults. Raising young salmon in a hatchery saves many from becoming food for other animals.
©K.Campbell/GLOBIO.org

Bears Aren’t the Only Ones Who Like Salmon

Salmon is an important food for people all over the world. Even the eggs are eaten by some people or used for fish bait by sport fishers. The salmon industry is worth millions of dollars. Commercial fishing boats in places like Alaska may catch 50-90% of all the sockeye salmon before they enter rivers to spawn. Fresh and frozen salmon is shipped all over the world.
Local names people use for different species of salmon include:
  • Chinook (also known as the king salmon)
  • Chum (also known as dog salmon)
  • Pink (also known as humpy salmon)
  • Coho (also known as silver salmon)
  • Sockeye (also known as the red or blueback salmon)

Salmon Feed Animals

Salmon help many animals survive, too. When the salmon return to freshwater, they become an important food for bears, bald eagles, and many other birds and mammals. Even after they spawn and die, the bodies of the dead salmon become food for many small arthropods living in and around the freshwater.

Environmental Changes Threaten Salmon

Fish ladders
Many salmon die each year trying to make their way up rivers and streams. Trying to get past dams is often one of the biggest causes of death. Fish ladders, which are designed to help fish make it safely past dams, have saved large numbers of salmon since being put into place.
©U.S. Army Corps of Engineers
Throughout most of world, environmental conditions have changed dramatically over the past 100 years. In Europe and North America, rivers and lakes where salmon return to spawn have been damaged, drained for irrigation, polluted, clogged by logging, and blocked by large dams.

Trouble in the Mighty Columbia River

The largest salmon river in the world is the Columbia River in western North America. The river is 1,954 kmlong, and salmon have lived in the river for centuries. Several species of salmon use the river, but the chinook is the most common. In the late 1800s, over 500,000 chinook were caught each year. In the last 100 years the numbers have dropped rapidly. In 2005, salmon fishing was put on hold, because fewer than 2,500 salmon had reached a critical point in the river.

The Forest Factor

Many factors combine to create difficult conditions for salmon. For example, clear-cut logging of temperate forests leaves hillside soils exposed to wind and rain. During rainy weather, soil and mud wash into the small streams and rivers salmon use for spawning. The gravel beds where the salmon eggs develop become choked with mud and the eggs die. Even though the cutting of the forest may have happened six months or a year earlier, the impact can still threaten the survival of the salmon.

Fish Hatcheries

Catching too many salmon can be a problem. Overfishing, combined with environmental damage to salmon rivers, has caused people to become very concerned about the survival of both Atlantic and Pacific salmon. Most salmon do not return to the old spawning areas of 50 years ago. Instead, they are caught. Valuable eggs are removed to be hatched and raised in nurseries called fish hatcheries. Then salmon are released back into the river after they become large parr.

Saving Salmon

The disappearance of salmon is sending a clear signal that more conservation is needed. Many people and governments now realize that salmon are in crisis. They are stepping up conservation efforts and passing laws to help restore and protect salmon and their habitat. In the lower Columbia River Basin, four Native American groups - the Umatilla, Nez Perce, Warm Springs, and Yakama – have started Wy-Kan-Ush-Mi Wa-Kish-Wit,or “Spirit of the Salmon,” a plan that is helping salmon populations in the Columbia Basin recover.

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