Conditions of Use
Salmon Cycle:The young salmon fry begin to move in schools and feed in the river. They feed mainly on zooplankton until they grow large enough to eat aquatic insects and other larger foods. Some species of salmon fry, such as chum and pink, start downstream toward the ocean immediately after emerging from the redd; others stay in fresh water for up to three years. Land-locked salmon, such as kokanee, never migrate to the sea but live their entire lives in fresh water.Loss of riparian habitat along streams, rivers, estuaries, and bays is one of the most serious dangers to the wild salmon's survival. Salmon need cool water, bugs to eat, woody debris to hide under, and sediment-free gravel in which to spawn. Riparian habitat along the rivers provide shade which helps keep the water temperature cool throughout the year. Cool, clear water holds lots of oxygen which the salmon also need. Logs, branches, or sticks that fall or hang into the rivers give salmon places to hide and provide food for insects and plants which the salmon feed upon. The roots of trees and bushes also help hold dirt and rocks in place on the bank which reduces sediment runoff. Although logging rules have been revised to protect riparian habitat, previous logging practices have already caused problems. Sometimes little growth was left beside streams and rivers. This resulted in higher water temperatures and increased sediment runoff. Also, without bushes, trees, or woody debris, fish had no place to hide and little food to eat. As the vulnerable fry grow, they will start to develop spots and vertical parr marks on their sides. These markings help camouflage them from predators such as mergansers and great blue herons. Unlike most fry, pink salmon fry do not develop these parr marks. After the fry have developed distinctive parr marks and are actively feeding in fresh water, they are called parr. This stage is generally reached by the end of the first summer. Most species of salmon parr are about five inches long. They feed mainly on aquatic insects but also eat worms, crustaceans, amphibian larvae, fish eggs. As the salmon parr begin migrating toward the sea, they will begin the smoltification process. The smoltification process refers to the changes that take place in salmon as they prepare to enter the sea. These changes include the development of the silver color of adults and the tolerance for salt water. As the salmon parr begin migrating toward the sea, they will begin the smoltification process. The smoltification process refers to the changes that take place in salmon as they prepare to enter the sea. These changes include the development of the silver color of adults and the tolerance for salt water. If the salmon parr encounter hydroelectric dams, they must be careful not to be sucked into and crushed in the powerful turbines. These dams and turbines generate electricity for people. The slow-moving lakes behind the dams have little oxygen, delay the migration of salmon, and attract predators in search of easy prey. Some hydroelectric dams have installed screens, channels, and other devices to create systems which help guide young salmon away from dangerous turbines and safely to the river below the dam. These systems are called juvenile fish bypass systems. As the salmon parr pass farms, factories and cities, they may encounter pollution in the water. Sprays and fertilizers that farmers and home owners use sometimes contain toxic substances which wash into rivers, pollute water, and poison fish. The water that runs rapidly off buildings, pavement, and other impermeable surfaces in cities also wash oil, anti-freeze, and other harmful substances into the rivers. Salmon parr may also be sucked into pipes which pump the cool river water into factories to cool machinery. Other pipes pump water out of the rivers for irrigation purposes.By the time the salmon reach the estuaries, they have silver sides, bright bluish green backs, and are called smolt. Here they will undergo osmoregulation. Osmoregulation includes the adaptation of the gills and the kidneys to salt water. After osmoregulation, the salmon head out into the seaThe salmon will feed and grow in the sea for the next one to eight years. They will remain in the sea until they reach full maturity. The salmon will also remain silver in color until they return to their home stream. .During their stay in the sea, the salmon travel hundreds, or even thousands, of miles searching for food and trying to stay out of the mouths of predators. They feed on small fish, shrimp, squid, etc. Orca whales, sea lions, and seals are a few of the natural predators that the salmon meet in the ocean. Humans also like to eat salmon, so commercial fishermen are another threat the salmon face while in the ocean.Depending on their species, mature salmon are anywhere from 14 inches to five feet in length and anywhere from two to 125 pounds in weight. At maturity, the salmon will travel back to the same estuary they visited earlier in their lives. Here they will undergo osmoregulation again to adapt back to fresh water. Once adapted, they will head up river to spawn where they were born.No one knows for sure how the salmon find their way back to the exact stream where they were born. Some scientists think that they can smell differences between the waters of different rivers and that they know where to go by their home stream's particular smell.Once the salmon start upstream toward the spawning grounds, they do not feed but derive energy from stored fats. The distance salmon travel upstream to spawn varies. The average spawning trip distance is about 150 miles. The longest known spawning trip length is from the Bering Sea to Lake Teslin in Canada, a total distance exceeding 2,400 miles and a 2,200 foot elevation gain (Migdalski 116-117).On the way upstream, the salmon face fishermen, fish ladders, waterfalls, and more predators in addition to the challenges they faced on their way downstream earlier in their lives. Humans may have also built more dams or increased river pollution.Although salmon do not feed on their way upstream, they can be caught by skillfully presented fishing tackle. In clear water, where the salmon can be seen, it is not uncommon for a fisherman to present his lure dozens of times before sparking the fish's interest enough to take the offering.Fish ladders are built to provide salmon with a way around hydroelectric dams and other obstructions. They are made of a series of pools arranged in a stair step fashion. Water falls from step to step, and salmon must jump from one pool to the next to reach the top. Salmon must jump up small waterfalls in rivers the same way that they climb fish ladders. Salmon can actually climb waterfalls which are higher than they can jump by swimming and leaping upward through the strong current using their powerful tails.The predators salmon face on their journey upstream include bears, wildcats, and eagles. The bones and scraps of salmon left in the forest by these animals fertilize the forest and help it grow.As the salmon travel upstream, they undergo color changes. The males' silvery colors transform into brilliant colors, probably to attract females. The males also develop hooked snouts to the point of sometimes overlapping the lower jaw and certain species develop humps on their backs. The females also change in color but not to such brilliant shades. Each species has its own spawning colors, which vary from greens and browns to lavenders and dark reds.These physical changes are caused by changes in theLife cycle summary salmon's fat composition, skin pigmentation, blood chemistry, enzymes, and hormones (Steelquist 43). At this stage, they are more susceptible to disease. The news that water flows downhill, and that fish depend on water, won't come as a shock to anyone.
Yet these statements add up to an often-ignored fact about the habitat needs of salmon (and everything else that depends on the river). Salmon don't just live in water--they live in watersheds. From the crest of the surrounding hills to the estuary at the mouth, a river's watershed is the entire basin from which it gathers its waters. As water percolates through the soil to the stream, down the stream to the river, and eventually out to sea, its quality and quantity is affected by everything it touches. Salmon are affected by anything that happens is the watershed, even though it may seemingly take place far from the river.
Salmon are affected by the water's temperature and nutrient content, by the amount of sediment and oxygen it carries, by the rate of its flow, and by other factors. All the natural systems in the watershed--forests, meadows, wetlands, rock outcroppings--contribute to the composition of the water.
The watershed determines the amount and force of the water in the river, and the material carried down by its flow from higher elevations. These factors shape the river bottom, which is another important aspect of salmon habitat. Here, behind a large log, the force of the stream may have dug a deep pool, where young salmon shelter in the summer and returning adults rest on their way to the spawning grounds. There, quiet eddies may have dropped their loads of silt, creating mud which supports a marsh. In another place, the river has deposited beds of gravel, which salmon need for spawning. Some species prefer to lay their eggs in pea-sized gravel, while other can use rocks as large as cantaloupes. The particular types of habitat provided by the river depend on the larger influence of the watershed.
Salmon evolved to cope with a sequence of habitats found in natural watersheds. In a typical river system, tributary streams in the upper reaches are heavily shaded by forests, which drop large quantities of leaf litter and other organic material into the water. Fallen trees in the stream trap spawning gravel on the upstream side, and create plunge pools below where young fish shelter and feed. Many of the aquatic insects available as prey in these areas belong to a group know as "shredders", which devour large bits of plant material floating in the water.
In the middle reaches of the river, the tree canopy opens up and more sunlight falls on the water, prompting algae growth. Here the prey species likely belong to groups know as "scrapers," which harvest algae from the rocks, and "collectors," such as net-spinning caddies fly larvae, which strain finer bits of organic material from the water.
At its lower end, the river may wander in many channels across its floodplain, providing a wealth of fish habitats in its wetlands, sloughs and oxbows. In these marshes and estuaries, ocean-bound salmon gorge on clouds of small crustaceans such as copepods and amphipods.
All human activity in the watershed affects salmon habitat. Timber-cutting, for instance, may remove shade and large streamside logs that once fell periodically into the stream. Road construction and agriculture often cause erosion, which in turn fills the water with sediment that can clog spawning gravel. Culverts can block fish passage and alter water flow. Removing creek meanders or beaver dams and filling wetlands eliminates feeding areas and the slow-water areas so important for sheltering young coho and other salmon from the raging winter currents. Dams can slow the force of the river's flow preventing it from cleansing sediment from its bed and moving gravel downstream.
Because human beings live in watersheds, we are part of the salmon's habitat. In many areas, small landowners, timber companies, fishermen, environmentalists, farmers, tribal members, agency representatives, and others are working together to restore watersheds and improve salmon habitat. Often called watershed, these coalitions are finding ways to put aside differences and pool resources to help the salmon. These groups work together to assess the health of their watershed, identify areas where restoration efforts can best help the salmon, and seek out willing landowners to implement habitat restoration projects.
Projects undertaken by watershed groups have included stream surveys, tree planting (to provide shade along stream banks), road and bank stabilization (to prevent erosion), culvert repair (to facilitate fish passage--for both young and adult fish), placing logs in streams (to create shelter and deep pools), side-channel construction (to provide slow water areas for winter shelter), and cattle watering and fencing (to keep cows and sheep out of streams). Participants have included loggers, fishermen, agency personnel, civic groups, environmentalists, and youth groups ...entire communities, taking responsibility for their watersheds.
Article posted November 30, 2011 at 02:58 PM •
comment • Reads 3410
Return to Blog List
Add a Comment