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Module 11 - Vertebrates in Salmonid Ecosystems
Anchors to Sections Within This Module
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Module 11 - Vertebrates in Salmonid Ecosystems
Lessons
Lesson 1 - The Role of Vertebrate Animals in the Life-Cycle of Salmon
A wide variety of vertebrate animals are common in all of the ecosystems in which salmon are found. These vertebrates are represented by fish, amphibians, reptiles, birds, and mammals. In most cases, the importance of these animals in the lives of salmon is a result of their relationship to salmon in the food chain. Some of the vertebrate animals are prey organisms that the salmon rely upon for nourishment. In other cases they are predators that feed upon the salmon. To refresh your memory concerning food chains and energy and material cycles in the ecosystem, refer to Module 2.
This module is designed to introduce the student to some representatives of the most important vertebrates that influence salmon. Due to the large number of vertebrate animal types that are found in salmonid ecosystems, not all can be represented here. Nevertheless, most important major groups are found on this page. The student should make an attempt to become familiar with these animals and to become able to recognize them by sight. This will provide the student with the ability to assess the structure and function of the various ecosystems that are utilized by salmon.
Fish, birds, and mammals are, by far, the most important vertebrates that influence salmon populations. Amphibians and reptiles, although often present in salmonid ecosystems, do not significantly act as important prey or predators in the food chains in which salmon operate. For that reason, amphibians and reptiles will not be represented in this module.
Most of the vertebrates presented in this module are native to northwest salmonid ecosystems. In naturally functioning ecosystems, these animals will be present continually or periodically. A few animals presented here are exotic. These latter forms are present when the ecosystem has been disrupted by natural processes or by human influences. They are included here because of their presence in disrupted salmonid ecosystems in the Pacific Northwest.
Assignment 1 - Becoming Familiar with the Birds and Mammals
In this assignment, the student will be asked to study a number of field manuals that depict birds and mammals. Using these manuals, the student should familiarize him or herself with the general taxonomic systems for these animals. Also, the student should review the animals that are present in the Pacific Northwest salmonid ecosystems, including those not represented in this module.
A. Obtain a copy of a field guide to North American birds. There are a number of good field guides available in most libraries. The best include the following manuals.
B. Obtain a copy of the field guide to North American mammals cited below.
C. Browse the two field guides (birds and mammals) so that you become familiar with the general layout of each book.
D. Study Lessons 2, 3, and 4, becoming familiar with the types of vertebrate animals that frequently are found in northwest salmonid ecosystems.
E. For each bird and mammal discussed in these lessons, find at least one other in the same phylogenetic order that has a range that includes the Pacific Northwest. The ranges of these animals is shown on maps in each manual.
F. Create a list of each animal discussed in Lessons 2,3, and 4. Within the list include the following.
Lesson 2 - Vertebrates in the Salmon Nursery
The vertebrate animals that have an important relationship to salmon while they are rearing in freshwater stream and lakes are predators. These fish and birds rely upon small freshwater aquatic animals for their food. Some of the most successful predators are the salmonid fish themselves. Larger salmonids routinely prey upon smaller ones. Therefore, resident rainbow trout can be a significant limiting factor in the success of rearing coho salmon populations. Because the characteristics of the salmonid fish are examined in detail in the next module, they will not be included in the discussion of vertebrates in this module. Therefore, only nonsalmonids are represented here.
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Immature salmon are normally found in habitats that include freely flowing water. In these conditions, the number of fish that prey upon them is relatively small. However, salmon that rear in lakes and side-channels must coexist with larger populations of predatory fish. As young salmon journey down river toward the sea, those that must pass through lakes and the reservoirs behind dams must also contend with this increased predatory pressure. The large-mouth bass is an example of a fish that is common in northwest lakes, ponds, and other still water. It is a voracious predator consuming frogs, insects, and small fish. Its close relative, the small-mouth bass, occupies a similar range. Lake Washington, near Seattle, and many regional lakes and ponds have healthy populations of bass. |
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The black crappie is another fish that is common in lakes and ponds. Although somewhat more timid, its feeding behavior is very similar to that of the bass. Although most crappie are no more than four inches in length, one exceeding four pounds was taken from Lake Washington in 1956. Although not shown here, sunfish are very similar to crappie. The two common sunfish found in the Pacific Northwest are the bluegill (having a blue spot on its gill) and the pumpkin seed (having a red spot on its gill). |
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The yellow perch represents still another common predatory fish in Washington lakes and ponds. The perch, and all of the other fish presented here, are referred to as warm-water fish. This does not mean that they thrive in the very warm waters of tropical regions. It does mean that these fish are most at home in still water environments. These environments include lakes, ponds, marshes, side-channels, and other areas where the water is mostly still. Usually such bodies of water become quite cold in the winter, but they also warm considerably during the summer. This is contrary to the flowing water in streams and rivers. This water usually remains much colder all year around because it is being continually fed by snow melt. Warm-water fish are not designed to successfully compete in cold flowing water and so are displaced by salmonid fish. |
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Walleye, or walleye pike, are members of the perch family that grow relatively large. They are residents in some of the larger bodies of water in eastern Washington. They are found in Banks Lake, the Potholes Reservoir, the Columbia River, and the reservoirs behind the Grand Coulee Dam, Chief Joseph Dam, and Wells Dam. Walleye, like bass, are voracious predators, but they are much larger. The record walleye weighed more than sixteen pounds. |
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The construction of hydroelectric dams has greatly increased the number of lakes (reservoirs) in the Pacific Northwest. This has also reduced the amount of flowing water. These conditions have promoted the proliferation of some species of warm-water fish that were not so numerous earlier. Many of these fish, like carp and suckers, are not predatory. However, one species, the northern squawfish, is an active predator. These fish have become so successful in the upper Columbia River system that their impact has greatly hampered the success of young developing salmon. In response to this, many northwest states have offered bounties to encourage sportsmen to eliminate as many squawfish as possible. |
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Catfish are scavengers, but they also can be predatory. Because catfish are bottom feeders, they do not frequently encounter healthy young salmon in a situation where they might be captured. As a result, their impact on salmonid populations is quite minimal. Nevertheless, they are represented here because they may, at times, represent a minor predatory pressure. Channel catfish are common in the large lakes and rivers in eastern Washington. A smaller catfish, the brown bullhead, is frequently found in small ponds and marshes in western Washington. |
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Mergansers are duck-like birds that are found in streams and rivers throughout the Pacific Northwest. These are diving birds, meaning that they plunge beneath the water from a floating position. While submerged, the mergansers swim with their webbed feet searching for small fish to consume. The common merganser is most often seen, but there can be occasional sightings of hooded mergansers and red-breasted mergansers. The female and male merganser have markedly different plumage, and immature mergansers may have variable and less striking colors. Mergansers are among the most significant of the predators in the freshwater ecosystem, taking many young fish. This is partially due to their efficient predatory behavior, but the abundance of these birds is also a contributing factor. |
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The loon is a summer visitor to salmonid nurseries. It spends its winters in the marine ecosystem along the Pacific Northwest coast. It occasionally will be sighted on freshwater lakes and streams near coastal regions in the winter. During summer, the loon migrates inland to breed. It is during the summer that loons may rely upon young salmon for food. Loons are also diving birds, but because their population is much smaller than that of mergansers, their impact on young salmon populations is not as great. Residents of Alaska and northern Canada may encounter another species, the arctic loon. |
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Like mergansers, cormorants play a major role as predators on young salmon. Similar to loons, the cormorants are residents of coastal regions during the winter. Often, these birds winter on protected lakes near the coast. Here they prey heavily on small fish. During the summer, the cormorants migrate inland. Near inland streams and lakes they nest and raise their young. During this season they prey on young salmon that are rearing in inland waterways. |
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Unlike birds that swim on the surface of water, herons and egrets rely upon wading behavior. With long legs and necks, these birds stand motionless in shallow water waiting for a passing fish. When a potential prey fish approaches, the heron strikes quickly with a powerful thrust of its bill. Herons also eat frogs, salamanders, and other small creatures. Although herons and egrets are good hunters, their relatively small number limits the impact they can have on salmon populations. Herons are wide-spread in their distribution. Their nest rookeries are found high in the branches of trees in wetland areas. |
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In the forested areas of the Pacific Northwest, one will find the belted kingfisher hunting in freshwater streams and lakes. This small bird perches in the branches that overhang water. Their sharp eyesight makes it possible for them to see prey fish from high in the trees. When a likely victim is spotted, the kingfisher makes a headfirst dive into the water and captures the fish. The fish is then carried back to the branches to be consumed. Because kingfishers are small birds they need consume fewer fish for their sustenance than do the larger herons, mergansers, and cormorants. As a result, their impact on salmon populations is not significant. |
As noted in Module 8, young salmon primarily consume insect larva while they grow in freshwater. As a result, they do not prey upon any vertebrate animals while in this stage of their life-cycle. Such is not the case after the salmon migrate to the sea. Here they become voracious predators, hunting many forms of small vertebrate animals in order to support their rapid growth to adulthood.
Lesson 3 - Vertebrates in the Marine
Ecosystem
A salmon's life in the marine ecosystem, which occupies the majority of its adult life, is a time of rapid growth. The young fish that migrated from the freshwater streams may grow into fish that weigh 15 to 20 pounds for coho, and as much as 100 pounds for chinooks. To support this growth, the salmon become savage and efficient predators, consuming any palatable creature that they can catch. This diet includes some invertebrates like squid, but the vast majority of their nourishment comes from smaller fish. Often, large salmon in estuaries feed directly upon the younger salmon just emerging from the streams.
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Most often, the small fish that are eaten by salmon in the marine environment are herring, smelt, candlefish, and anchovies. These small "feeder" fish swim in large schools. The salmon follow these schools and prey upon weak, slow, injured, and confused individuals. The ability of the marine ecosystem to support salmon populations is directly related to the ocean's ability to produce large numbers of these prey animals. During El Niño periods, this productivity is seriously disrupted, and salmon populations suffer. |
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Predators on salmon in the marine ecosystem are as numerous as those in the freshwater ecosystem. Preyed upon by other fish, birds and mammals, the salmon populations are constantly being culled of the weaker, slower, and injured individuals. The tremendous predatory pressure in the sea insures that only the most fit individuals will survive to migrate home to spawn. One such predator is the spiny dogfish. This small shark roams most of the marine waters of the Pacific Northwest. Primarily a scavenger, the spiny dogfish removes many young salmon while the fish are relatively small. |
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Cod are widely distributed in the oceans of the Pacific Northwest. These predatory fish survive primarily on small fish, making them competitors with salmon. They move into inland waters and estuaries in large schools during the winter breeding season. Since, this is a commercially important food fish, sport and commercial fishing pressure can be significant. In recent years, this pressure has reduced the numbers of these fish in the coastal waters of Washington and Oregon. |
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Much like the catfish in freshwater ecosystems, the rockfish is only an occasional predator on young salmon in the marine ecosystem. These fish, referred to as bottom fish, actually congregate around piles of rocks and rocky overhangs. There are over ten species of rockfish that inhabit the water of the northwest. One, a commercial food fish, is the red snapper. |
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The jack mackerel is not a native fish to the Pacific Northwest. This fish normally is found in the warmer water near southern California. During El Niño years, the water temperature off the coast of the northwest is warmed, and the mackerel follow the warmth north. In a marine environment that is already reduced in its productivity by El Niño, the mackerel encounter young salmon migrating from the mouths of river. The mackerel congregate in the estuaries and feed heavily. This predatory pressure, and the effect of the reduced ocean productivity, causes the number of salmon that survive the ocean phase of the life cycle to be very low during these years. |
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The Pacific lamprey is an ectoparasite that salmon encounter at sea. Lamprey are jawless fish that have a life-cycle very similar to that of salmon. They hatch from eggs in freshwater streams and rivers, migrate to the sea for their adult lives, and return to the freshwater to spawn. The lamprey attach themselves to the sides of fish by a sucker mouth, and a set of sharp teeth-like structures create a wound. Blood and body fluids provide nourishment for the lamprey. When the salmon that carry a lamprey return to the freshwater to spawn, the lamprey is simply carried along. |
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While salmon are young and newly emerged from their freshwater habitats, predatory birds play a major role in reducing the population. Gulls, like the herring gull, are scavengers but they also feed on small fish that they can catch near the surface. Being very opportunistic, gulls will mix with other species of feeding birds, harass and intimidate the other birds, and steal their catch. A number of other species of gulls frequent the northwest coastal areas including gloucous-winged gulls, California gulls, mew gulls, and Bonaparte's gulls. Although there is migration amongst the gulls, their distribution is wide and they are persistent residents in most areas. |
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Terns, a close relative to the gulls, are smaller and faster. The terns are expert migrators. The arctic tern's migratory routes extend from the Arctic Ocean to the Antarctic continent. Terns prey upon small fish by hunting and identifying potential targets from the air. When a prey fish is spotted, the tern dives into the water, captures the prey, and carries it into the air. Besides the arctic tern, Caspian's tern is a seasonal visitor. In southwest Alaska, the Aleutian tern is found. |
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Brown pelicans migrate along the Pacific coast from Mexico to British Columbia. These birds feed on schools of small fish by scooping them into their large extendable bottom bill. Because small salmon swim in such schools after emerging from the freshwater ecosystem, they fall prey to pelicans. The number of pelicans is relatively small, so their impact on the salmon population is not significant. |
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The tufted puffin is member of a group of coastal birds referred to as alcids. These birds nest on rocky outcroppings at the seashore. They hunt and dive upon schools of fish to supply themselves with a source of food. Included in this group, and exerting predatory pressure upon young salmon, are the murres, guillemots, murrelets, and auklets. |
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When salmon reach their adult size, the predators shift from being primarily birds, to being primarily mammals. Seals hunt adult salmon all along the Pacific coast. The California sea lion, the northern fur seal, and harbor seal are common. Seals that feed in large numbers in narrow waterways where salmon must pass to migrate can take a heavy toll on specific salmon populations. |
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Toothed whales, like the killer whale, also feed on large numbers of salmon. Other predatory whales that feed on salmon include pilot whales and Dall porpoises. The whale populations are very sparsely distributed, so their collective impact on salmon populations is small. |
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Of course, humans are significant predators on salmon in the marine ecosystem. A wide variety of fishing methods along the entire northwest coast successfully eliminates huge numbers of fish. |
Lesson 4 - Vertebrate Associations During
Upstream Migration
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When salmon begin their journey back upstream to their spawning grounds, they have become large powerful animals. Nevertheless, the journey upstream requires a huge amount of energy. This energy expenditure weakens the fish making it easier for predators to successfully capture and subdue them. Furthermore, the passageways back to their spawning gravel are often shallow and narrow. This makes it impossible for the fish to employ any kind of predator avoidance behavior. Osprey are among the larger birds that capture upstream migrating salmon. They simply capture them with their talons and carry their prey to their nests. |
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While osprey dive directly from above to capture their prey, the bald eagle spots its potential prey from afar. It glides down upon the fish and grabs the victim with its talons as it passes by. The bald eagle also feeds upon the decaying bodies of spawned out and dying fish. |
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Mammals also take advantage of the easy pickings as the salmon migrate upstream. Grizzly bears and other brown bears wade into the streams that are teeming with migrating salmon and gorge themselves. The bears are quick learners and often take advantage of fish that are leaping into the air to pass waterfalls. |
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River otters take a few fish in the smaller tributaries. Because river otters are few in number, and because they are small animals, their take does not significantly impact salmon populations. |
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Once again, humans are major predators during this portion of the salmon's life-cycle. Sport, tribal, and commercial fishing pressure eliminates a significant number of the returning fish. |
Assignment 2 - Observing Vertebrates in the Field
For the remainder of this course, the student is to make a concerted effort to observe as many varieties of wild vertebrates in the field as possible. Vertebrates can be observed in the following locations.
The student will need the following materials to successfully observe and record the vertebrates encountered.
Record all vertebrates observed in your field journal. Include a short description of the animal,s location and activities.
Module 11 -
Quiz
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