Aquatic Species and Their Environments

views updated


Approximately 1.4 pentillion tons (1,400,000,000, 000,000,000) of water cover the surface of the earth—466 billion tons for each of the six billion people on the planet. Amazing as it may seem, most of this water has been affected by human activity. Numerous aquatic species are in decline because of degraded water quality, development or alteration of aquatic habitats, and overhunting or overfishing. Figure 5.1 shows the number of aquatic and wetlands species at risk by watershed.


Humans burn fuels, produce wastes, and use large amounts of fertilizers, pesticides, and other chemicals. These by-products of industrialization end up in the environment and are often harmful to living organisms. The condition of water-dwelling animals is in fact often a good measure of the condition of the environment; their demise suggests that something may be wrong in their habitat. Figure 5.2 illustrates the overall condition of U.S. watersheds based on data collected by the U.S. Environmental Protection Agency (EPA). Large portions of the country suffer from serious water quality problems.


Pesticides are chemicals used to kill insects that feed on crops and vegetation. The first documented use of pesticides was by the ancient Greeks. Pliny the Elder (23–79 a.d.) reported using common compounds such as arsenic, sulfur, caustic soda, and olive oil to protect crops. The Chinese later used similar substances to retard infestation by insects and fungi. In the 1800s Europeans used heavy metal salts such as copper sulfate and iron sulfate as weed killers.

The invention of DDT (dichloro-diphenyl-trichloroethane) in 1939 marked a revolution in the war against pests. DDT was effective, relatively cheap, and apparently safe for people—on the face of it, a miracle chemical that promised a world with unprecedented crop yields. Its discoverer, Paul Muller, received a Nobel Prize for discovering the high efficiency of DDT as a contact poison against pests. In the United States, pesticide use in agriculture nearly tripled after 1965, as farmers began to use DDT and other pesticides, herbicides, and fungicides intensively and began to accept these chemicals as essential to agriculture.

For many years, it was thought that if pesticides were properly used, the risk of harm to humans and wildlife was slight. As the boom in pesticide use continued, however, it eventually became apparent that pesticides were not safe after all. The fundamental reason that pesticides are dangerous is that they are poisons purposely designed to kill living organisms. Part of the problem is biomagnification—a predator that eats organisms with pesticides in their bodies ends up concentrating all those pesticides in its own tissues. Eventually, the concentration of pesticides causes serious problems. DDT was eventually shown to have harmed numerous bird species, particularly those high in the food chain, such as bald eagles and peregrine falcons. DDT caused the production of eggs with shells so thin they could not protect the developing chick.

As the dangers of pesticides became more apparent in the 1960s and 1970s, some of the most dangerous, like DDT, were banned in the United States. However, the use of other chemical pesticides increased until the 1980s. Use levels have generally held steady since then. Farmers continue to apply about one pound of pesticide per year for every person on Earth. The majority of pesticide use—75 percent—occurs in industrialized countries. Unfortunately, the primary reason that pesticide use has leveled off in recent decades is not concern regarding its safety, but declines in its effectiveness. This is due to the fact that pest species quickly evolve resistance to pesticides. Worldwide, the number of resistant pests continues to climb. Unfortunately, increased resistance has only created a demand for more, and more powerful, chemicals.

Pesticides degrade numerous aquatic ecosystems after seeping into the ground as runoff from watering or rain. The U.S. Fish and Wildlife Service reports that pesticides harm about 20 percent of the country's threatened and endangered animal and plant species.


For decades, farmers have tried to increase the productivity of their land by using ever-increasing amounts of fertilizers. Fertilizers are biological products or chemicals applied to increase crop growth. Fertilizers may seep into water and collect in lakes, streams, and groundwater. While fertilizers are not poisonous by nature, large quantities of fertilizers can cause serious health problems in aquatic animals. Fertilizers also encourage the growth of aquatic plant life, disrupting food webs and biological communities. Aquatic plants and algae may grow so rapidly that they block off sunshine or deplete nutrients essential to other species.

Oil Spills and Runoff

Oil spills represent regular and devastating accidents to aquatic life. Oil spilled into the ocean floats on the water surface, cutting off oxygen to the sea life below and killing mammals, birds, fish, and other animals. The dangers presented by oil spills have grown worse over the years. In 1945 the largest tanker held 16,500 tons of oil. Now, supertankers the length of several football fields regularly carry more than 550,000 tons.

In 1989 the tanker Exxon Valdez ran aground on the pristine Alaskan coastline, spilling 11 million gallons of oil into the bay and killing millions of animals. In 1994 a federal jury assessed $5 billion in punitive damages and $3.5 billion in criminal fines and cleanup costs against Exxon. The Valdez spill led to additional safety requirements for tankers, including double hulls. Larger oil spills than the Valdez have occurred both before and since, but the incident alerted many people to the damage that can be done to marine habitats. Many species impacted by the spill, particularly seabird species, have yet to recover more than a decade later.

In January 2001 the tanker Jessica released 150,000 gallons of fuel near the Galapagos Islands, a biologically rich area harboring numerous unique species including Darwin's famous finches, marine iguanas, and a tropical penguin population. There was widespread relief when winds blew the oil slick seaward rather than towards the islands. Sea bird and sea lion deaths numbered in the dozens, and it was believed that a true catastrophe had been avoided. Ongoing studies of the Galapagos' unique marine iguanas, however, revealed in June 2002 that numerous iguanas likely died due to oil-related injuries after the spill. In particular, 60 percent of the marine iguanas on Santa Fe Island died in 2001, despite the fact that oil contamination was relatively low, with only about one quart of oil per yard of shoreline. Similar deaths were not found on another island where there was no contamination. Scientists believe that the deaths occurred when oil contamination killed the iguanas' gut bacteria, making them unable to digest seaweed and causing them to starve. Marine iguanas have no natural predators and generally die either of starvation or old age.

The U.S. National Research Council warns that, even without large catastrophic oil spills, many marine habitats are regularly exposed to oil pollution. Harbors and aquatic habitats near developed areas are in particular jeopardy. The U.S. National Research Council estimates that approximately 8.4 billion gallons of oil enter marine waters each year from street runoff, industrial liquid wastes, and intentional discharge from ships flushing their oil tanks. As little as one part of oil per million parts of water can be detrimental to the reproduction and growth of fish, crustaceans, and plankton.

Ocean Dumping and Debris

Ocean debris comes from many sources and affects diverse marine species. Waterborne litter entangles wildlife, masquerades as a food source, smothers beach and bottom-dwelling plants, provides a means for small organisms to invade non-native areas, and contributes to toxic water pollution. Records of interactions between ocean debris and wildlife date back to the first half of the twentieth century. Northern fur seals entangled in debris were spotted as early as the 1930s. In the 1960s, various seabirds were found to have plastic in their stomachs. By the early twenty-first century, a total of 255 species were documented to have become entangled in marine debris or to have ingested it.

Some scientists once thought it was safe to dump garbage into the oceans, believing the oceans were large enough to absorb sludge without harmful effects. Other scientists argued dumping would eventually lead to the pollution of the oceans. Metropolitan centers such as New York City once loaded their sludge and debris onto barges, took the vessels out to sea, and dumped the refuse, in a practice called ocean dumping. Problems with ocean dumping were not fully recognized until floating plastic particles were found throughout the Atlantic and Pacific Oceans.

The perils of ocean dumping and debris struck home both literally and figuratively in the summer of 1988, when debris from the ocean, including sewage, garbage, and biohazards from medical waste, washed up on the Atlantic seaboard, forcing an unprecedented 803 beach closures. In some cases authorities were alerted to beach wash-ups when children turned up hypodermic needles in the sand. Aquatic species also faced serious dangers from these materials, including absorbing or ingesting hazardous waste substances, and ingesting needles, forceps, and other dangerous solid debris. In 1994 hundreds of dead dolphins washed up on Mediterranean beaches, killed by a virus linked to water pollution. Scientists pointed to this event as an indication of what may happen to other marine animals (and humans) if pollution continues.

At the urging of the Environmental Protection Agency (EPA), the dumping of potentially infectious medical waste into ocean waters from public vessels was prohibited in 1988. In 1992 the federal government banned ocean dumping. In 1995 the EPA stepped up efforts to educate people about the dangers of polluting coastal waters through improper disposal of trash on land, sewer overflows to rivers and streams, and dumping by ships and other vessels. The EPA further warned that marine debris poses not only a serious threat to wildlife, but remains in the environment for many years. (See Table 5.1.)

Mercury and Other Toxic Pollutants

Mercury poisoning is a problem in many lakes and oceans. Mercury can cause brain damage and other serious health problems in wild species and in humans. During the 1990s scientists began to report widespread mercury contamination in fish, including those inhabiting remote lakes that were assumed pristine. As a result, many states now warn people against eating certain types of fish.

The Environmental Protection Agency's National Fish and Wildlife Contamination Program reported that in 2002 mercury was the cause of 2,140 fish and wildlife consumption advisories. This represented an 11 percent increase from mercury consumption advisories in 2001. Scientists believe that the main source of mercury pollution is rain-water that carries mercury from coal-burning power plants, incinerators that burn garbage, and smelters that make metals. Because mercury becomes concentrated in organic tissues like DDT, even small concentrations of mercury in the water can be harmful to health. (See Figure 5.3.)

While it is not the only pollutant causing fish and wildlife consumption advisories, mercury is the fastest-growing

Cardboard box2 weeks
Paper towels2-4 weeks
Newspaper6 weeks
Cotton glove1-5 months
Apple core2 months
Waxed milk carton3 months
Cotton rope3-14 months
Photodegredable 6-pack ring6 months
Biodegradable diaper1 year
Wool glove1 year
Plywood1-3 years
Painted wooden stick13 years
Foam cup50 years
Tin can50 years
Styrofoam buoy80 years
Aluminum Can200 years
Plastic 6-pack ring400 years
Disposable diapers450 years
Plastic bottles450 years
Microfilament fishing line600 years
Glass bottles/jarsUndetermined
source: Adapted from "Marine Debris Timeline," U.S. Environmental Protection Agency, Gulf of Mexico Program, Stennis Space Center, MS, October 9, 2003 [Online] [accessed February 17, 2004]

contaminant. Figure 5.4 lists the pollutants for which advisories were published between 1993 and 2002. The number of lake acres affected by advisories issued due to DDT, chlordane, and PCBs remained relatively stable during the ten-year tracking period, while those affected by mercury increased dramatically.

Figure 5.5 shows the total number of fish consumption advisories in each state in 2002, from mercury as well as other pollutants. The percentage of lake acres and river miles under advisory between 1993 and 2002 are shown in Figure 5.6. Pollution in aquatic environments has increased steadily in the past decade.


Some 100,000 dams regulate America's rivers and creeks. Of the major rivers in the lower 48 states (those more than 600 miles in length), only the Yellowstone River still flows freely. In fact, University of Alabama ecologist Arthur Benke notes that it is difficult to find any river in the United States that hasn't been dammed or channeled.

Dams epitomized progress, American ingenuity, and humankind's mastery of nature. In North America, more than 200 major dams were completed each year between 1962 and 1968. Dams were promoted for their role in water storage, energy generation, flood control, irrigation, and recreation. Worldwide, dams now collectively store 15 percent of Earth's annual renewable water supply. Figure 5.7 illustrates the primary uses of U.S. dams.

The very success of the dam-building endeavor accounted, in part, for its decline. By 1980 nearly all the nation's best-suited sites—and many dubious ones—had been dammed. Three other factors, however, also contributed to the decline in dam construction: public resistance to the enormous costs, a growing belief that dams were unnecessary "pork-barrel" projects being used by politicians to boost their own popularity, and a developing awareness of the profound environmental degradation caused by dams. In 1986 Congress passed a law requiring the U.S. Bureau of Reclamation to balance issues of power generation and environmental protection when it licenses dams.

Where Have All the Rivers Gone?

Dams have affected rivers, the lands abutting them, the water bodies they join, and aquatic wildlife throughout the United States. Water flow is reduced or stopped altogether downstream of dams, altering aquatic habitats and drying wetlands. Some rivers, including the large Colorado River, no longer reach the sea at all, except in years of unusually high precipitation. Keeping enough water in rivers is especially difficult in the arid West.

Numerous species of salmon are in decline, at least partly due to the effects of dams. In the Pacific Northwest in particular, most experts estimate that native salmon will be gone in 25 years. Salmon have an unusual life cycle that involves a migration from freshwater habitats to oceans and back. Hatching and the juvenile period occur in rivers, followed by a long downstream migration to the ocean, where individuals mature. Adult salmon eventually make an arduous, upstream return to freshwater habitats, where they spawn (lay their eggs, burying them in gravel nests) and then die. Dams are associated with high salmon mortality during both downstream and upstream migrations.

There are ongoing debates regarding dam management throughout the Pacific Northwest. In April 2002, for example, American Rivers, the National Wildlife Federation, and other fisheries and conservation groups initiated a lawsuit against the Grant County Public Utility District (PUD) in eastern Washington State over the management of two dams on the Columbia River. The NWF is charging that dam mismanagement is responsible for the continued decline of chinook and steelhead salmon, both of which are protected under the Endangered Species Act. Some 32 percent of juvenile salmon migrating downstream towards the ocean are killed at the dam. Many adult salmon are also dying as they swim upstream to spawning grounds. Fishermen are particularly outraged at the collapse of salmon runs, since they have been required to limit their catch in the hope of population recovery. There are a total of eight dams on the Columbia River, all of which must be surmounted successfully for salmon to complete their migrations.

Tearing Down Dams?

In November 1997, for the first time in U.S. history, the Federal Energy Regulatory Commission ordered the Edwards Dam removed from the Kennebec River in Augusta, Maine, to restore habitats for sea-run fish. The dam's owner, Edwards Manufacturing, appealed the decision, but the federal governmentprevailed. The 160-year old dam produced 1 percent of Maine's electricity. Normal river conditions were achieved at the site within days of water release. Environmentalists viewed the removal of the dam as a boon to both aquatic species and the terrestrial species that feed on them.

Conservation and fisheries interests have also argued for the removal of four dams on the Snake River in the Pacific Northwest, to allow salmon runs to recover. The issue was extremely contentious, with over 8,700 people attending public hearings on the debate and over 230,000 written comments submitted. The Army Corps of Engineers announced in February 2002 that the dams would not be removed, citing the fact that they produce $324 million in electricity and water with operating costs of only $36.5 million. The Corps will, however, budget $390 million over the next ten years to improve salmon survival, including trucking juvenile salmon around the dams. This decision represented the culmination of nearly ten years of debate regarding the Snake River dams.

Foreign Dams

As the era of big dams faded in North America, construction increased in Asia, fueled by growing demand for electricity and irrigation water. China now accounts for more than one-fourth of the big dams under construction, and China, Japan, South Korea, and India together account for more than half.

The Three Gorges Dam on the Yangtze River in China (see Figure 5.8) will be the largest dam in the world when it is completed in 2009. It will be 6,600 feet—over a mile—wide and over 600 feet high. The creation of a water reservoir upstream of the dam will flood 13 cities and countless villages, and displace well over a million people. In addition, the dam will disrupt water flow and increase water pollution, threatening unique species such as the Yangtze River dolphin, one of only five freshwater dolphin species in the world.

The Yangtze River dolphin was placed on the Endangered Species List in 1989 and is at extreme risk of extinction, with only 150 individuals remaining. Other species likely to be threatened or wiped out altogether include the Chinese sturgeon, the Chinese tiger, the Chinese alligator, the Siberian crane, the giant panda, and countless species of fish, freshwater invertebrates, and plants. Several U.S. agencies provided much technical assistance in planning the Three Gorges Dam. However, U.S. government involvement ceased due to a challenge under the Endangered Species Act, which prohibits government activity detrimental to listed species. The main part of dam construction has been completed, and filling of the Three Gorges Dam began in June 2003.

Although the long controversy surrounding the Three Gorges dam did not prevent its erection, it has perhaps raised awareness within China regarding some of the destructive impacts of other proposed dams. In 2003 China's Environmental Protection Agency and the Chinese Academy of Sciences announced their opposition to plans to dam the Nu River, a World Heritage Site that has been described as the "Grand Canyon of the Orient." The proposed series of 13 dams would affect over 7,000 plant species and 80 rare and endangered animals, in addition to requiring over 50,000 people to be relocated. Many of these are farmers and herders from ethnic minorities in China.


The Aral Sea is bounded by Uzbekistan and Kazakhstan, and was once the fourth-largest lake in the world. However, over the past 30 years, the lake has lost 60 percent of its water and shrunk to half its original area. This is due to the long practice of diverting water from the Amu-Darya and the Syr-Darya, two rivers that feed the lake, for irrigation and agriculture. With water loss, the lake has also increased in salinity—from 10 percent salt content to 23 percent salt content in 1999. Aral Sea habitats have been utterly destroyed. The Aral Sea was once a thriving fishery, with a total catch of 26,000 tons in 1957. Thousands of fishermen were once employed at the sea, and commercial species included carp, pike-perch, and roach. Commercial fishing in the Aral had ceased entirely by 1982.

The destruction of the Aral Sea has had numerous other consequences as well. Exposure of the lakebed has resulted in dust storms and air pollution, which affect much of the human population living around the Aral Sea. In the last 15 years, liver disease, kidney disease, and chronic bronchitis have increased 30-fold, and incidence of arthritic disease has increased by a factor of 60. The loss of the lake has also affected regional climate patterns, so that summers are now hotter and drier and winters are longer and colder. Agriculture in the region has also been severely impaired, both by the shortening of the growing season and the degradation of soil, which is prone to high salinity and erosion.


Worldwide, humans obtain 16 percent of their animal protein from fish. As the human population explodes, the fishing industry has tried to keep up with demand. Up to a certain point, fishermen are able to catch more fish without damaging the ecological balance. This is known as the maximum sustainable yield. Catches beyond the maximum sustainable yield represent overfishing. Overfishing removes fish faster than they can reproduce and causes serious population declines. Furthermore, once fishermen deplete all the large fish of a species, they often begin to target smaller, younger individuals. Targeting young fish undermines future breeding populations and guarantees a smaller biological return in future years. Swordfish have been seriously depleted in this way. In the early 1900s, the average weight of a swordfish when caught was around 300 pounds. By 1960, it was 266 pounds, and at the close of the twentieth century it was 90 pounds.

Technological advances have enabled numerous marine fisheries to be depleted in a short amount of time. In addition, the eight regional councils that regulate commercial fishing, all of which are dominated by the fishing industry, have been either unable or unwilling to set limits for themselves. As a result, most fishing areas are free-for-alls.

The U.S. government attempted to eliminate overfishing in U.S. coastal waters by passing the Magnuson Act in 1976. The Magnuson Act expanded the coastal economic zone claimed by the United States from three miles offshore to 200 miles offshore, preventing foreign fishing fleets from exploiting these waters. However, with foreign fleets gone, American fishermen built up their own fleets, buying large, well-equipped vessels with low-interest loans from the federal government. For several years U.S. fishermen reported record catches. Then these declined. Government officials now report that most of the major commercial fishing areas in the United States are in trouble. According to the National Marine Fisheries Service (NMFS), about 40 percent of the nation's saltwater species have been overfished.

From Drift Nets to Longlines

Drift nets are the world's largest fishing nets, reaching lengths of up to 30 miles. Conservationists refer to them as "walls of death" because they indiscriminately catch and kill marine species. Over 100 species—including whales, sea turtles, dolphins, seabirds, sharks, salmon, and numerous other fish species—have been killed in drift nets. Drift nets were eventually banned because of their destructiveness to wildlife.

After the banning of drift nets, many fishermen turned to longlines. Longlines are fishing lines with a single main line attached to many shorter lines that terminate in baited hooks. They are used to catch wide-ranging oceanic species such as tuna, swordfish, and sharks, as well as bottom dwellers such as cod and halibut. A single boat can trail thousands of hooks from lines stretching 20 to 80 miles.

Longline fishing kills fewer marine mammals than drift nets but captures more surface-feeding sea birds, particularly the rare albatrosses. Longline fishing has in fact resulted in the decline of numerous albatross species, almost all of which are now listed by the World Conservation Union (IUCN) as endangered. Australian scientists estimate that longline fishing kills more than 40,000 albatrosses each year. Longline fishing has also caused rapid declines in some fish species. Longlining is an old practice, but modern technology has vastly increased its efficiency and ecological impact.

Fish Declines and Deep-Sea Harvesting

As catches of shallow water fishes decline, trawlers have increasingly been used to scour the deep seas for new varieties of fish, such as the nine-inch long royal red shrimp, rattails, skates, squid, red crabs, orange roughy, oreos, hoki, blue ling, southern blue whiting, and spiny dogfish. Although limited commercial deep-sea fishing has occurred for decades, new technologies are making it considerably more practical and efficient. As stocks of better-known fish shrink and international quotas tighten, experts say deep ocean waters will increasingly be targeted as a source of seafood.


Numerous aquatic ecosystems have been degraded by invasive species. The primary source of aquatic invasive species has traditionally been ship ballast water, which is generally picked up in one location and released in another. In San Francisco Bay alone, it is estimated that a new invasive species becomes established every 14 weeks through ballast water. Invasive species are also established through transfer from recreational boating vessels; intentional release, usually in attempts to establish new populations for fishing; dumping of live bait; release of aquarium species; and accidental escapes from research facilities. The Nonindigenous Aquatic Nuisance Prevention and Control Act of 1990 and the National Invasive Species Act of 1996 are intended to help prevent unintentional introductions of aquatic nuisance species.

The zebra mussel is an invasive species that both degrades aquatic resources and threatens native species, particularly native freshwater mussels. Zebra mussels first appeared in the United States in 1988. Figure 5.9 illustrates the spread of zebra mussels throughout the Great Lakes and beyond during the following ten years. According to the U.S. Geological Survey, zebra mussels were found in Virginia in 2002, and in a lake in Kansas in 2003; signs of juvenile zebra mussels were detected in Nebraska, as well, in early 2004. This pest species reproduces rapidly and threatens aquatic habitats by clogging water passages and starving out native species. U.S. freshwater mussel species are in fact disappearing at an alarming rate. Figure 5.10 shows the decline in the number of pearly mussel species in the Mississippi River.

In the state of Georgia, invasive Asian eels have increased in number in many habitats. These species were brought over from Southeast Asia or Australia, where they are considered delicacies. The three-foot-long, flesh-eating eel preys on species such as largemouth bass and crawfish in and around the Chattahoochee River. The eels have gills but can also breathe air—this enables them to worm their way across dry ground to get from one body of water to another. Asian eels have few predators in their new habitat, and humans have found no effective way to control them. In March 2000 an Asian eel was reported near Florida's Everglades National Park, confirming fears that the eel would spread beyond Georgia.

Striking at the Base of the Food Chain

Phytoplankton (planktonic plant life) are microscopic photosynthesizing species that form the basis of nearly all marine food chains. (See Figure 5.11.) In many parts of the world, phytoplankton seems to be declining. The most severe damage appears to be in the waters off Antarctica, where phytoplankton are severely depleted. The depletion of phytoplankton has implications all the way up the food chain, affecting not only the zooplankton that consume them but larger species such as penguins, seals, and whales. Scientists believe that phytoplankton declines are a result of the thinning atmospheric ozone layer (caused by industrial pollutants such as chlorofluorocarbons, or CFCs), which allows increasing amounts of ultraviolet radiation to penetrate the Earth's surface. Ultraviolet radiation decreases the ability of phytoplankton to photosynthesize and also damages their genetic material.


Numerous aquatic species are endangered in the United States. In fact, Figure 5.12 shows that the biological groups with the greatest proportion of endangered species—freshwater mussels, crayfishes, amphibians, and freshwater fishes—are all aquatic. The U.S. also possesses some of the most diverse freshwater fauna in the world, including 29 percent of the world's freshwater mussels, 61 percent of crayfish, 17 percent of freshwater snails, and 10 percent of freshwater fish.

In 2004 there were a total of 125 listed fish species—82 of these were endangered (71 U.S. and 11 foreign) and 43 were threatened (all U.S.). Table 5.2 shows the listed fish species found in the United States. There are also 72 threatened and endangered clams and other bivalves (70 U.S. and 2 foreign), 33 threatened and endangered snails (32 U.S. and 1 foreign), and 21 threatened and endangered crustaceans (all U.S.). Table 5.3 lists the threatened and endangered U.S. bivalve, snail, and crustacean species as of 2004.

Freshwater Mussels

The United States has the greatest diversity of freshwater mussels in the world. Figure 5.13 illustrates Higgins eye, a species of pearly mussel. Unfortunately, many freshwater mussels are in decline. In 2002, of the 297 native mussel species in the United States, 12 percent were believed extinct and 23 percent were listed as threatened or endangered. Furthermore, numerous additional mussel species are being considered for listing. The Nature Conservancy and the American Fisheries Society estimate that about 70 percent of freshwater mussels will require protection. The decline of freshwater mussels, which began in the 1800s, has resulted largely from habitat disturbance, especially water pollution and the modification of aquatic habitats by dams. Dams have single-handedly caused the loss of 30 to 60 percent of native mussels in U.S. rivers. The invasive zebra mussel has also harmed native freshwater mussel species by competing with them for food and other resources.

The decline of freshwater mussels, scientists fear, is a sign of serious problems in freshwater ecosystems. Mussels perform many essential functions in these ecosystems, providing food for many species and improving water quality by filtering particles and excess nutrients. Other freshwater mollusks, particularly snails, may also be declining. Conservation efforts for freshwater mussels include the captive breeding and reintroduction of some species, as well as measures to restore damaged habitats.


Fish occur in nearly all permanent water environments, from deep oceans to remote alpine lakes and desert springs. They are the most diverse vertebrate group—scientists have officially catalogued nearly 24,000 fish species, about as many as all other vertebrates combined. Less than 10 percent of these species have been assessed for their conservation status.

The IUCN listed 750 species of fish as threatened in its 2003 Red List of Threatened Species, approximately half of the species examined. However, the IUCN reports that many more, perhaps as many as a third of all fish species, are likely to be listed once surveys are complete. The IUCN also reported that at least 60 percent of threatened freshwater fish species are in decline because of habitat alteration, whereas 34 percent face pressure from introduced species. The U.S. Fish and Wildlife Service listed a total of 82 endangered and 43 threatened fish species in 2004.


The cichlids are a large family of fish that evolved over a period of 750,000 years in African rift lakes including Lake Malawi, Lake Tanganyika, and Lake Victoria. Lake Malawi probably has more fish species than any other lake in the world, with over 1,000 identified—95 percent of these are cichlids. Many cichlid fishes, however, are now facing extinction. British colonialists introduced the Nile perch into Lake Victoria in 1954 because it is significantly larger (up to 300 pounds) than native fish species and can more easily be caught with nets. The aggressive Nile perch have since eaten about half the native cichlid species in Lake Victoria to extinction. With the loss of cichlid species, which feed on algae and insects, algae has grown out of control, damaging all lake habitats. Insects have also flourished.


In recent decades, many salmon species, particularly those that inhabit the Columbia and Snake Rivers in the Pacific Northwest, have declined. Salmon are of significant economic and social importance for the commercial food harvest as well as for sport fishing. Salmon are also important to Pacific Northwest Native American tribes for economic as well as cultural and religious reasons. Species in danger of extinction include the coho, sockeye, chinook, and steelhead. Two major causes of salmon endangerment are overfishing and dams, which interfere with salmon runs.

During the 1800s annual salmon runs were estimated to include some 10 to 16 million individuals. At present, total salmon runs have declined to an estimated 2.5 million annually. Declines prior to 1930 resulted largely from over-fishing. Since then, however, the major causes of salmon declines have been dam construction in the Columbia River Basin and water pollution, including nitrogen saturation below dam spillways. In 1992 the National Marine Fisheries Service began to designate critical habitat for salmon species and to develop recovery plans. In 1994 the Pacific Fisheries Management Council issued strict regulations limiting salmon catches. Soon after that, the government announced that Pacific salmon were nearly extinct and began to list species for protection under the Endangered Species Act. Listed species now include the chum salmon (threatened in Oregon and Washington), the coho salmon (threatened, California and Oregon), the sockeye salmon (endangered in Idaho and Oregon, and threatened or endangered in Washington), the chinook salmon (threatened or endangered in California, Oregon, Washington, and Idaho), and the Atlantic salmon (endangered in Maine). Figure 5.14 shows the locations of existing populations of chinook salmon, and Figure 5.15 shows population trends over various periods of time in the last two decades of the twentieth century. Some populations have increased in number since listing, while others have not. Listing of salmon species came after nearly ten years of study, and marked the first time vast urban areas saw land and water use restricted under the Endangered Species Act.


The Klamath Basin in southern Oregon and northern California is the site of a heated battle pitting farmers against a coalition of fishermen and environmentalists who wish to protect three listed species, the coho salmon, shortnose sucker fish, and Lost River sucker fish. Opponents are battling over water, which has been in particularly short supply due to recent droughts in the Pacific Northwest.

StatusSpecies nameStatusSpecies name
TCatfish, Yaqui (Ictalurus pricei)TMinnow, loach (Tiaroga cobitis)
ECavefish, Alabama (Speoplatyrhinus poulsoni)EMinnow, Rio Grande silvery (Hybognathus amarus)
TCavefish, Ozark (Amblyopsis rosae)E, XNPikeminnow (=squawfish), Colorado (Ptychocheilus lucius)
EChub, bonytail (Gila elegans)EPoolfish, Pahrump (Empetrichthys latos)
EChub, Borax Lake (Gila boraxobius)EPupfish, Ash Meadows Amargosa (Cyprinodon nevadensis mionectes)
TChub, Chihuahua (Gila nigrescens)EPupfish, Comanche Springs (Cyprinodon elegans)
EChub, humpback (Gila cypha)EPupfish, desert (Cyprinodon macularius)
TChub, Hutton tui (Gila bicolor ssp.)EPupfish, Devils Hole (Cyprinodon diabolis)
EChub, Mohave tui (Gila bicolor mohavensis)EPupfish, Leon Springs (Cyprinodon bovinus)
EChub, Oregon (Oregonichthys crameri)EPupfish, Owens (Cyprinodon radiosus)
EChub, Owens tui (Gila bicolor snyderi)EPupfish, Warm Springs (Cyprinodon nevadensis pectoralis)
EChub, Pahranagat roundtail (Gila robusta jordani)ESalmon, Atlantic (Salmo salar)
TChub, slender (Erimystax cahni)E, TSalmon, chinook (Oncorhynchus [=Salmo] tshawytscha)
TChub, Sonora (Gila ditaenia)TSalmon, chum (Oncorhynchus [=Salmo] keta)
XN, TChub, spotfin (Cyprinella monacha)TSalmon, coho (Oncorhynchus [=Salmo] kisutch)
EChub, Virgin River (Gila seminuda [=robusta])E, TSalmon, sockeye (Oncorhynchus [=Salmo] nerka)
EChub, Yaqui (Gila purpurea)TSculpin, pygmy (Cottus paulus [=pygmaeus])
ECui-ui (Chasmistes cujus)TShiner, Arkansas River (Notropis girardi)
EDace, Ash Meadows speckled (Rhinichthys osculus nevadensis)TShiner, beautiful (Cyprinella formosa)
TDace, blackside (Phoxinus cumberlandensis)TShiner, blue (Cyprinella caerulea)
EDace, Clover Valley speckled (Rhinichthys osculus oligoporus)EShiner, Cahaba (Notropis cahabae)
TDace, desert (Eremichthys acros)EShiner, Cape Fear (Notropis mekistocholas)
TDace, Foskett speckled (Rhinichthys osculus ssp.)EShiner, palezone (Notropis albizonatus)
EDace, Independence Valley speckled (Rhinichthys osculus lethoporus)TShiner, Pecos bluntnose (Notropis simus pecosensis)
EDace, Kendall Warm Springs (Rhinichthys osculus thermalis)EShiner, Topeka (Notropis topeka [=tristis])
EDace, Moapa (Moapa coriacea)TSilverside, Waccamaw (Menidia extensa)
EDarter, amber (Percina antesella)TSmelt, delta (Hypomesus transpacificus)
TDarter, bayou (Etheostoma rubrum)TSpikedace (Meda fulgida)
EDarter, bluemask (=jewel) (Etheostoma)TSpinedace, Big Spring (Lepidomeda mollispinis pratensis)
EDarter, boulder (Etheostoma wapiti)TSpinedace, Little Colorado (Lepidomeda vittata)
TDarter, Cherokee (Etheostoma scotti)ESpinedace, White River (Lepidomeda albivallis)
E, XNDarter, duskytail (Etheostoma percnurum)ESpringfish, Hiko White River (Crenichthys baileyi grandis)
EDarter, Etowah (Etheostoma etowahae)TSpringfish, Railroad Valley (Crenichthys nevadae)
EDarter, fountain (Etheostoma fonticola)ESpringfish, White River (Crenichthys baileyi baileyi)
TDarter, goldline (Percina aurolineata)E, TSteelhead (Oncorhynchus [=Salmo] mykiss)
TDarter, leopard (Percina pantherina)EStickleback, unarmored threespine (Gasterosteus aculeatus williamsoni)
EDarter, Maryland (Etheostoma sellare)ESturgeon, Alabama (Scaphirhynchus suttkusi)
TDarter, Niangua (Etheostoma nianguae)TSturgeon, gulf (Acipenser oxyrinchus desotoi)
EDarter, Okaloosa (Etheostoma okaloosae)ESturgeon, pallid (Scaphirhynchus albus)
EDarter, relict (Etheostoma chienense)ESturgeon, shortnose (Acipenser brevirostrum)
TDarter, slackwater (Etheostoma boschungi)ESturgeon, white (Acipenser transmontanus)
TDarter, snail (Percina tanasi)ESucker, June (Chasmistes liorus)
EDarter, vermilion (Etheostoma chermocki)ESucker, Lost River (Deltistes luxatus)
EDarter, watercress (Etheostoma nuchale)ESucker, Modoc (Catostomus microps)
EGambusia, Big Bend (Gambusia gaigei)ESucker, razorback (Xyrauchen texanus)
EGambusia, Clear Creek (Gambusia heterochir)TSucker, Santa Ana (Catostomus santaanae)
EGambusia, Pecos (Gambusia nobilis)ESucker, shortnose (Chasmistes brevirostris)
EGambusia, San Marcos (Gambusia georgei)TSucker, Warner (Catostomus warnerensis)
EGoby, tidewater (Eucyclogobius newberryi)ETopminnow, Gila (including Yaqui) (Poeciliopsis occidentalis)
ELogperch, Conasauga (Percina jenkinsi)TTrout, Apache (Oncorhynchus apache)
ELogperch, Roanoke (Percina rex)TTrout, bull (Salvelinus confluentus)
TMadtom, Neosho (Noturus placidus)ETrout, Gila (Oncorhynchus gilae)
EMadtom, pygmy (Noturus stanauli)TTrout, greenback cutthroat (Oncorhynchus clarki stomias)
EMadtom, Scioto (Noturus trautmani)TTrout, Lahontan cutthroat (Oncorhynchus clarki henshawi)
E, XNMadtom, smoky (Noturus baileyi)TTrout, Little Kern golden (Oncorhynchus aguabonita whitei)
XN, TMadtom, yellowfin (Noturus flavipinnis)TTrout, Paiute cutthroat (Oncorhynchus clarki seleniris)
TMinnow, Devils River (Dionda diaboli)E, XNWoundfin (Plagopterus argentissimus)
E = Endangered
T = Threatened
XN = Experimental population, non-essential
source: Adapted from "U.S. Listed Vertebrate Animal Species Report by Taxonomic Group as of 02/17/2004," Threatened and Endangered Species System (TESS), U.S. Fish and Wildlife Service, Washington, DC, 2004 [Online] [accessed February 17, 2004]

The Klamath River once supported the third-largest salmon run in the country. However, in recent years, water diversion has caused river water levels to be too low to maintain healthy stream conditions and temperatures. Over 7,000 fishing jobs have been lost due to salmon declines. Water diversion practices also violate agreements with Native American tribes to avoid harming healthy salmon runs. Water diversion in the Klamath Basin has

StatusSpecies nameStatusSpecies name
EAcornshell, southern (Epioblasma othcaloogensis)ERing pink (mussel) (Obovaria retusa)
TBankclimber, purple (mussel) (Elliptoideus sloatianus)TSlabshell, Chipola (Elliptio chipolaensis)
E, XNBean, Cumberland (pearlymussel) (Villosa trabalis)ESpinymussel, James (Pleurobema collina)
EBean, purple (Villosa perpurpurea)ESpinymussel, Tar River (Elliptio steinstansana)
EBlossom, green (pearlymussel) (Epioblasma torulosa gubernaculum)EStirrupshell (Quadrula stapes)
E, XNBlossom, tubercled (pearlymussel) (Epioblasma torulosa torulosa)EThree-ridge, fat (mussel) (Amblema neislerii)
E, XNBlossom, turgid (pearlymussel) (Epioblasma turgidula)EWartyback, white (pearlymussel) (Plethobasus cicatricosus)
E, XNBlossom, yellow (pearlymussel) (Epioblasma florentina florentina)EWedgemussel, dwarf (Alasmidonta heterodon)
E, XNCatspaw (=purple cat's paw pearlymussel) (Epioblasma obliquata obliquata)
ECatspaw, white (pearlymussel) (Epioblasma obliquata perobliqua)Snails
E, XNClubshell (Pleurobema clava)EAmbersnail, Kanab (Oxyloma haydeni kanabensis)
EClubshell, black (Pleurobema curtum)ECampeloma, slender (Campeloma decampi)
EClubshell, ovate (Pleurobema perovatum)ECavesnail, Tumbling Creek (Antrobia culveri)
EClubshell, southern (Pleurobema decisum)TElimia, lacy (snail) (Elimia crenatella)
E, XNCombshell, Cumberlandian (Epioblasma brevidens)ELimpet, Banbury Springs (Lanx sp.)
ECombshell, southern (Epioblasma penita)ELioplax, cylindrical (snail) (Lioplax cyclostomaformis)
ECombshell, upland (Epioblasma metastriata)EMarstonia, royal (snail) (Pyrgulopsis ogmorhaphe)
EElktoe, Appalachian (Alasmidonta raveneliana)EPebblesnail, flat (Lepyrium showalteri)
EElktoe, Cumberland (Alasmidonta atropurpurea)E, XNRiversnail, Anthony's (Athearnia anthonyi)
EFanshell (Cyprogenia stegaria)TRocksnail, painted (Leptoxis taeniata)
TFatmucket, Arkansas (Lampsilis powelli)ERocksnail, plicate (Leptoxis plicata)
THeelsplitter, Alabama (=inflated) (Potamilus inflatus)TRocksnail, round (Leptoxis ampla)
EHeelsplitter, Carolina (Lasmigona decorata)TShagreen, Magazine Mountain (Mesodon magazinensis)
EHiggins eye (pearlymussel) (Lampsilis higginsii)ESnail, armored (Pyrgulopsis (Marstonia) pachyta)
EKidneyshell, triangular (Ptychobranchus greeni)TSnail, Bliss Rapids (Taylorconcha serpenticola)
E, XNLampmussel, Alabama (Lampsilis virescens)TSnail, Chittenango ovate amber (Succinea chittenangoensis)
ELilliput, pale (pearlymussel) (Toxolasma cylindrellus)TSnail, flat-spired three-toothed (Triodopsis platysayoides)
E, XNMapleleaf, winged (mussel) (Quadrula fragosa)ESnail, Iowa Pleistocene (Discus macclintocki)
TMoccasinshell, Alabama (Medionidus acutissimus)ESnail, Morro shoulderband (=Banded dune) (Helminthoglypta walkeriana)
EMoccasinshell, Coosa (Medionidus parvulus)TSnail, Newcomb's (Erinna newcombi)
EMoccasinshell, Gulf (Medionidus penicillatus)TSnail, noonday (Mesodon clarki nantahala)
EMoccasinshell, Ochlockonee (Medionidus simpsonianus)TSnail, painted snake coiled forest (Anguispira picta)
EMonkeyface, Appalachian (pearlymussel) (Quadrula sparsa)ESnail, Snake River physa (Physa natricina)
E, XNMonkeyface, Cumberland (pearlymussel) (Quadrula intermedia)TSnail, Stock Island tree (Orthalicus reses [ not including nesodryas])
TMucket, orangenacre (Lampsilis perovalis)ESnail, tulotoma (Tulotoma magnifica)
EMucket, pink (pearlymussel) (Lampsilis abrupta)ESnail, Utah valvata (Valvata utahensis)
E, XNMussel, oyster (Epioblasma capsaeformis)ESnail, Virginia fringed mountain (Polygyriscus virginianus)
EMussel, scaleshell (Leptodea leptodon)ESnails, Oahu tree (Achatinella ssp.)
TPearlshell, Louisiana (Margaritifera hembeli)ESpringsnail, Alamosa (Tryonia alamosae)
E, XNPearlymussel, birdwing (Conradilla caelata)ESpringsnail, Bruneau Hot (Pyrgulopsis bruneauensis)
E, XNPearlymussel, cracking (Hemistena lata)ESpringsnail, Idaho (Fontelicella idahoensis)
EPearlymussel, Curtis (Epioblasma florentina curtisii)Crustaceans
E, XNPearlymussel, dromedary (Dromus dromas)
EPearlymussel, littlewing (Pegias fabula)EAmphipod, Hay's Spring (Stygobromus hayi)
EPigtoe, Cumberland (Pleurobema gibberum)EAmphipod, Illinois cave (Gammarus acherondytes)
EPigtoe, dark (Pleurobema furvum)EAmphipod, Kauai cave (Spelaeorchestia koloana)
E, XNPigtoe, finerayed (Fusconaia cuneolus)EAmphipod, Peck's cave (Stygobromus [=Stygonectes] pecki)
EPigtoe, flat (Pleurobema marshalli)ECrayfish, cave (Cambarus aculabrum)
EPigtoe, heavy (Pleurobema taitianum)ECrayfish, cave (Cambarus zophonastes)
EPigtoe, oval (Pleurobema pyriforme)ECrayfish, Nashville (Orconectes shoupi)
EPigtoe, rough (Pleurobema plenum)ECrayfish, Shasta (Pacifastacus fortis)
E, XNPigtoe, shiny (Fusconaia cor)EFairy shrimp, Conservancy (Branchinecta conservatio)
EPigtoe, southern (Pleurobema georgianum)EFairy shrimp, longhorn (Branchinecta longiantenna)
EPimpleback, orangefoot (pearlymussel) (Plethobasus cooperianus)EFairy shrimp, Riverside (Streptocephalus woottoni)
EPocketbook, fat (Potamilus capax)EFairy shrimp, San Diego (Branchinecta sandiegonensis)
TPocketbook, finelined (Lampsilis altilis)TFairy shrimp, vernal pool (Branchinecta lynchi)
EPocketbook, Ouachita rock (Arkansia wheeleri)EIsopod, Lee County cave (Lirceus usdagalun)
EPocketbook, shiny-rayed (Lampsilis subangulata)TIsopod, Madison Cave (Antrolana lira)
EPocketbook, speckled (Lampsilis streckeri)EIsopod, Socorro (Thermosphaeroma thermophilus)
ERabbitsfoot, rough (Quadrula cylindrica strigillata)EShrimp, Alabama cave (Palaemonias alabamae)
ERiffleshell, northern (Epioblasma torulosa rangiana)EShrimp, California freshwater (Syncaris pacifica)
ERiffleshell, tan (Epioblasma florentina walkeri (=E. walkeri))EShrimp, Kentucky cave (Palaemonias ganteri)
TShrimp, Squirrel Chimney Cave (Palaemonetes cummingi)
ETadpole shrimp, vernal pool (Lepidurus packardi)
E = Endangered
T = Threatened
XN = Experimental population, non-essential
source: Adapted from "U.S. Listed Invertebrate Animal Species Report by Taxonomic Group as of 02/17/2004," Threatened and Endangered Species System (TESS), U.S. Fish and Wildlife Service, Washington, DC, 2004 [Online][accessed February 17, 2004]

also caused the loss of over 75 percent of area wetlands, including portions of the Klamath Marsh National Wildlife Refuge in southern Oregon, at the headwaters of the Klamath River. This habitat supports the shortnose sucker and the Lost River sucker, which were listed as endangered in their entire ranges in California and Oregon in 1988. Both were once highly abundant in the Upper Klamath Lake, but populations have declined due to alteration of water flow patterns, habitat degradation, and water pollution. Suckerfish species live in the lake most of the year, but migrate downstream to spawn. Habitat alteration has particularly affected the survival of juvenile suckers. The Klamath Marsh National Wildlife Refuge also supports other listed species such as the bald eagle, northern spotted owl, and several species of endangered coastal dune plants.

A lawsuit regarding the distribution of Klamath Basin waters was brought against the U.S. Bureau of Reclamation by the Pacific Coast Federation of Fishermen's Associations, the Klamath Forest Alliance, the Institute for Fisheries Resources, the Oregon Natural Resources Council, and other groups. The plaintiffs argued that the Bureau of Reclamation had met farmers' demands for water, but left Klamath River flows much lower than that required for survival of the coho salmon, shortnose sucker fish, and Lost River sucker fish. Furthermore, the Bureau was charged with violating the Endangered Species Act in not consulting with the National Marine Fisheries Service regarding endangered species conservation. Farmers were also accused of wasting water.

In April 2001 the U.S. Bureau of Reclamation was found by a Federal District Court to have knowingly violated the Endangered Species Act when it allowed delivery of irrigation water required to maintain habitat of the three listed species. As a result of the court decision, federal agencies cut water to irrigation canals in order to preserve water levels in the Upper Klamath Lake for the two species of sucker fish and to increase water flow in the Klamath River for coho salmon. In April 2002, a lawsuit was filed on behalf of the farmers to remove all three species from the Endangered Species List. Water flow was an issue again in 2002. After a federal judge decided not to force the Bureau of Reclamation to provide water to listed species in 2002, there was a massive fish-kill involving approximately 33,000 salmon.


A similarly heated debate addresses the issue of water flow on the Missouri River. The U.S. Fish and Wildlife Service determined in 2000 that existing water flow patterns—managed to create a steady depth for barge traffic—were endangering three listed species: the pallid sturgeon, piping plover, and least tern. The U.S. Fish and Wildlife Service argued that increased water flow in the spring—a "spring rise"—was necessary for sturgeon spawning. In addition, it called for less water flow in the summer, which is necessary for exposing the sandbars used by the bird species as nesting grounds. The Fish and Wildlife Service gave the Army Corps of Engineers, which controls Missouri water flow, until 2003 to implement these changes. However, the Bush administration delayed decision on a final plan in 2002. The Washington Post reported that the administration had "begun an 'informal consultation' on possible changes to the wildlife service's demands." ("Bush Delays Action on Missouri River: Agencies Order to Consult on 'Spring Rise,'" Washington Post, 14 June 2002.) The issue has been extremely controversial in the Midwest, with environmentalists, recreation interests, and upper-basin officials favoring a spring rise, and farmers, barge interests, and Missouri leaders opposed. There have been 55,000 submitted comments on the issue, with 54,000 favoring a spring rise.


The razorback sucker is an endangered fish species found in the lower Colorado River. It is named for the razor-like ridge on its back that helps it swim in rapid waters. The razorback sucker is in danger of extinction due to habitat loss, competition with introduced species, and predation by non-native species such as carp. Habitat destruction is largely the result of dam-building, which has affected water temperature and

Recovery objectives: Improve the status and habitat of Paiute cutthroat trout and eliminate competition from nonnative salmonid species.
Recovery criteria: Paiute cutthroat trout will be considered for delisting when the following objectives are met:
1) All nonnative salmonids are removed in Silver King Creek and its tributaries downstream of Llewellyn Falls to fish barriers in Silver King Canyon;
2) A viable population occupies all historic habitat in Silver King Creek and its tributaries downstream of Llewellyn Falls to fish barriers in Silver King Canyon;
3) Paiute cutthroat trout habitat is maintained in all occupied streams;
4) The refuge populations in Corral and Coyote Creeks, Silver King Creek, and tributaries above Llewellyn Falls as well as out-of-basin populations are maintained as refugia and are secured from the introduction of other salmonid species; and
5) A long-term conservation plan and conservation agreement are developed, which will be the guiding management documents once Paiute cutthroat trout are delisted.
Recovery actions:
1. Remove nonnative trout from historic Paiute cutthroat trout habitat.
2. Reintroduce Paiute cutthroat trout into historic habitat.
3. Protect and enhance all occupied Paiute cutthroat trout habitat.
4. Continue to monitor and manage existing and reintroduced populations.
5 Develop a long-term conservation plan and conservation agreement.
6. Provide public information.
Total estimated cost of recovery ($1,000's):
YearAction 1Action 2Action 3Action 4Action 5Action 6
The total estimated cost of recovering Paiute cutthroat trout is $558,450, plus additional costs that cannot be estimated at this time.
Date of recovery: Delisting of the Paiute cutthroat trout could be initiated in 2013, if tasks are implemented as recommended and recovery criteria are met.
source: Adapted from "Executive Summary," in Draft Revised Recovery Plan for the Paiute Cutthroat Trout (Oncorhynchus clarki seleniris), Department of the Interior, U.S. Fish & Wildlife Service, Region 1, Portland, OR, November 2003

flooded habitat areas. Razorback suckers can live up to 45 years, and the fish that remain are generally old individuals. Over 90 percent of existing razorback suckers inhabit a single site, Lake Mojave in Arizona.

In an attempt to help razorback sucker populations recover, mature fish are collected and transported to the Willow Beach National Fish Hatchery each spring, where they spawn. In spring 2000, for example, 80 adult fish were collected from Lake Mojave and laid a total of over 300,000 eggs. Juveniles are then returned to various Colorado River habitats when they are larger and have a better chance of survival (usually when they reach 10 inches in size and 18 months of age). It is estimated that about 9,000 razorback sucker adults remain in the population, as well as some 3,000 to 4,000 younger individuals that have been reintroduced from captivity.


The Paiute cutthroat trout is found in the Silver King drainage on the eastern slope of the Sierra Nevada Mountains in California. The species was listed as endangered in 1970 and reclassified as threatened in 1975. Table 5.4 shows the recovery objectives, recovery criteria, actions needed, estimated cost of recovery, and date of recovery for the species from the recovery plan released by the Fish and Wildlife Service in November 2003. The Paiute cutthroat trout is threatened primarily by introduced trout species and is considered to have a high potential for recovery. Figure 5.16 shows adult and juvenile population size in one habitat from 1964 to 2001. Some years in which few or no fish were found correspond to treatment with the chemical rotenone, a naturally occurring compound used for fish control. Table 5.5 summarizes the threats and recovery recommendations for the species.


The snail darter, a small fish species related to perch, was the object of perhaps the largest controversy regarding endangered species conservation prior to the conflict surrounding the northern spotted owl. The snail darter was originally listed as endangered by the U.S. Fish and Wildlife Service in 1975. At the time, it was believed only to exist in the Little Tennessee River, and this area was designated as critical habitat for the species. That same year, the Tellico Dam was near completion on the Little Tennessee River, and the filling of the Tellico Reservoir would have destroyed the entire habitat of the snail darter. A lawsuit was filed to prevent this from happening. The case went all the way to the Supreme Court, which ruled in 1978 that under the Endangered Species Act, species protection must take priority over economic and developmental concerns. One month after this court decision, Congress amended the Endangered Species Act to allow for exemptions under certain circumstances. In late 1979, the Tellico Dam received an exemption and the Tellico Reservoir was filled. The snail darter is now extinct in that habitat. Fortuitously, however, snail darter populations were later discovered in other river systems. In addition, the species has been introduced into several other habitats. Due to an increase in numbers, the snail darter was reclassified as threatened in 1984. Currently, it is found in Alabama, Georgia, and Tennessee.


Sharks have been predators of the seas for nearly 400 million years. There are more than 350 species of sharks, ranging in size from the tiny pygmy shark to the giant whale shark.

Shark populations are being decimated because of the growing demand for shark meat and shark fins. Fins and tails sell for as much as $100 a pound. In the United States, some shark populations have already declined 70 to 80 percent from levels in the 1980s and 1990s due to overfishing. Overfishing is particularly harmful to sharks because they reproduce slowly. In 1997 the Fisheries Service cut quotas on commercial harvests of some shark

Listing factorThreat
AStreambank degradation from recreational activities
AStreambank degradation from cattle grazing
ADegradation of water quality and spawning substrates by beavers
BUnregulated angling
CNatural predators [not currently significant]
CFungal infections
DPotential budgetary constraints on agency commitment to recovery actions
EHybridization and competition with introduced trout
ENeed for fish barriers to prevent upstream migration of introduced trout
EHuman introduction of trout
EVulnerability to catastrophic events due to limited distribution
Listing factors :
A . The present or threatened destruction, modification, or curtailment of its habitat or range
B . Overutilization for commercial, recreational, scientific, educational purposes (not a factor)
C . Disease or predation
D . The inadequacy of existing regulatory mechanisms
E . Other natural or manmade factors affecting its continued existence
source: Adapted from "Appendix B. Summary of Threats and Recommended Recovery Actions," in Draft Revised Recovery Plan for the Paiute Cutthroat Trout (Oncorhynchus clarki seleniris), Department of the Interior, U.S. Fish & Wildlife Service, Region 1, Portland, OR, November 2003

species by half and completely banned harvest of the most vulnerable species—whale sharks, white sharks, basking sharks, sand tiger sharks, and bigeye sand tiger sharks. The annual U.S. commercial shark quota for the Caribbean, the Gulf of Mexico, and the Atlantic coast is 150,000 large coastal sharks. However, many biologists consider that number too high to be sustainable.

Fishermen in Costa Rica, where several manufacturers process shark cartilage for medicinal purposes, claim that the real cause of shark declines is trolling by large fleets from China, Japan, and other countries. A few shark species, including whale sharks and basking sharks, were given protection by CITES for the first time in 2002. This was considered a landmark decision because CITES had never before addressed fisheries.

A study published in 2003 by biologists Julia Baum and Ransom Myers of Dalhousie University in Canada showed that many shark populations in the Gulf of Mexico have plummeted since the 1950s. ("Collapse and Conservation of Shark Populations in the Northwest Atlantic," Science, vol. 299, 17 January 2003.) In particular, whitetip shark populations have declined by 90 percent. The researchers blamed the decline on overfishing due to demand for sharkfin soup, which is considered a luxury. Professor Myers said, "Researchers in the 1960s suggested that oceanic whitetip sharks were the most common large species on Earth. What we have shown is akin to the herds of buffalo disappearing from the Great Plains and no one noticing." Other species which have been affected include the silk shark, whose populations have dropped by 90 percent, and the mako shark, which has declined 79 percent.

Coral Reefs

Coral reefs are found in coastal, tropical waters and are the largest living structures on Earth. Biologically, the richness of coral reef ecosystems is comparable to that of tropical rainforests. The reefs themselves are formed from calcium carbonate skeletons secreted by corals. Corals maintain a close relationship with certain species of photosynthetic algae, providing shelter to them and receiving nutrients in exchange.

The IUCN reports that 30 percent of coral reefs worldwide are in critical condition—10 percent have already been destroyed. In 1997 researchers at the Florida Keys National Marine Sanctuary reported that unidentified diseases affected coral at 94 of 160 monitoring stations in the 2,800-square-mile coral reef sanctuary. Coral reefs are also threatened by coastal development that spurs the growth of unfriendly algae. Coastal development increases the danger of the reefs being trampled by divers and boat anchors. Other serious threats to reef ecosystems include marine pollution, blast fishing, and cyanide fishing. Collection of tropical reef specimens for the aquarium trade has also damaged a number of species. Perhaps the greatest immediate threat to coral reefs is rising water temperature due to global climate change. This has caused extensive coral bleaching in recent years.

Marine Mammals

Dolphins, whales, and numerous other marine mammals are threatened with extinction. Some species have declined due to centuries of hunting, while others have been harmed as a result of habitat decline or other forms of human activity.


Whales are the largest animals on Earth. The blue whale, the largest whale species, can reach a length of 80 feet and weigh 150 tons. Its heart alone weighs 1,000 pounds and is the size of a small car. Whales are found throughout the world's oceans and are highly intelligent. Some species communicate via haunting "songs." In 2004 eight whale species had been listed for protection under the Endangered Species Act: humpback whales, sperm whales, bowhead whales, right whales, sei whales, finback whales, blue whales, and gray whales.

Whale populations have declined due to a long history of hunting by humans. As early as the eighth century, humans hunted whales for meat and whalebone. In the nineteenth century, large numbers of whales were killed for whale oil, which was used to light lamps, as well as for baleen—the large horny plates that some species use to filter food. Baleen or "whalebone" was particularly valued for making fans and corsets. Today whales are hunted primarily for meat and for whale oil used in the manufacture of cosmetics and industrial lubricants. The Marine Mammal Protection Act, passed in 1972, made it illegal to import goods containing ingredients from whales. The International Whaling Commission (IWC) has imposed a moratorium on whale hunting since 1986, but animals continue to be killed by countries that flout its regulations or claim that the hunts are for "research."

The northern right whale is the most endangered of the great whales, with fewer than 300 individuals in existence. Once the "right" whale to hunt because it swims slowly and floats upon death, the species has been protected for several decades. However, northern right whale populations are not increasing. The primary threat to the species is continued mortality from collisions with ships. Entanglement in fishing gear and habitat decline in right whale feeding areas are additional causes of population decline. Research has also revealed that the northern right whale's huge fat reserves store an array of toxic substances, possibly affecting whales' health. The situation is so dire, says Dr. Scott Kraus, chief scientist at the New England Aquarium in Boston, that the right whale may become extinct in our lifetime. The National Marine Fisheries Service has declared an area off the coast of Georgia and northern Florida coast as critical right whale habitat.


The last remaining West Indian manatees, also known as Florida manatees, swim in the rivers, bays, and estuaries of Florida and surrounding states. (See Figure 5.17.) These mammals are often called "sea cows" and can reach weights of up to 2,000 pounds. Manatees swim just below the surface of the water and feed on vegetation. Females bear a single offspring every three to five years. West Indian manatees migrate north in the summer, though generally no farther than the North Carolina coast. In 1995 a manatee nicknamed "Chessie" made headlines by swimming all the way to Chesapeake Bay. Eventually biologists, concerned about his health in cooler waters, had him airlifted back to Florida.

Unlike most animals, manatees have no natural predators. The primary dangers to this species come from humans. Motorboats are the major cause of manatee mortalities—because of their large size, manatees often cannot move away from boats quickly enough to avoid being hit. Environmentalists have tried to protect manatees from boat collisions, and have successfully had several Florida waterways declared boat-free zones. There are also areas where boaters are required to lower their speeds. Because manatees do not produce young very often, their population is decreasing due to high death rates.

The manatee population has suffered severe losses in the last decade. In 1995 approximately 10 percent of Florida's manatees died suddenly, most likely from an unidentified virus. The following year 20 percent of the remaining population—a total of 415 manatees—died. Researchers attributed mortality to a variety of causes, including red tide, which occurs when toxin-producing aquatic organisms called dinoflagellates bloom in large quantities, and motorboat collisions. In 2001 the Florida Fish and Wildlife Conservation Commission and Florida Marine Research Institute reported 325 manatee deaths. Eighty-one were due to collisions with watercraft, and another 110 were due to unknown causes. The Florida Marine Research Institute reported that human-related activity accounted for 44 percent of all manatee deaths between 1976 and 2001, most from watercraft collisions.

A lawsuit by the Save the Manatee Club and other environmental and conservation organizations in 2000 successfully required the state to implement new boat speed zones and establish areas for manatee "safe havens." However, new rules were immediately challenged by individual boaters and boating organizations. The restrictions were upheld by Florida courts in 2002.

Biologists estimate that between 2,000 and 3,000 manatees remain in the wild. An aerial survey in 2004 counted 2,568 individuals. Most of these manatees have scars on their backs from motorboat propellers—these allow individual manatees to be recognized. The National Biological Service has catalogued about 1,000 manatees using scar patterns, and maintains manatee sighting histories in a computer-based system.


Large numbers of dolphins have been killed by the tuna fishing industry. These marine mammals are often found swimming over tuna schools—in fact, tuna fishers have learned to locate tuna by looking for dolphin pods. Dolphins die when they become trapped in commercial tuna nets and drown. Many millions of dolphins have been killed this way since tuna netting began in 1958.

In 1972 more than 360,000 dolphins were killed by U.S. tuna fishermen. Congress passed the Marine Mammal Protection Act the same year, partly to reduce dolphin deaths. Amendments to the law in 1982 and 1985 theoretically halted U.S. tuna purchases from countries whose fishing methods endangered dolphins. In the years after passage, however, these laws were often ignored. Public awareness of dolphin killings was critical in bringing more interest and attention to the issue. In 1988 a reauthorization of marine mammal laws required observers to be present on all tuna boats. Even this measure, however, had only limited impact. In 1990 StarKist, the biggest tuna canner in the world, declared that it would no longer purchase tuna caught in ways that harmed dolphins. Within hours of StarKist's press conference, the next two largest tuna canners followed suit. In 1991 the government established standards for tuna canners that wished to label their products "Dolphin Safe." The International Dolphin Conservation Act, passed in 1992, reduced the number of legally permitted dolphin deaths. This act also made the United States a dolphin-safe zone in 1994, when it became illegal to sell, buy, or ship tuna products obtained using methods that kill dolphins. Reputable tuna canners now label their canned tuna "Dolphin Safe."


In 2004 six species of pinnipeds—seals and sea lions—were considered endangered worldwide. These were the Caribbean monk seal, Hawaiian monk seal, Guadalupe fur seal, Mediterranean monk seal, Saimaa seal, and Steller sea lion. However, the Caribbean monk seal has not been sighted since 1952 and is believed extinct. The species was widely hunted for both blubber and meat.

Hawaiian monk seals are the only pinnipeds found on Hawaii and are endemic to those islands—that is, they occur nowhere else on Earth. Because Hawaiian monk seals have no natural terrestrial enemies, they are not afraid of humans and were once easily hunted for blubber and fur. Hunting was the primary cause of population decline. Hawaiian monk seals are also extremely sensitive to human activity and disturbance and now breed exclusively on the remote northwestern Hawaiian islands, which are not inhabited by humans. Most females give birth to a single pup every two years, a reproductive rate lower than other pinniped species. Hawaiian monk seals feed on fish, octopuses, eels, and lobsters. This species was officially listed as endangered in 1976. In 2002 seal populations were estimated at between 1,200 and 1,500 individuals.

The Guadalupe fur seal breeds on the Isla de Guadalupe and the Isla Benito del Este near Baja California in Mexico. Although populations once included as many as 20,000 to 100,000 individuals, decline and endangerment resulted from extensive fur hunting in the 1700s and 1800s. The species was believed extinct in the early twentieth century, but a small population was discovered in 1954. The species was listed as threatened in 1967. Protection of the Guadalupe fur seal under both Mexican and U.S. law has resulted in population increases, and there are

Gray whaletrap/crab01
Pilot whaleAtlantic Ocean, Caribbean, Gulf of Mexico large pelagics longline30
Bottlenose dolphinU.S. Mid-Atlantic coastal gillnet02
Gulf of Mexico menhaden purse seine14
Common dolphinCA/OR thresher shark/swordfish drift gillnet315
Gulf of Mexico menhaden purse seine01
Atlantic squid, mackerel, butterfish trawl fishery05
Harbor porpoiseAK Peninsula/Aleutian Islands salmon set gillnet10
Northeast sink gillnet03
Humpback whaleNortheast sink gillnet01
CA/OR thresher shark/swordfish drift gillnet10
Prince William Sound salmon drift gillnet10
Pacific white-sided dolphinCA/OR thresher shark/swordfish drift gillnet011
Risso's dolphinCA/OR thresher shark/swordfish drift gillnet02
Northeast sink gillnet01
Unidentified small cetaceanCA/OR thresher shark/swordfish drift gillnet41
Atlantic Ocean, Caribbean, Gulf of Mexico large pelagics longline10
California sea lionCA/OR thresher shark/swordfish drift gillnet023
CA angel shark/halibut & other species large mesh (3.5 inch) set gillnet025
Steller sea lionAK Bering Sea & Aleutian Islands groundfish trawl05
Harbor sealCA angel shark/halibut & other species large mesh (3.5 inch) set gillnet03
Northeast sink gillnet03
Northern elephant sealCA angel shark/halibut & other species large mesh (3.5 inch) set gillnet01
CA/OR thresher shark/swordfish drift gillnet11
Grey sealNortheast sink gillnet04
Unidentified sealAK Bering Sea & Aleutian Islands groundfish trawl01
CA/OR thresher shark/swordfish drift gillnet01
WalrusAK Bering Sea & Aleutian Islands groundfish trawl01
source: "Table 4. 2000 Marine Mammal Authorization Program Mortality/Injury Report," Administration of the Marine Mammal Protection Act of 1972 Annual Report 1999–2000, U.S. Department of Commerce, National Marine Fisheries Service, Office of Protected Resources, Silver Spring, MD, 2004

now an estimated 7,000 individuals in the wild. However, some individuals continue to be killed by driftnets.

Steller sea lions are large animals, with males reaching lengths of 11 feet and weights of 2,500 pounds. Females are significantly smaller. Steller sea lions are found in Pacific waters from Japan to central California, but most populations breed near Alaska and the Aleutian Islands. Populations have declined by 80 percent in the last three decades, most likely due to the decline of fish that provide food for the species. In February 2004 the North Pacific Universities Marine Mammal Consortium reported that population declines may be explained by the fact that Steller sea lions had switched from eating fatty fish to fish with low fat content. In particular, their diet now consists primarily of pollock and flatfish, rather than herring. The low fat content of the new diet prevents Steller sea lions from building up enough blubber to survive and reproduce in their cold aquatic habitat. In addition, many sea lions are also killed in driftnets. In 1990 the Steller sea lion was listed as endangered in Alaska and Russia and threatened in other habitats. There are currently about 30,000 individuals in the wild.


The Lacey Act

The Lacey Act was originally passed in 1900 and is the oldest wildlife conservation law in the United States. The Lacey Act prohibits interstate and international trade in wildlife that has been collected or exported illegally. In 1999 the U.S. Fish and Wildlife Service processed 1,476 cases under the Lacey Act. These included illegal commerce in endangered species, illegal hunting, and illegal harvest of shellfish from closed areas.

The Magnuson Act

The Magnuson Fishery Conservation and Management Act of 1976 established a system for fisheries management within U.S. waters. Examples of Magnuson Act violations include fishing without a permit, possessing out-of-season fish, or retaining undersized fish.

The Marine Mammal Protection Act

The Marine Mammal Protection Act (MMPA), passed in 1972, recognized that many marine mammals are either endangered or have suffered declines as a result of human activity. The MMPA prohibits the taking (hunting, killing, capturing, and harassing) of marine mammals. The act also bars importation of most marine mammals or their products. Exceptions are occasionally granted for scientific research, public display in aquariums, subsistence hunting (by Alaskan natives), and some incidental take during commercial fishing operations. The goal of the MMPA is to maintain marine populations at or above "optimum sustainable" levels. Under the MMPA, the National Marine Fisheries Service manages all cetaceans (whales and dolphins) and pinnipeds (seals and sea lions) except walruses. The National Marine Fisheries Service relies on the U.S. Coast Guard and other federal and state agencies to assist with the detection of violations. Table 5.6 shows the list of marine mammal injuries and mortalities that resulted from interactions with commercial fisheries in 2000. This is a standard part of the Administration of the Marine Mam-mal Protection Act of 1972 report that the National Marine Fisheries Service submits to Congress every two years.

The U.S. Fish and Wildlife Service manages polar bears, walruses, sea otters, manatees, and dugongs (manatee relatives).