Chapter 4
Threats to Aquatic Environments

According to the U.S. Geological Survey in "How Much Water Is There on (and in) the Earth?" (http://ga.water.usgs.gov/edu/earthhowmuch.html), about 326 million trillion gallons of water make up the total water supply of the planet. This provides an enormous aquatic habitat for a wide variety and number of animal and plant species. The aquatic environment is threatened by many human activities around the world. Humans consume vast amounts of freshwater and exert control over water flows in many rivers and streams. Land development, agricultural practices, industrialization, and commercial fishing have all affected the aquatic environment in some way.

DAMS

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. Of the major rivers in the lower forty-eight states (those more than 600 miles in length), only the Yellowstone River still flows freely. In fact, University of Alabama biologist Arthur Benke, the editor of Rivers of North America (Elsevier, 2005), notes that it is difficult to find any river in the United States that has not been dammed or channeled. According to Benke, "All human alterations of rivers, regardless of whether they provide services such as power or drinking water supply, result in degradation. The only exception is when we try to restore them."

Dams have epitomized progress, American ingenuity, and humankind's mastery of nature. In North America, more than two 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.

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.

The U.S. Army Corps of Engineers maintains the National Inventory of Dams (NID) at the Web site http://crunch.tec.army.mil/nid/webpages/nid.cfm. As of 2006 the inventory included approximately 76,000 dams throughout the country. Dams are listed that are at least six feet tall or hold back at least fifteen acre-feet (nearly five million gallons) of water. Dams are built for a variety of purposes. The most frequent purposes listed in the NID database are recreation, fire protection, stock or small farm pond creation, flood control, and storm water management. As shown in Figure 4.1 these purposes account for 70% of all purposes listed.

Although only a small percentage of dams listed with the NID produce hydroelectric power, these dams tend to be the largest in size and affect large watersheds. Figure 4.2 shows the components of a typical impoundment dam producing hydroelectric power. These structures provide numerous challenges to aquatic species, besides impeding water flow and migration paths. Turbines operate like massive underwater fans. Passage through running turbine blades can result in the death of many small aquatic creatures unable to escape their path. Some modern hydroelectric dams include stair-like structures called fish ladders that provide migrating fish a path to climb up and over the dams.

The Snail Darter

The snail darter, a small fish species related to perch, was at the center of a dam-building controversy during the 1970s. The U.S. Fish and Wildlife Service (FWS) listed the snail darter as endangered in 1975. At the time it was believed to exist only 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 (ESA) 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. Fortunately, 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.

The Missouri "Spring Rise" Issue

During the 2000s a heated debate has surrounded 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 (a fish) and two bird species, the piping plover and least tern. The FWS 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 FWS and the Army Corps of Engineers, which manages the flow of water on the Missouri River, implemented a water management plan beginning with the 2003 season. 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.

Salmon and Dams

Numerous species of salmon are in decline, at least partly due to the effects of dams. 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.

Scientists are increasingly learning of the importance of estuaries to juvenile salmon in the Pacific Northwest. Estuaries are areas where freshwater meets and mixes with ocean water. Juvenile salmon pass through estuaries on their downstream trip to the sea. Prior to excessive damming of the Columbia River system, spring and summer floods (called freshets) would have spread juvenile salmon throughout the estuaries into various marshes and natural channels. From there the salmon would make their way to the sea. Flow regulation has dramatically changed the river flows in this area and limited the amount of estuary habitat available to the salmon. Figure 4.3 shows daily river flows recorded in 1916, 1966, and 1980. The flows in 1916 were highly variable on a seasonal basis, reflecting the natural effects of melting snows and heavy spring rains. Damming the river dampened these seasonal changes and virtually eliminated freshets from occurring. This result has been beneficial for residents and farmers living along the river, but detrimental to the habitat of the Pacific salmon.

Tearing Down Dams?

In November 1997, for the first time in U.S. history, the Federal Energy Regulatory Commission ordered a dam removed when the Edwards Dam was ordered 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 government prevailed. The 160-year old dam produced 1% 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.

Conservationists and fisheries 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 more than 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 did agree, however, to budget $390 million over a ten-year period 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. The Three Gorges Dam on the Yangtze River in China (see Figure 4.4) will be the largest dam in the world when it becomes operational in 2009. It will be 6,600 feet—more than a mile—wide and over 600 feet high. The creation of a water reservoir upstream from the dam will flood thirteen cities and countless villages, and displace more than 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. However, generators have yet to be installed as of 2006.

FRESHWATER DIVERSION AND USE

Freshwater is a vital resource to humans. It is used for a variety of purposes—drinking water, hydroelectric power production, irrigation of crops, watering of livestock, and for commercial and industrial applications. Diversion of water from natural waterways, such as rivers and streams, stresses aquatic animals living in those habitats.

Klamath Basin

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 is needed for irrigation purposes by farmers in the area.

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. Over the years many of the wetlands in the Klamath Basin have been drained for agricultural purposes; however, there are still scattered wetlands and lakes throughout the area. 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.

A lawsuit regarding the distribution of Klamath Basin waters was brought against the U.S. Bureau of Reclamation (BOR) 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 BOR had met farmers' demands for water but left Klamath River flows much lower than required for survival of the coho salmon, shortnose suckerfish, and Lost River suckerfish. Furthermore, the Bureau was charged with violating the ESA by 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 ESA 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 suckerfish 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 BOR to provide water to listed species in 2002, there was a massive fish-kill involving approximately 33,000 salmon.

Between 2000 and 2002 the Bureau of Reclamation developed numerous operating plans for water flows in the Klamath Basin; however, these plans were continually challenged in court. In 2002 the agency issued a ten-year plan designed to achieve full protection for the river's salmon by 2012. A lengthy court battle over the plan culminated in March 2006 when a federal judge ruled that the plan had to be implemented immediately. The judge noted that salmon water requirements must outweigh the needs of farmers for irrigation water. Because a wet winter had produced large flows in the Klamath River, no immediate effects of the ruling on irrigation supply were anticipated. However, the issue is expected to continue to be a subject of continued litigation.

WATER POLLUTION POSES A THREAT

Water pollution poses a considerable threat to many aquatic species. Contaminants include chemicals, biological substances (such as manure and sewage), solid waste materials, and dirt and soil eroded from riverbanks or nearby lands. In general, aquatic creatures are not killed outright by water contamination. A major exception is an oil spill, which can kill many creatures through direct contact. The more widespread and common threat is overall degradation of water quality and habitats due to pollutants. Exposure to contaminants can weaken the immune systems of aquatic animals and make them more susceptible to disease and other health and reproductive problems.

Pesticides

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) 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-trichlor-oethane) 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 biomagni-fication—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. 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 new and more powerful chemicals.

Nutrient Pollution

Nutrient pollution is primarily composed of nitrogen and phosphorus. These chemicals are commonly used in inorganic fertilizers and are naturally found in biological wastes, such as manure and sewage. In addition, nitrogen compounds are emitted into the air during the combustion of fossil fuels, such as oil and coals. All of these factors combine to produce a heavy load of nutrients that enter waterbodies via land runoff, direct discharges, and atmospheric deposition.

While nutrients are not poisonous by nature, large quantities of them can cause serious health problems in aquatic animals. Nutrients 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 sunlight or deplete oxygen essential to other species. (See Figure 4.5.)

Oils

Oil enters waterbodies through a variety of means, including natural and anthropogenic (human-related) sources. Figure 4.6 shows the sources of oil input to the North American marine (oceanic) environment in 2002. Natural seepage accounts for 63% of marine oil exposure. Anthropogenic activities are blamed for the other 37%. Runoff of oil in municipal and industrial waste discharges is the primary source of oil exposure attributed to human activities. Smaller amounts are blamed on atmospheric fallout from additional anthropogenic sources, including air pollution (8%), marine transportation vehicles (3%), recreational marine vehicles (2%), and offshore oil and gas development (2%).

Oil spills are 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 eleven million gallons of oil into Prince William Sound 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 affected by the spill, particularly seabird species, had 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% 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. In 2003 the agency estimated that each year approximately twenty-nine million gallons of petroleum enter North American ocean waters due to human activities. Nearly 85% of this amount is attributed to street runoff, polluted rivers, and losses from airplanes, small boats, and jet skis. 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 nonnative 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 4.1.)

Mercury and Other Toxic Pollutants

Since 1993 the EPA has published an annual listing of all fish advisories issued around the country. These advisories are issued by states to protect residents from the adverse health risk of eating fish contaminated with certain pollutants. The EPA's 2004 National Listing of Fish Advisories (September 2005, http://www.epa.gov/ OST/fish/advisories/fs2004.pdf) showed that 3,221 advisories were issued during 2004 affecting 35% of the nation's total lake acreage and 24% of its total river miles. Nearly 14.3 million lake acres and just over 839,000 river miles were under advisory during 2004. As shown in Figure 4.7 more than two-thirds of the advisories were issued due to mercury contamination. Polychlorinated biphenyls (PCBs) accounted for another 24% of advisories. Dioxins, pesticides, and other contaminants contributed the other 9% of the total.

MERCURY

Mercury contamination is a problem in many of the nation's waterbodies. Scientists believe that the main source of mercury pollution is rainwater 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 4.8.)

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 2004 mercury was the cause of 2,436 fish and wildlife consumption advisories. Figure 4.9 shows the advisories in effect as of December 2004. Most states across the nation's northern border and in the Northeast had statewide advisories in effect for all their rivers and lakes, as did Florida. All of the Gulf Coast, Hawaiian coast, and much of the eastern seaboard were under advisory for mercury contamination in marine fish.

SEDIMENT—GOOD AND BAD

Erosion of river and stream banks brings dirt into waterbodies. Once in the water, this dirt is known as silt or sediment. Most of these particles settle to the bottom. However, sediment is easily stirred up by the movement of fish and other aquatic creatures, many of which spawn or lay eggs at the bed of their habitats. The dirt that remains in suspension in the water is said to make water turbid. The measure of the dirtiness (lack of clarity) of a waterbody is called its turbidity.

Freshwater aquatic creatures are sensitive to turbidity levels and choose their habitats based in part on their sediment preferences. Some fish prefer waters with large amounts of sediment. It provides cover that prevents predator fish from seeing them. Other species prefer clean waters with low turbidity levels. Excessive sediment may clog their gills or smother their eggs. (See Figure 4.10.)

Sediment levels in a water system can be drastically changed by deforestation of banks and nearby lands through forestry or agricultural practices. Excessive grazing of livestock along riverbanks can strip vegetation and permit large amounts of dirt to enter the water. Likewise, timber harvesting and crop production can expose loosened dirt to wind and rain that carry it into water bodies. Dams and diversion structures trap sediments behind them, interrupting the natural downstream flow of sediments that takes place in moving waters.

AIR POLLUTION AFFECTS WATER QUALITY

Water quality can be affected by pollutants emitted into the air during fossil fuel combustion or industrial, agricultural and forestry activities. Nutrients, oil and dirt particles, and some chemicals (such as mercury) are known to be carried through the air and deposited onto waterbodies. This process is called atmospheric disposition. In addition, aquatic environments can be harmed indirectly, through changes in climate and atmospheric phenomena due to human activities.

Phytoplankton

Phytoplankton (planktonic plant life) are microscopic photosynthesizing species that form the basis of nearly all marine food chains. (See Figure 4.11.) 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 photosyn-thesize and also damages their genetic material.

FISHING—FAR-REACHING CONSEQUENCES

Worldwide, the demand for fish and other edible aquatic creatures has risen dramatically in recent decades. The National Marine Fisheries Service in Fisheries of the United States-2004 (November 2005, http://www.st.nmfs.gov/st1/fus/fus04/index.html) summarizes data collected about commercial and recreational fisheries. The report notes that in 2003 the world's commercial fishery and aquaculture industries harvested 146 million tons of products. In 2004 U.S. commercial fishery and aquaculture industries produced 11.2 billion pounds of fish and shellfish. Per capita annual consumption of fishery products in the United States was 16.6 pounds of meat in 2004. This is up from fifteen pounds per person annual consumption reported in 1990. U.S. consumers spent nearly $62 billion on fishery products in 2004.

Overfishing

Up to a certain point, fishermen are able to catch 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. This can have far-reaching consequences on other species that rely on the depleted fish for food. 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 about 300 pounds. By 1960, according to the NMFS, it was 266 pounds, and at the close of the twentieth century it was ninety pounds.

Technological advances have enabled numerous marine fisheries to be depleted in a short amount of time. The U.S. Commission on Ocean Policy published An Ocean Blueprint for the 21st Century (September 2004, http://www.oceancommission.gov/documents/full_color_rpt/welcome.html). Commission members were appointed by President George W. Bush to develop recommendations for a new national ocean policy. The report noted: "Experts estimate that 25 to 30 percent of the world's major fish stocks are over-exploited, and many U.S. fisheries are experiencing serious difficulties."

MAGNUSON-TEVENS ACT

The U.S. government attempted to eliminate overfishing in U.S. coastal waters by passing the Magnuson-Stevens Fishery Conservation and Management Act (P.L. 94-265) in 1976. This act established U.S. control over fishery resources within 200 nautical miles of the coast. (See Figure 4.12.) This area was later deemed the Exclusive Economic Zone (EEZ). Under international law the United States has sovereign rights to explore, exploit, conserve, and manage living and nonliving resources within and below ocean waters within the EEZ.

When the Magnuson-Stevens Act was passed it prevented foreign fishing fleets from exploiting the affected 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.

The act established eight Regional Fishery Management Councils as follows:

• Caribbean Fishery Management Council
• Gulf of Mexico Fishery Management Council
• Mid-Atlantic Fishery Management Council
• New England Fishery Management Council
• North Pacific Fishery Management Council
• Pacific Fishery Management Council
• South Atlantic Fishery Management Council
• Western Pacific Fishery Management Council

The councils were instructed to prepare Fishery Management Plans (FMPs) covering domestic and foreign fishing efforts within their area of authority. FMPs must be approved by the Secretary of Commerce before being implemented. They are enforced by the National Marine Fisheries Service and the U.S. Coast Guard. The Fishery Management Plans for some species, such as highly migratory fishes that enter and leave the Exclusive Economic Zone, are prepared by the U.S. Department of Commerce. As of February 2006 more than forty FMPs have been finalized for various species. The plans can be accessed at the Web site http://www.nmfs.noaa.gov/sfa/domes_fish/FMPS.htm.

The Fishery Management Councils were intended to eliminate overfishing, while ensuring that the "optimum yield" was obtained from each fishery. Critics say the system has failed to do this. The National Academy of Public Administration in Courts, Congress, and Constituencies: Managing Fisheries by Default (July 2002, http://www.napawash.org/Pubs/NMFS_July_2002.pdf? OpenDocument) concluded that fisheries management in the United States was being driven by litigation and political processes, rather than sound science. At that time more than 100 lawsuits were pending against the NMFS; most involved stock assessments and catch limits and were filed by the fishing industry or conservation groups.

The Ocean Blueprint for the 21st Century complains: "Social, economic, and political considerations have often led the Councils to downplay the best available scientific information, resulting in overfishing and the slow recovery of overfished stocks." However, the report does acknowledge that overfishing has been relieved in some areas. During the 1990s increases were reported in stocks of Mid-Atlantic flounder, New England ground-fish, and Atlantic striped bass.

SHARK OVERFISHING

According to the San Diego Natural History Museum, 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 2003 the Pew Institute for Ocean Science instituted a project called the Pew Global Shark Assessment. Its purpose is to collect data regarding declines in global shark populations. According to the project's Web site (http://www.pewoceanscience.org/projects/Pew_Global_Shar/intro.php?ID=56) populations of dusky, oceanic whitetip, and silky sharks in the Gulf of Mexico have declined by 79% to 97% since the 1950s due to overfishing. Massive declines are also reported over the same time period for blue, mako, oceanic whitetip, silky, and thresher sharks in the tropical Pacific Ocean. Overfishing is particularly harmful to sharks because they reproduce slowly. In 1997 the Fisheries Service cut quotas on commercial harvests of some shark 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. A few shark species, including whale sharks and basking sharks, were given protection by the Convention on International Trade in Endangered Species (CITES) for the first time in 2002. This was considered a landmark decision because CITES had never before addressed fisheries.

Biologists Julia Baum and Ransom Myers of Dalhousie University in Canada in "Collapse and Conservation of Shark Populations in the Northwest Atlantic" (Science, January 17, 2003), showed that many shark populations in the Gulf of Mexico have plummeted since the 1950s. In particular, whitetip shark populations have declined by 90%. The researchers blamed the decline on overfishing due to demand for sharkfin soup, which is considered a luxury. 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%, and the mako shark, which has declined 79%.

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.

Bycatch

Bycatch is the term used for nontargeted animals captured during fishing. For example, during the 1960s, hundreds of thousands of dolphins per year were caught in the nets of tuna fishing boats and drowned. Although dolphins were not the targets of the fishing operations, they became victims anyway. Public outcry over dolphin deaths led to passage of the Marine Mammal Protection Act and promises by tuna canneries to sell only "dolphin-safe" tuna. Unfortunately bycatch continues to be a problem for many aquatic species, including those that are endangered and threatened.

FROM DRIFT NETS TO LONGLINES

Drift nets are the world's largest fishing nets, reaching lengths of up to thirty 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 destructive-ness 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 twenty to eighty 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.

Ghost Fishing

"Ghost fishing" is a term used by biologists to refer to the accidental entanglement of aquatic animals in abandoned or lost fishing gear. According to the 2004 report An Ocean Blueprint for the 21st Century ghost fishing kills hundreds of thousands of marine mammals worldwide each year. Dolphins, porpoises, and small whales are the primary victims. However, even large whales can be injured by entanglements or become exhausted after towing heavy nets and gear over long distances. Ghost fishing is one of the main causes blamed for the endangered status of the North Atlantic right whale.

Ghost fishing is an international problem. The U.S. Commission on Ocean Policy reports that between 1998 and 2002 more than 150 tons of fishing nets and lines were removed from reefs near the northwestern Hawaiian Islands. Oftentimes the nets were not the type used by local fisheries; instead, they are believed to have drifted from thousands of miles away in the North Pacific Ocean. Possible solutions to the problem of ghost fishing include the assessment of fees or deposits on fishing nets with the money raised used to collect derelict fishing gear, achieving international cooperation in identifying and removing derelict fishing gear, and development of biodegradable fishing gear. The NMFS already requires commercial U.S. fisheries to mark fishing gear with identifying information.

UNWELCOME GUESTS—AQUATIC INVASIVE SPECIES

Invasive species can be domestic or foreign. Some aquatic invasive species have been introduced purposely to U.S. waterbodies, for example, to improve sport and recreational fishing. Others have been introduced unintentionally. The primary source of these aquatic invasive species has traditionally been ship ballast water, which is generally picked up in one location and released in another. According to Leo O'Brien, executive director of Baykeeper (a group trying to protect and improve the water quality of the San Francisco Bay/Delta Estuary), it is estimated that a new invasive species becomes established every fourteen weeks through ballast water in the San Francisco Bay alone. Invasive species are also established through transfer from recreational boating vessels; dumping of live bait; release of aquarium species; and accidental escapes from research facilities and aquaculture pens.

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.

Invasive aquatic species include the common carp, bluegill, largemouth bass, smallmouth bass, shad, walleye, and brook trout. The common carp was purposely brought to the United States during the 1800s from Europe. It thrived so well that it soon spread across the country. Today the fish is considered a pest. It competes against native species for food and habitat.

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. As of 2006 three populations of Asian eel had been identified in Florida, confirming fears that the eel would spread beyond Georgia. According to a fact sheet prepared by the Florida Integrated Science Center of the U.S. Geological Survey, one colony was living in canals in the northern Miami area, once colony was near Tampa Bay, and one colony was within a mile of the eastern edge of Everglades National Park.

MULTIPLE THREATS COMBINE

Most aquatic lifeforms are not imperiled by a single threat to their survival, but by multiple threats that combine to produce daunting challenges to recovery. The lethal combination of historical overfishing and habitat degradation is blamed for the problems of many endangered and threatened aquatic species. Habitat degradation can be caused by many factors, including dams, water pollution, and invasive species.

Overcrowding of stressed fish populations into smaller and smaller areas has contributed to hybridization—uncharacteristic mating between closely related species resulting in hybrid offspring. According to the U.S. Fish and Wildlife Service environmental degradation appears to inhibit natural reproductive instincts that historically prevented fish from mating outside their species. In addition, shortage of suitable space for spawning has resulted in more mating between species. Cross-mating can be extremely detrimental to imperiled species, because the offspring can be sterile.

Coral Reefs

Coral reefs 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. Most people are familiar with the colorful coral reefs found in coastal, tropical waters. (See Figure 4.13.) These reefs are located in relatively shallow waters, making them more susceptible to human activities. Only 1% to 2% of warm-water corals are found in U.S. waters. Most warm-water corals are located in the waters of the South Pacific and around Indonesia. In addition there are numerous cold-water reefs around the world that scientists are just beginning to learn about. These reefs are found in cold deep waters from depths of 100 feet to more than three miles.

According to An Ocean Blueprint for the 21st Century, one-third of coral reefs around the world are severely damaged and all U.S. warm-water reefs have been damaged to some degree. Coral reefs are imperiled by diseases and coastal development that spurs the growth of unfriendly algae. Coastal development also 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. (See Figure 4.14.)