Library Index » Science Encyclopedia » Aquatic Species and Their Environments - Water Pollution—many, Many Causes, Dams, Water Diversion—the Aral Sea, Overfishing—too Many Boats, Not Enough Fish

Aquatic Species and Their Environments - Imperiled Aquatic Species

fish endangered salmon

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 FIGURE 5.9
Zebra mussel distribution, 1988 and 2003
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. FIGURE 5.10
Decline of pearly-mussels in the upper Mississippi River drainage, 1920–2000
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.

The marine food chain


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 FIGURE 5.12
Proportion of species at risk of extinction, 1997
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.

Endangered or threatened fish species, February 2004

Status Species name Status Species name
T Catfish, Yaqui (Ictalurus pricei) T Minnow, loach (Tiaroga cobitis)
E Cavefish, Alabama (Speoplatyrhinus poulsoni) E Minnow, Rio Grande silvery (Hybognathus amarus)
T Cavefish, Ozark (Amblyopsis rosae) E, XN Pikeminnow (=squawfish), Colorado (Ptychocheilus lucius)
E Chub, bonytail (Gila elegans) E Poolfish, Pahrump (Empetrichthys latos)
E Chub, Borax Lake (Gila boraxobius) E Pupfish, Ash Meadows Amargosa (Cyprinodon nevadensis mionectes)
T Chub, Chihuahua (Gila nigrescens) E Pupfish, Comanche Springs (Cyprinodon elegans)
E Chub, humpback (Gila cypha) E Pupfish, desert (Cyprinodon macularius)
T Chub, Hutton tui (Gila bicolor ssp.) E Pupfish, Devils Hole (Cyprinodon diabolis)
E Chub, Mohave tui (Gila bicolor mohavensis) E Pupfish, Leon Springs (Cyprinodon bovinus)
E Chub, Oregon (Oregonichthys crameri) E Pupfish, Owens (Cyprinodon radiosus)
E Chub, Owens tui (Gila bicolor snyderi) E Pupfish, Warm Springs (Cyprinodon nevadensis pectoralis)
E Chub, Pahranagat roundtail (Gila robusta jordani) E Salmon, Atlantic (Salmo salar)
T Chub, slender (Erimystax cahni) E, T Salmon, chinook (Oncorhynchus [=Salmo] tshawytscha)
T Chub, Sonora (Gila ditaenia) T Salmon, chum (Oncorhynchus [=Salmo] keta)
XN, T Chub, spotfin (Cyprinella monacha) T Salmon, coho (Oncorhynchus [=Salmo] kisutch)
E Chub, Virgin River (Gila seminuda [=robusta]) E, T Salmon, sockeye (Oncorhynchus [=Salmo] nerka)
E Chub, Yaqui (Gila purpurea) T Sculpin, pygmy (Cottus paulus [=pygmaeus])
E Cui-ui (Chasmistes cujus) T Shiner, Arkansas River (Notropis girardi)
E Dace, Ash Meadows speckled (Rhinichthys osculus nevadensis) T Shiner, beautiful (Cyprinella formosa)
T Dace, blackside (Phoxinus cumberlandensis) T Shiner, blue (Cyprinella caerulea)
E Dace, Clover Valley speckled (Rhinichthys osculus oligoporus) E Shiner, Cahaba (Notropis cahabae)
T Dace, desert (Eremichthys acros) E Shiner, Cape Fear (Notropis mekistocholas)
T Dace, Foskett speckled (Rhinichthys osculus ssp.) E Shiner, palezone (Notropis albizonatus)
E Dace, Independence Valley speckled (Rhinichthys osculus lethoporus) T Shiner, Pecos bluntnose (Notropis simus pecosensis)
E Dace, Kendall Warm Springs (Rhinichthys osculus thermalis) E Shiner, Topeka (Notropis topeka [=tristis])
E Dace, Moapa (Moapa coriacea) T Silverside, Waccamaw (Menidia extensa)
E Darter, amber (Percina antesella) T Smelt, delta (Hypomesus transpacificus)
T Darter, bayou (Etheostoma rubrum) T Spikedace (Meda fulgida)
E Darter, bluemask (=jewel) (Etheostoma) T Spinedace, Big Spring (Lepidomeda mollispinis pratensis)
E Darter, boulder (Etheostoma wapiti) T Spinedace, Little Colorado (Lepidomeda vittata)
T Darter, Cherokee (Etheostoma scotti) E Spinedace, White River (Lepidomeda albivallis)
E, XN Darter, duskytail (Etheostoma percnurum) E Springfish, Hiko White River (Crenichthys baileyi grandis)
E Darter, Etowah (Etheostoma etowahae) T Springfish, Railroad Valley (Crenichthys nevadae)
E Darter, fountain (Etheostoma fonticola) E Springfish, White River (Crenichthys baileyi baileyi)
T Darter, goldline (Percina aurolineata) E, T Steelhead (Oncorhynchus [=Salmo] mykiss)
T Darter, leopard (Percina pantherina) E Stickleback, unarmored threespine (Gasterosteus aculeatus williamsoni)
E Darter, Maryland (Etheostoma sellare) E Sturgeon, Alabama (Scaphirhynchus suttkusi)
T Darter, Niangua (Etheostoma nianguae) T Sturgeon, gulf (Acipenser oxyrinchus desotoi)
E Darter, Okaloosa (Etheostoma okaloosae) E Sturgeon, pallid (Scaphirhynchus albus)
E Darter, relict (Etheostoma chienense) E Sturgeon, shortnose (Acipenser brevirostrum)
T Darter, slackwater (Etheostoma boschungi) E Sturgeon, white (Acipenser transmontanus)
T Darter, snail (Percina tanasi) E Sucker, June (Chasmistes liorus)
E Darter, vermilion (Etheostoma chermocki) E Sucker, Lost River (Deltistes luxatus)
E Darter, watercress (Etheostoma nuchale) E Sucker, Modoc (Catostomus microps)
E Gambusia, Big Bend (Gambusia gaigei) E Sucker, razorback (Xyrauchen texanus)
E Gambusia, Clear Creek (Gambusia heterochir) T Sucker, Santa Ana (Catostomus santaanae)
E Gambusia, Pecos (Gambusia nobilis) E Sucker, shortnose (Chasmistes brevirostris)
E Gambusia, San Marcos (Gambusia georgei) T Sucker, Warner (Catostomus warnerensis)
E Goby, tidewater (Eucyclogobius newberryi) E Topminnow, Gila (including Yaqui) (Poeciliopsis occidentalis)
E Logperch, Conasauga (Percina jenkinsi) T Trout, Apache (Oncorhynchus apache)
E Logperch, Roanoke (Percina rex) T Trout, bull (Salvelinus confluentus)
T Madtom, Neosho (Noturus placidus) E Trout, Gila (Oncorhynchus gilae)
E Madtom, pygmy (Noturus stanauli) T Trout, greenback cutthroat (Oncorhynchus clarki stomias)
E Madtom, Scioto (Noturus trautmani) T Trout, Lahontan cutthroat (Oncorhynchus clarki henshawi)
E, XN Madtom, smoky (Noturus baileyi) T Trout, Little Kern golden (Oncorhynchus aguabonita whitei)
XN, T Madtom, yellowfin (Noturus flavipinnis) T Trout, Paiute cutthroat (Oncorhynchus clarki seleniris)
T Minnow, Devils River (Dionda diaboli) E, XN Woundfin (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

Endangered species of clams, snails, and crustaceans, February 2004

Status Species name Status Species name
E Acornshell, southern (Epioblasma othcaloogensis) E Ring pink (mussel) (Obovaria retusa)
T Bankclimber, purple (mussel) (Elliptoideus sloatianus) T Slabshell, Chipola (Elliptio chipolaensis)
E, XN Bean, Cumberland (pearlymussel) (Villosa trabalis) E Spinymussel, James (Pleurobema collina)
E Bean, purple (Villosa perpurpurea) E Spinymussel, Tar River (Elliptio steinstansana)
E Blossom, green (pearlymussel) (Epioblasma torulosa gubernaculum) E Stirrupshell (Quadrula stapes)
E, XN Blossom, tubercled (pearlymussel) (Epioblasma torulosa torulosa) E Three-ridge, fat (mussel) (Amblema neislerii)
E, XN Blossom, turgid (pearlymussel) (Epioblasma turgidula) E Wartyback, white (pearlymussel) (Plethobasus cicatricosus)
E, XN Blossom, yellow (pearlymussel) (Epioblasma florentina florentina) E Wedgemussel, dwarf (Alasmidonta heterodon)
E, XN Catspaw (=purple cat's paw pearlymussel) (Epioblasma obliquata obliquata)
E Catspaw, white (pearlymussel) (Epioblasma obliquata perobliqua) Snails
E, XN Clubshell (Pleurobema clava) E Ambersnail, Kanab (Oxyloma haydeni kanabensis)
E Clubshell, black (Pleurobema curtum) E Campeloma, slender (Campeloma decampi)
E Clubshell, ovate (Pleurobema perovatum) E Cavesnail, Tumbling Creek (Antrobia culveri)
E Clubshell, southern (Pleurobema decisum) T Elimia, lacy (snail) (Elimia crenatella)
E, XN Combshell, Cumberlandian (Epioblasma brevidens) E Limpet, Banbury Springs (Lanx sp.)
E Combshell, southern (Epioblasma penita) E Lioplax, cylindrical (snail) (Lioplax cyclostomaformis)
E Combshell, upland (Epioblasma metastriata) E Marstonia, royal (snail) (Pyrgulopsis ogmorhaphe)
E Elktoe, Appalachian (Alasmidonta raveneliana) E Pebblesnail, flat (Lepyrium showalteri)
E Elktoe, Cumberland (Alasmidonta atropurpurea) E, XN Riversnail, Anthony's (Athearnia anthonyi)
E Fanshell (Cyprogenia stegaria) T Rocksnail, painted (Leptoxis taeniata)
T Fatmucket, Arkansas (Lampsilis powelli) E Rocksnail, plicate (Leptoxis plicata)
T Heelsplitter, Alabama (=inflated) (Potamilus inflatus) T Rocksnail, round (Leptoxis ampla)
E Heelsplitter, Carolina (Lasmigona decorata) T Shagreen, Magazine Mountain (Mesodon magazinensis)
E Higgins eye (pearlymussel) (Lampsilis higginsii) E Snail, armored (Pyrgulopsis (Marstonia) pachyta)
E Kidneyshell, triangular (Ptychobranchus greeni) T Snail, Bliss Rapids (Taylorconcha serpenticola)
E, XN Lampmussel, Alabama (Lampsilis virescens) T Snail, Chittenango ovate amber (Succinea chittenangoensis)
E Lilliput, pale (pearlymussel) (Toxolasma cylindrellus) T Snail, flat-spired three-toothed (Triodopsis platysayoides)
E, XN Mapleleaf, winged (mussel) (Quadrula fragosa) E Snail, Iowa Pleistocene (Discus macclintocki)
T Moccasinshell, Alabama (Medionidus acutissimus) E Snail, Morro shoulderband (=Banded dune) (Helminthoglypta walkeriana)
E Moccasinshell, Coosa (Medionidus parvulus) T Snail, Newcomb's (Erinna newcombi)
E Moccasinshell, Gulf (Medionidus penicillatus) T Snail, noonday (Mesodon clarki nantahala)
E Moccasinshell, Ochlockonee (Medionidus simpsonianus) T Snail, painted snake coiled forest (Anguispira picta)
E Monkeyface, Appalachian (pearlymussel) (Quadrula sparsa) E Snail, Snake River physa (Physa natricina)
E, XN Monkeyface, Cumberland (pearlymussel) (Quadrula intermedia) T Snail, Stock Island tree (Orthalicus reses [ not including nesodryas])
T Mucket, orangenacre (Lampsilis perovalis) E Snail, tulotoma (Tulotoma magnifica)
E Mucket, pink (pearlymussel) (Lampsilis abrupta) E Snail, Utah valvata (Valvata utahensis)
E, XN Mussel, oyster (Epioblasma capsaeformis) E Snail, Virginia fringed mountain (Polygyriscus virginianus)
E Mussel, scaleshell (Leptodea leptodon) E Snails, Oahu tree (Achatinella ssp.)
T Pearlshell, Louisiana (Margaritifera hembeli) E Springsnail, Alamosa (Tryonia alamosae)
E, XN Pearlymussel, birdwing (Conradilla caelata) E Springsnail, Bruneau Hot (Pyrgulopsis bruneauensis)
E, XN Pearlymussel, cracking (Hemistena lata) E Springsnail, Idaho (Fontelicella idahoensis)
E Pearlymussel, Curtis (Epioblasma florentina curtisii) Crustaceans
E, XN Pearlymussel, dromedary (Dromus dromas)
E Pearlymussel, littlewing (Pegias fabula) E Amphipod, Hay's Spring (Stygobromus hayi)
E Pigtoe, Cumberland (Pleurobema gibberum) E Amphipod, Illinois cave (Gammarus acherondytes)
E Pigtoe, dark (Pleurobema furvum) E Amphipod, Kauai cave (Spelaeorchestia koloana)
E, XN Pigtoe, finerayed (Fusconaia cuneolus) E Amphipod, Peck's cave (Stygobromus [=Stygonectes] pecki)
E Pigtoe, flat (Pleurobema marshalli) E Crayfish, cave (Cambarus aculabrum)
E Pigtoe, heavy (Pleurobema taitianum) E Crayfish, cave (Cambarus zophonastes)
E Pigtoe, oval (Pleurobema pyriforme) E Crayfish, Nashville (Orconectes shoupi)
E Pigtoe, rough (Pleurobema plenum) E Crayfish, Shasta (Pacifastacus fortis)
E, XN Pigtoe, shiny (Fusconaia cor) E Fairy shrimp, Conservancy (Branchinecta conservatio)
E Pigtoe, southern (Pleurobema georgianum) E Fairy shrimp, longhorn (Branchinecta longiantenna)
E Pimpleback, orangefoot (pearlymussel) (Plethobasus cooperianus) E Fairy shrimp, Riverside (Streptocephalus woottoni)
E Pocketbook, fat (Potamilus capax) E Fairy shrimp, San Diego (Branchinecta sandiegonensis)
T Pocketbook, finelined (Lampsilis altilis) T Fairy shrimp, vernal pool (Branchinecta lynchi)
E Pocketbook, Ouachita rock (Arkansia wheeleri) E Isopod, Lee County cave (Lirceus usdagalun)
E Pocketbook, shiny-rayed (Lampsilis subangulata) T Isopod, Madison Cave (Antrolana lira)
E Pocketbook, speckled (Lampsilis streckeri) E Isopod, Socorro (Thermosphaeroma thermophilus)
E Rabbitsfoot, rough (Quadrula cylindrica strigillata) E Shrimp, Alabama cave (Palaemonias alabamae)
E Riffleshell, northern (Epioblasma torulosa rangiana) E Shrimp, California freshwater (Syncaris pacifica)
E Riffleshell, tan (Epioblasma florentina walkeri (=E. walkeri)) E Shrimp, Kentucky cave (Palaemonias ganteri)
T Shrimp, Squirrel Chimney Cave (Palaemonetes cummingi)
E Tadpole 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]

Evolutionarily significant units (ESUs) of endangered or threated chinook salmon, 2002

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.

Trends in the abundance of endangered or threatened chinook salmon ESUs, 1980–2002


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

Paiute cutthroat trout recovery plan overview

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):
Year Action 1 Action 2 Action 3 Action 4 Action 5 Action 6
2004 38 2 19.73 2.9
2005 31 49.5 31.23 2.9
2006 31 51.1 38.31 2.9
2007 8 37 20.73 2.9
2008 8 4.08 20.73 0.4
2009 8 3.6 23.81
2010 8 2 20.73 6
2011 8 2 20.73 6
2012 3.6 20.81
2013 4.08 18.73
Total 100 40 158.95 235.5 12 12
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 FIGURE 5.16
Historical Paiute cutthroat trout population estimates from the Upper Fish Valley reach of Silver King Creek, 1964–2001
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

Summary of threats and recommended recovery actions for the Paiute cutthroat trout

Listing factor Threat
A Streambank degradation from recreational activities
A Streambank degradation from cattle grazing
A Degradation of water quality and spawning substrates by beavers
B Unregulated angling
C Natural predators [not currently significant]
C Fungal infections
D Potential budgetary constraints on agency commitment to recovery actions
E Hybridization and competition with introduced trout
E Need for fish barriers to prevent upstream migration of introduced trout
E Human introduction of trout
E Vulnerability 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 FIGURE 5.17
Manatees, also known as "sea cows," are endangered throughout their range in Florida and the southeastern United States. (Corbis/Brandon D. Cole)
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

Marine Mammal Authorization Program mortality/injury report, 2000

Species Fisheries Injured Killed
Gray whale trap/crab 0 1
Pilot whale Atlantic Ocean, Caribbean, Gulf of Mexico large pelagics longline 3 0
Bottlenose dolphin U.S. Mid-Atlantic coastal gillnet 0 2
Gulf of Mexico menhaden purse seine 1 4
Common dolphin CA/OR thresher shark/swordfish drift gillnet 3 15
Gulf of Mexico menhaden purse seine 0 1
Atlantic squid, mackerel, butterfish trawl fishery 0 5
Harbor porpoise AK Peninsula/Aleutian Islands salmon set gillnet 1 0
Northeast sink gillnet 0 3
Humpback whale Northeast sink gillnet 0 1
CA/OR thresher shark/swordfish drift gillnet 1 0
Prince William Sound salmon drift gillnet 1 0
Pacific white-sided dolphin CA/OR thresher shark/swordfish drift gillnet 0 11
Risso's dolphin CA/OR thresher shark/swordfish drift gillnet 0 2
Northeast sink gillnet 0 1
Unidentified small cetacean CA/OR thresher shark/swordfish drift gillnet 4 1
Atlantic Ocean, Caribbean, Gulf of Mexico large pelagics longline 1 0
California sea lion CA/OR thresher shark/swordfish drift gillnet 0 23
CA angel shark/halibut & other species large mesh (3.5 inch) set gillnet 0 25
Steller sea lion AK Bering Sea & Aleutian Islands groundfish trawl 0 5
Harbor seal CA angel shark/halibut & other species large mesh (3.5 inch) set gillnet 0 3
Northeast sink gillnet 0 3
Northern elephant seal CA angel shark/halibut & other species large mesh (3.5 inch) set gillnet 0 1
CA/OR thresher shark/swordfish drift gillnet 1 1
Grey seal Northeast sink gillnet 0 4
Unidentified seal AK Bering Sea & Aleutian Islands groundfish trawl 0 1
CA/OR thresher shark/swordfish drift gillnet 0 1
Walrus AK Bering Sea & Aleutian Islands groundfish trawl 0 1
Total 16 115
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.

Aquatic Species and Their Environments - Laws Protecting Aquatic Species [next] [back] Aquatic Species and Their Environments - Unwelcome Guests—aquatic Invasive Species

User Comments

Your email address will be altered so spam harvesting bots can't read it easily.
Hide my email completely instead?

Cancel or