Chapter 6
Fish, Clams, Snails, and Crustaceans

Fish, clams, snails, and crustaceans are aquatic creatures. Fish are vertebrates, meaning they have an internal skeleton made of bone or cartilage. Clams, snails, and crustaceans are invertebrates.

FISH

Fish are cold-blooded vertebrates with fins. They occur in nearly all permanent water environments, from deep oceans to remote alpine lakes and desert springs. Marine fish inhabit the salty waters of oceans and seas. Freshwater fish inhabit inland rivers, lakes, and ponds. Anadromous fish are born in freshwater, migrate to the ocean to spend their adulthood, and then return to freshwater to spawn.

Fish are the most diverse vertebrate group on the planet and include thousands of different species. The largest known fish are the whale sharks, which can grow to be in excess of fifty feet long and weigh several tons. At the other end of the spectrum is Paedocypris progenetica, a tiny fish discovered in Sumatra, Indonesia, that is less than one-third of an inch in length.

FishBase (http://filaman.ifm-geomar.de/home.htm) is a comprehensive online database of scientific information about fish. It was developed by the WorldFish Center of Malaysia in collaboration with the Food and Agriculture Organization of the United Nations and is supported by many government and research institutions. As of February 2006 FishBase contains information on 29,300 fish species around the world, a number it calls "practically all fish species known to science." Scientists report that only a small fraction of these species have been assessed for their conservation status.

The U.S. Fish and Wildlife Service (FWS) listed a total of eighty-five endangered and forty-three threatened fish species in the United States as of February 2006. Nearly $475 million was spent under the Endangered Species Act (ESA) during fiscal year 2004 on imperiled fish.

General Threats to Fish

Fish species have become endangered and threatened in the United States for a variety of reasons, both natural and anthropogenic (caused by humans). Some scientists believe that natural threats, such as disease, have been aggravated by human actions that stress fish populations. Dams and other structures used for power generation, flood control, irrigation, and navigation have dramatically changed water flow patterns in many rivers. These impediments disrupt migration patterns and affect water temperature and quality. Likewise, dredging of river and stream beds to produce channels and filling of wetlands and swamps have changed water habitats.

Large nonnative fish species introduced to water bodies to improve recreational fishing prey on small imperiled fish and compete with large imperiled fish for food and space. Crowding also leads to uncharacteristic mating between fish species. This phenomenon results in hybrid offspring, some of which are sterile (cannot reproduce).

Many river and stream banks and adjacent lands have been stripped of vegetation by timber harvesting, crop growing, and excessive grazing of livestock. This eliminates habitat for insects and other tiny creatures that serve as foodstuff for fish. It also aggravates erosion problems and allows large amounts of dirt and silt to enter the water, effectively smothering the fish. In agricultural areas there is runoff of manure, fertilizers, and pesticides. Discharges of sewage and storm water contain high levels of biological contaminants. Industrial pollution introduces metal and organic chemicals to water bodies. Although not typically lethal, chemical and biological pollutants stress the immune systems of fish, placing them at greater risk of disease.

Imperiled Freshwater Fish

Freshwater fish listed under the Endangered Species Act are under the jurisdiction of the U.S. Fish and Wildlife Service. They include a wide variety of species and are found all over the country. The U.S. Geological Survey (USGS) estimates that the United States contains approximately 800 native freshwater species. Although most of these species are found in the eastern part of the country, the highest percentages of imperiled fish species are in the western states. According to the USGS this is because aquatic ecosystems in the western United States, particularly in the Southwest, have very high rates of endemism (that is, species found there are particular to that location).

Table 6.1 provides information about the freshwater fish species listed as endangered or threatened under the ESA as of February 2006. Most of the species have recovery plans in place. In general, imperiled freshwater fish are small in size and associated with flowing (lotic) waters, such as rivers and streams, rather than still (lentic) waters, such as lakes and ponds. Nearly half of the listed freshwater fish fall into four species groups: darters, chubs, daces, and shiners.

Table 6.2 shows the ten freshwater species with the highest expenditures under the ESA during fiscal year 2004. More than $45 million was spent on only two of the fish, the bull trout ($32.6 million) and the pallid sturgeon ($13.4 million).

BULL TROUT

Bull trout are relatively large fish that live in streams, lakes, and rivers. They can grow to weigh more than twenty pounds; however, those that inhabit small streams seldom exceed four pounds in weight. Bull trout are members of the char subgroup of the salmon family (Salmonidae). (See Figure 6.1.) Their backs are dark in color (green to brown) with small light-colored spots (crimson to yellow), while their undersides are pale. The fish prefer very cold and clean inland waters in the Northwest.

Historically bull trout were found throughout much of the northwestern United States and as far north as Alaska. Large populations have disappeared from major rivers, leaving mostly isolated pockets of smaller-sized fish in headwater streams. A variety of factors have contributed to the decline of the bull trout. The species is very sensitive to changes in water temperature and purity. Its survival is threatened by water pollution, degraded habitat, and dams and other diversion structures. In addition, introduction of a nonnative game fish called brook trout has been devastating. The two species are able to mate, but produce mostly sterile offspring—a genetic dead-end for the imperiled bull trout.

The legal history of the bull trout is extensive. In 1992 three environmental groups petitioned the U.S. Fish and Wildlife Service to list the fish as an endangered species under the ESA. In 1993 the agency concluded that listing for the species was warranted, but low in priority compared to other work of the FWS. This set off a long series of court battles that culminated in 1999 when all bull trout in the coterminous United States were listed as threatened under the ESA. In 2001 two of the original petitioners (Alliance for the Wild Rockies, Inc. and Friends of the Wild Swan, Inc.) filed a lawsuit against the FWS for failing to designate critical habitat for the bull trout. A settlement was reached in 2002. In September 2005 the FWS designated critical habitat for the bull trout as follows:

• Idaho—294 stream miles and 50,627 acres of lakes or reservoirs
• Montana—1,058 stream miles and 31,916 acres of lakes or reservoirs
• Oregon—939 stream miles and 27,322 acres of lakes or reservoirs
• Oregon/Idaho—17 stream miles
• Washington—1,519 stream miles, 33,353 acres of lakes or reservoirs, and 985 miles of marine shoreline

The shaded river basins in Figure 6.2 were designated as critical habitat. The unshaded river basins were considered, but excluded from the final ruling.

PALLID STURGEON

The pallid sturgeon is a unique and rare freshwater fish. The Fish and Wildlife Service calls it "the swimming dinosaur." It is descended from fishes that were common more than fifty million years ago. The pallid sturgeon has a long flat snout and a slender body that ends with a pronounced tail fin. (See Figure 6.3.) Adults range in size from three to five feet and typically weigh twenty-five to fifty pounds. The fish is a bottom-feeder and prefers large rivers of relatively warm free-flowing water with high turbidity (high mud content).

Historically the pallid sturgeon was found throughout the Mississippi and Missouri River systems from Montana and North Dakota south to the Gulf of Mexico. In the early 1900s specimens as large as eighty-five pounds and six feet long were reported. Over the next century the fish virtually disappeared. In 1990 it was listed under the ESA as endangered. Three years later a recovery plan was published by the FWS. The recovery plan blames human destruction and modification of habitat as the primary cause for the pallid sturgeon's decline.

Figure 6.4 shows the consequences of human alteration on the main stem of the Missouri River, one of the last known habitats of the fish. Forty percent of the river has been channelized (reconfigured to flow in a restricted path). Another 36% has been removed from contention due to construction of earthen dams during the early decades of the 1900s. The last 24% of river habitat has

experienced changes in water flows due to dam operations. The middle portion of the Mississippi River has also been extensively channelized and diked to prevent flooding and improve barge navigation.

Pallid sturgeons are believed to be very sensitive to changes in the velocity and volume of river flows. They are nearly blind and forage along muddy river bottoms feeding on tiny fish and other creatures that prefer turbid waters. Dams and channelization have reduced erosion of riverbank soil into the Missouri and Mississippi Rivers. This has given other fish species with better eyesight an advantage over the pallid sturgeon at finding small prey. In addition, mating between the pallid sturgeon and the shovelnose sturgeon in the lower Mississippi River has produced a population of hybrid sturgeon that is thriving compared to their imperiled parents.

All of these factors combine to provide a bleak outlook for the future of the pallid sturgeon. The Fish and Wildlife Service recovery plan notes that "it is unlikely that successfully reproducing populations of pallid sturgeon can be recovered without restoring the habitat elements (morphology, hydrology, temperature regime, cover, and sediment/organic matter transport) of the Missouri and Mississippi Rivers necessary for the species continued survival."

Herb Bollig and George Jordan reported in "U.S. Fish and Wildlife Service Stocks Endangered Pallid Sturgeons in Missouri River" (September 2005, http://mountain-prairie.fws.gov/PRESSREL/05-62.htm) that since 1994 more than 100,000 pallid sturgeons have been bred in captivity and placed in river waters in the states of Montana, North Dakota, Nebraska, Iowa, Kansa, Missouri, and Louisiana. The fish are spawned and reared at the agency's Gavins Point National Fish Hatchery near Yankton, South Dakota. This is the only hatchery in the nation engaged in breeding the pallid sturgeon. During 2004 the facility underwent a major construction program

that included the addition of new specially designed tanks for the endangered fish. Despite the success of the breeding operation, the FWS notes that "this stocking effort alone will not recover the species." Habitat improvement is the only step that biologists believe will save the pallid sturgeon from extinction.

In July 2005 the FWS initiated a five-year status review for the pallid sturgeon. The agency will collect scientific and commercial data that have become available since the species was listed as endangered in 1990. This information will be used to determine if the listing is still appropriate.

RECOVERY PLANS FOR FRESHWATER FISH

As shown in Table 6.1 there were recovery plans for nearly ninety populations or species of freshwater fish as of February 2006. Most of the plans have been finalized. Copies of the plans can be accessed from the Web site of the Threatened and Endangered Species System (TESS) of the U.S. Fish and Wildlife Service (http://ecos.fws.gov/tess_public/TESSWebpageRecovery?sort=1).

Imperiled Marine and Anadromous Fish

Marine and anadromous fish primarily inhabit salty waters. There were only nine such species listed under the Endangered Species Act as of February 2006. They are under the jurisdiction of the National Marine Fisheries Service. Listed species found in the Pacific Northwest and their current status (E—Endangered and T—Threatened) are as follows:

• Chinook salmon—E, T
• Chum salmon—T
• Coho salmon—E, T
• Sockeye salmon—E, T
• Steelhead—E, T

In addition there is an endangered species of Atlantic salmon found in the gulf of Maine. Imperiled non-salmonid species are gulf sturgeon (threatened), shortnose sturgeon (endangered), and smalltooth sawfish (endangered).

More than $79 million was spent under the ESA on marine and anadromous fish in 2004. Expenditures are broken down by species in Table 6.3.

PACIFIC SALMONIDS

Pacific salmonids are found in waters of the northwestern United States and belong to the genus Oncorhynchus. There are five species of Pacific salmon: chinook, chum, coho, pink, and sockeye. All but the pink salmon are listed under the ESA as endangered and/or threatened. As shown in Table 2.8 in Chapter 2, four of the ten species with the highest expenditures under the ESA in fiscal year 2004 were Pacific salmonids.

Pacific salmon pose unique protection challenges because they are anadromous. Salmon eggs (or roe) are laid in the bottom gravel of cold freshwater streams where they incubate for five to ten weeks. Each egg ranges in size from one-quarter to one-half inch in size, depending on species. The eggs hatch to release baby fish (or alevin) that are called fry as they mature. Once a fry reaches about three inches in length it is called a finger-ling. This typically takes less than a year.

At some point during their first two years the young salmon (now called smolts) migrate downstream to the ocean. There they spend several months or years of their adulthood. When they reach sexual maturity males and females journey back to the streams where they were born to mate and deposit eggs. This is called spawning. Pacific salmon make the round-trip only once. They expend all their energy swimming back upstream and die soon after the eggs are laid and fertilized. Their upstream habitats can be hundreds and even thousands of miles away from their ocean habitats. It is a long and dangerous journey both ways.

Predator fish and birds eat salmon fry, fingerlings, and smolts as they make their way to the ocean. Bears, birds, marine mammals, and humans prey on the adult fish as they migrate upstream. Waterfalls, rapids, dams and other water diversions pose tremendous obstacles to Pacific salmon as they try to travel across long distances.

Salmon heading to the same general location travel upstream in groups called stocks or runs. Stocks migrate at different times of the year depending on geographical and genetic factors. Figure 6.5 illustrates the life cycle of a stock that migrates upstream from late summer through

early fall. During its lifetime a Pacific salmon is exposed to three different water environments: freshwater streams and rivers, estuaries (areas where freshwater and saltwater meet), and the ocean.

Chinook salmon are the largest of the Pacific salmonids, averaging about twenty-five pounds in adulthood. (See Figure 6.6.) They spend two to seven years in the ocean and travel up to 2,500 miles from their home streams. Coho, sockeye, and chum salmon adults average approximately ten to twelve pounds.

The National Marine Fisheries Service estimates that as many as sixteen million salmon per year migrated upstream in waters of the northwestern United States prior to the arrival of European settlers. Extensive fishing and canning operations quickly decimated the salmon population. As early as 1893 federal officials warned that the future of salmon fisheries had a "disastrous outlook." During the 1890s hatcheries began operating and stocking rivers and streams with "farm-raised" salmon. Over the next century salmon populations were further stressed as natural river flows were dramatically altered with dams, navigational structures, and irrigation systems. Figure 6.7 shows the distribution of salmon hatcheries and dams in the Columbia River basin of the Pacific Northwest. As of 2003 there were twenty-three major dams on mainstem rivers in the basin, more than 300 smaller dams on tributaries, and more than eighty hatcheries.

Endangered and threatened salmon are identified by their water of origin and, in most cases, by their upstream migration season. In 1990 the winter-run stock of Chinook salmon from the Sacramento River was designated as threatened under the ESA, the first Pacific salmon to be listed. It was reclassified to endangered four years later. During the 1990s and early 2000s the NMFS identified thirty-five Evolutionarily Significant Units (ESUs) of Pacific salmonids and listed sixteen of them as endangered or threatened. (See Table 6.4 for the status of these fish as of January 2006.) Two ESUs are "Species of Concern" meaning that the agency has some concerns regarding threats to these species, but lacks sufficient information indicating the need to list them under the ESA.

Biologists blame four main threats, called "the four H's" for the imperiled state of Pacific salmonids:

• Habitat degradation—channelization, dredging, water withdrawals for irrigation, wetland losses, and diking have changed river, stream, and estuary environments.
• Harvesting levels—Over fishing for more than a century has decimated salmon populations.
• Hydropower—Impassable dams have rendered some historical habitat unreachable by salmon. Most modern dams have fish ladders, stepping-stone waterfalls that allow salmon a path up and over the dams. However, all dams affect water temperature, flows, and quality.
• Hatcheries—Biologists fear that hatchery releases overburden estuaries with too many competing fish at the same time.

In addition to these threats, scientists believe that climate changes and the presence of nonnative aquatic species are detrimental to salmon populations.

STEELHEAD

Steelhead are members of the Oncorhynchus genus and have the scientific name Oncorhynchus mykiss. Freshwater steelhead are called rainbow trout. Anadromous steelhead are also trout, but they are associated with salmon due to similarities in habitat and behavior. Steelhead are found in the Pacific Northwest and are anadromous like salmon with two major differences: steelhead migrate individually, rather than in groups, and can spawn numerous times, not just once.

As of January 2006 the National Marine Fisheries Service had identified fifteen distinct population segments (DPSs) of steelhead as shown in Table 6.5. Ten of these DPSs are listed under the ESA as endangered or threatened. In addition, there is one DPS classified as a "Species of Concern," and a DPS in Washington's Puget Sound is undergoing status review. Table 6.3 indicates that $13.4 million was spent on steelhead under the ESA during fiscal year 2004.

Steelhead face the same threats as Pacific salmon—habitat loss and alteration, over-harvesting, dams and other water obstacles, and competition with hatchery fish.

RECOVERY PLANS FOR MARINE AND ANADROMOUS FISH

Final recovery plans have been published by the NMFS for the shortnose sturgeon (1998), gulf sturgeon (2005), and Atlantic salmon (2005). Copies of the recovery plans are available at the Web site of the NMFS Office of Protected Resources (http://www.nmfs.noaa.gov/pr/recovery/).

In July 2005 the National Marine Fisheries Service announced its intention to develop recovery plans for sixteen populations of Pacific salmon and steelhead found in Washington, Oregon, and Idaho that are listed as endangered or threatened under the Endangered Species Act. The agency will collect data and information from state, tribal, and local entities regarding the status and threats associated with these fish. The first proposed recovery plan was released by the NMFS for public comment in late December 2005. It covered the Puget Sound area. Plans for populations in other areas were under development in 2006.

Imperiled Fish around the World

The International Union for the Conservation of Nature and Natural Resources (IUCN; now known as the World Conservation Union) listed 800 species of fish as threatened in its 2004 Red List of Threatened Species, nearly half of the 1,721 species evaluated. However, the IUCN notes that there are in excess of 28,000 known fish species. It is expected that many more fish species will be listed in the future as more evaluations are completed.

As of January 2006 the United States listed eleven foreign species of fish as endangered. The endangered fish and their primary habitat areas are as follows:

• Ala balik (trout)—Turkey
• Ayumodoki (loach)—Japan
• Mexican blindcat (catfish)—Mexico
• Asian bonytongue—Indonesia, Malaysia, Thailand
• Thailand catfish—Thailand
• Thailand giant catfish—Thailand
• Cicek (minnow)—Turkey
• Nekogigi (catfish)—Japan
• Miyako Tango (Tokyo bitterling)—Japan
• Ikan Temoleh (minnow)—Cambodia, Laos, Malaysia, Thailand, and Vietnam
• Totoaba (seatrout or weakfish)—Mexico (Gulf of California)

In addition, there is one foreign fish listed under the ESA as threatened—the beluga sturgeon, which is found in the Caspian and Black Seas and the rivers that drain to them.

Beluga Sturgeon

The beluga sturgeon (Huso huso) is in danger because it is the source of beluga caviar, one of the most coveted luxury foods in the world. Caviar is the processed and salted eggs of large fish. These eggs are called roe while they are still enclosed in the ovarian membrane of the female fish. The sturgeon must be killed to extract its roe. Felicity Barringer and Florence Fabricant reported in the New York Times that beluga caviar sold for $200 an ounce in the United States, and the nation consumed 60% of the world's supply of the delicacy ("In Conservation Effort, U.S. Bans Caspian Beluga Caviar," September 30, 2005).

In 2000 a coalition of U.S. environmental groups petitioned the U.S. Fish and Wildlife Service to list the beluga sturgeon as endangered under the ESA. The coalition, named Caviar Emptor (http://www.caviaremptor.org), claimed that the population of the species had declined by 90% between 1980 and 2000 due to overfishing. In 2002 the Natural Resources Defense Council sued the FWS, because the agency had not responded to the petition. Two years later the beluga sturgeon was listed as threatened, rather than endangered, under

the ESA. Environmentalists were highly critical of the decision.

In March 2005 the FWS imposed conditions that limited imports and domestic trade in sturgeon products. The agency gave importing nations six months to provide information regarding their conservation measures to prevent overfishing of the species. In September 2005 the FWS announced that it had not received the required information from five countries around the Caspian Sea. A ban was imposed on imports of beluga sturgeon products from Azerbaijan, Iran, Kazakhstan, the Russian Federation, and Turkmenistan. The ban can be lifted in the future if the proper information is submitted to the FWS. Conservation information was submitted by Black Sea countries and was being reviewed by the agency in 2006.

CLAMS, SNAILS, AND CRUSTACEANS

Clams, snails, and crustaceans are invertebrates. Clams and snails are in the phylum Mollusca. Mollusks have soft bodies usually enclosed in a thin hard shell made of calcium. The U.S. Fish and Wildlife Service uses the generic term "clam" to refer to clams and mussels, but there are physical and reproductive differences between the two creatures. In general, mussels are larger than clams and have an oblong lopsided shell, as opposed to the round symmetrical shell of the clam.

Crustaceans are a large class of creatures with a hard exoskeleton, appendages, and antennae. This class includes lobsters, shrimps, and crabs.

As shown in Table 1.2 in Chapter 1, there were 131 species of clams (including mussels), snails, and

crustaceans listed under the ESA as endangered or threatened as of February 2006. Most imperiled are clams/mussels (seventy U.S. species and two foreign species). There were thirty-six U.S. species of snails and one foreign species listed under the ESA. Listed crustaceans include twenty-two U.S. species. Table 6.6 shows the ten clam, snail, and crustacean entities with the highest expenditures under the ESA during fiscal year 2004.

The vast majority of imperiled clams/mussels, snails, and crustaceans in the United States are freshwater species that inhabit inland rivers, primarily in the Southeast.

Freshwater Mussels in the United States

Mussels are bivalved (two-shelled) creatures encased in hard hinged shells made of calcium. The freshwater species can grow to be up to six inches in length. The United States, with nearly 300 species, has the greatest diversity of freshwater mussels in the world. According to the U.S. Geological Survey (USGS) (March 2006, http://cars.er.usgs.gov/Southeastern_Aquatic_Fauna/Freshwater_Mussels/freshwater_mussels.html), approximately 90% of these creatures live in southeastern states. Most of them are found burrowed into the sand and gravel beds of rivers and streams making up the Mississippi River system. Mussels have a foot-like appendage that acts like an anchor to hold them in place. They can use this appendage to move themselves very slowly over small distances. Mussels tend to congregate in large groups called colonies.

Mussels are filter-feeders. They have a siphoning system that sucks in food and oxygen from the water. Their gills can filter impurities out of the water. Thus, mussels are tiny natural water purifiers.

Most mussel species have a unique way of spreading their offspring. A female mussel can produce several thousand eggs in a year. After the eggs are fertilized they develop into larva and are released. The larva latch on to the fins or gills of passing fish and they stay there until they have grown into baby clams. At that point they turn loose of the fish and drop to the river bottom. The larvae are called glochidia. It is believed that glochidia are harmless to the fish upon which they hitchhike. This parasitic relationship allows mussels to spread and distribute beyond their usual range.

MUSSEL DECLINES

Unfortunately, many freshwater mussel populations are in danger of extinction. Information about the seventy U.S. species of endangered and threatened clams and mussels as of February 2006 is shown in Table 6.7. Nearly $7.3 million was spent under the ESA during fiscal year 2004 to protect clams and mussels. Just over $1.3 million of this money was devoted to the Higgins' eye mussel, a species found in the Midwest.

The decline of freshwater mussels began in the 1800s. Many of the creatures have an interior shell surface with a pearl-like sheen. These pearlymussels were in great demand as a source of buttons for clothing until the invention of plastic. Collectors also killed many mussels by prying them open looking for pearls. Until the 1990s mussel shells were ground up and used in the oyster pearl industry. Another cause for decline has been habitat disturbance, especially water pollution and the modification of aquatic habitats by dams. The invasive zebra mussel has also harmed native freshwater mussel species by competing with them for food and other resources.

ZEBRA MUSSELS—AN INFESTATION

In 1988 an unwelcome visitor was discovered in the waters of Lake St. Clair, Michigan—a zebra mussel. The zebra mussel is native to eastern Europe. It is smaller than the freshwater mussels found in the United States and has a different method for spreading its young. The larva of zebra musses do not require a fish host to develop into babies. They can attach to any hard surface under the water. This allows zebra mussels to spread much easier and quicker than their American counterparts.

It is believed that the first zebra mussels migrated to the United States in the ballast water of ships. This is water held in large tanks below deck to improve the stability and control of ships. Ballast water is pumped in and out as needed during a journey. Zebra mussels have also been found clinging to the hulls of small fishing and recreation boats. These boats are hauled overland on trailers, and this allows the creatures to travel great distances between inland water bodies.

Figure 6.8 shows a USGS map of zebra mussel distribution around the country as of June 2005. Since 1988 this invasive species has spread dramatically from the Great Lakes south to the Gulf of Mexico and east to New England. Zebra mussels have been found on boat hulls as far west as California. Throughout waterways in the Midwest, colonies of zebra mussels have clogged pipes and other structures used for municipal and industrial water supply. In addition, the pests have significantly degraded native mussel colonies by competing for available food, space, and resources.

HIGGINS' EYE PEARLYMUSSEL

Figure 6.9 illustrates Higgins' eye, a species of freshwater pearlymussel native to the United States. These mussels are found in the waters of Iowa, Illinois, Minnesota, Missouri, Nebraska, and Wisconsin. The species was named after its discoverer, Frank Higgins, who found some of the mussels in the Mississippi River near Muscatine, Iowa, during the mid-1800s. Over the next few decades Muscatine developed a thriving pearl-button industry that lasted into the 1940s. Higgins' eye was also harvested for the commercial pearl industry.

In 1976 the Higgins' eye pearlymussel was listed as an endangered species under the ESA. More than a century of scavenging by humans had severely depleted the species. Dams, navigational structures, and water quality problems in the upper Mississippi river system were contributing factors to its decline. In 1983 the FWS published its first recovery plan for the Higgins' eye. The plan identified areas deemed essential habitat for the species and called for limits on construction and harvesting in these areas. Since 2000 scientists have collected and relocated hundreds of Higgins' eye mussels. Fish raised in hatcheries have been artificially infested with glochidia and released into rivers to enhance the spread of the mussel.

In 2004 a revised recovery plan was issued for the Higgins' eye pearlymussel. The new plan examines more recent threats to species survival, primarily the pervasive spread of zebra mussels. It acknowledges that there is no currently feasible way to eliminate zebra mussels to the extent needed to benefit the Higgins' eye. Instead, the plan focuses on development of methods to prevent new zebra mussel infestations and working to lessen the impacts of already infested populations.

CLAM/MUSSEL RECOVERY PLANS

All seventy species of clams and mussels listed under the Endangered Species Act as of February 2006 have recovery plans in draft or final form, as shown in Table 6.7. Conservation efforts for freshwater mussels include the captive breeding and reintroduction of some species, as well as measures to restore damaged habitats.

Snails

Snails belong to the class Gastropoda of mollusks. Snails typically have an external spiral-shaped shell and a distinct head that includes sensory organs. Snails inhabit terrestrial (land), marine, and freshwater

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As of February 2006 there were thirty-six U.S. species of snails and one foreign species listed under the ESA. (See Table 6.8 for a list of the U.S. species). Snails are found throughout the United States. Most imperiled species are located in western states (including Hawaii) and the Southeast (primarily Alabama). Nearly $2.4 million was spent under the ESA during fiscal year 2004 to conserve snail populations in the United States. Almost half of this money was devoted to only two species—Oahu tree snails ($613,532) and Utah valvata snails ($481,764).

OAHU TREE SNAILS

Oahu tree snails belong to the genus Achatinella and are endemic to the Oahu island of Hawaii. All forty-one species in the genus are imperiled and are collectively known as Oahu tree snails. These snails were listed as endangered under the ESA in 1981. The snails live in mountainous forests and shrublands and feed on fungi growing on the leaves of native plants. The spread of nonnative vegetation and invasive carnivorous (meat-eating) snails has seriously depleted populations of Oahu tree snails. They are also preyed upon by rats.

In 1992 the FWS released a final recovery plan for the surviving species of Achatinella in Oahu. The plan designated areas of essential habitat and called for captive propagation of the snails.

UTAH VALVATA SNAILS

Utah valvata snails were listed as endangered under the ESA in 1992. They are one of five species known as the Snake River snails that inhabit the middle portion of the Snake River in southern Idaho. All five species require cold, clean flowing water with high oxygen levels and low turbidity (suspended sediment) content. Unfortunately their habitat has been changed considerably over the past few decades by the construction of dams on the river for production of hydroelectric power. These dams have altered the flow and temperature of the river waters. Surviving Utah valvata snails are found in the mainstem of the Snake River and in tributaries fed by cold-water springs.

A recovery plan for the endangered snail has been in effect since 1995. The plan notes that the Utah valvata snail has a high degree of threat and a low degree of recovery potential. Restoration of habitat and water quality is indicated as the only means for saving the snail from extinction.

In late 2003 Utah valvata snails were discovered on a bridge being demolished near Firth, Idaho. Prior to that that time the species had not been found that far south in the Snake River. The Idaho Transportation Department suspended the demolition project so that biologists could conduct a survey of the snails. In 2004 the FWS announced that bridge removal could continue because it did not pose a threat to the survival of the species at that location. However, the discovery of the snails is expected to affect other construction projects planned for that part of the river.

RECOVERY PLANS FOR SNAILS

Table 6.8 lists the snail species for which recovery plans have been published as of February 2006. Two of the species that do not have plans—Pecos assiminea snails and Roswell springs-nails—were listed under the ESA during 2005. The white abalone snail is under the jurisdiction of the National Marine Fisheries Service. It is a marine snail that inhabits deep waters off the coast of Southern California.

Crustaceans

Crustaceans are a large class of mandibulate (jawed) creatures in the phylum Arthropoda. They are mostly aquatic and inhabit marine and fresh waters. As of February 2006 there were twenty-two U.S. species listed as endangered or threatened under the Endangered Species Act as shown in Table 6.9. They are found throughout the United States. However, California is home to more imperiled crustacean species than any other state.

More than $2.8 million was spent under the ESA during fiscal year 2004 on endangered and threatened crustaceans. Just over $1 million of these expenditures was devoted to the vernal pool fairy shrimp.

VERNAL POOL FAIRY SHRIMP

The vernal pool fairy shrimp was listed under the ESA as threatened in 1994. It is found in California and Oregon. Vernal is from the Latin word for "spring." This species inhabits temporary small ponds and pools of water that appear in the springtime and dry up after a time. The shrimp lay their eggs in these pools when they contain water. The eggs can go dormant in the dirt when the pools become dry. Baby shrimp hatch only when exposed to water at less than approximately 50° Fahrenheit. Adults typically reach 0.4 to 1 inch in length. The shrimp have a lifetime of two to five months.

In 2003 critical habitat was designated for the vernal pool fairy shrimp along with several other species of vernal pool shrimp. During 2004 a draft recovery plan was issued by the U.S. Fish and Wildlife Service for dozens of imperiled plant and animal species that inhabit vernal pool ecosystems in California and southern Oregon. The plan notes that vernal pool life forms are threatened by urban and agricultural development and invasion of nonnative species. The recovery of vernal pool species will require an ecosystem-wide approach. The FWS proposes establishing conservation areas and reserves to protect primary vernal pool habitat.

CRUSTACEAN RECOVERY PLANS

As shown in Table 6.9 nearly all endangered and threatened species of crustaceans found in the United States had recovery plans as of February 2006. Most plans were in final form. Two listed species (Hay's spring amphipod and squirrel chimney cave shrimp) are exempt from the requirement for a recovery plan.

Imperiled Mollusks and Crustaceans around the World

The IUCN listed 974 species of mollusks and 429 species of crustaceans as threatened in its 2004 IUCN Red List of Threatened Species (2004, http://www.redlist.org/). For mollusks, this number comprises 45% of the 2,163 species evaluated. The IUCN reports that approximately 70,000 mollusk species are known. Only 498 crustacean species were evaluated for the 2004 report. Threatened species comprise 86% of this total. However, the IUCN notes that there are approximately 40,000 known species of crustaceans.