Crayfish Biodiversity and Conservation - Publications and by zhangsshaohui123


									                                                                                                                                                                  publication 420-524

            Sustaining America’s Aquatic Biodiversity
                                     Crayfish Biodiversity
                                      and Conservation
                    Louis A. Helfrich, Department of Fisheries and Wildlife Sciences, Virginia Tech
                              Robert J. DiStefano, Missouri Department of Conservation

         f the approximately 500 crayfishes (some                                                 Like its saltwater cousin, the lobster, the crayfish is
         times called crawdads or crawfish) found on                                              sold as gourmet food. Nearly 75,000 tons of cray-
         earth, about 400 crayfish species live in wa-                                            fish, with a value of $50 million, are farmed in ponds
ters in North America, and about 353, nearly 70 per-                                              or trapped in wetlands each year. Crayfish also are
cent of the world’s total species,                                                                                  important indicators of water quality
inhabit waters in the United States.                                                                                and environmental health, flourish-
Freshwater habitats throughout the                                                                                  ing in clean waters and perishing
United States harbor the richest                                                                                    in polluted waters. Most crayfish
diversity of these aquatic animals                                                                                  live from 2 to 4 years, although
in the world.                                                                                                       some cave crayfish may live over 10
The majority of crayfish species
live east of the Rocky Mountains                                                                                   Crayfish are threatened by habitat
and in the Southeastern states.                                                                                    destruction caused by dams, water
Many live in streams, rivers, and                                                                                  pollution, erosion, siltation, in-
lakes, while others are restricted to                                                                              stream gravel dredging and, particu-
springs, swamps, and even un-                                                                                      larly, the introduction of nonnative
derground waters (cave crayfish).                                                                                  crayfishes and other exotics. About
Native crayfish come in a variety                                                                                  65 species of crayfish are endan-
of colors (white, blue, red, brown,                                                                                gered, threatened, or listed as spe-
gray, yellow), shapes, and sizes (1                                                                                cies of special concern by the states
to 6 inches in length).                                                                                            in which they live, and 48 percent
                                                                                                                   of our native crayfish species are in
They serve as important links in                                                                                   need of protection. These numbers
the food chain, feeding on living                                                                                  are best estimates only. The exact
and dead plants, other inverte-                                                                                    status of crayfish endangerment or
brates, and fish. Crayfish are a                                                                                   extinction rates in the United States
primary food for fish (bass), water birds (herons),                                               is largely unknown because very few distribution and
mammals (raccoons), and others. In fact, over 240                                                 population surveys have been completed.
species of wild animals in North America have been
found to eat crayfish.

                                     Produced by Communications and Marketing, College of Agriculture and Life Sciences,
                                                   Virginia Polytechnic Institute and State University, 2009
                            Virginia Cooperative Extension programs and employment are open to all, regardless of race, color, national origin, sex, religion, age,
                            disability, political beliefs, sexual orientation, or marital or family status. An equal opportunity/affirmative action employer. Issued in
                            furtherance of Cooperative Extension work, Virginia Polytechnic Institute and State University, Virginia State University, and the U.S.
                            Department of Agriculture cooperating. Rick D. Rudd, Interim Director, Virginia Cooperative Extension, Virginia Tech, Blacksburg;
                                                        Alma C. Hobbs, Administrator, 1890 Extension Program, Virginia State, Petersburg.
Most Americans believe that we should protect our               The cephalothorax of the body is entirely covered
native aquatic animals as a legacy to our children.             by the shell (carapace), whereas the back part of the
Citizens can help safeguard life in our waterways. To           body or abdomen consists of seven jointed segments
protect our aquatic biodiversity, they can join con-            and a large, fan-like tail.
servation groups, adopt a local stream or river, and
report all suspected water pollution problems to state          They have two large, compound eyes consisting of
natural resource agencies.                                      thousands of eyelets (providing a mosaic view like
                                                                that of insects) supported on stalks.
What Is a Crayfish?
                                                               They use their two pair of antennae (short, jointed
Crayfish are small lobster-like animals that live              inner antennules and long outer antennae) to taste the
in freshwater streams, ponds, lakes, swamps, and               water and find food. The inner antennules are used
marshes throughout the world. They are invertebrates           for chemoreception (tasting the water and food). The
(animals without a backbone) that belong to a group            outer ones are used for the sense of touch. The over-
called the Arthropoda (joint-footed) animals related to        lapping mouth parts and heavy tooth-like mandibles
the insects, spiders, scorpi-                                                             are used to crush and shred
ons, millipedes, and mites.                             Antennae                          food before it is eaten.
They belong to the class                                                     Movable
Crustacea (shell) and the                                                                 Crayfish have ten legs (one
order Decapoda (ten legs).         Pincer                                                 pair of large claws and four
                                                                                          pairs of slender walking
Some say the name comes                                                                   legs). The first pair of legs
from the word “cray” which                                                                has the claws (pincers),
refers to a hole or burrow.
                                                                                          which are used for defense,
Others believe it is from                         Head                                    mating, burrow building,
a French word meaning                                                                     egg laying in females, and
“crevice.” Some crayfish                                                                  feeding. These strong claws

dig and live their entire                    Thorax                                       are specialized for captur-
lives in burrows. Native                                                                  ing, cutting, and crushing
American crayfish are a di-
                                   Body Length

                                                                               Legs       food. Their pinch can hurt.
verse and interesting group                                                               When threatened, the cray-
of aquatic animals; they                                                                  fish assumes a defensive
come in a variety of sizes,                                                               position with the body lift-

shapes, colors, and forms.                                                                ed and the claws elevated
                                                                          Tail Fan        and spread. At this time the
Structure and                                                                             crayfish may retreat slowly
appearance                                                                                by walking backwards.
Crayfish, as other Crusta-
                                                                                            The first two pairs of small
cea (crabs, lobsters, and
                                                                                           walking legs are tipped
shrimp), are heavily armored with a hard exoskeleton
                                                                with small pincers that are used to probe in cracks
or “shell,” that must be shed periodically so that the
                                                                and holes for food, and are used for eating, walking,
animal can grow. This exoskeleton serves to protect
                                                                and grooming. The last two pair of legs are used for
the crayfish from predators and provides a frame-
                                                                walking and mating. Crayfish can regenerate their
work for the body. Despite its hard armored shell, the
                                                                limbs if they are broken off, but regenerated legs and
crayfish is agile and fast, thanks to flexible, jointed
                                                                claws often are smaller or misshapen when compared
                                                                to the originals.
                                                                The large, fan-shaped tail, flattened from top to bot-
The body of the crayfish consists of two sections:
                                                                tom, is used for quickly swimming backwards. Large
• the front of the body called the cephalothorax
                                                                muscles in the abdomen curl the tail fan forward
   (head and chest) and,
                                                                beneath the body propelling the crayfish rapidly
• the abdomen or rear half of the body.
                                                                backwards. Typically crayfish walk slowly forward

on their legs, but if they are startled, crayfish use         When crayfish burrow into the ground they create
rapid flips of their tails to quickly swim backwards in       “chimneys” made of mud balls that are excavated and
a series of jerking movements to escape danger.               rise above the tunnel. Burrowing crayfish may dig
Crayfish breathe by internal gills like fish, but many        their tunnels on lawns and golf courses with moist
(especially burrowing crayfish) can remain out of             soils that can be a long distance from surface waters.
water for considerable amounts of time under humid            Lawn owners and golf course managers dislike bur-
conditions. The plume-like gills are located in gill          rowing crayfish creating holes and mounds on their
chambers on each side of the body. Gill flaps attached        turf. Pond owners worry that too many crayfish bur-
to the mouthparts help circulate oxygenated water for         rows can cause their dams to collapse.
                                                              What do they eat?
Scientists use the size, shape, color, shell markings,
                                                              Crayfish are often found under rocks during the day,
and reproductive organs to identify the many species.
                                                              and most feed actively at night. Older crayfish usu-
Crayfish can vary in color from white to blue to red
                                                              ally are more active at night and on cloudy days than
to green to black or brown. Most crayfish are brown-
                                                              young crayfish. All are nocturnal, well adapted to
green in color in order to blend into the stream bottom
                                                              using their antennules to “taste” and “feel” for food at
and hide from predators.
                                                              night and in the dark.
Where do they live?                                           Crayfish are opportunistic feeders and will eat nearly
Crayfish live in a range of habitats including clean,         any plant or animal, dead or alive. Adults gener-
flowing waters (streams, rivers) and standing waters          ally are herbivorous and prefer to eat aquatic plants,
(ponds, lakes, marshes, swamps). They are found in            leaves, and woody debris, whereas young crayfish
almost any wetland, including drainage ditches; wher-         are more carnivorous and prefer to eat animals such
ever there is water. Some species have adapted to             as aquatic insects, tadpoles, snails, fish, and salaman-
living in ponds, but most                                                                ders. Both adult and young
live in streams and rivers                                                               crayfish are cannibalistic.
where water flows provide
an abundant oxygen sup-                                                                 This wide range of foods
ply for breathing. Crayfish                                                             allows crayfish to be very
live in a wide range of                                                                 adaptable to living in many
water temperatures from                                                                 habitats, and is important
55˚F to >80˚F.                                                                          in transferring energy up
                                                                                        the food chain. As crayfish
Nearly all crayfish use                                                                 consume dead and decay-
some type of shelter                                                                    ing plants and animals they
during part or all of their                                                             provide food for smaller
lives. Many spend most                                                                  aquatic animals and improve
of their lives walking on                                                               water quality.
stream and lake bottoms (largely at night), but quickly
burrow under rocks and logs to avoid predators. Some          How do they grow?
crayfish spend their entire lives underground and only
                                                              The hard outer shell provides protection, but limits
come out to feed and mate.
                                                              growth. As a result crayfish get too big for their shells
                                                              and regularly molt (shed) their hard exoskeletons
Burrowing crayfish are rarely seen above ground
                                                              (outer shells) to allow room for new growth. During
during the daytime. Burrowing crayfish dig holes in
                                                              molting a new soft shell develops beneath the old one,
stream banks and in moist soils. Crayfish usually dig
                                                              then the old shell splits between the carapace and the
tunnels from 1 to 5 feet deep or to the water table, so
                                                              abdomen and the whole crayfish emerges through this
that they can stay moist even during droughts and dry
                                                              opening. The old shell, including that covering the
                                                              antenna and eyes, is left behind.

Molting is stressful to crayfish, and sometimes cray-         about two to four years, although tagging studies have
fish die when halfway out of their old shells. The new        shown that individual crayfish of some species such
shell of the crayfish usually is soft for two to four         as the Tasmanian crayfish can live 20 years. Because
days. At this time, crayfish usually hide because they        most crayfish live short lives, rapid sexual maturity
are more vulnerable to predators and water pollution.         and many eggs are important for the survival of each
Molting occurs six to 14 times during the first year          species.
of life when young crayfish are growing rapidly, but
occurs less frequently, one to three times per year, as       Males can be distinguished from females by the pres-
they grow older. Growth and molting slows or stops            ence of gonopods, rod-like structures that extend for-
in winter.                                                    ward between the bases of the walking legs. Females
                                                              have a depressed sperm receptacle between the bases
Crayfish native to the United States range in size from       of the last two pair of walking legs.
1 to 6 inches in length. Newly hatched crayfish are
about 1/3 inch long, whereas adults can grow longer
than 6 inches. The world’s largest freshwater inverte-        Collecting Crayfish
brate, the Tasmanian crayfish (Astacopsis gouldi), can
grow to over 24 inches in length and weigh over 10            Crayfish can be trapped, netted, or simply picked up
pounds.                                                       by hand. Crayfish can be caught by hand after locat-
                                                              ing them by turning over rocks in stream riffles. A
                                                              minnow seine can be set across stream riffles and the
How do they reproduce?                                        upstream rocks turned, scaring crayfish downstream
                                                              with the current into the set net. Some collectors use
The mating season usually occurs in the fall, but can         a funnel-shaped minnow trap baited with fish or meat
occur during other seasons for some species. During           scraps, dog food, corn, or aquatic plants to attract
mating, a male grasps a female with his claws and             crayfish. Because crayfish are nocturnal, using lights
transfers sperm to the female sperm receptacle. Fer-          to collect them at night is more efficient than hunting
tilization and hatching are usually delayed until the         them during the daylight hours.
following spring when eggs are released.
                                                              In most states, crayfish are subject to fishing laws that
Females of most species lay eggs in the spring.               regulate what species, how many, and where they can
During egg laying, the female cleans her abdomen,             be harvested legally. A state fishing license usually is
releases eggs from her vent, and attaches (glues)             required to harvest crayfish. In some states, the use of
each egg to small appendages on the underside of her          crayfish for fish bait and the introduction of crayfish
abdomen near her tail. A female carrying a bunch of           into natural lakes or streams are illegal. Laws against
eggs is termed “in berry,” because the eggs look like a       the importation and transport of crayfish are intended
bunch of blackberries attached to the female’s abdo-          to limit the introduction of nonnative crayfish, some
men. A female may carry from 20 to over 700 eggs              of which can eliminate native crayfish, frogs, and fish.
for two to ten months before they hatch, depending
on the species and water temperatures. The egg color
becomes lighter toward hatching.                              What Good Are They?
                                                              Crayfish are ecologically and economically valu-
During egg incubation, the female protects and aer-           able animals. In many streams and lakes, they are the
ates the eggs by tucking her tail forward and fanning         most important link in the aquatic food chain. They
the young. Females of some species are inactive dur-          eat algae, waterweeds, and aquatic animals, and are,
ing the egg incubation period. After hatching, crayfish       in turn, eaten by over 240 species of wild animals.
remain attached and close to the female for safety and        Raccoons, black bears, otters, mink, herons, and other
protection for two weeks to four months when they             wildlife feed heavily on crayfish. Smallmouth bass
become independent.                                           and bullfrog diets, for example, are nearly 75 percent
Depending on the species, some crayfish mature and
are ready to mate their first year, but others do not         Crayfish play an important role in breaking down
mature until their second year. Most crayfish live only       dead plant material, and promoting decomposition

                                      MALE                           FEMALE

                                                       Hooks                              No Hooks

                                                                                           Sperm Receptacle
                     Abdominal                                                            Abdominal
                    Appendages                                                            Appendages

                                 Figure 2. Ventral View of Female and Form 1 Male. Sexually
                                           inactive males do not have hooks.

and recycling. By crushing and chewing, crayfish make           Crayfish Killers: Threats
organic materials more available and usable as feed
for smaller aquatic animals, thereby helping to link the        About 65 of the 400 crayfish species in North America
food chain. What would happen if all of the crayfish in         are endangered, and 195 native crayfish species are
a lake or stream were suddenly removed or killed?               in need of protection.These numbers are best esti-
                                                                mates only. Honestly, no one knows the exact status of
Crayfish are important indicators of water quality.             crayfish endangerment or extinction rates in the United
Many crayfish species are sensitive to water pollu-             States or elsewhere because very few distribution and
tion, and can be used as biological monitors to forecast        population surveys have been completed.
present and historical water quality conditions. A sud-
den kill of freshwater crayfish is an indicator of toxic        For crayfish and other aquatic animals, habitat loss
chemicals or other forms of water pollution.                    (sedimentation, siltation, dams, in-stream gravel dredg-
                                                                ing, water pollution, and the removal of submerged
Crayfish also are a flavorful, nutritious, and valu-            logs, rocks, and plants) is the leading cause of extinc-
able human food (similar to lobster) and are sold in            tion and population declines. The introduction of exotic
fish markets throughout the world. Every year, nearly           nonnative crayfish and other animals is the second
75,000 tons, valued at over $50 million, are produced           leading cause for declines in numbers and species.
in the United States alone. Crayfish are trapped in the
wild and farmed in ponds in Louisiana, Mississippi,             Nonnative crayfish are a major threat to aquatic bio-
Alabama, and Texas to be sold as food or fish bait.             diversity, causing the decline of native crayfish, fish,
                                                                amphibians, and water plants. Nonnative crayfish are
                                                                those that come from other countries, other states, or
                                                                other river systems and lakes. Most states have laws
                                                                prohibiting introductions of nonnative crayfish, which
                                                                sometimes are introduced illegally or escape from bait
                                                                anglers or from pet aquariums.
                                                                                        • Tasmania Giant Crayfish
Nonnative crayfish cause                                                                  site:
declines of native aquatic                                                                au/tasonline/dorsetww/Lob-
plants and animals through                                                                sterpage.html
the spread of diseases, such
as crayfish plague, to native                                                           • The Crayfish Homepage
crayfish; by predation on eggs,                                                           for teachers and students:
young fish, amphibians, and                                                     
native crayfish; by out-com-                                                              crayhome.htm
peting or preying on native
crayfish; and by the elimina-                                                           • See how crayfish move
tion of native water plants and                                                           on this site: http://www.
habitats. The rusty crayfish                                                    
(which is native to four states,                                                          esp/crayfish.htm
but has been introduced into
18 states) is an aggressive                                                             • Missouri’s Crayfishes:
crayfish that has been linked                                                             http://www.conservation.
with the decline of native                                                      
crayfish and other aquatic                                                                crayfish/varcraw.htm
species in states where it has
been introduced. If you collect                                                         • To see how crayfish
crayfish for an aquarium or na-                                                           breathe: http://www.mon-
ture study, please return them to the same waters from                          
which they were captured.                                                                 craybreath.htm

Many native crayfish have a limited geographic range.         •   The Crayfish of North Carolina: http://www.
Some species of crayfish are found only in one loca-     pg07_wildlifeSpeciesCon/nccray-
tion in one river system where only one pollution spill           fishes/nc_crayfishes.html
could cause their extinction.
Crayfish Web Links
                                                              We greatly appreciate the editorial review of Nancy
•   For a list of crayfish species in your state check out    Templeman, Virginia Cooperative Extension, and the
    this site:     support of Randy Rutan and Hilary Chapman, National
    cies_by_state.htm                                         Conservation Training Center, U.S. Fish and Wildlife
•   The crayfish corner: All about behavior and anato-
    my of crayfish:          Art illustrations by Sally Bensusen, Mark Chorba,
    index.html                                                Scott Faiman, Karen J. Couch, and Keven Peer.

•   Problems with the rusty crayfish and other exot-
    ics in the Great Lakes:

                    Reviewed by Michelle Davis, research associate, Fisheries and Wildlife


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