Exotic species

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Exotic species
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Proportion of nonindigenous fish species in SD by
family
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Proportion of nonindigenous fishes in SD by type
of introduction
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Proportion of nonindigenous fishes in SD by mode
of introduction
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Ecologically important invertebrate species not
found in South Dakota         Zebra mussels   The
zebra mussel Dreissena polymorpha is a small (up
to 40 mm) bivalved mollusk native to rivers near
the Caspian and Ural seas. It was first
reported from the Great Lakes in 1988 and has
since spread to the Mississipi River drainage
where it will likely lead to substantial changes
in unionid demographics. It was recently found
near Sioux City, Iowa on the Missouri River. Its
life cycle includes a free-floating larval stage
(veliger) followed by juvenile and adult stages
where the mussel is attached by byssal threads to
firm substrata. These life-history traits
contribute to the successful spread of zebra
mussels in North America. The free swimming
veliger attaches itself to any solid object by
means of a glue and byssal threads and zebra
mussels have been found on trailered boats in
Virginia and California.
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Rusty crayfish   Non-native crayfishes are one of
the most destructive invaders of aquatic
ecosystems in North America. Non-native
crayfishes can affect fish populations by preying
on fish eggs and reducing aquatic vegetation that
is important for juvenile fishes. The rusty
crayfish Orconectes rusticus , native to the Ohio
River drainage, is one of the most destructive
crayfishes and has spread rapidly throughout the
midwest. In addition to affecting fishes, the
rusty crayfish can also displace native
crayfishes such as O. virilis and O. propinquus.
Because they need refuge from predation, rock or
boulder substrates are usually an excellent
predictor of where the rusty crayfish can be
found. Because crayfishes are often used as
fishing bait, they are easily spread from one
location to another. Several states (e.g.,
Wisconsin) have banned the use of live crayfish
as bait. These regulations have had little, if
any, effect on the recreational fishing industry
and serve as a way to prevent the spread of
nonindigenous crayfishes. The rusty crayfish is
now found in close proximity to South Dakota
(Minnesota, Iowa, and Wisconsin) and may pose a
threat to South Dakota waters.
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Bythotrephes   The spiny water flea, Bythotrephes
(bith-o-TREH-feez) cederstroemi, a small
planktivorous crustacean, has an average length
slightly larger than 1 centimeter (0.4 inches) of
which 70 is a long, sharp, barbed tail spine.
First introduced into the Great Lakes ecosystem
in 1984 via ballast water that was discharged
into Lake Huron, they had spread to all of the
Great Lakes by 1987 currently they are found in
inland lakes in Michigan and Southern Ontario.
Their rapid reproduction, general lack of
predators, and direct competition with young fish
for food enhances their ability to alter aquatic
food webs. Bythotrephes eat small herbivorous
crustaceans, including native Daphnids. Daphnia,
however, are also an important food item for
small, juvenile fish. As a result, Bythotrephes
can compete directly with young fish for food.
Because of their unique reproductive pattern,
Bythotrephes can reproduce many times faster than
fishes. Their rapid population growth enables
Bythotrephes to monopolize the food supply at
times, to the eventual detriment of the fish. The
success of Bythotrephes in colonizing all of the
Great Lakes raises the possibility that it may
soon invade smaller, inland lakes in the Great
Lakes basin.
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Daphnia lumholtzi4   Daphnia lumholtzi is a
species that has recently invaded North America.
Easily identified, Daphnia lumholtzi produces
much larger and more numerous spines than do
North American Daphnia (see figure below). The
head and tail spines may be as long as the body,
which is partially covered with smaller spines.
Large individuals can reach total lengths of 5.6
mm (nearly 0.25 in), making them visible to the
naked eye. Scientists are concerned that
Daphnia lumholtzi may have negative effects on
North American ecosystems. The large spines make
it difficult for young fishes (larval and
juvenile stages) to consume. In the Midwest,
populations of Daphnia lumholtzi tend to peak
during mid-summer when juveniles of these fishes
may still be dependent on zooplankton as a
primary food source. Daphnia lumholtzi may
spread in a number of ways. Although it likely
does not swim against river currents, Daphnia
lumholtzi may travel upriver in baitbuckets as
well as bilge-water and livewells of
recreational and commercial watercraft. It may
also spread in its dormant egg stage.
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New Predator Invades the Great Lakes   One of the
most recent additions to the Great Lakes is
another tiny stowaway from Eurasia. Cercopagis
pengoi is a small (crustacean that was first discovered in Lake
Ontario in 1998. Cercopagis, which has become
known as the "fishhook flea," possesses a tail
spine that can be up to five times as long as its
body. In Cercopagis, the tail spine includes a
predominate curve, which separates it from the
closely related Bythotrephes cederstroemi that
invaded the Great Lakes in the 1980s. Because of
this long, spiny, appendage, Cercopagis and
Bythotrephes are often found fouling fishing
lines in the Great Lakes. The clogging of reels
and fouling of nets makes these exotic species
potential nuisances in these systems. Both
Cercopagis and Bythotrephes possess life history
traits that make them good invaders. Like many
other species of zooplankton, they reproduce by
means of cyclic parthenogenesis, which means
there is an alternation of reproductive mode. For
most of the year, only females are present in the
water. These females produce eggs asexually,
which in a few days are released as newborn
daughters. With this mode of reproduction, a
single introduced individual could potentially
colonize an entire lake!
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It is not known what effect this new species will
have on the Great Lakes ecosystem. When
Bythotrephes invaded Lake Michigan, its entrance
to the lake coincided with marked changes in the
food web. Both Bythotrephes and Cercopagis are
predators, eating other species of zooplankton
that are also the primary food for many species
of fish. Cercopagis is considerably smaller than
Bythotrephes, so it may fall victim to predation
by the larger predatory species. In addition,
Cercopagis and Bythotrephes may provide
additional food for fish. Bythotrephes is
commonly eaten by yellow perch and alewife,
although the benefit of eating this spiny species
for fish is unclear due to problems they
experience digesting and passing the spiny
leftovers. Cercopagis also was found in
alewifeguts last fall, but the potential impact
of these and other fish on Cercopagis is not
clear. Future research will help us understand
the role of this new species in North American
Lakes.
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Spread of Exotic Cladocerans Live animals
require water to be transported from lake to
lake. Therefore, the control measures used for
other exotic aquatic species (emptying of bait
buckets and live wells, washing and drying of all
gear) will also help to reduce the spread of
Cercopagis. The diapausing eggs are a different
story. These eggs can hatch after they have dried
up or frozen, even if it is several years later.
Moreover, since females carrying these eggs can
"stick" to fishing gear and other recreational
equipment, care must be taking to thoroughly
clean all equipment after leaving a lake (instead
of just allowing things to dry).  
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Steps for Preventing Spread of Cladocerans and
Zebra Mussels by Recreational Water Users
BEFORE leaving boat launch   1) Inspect boat,
trailer, and equipment 2) Remove any observed
plants and animals. 3) Drain, on land, all water
from the motor, livewell, bilge, and transom
well. 4) Empty water from bait buckets on land,
and dispose of unwanted bait in trash.     AFTER
leaving boat launch   Wash all equipment with
104F water or a high pressure sprayer,  
OR   Dry equipment for
at least five days.