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comfortable discussing invasive species here because these are the animals that we are really concerned with the
most. Invasive implies some kind of negative impact or potential for
negative impact based on past
some terms that we use to talk about the subject. The top 5 are more or less biological descriptions. It is suffice to say that some
animal is out of its historic range and
probable biological range too. Nuisance
is sort of a political term and I see
invasive as falling somewhere in the middle
between biological and political.
aquaculture represents one the greatest sources for future introductions of invasive species into North
American waters. One reason for the importing of foreign species is that
aquaculturists believe they will receive
a higher return on their investment if they market a species that has the mystique of being “exotic”, especially in
the aquarium trade.
aware that there are some risks of bringing in foreign animals and that no aquatic systems are immune to exotics.
In the northwest, introduced trout may
be negatively impacting amphibians populations and Atlantic salmon have escaped aquaculture operations
possibly threatening Pacific salmon
stocks. In south Florida we have the walking catfish and several species of cichlids established with an exotic eel poised to enter the Everglades. And in the southwest
and mountainous regions, cichlids,
tropical fish, and introduced crayfish threaten the habitat of several rare desert fishes.
is thousands of years old in Asia, but here in the US it is relatively new. Our government got involved in the
late 1800s by importing common carp and
brown trout to raise for food. Presently, figures from 1995 showed that world aquaculture production reached a record of 21 million metric tons of fish and
shellfish worth more than 36 billion in
US dollars. China makes up 60% by weight of the world’s total (mostly in carp). The US only accounts for about 2%
of the world’s total. Here in the US over 100 species of aquatic organisms
are farmed, 60% are freshwater fish of
which 50% of that is catfish. The rest is mostly trout, salmon, and some sturgeon. The dominant molluscs produced are the American oyster and the Pacific (Japanese) oyster.
The problem started hundreds of years ago when introductions
occurred with the earliest European settlers. But, the earliest documentation of introductions began
in the 1800s, many of
which were intentional such as the Asian common carp and the European brown trout that were introduced by
So it began In 1900, the Lacy Act was the first legislation aimed at
controlling unwanted introductions.
In 1969, the first American Fisheries
Society meeting on exotics was held headed by R.H. Stroud. This was about the time when the U.S. Fish
and Wildlife Service started taking notice of problems caused by invasive species and potential
problems that may cause.
In 1974, the Federal
Noxious Weed Act was legislated.
In 1977 President Carter’s Order
restricted all federal agencies from actively supporting projects that would increase the
spread of exotics.
1980, (A shameless plug for my office), the National Aquaculture Act
stimulated the USFWS to
establish the laboratory in Gainesville, Florida to oversee development of a research program that will support the
use of exotics for beneficial purposes while protecting the environment. That Center is no longer
functioning that way, instead is attempting to determine impacts and distributions of all
nonindigenous aquatic species.
In 1990, the arrival of the zebra mussel prompted Congress to
pass the Nonindigenous Aquatic
Nuisance Control and Prevention Act.
This Act was later reauthorized in 1996 as The Invasive Species
Act which focused heavily
on ballast water and is up for reauthorization in 2001. Finally in 1999 there
was another Executive
Order to stimulate more research. Okay,
from R.L. Welcomme states that any introduction made for aquaculture must be thought of as a potential
addition to the wild fauna in the
receiving country. The keyword here is
potential. Not always is that going to
happen, but the potential can be there.
chart shows the relative percentage of fish introductions internationally based on the purpose or reason for
which they were introduced. Aquaculture
is the largest, followed by Sportfishing, Unknown Origin, Accidental, Ornamental, and Biocontrol.
majority of species have been introduced into only a few countries. Eighty-six percent of the species introduced have
been recorded from 10 countries or
less. This graph is read for example
the first column means that 29
countries have only had 1 species introduced, 6 countries have had only 2 species introduced and so on. I am concerned with the farthest bar to the right that says 1 country has
had 70 foreign species of fishes
introduced in it and that happens to be the US. Canada falls out at 17 foreign species, Mexico with 33, and Hawaii with
45 species of foreign fish.
some selected species and the number of countries into which they have been introduced. The second name on the
list is a North American crayfish that
has been introduced in Europe and causing problems there. Introductions
are a two-way street. Largemouth bass have
been intentionally introduced in Asia and are viewed like we view the common carp here. I believe also that the Caspian
Sea is home to many North American
species, but they are mostly from ballast water.
figure charts the number of introductions over time beginning about the 1850s, when some records were kept, until the
1980s. It appears that introductions of
fishes peaked into 1960s. Did we run
out of possibilities for new fishes or
places to introduce them around the world?
It that possible?
can clearly see here there has been a steady decrease in salmon introductions worldwide.
decreases this time in centrarchids such as basses and sunfishes.
there has been kind of an up and down trend with a peak in the 1950s in Tilapia introductions. My guess that it did not increase much, if any, in the 1990s.
decrease in Asian carp too over the last two decades. I might suppose that data from the 90s would show a further
introductions slowed, shrimp and crayfish increased into the 1980s. I would venture a guess that it has increased
also into the 1990s.
other must include mollusks such as oysters, clams, mussels, and miscellaneous pet trade species which has been
steady right along over the past
almost as many ways for introductions to occur as there are introductions. But here is a list of the most
well-known and documented. I found one
example of shipping water very interesting.
Several years ago 3000 Pacific
oysters were shipped from California to Woods Hole. The shipment
had 2 certificates stating it was parasite and disease free. That was
all well and good but only 10% of the shipment was checked which I believe is standard. After arriving at Woods Hole
the water was examined that the oysters
were shipped in. The oysters were also washed and the water saved. There was a total of 29 species of
algae, diatoms, protozoans, and
list that demonstrates the number of different species introduced and how they were introduced in the United States
only. This includes more than just fishes.
includes some species outside the realm of commercial aquaculture by including all the gamefish that were
intentionally stocked by government
agencies. I have divided it into 2 groups, species foreign to the US and species native to the US that have been
transplanted around the country.
number from South America includes much of the cichlids (Tilapia) and the tropical fish for the aquarium
trade. We also get tropical fish for
the aquarium trade from southeast Asia.
makes a species a successful invader?
Every animal or species cannot
possibly survive in every instance of an introduction. Alien species
that are successful often exhibit a broader flexibility in characteristics that enhances its chance for
survival in a new environment.
can be simple or complex, direct or secondary.
one step back from what impacts introductions have, what about the hatchery itself?
Hatchery effluents can have a big impacts on water quality. Depletion of water supplies would also
impact the native fauna. Many trout hatcheries use a tremendous amount of
water for their flow through systems.
Hatcheries tend to attract thousands of birds and mammals. In a recent 4 year period, over 50,000
birds alone were legally killed at
aquaculture operations of which 20,000 were herons and egrets. I can
only imagine how many others came to an untimely end and were not reported. And there is chemical pollution with
herbicides and antibiotics.
we know so little of the natural workings of native aquatic ecosystems, most potential impacts by introduced
species are based on presumptions as to
cause and effect. But an increasing
number of studies have been done that
demonstrate negative effects on native species
as a direct result of introduced fishes.
Some introductions may take
decades to realize their full potential as an invasive species. Some scientists
believe every introduction should be treated as a potential “biological time bomb”.
for the commercial aquaculturist and we’ve all heard these before. But ways to prevent introductions or minimize
impacts might be to build dikes for
ponds, filter all hatchery effluent, don’t build in flood prone areas, assure triploidy which can be difficult, or
sterilize every animal.
are of course benefits from aquaculture. Most of us enjoy and a good catfish filet now and then or perhaps a shrimp
basket. Fish are an excellent source of
protein. Most of also enjoy fishing
opportunities that aquaculture has
provided. This in turn supports global into the billions of dollars and also local economies. Millions of people are able to enjoy their aquariums and bring a little of nature right
into their homes. And, of course, all this creates thousands and thousands of
Now on to
some examples. I want to begin by
mentioning huge impact that invasive
plants can have on ecosystems. This is
list of several plants closely
associated with the aquarium trade.
It is pretty well documented that hydrilla and parrot’s feather came from
aquaculture, more specifically the
verticillata was imported from Sri Lanka in the 1950s first to St. Louis and used as a popular aquarium plant. Hydrilla
is rooted but concentrates 70% of its
biomass at the surface forming a dense canopy during summer and early fall growing to depths of 15 meters. It can reproduce when detached stem fragments readily
develop into new plants and attach to
the soil. Recreational boating is the
most common method for the spread of
this plant now. Hydrilla can alter ecosystems by shading out native submersed vegetation. The production of
allelopathens by Hydrilla has been
shown to negatively affect the distribution of at least one native plant here in Florida, Ceratophyllum
demersum. Researchers have reported changes in lake water chemistry after
the introduction of Hydrilla in many
lakes. An obvious and important impact on fish communities occurs here when open water feeding is not longer possible.
water hyacinths are not associated with aquaculture I just wanted to show you another example of how an
invasive species has altered this
ecosystem. There’s no reason why the
next invasive plant could not be
brought in for aquaculture, intentionally or unintentionally.
60% of established exotic fishes are known or presumed to be associated with the aquarium trade. Release and
subsequent establishment of aquarium
fishes is not restricted to the U.S. It is common in many parts of the world. The convict cichlid
which was released into springs in
Nevada has contributed to the demise of the native Moapa White River springfish (Crenichthys baileyi) in Nevada. Other examples are the non-native sailfin molly which overlaps with
the native Ash Meadows pupfish, and the
non-native shortfin molly which overlaps with the Moapa White River springfish on 2 National Wildlife Refuges. These introductions are currently being studied to
determine any impacts on these 2 rare
bighead carp was imported by a private farmer in Arkansas in the early 1970s to improve water quality in his culture
ponds and feeds primarily on
zooplankton. Several studies showed when bigheads were cultured along with catfish, the production of catfish was
depressed. This bighead carp was collected in Lake Erie by
commercial fisherman just last summer. There have been several others collected in
the lake in the last five years. The most recent was a 17.5 kg and 937 mm
bighead collected on the Canadian side
last Fall. There is some preliminary data that indicates that there may be competition with paddlefish in the
areas represent drainages here bighead have been collected in open waters. However, there is evidence of
reproduction only in the lower Mississippi
and Missouri rivers and possibly the Illinois River so far.
silver carp was imported also into Arkansas in the 1970s by the state for phytoplankton control in eutrophic waters. It is
very attractive for culture because it
can filter very small phytoplanktors, often the kind that can produce nuisance blooms. Silver carp can change the composition from blue-green algae to the more favorable green
algae. But, by 1980 it had escaped into
open waters of the Mississippi drainage.
established in the Black River in Louisiana and probably the Mississippi River in Illinois and Missouri. Several months ago I saw a story on the news where, in the Mississippi River in
Missouri, Asian carp were jumping out
of the water like flying fish and landing in fishermans’ boats. One
commercial fisherman said 26 carp landed in his boat in an eight hour period.
The media saw it as some strange phenomenon, but I believe it is typical, especially of silver
carp. People were actually being injured by these flying fish.
carp has kind of been a poster child for “to introduce or not to introduce” species.
They were imported by the U.S. Fish and Wildlife Service from Malaysia in 1963 to study their
potential for aquatic weed control.
grass carp is established so far in only those 8 states and has been merely collected in open waters from 37 other states
or introduced in some of them. They are
illegal to possess in many states. Some states allow only triploids to be introduced. This species is still
controversial because it is hard to
insure all fish are triploids.
carp was accidentally imported with grass carp to a private fish farm in Arkansas in the early 1970’s. The next time
it was imported was intentionally as a
food fish and as a biocontrol agent to control snails which harbors the yellow grub, a catfish parasite in
aquaculture ponds. In 1994
approximately 30 fish escaped a facility into the Osage River in Missouri after high water flooded hatchery
ponds. So far the fate of those escapees is unknown. The black carp is known to be a
molluscivore and continued importation
of the black carp is currently being hotly debated.
photo is the rudd, a native of Europe that was brought to this country late in the 1800s. It is cultured in several
states and distributed to bait stores
in as many as 16 states. The rudd is established in New York and Maine and possibly Nebraska and South Dakota. On
the bottom is our native golden shiner,
Notemigonus crysoleucas. The problem is that the rudd can hybridize with the golden shiner. This hybridization is the first known non-salmonid intergeneric cross of an
exotic and a native species.
armored catfish, a native of South America, is established in Florida and Hawaii probably as a result of fish farm escapes
and aquarium pet releases. It was found
first in the 1980s in Hawaii and then later in Florida where it appears to be expanding its range rapidly.
Impacts are unknown, we are just
beginning to look at some of these species such as this in south Florida.
tilapia, a now popular food item, has escaped aquaculture operations in North Carolina, Oklahoma,
Pennsylvania, Colorado, and Texas where
they were collected in open waters in each of the states. I’ve
seen what this species can do in Florida lakes by totally dominating other species in biomass. The Mozambique tilapia, believe it or not,
can be found in several geothermal
springs and effluents in Idaho and is considered
a pest around the world. It has been established here in Florida since the 1960s. Both of these fishes were also stocked for biocontrol of aquatic weeds. I want to add that many small, tropical aquarium species such as mollies and guppies have
also been collected from geothermal
springs of the West.
salmon pen culture began in the 1960s in Washington and brings the risks of disease and competition to the native
Pacific salmon. There are accounts of escapees from these pens such as
when nearly 100,000 escaped in the
State of Washington back in 1996. In a
lawsuit brought again EPA, Atlantic
salmon where considered “biological pollution”. EPA was
found in violation of the Clean Water Act.
Swamp eel, Monopterus albus, is native to tropical and temperate climates of eastern and southern
Asia. It is now well established in several canals in the Miami, Florida
area over the past few years. They can grow to about 3 m and prey on fish,
crayfish, shrimp, frogs, tadpoles, etc.
They are capable of breathing air and can travel short distances over land.
No one is sure how it got here.
The aquarium industry does not
appear to raise them so maybe it was brought in as a food fish by some ethnic group. At this point the
impacts are unknown.
an assortment of animals introduced around the country linked to some step in the aquaculture process.
may have come in with the Pacific oyster many years ago
Orconectes rusticus (rusty crayfish) may have been
introduced into northern states from the bait industry for fishing
Melanoides tuberculatus (red-rim melania) popular in the
aquarium trade, is an intermediate
host for trematode parasites, the Oriental lungfluke and the liver fluke, which can affect humans. This snail
has been found in 7 states including FL, TX, NV.
imported from South America for fur and to control aquatic vegetation. It’s doing a lot of damage
to salt marshes in Maryland.
Trachemys scripta, the red-eared slider has always been a popular aquarium pet
for children. Established
in several states. Illegal to sell hatchlings in US now.
Potamopyrgus antipodarum, the New Zealand mudsnail, is
carpeting the bottom of the middle snake river in Idaho and near Yellowstone National Park. It may
compete with the few
native snails there.
ramshorn) another common aquarium snail
native to Central America found in FL, ID, and TX .
white shrimp have been reported as escaping shrimp farms along the Texas Gulf Coast since 1989. The greatest risk
these escapees pose is the introduction
of diseases. In 1995, the Taura virus from South America appeared at a hatchery in Texas where
mortality was 80-90%. At the same time
2 other diseases appeared also. It is not known how the diseases got to Texas, but shipments of stock shrimp
are moved globally. Another species the
giant tiger shrimp (Penaeus monodon) native to SE Asia have escaped mariculture facilities in South
Carolina where they were quickly
collected later that same year 500 km offshore and as far south as Florida.
species daphnia is native to Africa and Australia and may have come in with shipments of Nile perch to Texas where it
was first found in Texas in 1990. It
has since spread to 56 reservoirs in 15 other states. The impact
of this species is not yet known, but it has the potential to become the dominant zooplanktor because of its ability to
avoid predators because of its numerous
highly, aquatic amphibian is popular in the pet trade. It is a native of Africa and is established in California since as far
back as1968. It could be detrimental to
native amphibians and fishes because of its voracious and nonspecific feeding habits. It is illegal to
import or possess this species in
the green mussel, Perna viridis, a tropical, marine native of the Indo-Pacific region.
Green mussels are cultured extensively in the Southeast Asia and the South Pacific where they are
grown on suspended ropes and bamboo
poles. They are are very good source of
protein like any other mussel.
have green mussels in Tampa Bay and the Gulf of Mexico. In the summer of 1999, a power plant in Tampa reported
finding them in their intake pipes.
Since then they have spread out of Tampa Bay and into the Gulf of Mexico along southwest Florida. It is well
established and has survived water
temperature much below where it came from. This was probably not an aquaculture introduction but I
thought it worth mentioning because of
the potential for it to become one now that it’s here. This species
has also invaded Venezuela, Trinidad, and Jamaica in the Caribbean Sea.
really easy these days for anyone to purchase cultured animals from anywhere in the world thanks to the Internet. This
happens to be the green-lipped mussel
from New Zealand that is farmed there on suspended
ropes. Live mussels have in the past
been shipped from New Zealand to
California, but I think New Zealand has changed its policy and ships only dead animals now.
of millions of dollars are spent each year in reacting to introductions after they have become a problem. Many have suggested that being proactive is the way to go. Whoever wants
to bring a new species into the country
for aquaculture should spend a small fraction and do some research to determine whether that species
has the potential to be invasive. This
is not a new idea and I think it’s one that makes sense. A positive side to this business is that hopefully
it will take some pressure off ocean
fish stocks that are in real trouble.
What I have presented today is
really the tip of the iceberg. There is a lot of information out there on impacts of introductions but I don’t think near
enough has been done. It’s a totally
open field for more research.
to finish with a list of very good books on the topic for more information and enjoyment.