Science and Technology Division
18 September 2000
TABLE OF CONTENTS
THE NATURE OF INVASIVE SPECIES
THE NATURE OF ECOLOGICAL DAMAGE
THE ECONOMIC COSTS
WHAT CAN BE DONE: PREVENTION
A. The Problem of Ballast Water
Prevention Through Legislative Restrictions on Importation
C. Prospects for Eradication
Natural geographic barriers
have separated species from interacting since soon after life began on
Earth. Oceans, mountain ranges, rivers and deserts have prevented species
from mixing and have allowed the development of distinct ecosystems with
their own unique set of organisms. Since the dawn of exploration, however,
humans have transported organisms, whether inadvertently or for a purpose,
across these natural barriers. With increasing volumes of international
trade and movement of people, the rate of introduction of species into
ecosystems that would normally be beyond their range of distribution has
increased enormously. All types of organisms are transported including
disease-causing viruses, bacteria, fungi, algae, mosses, ferns, flowering
plants, invertebrates, fish, birds and mammals. Without human intervention,
few if any of these diverse organisms would be found in the new location.
The chances of cattle or Zebra Mussels or the West Nile Virus being transported
naturally from their native ecosystems, half a world away, to Canada,
is so small as to be virtually discounted.
Non-indigenous species provide
many economic benefits. Historically, they have formed the backbone of
the agricultural sector. In the United States, they provide more than
98% of the food system at an estimated value of $800 billion (U.S.).(1)
Increasingly, however, the costs of introduced species are being recognized,
both in economic terms and in loss of species diversity on a global scale.
Further focus on this issue has been created by discussion in the popular
press of some recent introductions such as Zebra Mussels and the West
Nile Virus. While the global movement of human diseases such as smallpox,
influenza and HIV/AIDS is also important, the issue of humans as international
vectors for disease will not be discussed. This paper will focus on the
problem of invasive non-indigenous species, and some of the action being
taken to minimize further economic and ecological damage on national and
NATURE OF INVASIVE SPECIES
Isolation of organisms caused
by geographical barriers has led to the development of distinct species
adapted to various environmental conditions. Some organisms, called specialists,
have evolved to require very specific environmental conditions. Should
the environment change, or should they be transported to an environment
at all different from that to which they are adapted, they will not survive.
Others can survive and thrive under a wide range of conditions and have
been described as generalists.
When an organism is moved
from its natural habitat to another beyond the range it occupies naturally,
and could not occupy without human intervention, it is called non-indigenous.(2)
What occurs subsequent to its introduction will depend on the nature of
the organism and the environment. A plant, for instance, which hitches
a ride from the tropics on a transport bound for Alaska is less likely
to survive in its new home than one which moves from Europe to temperate
Canada. Likewise, a generalist organism is more likely to survive than
is a specialist. The large majority of non-indigenous plants do not become
invasive; they remain restricted to urban, or other highly disturbed areas,
as small-scale garden escapes. Others, such as the Dandelion, can be found
in less disturbed, more natural habitats, but do not seem to pose a problem
to the native flora and fauna. Many of the non-indigenous plants that
survive and thrive are weed species adapted to sites that undergo regular
disturbance, such as urban areas and agricultural fields. Such organisms
grow rapidly; and they frequently produce abundant seeds, often with dissemination
aids, that remain viable for long periods of time.(3)
However, it is the small group of plants that thrive in agricultural and
natural habitats at the expense of crops and natural plants, which are
deemed to be invasive and economically and ecologically harmful.(4)
Such invasive species usually have few predators to keep their numbers
in check. Invasive non-indigenous animal species have similar characteristics,
such as a wide environmental tolerance, rapid reproduction and few natural
Non-indigenous species arrive
and spread by a number of different means, either intentional or unintentional.
Intentional introduction of species can occur for many reasons, e.g.,
agricultural or horticultural purposes. The large proportion of non-indigenous
plants in Canada are ephemeral garden escapes of deliberately introduced
species.(5) Such garden escapes can,
however, have drastic consequences, as has happened with the Old World
Climbing Fern in the everglades of Florida. Someone emptying an aquarium
into a natural system most likely introduced the imported Eurasian Milfoil,
a decorative aquarium plant, which is infesting many waterways of Canada.
Others are imported in attempts to control a pest. The Common House Sparrow
was introduced in an unsuccessful attempt to control the Canker Worm.
Still others are brought in for more esoteric reasons. In one well-known
case, someone who wanted to bring all the birds mentioned in the works
of Shakespeare to the United States introduced the European Starling.
A more recent type of deliberate
introduction has occurred through aquaculture. Farmed Atlantic Salmon
have escaped off the coast of British Columbia, and some of them have
been found in breeding streams and caught by fishers.(6)
Though the escaped salmon do not seem to have established themselves as
invasive, the worry is that they may compete for breeding areas and for
food with the native species. The same seems to have occurred on the east
coast of Canada regarding escaped exotic Rainbow Trout.(7)
of non-indigenous species occur as a result of organisms "hitchhiking"
on various modes of transport. Ballast water is a common means of transport
for many of the aquatic invasive non-indigenous species. Ships without
cargo need to take on water in order to remain stable at sea. When this
water gets exchanged for cargo at another port, the water and any
organisms in the water are released into the new system. Zebra
Mussels were introduced into the Great Lakes in this manner. The Brown
Tree Snake was most likely introduced into Guam in the wheel well of an
airplane with devastating results to the native populations of organisms.
The most likely means by which the West Nile Virus arrived was in a shipment
of infected birds, either pets or agricultural. The Brown Spruce Longhorn
Beetle, recently confirmed in Halifaxs Point Pleasant Park, is thought
to have arrived on wooden packing crates. The more goods that are shipped
around the world, the greater will be the chances of inadvertent introductions
of non-indigenous species.
A minority opinion holds
that non-indigenous invasive species cause no real ecological harm and
that their economic harm should not be treated any differently than native
pests.(8) This argument states that ecological
arguments against non-indigenous species are strictly aesthetic, that
ecosystems are always in a state of change, and that proliferation of
so-called alien species cannot be differentiated from natural changes
in the abundance of native species. Thus to argue that invasive non-indigenous
species are bad is strictly a matter of aesthetic values and not one of
science. While one person may like a lake surrounded by natural stands
of cattail, another would rather view the more colourful Purple Loosestrife.
Equally, the economic damage caused cannot be differentiated from damage
caused by native pests. In fact, it is argued, many unintentional non-indigenous
species, such as Zebra Mussels, are beneficial to the environment because,
for example, they increase water clarity.
The credibility of such
arguments is diminished by a lack of scientific rigour and the use of
a few select facts, such as water clarity, taken out of context of the
broad base of scientific studies.(9) While water clarity may seem to be a good thing, it is
the result of the Zebra Mussels stripping the nutrients and plankton out
of the water, which drastically changes the food chain in the lakes. In
addition, many species, such as the commercially important Walleye, prefer
more turbid waters. The general consensus is that the global movement
of organisms as a result of human activity is causing serious ecological
and economic damage.(10)
NATURE OF ECOLOGICAL DAMAGE
The most severe ecological
damage caused by invasive non-indigenous species occurs on islands. The
flora and fauna of islands can evolve in almost complete isolation, which
results often in species that are endemic, i.e., they are not found anywhere
else but on the island. The introduction of a predator into such specialized
ecosystems can wreak havoc. The introduction of the Brown Tree Snake into
Guam has caused the direct extinction of 10 of 13 forest bird species
and 9 of 12 native species of lizards.(11)
Since the arrival of humans on Hawaii, approximately 2000 years ago, 70
of the 140 known species of birds have become extinct, and invasive species
are a major culprit.(12)
Continental species also
suffer as a result of non-indigenous invasive species. Zebra Mussels have
displaced most native mussels from both Lake St. Clair and Lake Erie,
populations that have a natural history of over 10,000 years.(13)
Approximately 40% of the species listed in the United States Endangered
Species Act are threatened primarily as a result of competition from
invasive non-indigenous species.(14)
Although some ecosystems
may actually have more species after an invasion, there is mounting evidence
that the opposite occurs more frequently. In one study of ant populations,
a reversal in the normal trend of increasing biodiversity with more tropical
climates was seen along a study route from Florida to New York, a trend
that was correlated with the presence of the invasive Fire Ant. Even if
an invasive non-indigenous organism did add to the biodiversity of a habitat,
the tendency is that most invasive species are the same, such that, on
a larger scale, biodiversity is lost as the world becomes a "planet
THE ECONOMIC COSTS
While non-indigenous species
have traditionally been seen as beneficial in terms of the agricultural
and horticultural sectors of the economy, it is becoming clear that the
invasion of non-indigenous species carries significant costs. These costs
are very difficult to estimate, but one recent attempt estimated costs
to the U.S. economy at more than $130 billion (U.S.) per year.(16) The overwhelming costs were borne by
agriculture, the industry that also benefits the most from introduced
species. The total costs to the U.S. agricultural sector of loss and damages
combined with control of weeds, crop plant pathogens, rats, crop pests
and livestock diseases amounted to more than $80 billion (U.S.). Other
studies, although they vary in what they are attempting to estimate, confirm
that invasive non-indigenous species cost the global economy many billions
of dollars every year. Losses in biodiversity will, presumably, lead to
unknown economic losses in the future.
WHAT CAN BE DONE: PREVENTION
Article 8(h) of the Convention
on Biological Diversity, which Canada has ratified, states that Contracting
Parties, as far as possible and as appropriate, shall "prevent the
introduction of, control or eradicate those alien species which threaten
ecosystems, habitats or species." It is generally agreed that preventing
the introduction of non-indigenous invasive species is cheaper and more
effective than trying to control them after they have arrived.(17) The difficulty is in predicting what
the next invader will be. While invasive species seem to have certain
characteristics in common, there are no predictive models that can clearly
identify what will become an invasive species.
Predicting when an invasion
will occur also remains problematic. Some introduced species remain innocuous
for years and only then, for mostly unknown reasons, become invasive.
The introduction and invasion of Zebra Mussels into the Great Lakes had
been predicted since the 1920s; however, the invasion did not occur until
the late 1980s. Presumably some environmental factors play a role in determining
when a species might become invasive. For Zebra Mussels, it is theorized
that improving water quality in the Great Lakes facilitated invasion.
Climate change may also play a role in what becomes invasive.(18)
Without a means to predict what species may invade under which circumstances,
it is very difficult to control their entry.
Attempts can be made, however,
to minimize introductions by identifying pathways that are known to be
at high risk for causing introductions, such as ballast water and wooden
packing crates. Once identified, these routes can be regulated in a manner
that minimizes entry of organisms, without having to identify particular
organisms as potentially invasive. In the case of wooden packing crates,
the Canadian government is increasing vigilance at ports and is leading
discussions on the development of an international solid wood packing
material standard. There are many efforts on many scales to try and minimize
the transport of organisms through ballast water.
The Problem of Ballast Water
Over ten billion tonnes
of ballast water annually are transferred around the globe, potentially
carrying thousands of species.(19) The Zebra Mussel, introduced into the
Great Lakes by ballast water, has infested over 40% of waterways and has
caused billions of dollars worth of damage and control costs. The introduction
of the Comb Jelly Fish into the Black Sea in 1982 virtually destroyed
all fisheries at a cost of $500 million (U.S.) annually.(20)
A number of actions can
be taken to control entry of organisms through ballast water. The United
Nations International Maritime Organization (IMO) has produced guidelines
for the management of ballast water that include such measures as: minimizing
uptake of organisms by choosing when and where to take on water; regular
cleaning of ballast tanks; discharge to on-shore holding facilities; and
exchange of ballast water at sea. The fourth method is thought to be effective
because salt-water organisms generally will not survive in fresh water.
It is not perfect, however, particularly if a lot of sediment remains
in the ballast tanks and if water is taken on from an area that has organisms
with a wide salt tolerance, such as can be found in the Black Sea. Other
means being studied are more intensive and involve, for example, filtration
of water, sterilization by UV light or biocides, and the addition of predators
to the tanks. Currently, the United Nations IMO guidelines are voluntary;
however, work is progressing to incorporate them into a legally binding
convention, perhaps as an annex to the International Convention for the
Prevention of Pollution from Ships (MARPOL).
Various governments and
international organizations have in place a variety of guidelines or laws
to try and control this route of entry. The most common method is to require
ships to exchange ballast water at sea. The Canada Shipping Act,
as amended in June 1998, includes the authority to regulate ballast water;
however, ballast water control remains voluntary. False declarations regarding
ballast water management have been successfully prosecuted under this
Act. The United States has had mandatory regulations requiring
ballast water exchange for ships destined for the Great Lakes since 1993.
Both Canada and the United States report high levels of compliance; however,
a 1995 report noted that only 50% of vessels entering the seaway submitted
Canadian-requested reports on the procedures followed for ballast water
management.(21) The current ballast
water exchange programs such as the Vancouver Port Authority mandatory
ballast water exchange program may only require an 85% exchange,
which is insufficient to dilute the ballast water to lethal levels for
many organisms. One option would be to require a three times exchange
at sea, which is more effective. However, no ballast water management
program will ever have a 100% success rate, short of requiring biocide
use. Such programs can be used only to reduce risk.
Another problem with most
ballast water regulations is that they only encompass ships with ballast.
Ships that have cargo, or so-called NOBOBs (no ballast on board), are
not regulated but contain some unremovable sediment and water. These have
been identified as high-risk ships, especially if they enter the Great
Lakes, unload their cargo, and then take on ballast water to go to another
port within the Great Lakes.
Regulations regarding management
of ballast water are one of the few ways by which unintentional introductions
of invasive species can be mitigated. Some other countries, particularly
ones that have a history of significant invasions, have more stringent
rules such as the fumigation of arriving aircraft. Even with tight regulation
and relatively easy access to arriving transport, invasive species will
still enter. With the ever-increasing traffic in goods, unintentional
arrivals will increase in numbers. Intentional species introductions are
another problem and can be addressed through import restrictions of pest
Through Legislative Restrictions on Importation
Many countries have import
restrictions on animals and plants, particularly to prevent harm to domesticated
plants and animals. In Canada, the statutory authority to restrict the
movement of plants and animals is derived from a number of Acts.
The Plant Protection Act is designed to "prevent the importation,
exportation and spread of pests injurious to plants and to provide for
their control and eradication and for the certification of plants and
other things." A plant pest is determined through a risk assessment
process as outlined by the North American Plant Protection Organization,
NAPPO Standard for Plant Pest Risk Analysis, a standard largely based
on potential economic harm. NAPPO is a regional organization of the International
Plant Protection Convention (IPPC) of the Food and Agriculture Organization
(FAO) of the United Nations. The pests regulated by this Act include
obvious problem organisms such as various crop diseases and predators
but also include some true aquatic plants such as Hydrilla and Eurasian
Milfoil, which are defined as pests and whose entry into Canada is prohibited.
However, because the Eurasian Milfoil is already in Canada and
Hydrilla is widely touted as being the next invader of the Great Lakes,
it having already spread from Florida to Pennsylvania(22)
there seems little power in this Act to prevent invasions
without correctly identifying possible invaders and classifying them as
pests, before they invade. The IPPC has been recently amended to be in
accord with World Trade Organization phytosanitary standards, which exist
to ensure that nations do not use entry of potential threats as a technical
barrier to trade. Because species must be shown to be economically harmful
before action can be taken, the IPPC does not seem to be a very powerful
tool to be used as a precautionary measure to avoid invasions.(23)
In a similar manner, the
Health of Animals Act is "An Act respecting diseases and toxic
substances that may affect animals or that may be transmitted by animals
to persons, and respecting the protection of animals." Importation
of some invasive non-indigenous species is prohibited under this Act.
The Honeybee Prohibition Importation Regulations of the Act,
for example, are designed to prevent the importation of honeybees from
the U.S. because of the invasive Varroa mite, that was first found in
that country in 1987. In fact, the honeybee is a European import that
has largely taken over the position of pollinator from the native pollinators
for many insect-pollinated plants, making it one of the most important
insects from both an ecological and an economic point of view. Because
the honeybee was so highly invasive after its introduction, it is now
making those plants and industries which depend on it vulnerable to other
invasive diseases and pests of honeybees such as the Varroa mite.(24)
So far, for a combination of reasons including import restrictions, the
mites have not become a serious problem in Canada. Ironically, the invasive
African honeybee, the so-called killer bee, is being touted by some as
a remedy to the mite because it is more resistant to the mite than is
the European honeybee.(25)
The Wild Animal and Plant
Protection and Regulation of International and Interprovincial Trade Act
(WAPPRIITA), although largely designed to prevent the importation and
movement of plants and animals listed in the Convention on international
trade in endangered species of wild fauna and flora (CITES), also has
clauses to prevent the introduction of harmful species into Canada. Schedule
II of the Wild Animal and Plant Trade Regulations contains a list
of such species for which importation is prohibited. The list is currently
limited to the Racoon dog, a number of genera of mongoose, and a few birds.
A fourth Act that
can have the effect of preventing the importation and spread of potentially
harmful species is the Seeds Act. However, this Act is designed
to maintain crop seed quality rather than to prevent the spread of invasive
non-indigenous species in natural systems. Of the 44 species listed in
the Canadian Wildlife Service publication Invasive Plants of Natural
Habitats in Canada, the Seeds Act lists three that are prohibited
noxious weeds, one that is a primary weed and another that is a secondary
noxious weed. Prohibited weeds are not allowed in seed lots while the
level of harm and abundance of other noxious weeds are used to designate
a seed lot quality.
The federal Seeds Act
has been described as having potential only as a weak preventive measure
for control of invasive non-indigenous species. Provincial Weed Acts have
greater potential to require control of noxious weeds and many empower
municipal governments to list species as being noxious weeds.(26)
However, the listing of a species as a noxious weed may not be of much
benefit to the natural environment because most control measures are designed
for urban or agricultural purposes and may not be appropriate in natural
settings where they may also harm the native flora.
C. Prospects for Eradication
Although it is generally
recognized that prevention is better than trying to eradicate or control
invasive non-indigenous species once they are established, there is often
no other possibility than to react to an invasion after it has occurred.
For a well-established species, eradication is often impossible and there
is little alternative but to attempt to control its spread.
As stated in the World Conservation
Union (IUCN) Guidelines for the Prevention of Biodiversity Loss Caused
by Alien Invasive Species, control and eradication of invasive non-indigenous
species is far easier with informed and co-operating local communities,
appropriate sectors and groups. In Australia, where, according to some
accounts, the "average taxi driver" is aware of the serious
consequences of invasive species, it is far easier to mobilize public
support for drastic measures to eradicate them.(27)
At Easter in 1999, divers found a highly invasive small mussel, similar
to the Zebra Mussel, in three marinas in the vicinity of Darwin. Within
five days the Australian government had, despite boaters protests,
quarantined the marinas and soon thereafter had killed everything in the
water with a mixture of chlorine and copper. No mussels have been seen
since and the natural biota is beginning to return. A highly invasive
species of algae which has been causing great damage in the Mediterranean
region has been tentatively identified in a California lagoon causing
a consortium of agencies to cordon off the lagoon in preparation for eradication.(28)
In Canada, a park in the Halifax Regional Municipality has recently been
put under federal quarantine and thousands of Red Spruce are being destroyed
in an effort to eradicate the Brown Spruce Longhorn Beetle (BSLB).(29)
The ease of eradication
will depend to a large extent on how well the invasive non-indigenous
species has established itself. This in turn will depend on how early
the infestation is determined. The BSLB has actually been in the park
in the Halifax area since 1990, but at the time, samples taken were misidentified
as a North American species. Had the samples been correctly identified,
an earlier pest risk assessment may have saved a lot of the trees that
are currently being destroyed. Clearly, detailed monitoring and acute
vigilance is required to identify possible invaders at the earliest stage
possible, particularly when the threat is to one of the biggest industries
in Canada, such as forestry.
If the early stages of an
infestation are missed and the species becomes established, it is often
very difficult to eradicate. There are some examples of eradication of
established species, such as the Nutria, a rodent introduced for the fur
industry in the United Kingdom. Such eradications are, however, rare and
very costly. Controlling established invasives is usually all that can
be hoped for.
Control of invasive non-indigenous
species can occur through a number of means. Because most invasive non-indigenous
species are adapted to disturbed landscapes, one method of limiting their
spread is by limiting the level of disturbance of the landscape. This
is not an easy task given the amount of, and need for, agricultural land.
Physical methods of cutting plants and trapping organisms may have limited
success, particularly in the case of plants that produce seeds which have
an extended dormancy or with aquatic plants which can propagate from the
small pieces created by cutting. That being said, the eradication of the
Nutria was performed through a massive trapping campaign.
Various methods of poisoning
can be used. Clearly, the more specific the toxin is to the target the
better. The Sea Lamprey which established itself in the Great Lakes
and devastated the Lake Trout population after the completion of the canal
systems that form the St. Lawrence Seaway has been largely
controlled through the use of a very specific toxin directed against the
larval stage of its lifecycle. The effectiveness of a toxin will depend
on knowledge of the physiology of the target, when the organism is most
susceptible to it, and exactly how it is delivered. Basic research on
the life history of the target is thus essential to increase effectiveness
and decrease the chance of affecting non-target organisms.
One of the most promising,
though often risky, methods for long-term control is through biological
control. Non-indigenous species can become invasive, in part because they
may have very few predators or diseases. Thus, the introduction of a predatory
organism or disease from the invasive species native habitat could
theoretically establish a balance and keep the growth under control. This
type of control also requires a great deal of basic research prior to
release to ensure that the introduced organism doesnt affect native
plants or animals. The openness of the research process is also important.
In Australia, a virus was being studied on an island; the virus, which
was going to be released against rabbits on the mainland, escaped. It
has apparently been a success in controlling rabbit populations, but has
raised much concern regarding the openness and transparency of the study.(30) In an age where people have heightened concerns over
release of organisms, either genetically modified or non-native, it is
essential to keep the public informed of the procedures being followed.
In the past, many errors
have occurred in the introduction of species for biological control. The
English (House) Sparrow, introduced into North America to control the
Canker Worm, has since become a pest without affecting the Canker Worm.
Other introductions of biological controls have turned into a fools
game of having to introduce a series of control organisms to control the
latest unsuccessful attempt at biological control.(31)
Many of these examples of failures are derived from past mistakes, particularly
associated with vertebrate introductions, that would not occur given todays
more stringent standards, though errors still do occur. As has been pointed
out, however, the risks associated with the introduction of a biological
control agent cannot be weighed in a vacuum, but must be rated against
the risks of doing nothing or using other control mechanisms such as pesticides.(32)
Agriculture and Agri-Food Canada has been primarily responsible for the
approximately 70 exotic insect species that have been released since 1952
in an effort to control 21 weeds, largely of importance on rangeland.(33)
and control of invasive non-indigenous species requires co-operation at
the international, national, provincial and community levels. The introduction
of invasive species through primarily inadvertent means can best be approached
by identifying pathways at high risk of allowing introductions, such as
ballast water and shipping materials. Addressing the problem can occur
through legislation on a national level, but ultimately will require international
co-operation and possibly binding conventions, such as has been suggested
for MARPOL with respect to ballast water and a convention on shipping
materials to prevent such introductions as the BSLB in Halifax. Given
that introductions will continue to occur, it is essential that a comprehensive
monitoring plan be in place and, should an invasion be found, steps be
quickly taken to eradicate the organism.
Clearly, the federal government
has a role to play in research. Research is necessary to develop best
practices for eradication and control, develop preventive legislation,
and monitor non-indigenous species movements. Monitoring is an important
aspect in mitigating this problem, and such projects as the Invasive Plants
of Canada (IPCAN) project are invaluable.
Other international efforts,
such as the International Plant Protection Convention and the World Trade
Organizations phytosanitary standards, currently emphasize the economic
implications of trade in goods. Because of the emphasis on facilitating
free trade and the potential for the use of phytosanitary standards as
a non-tariff trade barrier, however, there would seem to be little in
these documents that could be used as a precautionary invasion-fighting
tool.(34) Action on article 8(h) of the Convention
on Biological Diversity, through implementation of the IUCN guidelines,
may be better able to prevent invasions for strictly ecological reasons.
With many international agreements that touch on this issue, the potential
for conflict between agreements is high.
Currently, legislation in
Canada, as in most of the world, is primarily designed to prevent damage
to agricultural crops. Legislation to address the impact on natural systems
is lacking, although WAAPRIITA could presumably be used more effectively
for this purpose. With many laws and government agencies involved at all
jurisdictional levels, co-ordination is of paramount importance. Recognizing
the importance of the invasive non-indigenous species issue, and the ad
hoc manner in which this problem is approached, United States President
Bill Clinton signed Executive Order 13112 in February of 1999. In part,
this Executive Order created an Invasive Species Council with the mandate
to produce an Invasive Species Management Plan, one that would help co-ordinate
the fight against invasive non-indigenous species. The draft plan seems
to have been received well.
Above all, an informed public
is necessary to help alleviate the problem. If people continue to transport
organisms unknowingly, or to plant organisms such as Purple Loosestrife
in their gardens, it will be next to impossible to prevent the spread
of harmful invasives. In addition, many of the control projects currently
underway depend on informed volunteers. An informed public is also necessary
to create the political will to allow for the formation of strong legislation
and to take decisive action upon the discovery of a potential invasive
(1) David Pimentel et al., "Environmental
and Economic Costs of Nonindigenous Species in the United States,"
BioScience, Vol. 50, January 2000.
(2) Other terms for non-indigenous used in the literature
include: exotic, alien, non-native and foreign.
(3) Erich Haber, Invasive Exotic Plants of Canada, Fact
National Botanical Services, Ottawa.
(4) Canadian Wildlife Service, Invasive Plants of Natural
Habitats in Canada,
(6) Associated Press, "Alaska Worried About Threat
Posed by Atlantic Salmon: Concerns include diseases, competition for food,"
Times Colonist, 28 August 2000.
(7) Paul McKay, "Ultimate Invader Threatens
Salmon: Aquaculture Complex Suspected Source of Rainbow Trout," Ottawa
Citizen, 15 June 2000.
(8) Ronald Bailey, "Preaching Ecological Xenophobia:
Ronald Bailey Asks: Are We Really Under Attack by Non-Native
Species? Should We Care?" National Post, 3 August 2000.
(9) Hugh MacIsaac and Anthony Ricciardi, "Why We Shouldnt
Let the Bugs In," National Post, 9 August 2000; see also
Paul Ehrlich and Anne Ehrlich, Betrayal of Science and Reason,
Island Press/ Shearwater Books, Washington, D.C., 1996.
(10) See Science, Vol. 285, 17 September 1999.
(11) Pimentel et al., January 2000.
(12) Richard Stone, "Keeping Paradise Safe for the
Natives," Science, Vol. 285, 17 September 1999.
(13) MacIsaac and Ricciardi, 9 August 2000.
(14) Pimentel et al., January 2000.
(15) David Quammen as cited by Joel Achenbach, "The
Invaders: Local Plants and Trees are Buried Alive as Foreign Species With
No Natural Predators Mount a Full-Scale Assault," Montreal Gazette,
5 August 2000.
(16) Pimentel et al., January 2000.
(17) IUCN (World Conservation Union) Guidelines for the
Prevention of Biodiversity Loss caused by Alien Invasive Species, February
(18) Martin Enserink, "Biological Invaders Sweep
In," Science, Vol. 285, 17 September 1999.
(19) Global Ballast Water Management Programme, UN Moves
on Alien Invaders, Media Release, 10 July 2000.
(20) Ballast Water News, Issue 1, April-June 2000.
(21) Proceedings of Maintaining Biological Integrity of
the Great Lakes: Preventing Harmful Invasions, International Joint Commission,
25 September 1995.
(22) Phil Surguy, "Waiting for the Unwary: Human
Inadvertance Will Probably Bring to the Great Lakes a Weed That Knows
No Limits," National Post, 20 June 2000.
(23) Chris Bright, Life Out of Bounds, Bioinvasion
in a Borderless World, W.W. Norton & Company, New York, 1998.
(25) Debora MacKenzie, "A Kinder, Gentler Killer,"
New Scientist, 1 July 2000.
(26) See the Canadian Wildlife Service publication Invasive
Plants of Natural Habitats in Canada for a more detailed description
of Provincial Weed Acts as they relate to invasive non-indigenous species.
(27) Jocelyn Kaiser, "Stemming the Tide of Invading
Species," Science, Vol. 285, 17 September 1999.
(28) Jocelyn Kaiser, "California Algae May be Feared
European Species," Science, Vol. 289, 14 July 2000.
(29) Canadian Food Inspection Agency Press Release, 30
(30) Elizabeth Finkel, "Australian Biocontrol Beats
Rabbits, But Not Rules," Science, Vol. 285, 17 September
(31) Bright, 1998.
(32) David Pimentel, "Biological Control of Invading
Species," Science, Vol. 289, 11 August 2000.
(33) Lethbridge Research Centre, Crop Sciences Section,
(34) Bright, 1998.