Pathways
Invasive species “pathways” are the means by which they
are moved from one location to another. Natural pathways could include
means such as wind or water currents. Other pathways can be enhanced
by, or even entirely created through, human activity. Sometimes this
is done intentionally, other times quite unintentionally.
Other Pathways:
Can You Give Me An Example?
Let’s take as an example a weedy species that has a pretty
flower and hooked seeds. The seeds of that flower may attach to the
fur of a rabbit and spread naturally within the valley that is home
to that rabbit. The same seed could have instead attached to the pants
or boots of a hiker who then carries it over the mountain to a new
valley and thus enhances its spread. Or, at trails end, the hiker
may fail to brush off his gear and then board a plane for his home
that is far away in a place that this seed may never have reached
naturally. Finally, since this plant had such a pretty flower, that
same hiker might remember it and upon his return home decide to go
to the internet and order a packet of its seeds to plant in his garden.
Each of these represent different pathways, natural or human-mediated,
enhanced or wholly artificial, intentional or unintentional, that
affect how rapidly and to what places a species is moved. If the species
thrives in its new home, the whole cycle of opportunities for spread
is begun again from this new location. Pathways are thus simply the
“modes of transportation” for how species move about.
Should We Focus on Species or Pathways?
Some individual species present unique or urgent challenges and offer
unique opportunities for controlling their spread. However, there
are literally millions of species around the globe that come into
contact with humans and are thus potential travelers along these pathways.
Even if it was technically possible and society wanted to, it would
be unimaginably expensive to develop unique methods for preventing
the human-assisted spread of each and every individual species. A
much more practical approach is to focus on these pathways and develop
methods to reduce the risk of spreading all species that have “access”
to these pathways.
What Are Some Important Pathways for Aquatic
Invaders?
For aquatic species, particularly coastal species, one of the most
significant pathways for the movement of species from one area of
the globe to another is transportation by ships – either on
the outside (hull) of the ship or in “ballast water” carried
within the ship. Large ships take water (and all of the organisms
living in that water) onboard into various internal compartments to
provide stability and trim, or ballast, while they are at sea. That
water is often taken in at one port and then pumped back out once
they arrive in a new port to take on a load of goods. The result is
that a stew of living organisms is transported and released in places
these species would never have made it on there own.
Among the thousands of species transferred around the globe in this
way, organisms such as the zebra mussel in the Great Lakes, toxic
dinoflagellates in Australia, and cholera along the Gulf Coast of
the United States have caused serious ecological, economic and human
health impacts. Ships discharge over 21 billion gallons of foreign
ballast water, along with all of its living non-native stowaways,
into U.S. bays, estuaries, lakes and rivers each year. This is a huge
source of potential aquatic invaders.
What Are Some Other Pathways for Aquatic
Invaders?
Aquaculture: Many non-native
species have been intentionally introduced for aquacultural purposes
– for example, oysters, Atlantic salmon, tilapia, carp, and
others. Many cultured species have caused little harm and produced
significant economic benefits. However, others have escaped containment
and become a source of potential harm to native species and their
habitats. Sometimes the larger concern is with smaller, undetected
species that can come along as unknown and unwanted riders with the
intended aquacultural species. For example, Pacific oysters were introduced
and remain an important seafood product; but their introduction also
brought along with them the oyster drill, a harmful pest to both commercial
production and native oysters.
Aquariums & Water Gardens: Aquarium pet dealers and water garden suppliers may offer hundreds
or even thousands of different species or varieties for sale. Often
the vast majority of these are not native to the location in which
they are purchased. Sometimes you even get more than you bargained
for! It is not uncommon to order one species and have it come with
other, potentially more problematic, species mixed in with the shipment.
If these non-native species stay in their aquarium or water garden,
or are returned to the dealer or otherwise safely disposed of when
no longer wanted, this may not present a problem. However, many invasive
plants and nearly half of all non-native fish that have become established
in U.S. waters are the result of escape from commercial or personal
holding facilities or disposals from personal aquariums or water gardens.
Hobbyists tired of their pets or unable to move them may think it
is humane to dump them into nearby waters, but this is not safe and
usually illegal. Released pets can be subject to the diseases and
parasites of native species or may spread their own exotic diseases
to native species. Many released pets will be eaten by fish, birds
or snakes. Some, like pirahna, can be dangerous to humans; others
will eat or compete with native species and damage natural ecosystems.
If you have a no longer wanted aquarium species, here are some ideas
for what to do protect the natural environment while caring about
your pet. Instead of releasing it:
- Return it to a pet shop to trade/sell
- Give it to another hobbyist friend
- Donate it to a school or other public facility (e.g., hospital)
- If none of these will work, you can put it to sleep at home by
putting it in a container of water and freezing it. Cold has a
natural numbing effect and is considered a humane way to put
it to sleep. If you’d rather not do this, your vet may be
able to help.
Recreational or Commercial Watercraft: Small boats, float planes, jet skis, and their trailers, or any other
recreational or commercial gear that is regularly in contact with
water can move non-native species around, often without us even realizing
it. Aquatic plants, in particular, are easily transported when plant
fragments get tangled on boat propellers, trailers and other gear.
An excellent source of additional information on how to be a clean
boater (or pilot) and help stop aquatic hitchhikers can be found at Protect Your Waters web site.
Bait: The use of live bait may
or may not be legal in your area. Always check the regulations. If
live bait is legal, it is essential that any “left over”
bait not be released into the wild. Some bait species, for example
certain chub and minnow species, can reach explosive population levels
when released into new waters and eventually overwhelm native sport
fish species.
Fish Stocking: Many fish species,
particularly those considered to be valuable for sport or commercial
fisheries, have been stocked in waters to which they were not native.
If careful studies are done on both the potential benefits and potential
risks of such introductions, and a well-reasoned protocol is followed,
these introductions can provide significant social benefits. However,
some ill-conceived introductions have caused a great deal of ecological
harm. These harmful introductions, often by well-intentioned but poorly
informed individuals not associated with the proper authorities, are
nearly always illegal. An unfortunate example of this in Alaska is
the introduction of northern
pike into southcentral waters, including the extraordinarily important
Kenai River drainage.
Live Seafood: This pathway is
similar in many respects to the “Aquariums and Water Gardens”
one discussed above. Both the live seafood itself (e.g., lobster,
tilapia, crabs) and the materials in which some live seafood is shipped
(e.g., seawater, moist algae) can cause problems if they are allowed
to escape confinement or are disposed of improperly.
Biological Control: One of
the reasons that some non-native species can become invasive is that
the natural controls (e.g., competitors, predators, and pathogens)
that kept them in check in their native habitat are not present in
their new homes. Sometimes these natural biological control agents
from their native habitats can be brought over to control them in
their new home as well. If the agent is truly selective and harms
only the non-native species that it is intended to control, this can
work well. However, sometimes the new introduction can cause other
problems of its own and compound the situation by causing additional
harm to native species or their habitats.
How Can You Reduce Risk Along an Entire
Pathway?
One important way to reduce the chances of introducing harmful invaders
is to use an approach called Hazard Analysis and Critical Control
Point, or HACCP (pronounced hassip). HACCP planning is essentially
a process for taking a close look at each step along the pathway,
identifying which ones present the greatest risks and the best chance
to reduce those risks (i.e., identifying “critical control points”),
and then taking specific actions at those points to reduce risks in
an accountable, tractable manner. Many Alaskans in the seafood industry
may already be familiar with HACCP planning from a different perspective.
Its original use was as a seafood safety technique for reducing the
risk of introducing biological contaminants and protect product quality.
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