A significant number of invasive aquatic species can be attributed to the aquarium industry and water garden trade and the associated practice of intentionally releasing unwanted pets. This includes fish, molluscs and aquatic plants but can also i...
A significant number of invasive aquatic species can be attributed to the aquarium industry and water garden trade and the associated practice of intentionally releasing unwanted pets. This includes fish, molluscs and aquatic plants but can also involve amphibians and reptiles. With the increasing growth of this industry, it is anticipated that this vector will continue to be an important source of introductions of invasive aquatic species. Future efforts should focus on prevention through increased public education and more stringent regulations.
Species involved in the aquarium industry routinely include ornamental fishes, molluscs and aquatic plants. Organisms associated with the water garden trade can include reptiles (e.g., turtles), fish (e.g., koi carp, goldfish, etc.), amphibians and aquatic plants. Many ornamental fish are imported from tropical areas such as Africa, South America and South-East Asia. Crossman and Cudmore (1999) attributed the introduction of almost one hundred species of fish to the aquarium trade. Mackie (1999) reported that of 22 species of molluscs, which have been introduced to North America, eight may be attributed to the aquarium trade. Pickrell (2004) reported 16 species of non-native tropical fish, attributed to freed aquarium fish, at 32 different locations along the southeast Florida coast.
Once imported, there are several potential means for exotic species being introduced into the wild. Escape, either from a breeding facility or during transportation, has been known to occur (Beyer, 2004). Many introductions are believed to have been deliberate releases, however. This may involve disposal of excess unsold or unwanted organisms, release as part of a religious custom, or the 'humane' disposal of a pet that has outgrown its holding facility or is left at the onset of winter when closing a water garden. In most of these cases, there is no intention of establishing a self-sustaining population. There is also the risk of introducing exotic organisms, parasites or pathogens from water used to transport aquarium fish (Trust and Bartlett, 1974).
Geographical Routes and Corridors
Once an invasive species has gained access into a new ecosystem, there are a number of ways in which they can expand their range. Natural movements using canals, streams and rivers are common. There are several large canal systems (Erie, Trent-Severn, Welland, Rideau, etc.) in eastern North America that have been associated with the dispersal of aquatic invasive species. Many species introduced to one of the Great Lakes have used interconnected waterways to become distributed in the other lakes. Invasive species can also be spread by a number of other means including recreational boating, use of live bait and water diversions.
Public education is important to prevent the introduction of invasive aquatic organisms. Most introductions from this vector involve the intentional release of an unwanted pet as a humane way of disposal. Some cultures also have traditions regarding the release of a pet for social or religious reasons. To date, attempts have been made to develop programs for the elementary school curriculum (McGarry, 2004). There are also collaborative programmes, such as Adapt-a-Pet, Habitattitude and Fish Rescue, which promote awareness and strive to prevent releases by aquarium hobbyists and water garden owners (Lichtkoppler and Jensen, 2005).
Many species of tropical organisms are unable to survive over winter in a temperate climate. There are numerous instances, however, where they were able to adapt and become established. Once introduced, an exotic species can rarely be eradicated. For example, there have not been any successful eradications of any alien species in the Great Lakes basin (Dextrase, 2002).
Once an invasive species is detected in the wild, a rapid response is required. In some cases, existing barriers, such as dams, waterfalls, etc. can be used to control the spread of exotic species. In other instances control measures need to be implemented. There are several types of potential control measures. Mechanical control involves manual measures, such as constructing wetland exclusions for carp, use of mechanical harvesters to control Eurasian water milfoil, placement of matting to control aquatic vegetation and uprooting stands of purple loosestrife. While there have been some successes with mechanical controls, many of these techniques are costly and time consuming and prove ineffective. For example, despite mechanical harvesting programmes to prevent its spread northward, water chestnut successfully colonized the Richelieu River system (Gratton, 1998).
Chemical controls usually involve the use of herbicides or pesticides which target a particular species and have minimal impact on other non-target species. The use of TFM (trifluoromethyl-4-nitrophenol) to control sea lamprey in the Great Lakes is an example of chemical control. The difficulty is having a selective chemical control agent for each of many different invasive species. Several new products are currently under development but require longer term testing.
Biocontrol involves the introduction of predators or pathogens of an alien species. This type of control has been attempted in several situations including the use of weevils for aquatic plant control (Shaw, 2004) and releasing European beetles to control purple loosestrife (Malecki et al., 1993). Unfortunately, biocontrol agents are not always species-specific and may become pests themselves with impacts on non-target species (Dextrase, 2002).
Undoubtedly, more regulatory measures are required to prevent the introduction and spread of invasive aquatic species. Specifically, restrictions, regarding the importation, sale or culture of high risk species are required. High risk species would be those which have potential to establish populations, are voracious and aggressive, have a proven capacity for environmental damage or are known to carry ecologically important diseases or parasites.
The Aquatic Nuisance Species (ANS) Task Force is an intergovernmental organization dedicated to preventing and controlling aquatic nuisance species, and implementing the Nonindigenous Aquatic Nuisance Prevention and Control Act (NANPCA) of 1990. The
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DIAS, Database on Introductions of Aquatic Species
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Sea Grant National Aquatic Nuisance Species Clearinghouse