Design in a Time of Uncertainty
By Rives Taylor, Principal, Global Resilience Research Lead
Accidental or intentional release of aquarium pets increases the potential of these species to spread and invade local ecosystems. Consider the common pleco, also known as the suckermouth catfish – a popular addition to an aquarium hobbyist’s tank.
A native of tropical regions of South America, the common pleco has taken to the waterways of Southeast Texas with a vengeance after being released to the wild by aquarium owners. Pleco, a member of the family of “armored catfish,” has adults that measure about 20 inches.
Its population burgeoning in its new Texas habitat, the species is cited by scientists as a prime example of what can happen when some “non-native” species that evolved in one region begin to thrive in a damaging way in a new location, far away, thereby earning biologists’ “invasive” descriptor in the process.
“The pleco can survive just about anywhere,” said Stephanie Glenn, a senior research scientist and program director for hydrology and watersheds at HARC. She listed some of the problems attributed to the pleco: “It causes erosion from burrowing in banks. Plecos are a problem for native species, because the pleco out-competes them for food and habitat. There are significant ecological and economic impacts.”
On top of all that, the common pleco is just one species of numerous non-native aquarium fish species that concern wildlife biologists in Texas. Others might also become “invasive,” they fear, if introduced in the right numbers or under the right conditions.
If worrisome signs are spotted involving a specific non-native fish species, a full-fledged “risk assessment” of its threats to a local ecosystem can be costly and time-consuming, however.
To address that problem, HARC worked from April 2012 until last December to develop an “invasive species scorecard” for aquarium fishes for the Texas Parks and Wildlife Department (TPWD).
Agency biologists can use the scorecard as what HARC research scientist Birnur Guven, who worked on the project led by Glenn, called a “prescreening” tool: With it, scientists can make a quicker appraisal of how to address potentially problematic species.
Scorecard results might indicate a species does warrant a full risk assessment, though other, less labor - and resource-intensive actions, might be triggered instead. Alternative actions can include such things as education and outreach programs to specific groups – aquarium-fish retailers and the aquarium-hobbyist public - such as informing them about alternatives to release or the implications of release.
Through a custom-built “decision matrix,” the scorecard developed by HARC can help wildlife officials set priorities for how to manage limited agency resources.
The initial phase of the HARC research project led by Pris Weeks, an environmental anthropologist and retired HARC employee, examined the social factors and thought processes that prompt people to release aquarium fish to the wild.
Making use of data from Weeks’ 2008-11 study, the next phase of the study led by Glenn produced a scoring system that incorporates both ecological and social factors behind the “invasive” potential of aquarium species’ populations. The scorecard enables users to calculate and combine a fish species’ hazard rankings in three categories – market-availability potential, release potential and survival/reproduction potential.
Scoring for a species’ market-availability potential pertains to the social and market networks through which aquarium fish are purchased or exchanged. Release potential scores reflect social and species’ biological factors that motivate people to release a certain aquarium fish to the wild. Survival/reproduction potential scoring yields a number that represents the ecological potential for a released species to achieve “invasion” status.
In the “release potential” category, for example, different numbers of points are assigned for yes and no answers to questions such as these:
- Is the species sold in superstores?
- Does the species breed easily (without encouragement) in captivity?
- Is the species able to grow to 24 centimeters and larger?
- Is the species rare, as defined by some ranking system such as one on the fishbase.org website?
- Is the species always aggressive towards other individuals in an aquarium?
- Does the species pose risks to humans in the aquarium (venom, wounds, etc.)?
Varying scores in the three categories can yield different recommended responses by resource managers.
For instance, medium or high scores for market-availability and release potential, combined with a high score for survival/reproduction potential might trigger a “rapid-response” action, with officials alerting different agencies and groups to be on the lookout for signs that a species is spreading. On the other hand, a high market-availability score, with low scores in the other categories might prompt management to keep a watchful eye for now but not target resources to other actions at this time.
The National Oceanic and Atmospheric Administration has concluded that invasive species’ ecological impacts are outweighed only by habitat destruction as a leading cause of declining biological diversity globally, Glenn said. Since aquatic invasives are typically very hard to eradicate once established, any tool that aids in prevention is considered a powerful resource for managers.