Harvesting invasive species receives some scientific guidance, and perhaps a place in the manager’s toolbox, this month with the publication of Pasko and Goldberg’s “Review of harvest incentives to control invasive species” (pre-pub proof) in the September issue of the scientific journal, Management of Biological Invasions.
The blind eating the blind, lack of guidance for harvests
Eating invasive species has received a lot of attention from the media over the last few years probably as a combination of 1) being kind of weird and 2) feeling like a good idea. It’s that second reason that has kept many natural resource managers and conservationists on the sidelines of the conversation. What has felt like a good idea for resource management in the past has often turned into something really bad. For example: kudzu, cane toads, and Nile perch are cases of well-intentioned introductions gone awry. That is, managers and conservationist may be a bit trigger-shy around tactics that just *sound* good. Indeed, the limited offerings in the scientific literature pertaining to harvesting invasive species urge caution due to the potential unintentional consequences of developing market or social values for invasive species (Nunez et al 2012). The biological and economic limitations of harvests, such as for Asian carp (Tsehaye et al 2013), make it clear that harvests aren’t a silver-bullet solution. However, there is recognition that harvests could play a part in larger control and conservation measures. Guidance for when and how to incorporate harvests into invasive management schemes has been missing; a new article by Pasko and Goldberg lays out the possible place for harvests of invasive species within a holistic, adaptive management framework.
11 Recommendations for harvesting invasive species
Pasko and Goldberg review the many issues that surround the potential benefits and risks of harvesting invasive species, and they conclude with the following recommendations to help maximize the success of harvest incentive programs:
1. Define the management plan and objectives
Defining a plan and objectives is a lot like getting all your ingredients in order before you start cooking, like this Almond tilapia.
The conservation goals of harvesting invasive species are obscure in many contexts, yet defining success is the first step. There’s no universal goal for all invasivores, and total eradication is far too lofty. Setting realistic goals will be an important part of integrating harvests into management.
2. Understand the costs
There’re costs to harvesting invasive species, more than just putting your mouth where your mouth is. Matt and Andy enjoy meal-worm Rice Krispies treats
Harvesting invasive species may seem like a win-win, and under ideal circumstances perhaps sales and recovery of ecosystem services could increase total social value. But it won’t be free. Any control program will have administrative costs that may be difficult to recoup.
3. Understand target species’ population dynamics
Models of population dynamics can be simple, like this logistic model, but detailed models tailored to specific species and populations will be more successful.
The population dynamics of an invasive population determine how- or if- the population will respond to harvesting effort. In some cases, harvests could actually increase population growth. Understanding population dynamics may prevent such unintended consequences and help determine how much populations should be reduced to achieve management goals.
4. Consider risks to human health and safety
Phragmites may sequester metals and other toxins, which could pose health risks if consumed regularly and/or in large quantity.
Some risks are obvious; for example, lionfish have poisonous spines. Others are not so obvious. Many species have high toxic loads, like sea lamprey in the Great Lakes.
5. Evaluate potential ecological outcomes
NOAA & Great Lakes Fishery Commission food web exemplifies the complex interactions linking many components of ecosystems that may change given alterations in invasive populations.
Invasive species, despite being undesirable by definition, often play substantial roles in the ecosystems which they have invaded. Understanding the “dominoes” to fall following removal is important. For example, while alewife are an invasive species in Lake Michigan, they are vital forage for salmon, which are highly desirable.
6. Monitor for unintended outcomes
One way to monitor for unintended consequences.
The complex ecological interactions of ecosystems makes unforeseen undesirable responses to harvest likely. For example, when cats where eradicated from Macquarie Island, the population of rabbits grew rapidly and with devastating results to the local ecosystem (Bergstrom et al 2009, Journal of Applied Ecology).
7. Prevent re-introduction
Andy standing guard to prevent further species introductions.
Harvesting programs will be ineffective if new target individuals (perhaps new species) are able to regain access to the ecosystem. Prevention, monitoring, and rapid response to new introductions will be required to prevent re-establishment.
8. Incorporate adaptive management
If a management plan is a recipe, adaptive management is tasting and flavoring a dish as you cook.
Adaptive management follows the principal that effective management requires periodic assessment of the invasive population and the recovery of ecosystem service in order to update management methods as new information becomes available.
9. Conduct outreach
Public understanding and support of invasive species management will make a project easier to manage. Besides, someone’s got to eat all this garlic mustard queso.
10. Restore impacted areas
Okay, once all this phragmites is gone, what’s going to grow here instead?
Pulling up a forest of garlic mustard is going to leave behind a mess. More importantly, just removing an invasive population doesn’t mean that native species and ecosystem services will return on their own. Management should include a clear idea about what services are desired from a target area, and how best to achieve them.
11. Determine appropriate points for government intervention
More than just funding projects, governments can provide outreach and education, as well as possible regulatory oversight. For example, adapting appropriate hunting regulations or monitoring food safety.