To interfere or not, that is the question?

By: Dana Sackett 

We are all familiar with the devastating impacts invasive species can have on aquatic ecosystems.  As a result of these adverse impacts, many studies have been dedicated to examining the invasive species problem, including: the process of invasion, predicting which species are likely to become invasive, and the ecological and economic damage they cause.

Silver carp in the Missouri 
by Jason L. Jenkins/University of Missouri, via Associated Press


As habitats become unsuitable, because of human alteration or climate change, many species are unable to move to more suitable locations (because of natural and man-made barriers to movement and population growth), and we may be forced to
move and introduce species to new habitats to conserve biodiversity.  In fact, some have already started this process.  In Great Britain, hotter summers and wetter winters have forced government agencies to move two species of white fish (vendace and schelly) to cooler waters in Scotland.

With rising temperatures and more severe climatic variation, many species are predicted to be ill-suited to their current distributions and at risk of extinction if we do not interfere through “assisted migration”.  However, we are now doing the very thing that has caused so much destruction to numerous ecosystems, introducing foreign species to new habitats.

Vendace: relocated by humans to prevent extinction; picture from


Scientists are considering all measures possible to prevent having to move species to new locations; in the case mentioned above, they had sharpshooters take-out cormorants that were eating the few remaining white fish in their natural habitat.  When left with no other option, scientists are being cautious and trying to take into account every possible negative impact of translocating a species to a new environment.  However, we still do not know everything about the ecology of an ecosystem and thus cannot understand all of the potential impacts on local native species.

Also problematic, there are a limited number of funds to relocate species to new locations and value judgments will often need to be made on which species to save.  Here we run the risk of basing those decisions on species notoriety rather than species need, as funding is often allocated to those species that are popular rather than ecologically important. 

Hawswater lake, where sharpshooters were used to try
and save the Cumbrian white fish; picture from

A study by Mueller and Hellman evaluating invasive risk from assisted migrations found that intracontinental invasions, as a proxy for an assisted migration, were less likely to result in an invasive species and significant harm to an ecosystem.  However, they also estimated that both fishes and crustaceans were exceptions to this trend.

There have been success stories and failures associated with assisted migrations.  However, we have not determined whether the economic and ecological cost of those failures is worth the successful relocations.

I personally struggle with the question of whether it is better to let nature run its course when we, collectively, had a hand in its current direction and the rate of change is faster than many species can evolve.  Do desperate times call for desperate measures?  Or are we causing more problems by interfering?  


BBC News. 2002.  Gunmen to guard rare fish. (news article)

Chorley M.  2011.  Fish threatened by global warming to be moved north: Scores of radical measures planned to help us and our wildlife cope with climate change.  The Independent,  (news article)

Confino J.  2011.  Climate change forces UK rare fish reintroduction further north.  The Guardian,  (news article)
Mooney HA, Hobbs RJ (Eds.).  2000.  Invasive species in a changing world.  Island Press, Washington D.C.
Mueller JM, Hellmann JJ.  2008.  An assessment of invasion risk from assisted migration.  Conservation Biology 22:562-567.  
More information on the debate about assisted migrations can be found here:


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