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Total eradication is not the best approach to invasive species

In a new report from UC Davis, experts have discovered that “total eradication” is not the best approach to target invasive species. According to the researchers, lessons learned from a failed experiment are leading to more successful strategies for controlling non-native species. 

“A failure in science often leads to unexpected directions,” said study lead author Professor Edwin Grosholz. “We slapped our foreheads at the time, but with thought and understanding, it’s told us a lot about what we shouldn’t be doing and provided a way forward for us. The world should get less focused on total eradication and work toward functional eradication.”

The researchers consider functional eradication to be a much more effective approach to invasive species management. This technique was described in a previous study led by the University of Alberta and co-authored by Professor Grosholz.

In 2009, intensive efforts were focused on fully eradicating the European green crab from Stinson Beach’s Seadrift Lagoon in California. This crab costs the U.S. commercial shellfish industry about $20 million in losses every year. 

By 2013, 90 percent of the crabs had been removed from the estuary, and the population had dropped from 125,000 to fewer than 10,000 individuals. A year later, however, the population had exploded to about 300,000 green crabs – nearly triple the pre-eradication population size.

The scientists were monitoring four additional neighboring bays, and no such population explosions of the green crab were observed at those sites. This finding indicates that the increase in crabs was the result of eradication efforts and not environmental changes.

The experts determined that the population explosion in the Seadrift Lagoon was due in part to the fact that the adult crabs typically cannibalize younger individuals. With most of the adults removed, juveniles grew unchecked and overcompensated for the loss of adults.

The study serves as a precautionary tale for natural resource managers. “Don’t try to get them all, or it could come back to bite you,” said Professor Grosholz.

“Instead of a one-size-fits-all approach, this study highlights the need to evaluate possible unintended consequences in selecting management strategies and tailoring these to the particular context and expected outcome,” said study co-author Greg Ruiz.

Just as researchers described in the Alberta-led study, the UC Davis team recommends a “Goldilocks level” approach, where the population is low enough to protect native species without risking a population explosion of the invasive species.

The study is published in the journal Proceedings of the National Academy of Sciences.

By Chrissy Sexton, Staff Writer

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