Erosion Control

New Zealand’s Unwanted Mammals

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In both Erosion Control magazine and our sister publication Stormwater, we’ve covered many different types of invasive species—plant and animal—and the ways people have attempted to get rid of them. In the early years of the 20th century, for example, it briefly seemed like a good idea to release nutria (very large rodents) throughout the southeastern US to devour the non-native water hyacinth, which was taking over the waterways. The nutria devoured crops, too, though, including sugarcane, and weakened dams and levees by removing most of their vegetation.

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Other biological controls—using one species to eliminate another—have been more successful. Salt cedar beetles have been used to kill tamarisk, or salt cedar, trees, which were once imported to the US from Asia to control erosion. Herds of sheep and goats are often used to eliminate plants like buckthorn that are hard to control by other means.

Now, in New Zealand, there’s a different sort of plan to reduce the numbers of non-native animals that threaten the local species. The country’s native birds and reptiles have few defenses against the rats, stoats, and possums that have arrived relatively recently as stowaways on ships from Europe and elsewhere. The government has tried trapping these unwanted mammals, but in hard-to-reach areas where that’s not possible, the new solution is to distribute poison—pellets containing sodium fluoroacetate, known as “1080”—by helicopter.

The practice is controversial, to say the least. Some protesters fear the pellets will kill the native species along with the invaders (although in reality the unintended victims are mostly other mammals like dogs and deer). Some say the mass poisoning is inhumane. Others fear the poisoned pellets will dissolve and enter the water supply. (Those in favor of using 1080 say it biodegrades into non-toxic components.)

We routinely use herbicides—some with unintended environmental consequences—to control unwanted plants. We’ve tried pesticides and the release of genetically modified mosquitoes to limit the spread of the Zika virus. All of these efforts have been met with protests at some point. At what point do you think the widespread use of poisons like 1080 is justified—and what tests would you want to see to determine their environmental effects, if any? EC_bug_web

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