Fighting one invasive species with another

As reported in the Austin-American Statesman, the invasive aquatic plant hydrilla (Hydrilla verticiallata) has invaded Lake Austin, and the state of Texas wants to introduce invasive grass carp (Ctenopharyngodon idella) to keep it under control. Hydrilla is an extremely pervasive aquatic weed that causes ecological damage to the flora and fauna of the lake and also impedes recreational activities like boating and swimming. At first glance, the grass carp may seem like the ideal biological control for a closed freshwater system like Lake Austin. But as fishermen pointed out at a public hearing on the subject, there's no way to control the grass carp once they're introduced; if they eat more than just hydrilla they could be reducing food sources for other fish in the lake. I'm a little skeptical about the claims made by officials that testing showed that they can keep the carp in the lake, given the risk of flooding, but it is likely that they will be using functionally sterile triploid carp, reducing the risk that populations would establish in the wild.

Thanks to D.V. for sending in the link to this article.