Once Persecuted, Alligator Gar Now May Drive the Fight against Invasive Asian Carp

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Charlene N. Simmons
An alligator gar at the River Giants exhibit at the Tennessee Aquarium in Chattanooga.

Once derided as a “trash fish,” a nuisance that was driven to extinction in parts of the country in order to make room for angler-favored “sportfish,” the huge, toothy alligator gar may at last be returning to the northern waters that it was once eradicated from decades ago. A new drive to reintroduce the once-maligned species is part of a last-ditch effort to halt the spread of one of the fastest growing invasive fish species to threaten US rivers: the Asian carp.

“Asian carp” refers to a group of four closely related species—silver, bighead, grass, and black—that were first brought to the US in the 1970s for the purpose of filtering pond water but by the early 1980s quickly began to infiltrate the American freshwater river system. According to the National Wildlife Federation, the huge fish, which can grow up to 100 pounds, makes up around 97 percent of the biomass of some sections of the Mississippi and Illinois Rivers and can today be found in the waters of 27 US states.

Asian carp aren’t a harmless introduction, and in fact have proven to be a major disruption to local river ecosystems. With no natural predators that can compete with their massive size and reproductive capability—a single female carp can lay as many as half a million eggs at one time—the Asian carp have over the years started to outcompete many other native species by gorging themselves on a singular food source that many freshwater fish rely on: plankton.

This is where alligator gar comes in. The gar, whose range used to span as far north as Illinois but today inhabits only the warm coastal waters around the Gulf of Mexico, is one of the few native species that can compete with Asian carp in terms of size: the gar can grow as large as 300 pounds, making it the second largest native fish in the United States. As a predator, the alligator gar can also target the carp when they’re most vulnerable: after they’ve hatched from their eggs but before they grow old enough to spawn, without being forced to challenge adult carp for plankton as a food source.

It’s not just local environmental groups fighting to bring the alligator gar back into northern waters. State-level lawmakers have begun to take up the cause, with Illinois lawmakers passing a resolution in May 2016 urging state natural resource officials to speed up the gar’s reintroduction program, as well as adopting regulations to protect all four gar species native to the state from the same kind of persecution that decades ago drove them from their natural habitats.

This move comes none too soon. Today, only a thin electric barrier separates the carp-infested waters of the Mississippi and its tributaries from the Great Lakes. These barriers have been shown to be permeable in the past. With Asian carp moving further north with each passing year, the reintroduction of the gar into its natural habitat may prove to be one of the few checks possible to keep this massive invasive fish at bay.