Threats to the Watercress Darter

Beaver teeth marks on wetland trees
- Photo Credit: Francesca Gross
Parking lot used for car repairs endangers fish
- Photo Credit: Francesca Gross
Northern Crayfish (Orconectes virilis)
- Photo Credit: R. Scot Duncan
Male Watercress Darter
- Photo Credit: Zac Napier
- Photo Credit: Francesca Gross

Though the Watercress Darter (Etheostoma nuchale) has survived nearly a 150 years of urbanization in Jones Valley, this small fish is still highly endangered. Its future is in such jeopardy that, in 2008, the Southeastern Fishes Council designated it one of the 12 most-endangered species in the Southeast.

The fish faces many threats. One of the greatest is alteration to the recharge areas that supply water to the springs where the fish lives. Large portions of these recharge areas are covered with buildings, houses, streets, parking lots, and other impervious surfaces that prevent rainwater from soaking into the ground. Though we can’t know for sure, it is likely that much less water flows from these springs than in historic times. Furthermore, the water that does seep into the ground after a rain will carry with it common – but dangerous – urban pollutants. This includes drippings from our vehicles (oil, grease, antifreeze), the chemicals we put on lawns and gardens (pesticides, herbicides, fertilizers), and carcinogens, such as nicotine from discarded cigarette butts.

A related problem is stormwater runoff from the impervious surfaces around the springs. Stormwater is rainwater that drains off of impervious surfaces. Stormwater is collected in drains on the margins of parking lots and streets, carrying with it pollutants and sediments. This water is then piped to the nearest stream or river. As a result, urban streams receive a much higher volume of stormwater during a rainfall than they did before development. Like a flash-flood, this high-volume, high-velocity pulse of water destroys stream habitats. Several of the springs or spring runs supporting darter populations receive piped stormwater, and this is causing the deterioration of darter habitats.

The darter populations are also vulnerable to catastrophic events. Since many live near roads and highways, they are vulnerable to the lethal chemical spills that can occur due to vehicular accidents.

Introduced species are an insidious threat that is hard to counteract. In 1977 at Thomas Spring (now protected by the National Wildlife Refuge), the landowner released several Grass Carp (Ctenopharyngodon idella) to clean the spring pool of the aquatic vegetation – where the darter like to hide. Quickly the plant-eating fish consumed all but a few slivers of the aquatic plants, and the darter population declined to a handful of survivors. The vegetation and some darter habitat returned after the Grass Carp were removed. In Roebuck Springs, and probably several other springs, the Northern Crayfish (Orconectes virilis) has been introduced. The crayfish is an omnivore that competes with the fish for prey species and probably also preys on the darter.

Water removal for irrigation from the springs or the spring pools has been a problem at several springs. A greater threat is the removal of the human-made and beaver-made dams often found at the springs or along their runs. While dams usually are destructive to stream habitats, the reservoirs created by the dams have provided more habitats for the fish and the plants and animals on which they depend. At least twice in recent years, such dams have been removed, causing habitat loss and declines in darter populations.

The North American Beaver has a complex role in darter protection. In pre-settlement times, beavers probably helped the darter by creating pond environments in streams and springs. For many decades, beavers were nearly absent from the region due to overhunting. But now they’ve returned and are busy building dams on streams in the metropolitan area. Sometimes, this seems to improve darter habitat, and at other times, this seems to create problems for the darter. Biologists are still trying to figure out how to think about the pesky beavers.

It’s clear that the Watercress Darter faces many daunting threats. And yet, it survives. Hopefully, landowners, biologists, and state and federal agencies can cooperate to diminish many of these threats and ensure the long-term survival of the species. Learn more about ongoing efforts to protect the darter here.

-R Scot Duncan