Physical Removal

Trapping & netting

Collecting crayfish using a dip net in a stream.

Photographer: C.J. Rice

A variety of manual removal techniques have been used to remove invasive crayfishes. Examples of manual removal techniques used to remove invasive crayfishes include seining, dip-netting, minnow/funnel traps, fyke nets, or Evo traps (Westman, 1979; FjÀlling, 1995). Manual removal of invasive crayfishes has proven somewhat successful, with some studies documenting strong declines in invasive crayfish abundances following extended periods of removal (Bills and Marking, 1988; Hein et al., 2007). However, the labor- and time-intensive nature of these methods may make them infeasible for the long-term management of invasive crayfish populations or for invasive populations occurring over a wide geographic area.

Electrofishing

Students backpack electrofishing in a stream.

Photographer: Kelsey Berke

Electrofishing can be used to capture and remove invasive crayfishes from lakes, rivers and streams. However, the ability to effectively reduce or eradicate invasive crayfish populations via this method is unclear. Because crayfishes are generally associated with the bottom substrate, electrofishing becomes less effective at greater depths, making the method impractical for large lakes and rivers (Westman et al., 1978). Crayfishes may also seek cover in burrow or underneath large substrates, allowing them to potentially escape the electrical field generated by an electroshocking device (Westman et al., 1978). However, this effect may be somewhat less pronounced in small, shallow streams than in other aquatic habitats (Rabeni et al., 1997).

Drainage or capping of waterways

Exposed riverbank from a drawdown.

Photographer: U.S. Fish and Wildlife Service (CC BY 2.0)

Draining and capping water bodies infested by invasive crayfishes are other methods by which they might be eradicated or reduced to a manageable level. Studies attempting to drain or divert water from a waterbody to manage invasive crayfish are rare, most likely due to their costly and time-consuming nature. Many crayfish species also possess the ability to burrow down to the water table when water becomes scarce (DiStefano et al., 2009; Kouba et al., 2016). This tendency can reduce the effectiveness of draining ponds or diverting rivers and streams to control invasive crayfishes, and as a result, such methods have been largely ineffective (Gherardi et al., 2011). The Wisconsin Department of Natural Resources demonstrated that red swamp crayfish (Procambarus clarkii) can be successfully eradicated by filling in a water body and by creating permanent physical barriers along a shoreline (Bunk 2018).

Barriers

An artificial barrier in a stream.

Photographer: Foster's Pond Corporation

Artificial barriers constructed in rivers and streams are also a potential method to prevent or reduce the spread of invasive crayfishes to upstream locations in stream networks. Such methods generally involve the construction of concrete barriers (i.e., artificial waterfalls) in the stream channel that maintain stream flow, yet prevent crayfishes from walking or swimming up the barrier. These methods have thus far shown mixed results (Kerby et al., 2005; Gherardi et al., 2011), and they may be most effective when used to control isolated or confined invasive crayfish populations (Gherardi et al., 2011). Control methods proposed for invasive fishes, such as electric or carbon dioxide barriers, may be one avenue to explore for invasive crayfish control.