In the U.S., farmers raise crawfish in man-made ponds constructed by flooding agricultural lands (Caffey et al.1996; McClain and Romaire 2004). Pollution is a concern, because farmers drain their ponds several times a year (LSU 1999). But other potential issues associated with this type of moderate-risk aquaculture system–disease transmission to wild populations and negative effects of escaped crawfish–are not a concern. Disease rarely affects farmed crawfish, and farm escapees are not known to transmit it to wild populations in the U.S. (McClain, pers. comm., 2006; AquaNIC 2006). The effects of escaped farmed crawfish on wild populations are also minimal for two reasons: 1) the vast majority of U.S. crawfish production occurs within the native ranges of the most widely farmed species, Red Swamp and White River Crawfish, and 2) wild and farmed crawfish populations are not genetically different (McClain and Romaire 2004; Boyd, pers. comm., 2006; Lutz, pers. comm., 2006).

Stocking densities of crawfish vary. Compared to other aquaculture operations, though, crawfish in farm ponds are at low stocking densities. Overcrowding is not an issue: higher densities of crawfish result only in smaller crawfish at harvest (Lutz, pers. comm., 2006; McClain, pers. comm., 2006; Shirley 2005).

Louisiana crawfish farms generate 90% of the crawfish produced annually in the U.S. (Caffey et al. 1996; Romaire et al. 2004; LSU 2005a). In Louisiana, there are 1200 farms that use 118,000 acres of flooded agricultural land to produce crawfish (LSU 2005a). However, these farms constitute less than half of a percent of the land area of Louisiana (Parr 2002).

In Louisiana, farmers raise more than 75% of the state crawfish crop in conjunction with agricultural crops, mostly rice and soybeans (Caffey et al. 1996; Hunner 2000).

Individual states have permitting programs for farm siting, building wetlands, removing and releasing water, and raising crawfish (LSU 2005b; AquaNIC 2006). However, there is little indication that crawfish farm siting is closely regulated, so we chose to not add here.

Farming crawfish does not require feed. Farmers raise crawfish in ponds created on flooded agricultural fields. Decomposing vegetation in these ponds forms the basis of the food webs that support crawfish, which consume a variety of the plants, animals, and decomposing matter in the ponds. The small animals that feed on the decomposing vegetation provide the majority of nutrition for the crawfish (LSU Ag 1999, 2005a; Shirley 2005; Lutz, pers. comm., 2006).

Farmers use wild-caught fish, such as Gizzard Shad and Menhaden, to bait traps during crawfish harvesting (LSU 1999). We chose to not subtract for baitfish usage, however, because the amount used is likely minimal compared to the amount of fish products used by other aquaculture operations.

No feed is used to raise crawfish.

No feed is used to raise crawfish.

No feed is used to raise crawfish.

Crawfish farmers do not treat the water they release from their ponds during harvest (AU and USDA 2004). However, they generally follow state-suggested best management practices (BMPs), which increase the quality and decrease the volume of wastewater drained from their ponds (Lutz, pers. comm., 2006; McClain, pers. comm., 2006). Most crawfish farms are far removed from receiving waters (i.e., the streams, etc. into which wastewater is disposed), so farmers channel pond effluent through vegetated ditches that lead to the receiving waters (McClain, pers. comm., 2006; Pitre, pers. comm., 2006; Romaire, pers. comm., 2006). This system allows solid particles and some nutrients to settle out from the effluent before it reaches streams or other bodies of water (McClain, pers. comm., 2006; Romaire, pers. comm., 2006).

Currently, little is known about the effects of crawfish pond effluent on nearby aquatic ecosystems (Johnson et al. 2004; LSU 2005a). Research conducted during the 1990s demonstrated that water drained from crawfish ponds in the spring and summer is of poorer quality (i.e., contains higher concentrations of nutrients and suspended solids) than water drained during the fall and winter (Tucker 1998; Parr 2002). However, further information on the quality and environmental impact of crawfish farm effluent is lacking (McClain, pers. comm., 2006).

The U.S. Environmental Protection Agency (EPA) sets aquaculture effluent guidelines through the National Pollution Discharge Elimination System (NPDES) program (SRAC 1999). However, when the EPA created the program, it determined that crawfish ponds did not need to be regulated (McClain, pers. comm., 2006). Individual states have permitting programs for farm siting, building wetlands, removing and releasing water, and raising crawfish (LSU 2005b; AquaNIC 2006). These programs, however, do not require that effluent be treated before discharge.

Although no feed is used to farm crawfish (LSU 1999; McClain and Romaire 2004; Lutz, pers. comm., 2006), the periodic draining of effluent from crawfish farms and the lack of effluent discharge regulations are a concern. Therefore we chose to award a medium score of 2.00 points here.

Scientists have conducted little research on the effects of effluent discharged from crawfish farms on the surrounding ecosystem, although current studies are underway (McClain, pers. comm., 2006; Romaire, pers. comm., 2006). We chose to not subtract here as we await the studies’ results.

Louisiana State University’s Agriculture Center and Auburn University have researched and established a list of best management practices (BMPs) for crawfish operations (LSU 1999; AU and USDA 2004). These BMPs include strategies for water conservation (including utilization of rainfall, minimization of pond water exchange, and reuse of drained water for irrigation), improvement of pond water and effluent quality (including pond aeration and ways to promote the settling of solids before drainage) and wetlands construction (LSU 1999; Lutz, pers. comm., 2006).

Most crawfish farmers follow these suggested BMPs, because they are often associated with economic advantages (Romaire, pers. comm., 2006). However, the use of BMPs on crawfish farms is not mandated (Tucker 1998; SRAC 1999). Since neither federal nor state agencies regulate crawfish operations with strong enforcement or regular monitoring, we chose to subtract for this factor.

Disease is not a problem in crawfish production, so farmers do not apply antibiotics to their ponds. Crawfish farming operations rarely use other chemicals, because they can kill crawfish (Johnson et al. 2004; Shirley 2005; McClain, pers. comm., 2006).

Crawfish farmers drain water from their ponds and release it into local waters without first treating it. However, more and more farmers are using best management practices (BMPs), which include strategies to reduce the environmental impact of effluent. For example, the BMPs call for the release of pond water from the surface of crawfish ponds instead of from the bottom. Doing this reduces the amount of suspended solids in the effluent, because these solids tend to aggregate at the bottom (Parr 2002).

Farmers also discharge pond wastewater into vegetated ditches that slowly channel the wastewater into public waters, allowing time for suspended solids and nutrients to settle out. Besides installing a filtration system, this effluent discharge technique is the most environmentally sound (Parr 2002). Other suggestions include planting native plants near pond drains to serve as natural effluent filters (LSU 1999). Some farmers use settling ponds to hold discharged water before releasing it into streams and rivers. However, this is not necessarily a common practice (Johnson et al. 2004).

A concern of crawfish farms is the depletion of dissolved oxygen in the ponds (Caffey et al. 1996; Johnson et al. 2004). Farmers counteract this problem by aerating the pond water (Caffey et al. 1996). Aeration decreases the number of times farmers must drain and refill the ponds and likely improves the quality of the pond water when it is discharged (Caffey et al. 1996; Parr 2002).

Escape does occur and is expected due to the nature of open-pond crawfish farms, but nearly all U.S. crawfish farms are located in areas where Red Swamp and White River Crawfish are native (Caffey et al. 1996; LSU 1999, 2005a; Johnson et al. 2004; McClain and Romaire 2004. There is no indication that escaped farm-raised crawfish negatively impact wild populations of Red Swamp and White River Crawfish or their ecosystems.

Farm-raised crawfish (in particular, Red Swamp Crawfish) have escaped and established populations outside of their native range in the U.S., as well as in South America, Asia, Africa, and Europe (NBIS 2005). In Europe, the negative impacts of these introductions have been well documented (Lodge et al. 2000; Duval-Smith 2004; NBIS 2005). However, this ranking is based only on U.S. production, the vast majority of which is located in the native ranges of Red Swamp and White River Crawfish. Therefore, we chose to award the medium score of 2.00 points here.

Farm-raised crawfish generally survive upon escape from ponds in the U.S. (Caffey et al. 1996; LSU 1999; Johnson et al. 2004). Many crawfish species are well adapted to surviving outside of their native range; and, Red Swamp Crawfish, in particular, can tolerate long dry periods and other environmental changes (Duval-Smith 2004; NBIS 2005).

In the U.S., more than 90% of crawfish production occurs within the native ranges of Red Swamp and White River Crawfish, the species most commonly farmed (McClain and Romaire 2004; Romaire et al. 2004; LSU 2005a; AquaNIC 2006). However, there are a limited number of crawfish farms in the U.S. that are located outside of the ranges of Red Swamp and White River Crawfish (NBIS 2005). For example, farmers grow Red Swamp Crawfish in North Carolina, where there are no regulations in place to prevent the spread of the non-native species. The North Carolina Department of Agriculture and Consumer Services only requires that farmers attain an aquaculture license to raise crawfish (NCDA&CS 2006). On the other hand, some U.S. states prohibit the transport of non-indigenous crawfish species across their borders and instead encourage the farming of native species (Brown and Gunderson 1997).

Due to the varying degrees of regulation and the fact that the vast majority of U.S. production occurs within the native ranges of Red Swamp and White River Crawfish, we chose not to subtract for this factor.

Where Red Swamp Crawfish are not native and have escaped from farms, they have often out-competed native crawfish, causing declines in their populations (Lodge et al. 2000; NBIS 2005). However, this ranking is focused on U.S. crawfish production, almost all of which occurs within the native ranges of Red Swamp and White River Crawfish.

Genetic studies have shown that no difference exists between farmed and wild populations of crawfish in the south-central U.S. (Lutz, pers. comm., 2006). Therefore, the interbreeding of farm-raised crawfish with wild crawfish will not likely jeopardize wild populations in the U.S.

Disease in U.S. farm-raised crawfish ponds is rare; therefore, the risk of transmitting disease to wild populations is extremely low (Johnson et al. 2004).

U.S. farmers raise crawfish in flooded agricultural fields (LSU 1999).

Farmers raise crawfish in flooded agricultural lands that act as constructed wetlands habitat for wildlife (Hunner 2000; Lutz, pers. comm., 2006). Increases observed in several waterfowl populations in Louisiana have been attributed to crawfish operations providing additional wetland habitat (Hunner 2000).

There is no evidence that crawfish farms cause substantial damage to the surrounding habitat or deplete groundwater (Hunner 2000; Lutz, pers. comm., 2006). Farmers use water from both surface (e.g., streams) and subsurface sources to flood their fields (LSU 1999). Reliance on groundwater is declining due to the high fuel costs associated with pumping groundwater (Shirley and Lutz 2005; Lutz, pers. comm., 2006).

In order to help crawfish farmers offset the increasing costs of energy, Louisiana state agencies and Louisiana State University, compiled a manual of Best Management Practices to follow (BMPs; LSU 1999; Lutz, pers. comm., 2006). These BMPs recommend economically and environmentally sound water use practices, like flooding crawfish ponds to a shallower depth and retaining rainwater to use for pond flooding (Lutz, pers. comm., 2006). Although laws do not mandate that farmers use BMPs, most farmers opt to follow them due to the economic gain they provide by reducing their energy costs (Lutz, pers. comm., 2006).

Because there is no evidence that crawfish operations cause substantial damage to the surrounding habitat or deplete groundwater, we chose to add here.

There is no indication that crawfish farming operations harm wildlife. It is illegal for farmers to kill most of the animals that enter their crawfish ponds (Lutz, pers. comm., 2006).

During harvest, farmers do not remove all the crawfish from their ponds. The remaining crawfish reproduce and naturally re-stock the ponds (LSU 1999). Farmers stock new ponds with crawfish from other ponds (AU and USDA 2004), although, in Louisiana, wild-caught crawfish from the local fishery are also sometimes used (D’Abramo et al. 2004). There is no indication that use of wild-caught crawfish to seed ponds in Louisiana depletes wild crawfish populations.