Red Swamp Crayfish

Red swamp crayfish are large (5-13 cm long), dark red crayfish with long, narrow claws (OFAH, 2021). They almost always have a blue-grey coloured line that runs along the underside of their tail (OFAH, 2021). Their raised bumps can help to distinguish them from other native crayfish species – they are more prominent, cover the body and claws, and can appear bright red, white or black (OFAH, 2021).  

Juveniles do not have the adults’ red colouring, making them difficult to distinguish from other crayfish species in the Procambarus genus (Boets et al., 2009, as cited in Global Invasive Species Database, 2021).  

Adults alternate between sexually active and inactive periods, with overall short cycles (Global Invasive Species Database, 2021).

The lifespan of most individuals is under two years, however they can live for up to four years (Huner, 2002, as cited in Mueller, 2007).

Juveniles reach sexual maturity within eight weeks (Global Invasive Species Database, 2021).

In warmer climates, red swamp crayfish can breed twice within a year (Nagy et al., 2021). The total generation time takes just 4.5 months (Nagy et al., 2021). Breeding males are highly mobile, moving up to 17 km in 4 days (Global Invasive Species Database, 2021).

Females can produce 100-500 eggs and can transport them underneath their tails (Global Invasive Species Database, 2021). 

These life cycle and reproductive traits contribute to the strong survival of populations of this species in its non-native ranges. Similarly, rapid sexual maturation and mobility give red swamp crayfish populations the capacity to grow quickly and spread.

Red swamp crayfish are native to northern Mexico and parts of the southern United States, including New Mexico, Texas, Tennessee, Illinois, Oklahoma, and the Florida panhandle (Krandall, 2010).

In its native range, the red swamp crayfish is a common food source, with a multi-million-dollar industry in Louisiana (Global Invasive Species Database, 2021).  It is the most widely introduced crayfish globally (Lodge et al., 2012).

In Canada, red swamp crayfish was first reported in Vancouver in 2017 (Oficialdegui et al., 2020). Although the source was unknown, it was documented that the states of Louisiana, California, and North Carolina exported commercial supplies of the crayfish to Canada (Oficialdegui et al., 2020).

Red swamp crayfish is invasive in states on the south-side of the Great Lakes, including Ohio, Michigan, and Wisconsin (OFAH, 2021).  Predictions suggest that 2% of the Great Lakes would be suitable habitat for the red swamp crayfish, and 0.88% would be considered optimal habitat (Egly et al., 2019). These predicted habitats are located on the southern shores of Lake Michigan and Lake Erie, Saginaw Bay (Lake Huron), Green Bay (Lake Michigan), and Henderson Bay (Lake Ontario) (Egly et al., 2019).

Under two different representation concentration pathways (or RCPs, greenhouse gas concentration trajectories used by the Intergovernmental Panel on Climate Change), Zhang et al. (2019) predict that the red swamp crayfish’s distribution in North America will decrease in 2050 and 2070.

While species distribution model (SDM) studies using RCPs can produce uncertain predictions, Zhang et al. (2019) expect that annual mean temperature will be an important factor in the distribution of the red swamp crayfish, especially given that it is a warm water species.

The red swamp crayfish likely spread across U.S. states where it is non-native through aquaculture (cultivating it for food or bait) and the aquarium trade (Nagy et al., 2021). Live crayfish may even be able to survive being flushed down toilets, enabling their transfer from households into aquatic ecosystems (Nagy et al., 2021). 

Ecological Impacts

The scope of the red swamp crayfish’s ecological impacts in its non-native range is wide, ranging from impacts on native wildlife to causing changes in the local ecosystem itself. For example, red swamp crayfish can induce the accumulation of toxic cyanobacteria by overfeeding on aquatic plants (Lodge et al., 2012).

With fish declining as their refugia is reduced, there is a resultant increase in phytoplanktons (like cyanobacteria) that the fish would normally feed on (Lodge et al., 2012). When cyanobacteria “bloom” (multiply rapidly), they can release toxins and take up more of the oxygen in the water, suffocating other organisms (CDC, 2021).

In addition to reducing aquatic plant biomass and diversity through feeding, red swamp crayfish have been associated with losses of biodiversity of amphibians and native crayfish (Cruz et al., 2006; Rodríguez et al., 2003). They can negatively impact native fish populations by consuming fish eggs, larvae, and aquatic vegetation used as spawning and nursery habitat (Fitzsimons et al., 2002).

Predation of fish eggs in particular can harm sportfish populations (Fitzsimons et al., 2002). They compete with and spread disease to native crayfish species and can transfer heavy metals and toxins up the food chain through bioaccumulation (Global Invasive Species Database, 2021).

In disturbed areas they can become a dominant species, magnifying these effects (Global Invasive Species Database, 2021).

Economic and Social Impacts

Red swamp crayfish impacts are not limited to native plants and wildlife. Their burrowing behaviour can cause major infrastructural damage to dams and irrigation systems (tip of the Mitt Watershed Council, 2021).

Erosion caused by red swamp crayfish burrowing can also cause safety hazards for waterfront visitors and increase the rate of infrastructure degradation (Anastácio & Marques, 1997). They pose a threat to agricultural practices by damaging and blocking irrigation systems (Correia & Ferreira, 1995; Loureiro et al., 2015).    

Algal blooms and reduced water quality from red swamp crayfish activity can disrupt waterfront recreational activities (like swimming and boating), and impose additional burdens on water treatment industries (Anastácio & Marques, 1997). 

Finally, reductions in native gamefish populations through crayfish predation may negatively harm commercial fishing, angling and tourism industries.