Abstract
BackgroundThe Australian redclaw crayfish (Cherax quadricarinatus, von Martens), is native to Australasia, but has been widely translocated around the world due to aquaculture and aquarium trade. Mostly as a result of escape from aquaculture facilities, this species has established extralimital populations in Australia and alien populations in Europe, Asia, Central America and Africa. In South Africa, C. quadricarinatus was first sampled from the wild in 2002 in the Komati River, following its escape from an aquaculture facility in Swaziland, but data on the current status of its populations are not available.MethodsTo establish a better understanding of its distribution, rate of spread and population status, we surveyed a total of 46 sites in various river systems in South Africa and Swaziland. Surveys were performed between September 2015 and August 2016 and involved visual observations and the use of collapsible crayfish traps.ResultsCherax quadricarinatus is now present in the Komati, Lomati, Mbuluzi, Mlawula and Usutu rivers, and it was also detected in several off-channel irrigation impoundments. Where present, it was generally abundant, with populations having multiple size cohorts and containing ovigerous females. In the Komati River, it has spread more than 112 km downstream of the initial introduction point and 33 km upstream of a tributary, resulting in a mean spread rate of 8 km year−1 downstream and 4.7 km year−1 upstream. In Swaziland, estimated downstream spread rate might reach 14.6 km year−1. Individuals were generally larger and heavier closer to the introduction site, which might be linked to juvenile dispersal.DiscussionThese findings demonstrate that C. quadricarinatus is established in South Africa and Swaziland and that the species has spread, not only within the river where it was first introduced, but also between rivers. Considering the strong impacts that alien crayfish usually have on invaded ecosystems, assessments of its potential impacts on native freshwater biota and an evaluation of possible control measures are, therefore, urgent requirements.
Highlights
Freshwater crayfish have been introduced globally, mostly for aquaculture and ornamental purposes, but generally their subsequent invasions have resulted in more ecosystem losses than benefits (Lodge et al, 2012)
P. clarkii has been introduced to several African countries and caused visible impacts (Lowery & Mendes, 1977; Mikkola, 1996; Foster & Harper, 2006), in South Africa the species is only known from a single locality and does not seem to be spreading (Nunes et al, 2017)
C. quadricarinatus has been translocated to non-native areas in Australia (Doupé et al, 2004; Leland, Coughran & Furse, 2012) and Indonesian territories (Patoka et al, 2016), and wild populations are known from Israel (Snovsky & Galil, 2011), Jamaica (Todd, 2005; Pienkowski et al, 2015), Mexico (Bortolini, Alvarez & RodriguezAlmaraz, 2007; Vega-Villasante et al, 2015; Torres-Montoya et al, 2016), Puerto Rico (Williams et al, 2001), Singapore (Ahyong & Yeo, 2007; Belle et al, 2011) and Slovenia (Jaklič & Vrezec, 2011)
Summary
Freshwater crayfish have been introduced globally, mostly for aquaculture and ornamental purposes, but generally their subsequent invasions have resulted in more ecosystem losses than benefits (Lodge et al, 2012). C. quadricarinatus has been translocated to non-native areas in Australia (Doupé et al, 2004; Leland, Coughran & Furse, 2012) and Indonesian territories (Patoka et al, 2016), and wild populations are known from Israel (Snovsky & Galil, 2011), Jamaica (Todd, 2005; Pienkowski et al, 2015), Mexico (Bortolini, Alvarez & RodriguezAlmaraz, 2007; Vega-Villasante et al, 2015; Torres-Montoya et al, 2016), Puerto Rico (Williams et al, 2001), Singapore (Ahyong & Yeo, 2007; Belle et al, 2011) and Slovenia (Jaklič & Vrezec, 2011) This species has been introduced into several other countries (where wild populations do not exist) mostly due to its use in aquaculture (Ahyong & Yeo, 2007), and due to being a very popular ornamental species that is readily available in the pet trade (Belle et al, 2011; Chucholl, 2013; Patoka, Kalous & Kopecky 2014). Considering the strong impacts that alien crayfish usually have on invaded ecosystems, assessments of its potential impacts on native freshwater biota and an evaluation of possible control measures are, urgent requirements
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