Biological invasions severely impact on marine ecosystems around the world, but to date management is rare and has not previously been attempted in Africa. This study documents a trial management programme aimed at informing a national management strategy for the invasive European shore crab, Carcinus maenas, in South Africa. The approach involved testing control methods used elsewhere (baited traps, crab condos, diver collections and sediment dredging) and adapting these to the local context. Following these trials, baited traps were deployed over the course of the year, and the catch per unit effort (CPUE) tracked. A total of 36,244 crabs were collected during the management period, six times more than a pre-management population estimate. The population was not extirpated and CPUE increased once trapping ceased. The cost of attempting nationwide eradication is prohibitive, particularly given the lack of current impacts by this crab in this region and the possibility of reintroduction. We highlight key administrative challenges encountered, and the importance of such pilot trials in setting long-term goals when attempting alien species management interventions.
Marine bioinvasions are occurring around the world at a growing rate (Levine and Antonio 2003; Rilov and Crooks 2009) and coastal systems, including rocky intertidal shores, sandy bays, estuaries and harbours, are becoming increasingly impacted and transformed by alien species (Grosholz 2002;Byrnes et al. 2007; Rilov and Crooks 2009). South Africa is no exception and increased shipping traffic and commercial aquaculture movements have resulted in the introduction and establishment of rapidly increasing numbers of alien marine species (Mead et al. 2011a). Despite this, the study of marine invasions in the region has a relatively short history, starting in earnest only in the 1990s (Griffiths et al. 2009a).The first inventory of alien species in South Africa was produced in 1992 and documented just 15 species (Griffiths et al. 1992). This was followed by two updates in the next decade (Griffiths 2000;Awad 2002) that increased the number of recognised alien species to 22. Robinson et al. (2005) first made the distinction between alien and cryptogenic species (species of unknown origin), reporting 10 and 18 such species, respectively. Up to that point, recent introductions had been the focus of listings, and with the recognition of long-established historical introductions, and a broadening of the taxonomic coverage of the lists, the number of alien species known from the region increased markedly, to more than 85 alien and 30 cryptogenic species (Griffiths et al. 2009b;Mead et al. 2011b). The most recent listing by Robinson et al. (2016) further recognises the distinction between alien species (whose presence in a region is attributable to human actions that enabled them to overcome fundamental biogeographical barriers) and invasive species (alien species that have self-replacing
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