Controlling Carcinus maenas in Hout Bay harbour: the first attempted extirpation of a marine invasive species in Africa

Controlling Carcinus maenas in Hout Bay harbour: the first attempted extirpation of a marine invasive species in Africa
Clova A. MABIN1,2, John R. Wilson1,3, Johannes J. Le Roux1, Kerry J. Sink2Tamara B. Robinson
1Centre for Invasion Biology, Department of Botany and Zoology, Stellenbosch University, Matieland 7602, South Africa
2Marine Programme, South African National Biodiversity Institute, Kirstenbosch Research Centre, P/Bag X7, Claremont 7735, Cape Town, South Africa
3Invasive Species Programme, South African National Biodiversity Institute, Kirstenbosch Research Centre, P/Bag X7, Claremont 7735, Cape Town, South Africa

The European shore crab, Carcinus maenas, is a global invader with ecological impacts across most of its invasive range. It was first detected in South Africa in 1983 and is currently confined to two large harbour populations, approximately 30 km apart. In 2013, the population in Hout Bay harbour was estimated to support 6 700 mature individuals. The crab is listed as a NEM:BA 1b species (i.e. a species requiring control) and as a result, a pilot control programme was initiated in Hout Bay. Several capture methods were trialled including the use of baited traps, diver collection and dredging. Both divers and dredging were found not to be cost effective so baited traps were used in the trial extirpation. After 219 trapping days, 36 244 crabs were captured. Catch Per Unit Effort (CPUE) declined over the 12 month project. Following the termination of the programme, the population was monitored for six months and CPUE increased over this period. We conclude that eradication of C. maenas from South Africa would require resource-intensive control programmes in both harbours, but without strong evidence of impacts by this species in South Africa, it is hard to justify a large-scale eradication programme without knowledge of why control failed in Hout Bay. This study was the first attempt at controlling a marine invasive species in Africa and provides important insights for the control of other marine species.

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