The effect of bait collectors on stocks of Callichirus kraussi and Upogebia species in Langebaan Lagoon

Abstract

The effects of collecting prawns (Callichirus and Upogebia spp.) in Langebaan Lagoon as bait were assessed in 1999–2001 and in 2012–2013. Langebaan Lagoon (part of West Coast National Park and a Marine Protected Area) is divided into three zones. One zone is a sanctuary, a second allows non-extractive visitation, and the third is for general use including bait collecting and fishing. In 1999–2000, the number of people visiting the sandflats to collect bait was highest during summer weekends (x̄ = 48 per day), and was concentrated at two sites: Centre Banks and Klein Oesterwal. Callichirus kraussi was the main species harvested, with an estimated 1 008 178 being removed annually. This represents 0.12% of the sandprawn stock at Centre Banks and Klein Oesterwal, and 0.012% of the estimated total stock. In 2012–2013, total bait-collecting activities had increased 23% compared with 1999–2000, but still constituted a small proportion of the stock. On average, each bait collector removed 86 prawns per outing: 36 more than the legal daily limit. The amount of sediment disturbed annually by bait collecting was estimated as 6189 tonnes. The surface area trampled by bait collectors and associated persons amounted to ~562 800 m². Thus, although the proportion of C. kraussi harvested constitutes no threat to the stock, associated disturbance has local adverse effects on the ecosystem.