Bycatch in South Africa's inshore trawl fishery as determined from observer records

Abstract

Abstract Attwood, C. G., Petersen, S. L., and Kerwath, S. E. 2011. Bycatch in South Africa's inshore trawl fishery as determined from observer records. – ICES Journal of Marine Science, 68: 2163–2174. Ship-based observer data were analysed to describe the volume, composition, utilization, and size structure of catches made by South Africa's inshore trawlers. The sampling rate was 3.5% of all trawls, including unsorted and discard samples. In all, 137 nominal species were recorded. Analysis of species composition separated the trawling grounds into seven areas, providing a framework for stratifying the ground for catch estimation and for selection of representative areas for conservation. The target species, Merluccius capensis and Austroglossus pectoralis, made up 58% of the pre-discard catch. Trachurus trachurus, Pterogymnus laniarius, Raja spp., and Chelidonichthys spp. constituted another 23%. Pre-discard catch volumes of the entire fleet were estimated. The average annual pre-discard catch of M. capensis and A. pectoralis was 9653 and 504 t, respectively, closely matching landing statistics. Argyrosomus inodorus, Rhabdosargus globiceps, Argyrozona argyrozona, and Atractoscion aequidens averaged 294, 230, 107, and 83 t annually, respectively, indicating significant overlap with the handline fishery for A. inodorus and A. argyrozona. A comparison of species composition in unsorted and discard samples revealed the species being preferentially retained. Argyrosomus inodorus and A. aequidens were trawled mainly below their size at maturity. Management needs to consider other species when determining catch or effort limits and area restrictions.