Can bycatch reduction devices be implemented successfully on prawn trawlers in the Western Indian Ocean?

Abstract

Bycatch reduction devices (BRDs) are increasingly being used in prawn trawl fisheries worldwide. This paper describes an experiment with a Nordmøre grid and a square-mesh panel on a prawn trawler off Moçambique. Although numbers of hauls that caught elasmobranchs were low, 75% of hauls with grids caught fewer large rays than those without grids; hauls using grids caught no large sharks at all. In its final configuration, the grid respectively reduced prawn, discard and retained fish catches by 5%, 25% and 32% relative to control hauls; the square-mesh panel increased prawn catches by 3% and respectively reduced discard and retained fish catches by 23% and 18% relative to control hauls. Changes in prawn catches were not statistically significant; however, when the grid and the square-mesh panel were used together, they reduced prawn, discard and retained fish catches by 25%, 47% and 26% respectively relative to control hauls (all significant except for retained fish catches). Overall, the Nordmøre grid successfully released large elasmobranchs, and the grid and the square-mesh panel individually reduced bycatch without reducing prawn catches. In combination, the two BRDs also reduced bycatch, but at the cost of substantially reduced prawn catches. The results indicate that there is scope for the wider use of BRDs on prawn trawlers in the Western Indian Ocean region, although this would require increased support from management agencies and industry.

Keywords: bycatch, bycatch reduction device, prawn trawling

African Journal of Marine Science 2007, 29(3): 453–463