An evaluation of the bottom trawl surveys in the Benguela Current Large Marine Ecosystem

• Published in: Fisheries Oceanography
• Main Authors: Axelsen, Bjørn Erik, Johnsen, Espen
• Other Authors: NORAD
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2014
• Subjects: Fridtjof; Fridtjof Nansen
• Online Access: http://dx.doi.org/10.1111/fog.12079; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Ffog.12079; https://onlinelibrary.wiley.com/doi/pdf/10.1111/fog.12079; https://onlinelibrary.wiley.com/doi/full-xml/10.1111/fog.12079

Abstract Demersal fish, shrimp and cephalopod assemblages on the continental shelves and slopes off A ngola, N amibia and the southern and western coasts of S outh A frica have been monitored in terms of fisheries‐independent trawl surveys since the 1980s. The time series have provided vital input to stock assessments and are widely used in studies of ecology and biodiversity. The objectives of this study were to evaluate the technical specifications of the vessels and trawls used, to examine effects of modifications on catching efficiency, and to assess implications of these modifications over time. We find that the demersal trawl data collected in S outh A frica are not comparable with those of N amibia and A ngola, and that the time series of A ngola and N amibia contain inherent differences in terms of catchability of bottom dwellers. The introduction of smaller bobbins gear on the RV Dr. Fridtjof Nansen in 1994 increased the catchability of bottom‐dwelling species, and catch rates of monkfish and sole were higher in surveys with commercial vessels than the RV Dr. Fridtjof Nansen . We recommend that temporal trends are interpreted with caution and that time series for the three countries are viewed in isolation.