Spatial variation in benthopelagic fish assemblage structure along coastal East Africa from recent bottom trawl surveys

Abstract

The structure of benthopelagic fish assemblages of the continental shelves and upper slopes along coastal East Africa (Kenya and Tanzania) was studied based on data from bottom trawls during 2012. These surveys are the most recent since the historical bottom trawls conducted in the 70s and 80s along costal East Africa. The bottom trawls sampled fishes in 27 stations along the Kenyan coast using FV Vega, while in Tanzania 24 stations were sampled by MV Mafunzo. A total of 66 fish species in 43 families were trawled in Kenya, while 40 species belonging to 22 families were sampled in Tanzania in depth ranges of 10 m to 230 m. The highest fish biomass was in shallow (<50 m) areas for both Kenya (123.08 kg/km2 ) and Tanzania (49.17 kg/km2 ). Numerically dominant species in Kenyan trawls included the largehead hairtail, Trichiurus lepturus (21.44%), the filesnout grenadier, Coelorhinchus denticulatus (9.50%) and the orangefin ponyfish, Photopectoralis bindus (7.57%), while in Tanzania, the hipfin ponyfish, Leiognathus leuciscus (27.09%), sulphur goatfish, Upeneus sulphureus (19.56%) and the finstripe goatfish U. taeniopterus (12.05%) dominated the trawls. The nMDS analysis indicated the fish assemblages to be influenced by both depth and area for Kenya, and mostly area sampled for Tanzania, while multivariate Correspondence Anlysis (CA) provided characteristic species associated with depth and area for both Kenya and Tanzania. Results of rarefaction curves showed the highest species diversity occurring in Tanzanian shallow depths (>50 m) of the south coast and shallow and mid-depths (50–150 m) of north coast. The lowest species diversity was associated with Kenyan samples of north coast in the mid-depth (50–150 m) and deep (>150 m) waters. The dominant species in the trawls differed with those documented in the historical trawls of the 1970–1980s. The results provide a taxonomic database on the fish species off coastal East Africa useful for monitoring spatio-temporal changes in fish assemblages in the face of climate change effects and increasing exploitation levels.