Biodiversity of invertebrate macrofauna from the shrimp trawlers fishery in ZEE Angolan waters

Discard studies are considered very relevant, both for assessment purposes and for obtaining information on adverse ecological impacts in marine ecosystems. In this context, trawl fisheries produce significant by-catches, which may be retained on board or discarded. Angola has been a traditional fishing ground for the Spanish fleet of deep-sea shrimp trawlers, mainly targeting deep-water rose shrimp Parapenaeus longirostris (stratum 1, 180-300 m) and striped red shrimp Aristeus varidens (stratum 2, 400-850 m). Since 2018, the IEO has implemented a scientific observer program onboard this fleet with the aim of obtaining the most reliable fishery and biological information for assessment purposes. This involves the collection of information such as: catch by species and biological data enabling the estimation of volume and length frequency of all catch fractions, biological parameters of target stocks, information for assessing the fishing impact on the marine ecosystem and detailed data on the activity of the fleet. A total of 949 fishing hauls were analysed in the period November 2018-December 2021. Invertebrates are present in all sampled fishing hauls, both as retained species and as discards. The abundance of invertebrates species has been estimated in terms of weight per unit effort (kg/hour). Retained invertebrates in stratum 1 are Parapenaeus longirostris (100% of retained catch), while Aristeus varidens, 75%, is the primary specie retained in stratum 2. The high diversity of invertebrate species that make up these discards is quite remarkable, accounting for 27% of these discards in relative weight irrespective of the fishing stratum, being crustaceans about 17% and cephalopods 6% and other invertebrates 4%. A preliminary analysis of the data collected shows a total specific richness of 46 taxonomic groups, with the highest values for deepest hauls, with a total of 15 species in stratum 1 and 43 in stratum 2. The species or group of species with the highest abundance found in the discards are: Nematocarcinus africanus, Stereomatis sculpta, Illex coindetii, Lithodes ferox, Bathynectes sp, Chaceon maritae, Parapenaeus longirostris, Plesionika spp, Polycheles typhlops, Acanthocarpus brevispinis, Aristeus varidens, Todaropsis eblanae and some unidentified actinians. Bathynectes sp and Stereomastis sculpta are the most frequent common species in the catches of both strata. Nematocarcinus africanus, Aristeus varidens, Polycheles typhlops and Glyphus marsupialis are the most frequent discard species found in hauls from stratum 2; while in hauls from stratum 1 the most frequent species are Illex coindetii, Munida sp, Solenocera africana, Chaceon maritae and Plesionika spp