The European industrial pelagic traw fishery in Mauritanian waters targeted at small pelagic species is geared towards sardine (Sardina pilchardus (Walbaum, 1792)), round sardinella (Sardinella aurita Valenciennes, 1847), flat sardinella (Sardinella maderensis (Lowe, 1838)), mackerel (Scomber colias Gmelin, 1789) and horse mackerel (Trachurus spp.). In 2003 the Instituto Español de Oceanografía (IEO) through its Centro Oceanográfico de Canarias (COC) began to follow up this activity under the European Project Data Collection (Regulation (EC) 1543/2000). In 2008 the COC-IEO began the study of horse mackerel (Trachurus spp.) under commercial codification “JAX”. Discharges were about 1,500 tonnes in that year (22 fishing trips) and 2,000 tonnes in 2009 (29 fishing trips). During this period, 5,180 specimens of these commercial catches were analyzed. Four different species were identified (in order of importance in commercial landings analyzed): Trachurus trecae Cadenat, 1950, Caranx rhonchus Geoffroy Saint-Hilaire, 1817, Trachurus trachurus (Linnaeus, 1758) and Trachurus picturatus (Bowdich, 1825). The assessments of the status of these resources carried out by International Working Groups are focused on T. trecae and T. trachurus. Previous studies of the area had not considered this. The present study aims to highlight the need to identify the mixture of these species in the landings, in order to ameliorate the quality of data used in the assessments and in the establishment of the level of exploitation.