Interannual variation of bycatch assemblages of artisanal bottom shrimp-trawling on the Patos Lagoon estuary, Brazil

Abstract One of the most concerning problems of trawl fisheries today is the bycatch, especially given that over the last decade the Ecological Approach to Fisheries (EAF) has increased in importance. Bycatch variation is an important issue in fisheries management, since non-representative assessments of this topic can lead to the implementation of inadequate legislation. The assemblages of bycatch species in shrimp trawlings on the Patos Lagoon estuary and their relation to salinity, the size of the main species captured, and the bycatch to shrimp ratio were studied. Samples were taken between January 2011 and May 2014, encompassing four fishing seasons. We analyzed a total of 173 trawls, containing a joint total of 32,835 individuals. Sixty-one different types of bycatch species were captured, which were mostly ( > 80%) juveniles/non-mature individuals of commercial species. Eleven species dominated the captures, the most abundant of which were Micropogonias furnieri (FO > 82%), Callinectes sapidus (FO > 90%) and Genidens barbus (FO between 1.30–66.7%). There was a shift in assemblage structure according to salinity, which was reflected in the presence or absence of the lesser abundant species, but also in shifts on the density of the dominant species. Temperature was similar throughout the studied fishing seasons (23.9 ± 3 . 3 ∘ C), but salinity varied between 8.6 and 21.9. The bycatch to shrimp ratio was very high during the studied period (2011 = 3.3:1; 2012 = 2.6:1; 2013 = 8.7:1; 2014 = 65:1), but highest values were recorded when salinity was lower. However, even when environmental conditions favored pink shrimp abundance (high salinity), the ecological impact of this fishery was high, confirmed by the higher richness of species in the samples. Results call for a better fisheries management and supervision of illegal trawls.