Composition of trawl catch fauna off the mouth of the Rio Baluarte , southeastern Gulf of California

From April to December 2007, experimental trawls (n = 44, 4 to 22 m depth) were made off the mouth of the Rio Baluarte ecosystem (MRB) and compared to experimental trawls (n = 54, 7 to 40 m) in the adjacent offshore region (AOR) from 2002 to 2007. For both ecosystems, a total of 143 species belonging to 5 phyla were collected. Fishes comprised ca. 80% of the bycatch biomass, while molluscs and echinoderms contributed <20% bycatch. Eight species accounted for 50% of the numerical abundance: the crab Portunus asper (11%), the Panama grunt Pomadasys panamensis (8%), the curvina Stellifer ericymba (7%), the comb sand star Astropecten armatus (6%), the fishes Orthopristis chalceus (6%) and Larimus effulgens (4%), and the crabs Callinectes arcuatus (4%) and Hepatus kossmani (3%). Species with a high or medium survival rate with respect to trawling activity were well represented in the samples, e.g. the crabs C. arcuatus, H. kossmani, and Euphilax robustus, the hermit crab Petrochirus californiensis, and the sea star Luidia brevispina. For the MRB and AOR, the estimated mean biomass was 2.08 and 0.72 t km–2, respectively. The population of the blue shrimp Litopenaeus stylirostris and white shrimp L. vannamei was composed of recruits, juveniles, spawners, and old individuals, whereas for grunts it was composed of recruits and juveniles, but rarely old individuals. The high diversity, population structure, and productivity of the studied fauna has positive effects, such as enabling the recruitment for coastal marine fisheries. This is an important reason to protect the river mouth and the adjacent shallow waters.