ABSTRACT The shrimp trawl fishery in the southeastern Gulf of California is one of the most important in Mexico due to the high economic value of the resource in the national and international market. The management of this fishery is based on permits, a no-trawling zone, a no-fishing season and regulations of fishing gears. In order to analyze the efficiency of the no-fishing season and the viability of a spatial closure, we analyzed the distribution and size structure of four species targeted by the commercial fishery during the 2005-2006 shrimpfishing season, the white shrimp (Penaeus vannamei), blue shrimp (P. stylirostris), brown shrimp (P. californiensis) and crystal shrimp (P. brevirostris). We found that the size distribution of four shrimp species was wide and with variable frequency during the fishing season. The average biomass for each species was different throughout the fishing season, and the white and brown shrimps were the most abundant species. However, the spatial distribution of the biomass was similar for the four species. Our results suggest that the nofishing season is more effective for brown shrimp because the individuals caught by the fishing gear have already reproduced at least once.