Population structure and temporal variation of the roughneck shrimp Rimapenaeus constrictus (Decapoda: Penaeoidea) in a coastal bay of the Southwestern Atlantic

Few studies have been performed regarding long-term variation of penaeids in coastal areas, especially of the marine shrimp Rimapenaeus constrictus, which is distributed along the western Atlantic Ocean (Canada to Brazil). This is the first study of R. constrictus in the Guanabara Bay, a tropical bay on the southern coast of Rio de Janeiro state, Brazil. We aimed to describe its population structure, focusing on sex ratio, abundance, size class and allometry, as well as its relationship with abiotic factors, over five years. Monthly trawls were carried out from January 2011 to December 2015, using a shrimp fishing boat equipped with a single-rig net. The shrimps were identified and sexed and the carapace length and total weight were measured. A total of 6358 individuals were sampled. Females were more abundant and larger than males, a common pattern found in penaeids. The annual abundance peak, which occurred in 2013, was influenced by total rainfall and seasonal peaks occurred in winter and spring. Abundance was positively related to salinity (r_s: 0.31, p?<?0.05), suggesting that the shrimp’s presence near shallower coastal regions is due to the presence of marine water at the bottom and/or a stronger stratification of the water column in the bay. A low seasonal variation in female allometry can be the result of a constant investment in gametogenesis, and a high seasonal variation in allometry for males can be due to their short life cycle, as was found in previous studies of the same species in other coastal regions worldwide.