Distribution and abundance of the argentinean (Artemesia longinaris) and the red prawns (Pleoticus muelleri) (Decapoda:Penaeoidea) in Southern Brazil during the commercial double-rig trawl fishery season

Abstract

Declining in landings of more valuable prawn species, such as pink prawns(Farfantepenaeus paulensis and F. brasiliensis), expanded the targets of double-rig ottertrawlers to other species such as Artemesia longinaris and Pleoticus muelleri. In attempting to increase information on distribution and abundance of these prawns, 64 samples were analyzed in summer/2005 during the commercial trawling fishery season off Rio Grande do Sul coast. Samples were collected from a research vessel (NOc. Atlântico Sul – FURG) in depths varying between 5 and 29 as a contribution to SALVAR project. Temperature, salinity and substrate play an important role on distribution of A. longinaris, concentrating greater densities in areas of low temperature and high salinity, associated to summer upwelling. Pleoticus muelleri showed a more homogenous distribution and did not avoid areas of lower salinity under the influence of estuarine runoff. By using a swept area method, a total of 3369 tons of A. longinaris was estimated between isobaths of 10 and 20 meters. Pleoticus muelleri presented lower abundances and a total of 2527 tons was estimated by using the swept area method. Size distribution indicated that larger individuals of both species are located especially between 15 and 20. However, large individuals of A. longinaris clearly avoided the areas of lower salinity, suggesting that spawning takes place outside the direct influence of Patos Lagoon estuary. Conversely, P. muelleri takes advantage of lower salinity areas, avoided by A. longinaris, for spawning.