Population structure of the seabob shrimp Xiphopenaeus kroyeri (Heller, 1862) (Crustacea: Penaeoidea) in the littoral of São Paulo, Brazil

The population structure of the penaeidean shrimp Xyphopenacus kroyeri was studied in Ubatuba Bay, Ubatuba, Sd̃ao Paulo, Brazil. The period and site of juvenile recruitment were monitored using a monthly sampling design with eight fixed areas (transects) from September 1995 to August 1996. The population structure was assessed using size frequency distributions (based on carapace length) for each month and sampling area. Females were significantly larger than males, suggesting a differential growth between sexes. The very low occurrence of large adults in the Bay can be related to offshore migration for reproduction. Recruitment occurred throughout the year, with a peak during the summer, when the highest recruitment rates were obtained along inshore transects. The present investigation revealed valuable information on the biology of the species mainly in the study region, which is considered a nursery ground for juveniles of X. kroyeri. The species showed an important variation from the typical life cycle that it is assumed to hold over its entire range and X. kroyeri should be classified as having a life cycle different from that proposed previously in the literature, i.e. the juveniles prefer inshore areas instead of estuaries. Some suggestions for the seabob fishery management are proposed as an alternative for minimising the impact during the harvest period and adjusting the protection schedule.