Population biology of Palaemon (Palaeander) northropi Rankin, 1898 (Crustacea, Decapoda,
Palaemonidae) in a tropical South American estuary
PRALON1, B.G.N. & NEGREIROS-FRANSOZO2, M.L.
1;2 NEBECC – Group of Studies on Crustacean Biology, Ecology and Culture. Depto. de Zoologia, Instituto de Biociências, Cx. Postal 510 - UNESP, 18618-000, Botucatu (SP), Brazil.
1pralonbra@hotmail.com; 2mlnf@ibb.unesp.br
ABSTRACT: The population biology of the palaemonid shrimp Palaemon (Palaeander) northropi was studied for one year in the Ubatumirim estuary, Ubatuba, state of São Paulo, Brazil. Sampling was carried out monthly from April 2003 through March 2004. The shrimp were collected with a sieve from under the bordering vegetation, during ebb tide. All specimens were measured for carapace length, and allocated to 17 size classes. Based on analyses of the allometric growth of some body dimensions (carapace length vs. pleura length), all females smaller than 4.41 mm carapace length were considered juveniles. Based on the body structures analyzed, in males the growth pattern was not differentiated between juveniles and adults, and therefore the size at sexual maturity of males could not be determined. Only salinity showed a significant correlation with the abundance of shrimp at the sampling site. The size-frequency distribution of P. northropi was unimodal. Median lengths of males and females were 3.77 (± 0.49) mm and 4.46 (± 1.19) mm carapace length, respectively. Males predominated in the population, with an overall sex-ratio of 1.39:1. Ovigerous females occurred only during winter and spring. Shrimp were not obtained during summer, because of low salinity in the estuary at that season; the shrimp migrated to other areas near the sea, where the salinity was higher. The estimated individual mean fecundity was 165 ± 12.3 eggs per female; the smallest ovigerous female was 4.49 mm in carapace length. Because some size classes were not collected in this study, further studies are needed to improve understanding of the dynamics of this population of P. northropi.
Key-words: Allometry, population structure, sex ratio, fecundity.