Se registra las especies de cangrejos braquiuros Ucides occidentalis (cangrejo del manglar) y Cardisoma crassum (Cangrejo azul o sin boca) en los manglares de San Pedro (Piura), ampliándose su distribución geográfica al sur de Tumbes, que era el límite conocido. El hábitat de estas especies se caracteriza por la presencia de dos variedades de árboles de mangle, jelí blanco (Laguncularia racemosa) y jelí salado (Avicenia germinans) y el arbusto halofítico llamado vidrio (Batis marítima), observándose que la profundidad de las madrigueras investigadas es superficial (< 60 cm). Se presenta además información biométrica y algunos aspectos biológicos de los especímenes colectados.

Is recorded the species of crabs brachyuran Ucides occidentalis (mangrove crab) and Cardisoma crassum (Blue crab or without mouth) in the mangroves of San Pedro (Piura), expanding its geographical distribution south of Tumbes, which was the known limit. The habitat of these species is characterized by the presence of two varieties of mangrove trees, Jeli white (Laguncularia racemosa) and salty Jeli (Avicenia germinans) and halophytic shrub called glass (Batis maritima), it observing that the depth of the burrows is shallow (< 60 cm). Biometric information and some biological aspects of the collected specimens are also presented.

Between April and November 2011 was analyzed a population of Pteria sterna (Gould, 1851) which was attached to a sunken purse seine in Zorritos, Tumbes, Peru (3º40'30.7"S - 80°40'20.8"W). Individuals presented from 5 to 94 mm valve height. The average size increased towards the end of the assessment period. The size structure indicated the presence of recruits in most months evaluated, with highest in April and August. There were five age groups. The sex ratio was 1:1. The spawns were continuous, except in June, with highest in November. Valvar height-total weight relationship did not differ by sex. The growth of this species was negative allometric. Other relationships (potential: body weight-total weight, and linear: body weight-total weight and muscle weight-total weight) showed high correlations. Muscle performance accounted for 6.3% of the total weight.

Between April and November 2011 was analyzed a population of Pteria sterna (Gould, 1851) which was attached to a sunken purse seine in Zorritos, Tumbes, Peru (3º40'30.7"S - 80°40'20.8"W). Individuals presented from 5 to 94 mm valve height. The average size increased towards the end of the assessment period. The size structure indicated the presence of recruits in most months evaluated, with highest in April and August. There were five age groups. The sex ratio was 1:1. The spawns were continuous, except in June, with highest in November. Valvar height-total weight relationship did not differ by sex. The growth of this species was negative allometric. Other relationships (potential: body weight-total weight, and linear: body weight-total weight and muscle weight-total weight) showed high correlations. Muscle performance accounted for 6.3% of the total weight.