Population structure and growth of Pinctada mazatlanica (Pterioida: Pteriidae), Golfo de Nicoya, Costa Rica

Population size structure and growth were studied in Pinctada mazatlanica between September 1993 to September 1994, in Isla Pan de Azucar, Golfo de Nicoya, Costa Rica. The population of specie are established mainly in those sites where the substrate offers protected shelters. Population density was estimated a 2.42 +/- 0.8 individuals per m(2), related to the total explored area 2250 m(2), between 0.4 m to 7.5 m depth). The most relevant morphometric variables for characterizing this species are shell height and shell width. The maximum height and weight found were 141.50 mm y 496.30 g respectively. The maximum class frequencies is 60-95 mm for the heigth (75% of the population). The equation of von Bertalanffy was A= 139.5[1 - e(-0.083(t-0,32)0,55 x 0.083/2 pi (t-0,65)-stn2 pi(0,32-0,65)]) for height and Pt= 445.46 [1 - e(-0.083(t-0.32))](3) for weight. Approximately 73.6% of the population is reached within twelve months of age. The average growth rate calculate for P, mazatlanica was 7.93 mm/mo during the first eigth months. in the next twelve months increments are en the order of 3.88 mm/mo, decreasing to 1.68 mm/mo in the last months. The relationship between shell height-weight was P= 5.31 x 10(-5) A(3.22848), indicate isometric growth.