Evaluation de la production d'une population littorale du crabe Hippidae Emerita analoga (Stimpson) par intégration des paramètres de croissance et de mortalité

Growth, mortality, production and biomass were evaluated in a Chilean population of the sand crab Emerita analoga. From May 1973 to June 1974, it was attempted to representatively sample on a monthly basis, the densities and size frequency distributions in the population ; proportion of soft individuals and proportion of females in berry in each size class were also assessed. Mean size and relative importance of each component age group in each sample were estimated by graphic analysis on probability paper. Age classes 0-IV represented most of the captures ; the males reached about 17 mm carapace length at end of age IV, while the females reached about 25 mm at end of age III. A linear growth equation was fitted by regression of the mean sizes on age, for each age group of each sex. Exponential mortality rates were estimated for each age group of each sex by linear regression of the logarithms of the densities on age ; the retained values ranged from 1.4-2.9. Exponential and knife edge approximations were used for modeling the recruitement. The length weight relationships were calculated for males and for females : W = 5.28 X 10(-4)L(2.90) and W = 3.39 X 10(-4)L(3.08) with W in grams and L in mm. Production Pk and mean biomass Bk of each age group of each sex were estimated by integrating growth, mortality and recruitment over time ; equations : Pk = 0? Dk(t).Mk Wk(t).dt and Bk = 0? Dk(t).Wk(t).dt are used for production and biomass, Dk(t) is the number of individuals/m2, Mk a mortality rate, Wk(t) the mean individual weight, while t is the time in years. Numerical approximations are developed for integrating production and biomass equations. Population's annual production in kg of wet weight/m2 is about 1.5 and mean biomass about 3.6/m2. [NOT CONTROLLED OCR]