Resumen de Crecimiento de la nécora Macropipus puber (L.) (Decapoda, Brachyura) en la Ría de Arousa (Galicia, NW España), y primeros datos sobre la dinámica de la población
In this paper different aspects of the growth of M. puber are studied, concentrating on morphobiometric aspects, the growth at ecdysis and the prediction of successive instars, as well as the molting cycle. General aspects on its population dynamics are treated (growth equations, total mortality, biomass virgin curves and yield per recruit), to facilitate a preliminary management.
The width-weight (CW-W) and width-length (CW-CL) relationships for males and females were found to be significantly different between both sexes; the equations obtained are:
males : W=0.00034 CW^2.964; CL=1.650+0.720 CW .
females : W=0.00045 CW^2.880; CL=1.942+0.725 CW .
Along the year, density values ranged between 0.080 and 0.0008 individuals/m2. The highest densities were obtained in December, and the lowest values in spring and summer.
Molt frequency in both sexes shows a seasonal variation throughout the year. Males show a higher ecdysis number in late spring and in summer, as well as a slight increase in some winter months. Females, besides the increase in molts in summer (somewhat delayed compared with males), also show a slight increase in December like males, and a higher frequency in late winter and at the beginning of spring, after the spawning and hatching period.
The increments at ecdysis were obtained for 98 crabs with pre-ecdysis size (CW) range from 14.50 to 73 mm, that molted in the first nine days in the laboratory. Growth increments varied from 31.39 to 10.00%.
The increment in size at ecdysis is similar for males and females before the “pubertal molt”. The pre-ecdysis:post-ecdysis relationship changes with the onset of sexual maturity, and after this is significantly different between sexes.
We can predict the successive instars and the increase in size at ecdysis for males and females until the reach maturity, using the expression Y=1.646+1.165X (where Y is the post-ecdysis carapace width in mm, and X the pre-ecdysis carapace width). The expressions obtained after the onset of maturity are:
males: Y=2.317+1.159X; females: Y=8.637+1.010X.
Von Bertalanffy’s growth equations were fitted for both size (width in mm) and weight (g) parameter, and are respectively:
males: L_t = 109 [1-e^(-0.65(t+0.41))] .
W_t = 372 [1-e^(-0.65(t+0.41))]^2.964 .
females: L_t = 96 [1-e^(-0.67(t+0.48))] .
W_t = 372 [1-e^(-0.67(t+0.48))]^2.880 .
There is a fastest growth rate in males related to a higher growth rate at ecdysis and/or a lesser number of molts in females.
M. puber molts around eleven times during the first year of life, three in the second year, and in the third and fourth years of life one ecdysis a year is estimated.
The total annual mortality values, Z, are 1.53 (78%) for males and 1.79 (83%) for females.
Based on the biomass virgin curves it can be concluded that the highest values correspond to age 11+.
The yield per recruit curves also show that the highest yields are obtained using the legal size as size of first catch, instead of the real one.
In order to achieve the progressive recuperation of the fishery, it is essential to respect the minimum legal size, and at the very least maintain the fishing effort at current levels.
