Resumen de Biología de "Venerupis Pullastra" (Montagu, 1803) y "Venerupis Decussata" (Linne, 1767) (Mollusca, Bivalvia), con especial referencia a los factores determinantes de la producción: N.º 281
Venerupis decussata and Venerupis pullastra are two species of great economic importance in Galicia (N. W. Spain).
The growth, first maturation age and natural mortality, as well as cyclic changes in meat condition and seasonal maturity of both species have been studied using various methods, in a beach in the Ría de Arosa.
Marking experiments showed that the rings appearing as surface sculpture on the shells of both species are a velid measure of annual growth. Growth rates estimated from these rings were found to be greater than those estimated from marking experiments.
Growth was highly seasonal in both species, being fastest in spring and summer. In the autumn and winter, growth slowed in V. pullastra and virtually ceased in V. decussata.
The first maturation age for V. pullastra is 1 year and spawning generally occurrs in March, April and May. In V. decussata, maturity is reached in 2 years and spawning normally takes place in July and August.
The flesh weight of a standard individual and the different condition indeces showed significant seasonal variation, which were related to the spawning cicle and differed between the two species. The maximum values of flesh weight for V. decussata were recorded in the spring and the minimum in the late summer and winter. In V. pullastra, however, the maximum was in late winter, spring and early summer.
Annual mortality was 8.5 % in V. decussata and was constant for clams between 10 and 60 mm in length. In V pullastra, mortality was constant for clams between 11 and 50 mm, with an annual mortality of 17.7 %.
The maximum biomass occurred at an age of 9 years in V. decussata and 4 years in V. pullastra.
The results obtained were applied to produce a rational plan for the explotation of the natural populations of the two species.
