SHELL GROWTH OF THE COCKLE CERASTODERMA EDULE IN THE MUNDACA ESTUARY (NORTH SPAIN)

In order to establish a growth curve for the life-span, age determination based on shell-ring analysis was undertaken in a population of the cockle Cerastoderma edule located in the Mundaca Estuary (Basque Country, North Spain). Mean values of height at shell rings showed non-significant differences between generations, meaning absence of interannual variations in growth rate. Frequent sampling and shell measurements over a 20 month period allowed determination of the seasonal pattern of shell growth, which was subsequently incorporated into a growth curve. An attempt has been made to relate growth rates to latitude for different populations of C. edule, using both data from the literature and the results of this study. The highly significant correlation found (P<0.01) confims the existence of a latitudinal trend, with growth rates increasing southwards. Low rates of growth recorded for cockles from Mundaca, by camparison with pupulations of similar latitude, are interpreted in terms of nutritional restrictions associated with both the high tidal position of the population and poor productivity conditions within this particular estuary.