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

In order to establish a growth curve for the life-span, agedetermination based on shell-ring analysis was undertaken ina population of the cockle Cerastoderma edule located in theMundaca Estuary (Basque Country, North Spain). Mean values ofheight at shell rings showed non-significant differences betweengenerations, meaning absence of interannual variations in growthrate. Frequent sampling and shell measurements over a 20 monthperiod allowed determination of the seasonal pattern of shellgrowth, which was subsequently incorporated into a growth curve. An attempt has been made to relate growth rates to latitudefor different populations of C. edule, using both data fromthe literature and the results of this study. The highly significantcorrelation found (P<0.01) confims the existence of a latitudinaltrend, with growth rates increasing southwards. Low rates ofgrowth recorded for cockles from Mundaca, by camparison withpupulations of similar latitude, are interpreted in terms ofnutritional restrictions associated with both the high tidalposition of the population and poor productivity conditionswithin this particular estuary. (Received 24 March 1989; accepted 20 June 1989)