The Callinectes arcuatus population of the Gulf of Nicoya and its current level of exploitation were investigated based on size frequencyanalysis of trap and trawl catches. Von Bertalanffy growth parameters (K= 0.89; CW∞ = 142mm for males) are in the range reported for otherspecies of this family and suggest that the male size at first maturity (CWmat = 94.3 mm) is reached in about a year. Total and natural mortality(Zyr = 2.49; Myr = 1.32) were derived from catch curve analysis and age at first maturity, respectively, and indicate that the stock is below fullexploitation (E = 0.47). A yield per recruit analysis suggests that yield could be maximised, if E was increased to 0.7 under the preconditionthat recruitment was independent of stock size. Until this has been verified, the use of a precautionary exploitation rate (E0.1) of 0.57 is advisedallowing for a 20% increase in fishing effort (from 300 traps currently being fished to around 360 traps). A maximum effort of 1600 traps,as recommended by the Instituto Costarricense de Pesca y Acuicultura (INCOPESCA), is unlikely to be sustained by the population, since adecrease in the proportion of large males in the catches has already been observed over the past years under the current fishing regime. Thisresource is as yet only sold locally, but present catches of around 145 t seem to already cause market saturation. A greatly increased catch(at E > 0.57) would thus not only be detrimental to the stock but also to the market price of the resource. Future developments of the fisheryshould be based on a co-management approach and should involve the exploration of new market opportunities such as the soft crab market.