We demonstrated through a 2-year field study that mortality rates of juvenile shrimps Farfantepenaeus duorarum in a coastal lagoon from the Gulf of Mexico decrease as the individual size increases. The size-dependent mortality was successfully modeled by a reciprocal function of length as well as by the conventional exponential decay model. The reciprocal model appears to provide a more reasonable prediction from a biological point of view, because the exponential model could underestimate mortality at smaller sizes.