Comparative feeding ecology and allometric growth of two spatially co-existing penaeid shrimps in Sofala bank fishery (central Mozambique)

The penaeid shrimps Fenneropenaeus indicus (white shrimp) and Metapenaeus monoceros (brown shrimp) co-occur and are suspected to have dietary overlap along the coast of the Sofala Bank in Mozambique. Stomach contents analysis of 155 female F. indicus and 119 female M. monoceros specimens of three different age groups (juveniles, sub-adults and adults) were done during August of 2007 and March of 2008, this latter associated with recruitment of juveniles to the “fishery”. The variance of the ecological indices food diversity, feeding efficiency and the Schoener's diet overlap were estimated by bootstrapping the sample data with replacement using Monte Carlo simulations. The two species are omnivorous with F. indicus having up to 25 - 33 % exclusive food items than M. monoceros in both seasons. The diets included components of benthic macro fauna, fish, plant fragments and sand. The results of the Schoener's interspecific dietary overlap index were biologically significant for similar early life stages in both periods assessed. There were also significant dietary overlaps across dissimilar age groups (i.e. M. monoceros juveniles vs. F. indicus adults) in March but not in August. The dietary overlap results are thought to be density-dependent and to have the potential to negatively affect recruitment of juveniles from coastal areas “to the fishery” in deeper Sofala Bank waters. There are statistical differences in the total (TL) and the carapace length (CL), the body weight, and in the allometric coefficient b (the slope of the linear CL-TL or linearized relationships W - TL) of the two species in both seasons. Those differences between F. indicus and M. monoceros, coupled with differences in their ontogenic feeding efficiency may minimize competition for food, therefore, the potential for this type of rivalry may only become real in situations of high population density such that occurs during the recruitment peak at the start of the year.