In the Punta San Juan National Reserve (PSJ), located on the southern coast of Peru, there are sympatric breeding populations of the South American sea lions (Otaria byronia) and the South American furs seals (Arctocephalus australis). One of the most common methodologies to determine the content of the diet is the segregation of hard parts of prey, such as fish otoliths, cephalopod beaks, and crustacean cephalothorax, present in pinniped feces. Using this method, differences in the composition of the diet of both species have been reported in PSJ, but it has not been evaluated whether there are differences in the size of the prey consumed. Interspecific segregation according to prey sizes could mean a greater spatial division and use of different resources by these two species of top predators within the same ecosystem. The present study proposes to measure the hard parts of the main species that make up both pinnipeds diet and apply regressions to estimate the real size of the prey, to finally evaluate if there is a partition of resources by sizes of prey consumed.