Shrimps are cannibals. They eat anything and everything they find in the pond. If you find a group of shrimps crowded around a dead fellow mate, chances are they might actually be relishing it! There is no need to be alarmed since feeding on a dead shrimp improves its own exoskeleton. One or two dead shrimps here and there is fine. One should be worried if there is a group shrimps lying around dead.