Scientists at the University of Maine wondered: how could bluefin tuna be starved for calories in a sea full of fish? It turns out, an abundance of Atlantic herring isn't good news for bluefin tuna during foraging. The herring population growth has translated to smaller body sizes, meaning tuna have to eat more fish to pack on the right amount of traveling fat. Tuna spend several months off the coast of Maine, attempting to pack on the pounds before their migration to mating grounds farther south -- so they need to be efficient.