If the herring was eaten by something that either ate or was being eaten by the gulls, then they would be affected differently. If the gulls had less food because there food source had less food if the herring disappeared, then they would have a lower or population of perhaps become extinct. If the thing eating the herring became extinct because it had less food, then the gulls population would increase and either boom and bust or grow and level out once they reached the carrying capacity.
