Since the gulls act both as prey and predator, if it is not eating herring it can be fed upon by higher bird and hence contribute to the ecosystem.
Explanation:
Gulls are specific breed of birds which are considered intelligent among all the species of gulls. It acts both as a prey and predator. Ecologically these bird are very important as they keep a check on both their prey and predators. Even if they do not feed on herring , they are an essential part of food ecosystem as large gull birds or other bird species prey on gulls. They become the food for higher birds.