Seabirds are special birds that live near the ocean. They love to eat fish because fish are their main food. Since fish swim in the sea, seabirds spend a lot of their time flying over the water, following fish wherever they go.
Imagine you want to find your favorite snack. You would try to follow the person who has it, right? Seabirds do the same. They watch the water and look for schools of fish swimming around. When they find fish, they fly close to catch them to eat.
So, the reason seabirds follow fish in the sea is simple: it's because fish are their favorite food, and they need to find them to eat and stay healthy!