In the film, they are portrayed as mindless eating machines who only shout one word: "Mine!"
They are first seen cawing "Mine!" while Nigel has a crab in his wing that he is going to eat, much to his irritation. However, he ends up relieving the crab when he overhears from his fellow pelicans that Nemo's father, Marlin, is trying to search for his son, although the crab manages to escape from the Seagulls.
Later in the film, the Seagulls surround Nigel, Marlin and Dory, and also nearly try to eat Marlin and Dory while trying to escape from Nigel (as they thought he was going to try and eat them when all he was trying to do was tell them that he knows Nemo and where he is), but Nigel saves them. They chase after Nigel until their beaks crash into a sail of one of the sailboats.
The Seagulls make their last appearance when Dory and Nemo try to get information out of a crab about where he saw Marlin go (Dory intended to feed the crab to the Seagulls if he didn't answer them).
Three of the Seagulls reside on the rocks outside the entrance to The Seas with Nemo & Friends at Epcot. Like their Disneyland counterparts, they periodically flap their wings and say "Mine! Mine! Mine!"
The Seagulls bear some resemblance to Feathers McGraw, the evil penguin from the Wallace and Gromit episode "The Wrong Trousers".
A different flock of seagulls resembling the ones from the first film make a cameo appearance near the end of Finding Dory when Dory and Hank drive the truck containing the quarantined fish into the ocean.
The Seagulls in the Harbor
"Mine! Mine! Mine! Mine! Mine! Mine! Mine! Mine!"
"Oh, would you just shut up!"
The Seagulls seeing the Crab being thrown by Nigel.