We saw more than 500 individuals during half an hour approximately. They were flying north along the coast of the river. Both adults and juveniles formed the flocks. Awesome!
There was a steady breeze and this kept the gull airborne without touching the water. I saw it descend and peck at something. I believed it could never take a fish out of the water, but it could. I saw it when I "developed" the photos at home.