How had James suddenly become the "captain of the ship"?

James took over when the sharks surrounded the peach.... he became the leader.... the captain.

James went over and put an arm gently around the Earthworm's shoulders. "I won't let them touch you," he said. "I promise I won't. But we've got to hurry! Look down there!"
There were more sharks than ever now around the peach. The water was boiling with them. There must have been ninety or a hundred at least. And to the travelers up on top, it certainly seemed as though the peach were sinking lower and lower into the water.
"Action stations!" James shouted. "Jump to it! There's not a moment to lose!" He was the captain now, and everyone knew it. They would do whatever he told them.