YA distopian novel. The world is over populated and the people have resorted to killing teens. Spoiler ahead

[A]

The world is overpopulated, and the government has resorted to killing teenagers with a promise of a better life elsewhere. They take the teens on a boat and dump them in the ocean.
They blame the missing teens on killer rats. Book from the 90s.

[Rainbowheart]

Smart Rats

[Rosa]

Almost a palindrome…