Ninja Seals!: Book 1: Night of the Mudskipper

Alx (pronounced "Alex") and his cousin Scooter are two ordinary seals by day. And at night, they dress up as ninjas! From the shadows, they fight crime and help other seals. When a mysterious monster commits a series of strange robberies, Alx and Scooter take action in order to protect their beloved town. But this is no ordinary thief! The ninja seals soon find they have their flippers full when they discover a plot that's bigger, more dangerous (and more goofy) than anyone could have imagined!