Pig Kahuna by Jennifer Sattler

From chapters.ca: Fergus and his little brother, Dink, love collecting the things that wash up on the beach, especially if it means that Fergus doesn't actually have to go in the water. Then one day, they spy the greatest treasure of all - an abandoned surfboard. When no one comes to claim it, they make it the star of their collection and name it Dave. But when Dave accidentally (on purpose?) gets cast back into the ocean, can Fergus find the courage to rescue him? Whimsically brought to life with Jennifer Sattler's bright, comedic style, here's a story about bravery and brotherhood that little kahunas (and their parents) are sure to love.