This might sound crazy, but I thought the chapter was leading up to the revelation that Sinaru’s parents, probably his dad, caused his accident/injury, not a shark attack. I thought maybe something happened while they were at sea–which would explain why Sinaru did not like/want to swim in the sea, but had such a desire and fascination with water and life beneath the ocean. Also, the way his parents don’t really interact with him that much and avoid looking at his arm– I realize it’s probably because his disability means it will be harder for him to get a job or care for his parents later, but I read it as guilt.
The chapter mentions through Ahrim’s thoughts on page 95 and 103 that shark attacks are rare, that “[v]ery few [people] were victims of sharks, as many assumed was the greatest fear in water” (95). Like I said, this could just be me reading too much into things, but with the emphasis on that fact and all the other details, I was waiting until the end to read something about how it was Sinaru’s parents after all, not a shark. (I was a bit disappointed when that wasn’t the case, not because I wanted his parents to be terrible, cruel people, but because I thought I was picking up on subtle hints that apparently were never actually there).