A different type of whale eat squid. The baleen combs of baleen whales is unsuited for chewing squidy bits.

Rusty ships are avoided, some of the iron is molecularly bonded to other metals and minerals, and rust from ships will sink immediately, and isn't really very bio available anyway. Rust flakes and particles are kinda difficult (and large) for crustaceans to rend and digest.

Irony whale poop has buoyancy, and the iron is bio available.