Near the end - at about 1:25 - Kraken and Nathan are reminiscing. "Remember the time you saved me from the creature near Tokyo that breathed atomic fire?" "And then that giant moth chased us off." Obvious allusion to Godzilla and Mothra.
Whales do not have gills. If you chained a whale up, like they do Nathan, it will drown. It is a mammal and needs to take in air directly.