People with Fishtails

Gayle has mommy issues. Her mom left when she was eight, abandoning her in the hands of a drunk and unstable father. Oh, and her mom was also a mermaid.
Sander has daddy issues. His dad is the CEO of KrakenGo, the largest renewable fuel company on the planet. Oh, and he's also destroying the planet.
When Gayle and Sander find themselves on an environmental pirate ship, bound for the four corners of the earth to pillage and plunder what's left of the ocean's magnificent creatures, they agree to band together to stop this madness. Oh, and they still have parent issues...