I agree that the couple deserves a happy ending, but if they did the story and message itself would lose its poignant effect.
The way we relate to the seagull and the shark and the way the authors humanise them to help us better understand and feel for them, only to show how cruelly they meet their end really visualises how cruel and inhuman shark finning is.
Yes, you're totally right. I think the message is very clear and striking. The cruelty of this fishery for sharks fin is cleverly showed, and it is a good thing to denounce it. In that way, I think the sad ending was a good idea from the authors.
Actually, I would have prefered two stories with these characters: one with this plot and sad ending, and another with a happy ending. It's so unusual to see this kind of characters and story that I would have loved to see a "true and longer" love story between the shark and the seagull.
But I don't regret the work of the mangakas because their story was really brilliant and beautiful.
I know. The story makes me feel so emotional every time I read it.
This story is very beautiful and heart breaking. I don't regret having read it even if I'm in tears now, but I would have loved to read a happy ending for this unusual couple.