Why shouldn't dolphins be eaten? Is there an ecological reason for it? Are they endangered? ARe we causing irreparable harm to an ecosystem? I know I sound like a smart-@$$ or something, but I swear I'm only curious. I understand dolphins are intelligent and cute and good helper animals and all of those things, but is there a reason beyond emotion why we should not eat them? To put a finer point on it, why is it more OK to eat pigs than dolphins? If you're a vegan, more power to you, but this question is for the omnivores. An like I said, not being sarcastic, I honestly want to know.
I'm going to try and give you a non-emotional answer to this. I'm actually surprised there haven't been people here trying to degrade you for asking this. I believe there are certain species that are endangered but honestly I'm not sure. I would however have to believe there is an extremely limited "supply" of dolphin and as humans are mass consumers they would easily be extinct before we knew it. I'm too lazy to google right now but if I'm not mistaken they have a really long gestation period so farming them wouldn't line anyone pockets quickly. Personally I couldn't eat dolphin. To me there are certain animals that have no use other than to be eaten (chicken especially comes to mind) but the dolphin isn't a useless animal.
In the film, many of the people in the town of Taiji actually have extremely high levels of mercury in there hair samples. This is believed to be caused by the frequent consumption of whale and dolphin meat by the people of the town.
ZombiBoi is correct - the population of dolphin is limited... if every country consumed dolphin as frequently as the Japanese did then the species would be extinct very quickly. The films states that this area of Japan kills 23,000 dolphins every year. The whaling practices used by these fisherman is actually illegal, but unfortunately dolphins are one of the few marine species not protected.
I would add to the other comments on here (how if many countries did what Japan does, dolphins would soon be extinct, it's bad for humans to eat them much at all due to the high mercury content, etc.), that dolphins aren't just extremely intelligent, but there is significant scientific evidence that they are actually self-aware. For example, in one experiment, a large mirror was lowered into a dolphin tank, and the experimentors would put little spots of paint on the dolphins on different spots on their bodies. The dolphins would then consistently swim up to the mirror and rotate their bodies in such a way that they had line of sight to the spot just put on their body by looking in the mirror (in other words, they were looking in the mirror at what had just been done to them). That seems like pretty clear evidence of self-aware sentience. (As opposed to say dogs or cats, that will attack their own reflection in a mirror, thinking it's another animal, or just ignore it). Their intellligence is apparently up there with chimps and the great apes. Some say that they are actually the most intelligent animals in the world. Why would you want to kill and eat such magnificent creatures, especially when it's really bad for you (due to the high mercury content)???
Well, there is the health issue, that they are toxic now due to the dumping of mercury in the ocean, and that they would rapidly go extinct.
But, well, for me the main thing is dolphins are intelligent. I know lots of the animals we eat are intelligent and I'm being a hypocrite to a degree because I eat pig, but last time I checked pigs don't name themselves and call each other by name. Every dolphin has its own name, called a signature whistle, which it is referred to by others during their complex vocal interactions. I couldn't bring myself to eat something that has its own name it calls itself, it feels like cannibalism. I see them as having a different order of intelligence too close to our own for consuming them as food to be moral.