I've written about the barbaric practice in Japan of slaughtering thousands of Dolphins in the town of Taiji. The good news is that rising levels of mercury in dolphin (and whale) flesh have started to reduce demand. Similar issues are also affecting worldwide tuna populations.
What's interesting is the cause: human pollution. As mercury enters the ocean it is absorbed by smaller fish. The larger predatory animals like tuna and dolphin consume these fish, thus accumulating larger and larger amounts of mercury in their bodies.