i think that mammals should not be held in captivity simply because they belong in the ocean or jungle where ever they came from they belong there. They are not made or created to entertain the humans in this world, for example Shamu is not made to entertain people at Sea World that is a Killer Whale which means he's made to kill. Also another example is the tigers that killed the barnum and bailey brother it wasn't the tigers fault its the mans fault because hes a wild animal and belongs in the wild like other free animals.