Your computer mouse is still technically a mouse, so why shouldn’t it have a tail? That’s the thinking behind the Oppopet 3 button Wireless Mouse from Elecom (JP). The cool part is that the tail is not just for looks, it actually detaches and plugs into your USB port as the mouse’s wireless receiver!
They come in a variety of different colors and matching tail styles- cat, fox, squirrel, dog, dolphin (which looks more like a whale tail (heh) to me), chameleon, pig, and rabbit
Wow that computer is really whale-tailing (btw, Googling “whale tail” may not be safe for work, depending on your situation). These mice come from Japan, so I’m not really sure how you can order one unless you live there or know someone who does. No price listed either.