I have found many plugs over the years but never one so intact as this, certainly not this size, its fair to say the male hit the spot! Plugs are usually released from the females cloaca the following day after copulation but in most cases only small fragments can be seen in the water flow of the aquarium. As disgusting as it may sound most are immediately eaten by the other rays hence the reason the plug is not always found making any pregnancy that much more sweeter when the first sight you see is pups moving around the females abdomen as late as half way through gestation.
Sorry if my post offended anyone...lol! it was meant to be educational.
Here is hoping for plenty more plugs in 2016