I bet if there was nothing to challenge them this wouldn't be happening..... They just don't seem skittish when they are in charge.
Just throwing that out there.... Been wrong before and will be again......
Armatus in there???? Hold on...... It's gonna be a bumpy culling. LOL I'm kidding, I hope.... Best of luck. You'll have a good deal of time before armageddon starts.... But as the saying goes "Resistance is futile"
ATF. The fish tank is a road course. Tats don't have the handling of an ATF. ATF makes the turn, Tat doesn't.
Rhaphs and Scombs don't have an attitude. They seem reclusive and when challenged would rather run or hide, or stay hidden enough they're never seen. Tats will chase....
You've said the Tats kinda hide and stay low in the tank. To me that kinda says they are being threatened. When they are the apex predator in the tank they usually patrol.
These are just guesses which is all we can do since we can't see it.
But random kamikazees and unexplained deaths isn't something Tats are known for.