generally speaking until at least 12-20 specimens of a new species have been seen it's considered scientifically unethical to intentionally kill one or allow one to be killed to study it. maybe they found a whole bunch at once?
At that depth killing one and bringing it up to the surface would be quite an undertaking in itself.. I would imagine they just sent a submarine camera down
my friend does freshwater mussel and fish phylogeny, and does a lot of specimen gathering in various parts of the world for university of north carolina and a museum there. i think once they discovered a new species (maybe more than once)- i should ask what their guidelines are for when they take specimens.