nearly right.

I tried them on a point of natural history. I had observed, coming
along, a great many dead eels lying on the bottom of the river,
that I supposed had died from spear wounds. "No," said Johnny,
"they are lamper eels. They die as soon as they have built their
nests and laid their eggs."

"Are you sure?"

"That's what they all say, and I know they are lampers."

So I fished one up out of the deep water with my paddle-blade and
examined it; and sure enough it was a lamprey. There was the row of
holes along its head, and its ugly suction mouth. I had noticed
their nests, too, all along, where the water in the pools shallowed
to a few feet and began to hurry toward the rifts: they were low
mounds of small stones, as if a bushel or more of large pebbles had
been dumped upon the river bottom; occasionally they were so near
the surface as to make a big ripple. The eel attaches itself to the
stones by its mouth, and thus moves them at will. An old fisherman
told me that a strong man could not pull a large lamprey loose from
a rock to which it had attached itself. It fastens to its prey in
this way, and sucks the life out. A friend of mine says he once saw
in the St. Lawrence a pike as long as his arm with a lamprey eel
attached to him. The fish was nearly dead and was quite white, the
eel had so sucked out his blood and substance. The fish, when
seized, darts against rocks and stones, and tries in vain to rub
the eel off, then succumbs to the sucker.