All through July the Tarpaulin Islanders had been troubled with dogfish.
Beginning with a few scattering old "ground dogs," which apparently live
on the banks the year round, they had become more and more numerous as
the month advanced. Bait was stripped from the hooks; fish on the trawl
were devoured until only heads and backbones were left; and the robbers
themselves were caught in increasing numbers. At last their depredations
became unbearable.

Jim and Percy had made a set one foggy morning on Medrick Shoal. When
the trawl came up it was a sight to make angels weep. For yards at a
stretch the hooks were bare or bitten off. Then came "dogs" of all sizes
from "garter-dogs," or "shoe-strings," a foot long, to full-grown
ten-pounders of about a yard. Mingled with them was an occasional
lonesome skeleton of a haddock, cusk, or hake.

"Look at the pirate!" said Jim.

Grasping a ganging well above the hook, he held the fish up for Percy's
inspection. It was two feet long, of a dirty gray color, slim,
shark-shaped, with mouth underneath. Before each of the two fins on its
back projected a sharp horn.

"Think of buying perfectly good herring at Vinalhaven, and freighting
'em way down here to feed a thing like that!" mourned Jim. "He's the
meanest thief that ever grew fins. Swims too slow to catch a fish that's
free; but good-by to anything that's hooked, if he's round. He'll gouge
out a piece as big as a baseball at every bite. I'd hate to fall
overboard in a school of 'em."

"Don't touch him!" he warned, hastily, as Percy reached out an
investigating hand. "He'll stick those horns into you, and they're rank
poison."

"Aren't dogfish good for anything?" asked Percy.

"Not a thing! No, I'll take that back. They can be ground up for
fertilizer; their livers are full of oil; and their skin makes the
finest kind of sandpaper for cleaning or polishing metal without
scratching it. They've been canned, too, under the name of grayfish; but
no fisherman'd ever eat 'em; he knows 'em too well."

Rod after rod of trawl yielded the same results.

"I'm almost tempted to save my buoys and anchors, and cut all the rest
away," announced Jim in disgust. "I've known it to be done. They wear
the line out, sawing across it. But I guess the best way is to save what
we can and stop fishing for a while. Sometimes they come square-edged,
like a stone wall, just as they have this morning; and in a few days
they'll have gone somewher