176 AMERICAN FISHES. 
size varies from year to year, sometimes very few barrels which can be 
rated as No. 1’s being found in our waters. A No. 1 Mackerel, accord- 
ing to the Massachusetts inspection laws, measures thirteen inches from 
the tip of the snout to the crotch or fork of the caudal fin. The average 
length from year to year for the whole coast is probably not far from 
twelve inches in length, and a weight of twelve to sixteen ounces. 
_ The gannet is one of the most destructive enemies of the Mackerel. 
These birds are often seen so heavily weighted with these fish that they 
are unable to rise on the approach of the vessel until they have disgorged 
from two to four good-sized Mackerel. This isso common an occurrence 
that there are but few fishermen who have not witnessed it. 
Porpoises and whales may also be included in the list of enemies of the 
Mackerel. It is by no means an unusual sight on the fishing grounds to 
see hundreds of the former rushing and leading among schools of Mack- 
erel, scattering them in every direction. 
The shark known to fishermen as the ‘‘ mackerel shark’’ is one of the 
principal enemies of the Mackerel. 1 have often seen them chasing 
Mackerel, and, when jigging was practiced, it was a common occurrence 
for sharks to drive off a school from alongside of a vessel. 
Dogfish often hover around the outside of large schools of Mackerel, 
and doubtless feed on them. Great difficulty is sometimes experienced in 
saving fish that have been inclosed in a purse-seine, owing to the immense 
numbers of dogfish that gather around and, in their efforts to eat the 
Mackerel, which they see through the meshes, bite off the twine, making 
large holes in the seine through which the inclosed fish escape. 
Among the other principal enemies of the Mackerel are the bluefish, 
and the cod. The appearance of a school of bluefish in waters crowded 
with Mackerel is an almost sure signal for their disappearance. 
The young Mackerel are eaten by squidsalso. Prof. Verrill has recorded 
the following account: of the maneuvers of the squid known to zodlogists 
by the name Ommastrephes illecebrosus : 
“« Messrs. S. I. Smith and Oscar Harger observed it at Provincetown, 
Mass., among the wharves, in large numbers, July 28, engaged in captur- 
ing and devouring the young Mackerel, which were swimming about in 
‘schools,’ and at that time were about four or five inches long. In attack- 
ing the Mackerel they would suddenly dart backward among the fish with 
the velocity of an arrow and suddenly turn obliquely to the right or left 
