THE SEA FISHERIES OF EASTERN NORTH AMERICA. 63 
to sustain life, as they feed not merely for subsistence but for material 
to keep up the animal heat. 
_ The cetaceans of various species are, of course, the most destructive 
by their much greater bulk, the larger of the porpoises being most no- 
table in this respect. Itis not unfrequently with feelings of satisfaction 
that the human spectator observes schools of bluefish that have de- 
voured and driven on shore schools of mackerel and menhaden, them- 
selves attacked and ‘subjected to a similar treatment by troops of por- 
poises, forming a line outside of them and devouring them with ex- 
traordinary rapidity, frequently forcing them on the beach in large 
numbers. Whales, too, take their part in this conflict, but probably con- 
fine themselves to smaller fishes, especially the herring, and possibly 
mackerel, capelin, or other species, of which large numbers, while 
schooling can be taken at a gulp. 
The method of feeding of the whale is, of course, only appreciable 
when the operation is conducted at the surface. Here they may be 
often seen (the finback whales especially), with the mouth wide open 
and swimming with great velocity against large bodies of herring and 
floating invertebrates, such as pteropods, jelly-fishes, &c. The greater 
the development of whalebone in the mouth, the less do the whales ap- 
parently feed on fish and the more on invertebrates. The finback is 
characterized by the small amount of whalebone. To what extent the 
sperm whale, which is essentially a large porpoise, feeds upon fish is not 
known; its principal food, however, is believed to be the giant cuttle- 
fish, which inhabits the depths of the ocean, with the largest of which 
it appears able to cope. It is very seldom that a sperm whale is cap- 
tured without having in its stomach some fragments of this large ceph- 
alopod, the beaks being almost always found in their intestines and 
excrement. Ambergris almost always contains such remains. 
Seals come next to the cetaceans in voracity and destructiveness, and 
occupy only a second place, in view of their more limited distribution 
and their confinement to acertain proximity tothe land. The numbers 
of fishes, especially of the Gadide, doubtless also of salmon, devoured 
by the seals in the North Atlantic must be something almost beyond 
calculation, and the destruction on the part of the much larger seals, 
sea-lions, fur-seals, &c., of the Pacific is probably still greater. 
How far the walrus is a destroyer of fish I am unable to say, although 
itis generally believed to depend, to a considerable extent at least, upon 
mollusea for food. 
Otters are also worthy of mention in this connection, the sea-otter of 
the Pacific Ocean being very destructive in proportion to its size and 
numbers. The common otter also devours large numbers of fish in 
- fresh water, levying tribute on many a fine salmon, shad, and other val- 
uable fish. 
Although at first sight we may not be inclined to attach much im- 
portance to birds as destroyers of fish, yet it is found that they, repre- 
