refractory they are often treated with the most revolting brutality; anything seems to be permitted which will urge them beachward and so lighten the labor of carrying blubber.

The old American method of utilizing the blubber is wasteful in every stage. After the slain "elephant" has been allowed to bleed thoroughly, the hide is slit lengthwise down the back, and then transversely in several places from the dorsal incision to the ground. The flaps of hide are next skinned off, and the remaining investment of white blubber, which may have a maximum thickness of about eight inches, is dissected away from the underlying muscle and cut into squarish blanketpieces. The animal is then rolled over and the same process repeated on the ventral side. Thus the hide, and the considerable amount of blubber which clings to it, are lost at the start.

The blanket-pieces of the blubber are hauled to the water's edge to be strung on short ropes called " raft-tails." These are towed to the anchored ship where each laden raft-tail is looped about a hawser which extends from bow to stern, and the blubber is permitted to soak for forty-eight hours, or thereabouts, until the red blood corpuscles have been practically all washed away. During the soaking process a certain proportion of the oil is lost, and, moreover, flocks of ravenous "Cape pigeons" (Petrella), and other ubiquitous sea birds, feed upon the floating fat with an interminable hubbub, both night and

TEE STRIPPED CARCASS OF A SEA-ELEPHANT, WHICH HAD BEEN KILLED ONE OR MORE YEARS EARLIER, lying on the South Georgian beach. Thousands of seal remains, in all stages of slow decomposition, tell of the former slaughter and of the wasteful methods.

THE THREE STAGES IN THE DISPOSAL OF A SEA-ELEPHANT, according to the method of the American sealers. The upper photograph shows a bull sea-elephant which was lanced by the writer at the Bay of Isles, South Georgia, on February 17, 1913. The second picture illustrates the removal of the hide, which is cut off in small flaps, leaving the blubber exposed. A curved knife with an eight-inch blade is used in skinning, and, by means of a long, sweeping stroke, the hide is cut away as closely and cleanly as possible. The lower picture shows the carcass completely stripped of its dorsal blubber, which has been dragged to the adjacent cove. The carcass is now ready to be rolled over so that the hide and blubber of the ventral surface may be removed in the same manner. Photographs by Captain B. D. Cleveland.

day. When the blubber is hauled on board it is cut into narrow strips called "horse pieces," and is afterwards "minced." The mincing differs from the same process in sperm whaling only in that the fat is cut very finely with hand knives. At this stage

an additional loss of oil occurs, particularly if the temperature of the air chances to be well above the freezing point. Finally the minced blubber is "tried out" in the familiar deck tryworks of the old whaling type. There is so little residue or scrap" from boiled sea-elephant blubber that the Heard Island sealers of last century used to calculate "a cask of oil from a cask of blubber."

66

The method as practised by Norwegian whalers at South Georgia is more economical, inasmuch as the chunks of seaelephant blubber are left attached to the skin, and loaded into a steamer's hold, after which the cargo-hide, fat, blood, dirt and all-is dumped into steam try-works at the whaling station and reduced to oil and slag.

During fifteen months of 1914-1915, 850,000 gallons of seaelephant oil are said to have been exported from South Georgia by the Norwegian whalers. The sea-elephants can not long withstand such a toll as that, and the question as to whether the magnificent species is to be perpetuated will depend upon protective legislation which, it is to be fervently hoped, the British government will see fit to enact after the war. The difficulties and expenses of the modern whale fishery at South Georgia make it almost impossible for any species of whale to be completely extirpated, however persistently it may be chased, but the unfortunate sea-elephants have no such hope of preservation. Slow, unsuspicious, gregarious, they can be hunted profitably until the last one has gone to his ancestors and the tragedy of the antarctic fur seal is repeated.

PRINCIPLES AND PROBLEMS OF FISH
CULTURE IN PONDS

By DR. R. E. COKER

ASSISTANT IN CHARGE SCIENTIFIC INQUIRY, U. S. BUREAU OF FISHERIES

F

ISH as living animals have essentially the same general requirements for growth and propagation as poultry or pigs. As animals living in water, however, they present their needs to us in a so much more obscure way that our problem in providing the proper conditions is relatively complex. We have to meet most of the requirements for successful rearing of fish by very indirect means, and in so doing we have to be guided by a knowledge of general principles and the application of common sense, rather than by any explicit rules.

The ordinary needs of fish, flesh or fowl are: air, water, food, cleanliness, exercise, shade, protection of adults and young from enemies and disease, some control of numbers in proportion to available space, proper conditions for breeding, and care of young. Looking at these requirements severally, we are at once confronted with a striking point of difference between fowl culture and fish culture. Air, or more strictly oxygen, is freely supplied by nature to animals. With the fish the oxygen problem is paramount, and the fish-farmer must give first thought to the maintenance of a favorable oxygen supply in his pond. Without food the fish would live for days or weeks; without oxygen, it would suffocate in a few hours.

OXYGEN

Here is an excellent illustration of the fact that many of the requirements of fish are supplied by indirect means. Before we can proceed intelligently, we must know how the fish gets the oxygen necessary for its existence, that is to say, by what processes the oxygen supply is maintained in a natural body of water. This is one of our problems in its broad aspect.

Two processes are continually depleting the oxygen supply: The respiration of animals and the decomposition of various materials. In warm weather, too, the water will hold less oxygen, and it is accordingly the more necessary that the supply of oxygen shall then be added to continuously and abundantly.

How is the supply of oxygen maintained in a body of water? There are two principal means, one of which takes care of itself, but which is not entirely adequate for the purpose in small bodies of water.

First we are concerned with the interchange of gases between the surface of the water and the air. Birge has aptly employed the term "respiration of lakes," suggesting that the lake or pond breathes through its surface. He and others have shown how the oxygen supply thus derived is distributed through the body of the lake, and how this distribution is affected by temperature, seasons, winds and other factors.

As regards the propagation and rearing of fishes in selfcontained ponds, we are led at once to certain very practical questions. What should be the size, the form, the depth and the relative proportion of deep and shallow waters in the several units of our pond system, or of our single pond if there can be but one? Obviously, for a wintering pond we must provide for storage of oxygen to carry over the winter; but in spring, the season of renewed activity, spawning, and the beginning of life for a new generation, the deep winter pond, now depleted of oxygen, proves ill-adapted for quick recuperation, since the warmer surface waters fail to carry the absorbed oxygen to the bottom. This is the season when the natural ponds and streams are accustomed to broaden their margins and flow out over the surrounding lands, and most of the fish in spawning activity are observed to follow the waters outward and to deposit their eggs in places more or less removed from the customary banks of the stream or pond. They find inducement to this outward migration, perhaps, in the warmer temperatures prevailing in the shallow overflow waters, or, perhaps, in the better conditions of oxygenation which may prevail at least temporarily.

Since it is being attempted to suggest rather than to outline problems, it may be in place to mention without comment two unrelated, but very interesting, facts. It is in the middle or late spring that the Bureau of Fisheries expects and receives. the most numerous reports of unexplained mortalities of fishes in closely confined lakes. The other interesting fact is this: For two years, at our Fairport station, the effort to get the buffalo fish to spawn in artificial ponds failed. Last year, Mr. A. F. Shira, the director of the station, made the experiment of causing the pond to flow out gradually over a considerable area of ground just as the temperatures were developing when