THE HABITS OF FISHES.
The following notes as to the habits of fish may prove of interest to the naturalist:—
“It has often been observed in the course of the Bell Rock operations, that during the cold weather of spring and autumn, and even at all seasons, in stormy weather, when the sea is much agitated by wind, the fishes disappear entirely from the vicinity of the rock, probably retreating into much deeper water, from which they do not seem to return until a change of weather has taken place; so much was this attended to by the seamen employed on this service, that they frequently prognosticated and judged of the weather from this habit of the fishes as well as from the appearance of the sky.”
“It was a general remark at the Bell Rock that fish were never plenty in its neighbourhood, excepting in good weather. Indeed, the seamen used to speculate about the state of the weather from their success in fishing. When the fish disappeared at the rock, it was considered a sure indication that a gale was not far off, as the fish seemed to seek shelter in deeper water, from the roughness of the sea, during these changes of the weather. This evening, the landing master’s crew brought to the rock a quantity of newly caught cod fish, measuring from fifteen to twenty-four inches in length. The membrane called the sound, which is attached to the backbone of fishes, being understood to contain, at different times, greater portions of azote and of oxygen than common air, the present favourable opportunity was embraced for collecting a quantity of this gas in a drinking glass inverted into a pail of salt water. The fish being held under this glass as a receiver, their bladders were punctured, and a considerable quantity of gas was thus collected. A lighted match was afterwards carefully introduced into the glass, when the gas exhibited in a considerable degree the bright and luminous flame which an excess of oxygen is known to produce.”
On showing this extract to my friend Dr. P. D. Handyside, who has contributed some interesting papers to the Royal Society of Edinburgh on the Polyodon gladius, he writes:—“Biot and De La Roche found that the proportion of oxygen in the air bladder increases with the depth of the water in which the fish usually lives, from a small quantity up to 87 per cent. Biot found in the deep Mediterranean fishes 87 parts of oxygen, nitrogen, and carbonic acid. Humboldt found in the electrical eel 96 parts of nitrogen and 4 only of oxygen. No hydrogen has ever been detected in this organ. In the air bladder of marine fishes oxygen predominates, and in that of fresh-water fishes nitrogen. No air sacs exist in rays, flounders, sole, turbot, and others which lie at the bottom.”
Dr. Handyside adds: “The extract shows with what a practical and accurate mind your father was endowed, and I think, in justice to him, you should give his observations.”
I also communicated Mr. Stevenson’s papers on fishings to the Honble. B. F. Primrose, C.B. (Secretary to the Fishery Board: Scotland), who has kindly sent me a letter explaining why the progress of the fishings in the Shetland Islands is slow, from which I give a few extracts:—
“I have read with great interest your father’s notes upon the fisheries of Scotland. They bear distinctly the impress of that practical and accurate mind with which he is described as having been endowed. It is also pleasant to see that his mind went a great deal further, and grasped the application of science to solve the mystery of fishings.
“He seems to have overlooked, as was universal in his day, that the secret of fisheries is not the presence of fish but the certainty of markets. Samuel Laing of Orkney, to whom he refers, was, I think, the first that struck this key note of truth. The Dutch came here and fished for herrings because they could not fill their vessels fast enough for the markets behind them in Holland. The Shetlanders did not fish for herrings because they had no remunerative market for them, but they fished, and fished boldly, where they had one, viz., for the whales of the Arctic Regions. They might have brought the herring home from off their own coasts and got nothing for them, but they could not bring the whale oil home without a secured profit.
“The same thing obtains still. Shetland, from its position, cannot compete with the mainland of Scotland either in the home market or in the great continental markets for herrings; but it yields large supplies of cod, ling, and tusk, for which it pushes distant adventures to Iceland and the Faroe Isles.”