Hal.—I will tell you all I know, which is not much. This is certain, that there are two migrations of eels,—one up and one down rivers, one from and the other to the sea; the first in spring and summer, the second in autumn or early winter. The first, of very small eels, which are sometimes not more than two or two and a half inches long; the second, of large eels, which sometimes are three or four feet long, and weigh from 10 to 15, or even 20lbs. There is great reason to believe, that all eels found in fresh water are the results of the first migration: they appear in millions in April and May, and sometimes continue to rise as late even as July and the beginning of August. I remember this was the case in Ireland, in 1823. It had been a cold backward summer, and when I was at Ballyshannon, about the end of July, the mouth of the river, which had been in flood all this month, under the fall, was blackened by millions of little eels, about as long as the finger, which were constantly urging their way up the moist rocks by the side of the fall. Thousands died, but their bodies remaining moist, served as the ladder for others to make their way; and I saw some ascending even perpendicular stones, making their road through wet moss, or adhering to some eels, that had died in the attempt. Such is the energy of these little animals, that they continue to find their way, in immense numbers, to Loch Erne. The same thing happens at the fall of the Bann, and Loch Neagh is thus peopled by them: even the mighty Fall of Shaffhausen does not prevent them from making their way to the Lake of Constance, where I have seen many very large eels.
Phys.—You have shown, that some eels come from the sea, but I do not think the facts prove, that all eels are derived from that source.
Hal.—Pardon me—I have not concluded. There are eels in the Lake of Neufchatel, which communicates by a stream with the Rhine; but there are none in the Leman Lake, because the Rhone makes a subterraneous fall below Geneva; and though small eels can pass by moss or mount rocks, they cannot penetrate limestone, or move against a rapid descending current of water, passing, as it were, through a pipe. Again: no eels mount the Danube from the Black Sea; and there are none found in the great extent of lakes, swamps, and rivers communicating with the Danube,—though some of these lakes and morasses are wonderfully fitted for them, and though they are found abundantly in the same countries, in lakes and rivers connected with the ocean and the Mediterranean. Yet, when brought into confined water in the Danube, they fatten and thrive there. As to the instinct, which leads young eels to seek fresh water, it is difficult to reason;—probably they prefer warmth, and, swimming at the surface in the early summer, find the lighter water warmer, and likewise containing more insects, and so pursue the courses of fresh water, as the waters from the land, at this season, become warmer than those of the sea. Mr. J. Couch (Lin. Trans. T. xiv. p. 70) says, that the little eels, according to his observation, are produced within reach of the tide, and climb round falls to reach fresh water from the sea. I have sometimes seen them, in spring, swimming in immense shoals in the Atlantic, in Mount Bay, making their way to the mouths of small brooks and rivers. When the cold water from the autumnal floods begins to swell the rivers, this fish tries to return to the sea; but numbers of the smaller ones hide themselves during the winter in the mud, and many of them form, as it were, masses together. Various authors have recorded the migration of eels in a singular way,—such as Dr. Plot, who, in his History of Staffordshire, says, that they pass in the night, across meadows, from one pond to another: and Mr. Arderon (in Trans. Royal Soc.) gives a distinct account of small eels rising up the flood-gates and posts of the water-works of the city of Norwich; and they made their way to the water above, though the boards were smooth planed, and five or six feet perpendicular. He says, when they first rose out of the water upon the dry board, they rested a little—which seemed to be till their slime was thrown out, and sufficiently glutinous—and then they rose up the perpendicular ascent with the same facility as if they had been moving on a plane surface.—(Trans. Abr. vol. ix. p. 311.) There can, I think, be no doubt, that they are assisted by their small scales, which, placed like those of serpents, must facilitate their progressive motion: these scales have been microscopically observed by Lewenhoeck.—(Phil. Trans. vol. iv.) Eels migrate from the salt water of different sizes, but I believe never when they are above a foot long—and the great mass of them are only from two and a half to four inches. They feed, grow, and fatten in fresh water. In small rivers they are seldom very large; but in large deep lakes they become as thick as a man’s arm, or even leg; and all those of a considerable size attempt to return to the sea in October or November, probably when they experience the cold of the first autumnal rains. Those that are not of the largest size, as I said before, pass the winter in the deepest parts of the mud of rivers and lakes, and do not seem to eat much, and remain, I believe, almost torpid. Their increase is not certainly known in any given time, but must depend upon the quantity of their food: but it is probable they do not become of the largest size, from the smallest, in one or even two seasons; but this, as well as many other particulars, can only be ascertained by new observations and experiments. Blotch states, that they grow slowly, and mentions, that some had been kept in the same pond for fifteen years. As very large eels, after having migrated, never return to the river again, they must (for it cannot be supposed that they all die immediately in the sea) remain in salt water; and there is great probability, that they are then confounded with the conger, which is found of different colours and sizes—from the smallest to the largest—from a few ounces to one hundred pounds in weight. The colour of the conger is generally paler than that of the eel; but, in the Atlantic, it is said, that pale congers are found on one side of the Wolf Rock, and dark ones on the other. The conger has breathing tubes, which are said not to be found in the other eel; but to determine this would require a more minute examination than has yet been made. Both the conger and common eel have fringes along the air bladder, which are probably the ovaria; and Sir E. Home thinks them hermaphrodite, and that the seminal vessels are close to the kidneys. I hope this great comparative anatomist will be able to confirm his views by new dissections, and some chemical researches upon the nature of the fringes and the supposed melt. If viviparous, and the fringes contain the ova, one mother must produce tens of thousands, the ova being remarkably small; but it appears more probable, that they are oviparous, and that they deposit their ova in parts of the sea near deep basins, which remain warm in winter. This might be ascertained by experiment, particularly on the coasts of the Mediterranean. I cannot find, that they haunt the Arctic ocean, which is probably of too low a temperature to suit their feelings or habits; and the Caspian and the Black Sea are probably without them, from their not being found in the Volga or Danube; these, being shallow seas, are perhaps too cold for them in winter. From the time (April) that small eels begin to migrate, it is probable that they are generated in winter; and the pregnant eels ought to be looked for in November, December, and January. I opened one in December, in which the fringes were abundant, but I did not examine them under the microscope, or chemically. I trust this curious problem will not remain much longer unsolved.
EIGHTH DAY.
HALIEUS—POIETES—ORNITHER—PHYSICUS.
SCENE—DOWNTON.
Poiet.—This is a beautiful day, and, I think, for fishing, as well as for the enjoyment of the scenery, finer than yesterday. The wind blows from the south, and is balmy; and though a few clouds are collecting, they are not sufficiently dense to exclude the warmth of the sun; and, as lovers of the angle, we ought prefer his warmth to his light.
Hal.—I do not think, as the day advances, there will be any deficiency of light; and I shall not be sorry for this, as it will enable you to see the grounds of Downton, and the distances in the landscape, to more advantage: nor will light interfere much with our sport in this valley, where, as you see, there is no want of shade.
Poiet.—This spot is really very fine. The fall of water, the picturesque mill, the abrupt cliff, and the bank, covered with noble oaks, above the river, compose a scene such as I have rarely beheld in this island.
Hal.—We will wander a little longer through the walks. There you will enter a subterraneous passage in the rock beyond the mossy grotto. Behold, the castle, or mansion-house, clothed in beautiful vegetables, of which the red creeper is most distinct, rises above on the hill! After we have finished our walk and our fishing, I will, if you please, take you to the house, and introduce you to its worthy master, whom to know is to love, to whom all good anglers should be grateful, and who has a strong claim to a more extensive gratitude—that of his country and of society—by his scientific researches on vegetable nature, which are not merely curious, but useful, and which have already led to great improvements in our fruits and plants, and generally extended the popularity of horticulture.
Phys.—We shall be much obliged to you for the favour—provided always, you know it will not be an intrusion.