Popular Science Monthly/Volume 20/February 1882/Longevity of the Oyster



IT is proposed to give an account of an interesting determination of the extreme age of a pair of venerable oysters which have just come into my possession. They were given me by a professional oyster-grower, Captain T. S. R. Brown, of Keyport, New Jersey, and belong to a planting in which he was concerned thirty years ago. The young oysters were obtained from Virginia, and planted in Raritan Bay, Keyport. At the proper time the crop was taken up and sent to market. In all such cases there are leavings or escapes from the dredging. The bottom being too hard, the bed was abandoned and never planted again, and these oysters were found there a few days ago. They are not "naturals" or natives, but simply naturalized "Virginies," a distinction which a practical oyster-raiser will make unerringly. Any one examining the shells would infer the nature of the bed whence they were taken, for the outer edges of the "shoots" or layers are smooth, as if worn by a gentle motion on a compact sandy bottom. The shells are large, though not larger than or even as large as many often seen in market; but the latter, if "primes," have been of much quicker growth, and the mollusk is larger and finer. In a word, they are many years younger than the pair I am considering, and were grown on a softer bed, and one which was for them in every way a richer feeding-ground. The two oysters in question measure, one seven inches long and three and a half wide, the other seven and a half inches long and four inches wide. The shells are quite heavy, and for their size the oysters are not so large as might be inferred; but they were eaten, and the verdict was that one was good and the other fair. As this was the judgment of an oyster-raiser, it had special value. The age of an oyster may be reckoned by counting the lines in the depression or groove of the hinge of the bivalve. These lines truly indicate the layers or annual shell-growths, being really the anterior extremity of the annual shell deposits. But the lower shell of an oyster, that is, the valve in which the animal lies when the shell is in normal position, is the deeper and heavier of the two, and, as its annual shell-layers correspond in number with those of the upper valve, it follows that they must be proportionally thicker. Hence the result is that the hinge-groove of the lower valve is longer than that of the upper valve, because the lines which are the extreme edges of the layers are thicker than the lines in the upper groove. Wherever the oyster has room and fair conditions this is the necessary law of its growth, viz., for gravity's sake the ponderosity is given to the lower valve; also for the comfort and growth of the animal, as it secures it a normal position and the proper trough or cradle in which the mollusk can grow. When oysters are excessively crowded they will grow standing on end, that is, side by side, with the nib or wide end uppermost, thus producing those worthless, elongated forms known in some localities as "strap-oysters" and "stick-ups."

Being interested in these specimens as uniques, to me at least, I was concerned to see if the natural record would tally with the well authenticated tradition of their age. To shorten the story, I will give the method of examination of but one of them. In this instance the distal end, that is, the oldest parts of the hinge-grooves, were coated with the skeletons of bryozoa, hence the line-record was partly obliterated, so that a clear count could only be got from the near end of the groove. Fortunately, the lines were so uniform in thickness that the estimation was reduced to a simple question of proportion. By actual measurement the length of the upper groove was one and a half inch, and that of the lower one was two and a half inches. Now, in the upper groove there were five of these annual layer-lines in a quarter of an inch, and in the lower groove there were, as nearly as I could make out, three lines and a third of a line in a quarter of an inch, which would give thirty of these annual lines for the upper groove and thirty in the lower groove, all which would tally with the tradition that the bivalve was thirty years old.

Two points are established by the above: first, the great longevity of the oyster; the specimens were in excellent condition, and there was nothing about them to disprove the belief that, if allowed to lie undisturbed, they might have lived and grown ten years longer; and second, that an oyster may be good and palatable food at a great age. I have seen old oysters obtained from newly discovered and crowded beds that as food were literally worthless; but the specimens discussed were not found in such conditions.

It is fortunate for science when some intelligent man like Captain Brown puts the student in the way of a fact so interesting; and that interest grows into an intense enjoyment when the tradition is ratified by a reading of Nature's own writing. I remember the case of an oyster-grower at Keyport, who noticed that a fine "prime" oyster was spoiled for market because the dredge had broken a piece, measuring three quarters of an inch, off the nib, so that the mollusk itself was exposed. This was in October. He took the broken oyster and put it in the water by the side of a pile. Next summer he examined it, and found that the animal had completely repaired his house, thus establishing two important facts—the great damage which the mollusk can repair, and the time needed for the reparation.