Gambar halaman

of the North are practically exhausted, and diminish the number of oysters? A bed is that the production of the Southern beds (of extended naturally by the drifting “spat," Maryland and Virginia) is greatly diminished. or young brood, attaching themselves to any. It is not probable, however, that the area of appropriate "cultch” contiguous to the bed. the latter has decreased, notwithstanding vari- This extension is greatest in the direction of ous estimates to the contrary, arising out of the currents, and unless some substance is inthe increased price of oysters, and the lack of terposed between the soft bottoms (which are care and protection to the oyster-beds. Ad- destructive to young broods) and the drifting mitting that the Northern beds are practically "spat," they will sink into it and be destroyed. exhausted, and have become mere fattening- Nature offers very little help in the way of places for the transplanted Southern oyster, preventing this destruction, and hence the it is still open to question whether the beds of great expansion of the beds must be assigned Maryland and Virginia are deteriorating. to other agents than natural causes. The dim

It being impossible to speak with perfect inution of the number of oysters might have accuracy of the entire area covered by oysters been effected by deposits of earthy or vegetain these States, it may safely be assumed that ble matter, so as to bury both old and young the condition and peculiarities of beds in one oysters; but there is no evidence of any such district will serve, approximately at least, to deposits ever having been made. Again, a express the condition of all the rest. The only change in the character of the water and botlocality which has been thoroughly studied lies tom might deprive oysters of their proper food, on the eastern shore of Chesapeake Bay, oppo- and cause their deterioration and destruction; site the mouth of the Potomac River. This but such a change would act suddenly, and was done in 1878-79, and includes the survey impair the flavor and vitality of those that esof the beds of Tangier and Pocomoke Sounds, caped. Inasmuch, however, as no such imand ascertaining the depth of the water over pairment has taken place, but on the contrary the beds, the direction and force of the cur- the oysters are larger and finer than formerly, rents, the character of the bottom, the effect no force can be attributed to this as a cause of of gales, ice, and freshets, and also of fishery the diminution of the oysters. These, then, bewith dredges or tongs.

ing dismissed as inadequate, the real cause is Tangier and Pocomoke Sounds are arms of to be sought in the agency of man. Chesapeake Bay, and lie opposite the mouth of The oyster-fishery in these localities is car. the Potomac, on the eastern side of the bay. ried on chiefly log the process of “dredging." The former extends about thirty-six miles This is performed as follows: A dredge or north, is separated from the bay by a chain of scrape resembles a large iron claw, the nails low, marshy islands, and receives the waters representing the teeth of the dredge. To the of several creeks and rivers. The shoals on back of this is fastened a bag of iron mesheither side of the channel are covered with work, large enough to hold two or three bushoyster-beds, and, where there are no beds, oys- els. Dredges vary in size from two to five ters are scattered in groups or singly. They feet across the mouth, and of greater or less are also found as continuations of the beds, weight. Dredging-vessels vary in size from and, generally speaking, oysters may be taken five to thirty tons, and all use two dredges. in varying numbers throughout Tangier, in These are dropped one from each side, and the depths of between one and six fathoms. Poco- vessel being kept under easy sail, they fill and moke Sound is twelve and a half miles long are hauled in by a small winch. They are and about nine broad near the middle. The then emptied, and the process repeated. The channel is narrow and tortuous, and the main mud, sand, sponge, etc., are separated from the body of the sound is shoal, and these shoals oysters, and, together with the oysters unfit covered with oysters, singly or in groups, or for market, thrown back into the water. As in large, well-defined beds. Several creeks and the limits of the dredging-grounds are not dethe Pocomoke River empty into this sound. fined, the vessels frequently drag quantities of The beds were located and marked off, and the shells and oysters beyond the boundary of the area ascertained approximately. The entire beds. After “culling" the oysters, or separatarea in both sounds upon which oysters were ing them from the old shells, these shells are found amounts to fifty-four square miles. The thrown back again, and many young oysters area of the beds proper, where the vessels for with them. If these fall on suitable grounds, dredging mostly work, amounts to six square sufficient to support them, they form a small miles in Tangier and four in Pocomoke Sound. colony, which soon after, by the action of the From the examination made in 1878 it appears dredges, becomes attached to the main bed, and that the number of oysters on the beds has thus increases the area of the latter. greatly diminished during the last thirty years, A further question presents itself. Will the that the area of the beds bas greatly increased, dredging also account for the diminution of and that there has been no change of the usual the oysters? Without discussing here the natural conditions to which oysters are sub- question of propagation, it may be stated that jected.

the male and female of the American variety The question then arises, What natural cause of oyster expel the generative matter into the or causes would both expand the beds and water, where the eggs must meet the male


OYSTER-DREDGE. fluid in order to be fertilized. Hence, the Stronger evidence, however, is afforded by inmore compact the bed, the greater the chance vestigation, made in 1879, in regard to areas in of the ova and spermatozoa coming in contact. Chesapeake Bay where oysters existed in a If the mature, spawn-bearing oysters are very locality known to very few fishermen. Here much diminished in number, or widely sepa- the oysters were found in clusters of from rated from each other, the chances of contact three or four to twelve or fifteen, with clean, are slight, and there is a failure of reproduc- white shells, and the spaces between the larger tion. But the removal of brood-oysters is not ones filled with the young growth and barnathe sum total, by any means, of the effects of cles. The mature oysters were long and narthe dredging. Millions of young oysters, unfit row; whereas, in beds worked for some time, for market, are carried off sticking to the shells oysters are usually single, or in clusters of two of the mature oysters, and nearly as many or three, the animals are fatter and thicker, and young are destroyed by being thrown from the the shells are dirty, with much mud or sand dredging-vessels upon soft or unfavorable bot- clinging to them. These new beds were found toms. As, then, theoretically, dredging would to be hard, and the clusters more firmly atextend the beds and destroy their fecundity, it tached to the bottom, while the beds in the may be asked whether this has been, practi- sound were soft, and the oysters easily obtained cally, the case.

by means of the dredge. All the oysters exThe testimony of the fishermen is unani- amined during the season of 1879 were measmous as to the extension of area, some of the ured and distributed into four classes, the first beds having donbled in size during the last two the mature, the last two the young growth. thirty years. They also testify that the beds Over twenty thousand were measured and clashave materially deteriorated during this period. sified, and the ratio of the young growth to

the mature was found to be as three to two. ture would probably outnumber the young, Over 100,000 oysters were taken from the beds and the ratio be abnormally small, as it was in the sounds, and measured and classified in abnormally large. With this large number of like manner, and the ratio of young to mature mature oysters. there would be increased prowas found to be as three to six. Thus on the duction, and at the end of three years, again, the new beds the young outnumbered the mature, ratio would change, while the number of oyswhile on the worked beds in the sounds the ters will constantly be diminishing. In time, mature outnumbered the young growth. however, the brood - oysters will become so

The action of the dredge is very destructive scarce that the fertilization of the eggs will be to the oysters remaining on the bed, by not more and more improbable, and the young reonly roughly detaching them from different main in the minority; so that, if the fishing objects to which they cling, but also leaving continue, the entire destruction of the breeding them in such positions as to prevent their open- power will be but a matter of time. ing the valves without letting in mud or sand. It was estimated, from careful investigation, Thus the dredge causes the destruction indi- that the number of oysters removed, in 1878, rectly of a large number of oysters that remai was over 1,500,000 per day, and in 1879, over after its passage, and hence the number of old, 700,000 per day. In the sounds the dredging empty shells should be greater upon a bed that continues throughout the year, though little is has been dredged than upon one that has not; done in the summer months. The law sanctions and if that number is very large, it shows that the working of the beds from October 1st to the population of the bed has been destroyed. May 1st. If confined to this period, with only The quantity of matter brought up by the three full working days each week, the dredging dredge was measured during the season of season would be about 120 days, and in that 1879, and also the quantity of oysters and of time there would be removed, by the estimate débris. On the unworked beds, this latter of 1878, over 184,000,000 oysters, and, by the amounted to 30 per cent of the whole quantity estimate of 1879, over 89,000,000 oysters. The of matter brought up; while in the sounds the number of young growth would be, by the first débris was much greater, and in Pocomoke estimate, 148,000,000; by the second, 36,000,Sound it amounted to 97 per cent.

000. The statistics of 1879, compared with During the season of 1878 a method was those of 1878, show that there were twice as devised by which the number of oysters to the many vessels at work in 1878 as in 1879; and square yard could be determined approxi- the difference of young growth is due to the mately; and in accordance with this the num- fact that the summer of 1879 was a bad one ber to the square yard should be greater upon for the “spat," and consequently there was & the old beds than the new. If, on comparing failure of "yoang.” The mortality among the the results of successive seasons on the same young after attachment is about 50 per cent, bed, it is found that the number of oysters to and consequently only about 74,400,000 of the the square yard is decreasing, it may be con young removed in 1878–79 would have atcluded that too large a number is annually tained the age of one year. If none of the oysremoved. Investigation showed that, on 60 ters had been removed from the beds, there per cent of the beds in Tangier Sound, there would have been about 259,000,000 more on was a decrease in the number of oysters in the beds than was actually the case, and of 1878–79, and that on 60 per cent of the beds that number 71 per cent were mature and the number of oysters to the square yard spawn-bearing. Now, as 65 per cent of those was less than on the newly discovered beds in in the beds are mature, the adiling of 250,000,the bay, and in no case was the number much 000 would increase the percentage to 68, or the greater. In Pocomoke Sound, on erery bed the young growth would be in a more hopeless minumber of oysters to the square yard was con- nority than before. siderably less than in 1878, and also much be There are, then, three indications of the delow the number on the new beds in the bay. terioration of the beds: The number of the

It is evident that, if the number of the young young is eitlier much smaller or much larger growth falls below the number of the mature than the number of mature oysters, and in the oysters, the fecundity of the bed is impaired; latter case is so large as to be abnormal; the yet it does not follow that, if the young out- amount of débris found on the beds is much number the mature, it is a sign of increased greater than in the newly discovered areas; production. From the beds in question many and the number of oysters to the square yard millions of oysters are annually removed, of not only falls below what it should be, but has which a largo percentage is mature, and, if decreased since the first examination in 1878. this removal of one class is excessive, it might Considering the testimony of persons living in show itself in the increased ratio of young to the vicinity of Tangier and Pocomoke Sounds, mature. Supposing this to be the case, the and the results of the comparison of the worked young would greatly ontnumber the mature beds in the sound with the unworked ones in for about three years, or the period to pass the bay, it may be concluded that the former from youth to maturity. During this period areas are much impaired in productive power, there is a constant removal of the brood-oys- and, the same reasons continuing to operate, ters, so that, at the end of three years, the ma- there will be a constant deterioration until that

productive power is entirely destroyed. This ported. Hence, by the deterioration of the deterioration and impaired fecundity can only beds, not only would the price be much inbe accounted for by the excessive and exhaust- creased for all classes, but the poorer among ive fishery in the sounds, from which hereto- our citizens would many of them be thrown fore the beds in the bay have been free. Quite wholly out of employment. probably, were the remaining beds in Chesa To this statistical and historical account we peake Bay examined carefully, they would subjoin a description of the natural history of show indications of deterioration similar to the oyster, with special reference to the procthose discovered in the Tangier and Poco- ess of reproduction, and the conditions influmoke beds.

encing the rate of increase. For material emIt can hardly be doubted that this deteriora- ployed here we are indebted to articles contion is due to the severe fishing, and that in tributed by Lieutenant Francis Winslow. time, unless this is stopped, it will produce ut An oyster-bed, in its natural and undisturbed ter exhaustion. Foreign experience aptly illus- state, consists of a long, narrow ridge of shells trates this. The records of production of the and oysters, lying generally in brackish water, beds of Cancale Bay, on the north west coast on and surrounded by sticky bottoms, a mixtof France, extending over a period of about ure similar to clay and mud being the most seventy years(1800 to 1868), are very instructive. favorable. The form and area of the bed are The beds comprise an area of about 150 acres, variable, but naturally the length is greater and, from 1800 to 1816, produced annually than the breadth, and the greatest dimension from 400,000 to 2,000,000 oysters. During this is usually in the direction of the current. The period the beds became so thickly stocked that bed itself is inade up of masses of shells and the oysters were in some places a yard thick. oysters, covering areas of different sizes, and Subsequently the fishery was much increased, separated from each other by mud or sandand the oysters were removed in larger quan- sloughs, though frequently it is unbroken, and tities till 1813. From 1823 to 1818 it is sup- the animals spread evenly and continuously posed that the dredgers were living on the over the entire area. The oyster thrives best oysters accumulated between 1800 and 1816. in slightly brackish water, and the finest vaIn 1817 the number produced was 5,600,000, rieties are usually found in water of a lower and until 1843 there was a constant increase, specific gravity than that of the sea. The main the number taken in that year being 70,000,- necessity is that the water should contain a 000. In 1848 it was 60,000,000, and thence- sufficient amount of lime to furnish the animal forward there was a constant decrease. From with the principal constituent of its shell. 1850 to 1856 the decrease was from 50,000,000 That part of the oyster usually known as the to 18,000,000. From 1859 to 1868 the de- heart is a muscle, called the adductor muscle; crease was from 16,000,000 to 1,079,000, the its office is to keep the valves or shell closed, oysters having almost entirely disappeared, and prevent the ingress of hurtful matter. though the inhabitants, on account of their The two valves are hinged at the round, blunt suffering, dependent condition, were not hin- end of the shell, and between this hinge and dered from fishing. In 1870 there was a com- the adductor muscle lies the body of the oyster, plete wreck of the bottom, which could only or visceral mass, which is made up of the lightbe remedied by a total probibition of the fish- colored reproductive organs and the darkeries for several years. Similar results oc colored digestive ones, packed together in one curred in other places on the west coast of continuous mass. The mouth of the oyster is France, where, when in 185455, 15,000,000 that part nearest the hinge, and what is usuoysters were taken from the beds, only 400,- ally called its “beard " is known as the “gills." 000 could be obtained in 1863–64. The testi- The oyster lies on its side in the shell, and the mony of English experience also corresponds minute animal and vegetable matter contained with that just given, and is equally valuable in the water forming the food of the animal with reference to the course which must sooner is passed between the gills to the mouth, by the or later be taken in our country for the pres- action of myriads of small vibrating hairs, ervation of the oyster-beds from complete ruin. called cilia. These cover the surface of the

It is true that our beds are so extensive, and gills, and cause a strong current to set into the oysters are so widely distributed and so easily lips of the valves, thus bringing in not only transported and transplanted, that the total what is suitable for food, but other minute parfailure of the American beds must be post- ticles of matter. poned for some time. But the failure of beds The European oyster (Ostrea edulis) and the in different localities may occur at any time, American oyster (Ostrea Virginiana) are variand probably those of Chesapeake Bay will not eties of the same family, and, though differing last many years. The deterioration and exhaus- in several particulars, are not so dissimilar but tion of our beds would cause great distress and that the conditions favorable to the growth inconvenience in the United States, where the and life of one may be considered as equally oyster is no luxury simply, but a means of sup- so for the other. With each variety the formaport to large numbers. Not only are oysters tion of the generative matter is gradual, and consumed with us in every part of the Union, the spawning-season of both is during the early but immense numbers are also annually ex summer months, its advent depending probably

upon the temperature, the higher temperature growth, the animal having passed through its hastening and the lower retarding that event. embryonic life; its organs are formed and in Generally, both in Europe and America, the active operation; it is but immature. The spawning-season may be said to be from June American variety increases more rapidly than 1st until August 15th, though variations of the the European. Observations during the sumtemperature and density of the surrounding mer of 1879 in Chesapeake Bay show that, in waters may expand or contract that period the first three months of existence, the oyster considerably.

increases in size from a hardly visible speck to All authorities upon the early stages of the an average length of one and a quarter inch, and European variety concur in the statement that a few were over two inches long. After the first the young oyster, or “spat," is formed by the year the increase is not so rapid, and oysters fertilization of the eggs of the female while of two or three years of age are about two within the shell of that animal, and that the inches broad and three inches long. In three “spat” is held between the gills and thus pro- years, at the most, the American oyster is contected by the parent until the shell is formed. sidered mature. With the European variety Many authorities are also of the opinion that the growth is much slower, and at maturity the parents are hermaphrodites; but the accu- they are very much smaller than the American racy of this view is open to much doubt. The oyster. most material difference between the Euro With all animals Nature strives to provide pean and American varieties is in the manner against the destruction of the young after birth of impregnating the eggs of the female. Ac- by insuring a sufficient number to allow for all cording to the best authorities, the eggs of the ravages; and the greater the danger to the im. European variety are fertilized by the passage mature the larger will be the number provided of the male fluid into the water, and thence to meet those dangers. Hence, as the embryo between the valves and gills of the female. European oyster receives some protection and The young resulting from the union of the ova the American none, it is inferred that the and spermatozoa are held and protected within number of American embryos in any commuthe gills of the female until the shells are nity will be subjected to greater danger, and formed, and until they are quite well advanced consequently it is probable that a larger numin development, having at the time of their ber of eggs and spermatozoa are provided, that expulsion locomotive powers of their own, the production may not be less. Investigations which enable them to swim about and seek á seem to support this conclusion. Professor fit place for attachment.

Möbius, in his work on the oyster and oysterThe American variety differs in this, that culture, estimates the number of eggs spawned the young oyster is not found within the gills by the European variety as nearly 2,000,000, of either parent, nor does the fertilization take and his estimate is supported by Eyton, in his place within the shell, but the contents of the “ History of the Oyster and Oyster Fisheries." generative organs of both sexes are expelled Professor Brooks estimates the possible numinto the water, there to stand the chance of ber of eggs spawned by the American variety coming into contact. It is evident that a large to be as large as 60,000,000, and the average measure of protection is afforded the young of number to be over 9,000,000, or about nine the European variety by the inclosing shells of times as many as the European variety spawns. the parent, and that this protection is given The number of embryos surviving and maturduring the most precarious stages of their ex- ing can not be accurately stated for either vaistence, while the ova and spermatozoa of the riety, as we have not data sufficient to deterAmerican oyster are not only left to a happy mine the question. The results, however, of chance for their successful union, but the re- Professor Möbius's examinations of the Schlessulting young are exposed, unprotected, to all wig-Holstein beds are valuable and suggestive. the vicissitudes of climate, and to the ravages These were made by government officials from of all enemies.

1730 to 1852, in the following manner: Each After the formation of the shell and the de- bed was dredged over in three or six places, velopment of the locomotive powers, the young according to its size, and the oysters taken of both varieties begin their search for a per- were divided into three classes, and carefully manent resting-place or point of attachment. counted. The classes were styled marketable, Such points of attachment must soon be ob- medium, and young growth. The first were tained, or the young oyster perishes. Any the full growth and mature, from two and moderately rough, hard substance, provided three quarters to three and a half inches in the surface is clean, is suitable for the purpose, length and breadth, and about seven tenths and such objects, placed so as to attract thé of an inch thick. The medium oysters were young brood, are called "cultch.” Pieces of those half grown, from six to seven tenths of wood, planks, stones, old shells, tiles, etc., have an inch thick, and about three inches in been successfully used. Upon finding the breadth. The young growth were those of “cultch," the “spat" attaches itself firmly, one or two years old. and thenceforward, so far as its own power is From these observations, made annually, concerned, is located for ever.

Professor Möbius discovered that there were The development is now one of ordinary on an average 421 medium oysters to every

« SebelumnyaLanjutkan »