(...) In 1940, the ribbed mussels, Volsella demissus, of Tidewater Virginia were discovered by Du Pont chemists to be rich in this  provitamin D.  This discovery was followed immediately by the development of a mussel fishery on the  Seaside  of Virginia\u27s Eastern Shore peninsula, the activity centering on the large intertidal marshes where the mussels grow and in the shucking houses along the water fronts of shore towns where the mussels are steamed, shucked, and packed for shipment. This fishery has since constituted the country\u27s principal available  provitamin D  source, and large war demands for eggs and poultry meat have been met by the poultry industry with the help of the previously unexploited Virginia mussels.
Because of the prospective importance of the mussel, the Du Pont company acted through the-Virginia Fisheries Laboratory in 1940 to initiate a biological study of this as yet little-known bivalve

Mackin, J.G.

Menzel, R. Winston

English

College of William & Mary: W&M Publish

W&M ScholarWorks VIMS Articles Virginia Institute of Marine Science 1945 Research seeks to expand new fishery J.G. Mackin Virginia Fisheries Laboratory R. Winston Menzel Virginia Fisheries Laboratory Follow this and additional works at: https://scholarworks.wm.edu/vimsarticles  Part of the Aquaculture and Fisheries Commons Recommended Citation Mackin, J.G. and Menzel, R. Winston, Research seeks to expand new fishery (1945). The Commonwealth, 12(2), 3-10. https://scholarworks.wm.edu/vimsarticles/2099 This Article is brought to you for free and open access by the Virginia Institute of Marine Science at W&M ScholarWorks. It has been accepted for inclusion in VIMS Articles by an authorized administrator of W&M ScholarWorks. For more information, please contact scholarworks@wm.edu. VIRGINIA FISHERIES LABORATORY OF THE COLLEGE OF WILLIAM AND :MARY AND COMMISSION OF FISHERIES OF VIRGINIA CONTRIBUTION No. 18 Research Seeks to Expand New Fishery J. G. MACKIN and R. WINSTON MENZEL Reprinted from THE CoM.MONWEALTt{, t f/ '1--(0J/ Vol. XII, No. 2, February, 1945 .... Research Seeks to Expand New Fishery' By]. G. MACKIN and R. WINSTON MENZEL Virginia Fisheries Laboratory Yorktown TIME was _when poultry farmers gave no attentwn to the vitamin require-rnents of their poultry, for the reason that nothing was known of this important subj ect. As a resu lt, egg laying was sub-Ject to great season al variations and for this condition. Fish oils and fish liver oils were the first readily available means of meeting deficiencies of this constitu-ent, and in the period from 1922 to the outbreak of the European war in 1939, Canada, Iceland, England, Norway, and V. S. C: of C. A transplanted clump of rmmels cibottt three months after planting chicks did not grow with proper vigor. Then, in 1922, the discovery was made that . t· . 1 . k f . . D van a ions 1_n t 1_e mta e o v1tamm Were responsible 111 no small measure ---;:---thi VaI~able assistance in the preparation of N s article has been given by E. I. du Pont de ernours & Company. Japan furnished American poultry raisers with vitamin D from these so-called natu-ral sources. By June, 1940, however, practically all importation of vitamin D from across the Atlantic Ocean was shut off, and even before Pearl Harbor the Japanese sources were excluded. Only [ 3 J nominal amounts of vitamin D oils were produced in the United States. Years of investigation had disclosed by 1936 that the edible sea mussel of Hol-land provided a suitable source of the raw material necessary for the production of a man-made vitamin D . Mussels from the tidewater marshes of Holland had been used commercially as human food for years, so an established Dutch indus-try was in a position to respond to this new discovery. The part of the mussel that supplied the vitamin D was a sterol. Sterols are fat-soluble, wax-like materials found in variable quantities in practically all forms of animal life. The particular sterol which can be converted into vita-min D by irradiation with ultraviolet light is known as "provitamin D." During the three years following 1936, the supply of American man-made vita-min D was dependent upon Holland and its established mussel industry for this "provitamin D." In 1940, the ribbed mussels, Volsella demiss11s, of Tidewater Virginia w.ere dis-covered by Du Pont chemists to be rich in this "provitamin D." This discovery was followed immediately by the development of a mussel fishery on the "Seaside" of Virginia's Eastern Shore peninsula, the activity centering on the large intertidal marshes where the mussels grow and in the shucking houses along the water fronts of shore towns where the mussels are steamed, shucked, and packed for shipment. · This fishery has since constituted the country's principal available "provitamin D" source, and large war demands for eggs and poul-try meat have been met by the poultry industry with the help of the previously unexploited Virginia mussels. Because of the prospective importance of the mussel, the Du Pont company acted through the-Virginia Fisheries Lab-oratory in 1940 to initiate a biological study of this as yet little-known bivalve. To produce the "provitamin D" efficiently and economically, information was needed on the distribution and abundance of mus-sel beds, the productive capacity of an area of marsh, the effect of digging operations on the growth of mussels, and the time required to grow commercial-size mus-sels. Considerable progress has since been made on this investigation. The mussel lives all-but-buried in the soft mud and is dug with a clam pick or similar implement. As in the oyster in-dustry, the bushel is the usual commercial unit. It holds about 600 mussels and is sold by the digger for from 40 cents to $1, depending on the labor situation. The av-erage number of bushels dug per day per man is between nine and ten. The best workers dig as many as sixteen bushels during a single low tide. Mussels are dug in the marshes and transported on scows to the shucking houses. There, after the mussels are steamed the meats are removed from the shells, washed, packed, and frozen for shipment. Life Cycle and Habitat of the Mussel In general, ribbed mussels are found wherever the reeded salt marshes occur. This takes in all the shores of Chesapeake Bay and its tidal tributaries as far up as the salinity is suitable. The most valuable commercial beds, however, are on the Sea Side of the Eastern Shore, in the extensive marshes situated between the m~inland and the outer-shore islands. Mussels range northward to Nova Scotia and southward to Georgia, beds of con-siderable size occurring in the Carolinas, but the center of the commercial supply is in Virginia. Three principal conditions are neces-sary for the mussel habitat. First, reeds must be present, to the roots of which mussels attach themselves by secreting a [ 4 J ~- ;;~...,, --... ":--~I,..),; ,.,,,. -'.. J .. · \· . S . l'. of C. A muJsel marsh at high tide. The tumps are recognizable by the taller and denser growth of reeds mass of threads. Immature mussels may also be found attached to oysters or other sheJls, to pilings, and to driftwood. The second important condition is that the bottom in which the mussels are em-bedded be composed of mud or a mix-ture of mud and some. sand. The third condition pertains to the position or level within the tidal zone. In Virg inia mussels are not ordinarily found higher than the upper limit of neap tides or lower than the middle of the entire tidal zone, a vertical range of about two feet. The mussel population may grow into one of three rather distinct kinds of formations, namely: tump, strip, and mat. Tmnp formation. Scattered throughout the soft mud marshes are clumps of mus-sels which are designated as tumps. They vary in size from a few inches to several yards in diameter, and a single tump may contain several hundred mussels of com-mercial size. Most of them occur toward the sources of small guts or drains through which tidal waters enter and leave the marshes. Tumps are the result of vital activities of the mussels themselves. A tentative reconstruction of the development of a tump is as follows: Larval mussels attach themselves to suitable objects in the marsh- ordinarily to reed roots or partly embedded coon oysters. They become cov-ered with the marsh mud until only the posterior or open end of the shell is visible above the mud line. By means of a special ciliary mechanism the mussel draws a cur-rent of water into its mouth and extracts microscopic living forms which it uses for food . The feeding process is funda-mentally the same as for oysters, although the actual elements of food required may be different. Mud is added to the tump as a result of metabolic activities of the mussels. It is composed of wastes and of debris from the decomposition of the reeds. These materials look like the black mud of the marsh substrate. N ew strike or attachment of mussels from year to year adds to the number of mussels in the tump and these in turn add to the pile of mud around the g roup. In the relatively quiet waters of the Sea Side of the Eastern Shore, tidal cur-rents and waves seem to be insufficient to remove the accumulation of silt in and around the tumps so that they gradually build up. Fertilized by the mussels, they are rich in elements needed for the growth of the reeds. Hence, reed growth on the tumps is constantly richer than that of the surrounding marsh. Tumps may be readily recognized at a distance because of the taller and thicker masses of reeds. Sides of the sheJls of the original mussels of a developing tump provide surface for attachment of larvae. These are partially protected by the shells of the larger mussels and by dense reed growth. However, increase in numbers of mussels in a tump is a slow process. The soft mud and waste products of the larger mussels seem to have a smothering effect on the minute mussels. Only a few man-age to survive and attain a size sufficient to afford self-protection. Although studies have not progressed far enough to deter-mine definitely the ages of different sized tumps, they are probably measured in terms of many years or even in decades. Individual mussels in a mature tump probably average between five and nine years of age. ' Until now, the tumps of the marshes have produced most of the commercially valuable mussels. Relatively few tump formations exist in Virg inia outside of the Sea Side of the Eastern Shore, where the industry has been centered. Strip formation occurs as narrow bands around the margins of shores, where the steeper slope of the intertidal zone causes the mussel zone to be narrow. These zones are subject to swift tidal currents or ( 6] wave and breaker action which prevents silt from accumulating. Thus, the mus-sels occur in small, compact groups or clusters, each group containing up to several hundred small mussels, firmly embedded in hard-packed mud, held together by roots of the reeds. Several clusters may grow together to form more extensive areas of tightly packed small mussels. In general, strip formation is favorable for the preservation of young mussels, with plentiful opportunity for attachment in the existing groups and freedom from the smothering silt of quiet, soft marshes. Strip formation is found discontinuously around the entire Chesapeake Bay shore as well as on the Sea Side. Crowding rarely allows many mussels to reach a mature size and enforces a comparatively slow growth. Mussels nec-essarily project above the substrate, and the larger ones, projecting farther, are more subject to attack by various natural enemies such as shore birds and crabs. Many mussels are literally squeezed out of the clumps by growth pressure and are thus left without protection. There are conspicuous differences in the averag<:; sizes attained by tump and strip mussels. In tump formation, the size class that has the most numerous mussels is that ranging in length from 9 to 10 cm. (roughly 3.5 to 4 inches) and estimated to be from five and one-half to eight years of age. The corre-sponding size g roup of strip mussels is the 3 to 4 cm. class (about 1.2 to 1.7 inches) in their second or third year of g rowth. The length range of mussels used for commercial purposes is from about 3.5 to 4 inches. With the present meth-ods of processing, mussels below two inches are too small to be used profitably. Mat formation does not differ materi-ally from strip formation except that it is composed of continuous and extensive ( 7 ) l)mwn hy ,l. G. lf1H.:ldn Cross section of a tmnp. The mus-sels live almost huried, with only the open end of the shell visible ctbove the mudline. To the left , above the tump, is an oyster. Snails cling to the 1·eeds Coker A scowload of mussels, taken in a Sect Side marsh, being pushed toward an open-water channel. In two days t,hese men gathered more than fifty bushels of mussels carpets of tightly packed small mussels. This growth form occurs to a limited ex-tent at va rious scattered localities, but extensively on ly near Chincoteague on the Sea Side. A square yard of mat' formation may contain more than 5,000 small mus-sels, none. of them large enough to be used commercially . Problems of the Industry As in all fi sheries the basic problem to be considered is that of the extent of natural production in relat ion to the de-mands of the industry. It was ea rly rec-ognized by the Du Pont company that the existing supply of mussels migh t soon be exhausted . As a result, the company as-sisted largely in ini tiat ing and carrying out bio logical studies on mussel culture. It seemed desirable to make an estimate of the probable time lapse before restric-tions or regulations would be requi red to prevent complete exhaustion of the commercial beds. It was .necessary to know whether natural production could keep pace with commercial utilization. If not, methods of mussel culture compara-ble to those used successfully by the oyster industry would need to be discovered and practiced. The problem of discovering a practical method of culture necessitated a careful study of the reproductive processes , growth, and li fe habits of the mussel. This study is still in progress but is far enough advanced to warrant a discussion of the results obtained up to this time. Ea rly in the invest igation it became clear that natural reproduction and g rowth of musse l tumps was d isappointingly slow, and that if the industry were geared [ 8 J down to the level of the natu ra l supply and hence to the level of natural replen-ishment it wou ld always remain a minor affair. The first two years of the industry witnessed the digging of upward of 80 percent of the choice marshes of the Sea Side and it became increasingly difficult for diggers to find "easy" tumps with large numbers of commercial-size mussels. Furthermore, it was soon discovered that dug-over tumps would recover only slowly, if at all. There remained two possibilit ies : that of working out methods of mussel cul ture which would step up production to a level approximating commercial needs, and that of increasing the production of provita-min D by synthetic means. With respect to the first prospect, two important condi-tions are favorable. First, there is no lack of space in the marshes, since the natural tumps, although numerous, are estimated to occupy less than l percent of the soft marsh favorable to tump growth. If meth-ods could be evolved to utilize the 99 per-cent of unused area, or even any significant part of it, the problem would be so lved . Second, certa in more or less closely re-lated bivalves, includ ing oysters and clams, have been cu ltured for many years. From this experience suggestions could be drawn that might be of value in deal-ing with the ribbed mussel. In addition to extensive surveys, mor-phological stud ies and growth experi-ments, two principal approaches to the problem of increased production, have been followed. The first has been an effort to produce conditions in the soft marshes favorable for an increase in the amoun t of "strike," that is, the numbers of microscopic, free-swimming larvae that have settled down or struck on the bottom where there is a suitable surface for at-tachment. Different surfaces for attach-ment have been tried with varying de-g rees of success. In nature, "strike" is heaviest in crevices and narrow angles of shells that are protected from enemies, silting, and other adverse cond itions. Types of culch that have shown promise are co rn cobs wired to stakes, coon oyster clumps, brooms made of pine needles, and pine cones. However, the securing of "strike" has so far failed to lead to the successful ~foore Cemented pine cone used c1s wlch, to which mussels have attached [ 9} outcome desired. Two factors have con-tributed to the failure, one being the fact that ribbed mussel larvae, after attaching, apparently either fail to survive or move off the culch. The second factor is failure of culch to accumulate larvae during suc-ceeding years. It was expected that culch would form the nucleus of new tumps, and, from the evidence, it is quite probable that coon oysters may be used to accomplish this purpose. However, the development may prove to be too slow to be commercially practical. A second approach to mussel culture has possibilities. It will be recalled that the strip formation mussels are too small to be used commercially and are widely distributed over large portions of the shores of Tidewater. It was conceivable that these mussels, if transplanted from their hard substrate to the soft marshes, might grow well in the new environment. Various experiments with such trans-plants have been carried out during the past two years. Questions bearing on mortality of transplanted mussels, rate of g rowth of transplants, and best methods of transportation are being investigated. In general, the clumps of mussels are dug out of the hard strips with long-handled shovels, care being taken to re-tain reeds and hard mud around the clumps. These clumps are transported by scows to the marshes, floated onto the transplant area at high tide, and dumped overboard in rows marked out by stakes. After the tide recedes, workmen go into the marsh and set the clumps into orderly rows with the mussels correctly oriented and set part way into the soft mud. A certain percentage of the transplant mussels die for various reasons, chief among them being crab predation, sil ting, and rough handling during transplanta-tion. Silting, as previously observed, is dead ly to very small mussels in the tump-bearing marshes. Blue crabs, possessing a voracious appetite and powerful crush-ing claws, can wipe out whole areas of transplants in a few days time. Ultimate success or failure of the culture experi-ments depends on control of losses oc-casioned by these two mortality factors. With respect to the possibility of syn-thetic production or production from other sources, scientific investigations by the chemists have disclosed that a "pro-vitamin D" similar to that in mussels can be produced from a packing-house prod-uct, cholesterol, and, as a consequence, the " provitamin D"' from Virginia mus-sels may not turn out to be the first choice. Furthermore, the biological chemist and the animal nutritionist continue to explore the field of sterol chemistry for ingredi-ents that were unknown yesterday but can be vital necessities tomorrow. Looking to the future, the possibilities are that the poultry industry will con-tinue to depend on production both from natural sources and from synthetic proc-esses. The relative extent of the use of these sources will probably depend upon comparative costs. During 1940-43, approximately 400,· 000 bushels of mussels were taken in Vir-ginia. Relat ively few have been obtain-able during the past year because of the shortage of labor. Digging mussels is not an attractive, easy job. However, the industry has proved to be helpful to watermen during slack periods when oystering and other long-established fishery industries are sea-sonally closed. Such a supplementary fishery will again be needed with the re-turn of peace. It is to be hoped that the problems of the ribbed mussel industry may prove amenable to solution, and that the com-monwealth's newest fishing industry will mature into a soundly based and depend-able source of revenue for all concerned. [ 10] 

Research seeks to expand new fishery

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Research seeks to expand new fishery

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