PROCEEDINGS OF THE N

ASSOCIATION

1947-48

E
Ee

ADDRESSES DELIVERED
AT THE CONVENTICN OF

NATIONAL SHELLFISHERIES ASSOCIATION

Asbury Park, New Jersey

June 3-l-5, 1917.

Edwin Warfield, Jr., F Dr. Victor L. Loosanoff,
President. Vice-Fresident.

Dr. J. Nelson Gowanloch, J. Richards Nelson,
Secretary. Treasurer.

ibs.

TABLE OF CONTENTS

197 Addresses
Title

Formation of the Gulf States Marine Fisheries Commission,
Jamcs N, McConnell.

Texas Rehabilitating Oyster Grounds,
J. L. Baughman.

Present Status cf the Chesapeake Bay Oyster Bars in Maryland,
Ralph C. Hammer.

Observaticns cn Fouling cf Shells in the Chesapeaxe Area,
G. Francis Beaven.

Distribution of Setting Guides the Maryland Oyster Progran,
James B. Engle.

Observaticns cn Oyster Drills: Chromesones of Urosalpinx
cinereus, Say (An Abstract), Dr. H. Malcolm Owen.

The Pros and Cens of Intrcducing Foreign Shellfish,
Dr. Thurlow C. Nelson.

Seasonal Chanzes in the Fattening of Oysters,
Dr. Walter A. Chipman, Jr.

Respiration in Oysters,
Dr. Paul S. Galtsoff.

Effects of Turbidity cn Feeding cf Oysters,
Dr. Victcr L. Loosanoff.

On Possible Physiological Species in the Oyster, Ostrcea
virginica, Dr. Leslie A. Stauber.

Effects ef Polluticn at Baltimore on pH and Oxygen Content
of “later, Fred YT. Sieling.

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FORMATION OF THE GULF STATES VARINE FISHERIES COMMISSION
James Ne. McConnell,

Director of the Louisiana Division of Oyster Bottoms

1-

Mr. Chairman, honored guests, and fellow members of the National
Shellfisheries Association, it is with a deep sense of appreciation of
the opportunity afforded me at this time to give you a little of the
bactground: ‘leading to the formation amd present status of the Gulf States
Marine Fisheries nee’ and also, the purpose for which this compact was
formed. ;

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-At the exploratory Intercoastal Fisheries conference, sponsored by
the Council of State. Governments and the Committees on Interstate Cooper-
ation, held in Washington, May 16 and 17; 196,:-and attended by a group
of men from the GulfiCoast, the “est Coast and ‘also -from the East where
the Atlantic States; Marine: Fisheries’ Commission has been. energetically
functioning under: its Compact for the past five years, Mrs Hugh Gallagher,
Associate Director of the Council of State: Governments:,, lr. Wayne Heydecker,
Secretary and Treasurer of the Atlantic States Marine Fisheries Commission,
and Mr. Frederick Zimmerman, Svecial Advisor to the Nev York Legislative
Committee on Interstate Cooperation explained to us numerous problems of
jurisdiction of¢the marine fisheries and improvement of interstate and
Federai-State cooperation with ré espect thereto.

At this time also at-a meeting held ae ie State Department offices,
it was implied to us that very shortly development might occur whereby the
State Department would vrish to.confer with authorized representatives of
the fisheries interests ,of both the Gulf and “lest Coasts relative to
possible international treaties. Seed She

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Upon return to our homes we ‘of: the ‘Gui area, after conference with
others, felt it’ essential to. our fi Sheri¢s interests, that a Gulf States
Marine Fisheries compact be formed, ~~ * *> * Fier

Accordingly, a preliminary conference was held on ‘October 10, 196,
again under the sponsorship of tHe ‘Council cf State Governments, ne re
representatives of the States of Alabama, Mississinni, Lovisiana and Texas
met to explore the desirability of such a compact and the procedure for the
organization of an interstate fisheries compact and commission comparable
with the Atlantic States Marine Fisheries Cormission which has been operat-
ing with such conspicuous success for the past five ycars.

’

These deliberations resulted in the earths Dokenieee te and 7,
another conference with the purpose of enunciating in precise terms the
nature, extent and tenets of such a compact and of initiating the necessary

actions that would bring into existence a Gulf States Marine Fisheries
Commission. :

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From these deliberations a basic fiftcen article tentative
compact was formed together with the discussion and further formu-
lation of procedures whereby individtal States could extend and
adjust the supplementary articles for each of the States.

At this mecting, we were fortunate to have with us, Gcorge K.
Aiken, Secretary to the Governor of the State of Oregon, and also
an official of the then tentative Pacific States organization, who
gave us a brief summary of the West Coast Compact, which, at that
time, was awaiting ratification, and which has now been ratified and
is in operation.

Copies of the compact as formulated at the meeting of December
5 and 6 were sent to the State Department in Washington for their
comments and tentative approval. Copies were also sent to the
Attorneys General of the five compacting Gulf States of Florida,
Alabama, Mississipni, Louisiana and Texas for their recommendations
and approval. .

A meeting was then called in New Orleans on April 10 and aia
1947 to complete the compact so that same could be presented to the
legislature of the States of Texas, Alabama and Florida, which were
either currently in session or about to be called into session.

At this meeting’ the Attorneys General or their representatives,
together with the state officials in charge of Conservation or
Marine Fisheries of the compacting States were present as well as
members of the United States Fish and Wildlife Service. In addition
to this and of most importance was the attendance of representatives
of both the House and Senate of the various legislatures of the
compacting States. From the State of Texas alone, one member of the
Senate and four members cf the House of LEG EIS oes SELES were very.
actively present.

The compact in its final form was adopted’ at this gathering and
has been presented to the legislature of the States of Texas, Alabama
and Florida, where it has passed the ‘House in all three States and
we confidently expect final passage of the Spares act from the
Hops s12baes of Texas, Alabama and Florida

The legislatures of Louisiana and Mississippi do not meet again
until 1948 at which time we fully ESBSe's these two States to approve
the compact.

ft this point I wish to sketch to you bricfly the aims and pur-
poses of this commact. The compact will promote, develop and conserve
the Gulf Coast Fisheries and for this purpose will establish a con=
tinuing Interstate Fisheries Commission whose duty it will be to
inquire into and report on methods, practices, circumstan 1ces, and
conditions relative to the prevention of depletion and physical waste
of the Gulf Fisheries. It is empowered also to recommend the’ co-
ordination of State police power and to draft and recommend legis-
lation to further the basic principles of the compact.

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By the compact the United States Fish and Wildlife Service is
designated the primary research agency of the Commission and will
cooperate with comparable agencies of each of the compacting States.

The compact will further the conservation and development of the
fisheries of the Gulf Coast Salt Water Fisheries and should assist
materially in bringing to an end numerous interstate controversies.

Another and very important aim of the Commission will be to present
in Washington a united front on fishery problems of the Gulf area.

“Ye believe that in unity there is strength and together with the
Commissions from the Atlantic States and the West Coast States we can
present a solid front in Washington that will be of inestimable value to
the entire marine fisheries of these United States,

To give you a concrete example of how the Gulf States Marine
Fisheries will work when occasion demands I will read to you a letter
sent by meas interim-Chairman of the Gulf States Marine Fisheries
Commission to interested partics of the five Gulf States pertaining toa
matter of the utmost importance to these States.

JOSH EESS ESCH CE ES UE BOER ey et ae ee se ne gee ae
The eaeSteoe response received and the quick action taken by
recipients of this letter in contacting their Senators and Congressmen
in Washington acquainting them with what was happening in our section
and what it meant to us was indeed gratifying and to me points plainly
to great benefits that will accrue to the marine fisheries of the Gulf
States when the compact and Commission is legally functioning,

In my humble opinion when all of the Coastal States are so
organized to promote, develop and conserve their marine fisheries it
will be of the utmost importance to all the fishing interests of the
entire natione

In closing let me thank you for this opportunity of presenting to
you some of the background leading up to the formation of, and what may
be expected from, the Gulf States Marine Esheries compact and resultant
Commission. .

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TEXAS REHABILITATING OYSTER GROUNDS
. Je Le Baughman

Chief Marine Biologist, Texas Department of Conservation

. . Oystering in Texas has been carriecd.on since before the white
man first discovered the American continent. Four hundred and
twenty-eight years ago Cabeza de Vaca, Texas' first white man,
found. .the Indians of the Texas coast subsisting partially on
oysters,:and the abundant.shell middens frem Galveston to Corpus
Christi attcst the fact that this was a common, practice. However,
it was net until the latter part of the 19th century that oysters
in Texas really came into their own.

To give some ideas of their former abundance I can do no
better than to quote from the letter of an old-time oysterman,
Louis Peden, of Galveston, who saw the industry at its height.
"In 1890 or '92," ho says, "the Givens Oyster Company operated an
oyster cannory at Corpus Christi, and yms a dominant factor in the
area, both in the canning and shucking of oysters, which they sold
by the thousands of gallicns. . The fleet of boats working for this
Company hauled from Galvesten, Matagorda, Port Lavaca, Rockport,
Fulton and Cerpus Christi, some of them carrying as much as 500
barrels and I recall that at one time the Givens Company imported
sever] hundred shuckers from. Baltimore,

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"Most of the oysters cane from 'O0ld Reef' just across the bay.
This reef was.a wonderful producer, both in.quantity and quality.

Mechanical Exploitation

"It was here I saw my first oyster dredge in operation. In
those days it was difficult to 9perate an oyster dredge from a
. Sail boat and gas engines were unlmovm. However, someone. brought
a steam.tug into the picture. This tug towed a big barge from which
two dredges, each having a capacity of five barrels, were opcrated,
one working while the other was dumped. <Abcut 30 Mexicans were
employed on the barge, sorting the oysters, and they were kept busy
as it only required about 5 minutes to fill one of the dredges. In
only a little over a year 'Old Resf' was gone.

"In the Port Lavaca arca a man could easily tong from 7 to 30
barrels a day, and, in one day, a crew of 3 men on the schooner
LEONORA, tonged 135 barrels. Oysters were so plentiful that dealers
placed a limit on the barrels a boat could bring in for supply far
outran the demand, and the difficulty was not to get the oysters,
but to find some place where you could sell them. I have seen
oysters sold for 15 cents a hundred, shucked.

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"Oystermen were everywhere, and one day, on ‘Half Moon Reef!
(off Port Lavaca) I counted 287 boats fishing that reef."

This was the heyday of Texas oystering, but even before that time
some of the more foresighted oystermen had felt that this was the
beginning of the end. The advent of power boats and dredges, the ruth-
less and uncontrolled stripping of the reefs, all combined, were too
much for the oysters and, although production in 190) reached a peak of
199,000 barrels, by 1908 the production had dropped to 102,000 barrels,
and from that time on the production and quality of Texas oysters began
a steady decline, reaching an all time low in 1943-hh of 36,981 barrels.

Other factors contributed to this also. In 1913 and 191 much of
the Texas coast was swept by freshets'from both the Colorado: and Brazos,
killing off the oysters in Matagorda Baye

A third cause for the decline, particularly in Galveston Bay, was
the use of oyster shell to produce lime, cement, chicken feed, and
magnesium. The result has been that, between the shell dredges and in-
creasing industrial pollution, there is hardly a producing bed in what
was once one of the most fecund producing grounds in the State.

Here then are the causes of our decline, in the order of their
importance: (1) Destruction of grounds by sedimentation and floods,
affecting the Matagorda area, (2) Lack of mamagement and uncontrolled
exploitation, affecting the entire coast. (3) Destruction of live reefs
by shell dredges, affecting Galveston, Corpus Christi, Aransas, Lavaca
and Carancahua Bays. (l) Industrial pollution, ee Galveston,
Nueces and Corpus Christi Bays.

A fifth cause, mortality from oyster pests, is negligible, as they
are few on the Texas coast, with the exception of Nematopsis. Very
heavy infestations of this parasite of the crab and the oyster are
present on portions of our coast, particularly Copano Bay. |

Our main problems, then, are rehabilitation of our reefs, and
perpetuation of our oyster crop by wise regulation and management. -

Present Program

It has not seemed desirable to attempt any extensive planting for
several reasons. In the first place it is expensive, costing, if we
plant seed oysters, at least $150 per acre, and with huge areas of
denuded reef and bottom needing reseeding this would run into many
millions of dollars. Moreover, this would amount to an outright sub-
Sidy of the oystermen, who can take oysters from these grounds just
as they can from natural reefs, without making any return to the State.

A second reason was the impossibility of patrolling such planting

thoroughly, except in limited areas, and the consequent lack of assur-
ance that the seed would be allowed to attain maturity.

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an

Consequently it was thought best to undertake: the study of
this problem by making a number of experimental plantings with
a view to discovering the best type of bottom in:the areca for
such replanting, always bearing in mind that because of our Texas
law it was not possible for the oyster farmer to lease the most
suitable area, ie Ce, a natural reef, even though denuded.

Secondly we wished to discover the most ‘desirable density
of planting for the area and, thirdly, what type of seed can be
used most advantageously.

This work at present is boing carried on in two areas,
Aransas Bay at Rockport, and South Bay at Port Isabel, but the
Fort Isabel work is of little interest except to determine the
rate of growth of oysters in the very high salinity of that por-
tion of our coast. The use of Aransas Bay close to Rockport was
the result of tvio very practical considerations. The first was
that we can see all our experimental plantings from the laboratory
windows, thus reducing the danger of unauthorized oystering. The
second was the closeness of the sced beds in Copano Bay. These
Copano oysters are of poor quality, thin, dwarfed, and the meats
are frequently discolored and almost always heavily-infested with
Nematopsis, the mantles, gills, blood vessels and even.the water
tubes of the gills being full of cysts and single spores.

‘ In. spite ‘of such infestation oysters transplanted from
Copano to Aransas Bay showed a remarkable recovery. Several weeks
after planting the mcoats were firmer, whiter ‘and contained more
glycogen, while there was a noticeable increase in the size of the
shells. So far (five months after planting) they are doing well,
and barring storms or other acts of God, there seems little reason
to apprehend any more than normal loss.

Cooperative Reseeding eon es

One thing that we are trying, however, is a considerable
departure from accepted methods of rchabilitation. This is the
salvaging of seed oysters from the shucking houses.

In Texas it is the custom for oystermen delivering oysters to
the shucking houses to be paid by the number of gallons shucked
from the load, rather than by the number of bushels entering the
plant, The resvlt is that the shell piles around the shucking plants
present a shocking and depressing sight, for nearly every one of
the shells opened by the shuckers has from 2 to 10 seed oysters
about one ‘inch long attached to it. At a conservative estimate,
the houses destroy, at this rate, five yourig oysters for every one
of marketable size that they open, for the custom has been for
years to allow the coastal countries to utilize this shell for road
building, and at times’ the stench of rotting oysters along a new
road was almost insupportable.

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At the beginning of this year, in the Rockport area, the State
laboratory instituted a new method of handling this shell. Almost
every barrel of it was returned to the water within 8 hours and
planted on suitable ground, with the result that most of this seed
was saved, and at the present writing is growing and doing well,
although there was some mortality in sizes less than 1 inch. Eleven
thousand barrels of 6100 cubic inches capacity of this seed were
planted at a cost of 15¢ per barrel.

It is’ our hope that by experimental plantings such as these
we can work out the problems that are too expensive for the ordinary
oystermen, and induce them to begin sowing in order that they may
reap, for if they do not the Texas oyster industry is doomed.

At the same time we arc not neglecting other thingse An effort
is being made to revise our leasing laws so that we can lease de-
nuded reefs for planting, and in the Galveston Bay area, much work
is being done on pollution control. Moreover, we now have under *
construction ‘a modern marine laboratory at Rockport.

To quote from Dr. Galtsoff, who was a recent visitor, "The
construction of a new State fisheries laboratory at Rockport will
give the State biologists an opportunity for a more critical study
of various fishery probloms of the State. Undoubtedly, the new
center of research will have great educational:-influcnce on -fisher-
men. Conservation of natural fishery resources is impossible without
_ the understanding of its aim by the fishermen and without-their
‘active ‘cooperation. APS oe a

"Tt is hoped that a good plan started by the State in showing
‘the oystermen how to grovy more and better oysters will bring results
and that local oyster dealers will gradually come-to-realize that
_ their business is doomed unless effective steps are made»to stop
wasteful practices. By lcasing from the State oyster bottoms suit-
able for cultivation and by returning to them the seed which is at
present destroyed, substantial oyster resources can be built and
. the oyster industry of the State may be placed on a sound basis.

"The State Game, Fish and Oyster CommiSsion can be of great
help in the rehabilitation of oyster resources: by providing, through
its technical staff and its laboratory, information and advice, and
by establishing demonstration oyster farms, This type of activity
seems to be very promising. It is believed that it may substantially
contribute to the rehabilitation and conservation of oyster resources
of the State",

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Page Corr iF 36 P3846

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Fe als STATUS. OF . THE, CHESS NS Bee Sao BARS . IN MARYLAND
. Ralph C. emer

Shellfish Culturist, feadenaene par anene of Tidewater Fisheries

This report will endeavor to briefly summarize the history, the
present condition, and. the need for restoration of ‘the Chesapeake.
Bay Oyster Bars... At this time,-however, it is with considerable
pleasure we acknowledge the very valuable and essential .technieal .
assistance supplied by the Maryland Department of Research and
Education and the U. S. Fish and Wildlife Service. These cooperating
agencies have been most helpful through their coordinated studies in
supplying the information necessary for the managenent of the oyster
resources of Maryland. Representatives of these agencies, Mr. G.
Francis Beaven and Mr. James R. Engle, will report on a portion of
their scientific studies following this presentation.

Maryland formerly enjoyed what seemed to be an unlimited supply
of eysters from her comparatively vast acreage of oyster bars. Like
many of our natural resources; the 272,15 acres of charted natural
oyster bars in Maryland have declined in production from an average
annual yield of 12,250,000 bushels, during the pemeds from 1870 to
1890, to the present annual production. of less than 23 million
bushels, or approximately one fifth of. the former high level of pro-
duction. There is little necessity to point out to this group that
the decline in Maryland's oyster resources is almost entirely a
result. of the same factor which has made us all conservation con- ©
scious; that is, man's rate of harvest has been in excess of natural
reproduction. Natural oyster enemies are virtually nonexistent in
Maryland, with the exception of occasional screw borer depredations
in limited areas of higher salinities and occasional mortalities as
a result of infrequent periods of low salinities in the upper Bay
areas. The destructiveness of the lowered salinities was.discussed
in detail at the 1946 Shellfisheries! meeting (Engle).- In’ the
absence of major natural catastrophies, the continued downward trend
in oyster production must be attributed to overfishing without regard
for rehabilitation. As a result, many bars are today completely
devoid of oysters and cultch, and it is these bars in the Chesapeake
Bay proper, that now need a well planned program of restoration.

The oyster bars of Maryland can be roughly classified into two
major groups, tributary and Bay bars. Production today is .derived
almost entirely from the tributary waters as a result of the more
consistent spat sets on these shallow water bars and to the relatively
inefficient use of tongs in harvesting. The tributary bars have
continued to be largely self-sustaining and will continue to yield
at a moderate rate, and following years of exceptionally favorable
Spat sets, may produce large quantities of oysters. State shell
planting has been largely successful on most of these tributary bars
and under existing conditions are to be continued. :

area

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eniined wit 4 a> Layiden told Yo oowendace ~ ©

The major problem of State Management lies in the wise utilization
of the dredging bars in the Chesapeake Bay. It is these bars or some
78,342 acres that are virtually barren. The Bay bars were originally
most productive and gave rise to the famous Chesapeake Bay oyster.
During the aforementioned peak years, 1870 to 1890, the yield of oysters
from the Bay bars averaged 50 bushels per acre annually. Upward of 1000
dredge boats were engaged in this free fishery but as one bar after another
became depleted, the number of dredgers decreased until last season,
1946-7, there remained but 8 licensed Bay dredgers. The catch in turn
dropped from the cited 50 bushels per acre to approximately one bushel per
acre last season or a total yield of less than 100,000 bushels.

Of the total charted bars in the Bay, 6,714 acres are in that area
commonly referred to as the Head of the Bay. This Upper Bay area is sub=
jected to periodic freshets, as evidenced by the vast accumulation of
shells and as revealed in recent scientific studies. -In view of this
hazard of freshets and the very infrequent spat sets, no consistent manage-
ment program has been undertaken. In recent years, the policy has been to
utilize this area as a source of seed and at times for the harvesting of
market oysters. Although this area is commonly called a seed area, present
studies indicate that the production of seed is infrequent; therefore, it
appears to be wise.to utilize promptly such seed or market oysters as may
develop. Of the remaining oyster bars in the Bay, it is estimated that a
minimum of 60,000 acres are ideally suited for.oyster growth and are capable
of producing quality oysters ‘in quantities comparable to the best leased
bars in other States. Due to the depth of water and exposure, these bars
are dredged by boats under sail. Dredging by power is prohibited by law.
In spite of the inefficiency of sail boats, the use of the dredge in remov-
ing both oysters and cultch, coupled with infrequent sets, is responsible
for the present condition of the bars. State Management although effective
in most tonging areas has not brought about a recovery of these dredging
areas. This failure cannot be attributed to the fault of the program,
since the practice has been to follow the best methods employed by the
private planter on personally controlled leased bottoms. In brief, State
Management has been to select favorable growing bars, plant seed oysters,
close the bars to public fishing until a majority of the oysters have
reached a’marketable size, and then open the bars to public dredging. A
tax of 20¢ per bushel, harvested, was collected in an effort to recover
the cost of planting. Although this tax of 20¢ has only in a few cases
been sufficient to cover costs, this large scale experimental planting
program has been successful and has produced oysters at a nominal cost.
During the past seven years, 865 acres or approximately 1% of the Bay bars
were planted with seed or shells, at an expenditure of $96,366. These
plantings produced over 210,712 bushels of oysters or an average expendi-
ture of l6¢ per bushel harvested. Although l6¢ may be considered a fair
price to produce a bushel of oysters, experience reveals that a consider-
able reduction in costs may be possible. For example, Poplar Island Bar
was planted in 194 and 1945 with seed costing $4,797. Last winter,
19L6-h7, 35,000 bushels of quality oysters were harvested at a production
cost of ll¢ per bushel. For those interested in oyster planting, 22,560
bushels of seed were planted to produce the 35,000 bushels of oysters.

-9-

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to yi othe = Litau yolict? aifeug of amd 2
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he ax ot toteetlon pee todew vat ,Lortord ty O00 SR le
WBE QO bec 95% Ye ner ohiP Wquetlé wae tnaky Woden. off <
pees siéad Gptcl Af) .220<9 10700 oF Ae ‘
Graken © fe restore Wetet ey aot bes Evlaeepa: ovyf 9° ~

| at aes = 7% term 2 ome cod atid
"at, *_cmrhéeme wm te clits bee we q Siw :
+ eres 1 3s otal te sdegtee” LIT 085 temo beeiegg irivne lq
7 ‘ py at aw Aurel t2 nye hg F fateat aay owe
(os a * caer) tsgie .ftS rw
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Seas bows 416 el bee.

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O82, SF .poliaety trees a) Seewial sect? 208
euerege to efetant TORZE Mi? ecutond of bedesit oad

- &-

The State's efforts to grow oysters at a nominal cost, upon

analysis, appear to be successful and indicate the need for an ex-
,pansion of the present methods. However, there are several serious
difficulties which have become apparent if the State is to embark

on a full scale program to bring all of the Bay bars back into
“maximum production., The foremost problems facing the State, if

such an ambitious program is to be undertaken, may be cited as
follows: (1) To return the Bay to productivity will require a con-
siderable period of time. The present supply of shells is inadequate
to launch into a prégram of rapid restoration without neglecting the
present policy of planting shells in tributary waters. Undoubtedly,
the industry would object ‘seriously to the usé of more than a small
portion of the: shells now: available from oysters: taken in the ‘tri-
‘butaries to restore the ‘Bay bars.” (2) A very large investment of:
_State furids would be necessary. With the present trend to curtail
state expenditures, it is doubtful whether a minimum of seven million
dollars would be appropriated over ‘a period of 25 years, with no ~-
assurance of this resource becoming self-supporting for many years,
if then. In addition, there is little assurance that the original
investment, a direct subsidy; would ever be recovered by the State..
.(3) Such a program of State Oyster Farming should te made self+
supporting, that is, a tax of at least l0¢ per bushel harvested must
be collected to defray planting costs. If such a tax were authorized,
its collection would be difficult, especially during periods of low
prices. The dredger, at present, resists the payment of ‘the preserit
_ 20¢ bushel tax in svite of favorable markets, Therefore, there is
_ “Somé doubt whether an increased tax would be authorized. (kh) The:
‘tongers fear over-vroduction and glutted markets if the Bay were

restored to full productivity; They also oppose any large scale

“ leasing plan because of the fear ‘that such a plan would gain suffic-

'_ ient momentum to eventually include the leasing cf the teats ry

bars. :

In conclusion, there is general ‘agreement throughout the State
that something must be done. The likelihood: that nvture alone can
re-populate the Bay is only remotely possible in the far distant
future, if ever, with the continuance of a free fishery system.
State Management can and has grown oysters at mireaAsonable cost.
The available funds, however,-limit this operation to a minimum, as
evidenced by the planting’of ae per cent: of the available acreage
in seven years. Studies of the problem indicate thus far but one
solution; that is, some form of private enterprise or leasing. Past
efforts to permit leasing have met with strong opposition from the
Tidewater communities, with the result that legislative defeat of
leasing prorosals has continued’ as recently as March 1947. The
practical and biological aspects of oyster culture are advanced
sufficiently to initiate and maintain production but, in spite of
these advances, the problem of. ‘restoration of this potentially,
valuable resource still remains in doubt.

-10 -

i
’ 7

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7 : “ide? aa a ite ort Cir

“4 4

OBSERVATIONS ON FOULING OF SHELLS IN THE CHESAPEAKE AREA
“.G. Francis Beaven

Biologist, Maryland Department of Research and Education

During recent years, extensive data have been accumulated at Solomons
’ concerning the attachment of fouling organisms to oyster shells in local
waters. Three phases of ‘thé problem have been studied; (1) the kind, and
range within the area, of the major organisms which cause fouling of oyster
cultch, (2) the rapidity and extent with which specific organisms occupy
the: shel surface, and (3). the season of attachment and effect upon the
organisms of climatological variations as reflected in water temperatures

+.and salinities. Observations also have been made which indicate the compar-

ative efficiency as cultch of planted oyster shell during the first and
‘second spawning seasons... Parallel data on the period:and intensity of

oyster setting indiecatsc-how improved timing of shell plantings might increase
‘the effective catch of: spat.

Data on fouling have been gathered during visits to shell plantings
at various’ seasons of the year, in connection with: periodic studies of the
,ecomposition of naturel bars, and from clean shells exposed in numbered wire
: bags’ for various time intervals throughout the year. Special collecting
trips were made during the summers of 19h3 and 19h to study the distribu-
tion of Bryozoa throughout the Chésapeake and in Chincoteague Bay.

- Fouling in the Chesapeake area appears, to be caused principally by
Pryozoa, barnacles, mussels, Molgula, sponges, tube building worns,
Folliculinids, Crepidula, Hydroids, Algae, and various microorganisms
forming organic films. Ina number of instances one:or more of these
agencies have been found to completely cover all exposed surfaces of
‘planted shells in a comparatively short pcriod leaving no suitable areas
for spat attachment. Such fouling may thus at times be a major factor
in determining the success. of spat fall. Competing organisms also may
smother newly attached spat in some instances or,. on the credit side, their
growth across the shell surface may result in loose attachment of the grow-
ing young oysters so TREN they easily scale off from the cultch and become
Single.

One of the most serious fouling agencies from the standpoint of oyster
setting is the group of small colonial, single celled animals known as
Bryozo2. Twenty-eight species have been found in the Bay but only two of
these are found to heavily encrust oysters and oyster shells. They are
Acanthodesia tenuis and Membraninora.crustulenta. Poth form a meshlike
layer of calcified walled cells across the shell surface, the former often
producing layer upon layer and sometimes making folds or frills several
inches in thickness. These two species occur throughout the oyster produc-
ing waters of the region but are especially abundant at salinities of
approximately 10-18 °/oo. Settins generally occurs when water temperatures
are 20° C or higher and is most intense during the latter part of the
surmer.

Salers

ar | SAPS SHY UI CLS We aAUOs nO Sao rvaye cio
: bs a eel Pony of? . 7 :

de esgaites brew nyu we Pagiin! oT Sires aghealt yfe hyotorn if j 7
_ | |

#6. Sots Lintpuom Aosd ovad atah & ‘Ce eeeies 2 taser galrT

BE oflens ~ilwyo of SPmineg ty Qril=is te Nw) s oft atone :
‘Wi °(.0) . ebetbeva- tp yan wali») Te Searls coud =. bretaw
iitsel] ocuqS Aolaw HERI Wold <ie Se , eae att middie obdet

tet inogie oitinag? Ase Usby dnstke Sen Ue itees ots (5) .sostive

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Seroyned i6Tén al bofsetine an afio tin tev Eottgeletenife Io enslnegia. >
if Odaclbts Aoltw obew Mee isd Gale miohtiy oot) Malstnkion Dea. ¢

PLD Bid gaat Crate tahiys etraty ‘te elle) 4) eanpindtts aebie

| et A Ee cenobad baw bo bred Ne Ao blob Peilors%. .dimckoe sh tawae buoaee

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Sate il’ bsaoaxe siforip qaefs west wed jean leiden Ye nolitaoums;

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- : :

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oO Moeroiic wamecieil ts wien ony tells ofingiw Sic

podiGus beeaigee Li» sen06 elosolarms of bawe? weed ewad prion od ~

eK? na To PR RUlem2 oats di Soe Perloat ia ghwan sartdors '
tome nt Sigdet vem eoeteay Live «42 sertos uot

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te — : 7 it
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to Tope lt of) (oa we Aversa ors fattest
; wren etlie> is ablo? anita tom foe
Sa0bbxc, toreye wi rvodgucndt uioe aalavge ont %
*). WW evieiattee 14 Mmnbaids eLislooqen win gud noty pats
“Dapaiegeet Jrw wonte exupno YLisieneg ynitte® ».60\" BLHOL |

7

© ‘sat We Mang 19040L std mitwh swotat toon at lew weigh

Be) .
| - irs

In reproduction Rryozoa produce ciliated larvae which swim
about for a short time, then attach to shells or other objects and
within a few hours metamorphose into an "ancestrula" or primary
individual of the colony. Occasionally a twin ancestrula is pro-
duced as is true of Acanthodesia. Buds of the first generation of
new cells or daughter zooecia usually appear within a few hours and
subsequent rows of new cells around the spreading colony may be pro-
duced at the rate of two a day. Although the length of a single
cell is only about one half millimeter, the colony, generally fan-
shaped at first and then circular, expands all around the border at
the rate of one millimeter a day so that it is possible for a single
‘colony to reach two inches across in 25’days. This rate of growth
frequently occurs during the summer under such environmental condi-
tions as prevail at Solomons. On clean shells exposed for one week
in this region, counts as high as 2009 colonies on the inner surface
of 10 shells at times have been made. It is thus not unusual to
find the surface of clean shells completely encrusted by Rryozoa
within a three week's period under favorable conditions.

Fortunately Bryozoa do not thrive as vigorously in the seed

- areas and other portions of the State as they do in the mid-bay
Section. Also, intense Bryozoa setting occurs in late summer so
that during the first part of the oyster spawning season ample
Bryozoa-free surface on planted shells is left for the attachment
of spat. Heavy subsequent growths of Bryozoa do not apnear harmful
to the young oysters but serve to prevent their firm adherence to
-the cultch and to. one another so that clustered oysters may be
separated easily. In most places, however, Bryozoa growth does
greatly decrease late season oyster setting on spring planted shells
_in the Solomons area, Delaying of shell planting until an oyster
set seems imminent appears to be the surest way of minimizing inter-
ference from this organism.

_ Barnacle setting also has-been found to’ be much heavier on clean
newly planted shells than on oysters and old cultch. Although
barnacles are found throughout the area they are more abundant at
salinities under 20 °/oo. In waters of higher salinity many barnacles
are killed by drills and again competition with sponges and other
organisms is’ more severe than at the lower salinities. Two periods
of intense setting are found in the Solonons area, one during April
or May and the other during November or December. Peak setting in
both cases occurs when water temperatures are about 15° C. High
counts of approximately 1500 barnacles per 10 inner surfaces of shells
during a week's exoosure were made in both May and November of 19h6.
After a few week's growth, barnacle sets of this intensity may com-
pletely encrust all exvosed shell surfaces. While spat are
occasionally found attached to barnacles, the efficiency of the
barnacle coated shells as cultch is greatly decreased. Few or no
barnacles have been found to attach on shells exposed during late
June and July, the usual period of most active oyster setting in
Maryland, and again during February and March. Unfortunately, the _
Spring period of heavy barnacle setting frequently coincides with
the time when State shell plantings are being made. Loss of cultch

- 12 - Fal

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A ee

efficiency from barnacle fouling: coma be almost entirely eLiminabed
by eens shell planting. until after June neh

Mussels are most abundant on the Fore of the upper ae of the
Bay and its tributaries where salinities-.are low. Setting’of this
organism appears to be. of_minor importance as a hindrance to oyster
setting on planted shells but may so-encrust growing oysters and old
cultch that all surfaces are completely covered. In one recorded
instance a typical bushel of dredged oysters from a State planting which
was ready for’ pero tne was found, when all mussels had been shaved off,
to consist of ¢ bushel of oysters and 4 bushel of mussels, thus greatly
lowering the cee value of oysters produced on this bar. Subsequent
working and culling decreased the proportion of.mussels, however, as:'.°
harvesting of the bar proceeded. - Mytilovsis,. a.bivalve very similar to
mussels, is commonly found on oysters and cultch at the -towermes’
salinities under which oysters occur.

Molgula or sea squirts become very abundant.on many bars during
the fall and winter months. They interfere with oyster harvesting but
do not appear to interfere seriously with oyster, setting. Heavy
aggregations of them sometimes die.en masse in late winter. or early
spring to'form a smothering. deposit of deoaying’ material which has ©
been believed to be the causative.agent.for occasional oyster mortalities
occurring simultaneously. SNe ne: epee

Various encrusting sponges are very abundant on the deeper rocks
of Tangier Sound during the fall where salinities are generally above
20 °/oo. They make harvesting difficult and apparently may smother
some spat or small oysters. Boring sponge is commoner also at higher
Salinities and often.riddles both shells. and oysters. Sponges in
general seem to cause little interference to oyster setting on planted
shells during the first season, but may be responsible for a con-
Siderable decrease in cultch efficiency during the following years.
These and the boring clam commonly found in shell in the Tangier area
convert the cultch rather ranidly to crumbly shell. fragments or "cinder ".

Several species of tube building annelid worms are commonly found
which may cover considerable surface on clean shells rather rapidly.
The Serpulids which build contorted calcareous: tubes are found where
salinities range above,15 °/oo and the Sabeilids or membranaus tube
builders are of more general distribution. Fouling by worm tubes
generally is not severe, but occasional local abundance of Sabcllaria
has completely encrusted shells. and oysters with deposits an inch or.
more in thickness, preventing attachment or killing ail.spat and
smothering many oysters. .Such.occurrences-are rare’ and have only been
observed under conditions where the. bottom contains fine sand or silt
which may be roiled by wave action keeping the water EL laden with ©
the silt used by the worms in constructing their tubes.

Crepidula and Anomia occur. in waters. where- the batiniey ranges
above 15 ©foo but have not been numerous enough to be considered serious
fouling agents. These and oyster drills fluctuate widely in abundance

-

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with seasons of varying salinities sometimes almost disappearing
in Maryland waters of the Chesapeake system after seasons of heavy
fresh water run-off and at other times building up to high levels
‘after a series of dry years,

Folliculinids are often abundant on clean shells and are found
at all seasons but do not appear to have adversely affected oyster
setting or survival. Hydroids are sometimes quite abundant locally
in winter but mostly disappear from the shells during the warmer
seasons and seem not to affect oyster life. Some of the larger
algae are of common occurrence in the Chesapeake but are usually not
abundant and have not been considered detrimental to oyster life.
However, in the shallow waters of Chincoteague Ray at salinities
ranging around 30 °/oo dense mats of algae sometimes accumulate
over oyster beds and, especially when the algae are dying, cause
serious interference with water circulation so that the oysters
become very poor or may die in large numbers locally.

An organic film containing many diatoms, algae, bacteria and
other small organisms together with accumulated silt usually
develops over most shell surfaces which have remained in the water
for some weeks. This decreases the number of other fouling
organisms as well as of oyster spat which may attach. In some
cases a fairly thick sheet of such film has been observed which
could be peeled off from the shell. A large shell planting which
had become heavily fouled in this manner during the first season
was found in the following spring to have the film loosened and
peeling off so that by early summer most shell surfaces were
comparatively clean and ae heavy set of. spat occurred. Earlier
presence of the film apparently had prevented the attachment of
many barnacles during the spring setting period of that organism.

Accurate records of the commercial set of spat on State
planted shells in various waters of Marvland have been kept during
the past six years. Spat counts were made in late fall after all
setting had ccased and when the current year's set had reached a
size making the spat readily distinguishable to the naked eye. In
a few instances new shell plantings had been placed on the same bar
adjacent to a planting of the previous year so that both groups of
shells wore under practically identical physical conditions of
exposure. All instances, ten in number, where the catches of such
Similarly exposed new and previous year's plantings were counted
on the same date have been tabulated. In only one instance was the
catch on the older shells greater than on the more recently planted
ones and in that case the set was very light on both plantings with
a difference of 8 spat. Shells planted during the current yerr in
the cases observed were found to be far more effective than those
which hed been on the bottom for one year longer, the newer shells
receiving an average of hh7% of the spat found on the older ones.

A fow comparisons were made between shells which had been

exposed on the same bar for periods of one, two, and three or more
years. It was found that after one year of exposure there was

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little or no appreciable decrease in the shell's effectiveness as cultch
during the following two or three years. Several instances of good
catches on old shells have been recorded but in every case clean shells
on the same bar yielded still higher counts. In some instances, deposits
of silt as well as the presence of fouling organisms on the shell sur-
faces, were responsible for the loss in effectiveness as cultch.

~ Comparative Evaluation of
Commercially Spring Planted Shells

As Oyster Cultch During First and Second Seasons -

Count on . Count on Effectiveness
at tight: current last year's .. of new over
Location Date ’ shells shells old shells
Hungerford Hollow : a
Patuxent R. : 10-17-0 a ; 22 <a -63.6%

. Inside Swan Pt. Bar 10-29-40 21h © )2 a y 509.5%
Parson Island Sands’ ll- 1-o 2688 . 282 ‘ecg ‘¢ 953.2%
Long Point tie oF Sar 4 awl
Choptank R. 1l- 2-0 86 68 126.5%

_ Bald Eaglé Rock " ll- 9-LO 508 eT 725.7%
“Middleground ,

Nanticoke R. 11-18-hO =—132 38 317 LS
Middleground ci é

Big Annemessex . 11-20-h0 72 ~ 5O 14h .0%
Lower Thoroughfare ORT bt ee ay
Honga R. 11-23-LO bh jeyl2ie tees 116.1%
Marunsco

Pocomoke Sound ll- 1-45 =)28 sess : 150.7%
Poplar Island

Narrows Swash 11-28-5 -1h6 ; 12 12116.6%
Average of all plantings 43.2 99.2 Uh6.8%

-15 -

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i] 7

DISTRIBUTION OF SETTING GUIDES THE MARYLAND OYSTER PROGRAM
James-B. Engle

“Aquatic Biologist, U. S. Fish and Wildlife Service

A program to facilitate oyster production is successful only in
relation to the reliability of the replacement of the crop removed
in harvesting. The whole history of the industry has told a story
that demonstrates the truth in this statement. Every oyster producing
State on the Atlantic and Gulf Coasts at-one ;time has come to realize
that replacement has not been adequate to the demands, and decline in
oyster production has been the result. In New England and elsewhere,
public control was relinquished to private management with satis-
factory results. In Maryland, public responsibility is still retained,
ahd the necessary management is under State control.

All of us here are aware of the simple but essential fact that
reproduction and the survival of the young oysters to marketable size
must at least equal the harvest. To some degree, this has been
ignored and the much worn idea that nature will provide and continue
to provide, regardless of how abused, still persists in some places.
Nature struggled hard, but found the job too difficult. Another group,
many here and many before us, faced by the stark figures of statistics,
saw this picture in another light and realized that nature was an ally
only when intelligent use of her potentials were considered and
applied. In hackneyed but appropriate words, "Nature helps those that
Help themselves." There are examples of the application of this latter
idea in Maryland and in many other places where oysters are produced.
Legislation has been formulated to attempt a control of production by
safeguarding the supply of young oysters, by regulating the size of
marketable oysters, by restricting the taking of oysters during the
reproduction and setting periods, and by setting aside adequate spawn-
ing and setting areas for seed development. All these factors con-
tribute to the success of oyster production, but the last named is
the most significant. I hope I may be able to demonstrate its im-
portance to the Maryland program by a discussion of the setting and
seed production of oysters in Chesapeake Bay and tributarics.

Production has slowly declined in Maryland, and a program of
management was inaugurated to effect a rehabilitation. Sporadic
efforts have been made over many years to stem the diminishing
returns in this State, but they have not been very effective because
the long range value of the effort was overlooked and the lessons not
learned. The present program carefully scanned the previous records
and weighed the results. From the analysis, a plan of essentials was
devised and first in order was the accepted need for a more complete
knowledge of oyster setting in the. Bay and tributaries. State and
Federal research organizations tackled the problems involved in

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a dhide gionuen dul. Ye vantirvegey sobivelq of i
hl Mig? att fhe’ ted , beet Golguuyies oeusat
lets + wll Siyguass evil re he vine tan coved qnee
ay jt a “hy tigtt valle at wtutoly old) wae
SEn $21 0igs04q Ste Wu oby tosg i fiend mudi ylao
a yeboerni iermvigy tu Syeural aad ar »debiqys
4 Ww teigums sm geet? ",covieamel? qfof
ry oe Sadi? vate yish nl the budterel rt vobt
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genes Wh terete Ww io Yfeae wel?
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“Maypeba sthsn act Oba prog pats eun Hee so otmabeyrs
aposdet owelt Lik thiieeie ho wal ana ‘Dae = 7
G2 bier Peal oid ted. pad M dren cAlb-at
te Eat TP stonecaecd 2 clon oh = eqs nario =. °F wit f=
Seis pridade eit) Jo noscaunelh » yt eure ery mut pis wind
7 . stotistudhss fie ¥Xj) ehoagoadi? ni. esdeyo Te ne fA elegy a
Yo Aetyoig « bre ,bonfeiet ai biatloobd yteo ge aml obey ? :
DS.) elbetoge sel tebbitcahen a Inthe o¢ besauqgrent ae
a Likinini eft mate of eragy Yona tore ‘onan Ap ;
WLiselle rev, need fon seed yas) Sad yotade |
fon atoteal at! bw bajloofrevo sew Bro Ys ef. Yo aulay
p) Sirtooet ewokroig oft bominde yLiilexso nowgetg Je .
oon eloitacees lo mela 6 \theylone off wort .82 hier oF
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Mie Siat2 .talrstudte! bas ad wl A
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answering the many questions of fundamental significance. The research
program gave priority to setting, and the results of the studies pointed
out several conditions: first, that there was a wide range in the in-
tensity of setting from one place to another; second, there was a
tendency for more regularity in setting from year to year in some places
than in others; third, there was a definite tendency for setting to be
more regular and heavier on the eastern than on the western side of the
Bay, (Table 1); and fourth, within the area studied, there appeared to
be a tendency for oyster setting to be heavier at the lower parts of the
rivers and the Bay than upstream or in the "Head of the Bay" section.

With the above conditions known, the program of stabilization and
increase of production was worked out. The oyster areas were now
considered under several categories: (1) places where setting was con-
sistent and heavy; (2) areas where setting was adequate for maintaining
the oyster population under normal working of the bars when cultch was
added; and (3) areas where setting was insufficient to replace the stock
of oysters removed during harvesting.

The treatment of the areas in the above categories may now be
planned on the basis of shelling bars and transplanting seed. The
several places where setting was consistent and heavy were recognized
as important for the development. of seed production, (Table 2). The
seed areas received intensive shelling of approximately 2,000 bushels to
the acre annually. The total acreage involved in this phase of the
program is still small, mostly limited by the number of shells available
and the funds to move them. Three seed areas are now being developed
and used, and the progress in rehabilitation and the increase in pro-
duction will depend largely on the rate at which the seed from these and
other seed beds can be produced and transplanted. These three seed areas
are .strategically located; one in Eastern Bay in the upper part of the
Maryland oyster waters; another near Tangier -Sound in Holland Straits;
and a third in St. Narys River in the lower western portion of oyster
producing waters. The search-is still on for additional seed areas, and
their development will further facilitate the production.

It might be well to point out here that the recent investigations
in oyster setting fail to substantiate the idea held in the past that
the "Head of the Bay" is a seed area. The results of the setting studies
Show only occasional sets of any sufficient intensity. The last big

’: setting was in 1931. The accumulation of oysters on the bars of this
area is slow, and if any large scale removal of oysters for secd purnoses

were made, oysters would not be available again for a long time unless an
unforeseen and significant setting occurred. This is not a seed area in
the true sense of the word because of its unreliability.

Dependable seed areas are essential to the Maryland program for two
reasons; first, a large portion of the oyster area does not receive an
adequate natural set to meet production demands, yet the social and
business economy of the scctions rely largely on oystering, so that
planting of seed is necessary to keep the oyster bars adequately stocked.

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: hae) Yo. ativert ede lie gopites 0d xs ttha hwy eveg CURE OmNS
on abin ia cin orev we oli cboe I thie, Lesa
0 a ee PG 97 AAR PAD cos) anthdee to yttened 7
Of Sem, ox th gonposer DesGlupot stom 76? yonhaes
to 43 RD Q@relirud oF (ep ine “ee bitte. pegetioe oF mate
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a Abed Phu ie WER aap es bes re aie (S) .<v wate datete
Baas tet eto Ani ee AO SAbiy nol): cogs yates wt
FOUl Sita ul JastsP Apart sow ded Simeile cserd (2) Grek (habbe
gait idee Low ore &yadzto Yo

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eat, ee Ee wxedw anol Pavuveq
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tebe Pa @tas, PEA. Chewiel hve! Ile nod ah
Nera Wee ‘jaa ahead toce (ally
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° we

Second, overfishing of the past has seriously depleted many of the
bars producing the quality oysters that~ once made Maryland the
oyster center of the world. Shelling alone cannot bring these bars
back into commercial production, it will take the planting of many
bushels of good seed oysters to reclaim them.

Fortunately for’ Maryland,’ there are. large acreages of oyster
bottoni; located mostly in the tributaries, where setting is adequate
to restock the bars. The simple method of replacing the cultch which
has been removed during harvesting is sufficient to maintain produc-
tion. The above named. sections where seed areas are located fall
into this category, as well’ as Fishing. Bay, Tangier Sound, ‘the
Choptank River and some of. the creeks emptying into it, ere there

are bars that respond: to shelling as the means of maintenance.

. Again, the limiting. factors in this part of the program are the
stockpile of available shells and the funds for transplanting them.

The oyster bars in a large portion of the western shore of
Chesapeake Ray, Chester River and the Patuxent River do not have
sufficient setting to keep them stocked by natural means. In these
sections the seed developed in the seed areas must be planted to
insure production. One might ask, "Why is it necessary to make this
extra effort to kecop oysters on the bars that have such a meager
natural replacement?" Ore of :the reasons, the social and business
economy of the arcas,-has already been suggested and is actually
“important in the Chester River and on:the western shore, and another
“reason is related to the psroduction of. quad rey oysters which can be
Ehown rapidly in the Patuxent River. -

Before the results of the research units studying. the distri-
bution of oysters were known, planting of shells was considered to
be the only operation necessary to maintain any oyster bar; provided
adequate adult oysters were present as spawners. Many thousands of
bushels of shells were put in these areas with results of negative
or dubious value. There is no doubt that the shells had some bene-
ficial: value in keeping the bars usable, but as ‘cultch for setting
they were wasted. A much better use of. the shells could have been
made by ‘putting them on seed producing bars and transplanting the
seed on these shells to the above bars. The Maryland Department of
“Tidewater Fisheries, the agency responsible for the management of
the oyster resources, now follows’ the seed’ transplanting: procedure
in these cases. Be es :

Rehabilitation of the depleted bars, mostly in the southern
part of the Maryland waters has not been tackled in a major way as
yet because of the shortage of seed, shells and funds. The im-
portance of rebuilding these areas, however, has not been overlooked,
and will be actively included in the program when the above shortages
are remedied.

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Table 1. Total average oyster set on 10 shells taken from test
bags placed at the sampling stations in Chesapeake Bay, Chester
River and the Choptank River during the setting season of 196,

Chesapeake Bay Proper

Eastern side Western side
Total Range Total Range
average bottom . 1 averages: bottom
~. oyster set salinity -oyster set salinity

Station 10 shells in o/oo Station 10 shells in o/oo
Gun 4.67 Middle 4.80
Thicket 102.0 12.81 Ground eS 13.78
Broad ee Y.26 : Sandy — 3.48
Creek 6.0 a3 Point 3.0 12.07
Love bs 27. Gibson 3432
Point 5.0 13.65 Island 1.5 9,2)
Tol- fresh Man-o- fresh

chester 5 user! ; war dO 8.08

Tributaries - eastern side

Chester River Pars Choptank River |
Rlunts 5.95 npn 7.02
Rar ees 12.39 Buoy 58.5 12.59
Oldfields . 5.70 Piney arab
Bar BELO) 2 10626 Island 10.5 12559
Kirbys 7265
Rar 6) Bes)

Stations are arranged in the table with the first in the column represent-
ing the lower or downstream portion of the area, and the last is the
uppermost station.

Salinity range is that of the period of the setting observations with the
figure at the top in each pair the salinity of the week of June 15, and
the figure at the bottom the salinity of the week of September 15.

19 -

Perrys Bev gt wkd
aT ® Med ai ~
7 * ik

=—_)

Papeete ii manios anf mg .21t sdx at: ie wide? GAT os Saplevts oe tholis32
a! saat ois tie, Gem ‘ott Lo nhicwyp eonaleaneh vo tenet art) pal
: mo) Peoria g

ond Atkw eno tiarreeds wiliree 342 te boliey of) Io aed Ob pape Winllez

bie (ef ww ie veaw ad! lo “tindfoe 32 akaq tase nf aol 2, ori {)
-2f sadimedqst Lo leew ald Io ys tion sty. eodand aff Je gtagl\ sc)

ec

‘Table 2. Oyster spat per bushel of pene shells in
designated seed areas.

~ - Se es sweet oven as be

Oyster ee counts per bushel of shells

Location, - | 1941 1912 1943 19hh 195
sees - ; Rare AUR oi,
St~ Marys River” : 4 53h 2,860 Vea 191 3,500
Holland Straits-Johnson Pt. 102" 175. 1345h° 907 eae
Holland Straits-T Creek 356 661 1,068
Eastern Bay-unper > Fie 70 39 “isis

Eastern Ray~lower . 868

The Potomac River, now being studied ‘by: a joint committee from
Maryland and Virginia, may require a treatnent combining shelling
and seed planting. An examination of some of the bars in the early
fall of 1946 failed to show any setting but, at the same time, gave
evidence of practically no unfouled shells. Even these fouled shells

* were in a seriously eroded and crumbly condition.. The-.bars are in
need of clean cultch as a first move in restoring them. A study of
the setting on the bars in the Potomac River. may show that shelling
alone will increase the oyster population of this.important area,

In conclusion, I should like to repeat that the Chesapeake Ray--

is ‘a large body.ef water which has a tremendous potential oyster
, yield. The actual production has been greatly reduced, but the

martagement has in the past tried ‘to. get along with very little know-
ledge of the biology and ecology of the oysters on the bars. That
the Bay may be returned to a substantial portion of its earlier pro-
duction is the aim and_belief of all_of..usy-providing we continue _
the search for the fundamental principles that control the reproduction
and apply them to the program of management.

Laeaore

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ie

OBSERVATIONS ON OYSTER DRILLS:

CHROMOSOMES OF UROSALPINX CINEREUS, SAY

Dr. H. Malcolm Owen

Biologist, Louisiana Department of Conservation

The Atlantic Coastal distribution of Urosalvinx cinereus, the
oyster drill, shows definite delineations as to the size of the
individuals. The phySical environmental conditions do not correlate
to the size of the individuals.

A cytological study of the maturation of the male gonads shows,
however, that the chromosome_number is constant, it. being 2n = 32.

A distinct chromosomal behavior characteristic was noted in the
smaller sized drills, which was not found to be present in the larger
individuals of a different geographical locations In all cases dur-
ing Anaphase I of the smal] drill one chromosome lags behind the other
chromosomes, forming a distinct chromosomal bridge.

It was therefore concluded that Henderson and Bartsch (1915)
were correct in recognizing two.races.of the species.

(An abstract by the author - the full text
of the address was not available.)

=o =

THE PROS AND CONS OF INTRODUCING FOREIGN SHELLFISH
Dr. Thurlow C. Nelson

Professor of Zoology, Rutgers University

At our Convention a year ago some possible advantages to be
cerived from the importation of foreign species of oyster were
presented, together with the urgent need of restricting wholesale
and uncontrolled admission of shellfish from distant shores. Dr.
Radcliffe, tollowing this meeting, appointed a committee, consisting
of Doctors A. E. Hopkins, Gowanloch and your speaker, to consider
all possible angles of this probiem and to near back to this
Association.

It has not been possible for your Committee to meet as a body,
but through considerable correspondence, we may now present for
your consideration some of the arguments for and against such im-
portation. Since this is to be a round-table discussion, my remarks
will be brief, and I hope, to the point.:

A. Evidence favoring importation of foreign oysters.

1. Stunted oysters, designated by the British as
"dumpy" or as "dumps" grow exceedingly slowly,
some individuals 10 to 12 years of age being no
larger than normal 2-3 year old oysters.

2. Depleted oyster beds nearly always show a high
percentage of such dwarfed individuals. Where
the 3-inch law prevails as in Chesapeake Bay, the
faster growing oysters are continually being re-
moved while the dumps are returned. On some planted
grounds these dumps are the culls, too small to
market, which are thrown back on a portion of the
bed. Within the past four weeks Dr. Carriker and
your speaker shucked more than 1000 oysters at a
meeting of our University Outing Club. Not more
than a dozen of these were strong vigorous bivalves,
the rest were dumps. Some of them 8-12 years old
were barely large enough to warrant shucking. Why
did we, oyster scientists with a reputation to main-
tain, shuck such poor stock? The answer: it was
Mav 11, the owner had no objection to disturbing
hese oysters, they had no spring growth to speak
of, They were the rejects of years----too small to
command a price.

- 22 - :

sie) 4 hod 1 a> CN BOR :
u My

=

-

3.

he

7.

While no scientific proof exists that crossing of
strains of oysters produces superior stock, the fact
renains that among the most successful oyster pro-
ducing areas today are those: to which oysters are
continually being brought from other regions.

Hybridization of farm crops and animals has yielded
large financial returns to agriculture. We need
mention but two: hybrid corn and the mule, which
between them yield added annual income to this
country of many millions of dollars. Other hybrids

too numerous to mention have been made, particularly: .
among flowers, of added value ‘of ‘millions more. ,

Among the most desirable results of hybridization

is increased vigor which. expresses itself in more
rapid growth and frequently larger size. We do not
want a larger oyster on this coast; our consuming
public has very definite ideas on whet it will eat
for half shells, for stews and for fries. .But why
should it take up to six years or longer to produce

a select or extra select in the three best oysters

of the world; our Atlantic coast oyster, species
virginica; the European oyster, species edulis; and -
the Australian oyster, species cucculata? The Pacific
oyster or so-called Jap oyster, species gigas, may
attain a size better than a sclect within two years
or less. Such growth in-oysters, therefore, is
possible; it has occurred.on our shores in the
Northwest. :

Although oysters have not yet been crossed, this is
no argument for not attempting it. Where would our
farmers be now in these days of high cost of labor,
equipment, and supplies were it not for their superior
strains of domestic animals and plants? If oysters
are to continue to compete with other food products,
the cost of production must come down. -Every year
which can be cut from the tine necessary to mature a
cron of oysters means quicker turnover of capital,
reduced losses from enemies, from storms and natural
mortality.

Oysters fall into two grouos with respect to their
critical spavming temperatures. In Group A, .to which
belong’ ovr own Atlantic oyster, the Portuguese.and the
Jap oyster, spayming docs not usually occur until
temperatures above 68° F. or 20° C. have been mein-
tained for some tine. From Delaware Bay, south to the
Gulf, there is good evidence that this critical temper-
ature may be 259 C., (77° F.). Even the temperature of
20° is above that existing along most of our Pacific
coastline and on the Atlantic, north of Cape Cod.

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In Group B are those oysters which, like the Olympia
oyster of our west coast and the European oyster,
incubate the young on their gills. . The critical
spawning temperature in these cystcrs is 1G Cs 2Or
59° F. This lower temperature opens much of the
north European coast to Ostrea edulis which in the
oyster pools of Norway breeds even within the Artic
Circle. Although slow growing, this is a superior
oyster which in England has brought the highest
price paid anywhere in the world.for oysters; a’
shilling apiece for the finest Colchester Pyefleets.
It thrives best in clear water of near oceanic salt-
ness, the .very conditions which obtain from Cape Cod
to Maine.

Because of its different life cycle, there is
practically no likelihood whatever that the edulis
oyster would hybridize with our own Atlantic oyster.
North of Cape Cod it would not even have the oppor-
tunity. If, however, favorable conditions were
found there, a new and valuable eye hee fEsheuy. might
be established there.

The small Olympic oyster is now America's most ex-
pensive shellfish. Since its breeding habits are

the same as those of the much larger edulis-of Europe,
a hybrid between these oysters should be of great
value. Both heve excellent flavor, but both are -slow
growing. In addition, the Olympic oyster is very
sensitive to frost. A hybrid between them should
grow much faster than either, and some of the cold
hardiness of edulis might replace the sensitivity. of
the little Olympia Cero os

B. As against: the importation. of feneten OyStens: must be urged:

1. The dangers of importation of enemies. The intro-
duction of the mud-worm, Polydora ciliata, into
Australia about 1870 drove the entire oyster industry
off the bottom. All oysters are now grown attached
to stakes: or slabs of: stone. Can you imagine such a
revolution in methods of culture here, particularly
in Long Island Sound? Some of our own Polydora have
been identified as P. ciliata though no one to my know-
ledge has actually compared our species side by side
with those from Australia and proven their identity.

Our own "double decker" Crepidula, known to the

British as the "slipper limpet", grows to giant size

in English waters. In competition for food it has proven
more than a match for the rather particular and somewhat
less vigorous European oyster Ostrea edulis. We never
know beforehand how any animal or plant will behave when
introduced into a new areca.

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2. If a hybrid oyster were produced, but turned out to
have objectionable qualitics, it could readily ,
become a serious pest. Like the black mussel, which
has great vigor, an undesireble hybrid oyster might
soon cover up and smother our best oyster beds with
a very inferior, even unsalable substitute. [J con-
sider the Portuguese oyster, specics angulata, as
approaching that category. In England in 1931 I had
no difficulty in fertilizing the eggs of our own
virginica with the sperm of angulata and in obtaining

- swimming young. Whether larvae of Seu rie size might
be obtained is not known.

From what has been said, it follows that we must
proceed with caution. Unrestricted and uncontrolled
importation of foreign shellfish must not be per-
mitted to our Atlantic or Gulf states. Where state
laws are lacking or inadequate to control the
‘situation, federal restrictions may temporarily be
needed. <a

ON THE IMPORTATION OF FORETGN Se

Report of Coes Moneaneee by Dr. Radcliffe for the Association

The following resolution was accepted at a joint meeting on Tuesday,
June 7, 1946, of The Oyster Growers and Dealers of North America, Inc.,
The ‘Oyster Institute of pNOEtD Amorica, and the National Shellfisheries
Association:

Whereas, considerable risks would be involved in uncontrolled intro-
duction of nonindigenous species of ‘oysters, including the possibility
of introducing other enemies of oysters, into production areas along our
Atlantic and Gulf coasts; and : '

Whereas, agriculture has benefited by many millions of dollars from
scientific research in selective breeding and the development of new
strains of domestic animals as well as better grades of cereals and other
crops, ; a :

Therefore, be it resolved that the introduction of new species of
oysters into the waters of the Atlantic and Gulf coasts be adequately
sefeguarded by requiring permits of the State Shellfish Commission or
other competent agency fully conversant with the risks involved; and
then only after comprehensive studics have been made and definite assur-
ance given that such action is warranted; and :

Be it further resolved, that ‘Federal and State and other research
agencies be urged to mndeerake scientific researches intended to
effectuate improvements in the strains of native oysters and studies of
nonindigenous species of prospective value to determine probable benefits
to be derived from such introductions; and

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Ba ane —_o*

ea

sitone!
a

» that the several Atlantic and Gulf
28S legislation to effectuate the above

purvoses,"

It is the opinion cf your Committee that this resolution
embodies adeauate :s for the protection of the oyster
industry while lee ay open for research aimed at two

primary objectives; ) 2aster growth; and (2) the introduction

of species capabie cl >s2recucing in the cold waters of the
northeastern Atlantic 252 the Pacific. The time has come when

we must devclov our csasi2i waters to a much greater degree for
the raising of food. w= Should be derelict in our duty if we
failed to encourage inc 2° undertake ourselves the research neces=
sary to establish a c2Sis ior action.

In those ssece im which competent biologists are located, it
should be poss ts conzrol the problem adequately by state laws.
States not having the oserezit of such advice would do well to pro=
hibit altogether the inmrcorvation of foreign shellfish though leaving

open to university or =2ceral laboratories the. opportunity to import
such species under license.
The New Jersey law is cited as an example.

"Article 6. PLANTING C= FGREIGN OYSTERS OR SHELLFISH.

—F

pla anted or lodged in the waters

from any foreign coun e
2rmission issued by the board for
a:

of this state withous
each separate shipment. applica
made in writing, and sna2-i state

50:1=3h. Pernissicn ant foreign shellfish; application
and contents. NO oyS72r=, secd oysters, or other mollusks, commonly
known as shellfish, native to, or brought directly or indirectly,

3) ¢
rye
4

on for such permission shall be

a. ° The species of such oysters, seed oysters or mollusks;

b. The location fro which they were, or are to be,
imiediately tazen;

c. The source from wiich they were originally obtained;
and

‘
ct

d. The country to wich their kind is native.
2 shown upon a tag attached to, or

The same informaticn shal
3 h shipment upon its arrival in this

=
upon the biljing eccomp2njize ea
State ‘

SOURCE.) 1 93S scien Soi Per we SONS
"50:1-35. Permissicn srented; prerequisites; form. The board

may issue such permissi sr due inspection and examination of
the nature, species, quar ziiy, source, location of proposed planting

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ve

or lodging, and the condition of the oysters, seed oysters or mollusks,
and after certification by the biologist of the board that the same will
not, in his opinion, be detrimental to the native oysters, or to the
oyster industry of this state.

Such permission shall specify the nature, species, quantity and
proposed location of planting or lodgment of the oysters, seed oysters
or mollusks and shall apply only to the particular shipment for which
Ht Ss puSSued.

SOU Cig Ley 9 So iCal RoHS cise ste Po BIOs, GOL.

'50:1-36, Costs. The board shall make such charge, and collect
in advance, for the issuance of such permission, such sum of money as
may be necessary to defray the cost of the inspection, examination ahd
certification.

Sounder Iyex cl 933 Cesta ps ap Oa.

"S0:1-37. Penalty for violation; revocation of license. Any
person or corporation who shall, without such written permission afore-
said, plant or lodge in the waters of this state such oysters, seed
oysters or mollusks, shall be liable to a penalty of one thousand
dollars recoverable in an action at law in any court of competent
jurisdiction brought in the name and for the benefit of this state by
the attorney general at the instance of the board.

The board may, in addition to such penalty, revoke the license of
any boat or vessel, licensed under the laws of this state, used or em-
ployed in the planting or lodgnent, without such permission, of any
such oysters, seed oysters or mollusks, and may also cancel the lease
of any person or corporation who plants or lodges, without such per-
mission, any such oysters, seed oysters or mollusks, upon any lands
under water leased from this state.

Source, Lb..1933, ¢., 345, 5,-ps 902.

"SO0:1-38. Shellfish affected. This article shall not affect the
planting or lodgment in the waters of this state of any oysters, seed
oysters or mollusks, commonly known as American or Eastern oysters, and
scientifically knowm as Ostrea virginica Gmelin, but shall be construed
to affect the planting or Iodgnient of all othcr species.

Soprces ale 93 55. Cen Sd, O5 Dan 902!

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eur sae

SEASONAL CHANGES IN THE FATTENING OF OYSTERS
Dr. Walter A. Chipman, Jr.

Aquatic Biologist, U. S. Fish and Wildlife Service

More and more attention is being placed on the production of
oysters with high quality meats. So often are we called into an
area to investigate the failure of oysters to fatten properly and
give,a good yield that consideration must be given as to what is
involved in this fattening process. ,

Oyster meats may be considered as being composed of water,
carbohydrates, fats, proteins, and the mineral salts. In general,
oysters are considered as a vrotein food, but large amounts of
carbohydrates at times make them even more valuable as food. The
Se poeta of the mineral content must not be overlooked.

True ee of oysters is reflected ina se water content
and a high carbohydrate content. Changes in, protein and fat are
not of particular importance in fattening. This accumulation of
carbohydrate reserve is almost entirely in the form of glycogen, or
animal starch. It is to be regarded as a reserve material stored
up for the carbohydrate needs of the organism, in this respect
playing an analogous role to that of starch in plants. As the
carbohydrate requirements of the organism vary, so does the quantity
of glycogen present fall or rise. In case of need, it is apparently
converted mainly into glucose, and ultimately undergoes complete
hydrolysis and cxidation. Rise of temperature, increased functional
activity and diminished food supply are the chief factors which may
produce a reduction in the amount of glycogen present in the oyster.

An oyster lacking in all reserves gives the appearance of con-
sisting merely of skin and water. This, condition is approached
after spawning, but there is usually rapid recovery. Failure of
oysters to store reserve material again and to become as plump and
firm as may be exvected does not occur too frequently, but does to
an extent that merits attention as to possible causes for this
deficiency.

Although the present paper deals with seasonal changes in the
fattening of oysters, it should be borne in mind that there is
considerable variation in the fatness of individual oysters on an
oyster bed, between oysters of different locations, both in the
immediate vicinity and in widely separated areas, and among the
Same oysters at different times.

There is, of course, an important relation between the periods

of spavming and the subsequent fattening, but the great variety of
conditions for fattening said to occur within a short space ina

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7

_ -

given locality requires investigation. It'seems probable that an
adequate food supply for fattening is.rarely absent from good oyster
beds and that this. factor-has beon overemphasized. While it is true
that the period of active feeding’ must coincide with a good supply of
food material in order for the oyster to store up food reserve, other
factors, particularly those involved in the metabolism of the oyster,
its anabolism or catabolism, and changes in these by outside forces,

need more attention.

_In the course of studics. made throughout a number of years, rather
extensive information has been collected on the chemical constituents
of oysters from a number of localitics, particularly of the glycogen
* content. Oysters have been analyzed from Long. Island Sound, various
localities in the Chesaneake Bay, particularly in the lower Chesapeake
Bay, the Piankatank’, York, and. James Rivers, and a few samples from South
Carolina, Texas, and other points. A number of these analyses were made
on oysters known to be in poor condition from.some cause, and, in some
instances, the examinations were not made..a sufficient number of times
throughout the year to give evidence of any..seasonal ehange, since the
experiments were designed to fit other purposes.- However, considerable
material has been collected from certain beds over sufficient times to
warrant analysis as to changes in fatness through the different seasons

of the year.

The samples of oysters were opened and, after the shell liquor was
discarded, the meats were drained of excess moisture, and ground to a
fine state. Samples of the meats were dried for determination of the
total solid content, and. other samples analyzed for: glycogen, using the
usual ‘methods of digestion with hot alkali, precipitation of the glycogen
with alcohol and purification of this vrecipitate, and, after conversion
to sugar, measuring of sugar content of the sample by an 2ccurate
titration method. The results are presented showing the percentage of
glycogen in the dried oyster meats. Since there was no measurable loss
of glycogen in the draining of the meats, differences in the method of
draining in the different IgeRs had no- effect on the ‘results.

If we examine the curves shovm in Figure 1, it can be°cllearly seen
that the accumulation of glycogen in the oysters follows a definite
seasonal pattern, as has .been pointed out. so-many times in the work of
investigators for many years past.. There is a period -of very low
Glycogen in the late summer, which is followed by en increased storag
of glycogen in the fall and early winter until the time of : ese
The period of high glycogen is followed by a sharp decrease in the spring
as the oysters resume: their activi.ty and spaym, reaching a cry et yecea
reserve ‘a igeae after spawning.

The curves of lj eorenie smcene of oysters collected from various ©
localities are of the same pattern, but differ quantitatively. The
oysters from Long Island Sound appvear to build up glycogen reserve
earlier in the fall than do the oysters from the lower Chesapeake Bay.
It should be pointed out that. fattening of oysters has barely started
in Sevtember when the oystcring season begins, and that the same oysters
would be fatter and give a much greater yicld if marketed in November
and December. This is more marked in the oysters of the Chesaneeke Bay
than those of Long Island Sound.

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Vis)

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2 SPW! OIE, Pratace 4
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sie. = ; ip ues! wr) tere
un sin ii bt
a: eee 2 Mitr ye 7
Gb oavull§ woh =
fay tee a . uy) 1s a ;
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ntl a sremeda) O20

ren: sy Arid tie. 4
: Uo paws: Poe
we m (nee We ee ie
in 138, es 'p Hi Nii nb fares

mie mprwe uty alae ae
ay HE o wees
igh ae ag fia a us oe,
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“ Suearict 46 Hadin , greg
_ Let afin ¢ ite i
3 ide = Qa OF piles #3
Wah - heise gree re eer lese ‘
“= ; sta

an € e .
suorns Wets cals lise ewdrye to- asians 2a
cae eplev iiss: hieaml 1eTt ih dl (ote itey Ce
wrinees Aoq6oyl5 qu’ bi furt m2 pudgy gue |
ona gage erred at? got mat oe why

* divtad 20 ererage Yo Qrimar

st ees ‘Ons Smite i Pabst

Fattening of oysters from the same beds diffcrs from year to year.
This is readily seen in Figure 2, which shows the percentage of
glycogen in the dry meats of oysters from Long Island Sound
examined in different years. It will be noted that the accumla-
tion of glycogen in 1933-3) was much greater than in 1932-33 and
that the loss of glycogen in the spring of. 193i. was not as early as
in 1933. The failure of certain teds to produce as fat oysters in
one year as in another has long béen a problem that needs more care-
ful study. :

Condition of the water, such as low temperature and abnormal
salinity during the spring, may alter the formation of the reproduc-
tive elements, and with this change in the development of the sexual
maturity of the ovsters, there may follow.a retention of the glycogen
reserve later in the ycar.. This’ may explain why the fatness of oysters.
may be longer continucd in some years than in others,

"Emphasis should be placed on the condition of the water, the

abundance of food, and, perhaps, the type of food available during

the late summer when the oysters are the most active and are vigorously
feeding. -This is ‘the most Orica time of ue year as regards fatten- -
ing as it is this time that reserve glycogen is being stored. If the
oysters fail to a epee during the late summer end early fall, they
Will not be fat at.ans time during. the year, .for there is oe any appre-
Chable increase in eee reserve during the colder.months,

It is generally considered that good fattening grounds often
differ from good producing grounds and good growing grounds. Very
often a good. stiff mud bottom, close inshore and protected from ex-
cessive current action, will prove to be an excellent fattening ground,
and oysters produced on other beds, or grown on other beds character-
istically good for oyster growth, are transplanted to these fattening
grounds to prepare them for market. When oysters transplanted to the
fattening grounds fail to fatten properly and give a good yield, one
must consider the possibility that this failure may well be due to one
or more of the weakening influences incurred in the transfer of the
oysters.

Outside factors regulating the fattening of the oysters, such as
water temperature, salinity, currents, availability and type of food,
bring about this regulation by changing or altering the inner activities
or physiological activities of the oyster itself. Changes in the salin-
ity, alkalinity, and chemical nature of the water, as well as the
physical conditions of temperature and turbidity, both from silt and
abundance of microorganisms, play an important part in the regulation
of the opening and closing of the oyster, the amount of water passed
through the gills, the muscular activity, respiration, and the other
vital activities of the rninal. it is throug? ». study of the metabo-
lism and physiology of the oyster, under both normal and abnormal
conditions, that we can interpret the mechanisms of fattening and the
loss of this carbohydrate reserve. It is to this end that our studies
are being directed. i

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7

>

GLYCOGEN

ER:GENTAG E

2)

i

FIGURE ), OYSTERS FROM LONG (SLAND SQUND
{

' LOWER YORK RIVER

@

O

O s ie 4 E
PIAWKATANK RIVER

ye \ ®
2 == Oa ee
a aa ee es eae NS
ae : oy SL Ose =
@ 22 on F we “<t
vA oO” 5 Ss i oO \ <7)
Ze : \
On \
oe Nees
{69 Pa t % —D
‘o) ese } aes elon ~ | ae | Ae ee Spex 252 tee es eee | ee
9 19 7 \2 Z. 4 5} 6 (

Zz
.S)

a

+

ae

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“ay !
=} me
mie

7

—<<

™m

> Q =
A

20300 =

ae BIVMIF NUM, BIKEY
MOMEE AOU BIAEY -
; rome wervup 2onwa

_

GLYCOGEN

PERCENTAGE

FIGURE
Ow
Uf
iy
Zi - a
y 6)
O
jO
OF x
1x ue.
nSy PS TVey

ee ay

a

|

Om

OSS 04

Hee2-s2

Od|
-.

MONTH OF THE YEAR

a
S
a

We

= 32 =

RESPIRATION IN OYSTERS.
Dr. Paul S. Galtsoff

_ Aquatic Biologist, .U. S. Fish. and Wildlife Service

Breathing or respiration is the principal function of every living
thing. Fundamentally, it consists in the burning of food materials
ingested or stored in the organism. It can therefore be measured by
determining the amount of oxygen consumed per unit of time and the amount
of carbon dioxide produced in oxidizing the food substances. The ratio
of the CO? produced and the oxygen consumed is called the respiratory
quotient or Rs Q. The numerical value of R. Q. mey be used to indicate
the relative amounts of food materials used as fuel in the body. If
carbohydrates only are being burned the R. Q. is 1.0. Protein gives an
R. Q. of about 0.8 and fat 0.7. The R. Q. values exceeding 1.0 indicate
that additional amount of carbon dioxide is liberated from one sources--
probably from the bicarbonates of the blood.

Chemical changes in. the organism which provide energy for vital
processes and activities are called metabolism. The gas exchange between
‘the organism and the surrounding water or air is one of the most imvortant
parts of the metabolic processes. The rate of such exehange, determined
when the organism is at comolete rest, is known as "basic metabolism";
it représents the minimum requirements necessary to sustain life. Its
determination in human beings is frequently made by the physician in
the course of his search for the cause of an ailment affecting his patient.
Physiological literature contains numerous data on the metabolism of
man and higher animals in health and disease but comparatively little is
knovm about the metabolism of lower forms.

‘When the receding tide leaves the seashore exposed, many of the
marine organisms inhabiting this zone withdraw into their tubes and
burrows, or tightly close their shells and suspend many of their vital
functions. The oyster is one of these animals of the tidal zone capable
of remaining inactive for hours and days. When it closes its shell and
stops ventilation of the gills, the ciliary motion of the gills and mantle
ceases and respiration is suspended. The heart beat becomes slow and
irregular and there is no exchange of gases and other products of me-
taholism between the body and the surrounding water or air. The limited
reserve of oxygen in the shell liquor and in body fluids and tissues is
used up and the organism incurs an "oxygen debt" which, as we shall see
later, should be "naid" when the shell opens again and normal functions
are resumed. It is therefore impossible to speak of the basic metabolism
of an oyster in the sense the term is applied to mammals. The minimum
requirements of an oyster for oxygen can be determined, however, under
certain specified conditions, namely, when the oyster maintains a steady
ventilation of its gills by pumping through them a current of water con-
taining neither food nor any irritating substances.

Raw Cee

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> zi ow SR * eH es (i LAG feat tonp

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we <4 CG OW Gare Bele tas «| weatplces:

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is. aa Severe see wi lp Lay i Pune Inte
,i tay ats Iw @ ~ p LL ania

L

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igs Fe mit D'S ee
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aqsti ioe Se tert
et gal wilt) er Airy, at?
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» eG gehua @ pid ‘le Gira nit

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eieysyewd vat or) a)

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a se Se lente atkie badd eno, cE sinoitonvt
] ae rte gol ueliqant gointamy to «(=P
vied aot Rigs fro P hist wi “In nerfaltingy aqors —
wl, tae ine Pibtledeus ef neotiotiqewt bro aopsed,
ewe wie oe Sioa Yo apiece Os at oriedt baa se ligerrt
; tedbuane ‘oT ile v> THK gn tewoite ptt Bae ghad 4: noowsod’ ae onfsg”
» 795 (2) tal Meinl) god Gb Aan seopit ELode ed ox mugyxe Jo ovtenet
gaa f aw te folie "eo nye me ewont- metenyio ons bok quboee
eeoleivet Cacrion imc ALi neege Five ots nadw Maja" od ‘Atwerth yievar-
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;
: gute. we aciannen oF bodtque AF aes ed? oxgoa ody A} yese~o ae. To”
- orwend. jutimiand. wf abe pigeka Sel Teleco. co Yo mer :

0 ofostizes 2 su er @bt! yalieewt Pr crud

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stog Toler ‘le tabrae a eats (Quen) grigque “a altig afd)
Ted whe gAariari “= wt bool

- EC =<

We know that physical exercise increases our rate of breath-
ing. Likewise, the oyster consumes ‘more oxygen when its shells
move more frequently than when they remain steady or are brought
together only occasionally. In conducting a metabolism test in
oysters, it is therefore necessary to avoid conditions which may
cause excessive shell movements and thereby increase the consump-
tion of oxygen. This can be attained by selecting healthy oysters
and keeping them at a constant temperature in filtered sea water
which contains no food and is free of any pollutants which’may
stimulate- the highly sensitive neuromuscular system of the mollusk.
Furthermore, shell movements of the oyster. must be watched all the

;,r, time when the test is made, because no oxygen is consumed while

the valves are closed. The failure of previous investigators to
observe these precautions leads to great confusion in interpreting
their-data,

. The old method consisted in placing the oysters in a small
closed container filled with sea water and determining its oxygen
content at the beginning and at the end of the test, paying no
attention whether the oysters were open or closed. The results of
such experiments are erratic and unpredictable,.

The more accurate test of oyster metabolism, used. in the
present investigation requires a rather complex apparatus... It
consists of a. large supply of filtered sea water which is run
through a.small chamber in which the oyster is; kept. . By testing
the water before it enters the chamber and after it has passed -
through it, it is possible to compute. the amount of oxygen re=-
moved by the oyster in a given period of time. The rate of flow
of water is regulated by a constant head and the temperature is
kept at a desired degree. Oysters are starved for 2) hours before
beginning the experiment to avoid the effect of feeding. Their
shells are thoroughly scrubbed to remove all organisms attached
to them, and after that they are painted with melted paraffin.

The tests, made only with adult oysters of marketable size,
were designed to answer the following questions: (a) what is
the minimum requirement of oxygen for an adult oyster, (»b) are
there significant changes in oyster metabolism during various
seasons of the year, and (c) are there significant differences
in the respiratory quotient of oysters of different sex and during
cifferent seasons,

In order to determine whether there is a significant change
in the rate of metabolism during the various seasons, each oyster
used in the test was marked by engraving a number on its shell and
was kept in sea water either in a live box susvended from the picr
in the harbor or in a large outdoor tank filled with sea water,
Regardless of the season, the rate of Op-intake was determined at
the temperature of about 25°C. Records were obtained for eleven
eysters which were tested at various intervals from July 190 to

.

= 3h =

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Aevets ww), Wentané' ev. Threask {O° 2 peoda To orwlaings) ol)
O2 CRD cit pos! Cloves akoltw te terasy etew tahiv mistuge

- i

July 1941. From the results of these tests summarized in Table 1] and
from observations on other oysters presented in Table 2, two inferences
can be drawn: First, that the minimum oxygen requirement of an adult
oyster under the condition of the experiment varies from 1.1 to 5.8

cubic centimeters of oxygen per hour. Secondly, that oxygen consunption
during the fall and winter months is less than during the summer. Addi-
tional observations were made to find the reason for these changes in the
metabolic requirements. It was found that there was a marked decrease

in the rate of oxygen intake immediately after the completion of spawning.
The data summarized in Table 2 clearly indicate this trend. It is knovm
that in spawning the oyster loses a considerable portion of its solids
which are replaced by water. This undoubtedly is the principal cause of
the reduction in the rate of 02-consumption by individual oysters»

In several instances the oysters spawned during the test, while
they were still in the metabolism chamber. Each time this happened the
rate of oxygen consumption immediately increased by as much as 1% due
to the presence of the discharged sex cells in the water. From this
observation inference is made that the oxygen demand of the sex cells
inside the gonad is much less than after their release from the body.

Loss of gonad material is not the only cause for the decreased
metabolic rate during the fall and early Winter, We know that this is
the period when oysters accumulate reserve material and:fatten. It is
reasonable to assume, therefore, that a low metabolic rate is somehow
associated with the storage of glycogen because it is generally true
for all animal forms that a gain in the weight of their bodies results
from the failure of the organism to burn the supnly of food which it
consumes. JI hove that our further investigations will throw light on
this interesting phase of oyster metabolism which is closely related
to fattening.

Under stable conditions of the environment, i.e., when the tem-
perature, salinity and pH of the water remain constant, the intake of
oxygen by individual oysters continues at a Se! evel fora ee

eriod of time.

A decrease in the pH reduces the oxygen consumption, and at pH 5.5
respiration slows down to less than 10 percent of its normal rate.

A sudden decrease in the salinity of water from 31 to 2h o/oo
resulted in an increased oxygen consumption. Whether this effect holds
true for the greater change in the concentration of salts will be shown
by further experiments which are now in progress.

The respiratory quoticnt (R. Q.) was found to fluctuate from 0.7
to 1.2 with no significant correlation with the sex of the oyster or the
Season of the year.

Oysters which were kept for a long time out of water show an in-
creased demand for oxygen during the first hour of the test. This is due

- 35 -

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to the depletion of the oxygen supply in their tissues--the so-called
oxygen debt. After the demand for O92 is: satisficd, the intake of,
oxygen falls to its normal level.

Several conclusions of practical value to the oyster growers can
be drawn from these studies of respiration. Since the oxygen demand
of oysters is greater during the spawning season, an additional supply
of oxygen, greatly in excess of the normal requirements of adult
oysters, is necded for the spavm. It is, therefore, important that
in selecting the spawning grounds the oyster growers are certain that
the water near the bottom is well oxygenated.

° After the oysters are removed from water and kept in the air for
several days, their metabolic rate.is greatly increased to satisfy
the incurred debt of oxygen. This fact.should bé kept in mind when
oysters are conditioned for the market in purification or storage

tanks which are frequently overcrowded and the water thus is Subject
to oxygen depletion.

An increased acidity of sea water measured by the decrease in
its: pH value reduced the rate of respiration and creates conditions
unfavorable for oyster metabolism. Acid conditions on: oyster bottoms
may be caused by overcrowding, fouling of shells and pou. of
water _by chemical wastes.

Novstens of good mete cannot be produced in the waters con-
taining substances which sunpress their normal rate of respiration.
Likewise, good, fat oysters are not expected to be found in waters
contaminated with trade wastes or other materials which irritate their
neuromuscular system and cause increased shell movement. The presence
of these foreign substances in Seg: waters increases the oxygen
demand of oysters and results in the burning up of reserve material
in their meat. Oysters grown under these conditions fail to fatten.
and are generally poor. Sasa

53608

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a, fe Ht ego . . S Tedelithae ap Gala
Peesifhs v4. °h 9 ari ’ Lidnipa? ony Selsey atnet
é i= inziuiog mye

a) gears «tt ol &

vid ieee pepe

he pfen od >. poy sata Or hel
‘ellots) @ ~S20u0 wo? olin sh
<uttonntawese Mf feigunt bef, ynar
Sudan (esiheptio V4 sHge
Femme wtlivp boog, 6 erate T.
eeepqus ddliie 2osnétedu2 anbidel

rib. jeite “:aktet: Wipailtcmt eth . _

TABLE 1. -- Seasonal changes in the oxygen intake of adult Long Island

oysters about 10 cms. long:and 7-cms. wide. ‘All tests made at 25°C.

Oysters 50-62 were tested in 1940 at Woods Hole.

at Milford, Connecticut.

OYSTER

NUMBER

50
pa
52
53
D5
56
62
M-1
M-l,
M-6

M-9

(Editor's note:-=

All other tests made

July Aug. Oct. Nov. Dec. Jan. Feb. March Apr. May June July
3.51. 2.92 Oe | ae ING Hel es
2.69 230 es;
25) OG: dee 3 17 on The
3.08 (a5
3.65 2.10 205) Zee 1.9 3.3 3.0
2.86 Met ee 2.0 7 SCA)
3.28 1.8 . 1.u 252 3.6) 360
2.4 Dye Ope lee
20h Cet 267
269 20) Sek
era 202. ell

No records were noted for September. )

29S

—
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(Anite oe >t ei Seer does a <peten ©) vou uit)

x

re
i

~ = =

TABLE 2. -- Mean O9-intake, in ml per hour, per oyster, determined
- in July, before spawning, and two weeks and 1 month after spawning.

The figures are the mean values computed from 6 observations made

“

at half an hour intervals.

TIME OF OYSTER NUMBER
OBSERVATION 1 2 3 h 5 6 7 § 9 10 12

- Before. Pees
spayvming

“duly” 4.29 3.39 3.00 5.13 4.01 2.53 5.8 4.89 3.11 .3.64 5.17

Tyo -

weeks

after

sparming :

August —~ 73 3.02 2.8) 3.89 3.21 3:10 h.11 4.00 3.08 2.78 5.10
MOncue warts . os

month

"after

spavming

August 3296 2638: 11593 3.639 2.26 3403 2.95 3.12 2253 2029 N37

- 38 -

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a
7 .
“a bis
- é =
ra _
2
2
oy
-
.
Or _ 7 - :
= -

TABLE 3...-- Oxygen intake in ml O5 per hour of adult oysters from
Long Island Sound, about 10 cms long and 7 cms wide, determined in
July, before spawning. t9 ~ 2h-25°C. Nos. h,8, and 11 are females,

the others are males,

HOURS "OYSTER NUMBER

APIS RISTART stele teeter jritielinanh). 16 Cie emekmengeneslONe 1!
0.5 e52 1679 2.93 5.07 3.90 1.97 6.31 80 3.62 3.73 4.76
1.0 _ 5elh2 2.63 2.97 5.07 h.21 2.48 5.69 4.69 3.28 3.80 4.85
Hoe 4.28 3.00 2.90 5.18 2.00 5.69 5.0 3.79 3.66 5.15
2 <O.case® (oysdly 3.2 2686 5 .) tns0002-69' S90. leSguseounsesons.o5
255 1.39 WWOK 3466.2.970 S.2ly 07) 2.97 5259 5507 2.9303 25205. 71
3.0 ,, ° 3.93 3.86 3.35 5.1h 3.97 2486 5.83 5.2h 3.0h 3673 Sobli
345 3.69 3.76 5.0 3493 2679 * be59 3407 4.92

MEAN 4s29 3.39 3.0 5213 01 2153 5.8 89 3.11 3.6 5317

- 39 -

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——————————— ——

EFFECTS OF TURBIDITY ON FEEDING. OF OYSTERS

Dr. Victor L. Loosanoff

Aquatic Biologist, U. S. Fish and ‘ldlife Service

Our oysters aré shallow water mollusks normally living in gulfs,
bays and harbors in which rivers and creeks discharge their waters,
Because of the differences in river discharge the conditions in such
brackish bodies of water may vary a great deal within a short period.
To meet such changeable conditions ‘nature endowed oysters with the
abil:ty to withstand rather wide changes in their environment. “e
‘ alreacy knorr of the ability of oysters to survive sharp changes-in
temperature or saiinity, and may predict with reasonable accuracy
how such changes would affect the oysters. Hewever, there are sev-
eral other factors in oyster environment, vhich are considerably
affected by river discharge, but of which we have a rather limited
knowledge. One of these is turbidity. =. os : °

A discussion of the effects of turbidity ppon oysters is of
especial interest to a large group of oyster growers because many
of their cultivated beds may be sometimes included within the areas
the waters of vhich are rendered turbid by man's activities. In
other words, besides the turbidity which is caysed by large quan=-
tities of inorganic and organic substances brought down to the
estuaries of the rivers, such as the Mississippi, we may face condi-
tions when the waters of oyster-producing areas are made turbid by
the dredging of channels or by other operations in which the upper
layers of bottom ‘soil are disturbed, Naturally, it is of interest
to all of us to know how different concentrations of turbidity-_.---
creating substances in the water affect the oysters, or at least
some of their activities.

Quite extensive studies of the gross effects of dredging and
resulted turbidity upon oysters were made by G. R. Lunz, Jr., for
the U. S. Engineers! Office in 1936. Dr. Lunz concluded that the
dredging operations conducted in the Intracoastal Waterway of South
Carolina "were not injurious to oysters and killed only those
actually buried by spoii", He also concluded that dredging operations
did not affect or influence the spavming and setting of oysters, and
that "no connection can be found between the yield of ounces of canned
oyster meats per bushel and dredging operations.....".

Judging by Lunz! results one may conclude that oysters remain
to exist almost undisturbed in water the turbidity of which is greatly
increasccd, There is no doubt that Dr. Lunz! observations were correct
for the area where he did his work. However, his conclusions are some-
what contradictory to the findings of Kellogg, Yonge, and to a large
extent to our ovm, namely, that oysters, as. well as other closely re-
lated mollusks, are primarily clear water inhabitants and that they -

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can feed most efficiently only when the water is relatively free of
solid particles. Therefore, to verify at least some points of the
question in dispute we thought it desirable to determine how different
concentrations of turbidity-making substances would affect the rate of
water pumpine and, therefore, the feeding of oysters. Several years
ago we began to experiment at Milford Laboratory and now certain results
of our work may be reported and some deductions made. I would like to
take the opyvertunity to express my appreciation and thanks to Miss
Frances Tommners, who so ably assistcd throughout these studies and to
my colleague, lr. Janes Engle, who participated in the early stages of
the work.

Our experiments consisted in observing the changes in the rate of
feeding and shell movements of the oysters when the concentrations of
turbidity in sea water were changed. “le used from 0.1 gram to .0 grams
of turbidity-creating substances per liter of water. In the first series
of experiments fine silt collected from the tidal flats of Milford Harbor
was used. This silt was placed in suspension in the water and filtered
through a fine nets Later the heavy scdiment consisting mostly of sand
particles was discharged, while the lighter portion was dricd and pul-
verized. During the entire series the silt of the same batch was used.
At the beginning of cach experiment the needed quantity of silt vas
taken from the air-tight jar and placed in a vessel containing the nec~
essary quantity of water and then stirred until all the particles of
silt were in fine suspension. In addition to natural silt we used a
clay-like substance - kaolin (aluminum silicate), chalk (calcium carbonate)
and a few experiments were conducted with Fuller's carth.

All the substances tried in our experiments may be found sometimes
under natvral conditions in suspension in inshore waters. Silt, which
is a mixture of organic and inorganic substances, is, of course, very
common and is always present in varying quantities. Dredging, or heavy
rains which increase river discharge, usually increase the quantities
of suspended silt. Clay-like substances, such as kaolin, are also of
wide occurrence, sometimes forming a definite stratum under the oyster
beds or are encountered in various mixtures with sand. Large quantities
of clay are also brought dovm by thc rivers. Chalk, or calcium carbomte,
may sometimes be found in the regions of the oyster beds. The shelis of
the oysters, as everyone knows, are made mostly of this material. Fuller's
earth consists largely of shells of small water plants called diatoms.

In our first series of experiments the water was made turbid by the
addition of different quantities of silt. “Ie noticed that even when
suck smal] quantities as 0.1 gram per liter were added the bchavior of
the oysters was noticeably affected (Table 1). Usually the type of
their shell movement changed and the rate of flow considerably decreased.
In the most scvere casc such a decrease, as compared with the rate of
pumping before the oystcr was exposed to turbid water, was 87 percent.
For the group as a whole, however, the reduction in the rate of pumping
averaged 57 percent. In other words, when turbidity was such that there
was one part of silt in 10,000 parts of sea water the average pumping
rate of the oysters was less than half of that recorded under normal
conditions. :

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Concentrations of 0.25, 0.5, 1.0, 2.0 and .O grams of silt
per liter of sea water were later tried using a large number of
oysters. The results showed that in all groups there was a sharp
decrease in the pumping rate (Table 1). When the concentration
of silt in sca water was 1.0 gram per liter or more the average
rate of pumping decreased more than 80 percent reaching approxi-
mately 9 percent in very heavy concentrations of 3 or grams per
liter. Although such heavy concentrations seldom occur, they may,
nevertheless, arise during heavy floods or be created and maintained
for long ‘periods within the arcas where intensive dredging opera-
tions are in progress, especially if the dredging methods used are
of such type that they will altow large quantities of mud to escape
overboard. :

’ As a rule; the experimental oysters were filtering off large
quantities of silt. Nevertheless, particles of silt passed through
‘the gills and. some was found in the stomachs and intestines-of the
oysters, In other words, our observations showed that although
their efficiency of feeding was greatly depressed, the oysters
could ingest small quantities of solid particles even while surrounded
by very turbid water. Some oysters, however, stopped reed tag en=
winedy although their shells remained open ane mOViNnge

The shell movements of the oysters were markedly asfeetea he
the addition of silt to the water. Thais was especially well
demonstrated in stronger concentrations. Usually the shell move-
ments became of greater amplitude and their character was of a
different type than that observed in the same oysters under normal
conditions. This tyve of shell movement was associated with ejec-
tion at frequent intervals of large quantities of silt which was
accumulating on the gills of-the oysters. This tyve of shell move-
ment closcly resembled that observed in our experiments where. the
oysters were exposed to large quantities of microorganisms, such
as Chlorella, Nitzschia or commercial yeast. In general, the results
of the two studies showed a definite similarity in the behavior of
oysters in turbid waters regardless of whether this turbidity was
caused by a large numbor of microorganisms or just silt.

In almost all instances vhen the flow of silt-laden water was
substituted with rcepvlar sca water the oysters quickly recovered.
The character cf their shell movement soon changed to normal and
ths numping increased to the normal rate or even exceeded it. This
cleansing reaction was also notcd in our expcriments on the feoding
of oysters and was usually associated with the change from water
too rich in food forms to normal conditions.

In the next group of experiments turbidity was created by add-
ing to the water different quantitics of kaolin ranging from 0.1 to
4.0 grams per liter. The results of these experiments were very
Similar to those obtained when silt was used. .Again we found that
the addition of even such small quantitics of kaolin as 0.1 gram
per litcr noticeably decreased the pumping rate of the oysters

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(Table 1) and changed the character of their shell movement. As the
concentrations were increased, these reactions became more and more
prominent. At high concentrations, such as 2.0 or ,0 grams of kaolin
per liter of sea water, the shell reaction was cspecially vigorous show-
ing that the oysters were cleaning thcir gills from foreign particles,
Nevertheless, even in high concentrations the majority of the oysters
kept their shells open most of the time and pumped some water, However,
judging by the reduction of the rate of pumping and changes in the shell
movements, it was evident that the oysters were under unfavorable condi-+
tions.

Again, as in previous experiments, the oysters wpon return to
recular sca watcr quickly resumed a normal or even more than normal rate
of pumping as if to cleanse their gills. Their shells also soon began
to move normally.

Experiments with chalk (calcium carbonate) fully corroborated the
conclusions obtained in the two previous scries, namely, that the
presence of turbidity-creating substances in the water greatly reduced
the rate of pumping, and therefore feeding, of oysters and affected the
character of thcir shell movements. The latter was especially evident.
The experiments with Fuller's ecarth were conducted only with a small
number of oysters and onlv one concentration of 0.5 gram per liter was
used (Table 1).

In our experiments the oysters were kept in turbid water for con-
naratively short periods rarely excceding six hours. Therefore, we
cannot say definitely what would have happened to the oysters if the
experiments had been carried on longer. Nevertheless, on the basis
of our observations we may safely conclude that oysters are vory sensi-
tive to the presence in the water of turbidity-creating substances, such
as silt, clay or chalk. “hen the concentrations of these substances ere
increascd the quantity of water pumped by the oysters through their gills
is sharply decreased. Our data also indicate that there may ba a corre-
lation betyeen the increase in turbidity and the decrease in the rate
of pumving. In strong concentraticns oysters may cease pumping entire-
ly. Therefore, we should always consider with suspicion and caution
any condition where the turbidity of the sea water is raised considerably
above its normal level, be it because of a heavy river discharge or
because of man's activities, such as dredging, well drilling or similar
operations.

In conclusion I would like to emphasize that our studies were made
only with Long Island Sound oysters which are accustomed to living in
comparatively clcar water. We know, however, that in other parts of
the country oysters live and propagate in very turbid water. At this
time I am not prepared to offer an explanation for this phenomenon, but
it may be possible that we are dealing with different races of oysters.
It is my opinion, nevertheless, that we cannot discuss intelligently
the effects of turbidity unon the behavior of oysters unless we have
in our possession certain facts based upon extensive experimental obser-
vations. Therefore, I feel that ovr studies of the effect of turbidity

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on the rate of water pumping by the oysters of Long Island Sound

are a necessary step in our understanding of oyster behavior and

I hope that similar studies will soon be ccnducted in other geo-
graphical sections of the country where oysters live under different
ecological conditions.

i)

Percent reduction in pumping rate of oysters
subjected to different concentrations of
turbidity-creating substances. Rate of
pumping in sea water at the beginning of
the experiments was taken as 100 percent.

TABLE

SUMED sy Lon tes Latcr eee het De ERAGH SRE DUC Ole
SUBSTANCE CONCENTRATION IN RATE OF
USED gr/lit PUMPING IN %

57.0
(EOS
68.5
81.0
85.0
Biol
94.0
6.0
68.0
68.5
{LO
78.0
85.0
38.0
76.0
87 20
89.0
60.0

SILT

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ON POSSIBLE PHYSIOLCGICAL SPECIES IN THE OYSTER, OSTREA VIRGINICA
as ; Dr. Leslie A. Stauber

Department of Zoology, Rutgers University

It should be clearly understood at the beginning of this report
that my role is a minor one, that the actual data to be discussed are
mostly the results of the long term efforts of others who have generously
made available to me for study even unpublished material. That physio-
logical species of Ostrea virginica might exist was first suggested to
me about 17 years ago by Dr. Thurlow C. Nelson. I believe the data to
be presented here resolve some of the difficulties which, at first, seemed
inccnsistent with such a view. Though the data are largely the findings
of others the responsibility for the intervretations is clearly mine.

It is important to note, that, prior to 1931, for both the waters
of Prince Edward Island, Canada and of various parts of the United States
various authors stated 20°C. to be the water temperature at which spaym-
ing was initiated in the Eastern oyster, O. virginica, under field con-
ditions. The most extensive data are for the waters of Barnegat Bay
where observations were made by Dr. Julius Nelson and Dr. T. C. Nelson
for almost 50 consecutive years. For over a decade these observations
included water temperatures automatically recorded by a continuously
recording thermographe From this body of data the essential relation-
ships between water temperature and the spavming of oysters on the
oyster beds were firmly established and have been amply confirmed.
These relationships may be stated simply as follows: On an oyster bed
with the gradual rise of water temperatures in the spring of the year
oysters begin to feed, grow and become sexually rive but there is a
minimum temperature requirement for the initiation of the act of spayn=
ing. Not all oysters spaym when this level is reached and some will
spaym experimentally at lower temperatures anc under other special
laboratory conditions. There may even be some oysters which naturally
deviate from this minimum level especially under unusually rapid
temperature rises but the year after year picture for a carefully
studied body of water is essentially the same - no spavming until the
minimum temperature is reached and then mass spavming of a significant
proportion of the oysters on the beds Subsequent spawnings may occur
at highcr than the minimal temperature but in the autumn again after
temperatures fall below the observed minimum no further spawning is
noted,

The kinds of data used to drav’ such conclusions are gathered by
observing the meats of the cysters themselves either in the gross or
in section, by examination of water samples for the distinctive larval
stages of the oyster with their known cycle of development or by the
collection of recently attachcd young oysters set on clean shells
regularly exposed, rcmoved and cxamined. All mothods give significant
data but, for any one arca, one or more of the methods may be easier té

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apoly especially when dealing with large bodies of water and widely
scattered areas of oyster bottome

The first published evidence that not al] oysters in the
geographical range of 0. virginica spawn at a minimum level of
20°C. is that of Hcpkins in 1931. Reporting for Galveston Bay,
Texas he found that spayming did not start until 25°C. was reached
and that when 20°C. was reached the oysters were just beginning to
develop mature egzs and sperms. lLoosanoff (1932) reported sinilar
findings. for the James River. The next deviaticn reported was that
of Locsaneff’ and Engle in 19h0 who claim a minimum spayming temper-
ature cf 16.4°C. for Long Island Sound. It should be noted, however,
that an unpublished deviation had been observed elsewhere. When Dr.
T, C. Nelscn’ shifted the scene of his activity frem Barnegat Bay to
Delaware Bay, N. Je, in the late twenties he scon learned that spawn-
ing phenomena were nct the same in these two locaticns. Indeed, on
several occasions he noted that spavming and setting might occur in
Barnegat Bay before spavming had begun in Delaware Bay although the
latter was farther south and warmed up at least cquallyas rapidly.
Subsequently the findings of Dr. Nelson, Nr. J. Richards Nelsen and
myself over the folloving decade and a half amply. support, I believe,
the contenticn that mass spayming cf oysters over the larger beds of
oysters in Dolaxare Bay does not occur until water temperatures reach
25°C. (I think we must cxclude the very shallow inshore areas from
consiferation because of the greater amplitude cf the teniperature
fluctuations noted in then.)

It might then be stated that three types cf cysters exist on
the Atlantic seaboard cach of which shows a diffcrent minimum ‘spaym-
ing tenperature. The great problem in accepting this viewpoint was
the apparent difficulty of reconciling the 20°C. minimum spawning
temperature of the cysters of Eastern Canada with that of a lower
minimum spayning, temperature for Long Island Sound, geographically
some 600 miles airline nertheast cf Long Island Sound. The year
1937 presented the oovcrtunity for resolving this problem. Figure
1 is a graph on which are plotted the published data of Loosanoff
and Engle for bettcm watcr temperatures at three stations in Long
Island Sound off Stratford Point in 10, 30 and 60 feet of water dur-
ing the surmer cf 1937. Alsc plotted are the published findings of
Medcof for the same year (1937) for the waters of Bideford River,
Prince Edvard Island, Canada and cur cym unpublished records for
several scattered stations in the New Jerscy waters of Delaware Bay.
It is immediately evident from this figure that practically no over-
lapping cf temperatures occurs in the three arcas and’ that they fall
in the sequence of the minimal spavming temperatures of 25°, 20° and
16.),\°C. reported, with the Bideford River falling between those. of
the other two though gecgraphically so much farther north. It might
be claimed, however, since all three areas do'reach 20°C. at some
time in the summer, that the same 20°C. temperature could cenceivably
initiate spavming in each area. For. Delaware Bay the water temper=
ature was maintained: above 20°C. after May 2h, 1937, in Bidefcrd River
after June 25 but in Long Island Sound net until after July 12 ora

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spread of 18 days for the three areas. The times given by the observers
for the first general spawning in the areas mentioned, however, (exclud=
ing minor spaymings of inshore areas) are July 7-8 for Delaware Bay,
June 26-30 for Bideford River and July 3 for Long Island Sound, a spread
of only 12 days for such widely separated areas. To me this seems more
than coincidence. I regard these observations as a very likely indica-
tion of the presence of three physiclogical varieties of oysters with
different minimum spavming temperatures, most probably the 25°, 20° and
16.1°C, values already mentioned.

let us look at the problem in another way. Figure 2 represents
the annual cycle of water temperatures for Delaware Bay where the 25°C.
minimum spavynming temperature occurs. ‘Je sce approximately a six-week
period with temperatures above the minimum spavming level. At the other
extreme we see a period of about 15 weeks with temperatures below 5°C.
This 5°. temperature according to the work of Galtsoff, Nelson and others,
represents the point at which ciliary activity of the gill, shell movements
and heart beat cease in the oyster. It is a point limiting the activity
of the oyster. Actually in Delaware Bay no food is found in the oyster
stomach until acoproximately 10°C. is reached. There remains then a period
of 11-12 weeks in the spring for growth and maturation of sex products
and a similer period in the autumn for growth and storage of food reserve
for the so-called winter "hibernation" period.

For Barnegat Bay in 1933 there were 18 weeks above the minimum
spayming level of 20°C» and 9 weeks each in spring and autumn between
5° and 20°C. If these intervals represent a favorable balance between
periods for growth and for reproduction in the oyster on the natural
oyster beds and if the 20°C, sparming level were the limiting factor
throughout the range of the species O. virginica then oysters in Long
Island Sound and Texas might not have persisted in their respective
localities; in the latter case because of reproductive over-activity
(33 weeks above 20°C.) and in the former case because of prolonged hiber-
nation or reduced opportunities for spavming (9 weeks above 20°C.). Many
investigators already believe that the explanation for the great masses
of oyster shells in the kitchen middens of Maine can best be explained
in such a fashion by the failure of favorable spavming conditions to
occur probably due to a combination of climatic conditions plus the
depredations of man.

Table 1 illustrates this point in another way showing the water
temperatures observed in several geographical areas. Actually, Delaware
Bay seems to be the borderline between more northerly areas with brief
or no periods of water temperatures above 25°C. and more southerly areas
with few or no consistent temperatures below 5°C. Obviously, conditions
along the sea coast from Long Island Sound to Texas are so different that
the assumption of biological varieties of the oyster would make more
reasonable the observed distribution of the oyster since it would make
possible combinations of periods of growth and reproduction more consistent
with the survival of the species. However, it must be noted that for any
given species there are extremes beyond ~chich ne further such combinations
are pessiblc. One of these for the oyster is the cessation of ciliary

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activity. Thus the total number of such combinations is limited.
In the case of the oyster the evidence presentcd here today seems
to indicate three varieties.

Furthermore, as Setchell, and Nelson and Crozicr have pointed
out, there are certain éritical temperatures in the activitics of
living organisms associated with the initiation of vital processes
and that these points do not form a continuous intergraded serics
but a discontinuous one with the critical points most frequently at
W.5°, 9°; 15°, '20°3..25°, 27° and 30°C. Thus, the mumber of possible
varictics may be limited to the three which now seem existent.

There is no doubt that much more data necds to be accumulated
before a more accurate picture can be presented but the broad
indications secm already to have been outlined. Similar evidence
is available that the oyster drill, Urosalpinx cinerea, is represented
by three ovipositing varietics in Narragansett Bay, Delaware Bay and
Hamoton Roads. In fact the data for the oyster drill are in some
respects even better than for the oyster. Here the response of

egg-laying is an individual one rather than the mass spawning reaction
of the oyster and lends itself to casy observation in the laboratory
or in experimental cages in the natural habitat. The three biological
varieties oviposit at) 10°, 25° and 20°C:

Geographical isolation is recognized by biologis sts as an
important factor in the origin of new specics. For the thousands
of years before the white man began to shift oysters from bay to
bay on our seaboard, the degree of isolation of the oysters of Delaware,
Barnegat and Chesapeake Rays and Long Island Sound was practically
complete. The oyster, as we know it, is not an ocean but an estuarine
dweller so it is cxtremely difficult to conceive that interbreeding
at the margins of the group areas could have occurred in recent time.
Assuming that mutation occurs in oysters as in other forms of life
the existing geographical isolation and the time available would have
been favorable for the action of natural selection and the production
ef biological species of the oyster.

Although there is no supporting evidence available I believe
other organisms along our scaboard will prove divisible into similar
races. For example, judging by the range of Venus mercenaria and
the hydrographical conditions reported I scriously question Belding's
report of sparming in Massachusetts at 2 minimum value of 2h-25°.
though I feel certain that Nelson's value of 25°C. for Delaware Bay
is well substantiated.

“hether these are true species in the usual sense of the word
can only be determined by experimentation. It should be recalled,
however, that interbreeding can be prevented by lack of coincidence
of soxual maturity as well as by other kinds cf isolation.

If these physiological varietics are as real as they seem to be
there arc a number of practical implications for the oyster industry.

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Suppose, for example, oysters from Chesapeake Bay with a probable
minimum spayming temperature of 25°C. are introduced into Long Island
Sound for spavming purposes. This temperature rarcly if ever is reached
in most portions of Long Island Sound. How then can interbreeding or
even spayning occur as a.result of this procedure? Loosanoff and Engle
have shorm that the minimum temperature for spawning of the Long Island
Sound oyster is 16.°C. If transplanted to Chesapeake Bay they would
probably begin spatming in late April or two menths before the local
oysters would spawne Most likely the introduced Sound cysters would be
spavned out before the local ones begane No interbrecding is likely if
such a difference in spawning dates occurs.

It is cvident that many more observations are necessary to test
the hypothesis pronosed but before that evidence is available I believe
we can draw one conclusion cencerning the rchabilitation of oyster beds
in any given arca. Until the biologist can breed in the laboratory a
new and better varicty of oysters the oystermen would do well to special-
ize with the cyvsters of his local area and take advantage of the selec-
tive processes cf nature which for thousands of years have produced
oysters cspecially fitted for survival in that given locality.

TABLE 1. Water Temperatures - Eastern and Southern North America.
LOCALITY & WEEKS OF DURATION

REFERENCE Above 25°C Above 20°C Above 10°C Below 10°C Below 5°C
George's Bank @) 6) 22 30 19
(Riley) Highest. crvise mean 16.5

Prince Edvard Is. ) 6—8 Ice="ov. At least
(iedcof ) to May 28

Long Island Sd. 9) 8-9 27-28 2h-25 13
(Loosanoff ) (Riley)

Barnegat Bay 3 15-18 29 23 1h
Nelsen) (not continuous)

Delaware Bay 6 17 31 21 15
(Staubcr)

Solomen's, Fd. 1+ ? 17 33 19 h
(Heweembe )

Virginia 9 22—2); 35=<l1 11-17 1-9
(Fedorighi )(Galtsoff)

Beaufert, S.C. 19-21 29 52 8-11 fe)
(Smith)

Apalachicola, Fla. 19-21 29 52 O (?) 0
(Pearse ) (Smith)

Louisiana 18 28.5 52 ) (0)
(Kavanagh ) (Owen)

Texas 27 33 6 6 (@)

(ifoore ) (Hopkins )

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EFFECTS OF POLLUTION AT BALTIMORE ON pH AND OXYGEN CONTENT OF WATER
Fred J, Sieling

Biologist, Maryland Department of Research and Education

Since the end of the war, interest has been revived in water
pollution control. As a result of this and the fact that the offend-
ing parties can not now stand behind the Services and declare their
invichbilitvy, it was felt that an investigation of present conditions
was timely. A public ccensciousness of the pollution vroblem is forc-
ing the local conservation agencies as well as federal to take steps
toward rather stiff control methods. Maryland, during the late
legislature, set un a Commission on Pollution Control with an execu-
tive secretary and mcney to enforce its regulation. The Department
of Research and Education of Maryland was designated as their research
agencye

Baltimore Harbor, the second largest port in the East, is
Maryland's greatest pollution problem. As this Department had con-
ducted rather extensive investigations there before the war and during
the early part of the hostilities, ve fclt that we should resume our
investigations, which were halted by lack of man power. Through the
Baltimore City Harbor Board which has provided boats for our use, we
resumed sampling trips in February 19:6. These trivs are made at bi-
weekly intervals, depending on suitable weather conditions, to eleven
stations selected as being representative of general conditions in
the scveral areas of the Harbor. These also form a pollution gradient,

The water at these stations is being analyzed to determine the
following conditions: the temperature; the pH or potential hydrogen,
which gives an index of the relative alkalinity or acidity of the
vater; the oxygen content, the variations of which is indicative of
pollution as well as dencting whether animal life could exist in the
water; the salinity, which is useful to know in connection with the
other analyses; and the ferrous and ferric iron content.

The temperature is taken with a calibrated reversing thermometer
which is attached to a Nansen-Knudsen water sampler with which the
water samplcs are taken. The pH is determined by using a Becknan pH
meter with a flow electrode. Ths oxygen is determined by the modi-
fied Winkler method. The salinity is determined by titration with
Silver nitrate. A roush qualitative detection method is used in the
field to determine the ferrous iron content. The fcrric iron samplcs
are treated and analyzed at the laboratory with an clectrophotometer.

large natural oystcr bars lie across the entrance to Baltimore
harbor and were oncc grcat producine arcas, which now are nearly
barren. This condition, it is contended by some, was caused by :
pollution. Last year at this mecting, Messrs. Engle and Beaven

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reported on the high oyster mortality on the upper Bay bars. Their
conclusion was that fresh water had killed the oysters,

Industrial and municipal wastes are both large factors in the
pollution of Baltimore harbor. The industrial effluent is principally
iron sulphate of which a large amount comes from copperas. The
polluting chemical in this is FeS0),.7H20. This, when dumped into the
Harbor, hydrolyzes to form sulfuric acid and ferrous hydroxide. The
pollutant comes from the steel mills and from the different pigment and
paint manufacturers. Other large sources of industrial pollution are
the industrial alcohol plants, which throw mash into the water, and the
fertilizer vlants which dump quantities of spent sulfuric acid into the
Harbor. Of course there arc many small contributors such as canneries
and small chemical manufacturers whose cumulative effect is undoubtedly
felt.

Municipal wastes have increascd greatly since 190 when the popu-
lation of the City was greatly boosted by the influx of war workers.
Up to that time the City had managed to trcat most of the sewage, but
from then on and continuing to the present time, nearly half of the
seviage of Baltimore City is dumped untreated into the Harbor. The
depressing effect of this on the oxygen content is fcolt over a large
arcae

These effects were first studied by Olson, Brust, and Tressler in
1939-191 and later by Stern and Davis in 192. Several exploratory
trips were made by the author in 1938 but no data were published as it
was fragmentary.

At the earlier date conditions were bad at several areas but it
was decided that further studies should be made before any conclusions
could be drawn. Olson, ct al., started their comprehensive study in
1939 and their data show a high degree of pollution over a wide arca.
Later, after the start of the war, Stern conducted a study over the
same area yith some additional stations being observed. At this time
the degree of pcellution was less than it had been. However, at the
present time, the degree of pollution is greater than during any
previous investigation. These changing conditions were brought about
in the following manner,

Before the war industry and shipping were at a normal levcl and
Baltimore City was trcating most of the scwage. After.the start of
the war industry was converting and not dumping as much waste because
their production was dovm from a prewar level. The sewage had not
appreciably increased and shipping was somewhat below normal, The
steel mills were producing ingots and large plates which use very
little pickling liquor, rather than sheet metal which uses a great
volume of acide The pigment companies could not obtain raw materials
so their waste was far less than previously . Other manufacturers
were affected in a similar manner so that there was less pollution
from industry during the war. However, larger volumes of sewage were
being dumped in the Harbor during this period. Since the end of the

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war, because industry is now producing far above the prewar level,
pollution has greatly increased. Industry has again reconverted to
peace time vroducts which, as stated before, give large volumes of
copperas which is discharged into the Harbor. Small concerns, as
well as the large manufacturers contribute to this condition. Sew=
age also is at a high level.

The enormous volume of copperas discharged into the water has
the following offect. The ferrous sulfate or-copperas hydrolyzes
readily in water solution, lovcring the pH and forming the ccrres-
ponding basc, The rate of hydrolysis decreases with acid concentra=
ticn and the rate of oxidation of ferrous hydroxide depends on the
concentraticn of oxygen in the water. Both the formaticn of sulfuric
acid and the use of oxygen for the conversicn of ferrous hydroxide
to ferrie hydroxide are harmful to marine organisms. The first, be-
oause it lowers the pH to a point which is lethal to marine life and
the second, because it lowers the oxygen tension below the safe linit
for life ef marine organisms, The iren in the water is nct in itself
in sufficient quantities to be lethal, but its effect on the pH and
oxygen is very harmful.

Sewage in the water decreases the oxygen content but does not
greatly depress the pH. The effect is very local and further away
from the source may even be beneficial to aquatic life, though not
conducive to human health.

The approximate lower limit of tolerance cf mzrine organisms
to pH is l.5 and for oxygen is 3.5 cc/l. according to Ellis, 1937.
It will be seen that these lower limits were violated many times at
most of the staticns,.

The denth of water at the diffcrent stations ranges from 10
to 30 fect; tidal variations are not great, being from 12 to 25
inches. The current velocity is variable, ranging from zero to 0.2
knots per hour (Haight, 1930). Winds affect the Harbor waters even
more than tides. Stations were selected as being representative of
the different areas as much as possible and also to make a polluticn
gradient. The station farthest out is just 200 yards frem an oyster
bed. This is at Seven Foot Knoll which is about 5 miles from the
nearest source of pollution.

Discussion of Results of Different Stations:

Station I is lecated on Colgate Creek which is about 10 feet
deep where cne of the larger plants is dumping waste, The pollution
here is mainly copperas or ferrous hydroxide which, as was explained,
lowers the cxygen and pH to a very dangerous point. The average
Surface oxygen concentration during the sixtecn menth period was
0.72 cc/l. and the average pH was 3.3. The ccncentration of oxygen
at tne bettom averared 0.51 cc/l. and the pH there was 3.1. This
is the worst station in the grcup as the readings were ccnsistently.
below the lower limit for life to exist.

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Station 2 is located at the mouth of Colgate creek where the depth
4s 16 fect and sone mixing with other water has taken placee Here the
exygen concentration has risen to heO cc/l. at the surface while the
bottcn is 3.3 cc/l. average. The pH is also higher being 6.e at the
surface and 6.); at the bottom. However, at these two stations it must
be remembered that for lens periods the oxygen and pH are both below
the accepted minimum for maintaining aquatic life,

Station 3 is locatcd near tho mouth of Bear Creek which is one of
the draping arcas for a large stecl plant. Here, a great volume of spent
sulphuric acid is dumped which has been used in pickling sheet metal and
carrics 2 large anount of ferrcus and ferric sulphate. This acid de-
presses the oxygen and pH levels for long pericds of time although the
average is not at a point too dangerously low. The volume of water where
this is dwined is large being nearly 20 feet decp and a half mile wide.
The average oxygen is lhs2 and 3. cc/l. at top and bettom respectively,
and the pH is 6,1 end 6.3. This station is about 5 miles from the nearest
oyster bars. :

Station 10 is lotated farthest from the Bay, being 15 miles from the
nearest oystcr bars. This is in the Patapsco River proper and the depth
is about 30 fect. It is located a mile from a very large sewer outlet
of the municipal sewerage system. Here the cffects cof raw sewage is noted
by the low oxygen which is 3.6 and 2.2 cc/l. at top and bottom respective-

y. The pH is not affected as much, being 6.7 at both top and bottom,

Stations 9, 8 and 7 may be considered in sequence as they are all
in Curtis Bay, ranging from the upper part to the mouth, Station 9 which
is slightly above the main sources cf pollution had an average surface
oxygen of .O and an average bottom cxygen of 1.1 cc/l. The pH was ).7
and 5.2 for tep and bettom respectivcly, Station 8, which is very close
to the sources of pollution, anproximctely .h mile, had an average sur-
face cxygen reading of 3.9 cc/l. and an average bottom reading of 1.3 cc/le
The pH was 5. and 5.5 for top and bottcm. Station 7, at the mouth of
Gurtis Bay, about 2 miles from the source of pollution, showed less pro-
nounced effects. The average surface oxygen was .2 cc/l. and on the
bettom it was 2.0 cc/l. while the pH averaged 6.3 at both top and botton.

Stations h, 5, 6, and 11 are in a direct line toward the Bay and
form a gradicnt from the polluted areca to the water of the Bay. Station
4 is off Sparrows Point, where one of the largest sources of polluticn
is located. The oxygen at the surface was 5.1 cc/l. and the bottom was
2.7 cc/l. The pH was 6.9 and 6.6 for top and bottom respectively.
Staticn 5 is further toward the Bay just off North Point, The pH is
Tel) and 7.0 for top and botton and the oxygen is 5.3 cc/l. and 3.1 cc/l,
for top and bettom resvectively. Station 6 is at the mouth of the Harbor
and presumably affected by the Bay watcr te a considerable extent. The
oxygen averaged 5.6 cc/l. at the surface and 3.0 cc/l. at the bottom.

The pH was 7.5 and 6.9 at the tcp and bottcm respectively. Staticn 11

is in the Ray just outside the Harber and adjacent to several oyster bars.
The average oxygen was 5.0 cc/l. at the surface and 2.9 cc/l. at the
bottcm while the pH was 7.5 and 7.1 for surface and bottom respectively.

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These figures show the decreasing affect of the pollution as you

go farther away from the scurce. Stern, 192, neted ne effect past
Sparrows Point (Staticn h) but here can be secn the depressing effect
much farther cut toward the Bay.

Cenclusions

Frem results cbtaincd in these analyscs it is felt that sufficient
samples were taken over a period long encugh for the result to be
considered as avorage fer the several areas. The very worst con-
diticns are local for the several areas, i. ce, Colgate Creek, Bear
Creck and Curtis Bay, but the effect cf the polluticn is felt to a
lesser extent over a very wide arca. ‘When, for instance, one plant
in Curtis Bay is dumping an average of 300,000 peunds of ccpperas
per day alone and cnc steel plant on Bear Creel is dumping 38 million
Seunle: of copreras annually, these pollutants are bound to make their
influence f:1t mere than just locally as this matcrial is carried by
current, tides and wind action, Other plants for which we have no
recerds of dumping are ccrtrinly in the aggregate, dumping as much
as the tvo previously cited. The scvage cannct be estimated, but
is in tremendous volune, about half the sewage fror: a city of a
million people.

Comparisen of these data vith that obtained by Olsen in 1938
and by Stern in 192, shcws bevond a doubt that cenditicns are far
worse now than Hoa were then and that the areca cf lowered pH and
oxygen is larger

The effects of pellutants extend with decreasing damage into
the Bay where our notural rescurces - oystcrs, fish and crabs, are
still caught in cormercial numbers.

Present conditions do not indicate damage to our oyster bars,
but continued increase in pcllution might sericusly affect them,
These oyster bars arc at prescnt in a very depleted state but can
be brought back into producticn if the condition cf the water is
such as te suppert marine life. It is felt, however, that unless
something is dene te curb this practice of dumping waste, it will
be a very sericus threat to our upper Bay natural resources. It
is hoped that something will scon ie done tc at least halt the
further spread of this biighted are There is, however, 2 strong
sentiment arncng some pecple that aS eccnomic value of the Harbor
offsets the valuc cf the natural resources in this area. We feel
that a balance betyreen the two is important. Industry can exist
along with pure water and proper disposal methods would permit both
industry and natural resources to prosper. This has already been
proved in many places. Effective research and understanding cf the
kind and extent cf polluticn is essential to real protection ef our
natural resources,

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ADDRESSES DELIVERED
AT THE CONVENTION OF

NATIONAL SHELLFISHERIES ASSCCIATION

Asbury Park, New Jersey

June 2-3-l, 198.

Dr. Victor L. Loosanoff, Dr. Je Nelson Gowanloch,
President. Vice-President.

-James B. Engle,

Je Richards Nelson,
Secretary.

Treasurer.

7

ei oiateaye! wil sneer
ae tn

TABLE OF CONTENTS

1948 Addresses
Title

Address of “lelcome,
Dr. Victor L. Loosanoff.

ate Swamer and Early Fall Spavming of Oysters and Its
Relation to Sets of Commercial Value, A. F. Chestnut.

The 19:7 Cyster Strike in the James River,

Dr. Jay D. Andrews.

Some Observations on the Spavming of Oysters and Rearing of
Oyster Larvae Throughout the Year, Harry C. Davis.

The Rearing of Ovster Larvae in Ponds and Tanks, Its Problems
and Prospects, Dr. P. horringae

Effects of Flood Conditions on the Preduction of Spaym in the
Oyster, Dr. Philin A. Butler.

Spatfall Prediction in Holland,
Dr. P. Korringa.

Shell Disease in Ostrea edulis, Its Dangers, Its Cause,
Its Control, Dr. P. KXorringa.

Page

55

57

61

67

(l5}

78

82

86

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ADDRESS OF WELCOME
Dr. V. Le Loosanoff

President, National Shellfisheries Association

We welcome this opportunity to meet for an exchange of information
and ideas, and for formulating plans for the future. As President of the
Association, I welcome all ovr guests and members. May I say frankly that
we are glad so many of you have come to this meeting.

This meeting coincides with the beginning of a new period in the
existence of our organization and perhaps with a new era in shellfisheries.
I think so because of the following reasons:

1 - Until recently research in shellfisheries was almost exclusively
carried on by a small group of biologists of the U. S. Fish and Wildlife
Service and biolcgists of several states, mostly of the Niddle Atlantic
region. During the last few years the situation has changed radically.

a - First, several new states have realized that the only
intelligent and practical way to develop a fisheries and main-
tain it on a productive basis is by getting and properly apply-
ing a knowledge of the biology of conmercial species. Asa
result, several more aquatic biologists have been engaged by
the states, and some of these states are either building or
planning to build laboratories where the work will be centered.

b - Second, several industrial companies of the Gulf of
Mexico, which at first glance have no relation whatsoever to
shellfisheries, have established large centers of research by
hiring a number of biologists who will, no doubt, make signi-
ficant contributions to our knowledge.

c - Finally, many large private oyster companies have
come to the cenclusion that it may be of definite advantage to
include a biologist on their staff. Several of these men were
sent by their companies to be trained in certain aspects of
marine biology at our laboratory at Milford. We are glad to
see some of our graduates attending this convention,

Thus, many more men are now working on the biology of shellfish.

2 - The second reason that makes me assume that we are entering into
a new period jis that the oyster has ceased to be the only shellfish to
which almost the entire research has been confined. Those of you who are
familiar with the literature on shellfisheries will remember that since
the days of Belding, which is roughly lO years ago, practically no re-
search on clams has been done on the Atlantic coast. The exceptions are
Newcomb's papers on the growth of clams, my articles on the hard~shell

Page.

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clam, and a few others. In other words, these fisheries have received
very little attention from scientists. Recently this situation has
also changed. In New Jersev a comparativcly large group of scientists,
under the general direction of Dr. Nelson, is working on the life
history and methods of propagation of the hard clam, Venus mercenaria.
In Canada a great deal of work has alrcady been accomplished on the
soft clam, Hfya arenaria, by Dr. Medcof and his co-workers, The State
of Maine has a biologist working on the sceft clam, and in Massachusetts,
the Woods Holc Oceanographic Institution has undertaken clam studies.
Perhaps soon the Fish and ‘Wildlife Service will participate in the clam
studies,

3 ~- The third consideration is also an important one. My contacts
and conversations with the more experienced men of our group have led
me to the conclusion that most of us are beginning to understand the
necessity of concentrating on the basic studies of the physiological
requirements cf oysters and on their relation to the environment. We
must confess that we still do not know what stcops should be taken to
produce fat oysters - which is the chief purpose of every oyster grower.
It is imperative, therefore, to concentrate on studies of the nutrition
of oysters.

Equally important are studics that will give us a better under-
standing of the conditions controlling the existence of oyster larvae.
We must know what factors are responsible for the failure of oyster
larvae to reach the setting stage. For this we must learn what con=
stitutes the food of larvae, what marine fcrms are larvae enemies,
what effects have different factcrs, such as temperature, salinity,
etc. All these things are still virtually unknom to us. However,
failure of larvae te survive to the setting stage results in heavy
financial losses to the oyster growers who plant hundreds of thousands
of bushels of shells in the hope of getting oyster set.

l - Finally, this is the beginning of the period when the shell-
fishery industries have decided to break away from the old methods
of cultivation and harvesting. In Long Island Sound modern suction
dredges arc definitely displacing the old type oyster boats. I was
fortunate to see some of these in operation and am impressed with
their cfficiency and versatility. In the Gulf of Mexico a clam-
harvesting device has been perfected and will probably be accepted
with minor modifications in other parts of the country. Many of
these innovations will be described by the speakers appearing on
our program,

In conclusicn, I wish to extend once more a sincere welcome to

our guests and the members of the three organizations meeting here.
let's try to make this meeting a successful one!

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"

LATE SUMMER AND EARLY FALL SPANNING OF OYSTERS
AND ITS REIATION TO SETS OF COMMERCIAL VALUE

A. F. Chestnut,

New Jersey Oyster Research Laboratory, Rutgers University V/

Practical oysternen from many of our oyster preducing areas along the
Atlantic seabcard will often tell you that svawning and setting of oysters
takes place throughcut the winter months. For evidence to support their
ccntenticn the oystermen will show you very small spat, a quarter of an
inch and less in diameter which have been dredged during the early spring
months. The explanation that has been offered for the occurrence of
these small svat is that a set occurred late in the fall and with the de=
cline in water temperatures the rate of growth of the spat beccmes very
slow or ceases entirely. This appears tc be a suitable explanation. How-
ever, there are some interesting facts that may have a bearing on this
matter.

In Delaware Bay occasicnal straight hinge larvae have been found late
in November with water temperatures as low as 5° or 6° centigrade. In
some cases it is not certain these were oystcr larvac, for it is difficult
at tines to distinguish the various bivalve larvae in their earliest
stages. Loosanoff (1939) recorded finding a feraie oyster in a partially
spaymed cenditicn on March 20 and a male cyster with ripe and active sperm
about the same time in Long Island Sound with the water temperatures near
0° centigrade. There may be scmc dcubt whether such oysters were spaym=
ing, yet A. E. Hopkins reported that the Pacific oyster (0. gigas) will
spavm at temperaturcs as low as about 8° centigrade. These cysters
normally spavm at temperatures above 20° centigrade. In recent years a
good deal of evidence has b2en presented shcewing that temperatures alone
may not be the all imortant factcr involved in stimulating spayming.
Individual variations among oysters are well knovm from physiological
studics and such cascs of possible winter spavming, if it may occur does
so but rarelye Such cascs are of interest and add to the general knowledge
of the cyster.

In the past twenty-five years the many investigators have shcvm that
spavming and setting may generally cccur throughout the summer months. A
study of these results shows that variations in time of setting may fre-
aucntly occur. In some years the heaviest set may follow the initial spaym-
ing pericds; in cther years, the heaviest set may not take place until a
month cr two after snayming first began and still in cther years there
may be two or even three peaks of intense setting during the same season.
Briefly, to illustrate these points from the literature, Nelson (1929)
Showed two pcricds of intense setting to occur at the Cape Shore,

a

a
now with the University of North Carolina, Institute of Fisheries Research,
Morehead City, N.C.

Sere

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F oe
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7 a 4; aT :

Delaware Baye The first intense set tock place on July 30 a> the
second between August . and 20. The next year (1930) three -raves
of intense setting took place, the first on July 30 with a count of
367 spat per shell, the second on August 8 with a count cf 2s spat
per shell and the poi set cn August 20 with a ceunt of 125 spat
per shell.

Prytherch (1929) found two spawnings tc occur in Long Is <and
Sound, the first abeut the middle cf June and a second SPAVT wg about
the first cf August, resulting in tvo sets. The first set being exe

tremely light, OTTO! by a heavy final set about the middle ¢
August. lLocsanoff and Engle, however, found the heaviest sct to occur
about July 20 in Leng Island Sound with a light set fcllowins late

in Aumust of 1937.

In the Chesapcake Bay area, Loosanoff (1931) found settix- to
occur continucusly throughout the season in the James River, Virginia
with the peak cf setting about September 16. Galtsoff et al.. (1936)
reperted twe periods cf heavy setting from tne lower York aoe:
Virginia, the first in the latter half cf July and the seccrc about
the middle of Sentember. Mackin (195) records the major strike in
seaside Virginia taking place between July 15 and 25.

In fellowing the intensity of setting at various staticns in
Delaware Bay for the past fcw years similar variaticns have teen
observed as to peaks cf setting at the same staticn and at dcilferent
staticns each year. The intensity of setting was determined in the
ecnventicnal manner cf using test shells in wire baskets chan--od at
approximate five day intervals. The results of setting fcr the past
three years at one area, station 9, Delaware Bay, N. Je, are »resented
in the accemmanying figure 1. In 1945 the heaviest set cecurrod abcut
July 5. Continueus setting was reccrded from June 2h te July 30,

Then after 20 days cf ne reccrded sect cf cysters, a light set was found
between August 20 and 25. Similar results were obtained in i<h5 vith
the heaviest set about 20 days later than in 19h5. Setting in 19h6
ceased entirely by August 5 with a light set cceurring between August
15 and 20¢ In 1947 the pericd of setting was delayed, begirning July
15 and setting continuously until the first cf Octcber, with the
maxinum setting taking place between August 15 and 25,

An interesting observation at the same station 9 in 19h). and in
1947, vhich may be ccincidental, was that the water terperatuws aver-
aged 22.5 degrees centigrade when spavming first commenced as well
as at the time ef sparming prior to the sst recerded sete IN the
first case the water temperatures were rising and in the latter, the
temperatures were declining from the higher temperatures of 20 and
27 degrecs centigrade in July and August.

In the studies cf setting a point of interest is the set which
ecntinucs to anpear late in August or September and may be cf econmer-=
cial importance. In the Chesapeake Bay area and south the late set
often proves tc be the one cf ccmmercial value. It should nct be

asc

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overlooked in other areas, particularly in thcse years when the early
set is a failure. In such cases it is impcertant to watch the fouling
of shells which have been scattcred as cultch earlicr in the seascn,.

The imoortance of getting shells overboard at the proper time has
been well emphasized in the past. However, sometimes it is not possible
to held shells until the prever time due to circumstances or perhaps
as a natter cf habit. In Delaware Bay, for example, it is the general
practice to scatter shells fcr cultch befcre July ). In sone seasons
this works cut well as in 1945 and 196 when the peak cf setting was in
July. In 19h7 with the peak of setting coming late in August, the majority
ef the plantce shells had lost their efficiency as spat ccllectors because
of heavy growths of tunicates, bryozcans and hydroids cn the shells. A
single experimental clam shell, measuring 3 1/2 by lh inches was completely
covered with bryczoa in 15 deys. One cysterman on finding his shells in
this conditicn was able tc secure a set of importance by dragging the
shells and turning them over.

The question may arise, "How can you account for a late set?" or
What is the explanation fcr a late set?" There are undoubtedly many
factors involved and any single answer may be far from complete. The
following factors may be amcng these involved in a late sct.

First, cur native eastcrn cysters as a rule do nct spawn out com-
plctely when spavming is first stimulated, Throughout the summer months
we find oysters at various stages, scme may be ccmpletcly spawned out
while cthers are cnly half or partially snavmed out. Nelson (1928) in
Barnegat Bay and Loosanoff (192) in Long Island Scund have shcwm that
there may be grcat differences in the degree of maturity among cysters
from the same bed at the same time. Successive spavmings throughout
the summer reaching into the fall may cffer one explanaticn for a late
sete

Seccnd, oysters have often been cbserved going into spawn a second
time in the same seascn. Shucking hcuse cperators are well aware of
this fact and are not too pleased to find this ccnditicn. Te cite one
instance, oysters which had spavmed out in the Mullica River, N. de,
when brought to the Cape Shcre cf Delaware Bay August 1 were found to
have gene into spaym a secend time by the end cf August. Possible spaym-
ing cf such cysters would produce a late set.

Third, with decreasing water temperatures the pelagic or free
swimming pericd of the cyster may be prolonged. Prytherch (193) and
Medcof (1936-37) have presented evidence tc suppert this factcr. Medcof's
studics in the Bidefcrd River district have shcym that the larval pericd
may extend fcr as long as 30 days before setting. Thus with oysters spaym-
ing during ceclining water temperatures, the setting may be delayed for a
considerable pericd.

A fourth factor may be that of salinity influcneing the larval stages.
Prytherch (193) pointed cut that in Long Island Sound vith lower salin-
ities the larval pericds are shorter and conversely when salinities are

ays we

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higher than usual the larval period may be prelonged. This factor
may well supplement the influence of declining water temperatures
in such areas as Delaware Bay where salinities are usually at their
maximum in Octcber cr November.

In cenclusicn, the many factors that are apparent in stimulat-
ing spayming and influencing the larval pericd of oysters make it
unwise to predict from a long range basis when the greatest intensity
ef setting may occur before oysters have commenced to spawn.

= 60 -~

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ih

THE 1947 OYSTER STRIKE IN THE JAMES RIVER

Dr. Jay D. Andrews

Biclogist, Virginia Fisheries Laboratory

Abstract

The 1947 weekly spat strike and scasenal survival of spat were
studied cn public bars in three widely varying areas of the James River
by planting shells in wire bags, The strike was good throughout the
river. The number cf larvae setting was very high, and despite the low
rate of survival, the set was effective. On the best bar, an average of
31h spat per shell set during the season of vhich 1) were still alive in
November 1947. Each bar was characterized by a particular level of sett-
ing regardless of the time shells were planted. Setting varied much
more from bar tc bar than as a result of different times of planting
shells on the same bar.

The setting of oyster larvae in Virginia waters may occur anytime
between the first of July and the first of October. The James River
seed arca usually gets a ccontinucus set throughcut this pericd. In
contrast, the setting pericd in more nerthern waters is shorter and
setting is often limited tc one cr twc broods of larvae. It has become
the practice cf oyster biolegists frcm several states north of Virginia
to study larval brecds clcesely each year. Shell plantings are made just
a few days ahcad cf the expected setting of larvae. This precedure has
never been practiced in Virginia. The ccmbinaticn cf a long setting
pericd and the presence of many cverlapping broods makes recormendations
for time ef planting shells more difficult.

A number of investigators, including Loosanoff (1932), and Newcombe
(1946) and his associates, have observed that the effective sets in the
James River have occurred in late Aucust cr in September. In 196, the
vriter observed an effective strike occurring very late in September and
in Octcber. In accord with such cbservations, some Virginia oyster
biolegists have reccmmended late shell vlantings -=- August or September.
Since neither state nor private planters have followed these recommenda-
tions for varicus practical reasons, it behccves us tc make further in-
quirics abcut the value of late shell plantings in the James River.

This report is an attempt to evaluate the importance of time in shell
planting cn the basis cf the 1947 sect. Since data have been ccllected
for only one year, ccnelusicns are tontative.

In order to duplicate as nearly as possible the conditions obtained
in commercial plantings, cyster shells in wire bags were placed on the
bottoms cf representative bars. However, freshly shucked oyster shells

= (lo

% 7 A
Bilt _

oe re Sa err. .

: ' ‘eestat oft —— @) : :
fas? Va Vainio |

vi eae by akg |

H ee oan Popdcnay Na endian oth Yybtoune Guyz on? E
; Glory ce Me eee « epenp bethnze |

se ‘fa out = pe eer 6 Li a Sear oy eed.
Weve e/a vie wm Ger mS (iow Gye owt 24
Pr wal .«st nae Coie Sint ples To pies
eat? Ne Addr. cif pein Pome € On iat So fre ee ;

i ae hays tt Kes ele otd | STURE xntawnt!

; Ea jet . Y eee abana wos ae “lo neha :3 ;
mimi Die ey Th ALi = ae nuit’ es esd Os erie ;
thd ated | ot @ br mir | j |
a —— q
j

me Grader Bishi il i: unvind tos ee~ 44 Pak sine saak
. Pile be Sooke. Oe Te oh “ie et Sey nvenese @
Srey! Ces PSU 2) ve ey oy Tt i\inohdag. oa ‘

PUR a Shia sa as) es al) Seatia pe
Ws Geow et re Su ~ Pa HITEC rigs 1c er Sos
ee oe Bes Gm es ae cn aed]

yi GIA i wx be ae Sy fads. aa
prvert ty IAS S2 Sisese: * bride aye wes > |

ine WeaeS > SIS. etter! fi spre yar O08 Gavat- |

: entlar whos wdeqatacvs per eee ry ay tna cr ihrer

+hlortet hE bed waders: iy bs weed x08

iS peg aete = Hatos L yet: Hints? me E46 ig ig :
Bio 44) ite Te CD oe seatnt satin & Arhriae: « :
pices wl ote Tees sre eben er Seve eptin ,
Th Trams Obes Jirse c@Rla~! ers ep ady Ft dra =
ty re ee mG 1 are (re ltwuas AD serttitod 2h
A anette dh te, Birt eee sey gah soalaed sit
he OV SRR BEIM Sy opel cI Tl Reon" wale
Rit as witb? od AF pa iaL ids feobens niobate . ne
Raul. WEI NE Ryn t Sealy Abate otal My Ste ny cra oo mad:

Re bine ri i oAh wiles Bees ed! are ees

ravi aeit Gta ES. gat T a
7 eam a hx anu:

7% as a
Bare ee See oe ai

were used and all shells were washed before planting. Three oyster
bars were chosen from the public grounds in the James River -- two

in the seed arca, and cone market oyster producing bar (Fig. 1) “Shel
bags werc planted in duplicate at all staticns.

Two sertes of shell bags were planted. In the first scries, bags
of shells were expcscd for successive weekly pericds from late May
until November to cbtain the weekly spatfall. The spat on the inside
faces of twenty shells were counted from cach cf these bags. In the
secend scries, shells planted the first of cach month frcm June to
October were left until Nevember for a ccmpariscn of the number and
size cf spat surviving. All spat cn one hundred shells frem each bag
were counted in this sericse

The three cyster bars chcsen are bricfly characterized in Table 1.

1

Table 1. Characteristics of three cyster bars in the James River.

Nansemend Ridge Wreck Sheal Deep Water Shoal
(lever river) (middle river) (upper river)
1. High salinitics Mederate salinities Low salinities
2. Intensive feuling Mcderate fouling Moderate fouling
(many species) (few species)
Bere Dragklisnpresent Drills absent Drilis absent
le Nc fresh-water kills Rare, if ever Fresh-water kills
5. Iseht sitting Moderate silting Heavy silting
6, Mostly market cysters Mostly seed oysters Mcstly cinder,

few sced oysters

Conditions vary widely on the three bars chcsen for study. The
lower bar, Nansemcnd Ridge, is primarily a market oystcr ground. The
salinity measures abcut 20 parts per thcusand in mid-summer. Drill
predaticn is hcavy and fculing intense. Several species cf sponges,
as well as Crepidula and jingles, are present. Wreck Sheal, the second
station, is in the heart of the seed oyster area. The bottom has
mostly seed cysters and very little shcll. The salinity appreximates
an average of 16 p.v.t. in mid-summer. Drills, sponges, Crepidula
and jinglics are usually absent. Deep Water Shoal, the voper station,
is characterizcd by fresh-water kills -- one of which cccurred in the
spring of 1948, In May 1948, heavy mcrtalities were found on this
bar, including spat, yearlings, and twc-year-old oysters. A large
perticn of the material on the bettcm is cimder (shell fragments).
Silting is frequently heavy.

Weekly spat strike

The weckly spat strike on shells in bags was ccunted for all three
bars. Setting began the week cf July 9-16 and was ccntinucus until
the first cf Octcber. On the typical seed cyster bar, “reck Shoal,
the intensity of setting increased regularly until the last week of.
August when a peck of 63 spat per shell per week was reached (Table 2).

DEE

ow - ee ee ' i
bias 251, cSt, * it Ge rs eu ; sor ? ; :
al wr i> j A : r ;
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ei : _ nl ‘stasyas)
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; me. Tt "i e 4
. RY rau i
a ae ae i ue (ated
‘421,288 Paar aio Ws 20 1! i secre — |
E< r & a
y Berea) «cmt ettaiui Pha Cent t rare i aor! Gay
id Li ? : i r
o - ~~
za on jis lery } relat Than rut it
"howl | Pesan f
5

oa i te =

ry td a saa hy: ier: “ose ui® Se Serednk °
50 .) SSiati® AQihas|
a2 )ul bees ar riliv Wier ee
- y ee ne °F. pid F ps
ie agdhe Ou! hii be oP=s4 that

: ma @ti9 a! T St o_o 4 {t=
eye) Oey 0 e -21* h ’
WPL cteealts coirs 7D ws ree equastene. |
CPST Seery aN e4 (2 on Ses ind erent)
fe <a a Pox Lega iid 1h 1%, Soe eons Sa) qenetes
>} = Ent + Pe | a r 5 ia) ‘Vers , a id

=o

Van : tne. ok} :
et er ree e instep an’ LE

pas ‘acy aS Sei as Se Stoai y th at. AORBs ae
> w@sesgitar = : ale Ma ¥ tt she ef an

. .- o ge lit rene! bo Setar St ae papa Vie =.
a eee it? get Wake ~e< ‘ fee) (reat ote elfen pate
ty re Freres fice en ©!) —[aeyi we Ba sinotnreuts af
ery Ps ee > Peon Ele ret TS Te: gay
SU) gard : rine 32 “ince 22185 ant: gend
pate lel rele ts at te ited 41.) wastegate ne a8 ay

a ee Ia iad ee apne es

7 crs VE vines

>

> ae. a gyorg
2 =

@ ike Wi) cand) new et eee an si pres dogs’ eel
Efe Wis ti ast im dak tipo tie oalut Md — ae nose % }
ry sfgvyth 4 " ater —“3hy\0 Cie Lose

i Mote te i: =o Cert wri Lee re Wii eat eae ard rack om

test) bernie ft 4 any Ly rate sy haar

a

_— , &4 _

The peak of setting at the other two stations occurred essentially at
the same time with only minor fluctuaticns. However, fewer spat set at
Nansemcnd Ridge and Deep Water Shoal.

Table 2. “eekly spat strike - James River, 197
(no. of spat per shell per week)

Dates set Nansemend Ridge Wreck Shoal Deep Water Shoal

June 27 - July 3
July 3 - July 9
July 9 - July 16
July 16 - July 23
July 23 - July 30
July 30 = Aug. 6
huge 6 - Aug. 1h
huge 1h - Aug. 21
Aug. 21 — Aug. 28
hug. 28 - Sep. 3
Sep. 3 - Sep. ll
Sepe 11 = Sep. 18
Sep. 18 = Sep. 26
Sepe 26% Oct. 2
Oct. 2 = Oct. 10
Oct. 10 = Oct. 2h

wy
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EFowonwoneoarrnd

DDOOKFPOWMNOANFPRFWODODOO

In order tc shew more clearly the distribution of spatfall by weeks,
Table 3 shows cach weekly set as a percentage of the total seasonal set.
Discounting small variations, each station shows a single peak in late
August and early September. The set in the James River has been found in
previous years to be progressively later from the lower to the upper river.
There is scme indication in the 197 data that the set was abcut two weeks
later on Deep Water Shoal than cn Nansemond Ridge.

Table 3. Percentage of total set occurring each
week - James River, 197

Week of Nansemond Ridge Wreck Shoal Deep “ater Shoal
July 10 - July 17 0.5 123 0.5
July 17 - July 2h 1.0 0.9 0.3
July 2h = July 30 Dei? 3.0 a3}
July 30 - Auge 8 2.5 4.8 Hal G3}
Auge 8&8 — Auge lh BEALE 9d he3
Auge 1h - Auge 21 2909 avert 53
Auge: Zip — huge a26 Led 19.9 CA
Aug. 26 = Sep. alos 19.3 26.4
Sen. h - Sep. ll 12.8 usioS) 18.)
Sep. 11 - Sep. 18 Wee 5.8 258
Sep. 18 - Sep. 26 1.6 2e7 3.2.
Sep, 26 - Oct. 2 0.3 1.2 1.1

- 63 -

‘oj 1) g Morera @o 4! Se; i on
, :

= | 4 _
_ oe ‘ane | - ¢ set

7

Pr éi natty). = GArsid ay

4 or a fhade OF 8 vu las any

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: i a

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9 : yy f . 4 S| %
OL T./ f wn. @ & ref ai,
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7 «ay Z.16 z ip onus
Yet a Pra = of cs “apa
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> Bake’. 2, it «< oe
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A rearrangement of the setting data by adding all the weekly
sets gives a seasonal total which I have called potential spatfall.
This amounted to 31) spat per shell at Wreck Shoal. From this
arrangement of the data, the percentage of set occurring after cer-
tain dates can be readily determined, (Table ). Thus, 95% of the
potential spatfall occurred after July 30 and only 5% in July.
likewise, about 25% of the set occurred after the first of September,
leaving 70% setting in August. The seasonal distribution of weekly
spatfall for the other two stations is almost identical,

Table 4. Potential spatfall - Wreck Shoal, 197

Week Setting Per No. of spat %Z of
beginning days bushel per shell total
July 9 85 188, 280 313.8 100.0
July 16 | 78 185,910 309.8 98.7
July 23 (a! 18h, 370 307 3 97.8
July 30 6h, 178,00 29763 94.8
Aug. 6 Si) 169,370 282.3 90.0
Aug. 1h 9 152,300 253.8 80.9
Aug. 21 2 118,310 197 2 62.8
Aug. 28 35 80,720 134.5 2.9
Sep. 3 29 Lb. 50 Weed 23.6
Sep. ll 21 18,200 8053 SA)
Sep, 18 WwW 7,400 Wess} 3.9
Sep. 26 6 2,300 3.8 Wee
Oct. 2 0 e) 0 O

Survival of spat
PEO EE

Information on the survival of spat was obtained from shell bags
planted at the beginning of each setting month and left until November.
The data show a characteristic level cof spat survival for each bar
regardless of the time shells were planted (Table 5). Secondly, August
planted shells showed a higher survival of spat on all three bars,
although the advantage was not great.

Table 5. Average number of oyster spat surviving
until November ~ James River, 197
(no. of spat per shell)

Shells planted lst of:

Station June July August Sept.
Nansemond Ridge 2258 2 h2 beliS 370
Wreck Shoal. 132 - 14.37 8.28
Deep Water Shoal 7.06 (Ost 8.71 6.67

A study of size relationships showed that spat on shells on Wreck
Shoal were consistently smaller but, with less than 15 spat per shell,
it does not seem probable that overcrowding could have been the cause

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(Table 6). The most unexpected result was that spat on August planted
shells averaged larger than those on shells planted earlier, This suggests
that fouling interfered with setting on the early planted shells, and that
setting was delayed until late summer, perhaps after some fouling organisms
had sloughed off in the fall. Some large spat were found on the early
planted shells, so retarded growth probably is not an explanation for this
reversal of size groups. A more detailed analysis of the size groups shows
that there is a single size mode apparently corresponding with the peak of
weekly setting found in late August. There were consistently more spat in
tho larger size groups from the August bags than from those planted in June.

Table 6. Average length of surviving oyster spat
in November - James River, 1917
(length in mn.)

; Shells planted lst of:
Station June July August Sept.

Nansemond Ridge 11,8 ale ira LSAT 9.2
Wreck Shoal 9.6 - ave? 6.5
Deep Water Shoal 12.0 12.7 Wye2 99

A comparison of the number of spat surviving with the total of the
weekly strikes--the potential strike-~-reveals a very low percentage of
survival (Table 7). However, the survival of spat setting in September
was three or four times greater than for earlier sets. At Deep Water Shoal,
the area with the lowest potential set, the percentage of spat surviving
was higher than at the other bars, yet, the ratio between the survival of
September set spat and earlier ones remained the same at this station,

Table 7. Percentage of spat surviving until
November ~ James River, 197

Shells Number of spat per shell a
planted Potential Surviving Survival
ist of: set set
June 113.2 2.6 2.3
Nansemond Ridge July a3 52 2.4 Baal
Aug. 109.6 Led Peal
Sept. Cth oal 367 ae
June Zig Us) oak yea
Wreck Shoal July 313.8 - -
Aug. 297 3 Vy. 4.8
Sept. Thal 8.3 11.2
June BIZ thea 2200
Deep Water Shoal July 3152 8.0 25.6
Auge 30.6 Bet 28.4
Sept. eo 6.7 8.8

The only comparable data for the James River on the weekly strike and
survival of spat are those collected by Dr. Loosanoff in 1931. The 197

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——

strike was one of the best ina decade while the 1931 strike was
average to poor. In 197 forty times as many spat settled on the
weekly bags as in 1931, but only three times as many survived. It
is not thought that overcorwding was a serious factor, for the best

surviving set averaged only 15 spat per shell.
Conclusion
Zoe

A study of three widely varying bars in the James River in-
dicates characteristic setting ratcs prevail for each bar and that
greater differences occur between bars than result from different
times of shell planting on a single bar. No great advantage was
found for any particular time of shell-planting. August planted
shells showed about a 20% advantage both in size and number of- spat
over earlier plantings, The enormovs magnitude of the potential
set suggests that much larger quantities of shell than were present
on the sced grounds could have received an adeauate sct.

The 197 data imply thet planting more cultch at the right place
would mean more to the James River seed arca than rigid selection of
the time of planting.

\

Literature cited

Loosanoff, Victor L. 1932. Obscrvations on propagation of oysters
in the James and Corrotoman Rivers and the Seaside of
Virginia. Virginia Commission of Fisheries, lievport News,
1932 . 1-6 pp e

Newcombe, Curtis L. 1946, Revort of the Virginia Fisheries Laboratory,
19LH-19L45, Richmond, 1946. 1-3

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-_ _

SOME OBSERVATIONS ON THE SPAWNING OF OYSTERS
AND REARING OF OYSTER LARVAE THROUGHOUT THE YEAR

Harry C. Davis

Aquatic Biologist, U. S. Fish and Wildlife Service

The immediate goal of the work I am reporting is to develop a standard
methed of growing oyster larvae to the setting stage, in the laboratory.
The final purpose of the investigation is to study the effect, on the growth
and survival of larvae, of varying environmental factors, such as temper~
ature, salinity, turbidity, food organisms, enemies, diseases, etc. It is
only by determining the cffect of these factors in the laboratory, under
conditions such that each factor can be varicd separately, that we can hope
to evaluate their combined effects and predict the survival of larvae and
the intcnsity of setting under natural conditions. This information should
be invaluable to the oyster industry.

It is desirable to conduct such studies on a year round basis, not
only to expedite final results but also because certain comitions, such
as temperature, are more easily controlled during the winter months.

It is convenient to discuss rearing of oyster larvae in the labora-
tory throughout the year under two headings: first, methcds of obtain-
ing spawn throughout the year and second, methods of culturing the result-
ing larvae.

D

I. Methods of obtaining spaym throughout the year

Seasonal gonadal changes of Long Island Sound oysters were described
in 19l\2 by Loosanoff. He found that spring gonad development is resumed
in May, soon after the water temperature reaches 10.0°C. Spazning begins
late in June or early in July and is usually completed by the middle of
September. Thus, if, in his experiments, one had to depend on the spawn
produced under natural conditions, his work would be limited to approxi-
mately three months. Fortunately, Locsanoff in 1945 offcred a method
for inducing gonad development in oysters during the winter months. His
method consisted in keening oysters in heated aquaria at temperatures
between 20° and 30°C. Korringa reports that Dannevig in Norway success-
fully applied the method to the European ovster two years later. The
same method, with some modifications, was used for obtaining spawn in the
experiments which I carricd on during the last two winters. The results
_2re presented in this paper for any suggestions they may offer other
workers, but it should be emphasized that this is a preliminary report,
and thet future experiments may modify some of the ideas presentcd here.

In the preliminary exneriments, oysters were kept in aquaria at
25° and 30°C, for periods of 30 and 35 days, but better gonad develop--
ment occurred in later experiments in which the temoerature was held
betrreen 22° and 26°C. for psriods of 20 to 30 days. Nevertheless, appar-
ently normal straight hinge larvac have developed from fertilized eggs

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of oysters induced to spayn after only 10 days at 30°C. and after
only 15 days at 25°C. Although fertilizable eggs and active sperm
have been obtained at these conditioning temperatures in much shorter
pericds, normal sparming covld not be induced. A more complete
report on the relation of temperature to sonad development is new
prepared for publication by Locsanoff and Davis.

Aquaria having a ratio of about lh liters of sea water per oyster
and a rate of flow sufficient to give at least four changes of water
per day were maintained in later conditioning experiments.

In the early experiments eggs and sperm were taken from condie
ticned oysters by stripping. On April 25, 19h7, hoviever, it wos
noticed that some oysters had spavmed in one of the conditioning tanks
and that the eggs were developing normally. This was the first indi-
cation that the conditioned oysters would spaym or could be induced
to spawne

After this observation nearly all subsequent experiments were
with eggs and sperm frem oysters induccd to spawn, by rapidly increas-
ing the temperature from that cf the conditioning tanks to 30° or
32°C., or by the addition cf sexual preducts. Temperatures higher
than 32°C., however, have not been found effective and in some instances
have secmed to inhibit spayvming. Prytherch used high temperature to
induce spavming in the summer of 192) and Galtsoff in 1938 and 190
describes this and various other agents used to induce spavming of
oysters.

On November 25, 1947 the first conditicned oysters cf the fall
were opened without attempting to spaym them. Some of the males and
females had ripe gonads. During the latter part cf January and during
February several groups were induced to spawn and since March lst,
at least one group per week has becn spaymed. Nearly every oyster,
in the latter experiments, was induced to snavm and was spayvmed two
or more times at intervals of four or five days. Few eggs were
cbtained after a third spavming and, when opened, the oysters appeared
"Spayned out",

Spavming in the conditioning tanks has been cbserved on several
occasionse In the 30°C. tank, for cxample, mass spayming occurred
on the fourteenth day with no apparent extcrnal stimulaticn, i. e.,
the temperature remained ccnstant and no sperm or eggs could possibly
have been intreduced from cutside. An accidental increase of two or
three degrees centigrade has been fcllowed by an cbserved light,
pessibly premature spavming on the ninth day in the 22° to 26°C, tank.

Unintentional intreducticn of sperm or eggs frcm a beaker or
thermometer used ahout the spawning table and returned tc the condi-
tioning tanks can also result in unscheduled spavmings. On several
occasicns the presence cf white feces composed almost entirely of
sperm has been the only indicaticn of a spavwning that has occurred
in the conditioning tanks during the night. In onc grcup of oysters
kept at 30°C. for 30 days, although the only cbserved snawninzg was

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the mass sparning on the fourteenth day, at the end of the 30-day period
all oysters were found to be spawned oute Undoubtedly several lighter
unncticed spavmings had occurred. In many cases it was found difficult,
if nct impossible, to keep the oysters in the conditioning, tanks for
leng periods vithout having such unscheduled spavmings.

It is now believed that the relatively poor conditicn of seme cf the
eysters in the early experiments, as manifested by the very thin gonadal
layer and almost complete lack of glycogen, was a result of spavming out
curing the 30 to 35-day pericds of conditioning at the high temperatures.

It has been established that it is not necessary for the oysters of
the Long Island Sound recion to undergo hibcurnaticn before gonad develop-
1ent can again be induced. Spavmed cysters taken from Milford Harbor on
Octcber 17th, when the cutside water was still well above the temperature
at which oysters hibernate, were induced to develop ripe gonads when con=
diticned at temperatures cf 20°, 25° and 30°C.

Exocriments are new in pregress to determine whether oysters that have
been induced to develep gonads and spaym during the winter menths will again
develcp gonads and spzwn during the regular spayming seascn. Other experi= _
ments are planned to determine just hew scon after being snavmed out, cysters
will acain develep new, rine gcnadse It is alsc planned to determine more
accurately just how carly in the fall gonad development can be induced.

Ancther techniaue was tried that hclds some promise of supplying
spavm fcr the late summer and carly fall experiments after it cannot be
obtained from the oysters living under natural conditions. On August 13th
a group of cysters, brcught into the laboratory from decp water, was placed
in an ordinary clectric refrigerator at about 5° to 7°C. Although the
conditicns cf the experiment were rather crude and the oysters suffered
considerable dehydration, fertilizable eggs and active sperm were obtained
from them as late as Sentember 30th, aftcr 45 days of refrigeration. Liv-
ing larvae frem these oysters were maintained in the labcratory at Milford
as late as Octcber 1)th.

Male oysters were induced to spawn ncrmally up to and including the
37th day of refrigeration. In fact, one male spaymed more or less ncrmally
even after 2 days cf refrigcraticn. Thceugh ne cysters could be induced to
spavm later than the 2nd day, cn the LSth day when the experiment ended,
it was still oqssible to secure active spcrm by stripping.

Female oysters were induced to spaym ncrmally after as long as 20
days of refrigeration. A fow eggs were discharged on the 37th day and
again on the 2nd day, but spavming in these cases was abncrmal. Eggs were
ebtainsd by stripping cn the 37th, h2nd and hSth days, and scme in each case
were fertilizable. However, on the 37th and h2nd days some of the eggs
appeared shrunken, probably due to dehydration, and cn the Sth day some of
them had porticns of the membrane and bits of cytoplasm missing from the
margin. This suggests that rescrption may have begun by the Sth day, but
the abnormalities cbserved may have been vrimary or secendary effects of
dehydretion.

~ 69 -

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It seems probable that dehydration, due to refrigeration, inter~
fered more with the spavming mcchanism of the female than with that
of the male oyster. This should not be surprising since the female
normally forces the eggs threugh the tiny openings cf the gills into
the mantle cavity and then ejects them by a clapping motion of the
shells, while in the male the sperm pass directly from the gonaducts
jnto the cloaca and are carricd out by the excurrent water pumped by
the oyster.

Larvae of one culture, frem the seven-day group, were the only
ones from the refrigerated oysters to reach the setting stage. However,
many larvae from the 23-day oysters grew to the 150-200 micron, medium
umbo stage, and larvae from the 30 and 37-day cysters grew to early
umbe stages, many living for 20 days or more. The 2 and h5S-day groups
gave normal ciliated larvae but they did nct develop into ncrmal
straight hinge stages. Some abnormally small straight hinge larvae
were found in these cultures but most larvae either failed to develop
a shell or the shell formed was net normal. Probably all larvae that
reached the normal straight hinge stage should be considered viable,
since even during the regular spawning season larvac could not in-
variably be carried beyond this stage.

A different type of refrigeration, such as running sea water at
5°c. or less, would not cause dehycraticn and would carry away waste
products of metabolism, This should keep the cggs in more normal
condition, thereby resulting in. more nermal larvae. It might also
prelong the period during which the refrigerated cysters could be
induced to spaym nermally. By such improved refrigeration metheds
it should be possible to extend the period during which spawn may be
obtained certainly for cone or two mnths, perhaps longer. This will
be determined next fall.

It is believed that, with the experience gained this year, a
dependable supply of cysters in spawning ecndition can be maintained
in the laboratcry throughcut the year tc provide spawm for larval
studics. By using the refrigeraticn technique, oysters with active
“sperm and fertilizable egss have becn kept in the Milford laboratory
-as late as Septerbcr 30th, and by the use cf heated conditioning
tanks, they have been induced to develcp gonads as early as the 25th
cf Novenber. It appears prcbable that the two methods can be further
develcped to have spawning oysters continucusly throughout the year.

II, Methods fcr rearing cyster larvae under laborato conditions

Werk on methods cf culturing cyster larvae has been directed toward
devising a standard methcd by which larvae can be growm to the setting
stage. As yet no completely satisfactcry method has been devised,
though scme pregress has been made in that directicn.

Thus far, all methcds designed tc maintain a ecntinucus flow of.
sca water have been found unsatisfactcry. — Several methcds have been —
found to retain the larvae and give a fairly satisfactory flow of sea

water, but cause the larvae to ccngregate near the overflew. Though

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seme larvae live as long as 18 days in such cultures, they fail to grow
beyond the straight hinge stage and. eventually all die.

The most AEE results. have been selene Ss bye peeves

eee nesting screens of 100, “260 aan BY25), meshes. per_ Ane To start the
culture the fertilized eggs ane placed in clcar sea water and aerated
rather strongly. If the tomperature is maintained between 19° and 2)°C.
and the culture is clean, that is, withcut too great an excess of sperm
and little or ne blcod and tissue cells, it can be left as long as 8
hours withcut fculing. Under less favcrable conditions the first change
of sea water shculd be made between the 2lith and 36th heurs.

If the eggs are mature and in gcod cenditien, the larvae should
have shells that completely cover them, that is, be in the straight
hinge stage, by the 18th to 36th hovr. They will usually be large enough
to be retained by the 325-mesh screen and be strong enough to withstand
screening by the 2lith to 36th hour. After the first 8 hours the water
in the culture jars is changed daily by filtering it through the set of
screens. The larvae are retained on the screcns and are returned to the
culture jars, which are then filled with fresh, cotton-filtered sea water.
Copepods and other larger forms are retained on the 100-mesh screen and
can be discarded until the larvae become large enough that they too are
retaincd by the 100-mesh screcn, after which, of course, all material re-
tained by the screens is returned to the culture jars.

During 197-8 billions of cyster eggs have been collected, ferti-
lized and successfully carricd to the straight hinge stage by this method.
In scme cultures as many as 2,000 larvae per cubic centimeter were brousht
through the first 8 hours in this fashion with no apparent harmful effects
from overcrowding. Gencrally, however, numbers have not exceeded 500 y
larvae ver cubic centimeter. Thore is scme evidence that larvae 3 days
old_and_ elder are cverercwded when present in ecncentraticns above 100 _to WA
200 per cubic centimeter. eet

eer

It seems strange that ina few cultures some larvae reached the
setting stage and that in a number cf cultures some larvae develcped to
the medium umbe stage, 150-200 microns in size, while in other cultures
under apperently identical ccnditicns nene cf the larvae showed any in-
crease in size after reaching the 75 micrcn, straight hinge stage.

While the screening methced has been the mest satisfactery tried, it
does nct enable the larvae tc egrcw and develep to the setting stage in
most cases. One change of water per day may nct be sufficient te remeve
the waste preducts of larval metabolism, or, mere likcly, cne change of
water per day dces net intreduce encugh fecd to support larvae in the cen-
contraticns necessary te be practical fer labcratcry werk and expcrimenta-
ticn.

Supplementary fecding with pure and mixed cultuves of possible focd

organisms has been tricd with nc ncticeable difference in grewth cr sur-
vival over larval cultures nct recciving supplemental feeding. Some of

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the forms used, such as Chlorella, can definitely be seen in the
stomachs of the larvae but do nct seem tc be utilizable. Wells

in the swnmer of 1925 was able to grcw larvae to the setting stage
and dces not seem tc consider supplemental feeding necessary, while
Cole and his co-workers in England, in their tank experiments re-
ported in 1936, make constant use of enrichment with apparently ex-
cellent results,

In our experiments more summer cultures of larvae show growth
beyonce the straight hinge stage than do the winter cultures. Even
in summer, however, certain pericds seemed much more favorable than
others for growth cf larvae. Perhaps, except for short periods,
natural sea water dees not contain sufficient suitable food for the
high concentrations cf larvae necessary for practical laboratory
cultures. It would seem that fcod organisms are the variable factor
most likely to fluctuate in this manner. It is to find a practical
supplemental fccd, or foods, tc overcome this difficulty and permit
us te rear larvae to the setting stage throughout the year, without
regard to lack of focd organisms in natural sea water, that our
present werk at Milford Labcratory is directede

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THE REARING OF OYSTER LARVAE IN PONDB AND TANKS,
ITS PROBLEMS, ITS PROSPECTS

Dr. P, Korringa

Biologist, State Institute for Fishery Research
Bergen op Zoom, Holland

One of the main targets in oyster culture is to raise the production
of spat. Though every oyster produces hundreds of thousands of larvae
annually, very few of these larvae succeed in settling down on a suitable
piece of substratum, and thereafter survive the perilous first months of
their sedentary existence.

Quantitative studies carried through in the Qutch oyster centre, the
Oosterschelde, demonstrated that under favorable temperature conditions
only about 5% of the larvae produced reaches the mature stage, ready for
fixation. At temperatures below 19°C, the percentage is still less. Our
oyster farmers offer the mature larvae millions of tile collectors and
thousands of cubic metres of mussel]. shells on which only about 1% of the
mature larvae succeeds in finding a suitable piece of substratum to
settle on and attach, while the remainder-perish. In the first few months
of sedentary life about 9 out of 10 young spat are killed by smothering
sand and silt or by starfish; others are destroyed by creatures of a more
stalwart nature.

Yet, the Oosterschelde can be reckoned among Europe's most prolific
spat producing centres, together with the Gulf of Morbihan and the Basin
of Arcachon in France. In many other oyster districts of Europe no spat=
fall of commercial magnitude can be obtained today where rich mtural
oyster beds once were encountered. The reasons spat production became
negligible are (1) a reduced stock of mother oysters producing too few
oyster larvae, and (2) the dispersing action of the currents, which
scatter the few larvae so much that collectors placed in these waters
are only found by an occasional mature larva, so that spat producing
operations cannot paye In such regions one often pondered over the
possibility of rearing oyster larvae in ponds or tanks. In such enclosed
basins the dispersing action of sca-currents has been eliminated and
predators are kept down adequately, so that even a relatively small number
of larvae could lead to a profuse setting on the cultch placed in the
ponds. Moreover, any protraction of the pelagic phase, owing to low water
temperatures, could not easily produce a fatal effect as so often proved
to be the case in open waters, where the daily toll levied on the larvae
is heavy.

Though theorgtically no reasons can be conceived why the rearing
of oyster larvae in tanks should be reckoned among the impossibilities,
the many attempts made usually led to failure, sometimes alternating with
an occasional very moderate successes :

SFE

As maatiee bee Holland possess en oyster roducing centres,
these two countries were never in a dire need to develop a system
for rearing oyster larvae in tanks and the same holds good for the
U. S. Recently other considerations cdme to the fore. Our methods
of oyster culture are well established, approved, and highly differ~
entiated, but so far little attention has been paid to the possi-
bility of sclecting special strains of oysters characterized by
superior qualities in growth, flavor, resistence to diseases, and
so on. ‘We may rest assured that research on heredity and selection
in oysters eventually will yield important results to the oyster
industry. In such research one ought to be able to rear the larvae
of limited numbers of well selected oysters, and to this aim re-
production in ponds or tanks, or in the laboratory is the only
feasible method.

Important experiments carried through at Port Erin, in which
| oyster Jarvae were kept in glass plunger jars, placed in dim light,
| demonstrated that oyster larvae require small naked nannoplanktic
| flagellates as food, When feeding larvae pure cultures of flagellates,
one eventually succecded in rearing to settlement about 90% of the
larvae originally introduced into the jars.

Most probably the many failures in rearing oyster larvae in tanks
' and ponds should be ascribed to a lack of adequate quantities of the
appropriate naked flagellates, so that the oyster larvae suffered from
starvation and died. Onc should remember that the density of larvee ©
in the tanks is far greater than in open waters, so that the number of
food organisms must be commensuratelyv high. Therefore we understand
why the results of the many experiments carried through in the U. S.,
J in which the rearing tanks were fitted with a regular supply of normal
/ sca water, were discouraging so far.

British investigators working along other lines, sustained their
efforts and after many years of morc or less complete failures, they
developed an adequate and reliable system to produce oyster spat in
tanks. The principle of their system is to use stagnant water and to
offer the larvae an abundance of naked nannoplanktic flagellates. It
is Dr. H. A. Cole of the Conway Fisheries Experiment Station who should
be given credit for inventing the enrichment of the water with minced
shore crabs, which leads to a rapid development of the required flagel-
lates, so that the oyster larvae in the tanks can develop and settle.
Dr. Cole worked mainly along empirical lines. Hecbnonstrated that
absence of adequate food has probably been the cause of so many. earlier
failures, and not unsuitable temperatures or salinities. Dr. Cole

told me that he repeatedly observed that differences in the viability
of the larvae used may interfere more or less with normal development.
He was not in a nosition to explain, however, why development and
setting regularly was accomplished in the Conway mussel purification
tanks which are about 8 feet deep, and why the samc methods practically
alvays lead to failure in tanks half as decn.

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In 1946 one of our oyster farmers asked me to conduct an effort to
produce oyster spat in his basin at Tholen. Though this offered me a
welcome opportunity to gct acquainted with the tank breeding technique,
following Cole's approved prescriptions, I saw immediately two reasons
for a possible failure. In the first place we could never dispose of
offshore water in Tholen, so that it might prove to be imvossible to raise
the number cf flagcllates without calling forth a rapid multiplication of
veeds like non-motile algae and diatoms. In the second place the basin at
Tholen was only about l fect deep. We could not dispcse of tanks of a
depth of those at Conmvay.

I was successful in producing a dense culture of nannoplankton
flagellates by scattering regularly some minced shore crabs in the tanks.
The flagellates developed so well that the water socn acquired a green
hue, which ultimatcly even concealed to the cye the bottem of the tank,

h feet dcep. Non-mctile algae and diatoms were rare in the course of the
expcriment. This favcrable development demonstrated that the unsuitability
of shallow tanks, recorded by Cole, need not be ascribed to the impossi-
bility to raise the mumber of small flagellates in them.

In the course of my experiment oyster larvae were amply produced by
the mother cysters present in the tank. Temperature and salinity fluctu-
ations remained within ncrmal bounds so that conditions were apparently
highly favorable,

Contrary to expectations the larvae in the basin did not develop
at all, soon decreased in numbers and showed features of ill-health.
Large and mature larvae were nct observed at all; no spat settled dowm
on the cultch laid out in the basin. The 1916 experiment was a complete
failure.

Which factors can be held respensible for a failure like that? Food
was abundant, and salinity, temperature and pH left nothing to be desired.
To investigate whether oxygen could have shevm a deficiency detrimental
to the tiny oyster larvae, I measured the quantity of oxygen present in
the water near the bottom and near the surface of the experimental tank.
It may be assumed that during broad daylight flagellates produce ample
oxygen by the process of carbon dioxide assimilation, but that they ccn-
sume oxygen, lilie the oyster larvac, the adult oysters and cther creatures
during the dark hours of the night. This principle was corrcborated by
a series of observations carried through during 24 hours. Though a marked
drop in the quantity of oxygen could be observed in the second part of the
night, the values measured in the tank always remaincd higher than those
observed simultaneously in the open Oosterschelde. Therefore it was con-
Sidered highly improbable that a lack cf oxygen could have been the cause
of the 1946 failure in rearing oyster larvae in the experimental tank.

I studied the swimming behaviour cf the larvae by placing them in
glass dishes and glass tubes of different lengths in the laboratory, where
they have been fed with pure cultures of flagellates, Conditicns in
Norwegian cyster polls with their layer of fresh water cverhcad and -their
bottom layers devoid of oxygen, demonstrate that cyster larvae necd not

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rest on the bottom or at the surface film during pelagic lifee Yet,

I observed that oyster larvae take a rest now and then. They swim
about for several minutes and then come down motionless, sometimes
with their valves closed, at a rate of 0.8 cm/sece, often with their
velum expanded like a little parachute, at a rate of 0.) cm/sec.

They seldom dropped for more than 50 cm., in succession and usually
started swimming upwards again after dropping for half a minute, Moree
over larvae dropped on the bottom could easily rise again, and were by
no means trapped on the bottom. I cannot see how this typical swimming
behaviour of oyster larvac could be held responsible for their failure
to develop normally in a tank of about feet deep.

Is there another factor showing abnormal values under tank con-
ditions? I believe there is one. My oxygen measurements demonstrated
that the quantity of oxygen present in the tank was actually higher
than in cpen water and in fact supersaturation prevailed in the tank.
The same holds good for ccnditicns in my glass tubes in the laboratory.
Could it be that a surplus of oxygen is injurious to oyster larvae?

I decided to make an effort to keep the oxygen level down to more
normal proportions in a new experiment, carried through in 19h7. As
-the oxygen in the tank is produced by the flagellates, I thought it
might be feasible to check oxygen production by keeping the number of
flagellates within bounds. The latter could be achieved by adding
fewer crabs, The data on the 1947 experiment demonstrate that my
premise was right. By adding fewer crabs a more modest number of
flagellates made their appearance. The water acquired a green hue,
but the bottom remained visible. This resulted in a more modest
oxygen production during the daylight hours, but scldom supersatura=-
tion values were observed. The course of events during 2); hours
sampling resembled that in the year before, but was performed at a
lower level, closer to that observed in the open Oosterschelde. For
comparison purposes I once carried through 2) hours oxygen sampling
in the centre of the Oosterschelde, and found that the same daily
rhythm in oxygen could be found here, but with a far narrower ampli-
tude than in the tank, no doubt because the number of flagellates in
the tanks was more than 10 times as high as in the open Oosterschelde.
Supersaturation values were not observed by me in the oven Oosterschelde.

What has been the result of this difference in oxygen production
in the experimental tank? Temperature, salinity and pH were normal
once again. The oyster larvae appeared, they developed rapidly, large
and mature larvae were seen in great numbers, a hcavy setting occurred
on the collectors placed in the tank. On one of the tiles I counted
900 spat.

This led me to believe I had found the key to cpen up spat pro-
duction in shallow tanks. One should prcvide for ample production of
small naked nannoplanktic flagellates to feed the oyster larvae, but
the production of flagellates should be kept within bounds to avoid |
the development of too extreme conditicns injurious to oyster larvae.

276

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At first I thought that it could be oxygen itself which impaired
the larvae. I could not produce convincing evidence for this vicw,
however. Though a modest oxygen preducticn in the tank and successful
larval develepment and setting ran parallel in the year 1947, it did not
follow that oxygen itself was the limiting factor in 19li6. A high level
of oxygen points at vigorous carbon dioxide assimilation. As in 19h7
the number of flagellates has been kept dorm to about 1/3 of the number
reached in 196, it is easily understood that assimilation and oxygen
production demonstrated a lower level in the 197 experiment. Apart from
oxygen other products of assimilation are released by flagellates and
kindred minute crganismss It is kncvm that various dinoflagellates pro=
duce highly tcxic metabolites during assimilation. Recent investigations
carricd through by Loosanoff and Engle demonstrated that several phyto-
planktcn organisms, if kept in dense cultures, excrete products in quan-
tities noxious cven te adult cysters. Several other cases of toxic meta-
bolites preduced by phytcplanktcn organisms are knovm new, Therefore I
am inclincd to assume new that toc dense populaticns of flagellates in
experimental tanks hampcr the development of oyster larvae by prcducing
dangerous quantities cf toxic excretes. A high level of oxygen is only
an indicator of toc vigorous assimilaticn activities, which may lead to
concentraticns cf extcrnal metabolites injuricus to cyster larvae.

This view corresponds with some successful experiments in the rear=
ing of oyster larvae in which high ccncentrations of flagellates have been
effered to the larvae, while assimilation has been kept dcwn adequately.
This was attained in the Pert Erin plunger jars kept in dim light, and
supplied with pure cultures of flagellates, and in Dr. Imai's recent ex-
periments in Japan, in which light is prevented from entering his experi-
mental jars and tanks, and colourless flagellates, fed with starch, are
used as an adequate source of fcod.

I am anxious to learn the secret of the deep tanks at Conway.
Obviously conditiens injurious to oyster larvae do not easily develop
there. Could it be because scanty illumination in the lower half keeps
dovm the number cf flagellates? In fact Dr. Cole regularly observes the
same number of flagellates in his tanks as I did in my 197 experiment.
Further investigations in the laboratory and in tanks are required before
we can state that we know all about it. '

The results sc far obtained are encouraging and premise to cpen up
the wide, so far unexplored field cf heredity and selection in the oyster,
which ultimetely may yicld mcst important practical results to the oyster
industry. ‘le should steer clear of the rocks by offering the oyster
larvae ample nannoplankton flagellates but prevent a too intense assini-=-
laticn of the fcod crganisms leading to injurious cencentrations of
external metabclites.

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EFFECTS OF FLOOD CONDITIONS ON THE PRODUCTION OF SPAWN
IN THE OYSTER

Dr. Philip A. Butler

Aquatic Biologist, U. S. Fish and Wildlife Service

The effects of seasonal floods on oyster bars have been subject
to investigation for many years at various locations along the eastern
seaboard and in the Gulf of Mexico. The damages caused by these fresh
waters usually have been observed several months after the actual
environmental changes took place, when local watermen working the area
discovered extensive mortalities. Such a disaster was reported at the
last meeting of this convention, when Messrs. Beaven and Engle described
the effects of the floods of 195-6 in the upper Chesapeake Bay. These
floods caused the death of nearly 70 per cent of the oysters in the area
and apparently were quite similar to the floods which had caused high
losses here several times in the past century.

During the spring of 1946 we were able to collect oyster samples
regularly from the bars which were located nearest to the entrance
of the flood waters from the Susquehanna watershed into Chesapeake Bay.
Consequently, the opportunity presented itself to study microscopically
the changes in these oyster meats and see what effect there had been
on the production of spawn.

When the collection of samples was initiated in May of 19h6, it
was possible to find from 50 to 100 oysters per bushel of dredged
shells, but by the end of that same summer it was necessary to examine
from 2 to 3 bushels of shell in order to obtain 25 live oysters for
examination. The oysters were characterized by the cleanliness of
the shells. lost of the usual fouling organisms had been killed also
by the fresh water and washed away. The oysters themselves were
svollen and nearly transparent; many were unable to close their shells
tightly. The muscle of the oyster was scarcely attached and the meats
could be pushed out of the shells without using a knife. Local
fishermen reported that on past occasions, the muscles have become
entirely loosened and the oyster meats have been seen floating in
windrows on the surface water over the bars. Determinations of the
water content of the oyster meats showed that in many samples the
total solids had been reduced by as much as 50 per cent.

Of the many oysters examined, about 10 ner cent had the normal
opaque, creamy-white appearance and would have passed as poor to fair
market quality. But these, as well as the "glassy" oysters, always
had empty stomachs and gave no evidence of feeding activity. A
majority of those examined revealed heavy deposits of the green copper
compound in the palps and gills and throughout most of the mantle. ~

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In order to interpret the changes in these oysters, duplicate
samples were collected at weekly intervals in another part ofChesapeake
Bay where the oysters appeared to be quite "normal" and the salinity of
the water was only moderately reduced by the floods. In this higher
salinity areca, the oysters were of good market quality. During the
summer there was a commercial set of young oysters in this area indicat-
ing that the population had spaymed normally.

The changes which were found on microscopical examination of the
oysters from the low salinity area can be best understood if we describe
first what normally happens in the production of spawn. This process
has been fully described by Dr. Loosanoff for oysters in Long Island
Sound and only the principal stages will be mentioned here. In the late
summer, when spawning is usually complete, the gonad goes through an
indifferent stage and it is difficult to tell from these resting cells
whether the oyster is male or female. This period is of very short
duration and when the oysters are feeding heavily in the fall, the spawn
for the following summer starts to grow and the sexes of the oyster are
readily distinguishable. Few changes take place during the winter hiber~
nating period. In the spring, as water temperatures approach HGor., the
oyster commences feeding again and the spaym develops very quickly.
Final differentiation of the spermatozoa takes place and the deposition
of yolk in the eggs is complcted. In the Chesapeake Bay area, larvae
may be found in the water by the end of May, but the actual time of
their appearance varies from year to year and with the latitude. The
eggs continue to ripen and spavming goes on for most of the summer
until the end of August, when once again the oysters are spavmed out
and the gonads go into the resting stage. Although there is considerable
variation among individual oysters as to the time when they achieve
"ripeness", in this area at least, it appears that there are two major
spavmings during the summer and also a small but continuous production
of larvae during the entire period.

In contrast to this course of events in the high salinity area,
nearly half of the oysters examined from the flooded area during the
months of May, June and July had gonads which were in the resting or
indifferent stage, that is, the stage of activity they should have shovm
8 to 10 months earlier. Another lO per cent had developed just enough
so that their sex could be determined and a scant 10 per cent had spavm
that approached the ripeness of oysters from the high salinity area.
After the first week in August, however, there was an abrupt increase
in the development of spavn in the oysters from the low salinit)’ area.
The gonads rapidly increased in thickness, and free-swimming larvae were
found in the plankton samples. Then, from the middle of August until
late December, the same development of spaym took place which had occurred
in the oysters of the high salinity area during the period May through
July.

In Figure 1, the devclopment of spawn in the two areas has been
raphed to illustrate this differential in gonad development. The
sequence of stages is, of course, the same for cach group. Each point
on the graph represents the dominant stage of gonad activity which was

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found in the sample of oysters in any one period. Each sample was
nado up of from 10 to lO oysters collected over a two weeks or longer
period. The striking change which took place during August in the

LS or low salinity group corresponds precisely with the salinity in-
crease shovm in the line graph in Figure 2, which depicts the seasonal
fluctuation in salt content in parts per mille for the area.

Correlated with the sudden development of spavm in August in the
flooded area were two very obvious factors. The salinity, which until
that time had been fluctuating between 0 and 3 parts per mille, jumped
to 6 ppm and then more gradually increased to 13 parts per mille. The
second factor was that the oysters started feeding actively. It should
be mentioned here that the bottom water temperatures in the two areas
studied did not vary more than 1°C. throughout the period and it is
assumed that temperature was of no significance in the delay of gonad
development in the low salinity area.

Now in discussing the cause for the delayed production of spawn
there is no doubt that the fresh water was the underlying factor but
it appears that there is more to the problem than salinity alone. It
will be recalled that from early last spring, about 10 per cent of
the oysters were in better condition than the remainder, i. e., not
so transparent in appearance, and also that approximately this same
percentage produced mature eggs at the normal time in the spring.
Since neither this group or the remaining 90 per cent were feeding
during the first half of the summer, it is suggested that the direct
cause for the spavming delay was the absence of stored food. The 10
per cent group had maintained sufficient stored glycogen to permit
the normal development of spawn and this activity was not prevented »
by the presence of the fresh water. Then when the salinity increased
in August, the remaining oysters started feeding and immediately
began to develop mature sex products. It is of interest that no
abnormalities in gonad development were found either in the small
group which ripened early or in the majority which matured late in
the summer. This again indicates that fresh water, in itself, does
not directly affect the production of spawn in the gonad.

The first reaction of the oyster to fresh water is to close its
valves tightly, automatically cutting off its food supply. Hence,
the survival of the animal and its ability to reproduce is going to
be a function of how long it can exist without additional nourishment,
The more reserve food it has on hand in the form of glyccegen, the
better will be its chances for not succumbing to seasonal flood con-
ditions. There are, of course, factors concerned here other than
the simple fact that the shells may be kept closcd. The decreased
food supply might just as well be due to absence of food from the
water, or to the inability of the cyster to collect it beeause of
impairment of ciliary action, or even to the oysters! inability to
digest food when it is so swollen from the absorption of fresh water.
In the final analysis, however, the delay in the production of spawn
would appear to be the result of tissuc starvation.

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The small group of oysters which survived better and did produce
spavm normally are of considerable interest to us. The reasons for:.
their having had more stored food than the majority of the population
are nct clear, but if we may assume that this sample was representative
of oyster populations in gencral, we have a better understanding of the
"comeback" which many oyster bars have staged in the past. In these
cases, oyster bars which had become suddenly barren through natural
causes have been observed a few years later to be densely populated with
young oysters. The remnants of the former population because of their
inordinate productivity were able to cope with such natural disasters
in a relatively short time and thus perpetuated the species.

Literature Cited

Beaven, G. F., 1916. Effect of Susquehanna River stream flow on
Chesapeake Bay Salinitiecs and history of past oyster mortalities
on upper bay bars. Maryland Board of Natural Resources, Third
Annual Report, pp. 123-131.

Engle, Je Bs, 1946. Commercial aspects of the Upper Chesapeake Bay
oyster bars in the light of recent oyster mortalities. Maryland
Board of Natural Resources, Third Annual Report, pp. 13-10.

Loosanoff, V. L. 19h2. Seasonal gonadal changes in the adult oysters,
Ostrea virginica, of Long Island Sound, Biol. Bull., 83: 195-206.

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SPATFALL PREDICTION IN HOLLAND
Dre Pe Korringa

Biologist, State Institute for Fishery Research
Bergen op Zoom, Holland

The oyster farmers all over the world are faced with the problem
of deciding when to plant cultch so that it shall not be silted over
or covered with organic growth before the oyster larvae are able to
attache This problem is of paramount importance in regions where the
kind of cultch used is rather expensive, and where the preparation and
the planting of cultch requires a good deal of manual labour. The
higher the price of labour the greater the necessity to ensure a good
spatfall on the cultch used. Therefore a reliable scientific system
to predict the intensity of setting of oyster spat is of great im-
portance in regions where manufactured collectors (e.g. tile collectors)
are widely in use.

The events in the Dutch oyster centre, the Oosterschelde, give
a vivid illustration of the growing demand for adequate information
on spatfall prospects. The old timers in the 19th century used to
place a great many tile collectors but, even in seasons characterized
by good setting, only a limited percentage of these tiles bore the
maximum number of spat. Often up to 2/3 of the tiles were placed
ashore in the fall, as it was not considered worth while to attend
any further to the mere sprinkling of spat they carried. The oyster
farmers tried to overcome this disadvantage by placing "test-collectors",
Small numbers of tiles were placed at intervals am as soon as these
tiles were found to be covered with spat, the oyster farmers started
to plant their entire supply of collectors. As the spat can only be
seen with the naked eye about a week after attachment, it goes without
saying that this method frequently led to disappointments, the best
time for setting often being over when the cultch was planted. In
later years the number of tile collectors in use in the Dutch oyster
region greatly diminished and in their place shells were scattered
over the beds, a cheaper kind of collector requiring little care,

A crisis in the Dutch oyster industry in the vears following 1930,
caused by an explosive propagation of the slipper limpet and a sudden
aggravation of shell disease, compelled Dutch oyster farmars to abandon
Spat collecting with shells and to revert to tile collectors. In this
difficult period the Dutch Government assisted the oyster farmers in
various ways, one of which was the establishment of a service to predict
the intensity and the time of setting, by which the chances to obtain
a satisfactory setting greatly increased. Dutch oyster farmers are,
as a rule, very modern=-mimied people and they immediately seized this
opportunity to acquire adequate information on spatfall prospects.

The result has been that seldom, if ever, tiles are brought ashore
because they show an insufficient number of spat. Of course there are

= 82 —

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aifferences in the intensity of setting from year to year, but the
difference in output between the various batches of tiles are greatly
reduced nowadays. Since the oyster farmers do their utmost to place
all their collectors in the period indicated by us as favourable for
setting, they are approaching the eoptimum catch of spat under the given
natural conditions.

Nowadays to collect a given number of spat, the oyster farmers
need only about 1/3 of the number of tiles and 1/3 of the expenses for
Jabour and transportation that they would have needed without spatfall
prediction under the same natural conditions. This clearly demonstrates
the economic importance of spatfall prediction in regions where tile
collectors or other manufactured cultch are in use.

What are the basic principles of a system to predict the intensity
of setting?

First of all a thorough knowledge of hydrographic conditions of the
refrion cencerned is required. One should be familiar with local tidal
movements such as the speed of water currents and the degree of water
renewal during a tidal cycle. Further salinity conditions end water
temperatures are very important factors in pelagic life and setting of
the oyster.

Next one should be familiar with the behaviour of the oyster
larvae during pclagic life. It is important to know whether or not the
larvae remain uniformly distributed during any part of day and night,
during any vhase of the tidal cycle and under any kind of weather.

Further it is important to know how long the pelagic phase lasts
at different tomveratures and what percentage of the larvae may settle
dovm under different conditions. The greater the knowledge acquired on
quantitative relavions petween the number of young larvae encountered
in the plankton, the number of mature larvae ensuing, and the following
intensity of scttinge, the greater the accuracy of spatfall predictions.

In Holland quantitative plankton samples are procured twice a day
“in summer by straining exactly 100 litres of water pumped at high and at
lov; tide in a fixed station. All the oyster larvae present in these
samplcs are countcd and measured. The number of young larvae present
in the samples is a reliable measure for the emission of larvae by the
mother oysters lying on the beds.

The percentage of the larvae reaching the so-called "mature" phase,
ready for fixation, greatly differs according to environmental conditions
prevailing during pelagic life. In the Oosterschelde water temperature
proved to be the predominant factor in this. Fluctuations in the quan~
tity of food are only of secondary importance here. I repeatedly observed
that the number of naked nannoplanktic flagellates, the basic food for
the oystcr larvae, did not differ much in the course of the summer season.
This docs not imply that focd conditicns cannot be the limiting factor
in larval development in other centres of spat production.

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With the temperature conditions largely the predominating factor
in the Oosterschelde, spatfall prediction is not too difficult when
the production of young larvae is regularly checked.

A far greater degree of accuracy in predicting is attained by
following closely the development of the pelagic larvae, which is done
by measuring all the larvae present in our samples. The number of
grovm—-up and mature larvae present in the samples provides an excellent
measure, for the intensity of setting in the next few days.

Thus the number of young larvae recently produced served to pre+
dict the approximate setting about 10 days ahead. Data on the
subsequent growth and development of these larvae are used to prepare
predictions on shorter notice with a greater degree of precisicn.

As a measure of control, spatfall is measured quantitatively through-
out each summer season, The data thus obtained are of great import-
ance in consolidating the basis of cur prediction system. The practical
results obtained led the Dutch oyster farmers to attach great value

to our predictions and none of them plants his cultch without consult-
ing our bulletins.

However important our predictions on short notice are, it would
be a great heln if we could predict ahead the amplitude and periodicity
of larval production. Scrutiny of our quantitative data collected in
several consecutive years, demonstrated that the establishment of such
a long term prediction is not chimerical}

Fluctuations in the number of larvae produced from year to year
proved to be closely correlated with the number of mother oysters
present on the beds. When a year is characterized by a limited pro-
duction of larvae, only a really warm summer, resulting in a high
percentage of the larvae reaching maturity, can lead to a profuse
setting. If a year is characterized on the other hand by an ample
production of larvae, the chances for a good setting are far greater,
as even at moderate temperatures a fair number of mature larvae can
be expected. Temperature conditions and food determine the percentage
of larvae reaching the setting stage, but it is the initial number
of young larvae which determines how many mature larvae will occur
and with vhat spatfall prospects. Therefore it is of paramount im=
portance to prevent a serious reduction of the number of mother oysters
in the spat preduction centres.

Still more interesting was our finding that a correlation exists
between the ups and dcwns of larvae production in the course of each
summer and the moon's phases. Maxima in the production of larvae
can be expected to occur about 10 days after new and full moon. In-=
cubation requiring about 8 days in Ostrea edulis, we can deduce that

One of the maxima prevails largely and, curiously enough, covld be
located between June 26 and July 10 in every year under consideration
(1935-1947). This led to the formula, valid for the Oosterschelde: ~
"The big maximum in swarming is te be expected between June 26 and
July 10, about 10 days after full or new moon".

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In case high water temperatures prevail in that period, an excellent
spatfall can be expected scme 8 to 10 days later. When it happens to be
unusually cold, even the amole production of larvae of the big maximun
cannot lead to a fixaticn of commercial magnitude, and one should wait
for the next maximum in larvae producticn, a fortnight or h weeks later.
If any doubt remains, predictions on short notice, based on plankton
investigaticns serve as a reliable guide to spat-collecting operations.

These are the leading principles of spatfall prediction to-day.

GE

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ae ,

SHELL DISEASE IN OSTREA EDULIS ~
TTS DANGERS, ITS CAUSE, ITS CONTROL

Dr. P. Korringa

Biologist, State Institute for Fishery Research
- Bergen op Zoom, Holland

Complaints concerning a mysterious disease in the Dutch oysters
wore heard on all sides in the years following 1930. Green, rubber-
like spots and warts appeared in the formerly spotless shclls, many
oysters suffercd from seriously c¢cformed shells, and mortality,
especially amcng the young oysters, rose alarmingly,

The green spots were soft and elastic like rubber which led
many to believe that the diseased oysters were apparently incapable
of secreting normal hard shell-layers, or even that the calcareous
substance had been dissolved after its deposition, leaving behind
conchyolin, the organic material interwoven with calcareous matter.
in mollusk shells. The quantity of conchyolin in mollusk shells is
very modest, however, and after artificial decalcification only some
thin remnants are left behind. The green warts, though apparently
consisting of conchyolin, could not be explained by a mysterious
disappearance of the inorganic compound of the shell, but could only
be accounted for by assuming a local abnormally intense secretion
of conchycline As the mollusk shell is inanimate itself, like
man's hair and nails, investigations to clear up the cause of abnormal
shell secretion should focus on the living tissucs of the oyster and
notably on the mantle epithelium, which is in charge of secreting
the shell. 5

Laboratory investigations - carrying through histological
observations on healthy and diseased oysters, my serial sections
showed. that the mantle epithelium normally ccnsists of small nearly
cubical cells, interspersed with small unicellular glands. In
one place, however, opncsite the ligament which connects the valves,
very high and slender cclls were found to compose the mantle epi-
thelium. The cystcr's ligament, consisting of a tough rubber-like
material, is apparently secreted in successive layers by those high
slender cells, while the small cubical cells with the interposed
glands are in charge of the secretion of the calcareous part of the
shelle

Opposite the green warts and spots in diseased oysters I found
a mantle tissue consisting of the very same high and slender cells
which secrete the ligament in healthy oystcrs. For some still
obscure reason diseased oysters proceed to seercte the normal green,
rubber-like ligament material on abnormal places in the shell and
in abnormal quantities.

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Death appeared tec be threatening in case the diseased spot was
situated under the muscle scar. Then often large parts of the muscle
tissue appcared to be replaced by the typical diseased mantle tissue,
thus dangcrously interfering with the oyster's shell movements. In
case the disease happened to be located along the shell's edges, normal
shell growth was impossible. Many oysters dicd, others were sericusly
cisfigured and could never grow up to a normal marketable cyster.

Further it could be demonstrated that the formation cf the green
spots and warts was a symptom of an advanced phase of shell disease,
Earlier symptoms were cloud-like spots cf a chalky white colour, con-=
trasting with the pearly lustre of the normal shell and not to be
confeunded with the so-called chalky deposits, which are thick and
porous, The white clouds in the shell'ts interior proved to be pre=
ceded, in their turn, by tiny specks of a chalky white colour of the
size of a pin's head. These tiny white specks, the first symptom of
shell disease to be observed with the naked eyc, could be found in
oysters of different age groups. Even oyster spat, a few months old,
often appeared to show these specks and were thus marked as discased
in their carly youth.

Laborater; investigaticns could not casily bring us much further
than revealing macrosccpic and microscopic characteristics of this
disease.

Field investigations - only field observations and deliberate
experiments carried through under matural conditions could give the
answer te the multitude of questicns which arose. First of all it
was necessary to clear up the evidemiolcgy of this diseasc.e It should
be known where and when the disease spreads, and what is its course
under diffcrent external conditions.

The factor place - to find out which part of the oyster beds were
the heaviest infested by shell disease and whether certain parts of
the Dutch oyster beds happened to be free of it, I examined a great
number of samples cf spat. After having found out that the number of
white specks shows no further increase after about October lst, I
collected samples in Octcber and November and examined them in the
laboratory, noting the percentage cf the spat showing white specks and
recording the number of specks per shell. After these data had been
depictcd on a map cf the oyster district, it could easily be demon-
strated that shell discase is not evenly distributed. On the contrary,
pronounced niduses, shciring high figures, could be located in several
places. Elsewhere shell disease appearcd to be cf little or no im=
portance. 4 is a very characteristic feature that each nidus gradually
blends into mere healthy arcas. No sharp limitations were ever observed.
Such maps shoving the distribution of shell disease in the spat, have
been prepared for several years. There appeared to be a great differ-
ence in intensity cf attack from ycar to year, but each nidus, as well
as the healthy sites, appeared to occupy a fixcd place on the map.

Su07) =

The factor time - after having cleared up the influence of the
factor place, I tried to find out the effect of the factor time.
Is the oyster liable to infection during all its life? Under what
external conditions dces the disease attack new victims? What is
the fate ef oysters once fallen victim to the disease?

Oyster spat appeared tc be very sensitive to shell discase.
Further, oysters one year old are an easy prey, Thus far, healthy
cysters of two years and older appeared to be quite resistant and
suffered little, as a rule, even when exposed in the nidus of disease.
Placing trays with young oysters in a nidus of disease and examining
weekly samples proved to be an excellent measure to follow the events.
It soon became evident that shell disease spreads in the summer season,
often during a few weeks only. In the remainder cf the year the symp-
toms may aggravate or temporarily come to a standstill, but no new
victims are made.

After many years of experiments and observations I was in a posi-
tion to discover the uniformity in this process. It became clear to me
that shell disease only spreads at water temperatures above g9°C', the
higher the temperature the more vigoreus the attack. Curiously enough
a temperature of 19°C. cr higher should be maintained for some 10 days
before shell disease makes its appearance. If the temperature drops
before this pericd has clapsed, nething happens. This close correla-
tion between water tomperature and attack of shell disease explains
the great difference in ciscase frem year to year. In the meantime it
offers a possibility to predict a fcerthcoming attack.

As the appearance of white specks in the shells has been used as
an indicator for the spreading cf shell disease, we wonder whether
cor not the first phase of the attack, not to be observed with the
naked eye, should be placed much earlier. I carried through extensive
transplantation schemes with young oysters, regularly interchanging
batches from hcalthy and diseased places, and fcund cut that the
period cf incubation is very short. The white snecks appear within
a few days after the first attack has taken place. Therefore the
appearance of white specks is an adequate indicator of the appearance
of shell disease. Their number is a measure for its intensity.

What is the fate cf oysters fallen victim to the disease, when
kent under different external conditicns? To investigate this point
discascd oysters have been kept under observation during prolonged
periods, up to twe years. I used oysters of different age groups
and placed them under natural conditicns in several well selected
stations. From thesc investigations it became evident that noth-
ing hapnens curing the winter season. From Octcber till the end
cf May the symptoms remained ccnstant. In the warmer season, on
the other hand, the discase may aggravate rapidly. ‘White specks
increase in numbers, congregate into groups of specks, develop
into white clouds in the ccnter of which green, rubber-like
material will be laid dcwm in due time, The green spcts grow and -
unite with cthers, ultimately blockade the edge of the shell, thus

making shell growth impcssible or shift under the adductor muscle,

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which development may prove to be fatal.

As long as shell growth takes place the symptoms of the disease
march one In oysters showing apparently innocent white specxs in
spring, green spots and warts may appear as early as June, death may
follow in July or August. Light cases develop malformations of the
shell only. Spat heavily attacked by shell disease may die off
quantitatively within a few months. Spat showing a Jight attack only,
survive, as a rule, but develop into oysters with badly disfigured hinge
parts. “If oysters of one year old are soverely attacked, there is no
hopes They die off quantitatively.

| Tt is no use to transport discased oysters into a healthy area.
As soon as shell growth begins, the symptoms of the disease aggravate,
irrespective of where the oysters are grovme

‘Different methods of oyster culture - it was of the greatest
practical importance to find out whether or not spat produced with
different methceds of oyster culture is cqually subject to shell disease.
I compared svat on tile-collectors with that .on mussel shells and with
that attached on the most natural collector, the new shoots of older
oysters. I found that the percentage of the spat diseased only de-
pended on the place where I sampled and not on the kind of collector
used. Even spat kept well above the bottom on wire covered trays
showed the same percentage of diseased as those lying on the bottom
nearbye Spat kept within the enclosure of a flood basin and there-
fore never exposed at lew tide, showed the same percentage of victims
as Spat kept immediately outside that basin and therefore exposed for
several hours every day.

This all led to the conclusion that it is the place where the
spat is kept during the spreading of the disease in the summer season
which determines to what degree it will be liable to shell disease, and
not the method of oyster culture practiced.

This ccnclusion does not involve, however, that the method of
oyster culture is of no importance whatever in this connection. Sloping
banks along the dikes, the healthiest areas, are best suited for the
placing of tile-collectcrs, but not for the scattering of mussel shells.
The oyster farmers, kept informed about the results of our investiga-
tions, soon proceeded to place all their tile-collectors in the area
indicated by us as free of disease, though this entailed greater ex-
pense, The result has been that spat produced with tiles is, to a high
degrec, free cof shell disease and therefore much in demand. Further,
the oyster farmers stopped scattering mussel shells on the grounds
indicated as the nidus of shell disease. Much spat is still produced,
however, on beds at close quarters to the niduses, with the result that
its quality is found to be unsatisfactory after warm summers, character-
ized by a severe attack of shell discase.

The true nature of the disease ~ though the knowledge acquired on
the influence of place, time and methcd of oyster culture proved to be

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of the greatest practical importance and led to instructions to
evade an attack of shell disease, we could not be satisfied with
abandoning the nidus of shell disease. ‘We wanted to find out the
cause of this disease and of its sudden aggravation in the years
following 1930.

Generally speaking, there are several different kinds of
disease, Some are caused by infection, others by a deficiency in
certain constituents in the food. Further, there are diseases
caused by extreme deviations from the normal environmental condi-=-
-tions and still other diseases are ascribed to degeneration after
‘prolonged inbreeding.

The characteristics of shell disease, already discussed, allow
us to deduce that shell disease in the oyster should be reckoned
,among the contagious diseases. The short period of its distribution,
‘its regular appearance from year to year, its correlation with water
temperature, the occurrence of marked niduses, next to the observas-
tion of favourable growth and fattening in non-diseased oysters in
the same waters, all point in this direction.

In my pursuit of the cause of this disease I tried to find out
whether a parasitic organism could be detected in the diseased mantle
epithelium opposite the green spots in the shell. No fungus, bace
terium or protozoan could be demonstrated to occur regularly in the
- Giseased tissues. The curious and different patterns of green spots
in the individual oysters could hardly be explained by assuming a
virus as the cause of the disease. Efforts to isolate an infectious
organism from the diseased tissues by the approved laboratory tech=
miaues failed to yield positive results and so did my efforts to
infect healthy oysters by injecting preparations of diseased mantle
tissue.

Though the diseased tissue cppesite the green spots and warts
can easily be recognized under the microscope and often even with
the naked eye, I failed to recognize any aberrant feature in the
mantle epithelium opposite the white specks, which always precede
the appearance of green spots in diseased oysters. After many vain
attempts I decided to follow other paths in investigating this
particular phase in shell disease. If the white specks in the
shell should be ascribed to slight aberrations in the shell secrete
ing mantle tissue, though I failed to detect such aberrations in
my serial sections, they should be reproduced in the same character-
istic patterns in case that particular piece of the shell had been
taken away. I carried through this experiment and was surprised to
find that the shell layers, which had been secreted to replace the
pieces of shell taken away from the edge, were always free of white
specks and other symptoms of disease. Then I started another ex-
periment in which a picce of shell, bearing white specks, was care]
- fully implanted in the shcll edge of a healthy oyster. After new -
growth had been put on, the layers of shell deposited on the
implantate appeared to suffer from shell disease, while the remainder
of the shell was as healthy as before.

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These experiments proved that the disease, in its early develop-
ment, had its seat in the shell itself and that aberration of the
living mantle tissue is a feature of a later phase.

Further, I found out that shells of oysters living in a nidus of
shell disease are not attacked throughout their entire surface, Only
recent new growth and other parts of the shell, which happen to be very
thin, such as the shells of young spat, can be invaded by the white
sneckse Thickerparts of the shell cannot be attacked. Moreover, parts
of the shell which are not freely accessible from the outside like the
undernost shells ef spat settled on tile- collectors, are always frce
of shell disease, even when the shells are very thin.

This all eventually led to the ccnclusion that the shell is
attacked from the outside. The infective organism must have the power
to perforate thin parts of the shell before it can start exercising ite
fatal influence on the living tissues. This influence first causes
only minor aberrations in shell secretion, resulting in tiny white
specks on the inside of the shell. Later its action brings about irre-
versible changes in the living mantle tissue, ultimately resulting in
serious defcrmations of the shell or even in death.

It seems incredible that a bacterium or a virus is able to
perforate oyster shells, which cnly a fungus can do, Using the tech-
nique of the geologist, I produced thin slides of oyster shells. In-
vestigating carly phases of shell disease, I found that cvery white
speck has a narrow hole in its centre, in which hole a fungus thread
can be found making its way towards the shell's interior. After its
arrival there it branches abundantly and obviously starts irritating
the living tissues. This first leads to minor aberraticns, like the
white specks and white clouds, but ultimately to serious defects and
even death.

The entire proccss resembles strikingly the events during the
formaticn of plant galls. There, too, the secretion of a tiny organism,
an egg, a magector a fungus, leads to aberrations in the normal develop=
ment of the growing plant tissues, and ultimately leads to complicated
deformations, constructed of the plant's normal cells, but produced in
abnormal places and in abnormal quantities.

Characteristic features of a nidus of shell disease ~ the next
problem was to find out why the fungus is so abundant in the nidus of
disease and not elsewhere. The gradual transiticn from a nidus of disease
to a healthy area and the fact that cysters kept on trays suffered as
much as those lying on the bottom, led me to the conclusion that shell
disease is waterebcrne.

I assume that large numbers of spores of the funzus responsible
for shell disease are produced in each nidus, attacking all the oysters
there and spreading gradually to more healthy areas carried by the tidal
currents, The further away from the nidus, the more the spores become
diluted, hence a smaller and smaller number of white specks in the oysters
and a larger and larger nercentage of oysters entircly free from specks
as we enter a healthy area.

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A closer investigation of the nidus of disease led us to the
remarkable conclusion that the number of diseased oysters, which
could be considered to represent the source of each new infection,
often is very limited. Even on several of the mest dangerous spots
diseased oysters, more than one year old, were totally absent. The
enly constant feature of each nidus of shell disease appeared to be
a high percentage of old shells in the superficial bottom layers.
These old shells, most of them cockle shells (Cardium edule), were
breught there in earlier years as collecters but, owing to o fouling,
ne longer served for this purpose. Maps depicting the quantity of
shells in superficial bottom layers resemble so closely the maps
depecting the distribution of shcll discase that they are virtually
identical.

The colour of the old shells is green due to perforating algac.
Next to algac the cld shells appeared to lodge an abundance of fungus
threads. The shclls being free of organic matter themselves, the
fungus prebably gets its food frcm the perfcrating algae.

Is it too bold to assume that the spores infecting the oysters
are produced by the fungus living in the old shells and reproducing
in the warmest part of the summcr scason? I was in a position to
demonstrate that this is really what happens! In a season charactere
ized by a very intense spatfall some spat could be found on the old
fouled green shells. This spat was invariably in a very bad state.

It proved to suffer from an immediate attack of the fungus living
inside the cld shells. Apparently it is very easy for the fungus

to perforate the thin undermost shell of the newly settled spat

This undermost shell, which cannct be reached by the spores, is sine
frec of disease in spat on tiles and on newly scattered shells. This
treacherous attack in the rear even takes place at water temperatures
below 19°C. during which no spores are produced, so that spat on tiles
and newly scattered shells remain healthy.

The immense jigsaw-puzzle was new complete. The fungus living
in the old preen shells precuces spores on a very great scale in
the warmest part cf the swamer season. Those spores are carried
about by the water currents. The spcres are able to perforate the
yceung growth of cystcr shells and to start a parasitic life there,
with all the disagrecable consequences knovm to us as shell discase.
Other spores fine their way to old shells and start a more innocent
life in co-operaticn with perfcrating algae.

This makes clear why, in our experiments, a limited number of
diseased shells and limited quantities of old shells failed to in-
fect healthy young oystcrs kept on the same tray in a healthy areca.
Obviously, the dilution of the spores by the water currents is far
too great under such ccrditions. Further, it is now casily under«
stood why it proved to be useless to clean a limited space in a
nidus of shell disease from old shells, for spores are amply suppliéd
from the surrounding grouncs,

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The cause of the explosion of disease about 1930 = an explanation
could be found for the remarkable fact that shell disease spread’so
rapidly and fatally in the years following 1930. Our first Governnent
Fisheries Biologist, Dr. Hoek, described shell disease in 1900 and
stated that it occurred cnly in a limited percentage of the oysters at
that time. Between 1920 and 1930 enormous quantities of cockle shells
had been scattered as collectors in a foolish effort tc raise the pro-
duction cf young oysters. Instead of about 5,000 Ne shelis, 0,000 to
50,0C9 w3 were used annually. This gave the fungus its chance to
proliferate enormously. Hence the number of spores preduced annually
soon rese to an alarming and fatal level, and shell discase, once obscure,
exploded.

I belicve that shell disease occurs on many of the European oyster
bedse Most probably it is identical with the French Maladie-du-pied.
I have scen its victims in Brittany and once I came across a batch of
eysters from a natural oyster bed in Britteny, which were diseased in
a very high percentage and in a very bad state. It turned out that
hey came from a bed rich in old shells, which were kept there as a
method cf conservation.

Methods cf control - our profound knowledge of shell disease,
gathered in the course of many years, eventually led to apprepriate
methods of control,

Our earliest advice was to evade the niduses of disease and to
concentrate spat production in the arca indicated as healthy. Ulti-
mately we could encourage the wholesale cleaning of old abandoned beds
to get rid of the cld green shells, which produce the fatal speres every
summer. I cannot deny that a lot of red tape had to be umvound before
the united oyster farmers started tc clean the unpreductive abandoned
oyster beds at their om expense, “We try now to keep the oystcr beds
in perfect condition and to avcid any accumulation of shells by regi-
menting the use of mussel shells as collecters. It is prohibited now
to use the resistant cockle sheils as cultch.

The mest spectacular method of ccntrol, giving almost immediate
success and recently applied on a vory large scale by our oyster
farmers, is a disinfecticn cf the diseased cysters, Aftcr extensive
experiments it anpeared to be possible to kill the fungus within the
oyster shell by bathing the oyster for an hour in a toxic solution,
using an organic salt of mercury. The oyster closes its shells tightly
in this solution and is not injured at all, but the fungus is killed
within the shell because the toxic product enters through the hole the
fungus drilled in entering the shell. This methed can cnly be applied
as long as the disease is in its early developmental stage. As scon
as green rubber-like spots make their appearance in the shell, indicat-
ing that the living tissues have been changed irreversibly, chemical
contrel is no longer possible. Disinfccticn has been practiced on a
very large scale and with great success after the heavy attack of shell
disease in the warm summer of 19:7. :

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Shell disease, once a serious menace to the Dutch oyster culture,
threatening to destroy this important industry, had its mysteries
revealed bit by bit in the course of our investigations, Difficulties
arose from the necessity of carrying out all the crucial experiments
in the field and obtaining the results at the end of each summer
season. A new set of experiments could not be started before the
onset of growth in the next spring. It goes without saying that war
difficulties during the German occupation hampered our work in no
little measure. We were short of adequately equipped boats and
fuel amenable to German restrictions in the coastal area, and often
exposed to the dangers of ware

Wie know now hew to combat this disease which caused such heavy
losses and reduced so much the quality of our oysters. Oysters
recently attacked are saved by applying disinfection. The wholesale
cleaning of the niduses cf disease now in operation will, no doubt,
relegate this disease to the modest place it formerly occupieds

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